Fatty acid homeostasis in the normoxic and ischemic heart.

PHYSIOLOGICAL REVIEWS Vol. 72, No. 4, October 1992 Printed in U.S.A.

Fatty Acid Homeostasis in the Normoxic and Ischemic Heart GER J. VAN

DER

VUSSE,

JAN

F. C. GLATZ,

HANS

Department of Physiology, Cardiovascular Research Institute and Department of Biochemistry I, Erasmus University

C. G. STAM, Maastricht, Rotterdam,

AND

ROBERT

S. RENEMAN

University of Limb-g, Maastricht; Rotterdam, The Netherlands

I. Introduction ........................................................................................... II. Uptake of Fatty Acids by the Heart .................................................................. A. Extracellular sources of fatty acids ............................................................... B. Release of fatty acids from circulating triacylglycerols .. .. . .. .. .. .. .. .. .. .. . .. .. .. .. .. .. . .. .. .. . C. Myocardial fatty acid transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III. Fatty Acid Metabolism in the Normoxic Heart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Tissue levels of fatty acyl moieties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Fatty acid oxidation in mitochondria and peroxisomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Interrelationship between fatty acid and carbohydrate metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Fatty acids in cardiac lipid pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Spatial and cellular differences in fatty acid metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Effect of maturation on cardiac fatty acid oxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Production and function of arachidonic acid metabolites in the heart . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Platelet-activating factor .......................................................................... IV. Fatty Acid Metabolism in the Ischemic and Reperfused Heart ...................................... A. Cardiac fatty acids and esters during ischemia and reperfusion ................................. B. Endogenous triacylglycerols during ischemia and reperfusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Impairment of phospholipid metabolism during ischemia and reperfusion . . . . . . . . . . . . . . . . . . . . . . D. Eicosanoid production in ischemic and reperfused cardiac tissue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Platelet-acti vating factor in the ischemic and reperfused heart V. Effects of Lipid Amph iphiles on Cardiac Functioning . . . . . . . A. Fatty acids and heart function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Fatty acyl-coenzyme A and acylcarnitine ’ cardiac performance C. Biological effects of lysophospholipids . . . .. .. D. Uncertainties regarding detrimental effects of lipid amphiphiles on the in situ heart . . . . . . . . . . VI. Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. INTRODUCTION

Fatty acid homeostasis in cardiac tissue is characterized by a variety of chemical and physical processes, the interrelationship and regulating factors of which are only partially elucidated. Various storage forms of fatty acids are present, while numerous lipid-converting enzymes and transport routes are involved (25, 254, 392,440). A large portion of the circulatory fatty acyl moieties is delivered to the heart as a complex with plasma albumin (134,135). An additional part is released from triacylglycerol-containing lipoprotein particles after hydrolysis by lipoprotein lipase, which is attached to the luminal surface of the endothelial cell membrane (98, 549). Fatty acids then successively transverse the endothelium, the interstitial space, and the sarcolemma of the cardiomyocyte. Inside the myocyte a specific fatty acid-binding protein (FABP) is probably involved in the transport of fatty acids from the sarcolemma to the mitochondria and other cytoplasmic sites of conversion. 0031-9333/92 $2.00 Copyright 0 1992 the American

Physiological

881 882 882 883 886 890

890 891 893 894 902 903 903 906 906 907 909 911 916 918 924 924

Likewise, FABP is thought to be responsible for the transport of fatty acids inside the endothelial cells (25). The majority of fatty acids is oxidized in the mitochondria to provide energy for electromechanical activity and other ATP-requiring processes (254,392). Part of the fatty acids will be (temporarily) esterified and stored in such pools as triacylglycerols and phospholipids. Under normal conditions, the tissue level of fatty acids is very low (589). During restriction of flow (ischemia), which results in a lack of oxygen in the cardiac cells, fatty acid homeostasis is severely disturbed. Oxygen deprivation will diminish or completely abolish mitochondrial P-oxidation, tricarboxylic acid cycle, and respiratory chain activity, and hence accumulation of fatty acids and their metabolic derivatives readily occurs (325, 586). In the initial phase of ischemia, when hardly any irreversible cell damage occurs, the metabolic rate of the triacylglycerol-fatty acid cycle is enhanced, leading to wasteful energy consumption (572, 579). Among other fatty acids, arachidonic acid accumu-

Society

881

Downloaded from www.physiology.org/journal/physrev by ${individualUser.givenNames} ${individualUser.surname} (139.184.014.150) on August 7, 2018. Copyright © 1992 American Physiological Society. All rights reserved.

882

VAN

DER

VUSSE,

GLATZ,

lates in oxygen-deprived cardiac tissue, which indicates an impaired balance between degradation and resynthesis of membrane phospholipids. Lack of phospholipid resynthesis and/or accelerated hydrolysis of these lipids have been proposed to play crucial roles in ischemiainduced irreversible damage of cardiac cellular membranes. Alternatively, loss of cellular phospholipids reflects chemical lysis of irreversibly damaged cells and should therefore be considered as the end stage in the chain of events in the ischemic and reperfused myocardium (594). Restoration of blood flow (reperfusion) following ischemia does not automatically result in the immediate normalization of cardiac fatty acid homeostasis. Mitochondrial fatty acid oxidation seems to remain impaired, and energy production is temporarily shifted from lipid- to carbohydrate-utilizing processes (494, 495). The tissue levels of fatty acids remain high and even increase further, despite restoration of blood flow (579). Part of the arachidonic acid accumulated in the previously ischemic cells is converted into biologically active compounds, such as prostaglandins (129, 278). Accumulation of fatty acids and their derivatives might be detrimental for proper myocardial function (284, 286). Because of the amphipathic character of these substances, intercalation in cellular membranes will alter the physicochemical properties of the membranes, resulting in changes in activity of membranethe formation of membrane-linked bound enzymes, multilamellar vesicles, and structural disruption interfering with transmembrane ion homeostasis. Fatty acyl moieties may also directly inhibit other enzymatic processes. In this review recent advances in our knowledge of myocardial lipid homeostasis are discussed in relation to the functional performance of the heart and the maintenance of cellular integrity. Future directions of research aiming at the physiological importance of appropriate fatty acid homeostasis in the heart are presented.

II.

UPTAKE

OF FATTY

A. Extracellular Fatty

ACIDS

BY THE

Sources of Fatty

acids are important

HEART

Acids

substrates

for the heart

(22, 39, 97, 120, 135, 193, 194, 215, 558). They serve as oxidizable compounds to generate energy for electromechanical performance, ion transport, anabolic processes, and the maintenance of cellular integrity and as substrates for the synthesis of phospholipids, which are vital constituents of cardiac membranes, and other complex lipids. A quantitatively minor part of some polyunsaturated long-chain fatty acids is used for the synthesis of biologically active eicosanoids (276, 278, 575). Because the capacity of cardiac cells for de novo synthesis of fatty acids is small (179), the heart strongly relies on the supply of these substances from the vascular compartment.

STAM,

AND

RENEMAN

Volume

72

Fatty acid moieties are present in blood either as unesterified molecules or in the esterified form incorporated in mono-, di-, and triacylglycerols, phospholipids, and cholesteryl esters.’ In blood plasma, fatty acids are complexed to albumin, which increases the solubility of these amphipathic substances several orders of magnitude. Normally, the arterial fatty acid level varies from 0.2 to 1.0 mmol/l plasma, whereas the concentration of albumin is on the order of 0.6 mmol/l plasma. These numbers indicate that plasma albumin, which contains several fatty acidbinding sites per protein molecule, can easily accomodate the fatty acids present in the vascular compartment. Fatty acids, before binding to albumin, are mainly released from adipocyte triacylglycerols, present in fat tissue in the body. A second source of fatty acyl moieties for the heart is fatty acids hydrolyzed from blood-borne triacylglycerols, esters of three long-chain fatty acyl chains and glycerol (114, 158, 216). In the circulation the hydrophobic triacylglycerol molecules form the core of lipoprotein particles, which are coated by a relatively hydrophilic layer mainly consisting of phospholipids, cholesterol, and so-called apoproteins (121). Depending on their size, their site of formation, and their chemical composition, these triacylglycerol-rich particles are called chylomicrons or very low-density lipoproteins (VLDL). Chylomicrons are synthesized in epithelial cells of the small intestine and reach the circulation by the chyle duct. Very low-density lipoproteins are synthesized by parenchymal liver cells and are directly secreted into the hepatic vein (535). Although studies conducted with isolated rat hearts (485) suggested that part of the circulating triacylglycerols can be extracted without chemical modification, a phenomenon substantiated by the observation that endothelial cells are capable of interiorizing intact lipoprotein particles (99), it is generally accepted that the majority of the fatty acyl moieties is extracted by cardiac tissue after hydrolysis of the triacylglycerol portion in chylomicrons and/or VLDL on the luminal side of the endothelium (98 9 99, 551). Although in vitro studies indicate that fatty acyl moieties present in chylomicron and VLDL triacylglycerol can serve as the major source of cardiac energy (114,131), the contribution of fatty acids from circulating, esterified lipids to overall fatty acid uptake by the heart in situ is most likely moderate (60). The amount of fatty esters present in the various lipid pools in lipoproteins strongly depends on the nutritional state of the individual. In adequately fed dogs the total fatty acyl content of triacylglycerols, cholesteryl esters, and phospholipids is ~2, 3, and 3 mmol/l blood plasma, respectively (591). ’ In this review the term “fatty acids” is used to designate chain fatty acyl moieties in their unesterified form. These fatty may be either present in solution as acids or salts, dissolved in membranes, or bound to proteins. Covalently bound fatty acyl eties, for instance, to glycerol or cholesterol, are refered to as esters (183).

longacids lipid moifatty


October

MYOCARDIAL

1992

B. Release of Fatty Triacylglycerols 1.

Hydrolytic

Acids

From

action of lipoprotein

FATTY

ACID

883

HOMEOSTASIS

Circulating LPL gene transcription, synthesis of inactive proenzyme. release in lumen of RSR

lipase in the heart

Hydrolysis of the triacylglycerol core of lipoproteins occurs at the luminal surface of the coronary vascular endothelium (99). This hydrolytic process is mediated by lipoprotein lipase, an enzyme attached to specific binding sites at the luminal surface of endothelial cell membranes. In addition to lipolytic activity toward triacylglycerols, lipoprotein lipase exhibits phospholipase A, activity (198). This activity, exerted by breaking down the outer phospholipid layer of the lipoprotein sphere, enables exposure of the triacylglycerol core for hydrolysis. For optimal activity lipoprotein lipase needs a neutral-to-alkaline pH and the presence of activator apoprotein CII (99). This apoprotein is embedded in the outer phospholipid layer of chylomicrons and VLDL. Inhibitory CIII apoproteins are also present in the eirculation, but they are not directly associated with the triacylglycerol-rich lipoproteins (198). At least partially purified lipoprotein lipase has a certain substrate specificity. Studies with rabbit heart lipoprotein lipase demonstrated that trans-monounsaturated and some saturated fatty acids are more easily hydrolyzed than polyunsaturated cis-fatty acids (28).

Conversion of inactive, glycosylated LPL (high mannose type) into secretable, fully active LPL (complex type)

Vesicular transfer from Golgi to sarcolemma, or lysosomal degradation Secretion interstitial

sarcolemma interstitium

Transfer across endothelium

endothelium glyoocal vascular

into space

Binding to endothelial plasmalemma, catalytic activity towards chylomicrons and VLDL

space

FIG. 1. Schematical representation of synthesis, transport, and site of action of lipoprotein lipase (LPL) in heart. LPL is synthesized as inactive glycosylated proenzyme in lumen of rough sarcoplasmic reticulum (RSR). After trimming of high mannose N-oligosaccharides, activation and modification of LPL take mace in Golei svstem where progressive N-linked glycosylation with Complex-type N-oligosaccharides occurs. Fully active intracellular LPL is packaged in secretory vesicles. In presence of secretagogues (e.g., heparin), active LPL is transported and secreted. If not, degradation of LPL takes place by lysosomes that fuse with secretory vesicles. After secretion, LPL is transported across endothelium (mechanism unknown) and is fixed at luminal extent of glycocalyx, which is anchored in basement membrane of endothelial cells. Extracellular LPL hydrolyzes chylomicron (chylo) and very low-density lipoprotein (VLDL) triacylglycerols. I

2. Fate of hydrolytic

products

The products of lipoprotein triacylglycerol hydrolysis, predominantly fatty acids and monoacylglycerols, are taken up by the endothelial cells and cardiomyocytes where they are used for catabolic and anabolic processes (525). The degradation of triacylglycerol-rich lipoproteins by vascular lipoprotein lipase is not complete. After interaction with the enzyme, remnant particles (intermediate-density lipoprotein and low-density lipoprotein), largely deprived of triacylglycerol but enriched in cholesterol and phospholipid, are formed. Because these particles are much smaller than the original chylomicron or VLDL, parts of the outer layer are shed off. The latter are called surface fragments that consist of phospholipids, apoprotein, and cholesterol. It is conceivable that the transport mechanisms, described in section IIC, for albumin-bound fatty acids are also applicable to the transendothelial and transsarcolemmal transfer of fatty acids derived from bloodborne triacylglycerols through hydrolysis by endothelial lipoprotein lipase (134). The results obtained in experiments with labeled fatty acids, either complexed to albumin or present in triacylglycerols, are in agreement with this idea (485). A small proportion of the lipolytic degradation products of lipoproteins, i.e., fatty acids and monoacylglycerol, is released into the vascular space and removed from the heart by the bloodstream or released through the interstitial fluid into the cardiac lymph (238,551).

LPL

3. Origin of lipoprotein

I

lipase

There is increasing evidence that endothelial lipoprotein lipase is synthetized de novo in the parenchymal cells of the heart (228). Conclusive evidence has been provided that the gene expressing lipoprotein lipase is exclusively located in the cardiomyocytes (58). After a number of posttranscriptional processing steps in the cardiomyocyte the enzyme is secreted into the interstitial space and transported to the site of enzymatic action at the endothelial surface (Fig. 1). As pointed out (99) the expression of lipoprotein lipase at the luminal surface of the endothelium is the result of a complex series of interrelated processes operating at a variety of physicochemical levels. They include control of the rate of synthesis of the (pro)enzyme protein in the cardiomyocyte; its chemical modification and activation; enzyme storage, transport, and degradation in the cardiac parenchymal cell; release of the enzyme into the interstitial space and its binding to the outer surface of the plasma membrane of cardiomyocytes and mesenchymal


884

VAN

DER

VUSSE,

GLATZ,

cells; transfer of the enzyme from the interstitial space to the site of action at the endothelial cell; attachment to and release from the luminal surface of the endothelium; and the interaction of the enzyme with its physiological substrate supplied to the heart in the form of chylomicrons and VLDL. In addition to lipoprotein lipase, triacylglycerol lipases are present in the heart that are destined to function primarily inside the cardiomyocytes (see sect. IIID~). 4. Binding

of lipoprotein

lipase at the endothelium

Lipoprotein lipase, a 55kDa glycoprotein, is attached to the luminal membrane of the endothelial cell through association of the protein with the glucosaminoglycan chain of the heparan sulfate proteoglycans in the glycocalyx of the plasma membrane. The latter compounds are characteristic components of the surface of endothelial cells (99). The functional unit of the enzyme is most likely a dimer (168). Both chylomicrons and VLDL can bind to the endothelial wall in a specific and saturable way. The binding sites of the two classes of lipoproteins may be closely related or identical, since chylomicrons and VLDL are competitive substrates for the activity of lipoprotein lipase (99). These binding sites are different from the sites to which lipoprotein lipase is attached (99). 5. Localization

and release of lipoprotein

lipase

Lipoprotein lipase is continuously synthesized, secreted, bound, and finally released from the luminal endothelial surface. Immunocytochemical studies in young mice by Blanchette-Mackie et al. (41), using electron microscopy, have indicated that in the fed state -78% of overall myocardial lipoprotein lipase is localized in the myocytes, ~4% is localized in the extracellular space, and -18% is localized in capillary endothelium. Myocyte lipoprotein lipase is located primarily in the sarcoplasmic reticulum, Golgi sacs, and transport vesicles but also in secretory vesicles at the cell periphery (Fig. I). Extracellular lipoprotein lipase is present near the orifice of secretory vesicles of myocytes and in the narrow zones spanning the space between myocytes and capillary endothelium. In endothelial cells the lowest density of lipoprotein lipase is at the basal plasma membrane, whereas the highest density is found at the surface of the luminal projections. Under normal circumstances the half-life of lipoprotein lipase present at the luminal surface of rat heart endothelium is on the order of 90 min (553). This implies that within 90 min one-half of the lipoprotein lipases is lost from the endothelial locus and replenished by enzyme transported from the intracellular sites of protein synthesis and storage in the cardiomyocytes. It should be noted that a considerable shorter half-life of extracellular lipoprotein lipase (on the order of 10 min) has been calculated by Bagby (20). The short half-life is consistent with the notion that continuous release of the

STAM,

AND

RENEMAN

Volume

72

enzyme from the site of production into the vascular compartment is an important regulator of the actual activity of the enzyme at its physiological site of action. In a recent study Saxena et al. (482) demonstrated that bovine milk lipoprotein lipase, brought in contact with cultured porcine aortic endothelial cells, is not only subsequently released from the cells during incubation with chylomicrons and VLDL but also during incubation with increasing molar ratios of oleic acid to albumin. The release of radiolabeled lipoprotein lipase under the influence of VLDL correlated with the generation of fatty acids through hydrolysis of VLDL triacylglycerol by lipase bound to the endothelial cells. Inhibition of lipoprotein lipase activity by a specific monoclonal antibody diminished the amount of radiolabeled lipoprotein lipase released from the endothelial cells during incubation with VLDL. These findings strongly suggest that the chemical products of triacylglycerol hydrolysis affect the binding of lipoprotein lipase to the endothelial wall. Part of the lipoprotein lipase molecules in the extracellular space is probably present in an inactive form (239). In vivo prolonged treatment with lipopolysaccharides, constituents of various endotoxins, was found to result in depressed levels of heparin-releasable lipoprotein lipase activity, whereas immunological techniques revealed the presence of appreciable amounts of enzyme protein in the extracellular compartments of the heart (239). Loss of enzymatic activity of lipoprotein lipase inside the vascular compartment was also observed by Noel (395). The protein molecule, once removed from the heart, is cleared from the blood by the liver. Internalization of the enzyme by cardiomyocytes and subsequent digestion in cardiomyocytes do not occur (99). Also endothelial cells and fibroblasts take up and degrade minimal quantities of secreted lipoprotein lipase (160). The relative inability of these cell types to clear lipoprotein lipase may indicate that the enzyme is “preserved” for extracellular functions, i.e., the hydrolysis of chylomicrons and VLDL at the endothelial membrane (127). Exogenous heparin is a potent agent to release and subsequently stabilize lipoprotein lipase from the luminal side of the endothelium (379). This effect of heparin has been shown to be of great value in studies with isolated heart preparations in which the occurrence and physiological function of the enzyme was investigated. It is unknown whether other physiologically relevant factors are responsible for the continuous loss of endothelial-bound lipoprotein lipase from the heart in situ. In addition to triacylglycerol-rich lipoproteins and endogenous heparin-like substances, mechanical and rheological factors may be involved. 6. Regulation of lipoprotein lipase activity

The rate of hydrolysis of blood-borne triacylglycer01s is governed by the plasma concentration of triacylglycerols, the amount of enzyme attached to the endothelial luminal surface, and the presence of specific activator proteins in the coat of the lipoprotein particles. As


October

--.

---.

MYOCAl-WlAL ----

1992

- -.

k‘A'l"l'Y ---- ACID

described in section IIBI, full activity of lipoprotein lipase needs the presence of apoprotein CII, a protein component present at the phospholipid-rich surface layer of lipoproteins. In the absence of a fatty acid carrier, such as albumin, fatty acids and monoacylglycerol accumulate at the site of triacylglycerol hydrolysis and inhibit the hydrolytic reaction (402). No exact data are available on the actual rate of exogenous triacylglycerol hydrolysis in the heart in situ under normal circumstances. Studies conducted in humans suggest that in vivo on the order of 20-40 nmol triacylglycerol min-’ g cardiac tissue-’ are utilized by the heart (60, 61). In isolated rat hearts the rate of VLDL triacylglycerol hydrolysis is on the order of 150 nmol (fatty acid) triacylglycerol min-’ . g cardiac tissue-’ (569). Direct assessment of the enzymatic activity of the total pool of lipoprotein lipase attached to the luminal surface of endothelial cells in rat heart, i.e., the heparin-releasable portion, revealed that this enzyme pool liberated ~30 nmol fatty acids. g wet wt-’ mine1 when an artificial substrate was used (548). These observations suggest that all lipoprotein lipase enzymes attached to the endothelial wall operate at their maximum activity. However, Cryer (99) calculated that in vivo only enzymes in the vicinity of chylomicron-binding sites, i.e., on the order of 5-10% of the total amount of lipoprotein lipase attached to the endothelial membrane, are active in hydrolyzing blood-borne triacylglycerols. The quantity and activity of endothelium-bound lipoprotein lipase in the heart are not constant but increase during fasting (46) and fat feeding (241,261,432). However, other studies failed to show a positive effect on the activity of lipoprotein lipase in cardiac tissue following these interventions (21). Using the same electron-microscopic techniques as described in the previous section, Blanchette-Mackie et al. (41) demonstrated that the greatest increase of immunolocalized lipoprotein lipase occurred at the surface of intraluminal endothelial projections. Intake of large amounts of carbohydrates depressesthe heparin-releasable activity of lipoprotein lipase in the heart (302,431). The effects of hormones and related substances on endothelial-bound lipoprotein lipase activity have been reported for a variety of tissues (for review seeRef. 127). Norepinephrine and glucagon perfusion of isolated rat hearts increases the functional activity of lipoprotein lipase attached to the luminal side of the endothelium (the heparin-releasable portion) with a concomitant and quantitatively comparable decrease in activity of non-heparin-releasable enzyme, i.e., present in the tissue compartment of the heart (548). These inverse changes in lipoprotein lipase activity favor a hormoneinduced stimulation of lipase transport from the intracellular compartment to the vascular endothelial site of enzyme action. l

l

l

l

HOMEOSTASIS

885

nose units are trimmed and the lipase is transferred from the endoplasmic reticulum to the cis-Golgi where N-linked glycosylation (using N-acetylglucosamine) occurs in the cis- and medial Golgi (9). This finding in adipose cells might be well applicable to heart cells, since synthesis and processing of lipoprotein lipase appears to be identical in various tissues (127). Fully active lipoprotein lipase accumulates in the trans-Golgi (Fig. 1). The half-life of this portion of lipase was found to be ~60 min (402). A secretable pool of lipase is then packed in secretory vesicles and transported through the cytoplasm to the sarcolemma. After fusion of the vesicles with the sarcolemma the lipoprotein lipase proteins are released into the interstitial space. Via an incompletely elucidated transport route through the endothelial cells the enzyme finally reaches the vascular endothelial surface where it is positioned near the luminal extent of the glycocalyx, which is anchored in the basement membrane of the endothelial cell (401; Fig. 1). Because colchicine, a drug known to depress lipoprotein lipase release (loo), counteracts the norepinephrine-induced shift in cardiac lipoprotein lipase activity (544), stimulation of the cardiac microtubular system is likely to occur. This is possibly associated with increased fusion of intracellular lipoprotein lipase-containing secretion vesicles from the Golgi system with the sarcolemma. Recent experiments conducted with isolated cardiomyocytes in the presence of taxol, a microtubule-stabilizing drug, underline the notion that microtubules participate in the transport of lipoprotein lipase from the sites of synthesis and glycosylation, i.e., the Golgi and endoplasmic reticular membrane system, to the sarcolemmal surface binding sites (505). Earlier studies of Cryer et al. (100) have shown that glycosylation is an obligatory step in the secretory process. Propranolol was found to block the action of norepinephrine on lipoprotein lipase transport, suggesting the involvement of adenosine 3’,5’-cyclic monophosphate (CAMP) in the activation of the microtubular system (548). Cyclic AMP may also be the mediator of the glucagon-induced stimulation of transport of lipoprotein lipase from cardiomyocytes to the endothelial site of action (548), although conflicting results have been published on the putative role of this second messenger on secretion of lipoprotein lipase from isolated cardiac cells (100). The deviant observations between intact hearts and isolated cardiomyocytes suggest that the endothelium itself secretes a regulatory factor required for the glucagon-mediated effect on intracardiac lipoprotein lipase transport. Besides the stimulatory effect of apoprotein CII and phospholipids and the stabilizing influence of heparin-like substances, no direct effect of hormones or CAMP on lipoprotein lipase activity has been observed.

7. Cellular transport of lipoprotein lipase

8. Long-term regulation of cardiac lipoprotein lipase activity

After synthesis as an inactive precursor in the rough endoplasmic reticulum the N-linked high man-

The above-described hormone- and drug-mediated regulatory events are related to short-term effects on


886

VAN

DER

VUSSE,

GLATZ,

the intracellular transport and the amount and rate of secretion of myocardial lipoprotein lipase. In these situations the signal response time is relatively short (~3 h). Long-term stimulatory effects on overall (heparin releasable and nonreleasable) lipoprotein lipase activity have been described in rats after treatment with corticosteroids, adrenocorticotropic hormone (ACTH), and thyroxine (553). These changes in cardiac lipase activity are probably caused by either increased rates of enzyme protein synthesis or decreased intracellular degradation. The enhancement of rat heart lipoprotein lipase activity after fat feeding is most likely mediated by glucocorticoids (432). Fasting and diabetes also increase lipoprotein lipase activity in the heart (98, 289, 553). In skeletal muscle the level of lipoprotein lipase activity generally falls or does not change after consumption of mixed nutrients (carbohydrates, fats, and proteins) (45,260). Insulin is thought to be the major regulator of the feeding effect, since under conditions of euglycemia insulin infusion diminishes lipoprotein lipase activity within 6 h (127, 475). As the insulin-induced changes in lipoprotein lipase activity are preceded by alterations in the amount of lipoprotein lipasespecific mRNA, regulation takes place at the level of lipase synthesis (127,407). Unlike skeletal muscle, insulin hardly affects overall lipoprotein lipase activity in rat heart (47, 553). However, insulin might be required for optimal expression of glucocorticoid-mediated effects on cardiac lipoprotein lipase activity (161). Because lipoprotein lipase is physiologically active at the luminal surface of the vascular endothelium, hormone-induced variations in the number of lipase-specific binding sites, and hence the actual number of active lipase molecules, may be an important mode of regulation of the intravascular hydrolysis of chylomicron and VLDL triacylglycerols. Until now, however, no studies have been published challenging this hypothesis. C. Myocardial

Fatty Acid Transport

The extraction by the heart of fatty acids complexed to albumin is very efficient. Extraction ratios up to 70% have been measured during one single transit of blood or perfusion fluid through the cardiac capillary system (22, 120, 313). The total amount of fatty acids extracted by the cardiac cells is mainly determined by the arterial concentration of fatty acids, the actual workload of the heart, and the presence of competing substrates (122, 179, 252, 394, 518). The route of fatty acid transport from the vascular space to the cytoplasm of the cardiomyocytes comprises a sequence of events, which in the heart, unlike other organs such as liver, is much more complicated due to the presence of closed fenestrae between the endothelial cells (25). In short, release of fatty acids from albumin is followed by translocation across the luminal membrane of the endothelial cell (Fig. 2). Diffusion through the cytoplasmic compartment of the endothelial cell is supposed to be facilitated by intracellular proteins. Cytoplasmic fatty acid-binding protein (FABP,) might be in-

STAM,

AND

RENEMAN

Volume

72

volved in this process. After translocation through the abluminal membrane of the endothelial cell, diffusion of fatty acids occurs through the interstitial space between the endothelial and parenchymal cells of the heart. Interstitial diffusion is most likely mediated by albumin. The sarcolemma is crossed either passively or facilitated by specific membrane proteins identified as plasma membrane fatty acid-binding proteins (FABP,,). After translocation across the sarcolemma, binding to myocardial FABP, might occur to facilitate cytoplasmic transport. Although the major driving force for net cardiac fatty acid uptake is most likely the mass action of fatty acids (533,558), as caused by a substantial difference in vascular and intracellular concentration of these substances (590, 591), the mechanism of transport of fatty acids from the blood compartment to the cytoplasmic sites of conversion does not appear to be a simple diffusion process through lipophilic membranes and hydrophilic fluid compartments that separate the sites of fatty acid supply and conversion in the heart. In this short description of the transport route of fatty acids from the vascular to the cytoplasmic space, a variety of details has to be considered, which are discussed next. I. Endothelial delivery of fatty acids Fatty acids are tightly bound to albumin. At least six to eight fatty acid-binding sites are present per albumin molecule (537); two sites display a relatively high affinity for these compounds (192,301,536). When fatty acids and albumin are present in blood or buffer in equimolar amounts, ~0.1% of the fatty acid molecules is present in a free, non-protein-bound form (534). Transport of fatty acids across the endothelial barrier as fatty acid-albumin complex is highly unlikely. Because of its large size, albumin does not diffuse through the clefts between cardiac vascular endothelial cells in sizable amounts (25). Although vesicular transport of albumin through endothelial cells in culture has been demonstrated (511), the quantity of protein transported in this way is insufficient to cover the actual flux of fatty acids from the vascular to the interstitial compartment. The inference is that fatty acids are released from the intravascular carrier albumin before crossing the endothelial barrier. Recent studies on fatty acid uptake in isolated rabbit heart, using the multiple indicator dilution technique (24,26), showed that it is unlikely that the entire process relies on penetration through the interendothelial clefts or diffusion through the endothelial cells of the non-protein-bound part of the plasma fatty acid pool (25,585). Hence release from albumin in the vascular space and uptake by the endothelial cells cannot be viewed as separate processes. This conclusion can at best be illustrated by calculating the fatty acid flux through the endothelial barrier. The capillary permeability-surface area for non-albumin-bound palmitate was found to be -6 ml min-’ g tissue-’ (585). The call

l


October

887

1992

FA

FIG. 2. Schemati cal represen involved: 1) acyl-CoA synthetase, fatty acid-binding protein.

tation of uptake, transport, 2) carnitine acyltransferase

and activation I, 3) carnitine

culated concentration of non-albumin-bound palmitate in normal blood plasma is -0.04 pmol/l. With the flux of a solute being the product of its arterial concentration times capillary permeability-surface area, the maximal flux of palmitate, free in solution and in close vicinity of the endothelial barrier, will be 0.24 nmol min. g tissue? Because the observed flux of fatty acids from the vascular compartment to the cardiomyocytes, as calculated from arteriocoronary venous differences and myocardial blood flow, is usually -500 times higher (591), the conclusion must be drawn that other mechanisms are involved in the bulk transport of fatty acids across the endothelial layer (25). The preceding calculations suggest the existence of interactions between the luminal site of the endothelial plasmalemma and the circulating albumin-fatty acid complex. Theoretically, the interaction between the outer leaflet of the luminal endothelial cell membrane and the albumin-fatty acid complex might influence the affinity of the protein for its ligands, promoting the release of fatty acids from their carrier proteins. In addition, such interaction would deliver fatty acids directly to the lipid bilayer, forming the endothelial plasma membranes. If this is the case, the non-protein-bound fatty acids, dissolved in the water layer in close vicinity of the membrane, do not play a crucial role in transcapillary transport. The driving force of fatty acid transport is then generated by the total concentration of (mainly protein bound) fatty acids in the vascular space rather than that of fatty acids that are free in solution. In favor of the notion of specific interaction sites for the albumin-fatty acid complex at the luminal endothelial plasma membrane is the observation that an increase in the concentration of the albumin-fatty acid complex at a fixed albumin-to-fatty acid ratio displays saturation of the unidirectional flux of fatty acids across the endothelial cells (329, 585). Although an all

of fatty acid s (FA) in myocard ial tissue. acylcarniti ne translocase, 4) carnitine

Numbers refer acyltransferase

to enzymes II. FABP,

ternative explanation has been offered for the observed saturation kinetics of fatty acid uptake, i.e., interaction of albumin with the unstirred buffer layer adjacent to the cellular membrane (635), the possible existence of a specific interaction of albumin with the cardiac endothelial membrane is not excluded. Specific albumin binding to microvascular endothelium in culture has recently been reported (177, 486). Earlier work of Sage et al. (477) has identified a glycoprotein, secreted by cultured endothelial cells, that may serve as an albumin-binding substance. Ghinea and associates (175,176) discovered a specific albumin-binding protein exposed on the cell surface of the plasma membrane of capillary endothelium. These observations are indicative of a physiological interaction between albumin, carrying ligands such as fatty acids, and the luminal side of the endothelial plasma membrane. The findings of recent studies in which transcapillary fatty acid transport was investigated by monitoring differences in fatty acid content between the vascular and interstitial space of isolated rat hearts suggest that the rate at which fatty acids are released from the albumin-fatty acid complex is a denominator of the overall rate of transendothelial transport (573). Taking into account an apparent dissociation half-time at 37°C of oleate from albumin of 4-5 s (634) and a capillary transit time of -0.8 s (25), the release rate appears insufficient to explain the observed arteriovenous differences in fatty acid content of %50%, as commonly observed across the heart (22,120,375), which again points toward a specific interaction between the albumin-fatty acid complex and the endothelial membrane. Under steady-state conditions, apparent saturation of uptake of fatty acids occurs at high fatty acid-to-albumin ratios (254,416). This finding most likely implies saturation of intracellular metabolism rather than the saturation of the transport process, because unidirec-


888

VAN

DER

VUSSE,

GLATZ,

tional influx of fatty acids, as measured with the multiple indicator dilution technique, is linearily related to the fatty acid-to-albumin ratio at fixed albumin concentrations (585). Comparable results were recently obtained in studies on isolated cardiomyocytes (213).

2. Transendothelial

transport

of fatty acids

Pioneering work of Rose and Goresky (467) indicated that the capillary endothelium is a major barrier to the extraction of fatty acids by the heart. However, the mechanism of transport of fatty acids across this biological barrier is incompletely understood. Transport may occur by lateral diffusion within the leaflets of the plasmalemma of the endothelial cell from the luminal side around the edges of the cell to the abluminal side, as has been suggested by Scow and co-workers (498, 499). Alternatively, fatty acids might be transported across the luminal and abluminal membranes of the cell in combination with diffusion through the endothelial cytoplasm. A significant contribution of the first possibility can likely be excluded on the basis of the calculated maximum lateral flux of fatty acids in leaflets of the endothelial cell membrane (25). Therefore transendothelial flux implies transport across both the luminal and abluminal endothelial membranes. Whether fatty acids cross the endothelial membranes by simple diffusion or transfer, mediated by an integral membrane protein (possibly forming part of the albumin-binding protein), remains to be established. Calculation of transendothelial permeation rates showed that diffusion through the endothelial cytoplasm is not rate limiting in the overall transendothelial transport (25). It has been hypothesized that diffusion of fatty acids through the endothelial cytoplasm is facilitated by an endothelial FABP. The presence of appreciable amounts of FABP in cardiac endothelial cells has been demonstrated by Fournier and Rahim (147) in a semiquantitative way using immunohistochemical techniques. However, recent attempts to measure FABP by biochemical means in cardiac cultured endothelial cells revealed a very low content of FABP in this particular cell type (328). Further experiments are obviously required to identify the carrier of fatty acids in cardiac endothelial cells.

3. Interstitial

transport

of fatty acids

Transport through the interstitial space, in between the endothelial cell and the cardiomyocyte, is most likely mediated by albumin. Diffusion through the interstitial space is thought to occur at the rate of diffusion of albumin. Because the distance between the abluminal side of the endothelial cell and the sarcolemma is normally ~0.5 pm, transport through diffusion is fast (25). Earlier work of Julien et al. (266) has shown that the concentration of oleic acid is slightly, but significantly, less in cardiac lymph, representing the intersti-

STAM,

AND

RENEMAN

Volume

72

tial fluid, than in the vascular compartment. These findings indicate a gradient of fatty acids from blood to the interstitial fluid compartment. On the basis of studies with labeled fatty acids, the same authors concluded that a limited proportion of the fatty acid pool in the interstitial space exchanges with fatty acids supplied from the coronary vascular space, implying that not all of the fatty acids present in the interstitium are transported from the endothelial cells to the cardiomyocytes (265). Direct transfer of lipid material through lateral diffusion in membranes from the endothelial cells to cardiomyocytes (498, 643) is less likely, since proof is lacking that the heart possesses contact sites between these two types of cells.

4. Transsarcolemmal

transport

of fatty acids

Similar to the mechanism of translocation of fatty acids through the endothelial plasmalemma, uptake of fatty acids from the interstitial space by cardiomyocytes is, theoretically, either a passive process, the rate of which is governed mainly by concentration differences of fatty acids between the interstitial fluid and the cytoplasm of cardiomyocytes, or mediated by specific interaction between the albumin-fatty acid complex and the sarcolemma. As for endothelial cells, elucidation of the physiological mechanism is hampered by the diversity of possibly involved interactions. For each concept experimental support is presently available. From studies with isolated rat heart myocytes, DeGrella and Light (108,109) proposed that fatty acids are taken up into the cell by a simple diffusion process, the rate of uptake being largely determined by the rate of subsequent metabolic reactions inside the cell, such as the activation of fatty acids by acyl-CoA synthetase. More recently, further evidence for this mechanism has been presented by Rose et al. (468), who measured initial fatty acid uptake rates into isolated cardiomyocytes that could be stimulated electrically so as to vary the metabolic needs. Their data suggest that fatty acid transfer across the sarcolemmal membrane is determined by their physicochemical partition between extra- and intracellular binding proteins, the membrane lipid phase, and the respective aqueous phases. The regulatory role of the intramembrane concentration of fatty acids on their rate of uptake has also been described for rat liver (82,398). However, passive transport would require the rate of dissocation of fatty acid from its albumin complex to be fast, which is questionable, as discussed in section IICI. Available evidence for protein-mediated sarcolemma1 transfer of fatty acids includes the putative involvement of both a plasmalemmal albumin receptor and a FABP,, serving as a transsarcolemmal fatty acid transporter. The participation of a specific receptor for albumin or a nonspecific interaction between albumin and the cardiomyocyte surface was concluded from uptake studies with isolated hearts (247, 248) as well as single


October

1992

MYOCARDIAL

FATTY

cells (454). Attempts to define the putative albuminbinding site on the sarcolemmal membrane, however, have been unsuccessful so far. The albumin receptor concept was first proposed by Weisiger et al. (633) for fatty acid uptake by hepatocytes. Interestingly, these authors have subsequently left this view (634, 635) and stated that the uptake kinetics found in hepatocytes could also be largely explained when taking into account more recently obtained knowledge on the effect of albumin on fatty acid flux across lipid-water interfaces. This alternative explanation for the mechanism of cellular uptake of albumin-bound fatty acids may also apply to cardiomyocytes. The concept of a fatty acid-specific binding protein annex carrier in the cellular membrane has been put forward by Abumrad and colleagues (2, 3) for permeation of fatty acids into adipocytes. Recently, a basic (p1 9.1) 40-kDa protein that shows a high affinity for the noncovalent binding of long-chain fatty acids has been identified and isolated from the plasmalemma of various cell types, including cardiomyocytes (440, 529, 561). Monospecific antibodies raised against this could selectively inhibit specific membrane FABP,, binding as well as cellular influx of oleate. With rat cardiomyocytes, the influx was inhibited to 60% (561), suggesting that at least a portion of fatty acid uptake is mediated by FABP,,. Earlier, a 60-kDa protein, showing high affinity for fatty acids, was isolated from rat cardiac sarcolemma (165). It is unknown whether this protein is functionally involved in transsarcolemmal fatty acid transport. Sodium and electrochemical gradients have been proposed to act as driving forces for the fatty acid carrier system (561), but other investigators found uptake of fatty acids to be neither sodium nor energy dependent (426,530). These apparently conflicting data may be explained by the different experimental conditions of the respective studies, such as the composition of the perfusion or incubation buffers employed (440). Thus it appears that the actual mechanism of transsarcolemmal translocation of fatty acids is still unclear. However, it is conceivable that the various proposed mechanisms exist simultaneously. At normal physiological concentrations of albumin and fatty acids, uptake of the ligand into myocytes is a saturable function of the concentration of unbound ligand (529), but during periods of limited fatty acid availability FABP,, may function in trapping of fatty acids, whereafter transfer across the sarcolemma may occur either passively or be carrier mediated. The physiological significance of the possible simultaneous existence of these uptake mechanisms is that it presents additional elements for the efficient modulation of fatty acid extraction and metabolism. 5. Intracellular fatty acid transport: role of cytoplasmic fatty acid-binding proteins Inside the cardiomyocyte, fatty acids migrate to various subcellular sites, such as the mitochondria and

ACID

HOMEOSTASIS

889

sarcoplasmic reticulum, for activation into fatty acylCoA and further conversion. Their intracellular translocation is generally considered to be facilitated by a tissue-specific FABP,, although conclusive evidence for this particular role for FABP, is still lacking (77, 184, 185, 267, 351, 522, 538, 600). The heart-type FABP, is a small protein (15 kDa) present in cardiac cells in a remarkable abundance. Early studies have indicated that in adult rats it forms 5-6% of the cytosolic protein mass or --IO% of the number of soluble proteins (96,181,182, 185). However, applying a sensitive immunochemical assay, Vork et al. (615) recently found the FABP content of adult rat heart to be 49 nmol/g wet wt, which is onehalf as high as the value reported earlier. Although largely confined to the soluble cytoplasm, heart FABP, has also been identified inside subcellular organelles, like mitochondria and nuclei (44). The cytoplasmic protein noncovalently binds longchain fatty acids as well as their carnitine esters, but its affinity for these ligands [the apparent dissociation constant (&) varies from 10s7to 10s6M] is significantly less than the affinity of albumin for fatty acids (apparent Kd 10m8M) (185). Unsaturated fatty acids are bound by FABP, somewhat more avidly than saturated fatty acids (23). Heart FABP, belongs to a family of small proteins binding hydrophobic ligands, all possessing a clamlike tertiary structure formed by two P-sheets and thus creating one ligand-binding site (the so-called ,&barrel) (474). The number of fatty acid molecules that can be accommodated by one molecule of FABP, varies from one to two, depending on the techniques used (399,616). The total cardiac content of FABP, appears modestly responsive to changes in dietary fat intake (147); hormonal influences have not yet been documented. By facilitating substrate supply or product removal, FABP, stimulates the activity in vitro of several membranebound enzymes of lipid metabolism (23,150,481). Similarly, it has the ability to sequester and hence to prevent long-chain fatty acids and esters from exerting their inhibitory effect on enzymes, such as Na+-K’-ATPase and mitochondrial adenine nucleotide translocase (23). This putative protecting effect of FABP, may be of critical importance in the heart during ischemia when a marked accumulation of fatty acids occurs (184,186,541, 591; see sect. IVAN). With respect to its physiological function, myocyte FABP, is generally viewed as the intracellular counterpart of plasma albumin, facilitating the transport of fatty acids from the inner leaflet of the sarcolemma to the intracellular sites of metabolic conversion. It remains to be established whether besides diffusion as fatty acid monomer, fatty acids diffuse through the aqueous cytoplasmic compartment as a FABP-fatty acid complex (facilitated diffusion) or whether fatty acyl moieties are passed on from one FABP, molecule to the other. The latter mechanism would be in line with findings of Gershon et al. (173), who reported that in the cell, diffusion of proteins is limited, since most of the native proteins in cytoplasm are associated to the cyto-


890

VAN

DER

VUSSE,

GLATZ,

plasmic matrix rather than being freely dissolved in the aqueous phase. In further support of this model of enlarging the effective solubility of fatty acids are the abundance of FABP,, its moderate affinity for its ligands, and a relatively fast rate of dissociation of the FABP-fatty acid complex (185,560). On the other hand, theoretical calculations made for rat hepatocytes by Tipping and Ketterer (571) have revealed that in these cells the diffusional flux of the FABP-fatty acid complex is an order of magnitude larger than that of the ligand itself, suggesting that the diffusion of the complex contributes considerably to the intracellular fatty acid flux. Fournier and Richard (148, 149) have suggested that FABP, plays a critical role in the transport of acyl moieties from the cytoplasma into the mitochondria (see sect. III&). Support of the notion that FABP, is involved in facilitating fatty acid and/or acylcarnitine transport to the mitochondria is provided by studies showing that the increased oxidative consumption of fatty acids in the developing heart (187) is paralleled by increased ventricular levels of FABP, (96,430). In addition, FABP, was found to facilitate the transfer of fatty acids from lipid vesicles to mitochondria in an artificial system (433). Recently, another cytoplasmic protein with a specific binding affinity for fatty acyl-CoA esters (not acids) has been identified in heart and other tissues (296). This acyl-CoA-binding protein of 9.9 kDa represents -2 nmol/g wet wt in rat heart, which is ~25 times lower than the content of FABP,. On a theoretical basis, in rat heart the total acyl-CoA-binding protein content provides only a few binding sites for the total amount of 15-35 nmol/g wet wt of acyl-CoA esters present. However, differences may exist in the subcellular localization of acyl-CoA-binding protein and its ligands, as earlier studies of Neely’s group (252,338) have shown that the major part of acyl-CoA is localized in the mitochondrial matrix. In summary, available evidence suggests FABP, to be involved in the transcytoplasmic transport of fatty acyl moieties, e.g., from the sarcolemma to the sites of esterification or oxidation. In the heart the existence of a tissue-specific type of FABP suggests a specific adaptation of this protein to the metabolic needs of this tissue. Therefore its biological function is likely to reach beyond simply aiding the cytoplasmic solubilization of fatty acyl moieties and perhaps may include aspects of regulation of cellular lipid homeostasis, such as subcellular targeting of fatty acids and carnitine esters, temporary storage of these compounds in lipid pools from which they are readily available, control of mitochondrial ,&oxidation, and protection of the cardiac cell against the detrimental action of pathologically increased levels of fatty acyl moieties. III. FATTY ACID METABOLISM IN THE NORMOXIC HEART Inside the cardiac cells fatty acids, extracted from the interstitial compartment, are either oxidized for en-

STAM,

AND

RENEMAN

Volume

72

ergy production or incorporated into phospholipids, triacylglycerols, and other complex lipids. Under normal conditions fatty acids are important substrates for cardiac ATP production (321). A relatively minor proportion of the extracted fatty acids is permanently incorporated in the esterified lipid pool. In virtue of the dynamic nature of the triacylglycerol pool, part of the fatty acids are temporarily stored and, after release by hydrolytic enzymes, used for catabolic energy-producing processes (90). A. Tissue Levels of Fatty

Acyl Moieties

Canine cardiac tissue normally contains ~50 pmol fatty acyl moieties/g wet wt. The majority (85-90%) of these fatty acyl chains is incorporated in the phospholipid pool, -0.5% in cholesteryl esters, and ~12% in triacylglycerols (587). Only a minor portion (~0.1%) of the total amount of fatty acyl moieties in cardiac tissue is present in the unesterified form. In the normal dog heart this content is on the order of 30 nmol/g wet wt (587,591,592). After correction for the fatty acids present in blood and interstitial fluid trapped in the tissue biopsy, it was calculated that the fatty acid concentration in the cytoplasmic space is -10 pmol/l (591). This calculation is based on the assumption that all fatty acids are localized in the aqueous cytoplasmic compartment of the cardiac cells. However, because of their amphiphilic nature it is very likely that part of the fatty acids intercalates in cellular membranes. Therefore 10 pmol/l has to be considered as an upper limit of the concentration in the cytoplasm. This value is considerably lower than the FABP-binding capacity in the heart (see sect. IIC~). Cytoplasmic levels of this protein are reported to be on the order of 150-400 pmol/l, which suggests that this specific class of proteins can easily accomodate intracellular fatty acids under normal conditions (184). Recent studies have shown that in isolated rat hearts the fatty acid level varies between 15 and 45 nmol/g wet wt, depending on the type of extracellular substrate supplied (111, 579). Earlier some debate occurred about the content of fatty acids in normal cardiac tissue (589, 605). At present it is agreed that the level of (nonesterified) fatty acids in normal cardiac tissue is very low and that studies reporting high levels of fatty acids under these circumstances are marred by technical imperfections (246, 592, 593). In the heart the fatty acyl composition of the various lipid classes not only depends on the composition of the lipids in blood, and hence the dietary intake (66, 209, 564), but also on the fatty acid specificity of lipoprotein lipases (28). In general, changes in the fatty acid composition of the dietary fat are reflected in the fatty acid pattern of cardiac lipid pools. Thus normally canine myocardial tissue triacylglycerols contain a high proportion of palmitic and oleic acid. These fatty acids serve as potential substrates for mitochondrial oxidative energy production. In contrast, long-chain polyun-


October

1992

MYOCARDIAL

FATTY

saturated fatty acids, such as linoleic and arachidonic acid, are the main fatty acyl components of phospholipids and cholesteryl esters (210, 400, 591, 644). B. Fatty Acid Oxidation and Peroxisomes I. Fatty

in Mitochondria

acid activation

Before entry into either the catabolic pathway, leading to partial or complete oxidation of the fatty acid molecule, or incorporation in the cellular esterified lipid pool, the relatively unreactive carboxylic headgroup of the fatty acid has to be converted into the more reactive CoA thioester (392). Because details of the oxidative catabolic conversion of fatty acids are provided in several extensive reviews published earlier (321, 392), this subject is only briefly reiterated and supplemented here. The conversion of fatty acids into their acyl-CoA esters, a process referred to as fatty acid activation, is catalyzed by long-chain acyl-CoA synthetase (Fig. Z), which in the heart is predominantly localized on the outer side of the mitochondrial outer membrane (396) but probably also to some extent at the sarcoplasmic reticulum. Myocardial tissue also contains short-chain and medium-chain acyl-CoA synthetases. The energy for the activation reaction is obtained from hydrolysis of ATP, by which AMP is formed. The affinity constant for palmitate is on the order of Z-40 ,uM (199,252). The reaction is effectively controlled by the cytoplasmic acyl-CoA-to-CoA ratio and the total concentration of CoA (254) and is inhibited by its reaction products inorganic phosphate and AMP (199,321). In the normoxic heart, total tissue contents of fatty acids and fatty acyl-CoA esters are of comparable magnitude, being 30 and 15-35 nmol/g wet wt, respectively (254,587). The formed long-chain acyl-CoA is relatively insoluble in water and, like fatty acids, is probably bound to FABP,, acyl-CoA-binding protein, and lipid membranes (see sect. 11c5). 2. Mitochondrial

fatty

acid uptake and oxidation

Once activated, fatty acids can be degraded by ,&oxidation in either mitochondria or peroxisomes. Peroxisomes (or microbodies) are spherical, single-membrane pm, which were named after their organelles of -0.5-I involvement in the production (oxidases) and degradation (catalase) of hydrogen peroxide (107). The presence of CY-and w-oxidation has not been established in heart. To undergo mitochondrial ,&oxidation, the acyl residues have to be transported into the mitochondrial matrix via a carnitine-dependent shuttle mechanism (50, 163). Acyl-CoA esters are converted into acylcarnitine by carnitine acyltransferase I, localized at the inner surface of the mitochondrial outer membrane (35,382). Subsequent transport of acylcarnitine across the mito-

ACID

891

HOMEOSTASIS

chondrial inner membrane involves a 1:l exchange with carnitine, achieved by the action of carnitine-acylcarnitine translocase. Inside the matrix acylcarnitine is reconverted into acyl-CoA by carnitine acyltransferase II, localized at the inner surface of the mitochondrial inner membrane (Fig. 2). By this mechanism the cytoplasmic and mitochondrial pools of CoA are strictly separated and the sum of the contents of carnitine and its esters on both sides of the membrane are kept constant. The enzymes of this transfer process show a high specificity for the L-isomer of carnitine. Exchange transport appears to be driven by concentration gradients and is independent of metabolic energy. Inside the matrix ,&oxidation of acyl-CoA yields acetyl-CoA residues, which condensate with the tricarboxylic acid cycle intermediate oxaloacetate to produce citrate and free CoA. Citrate is then decarboxylated in the tricarboxylic acid cycle. The reducing equivalents produced during p-oxidation and the tricarboxylic acid cycle are transferred by NAD+ and FAD to the respiratory chain, located within the mitochondrial inner membrane, and finally react with molecular oxygen. At various sites of the respiratory chain ATP synthesis takes place (oxidative phosphorylation). In addition to a transfer route for long-chain acyl moieties, a second mitochondrial inner membrane transferase-translocase system has been identified that shows specificity for shunting acetyl-CoA and shortchain acyl-CoA. This mechanism is also carnitine dependent (35, 163). Although the precise physiological function of this shuttle is not fully understood, it will enable the end products of peroxisomal ,&oxidation (see next section) to enter mitochondria for further degradation and may be involved in the regulation of the overall rate of fatty acid activation and subsequent transmembrane transport by modulating the availability of reduced CoA (35,253, 321,392). 3. Peroxisomal

fatty

acid oxidation

Whereas both long-chain and short-chain fatty acids can be oxidized within the mitochondrial matrix, an additional site of long-chain acyl-CoA oxidation exists in the peroxisomes. These organelles do not contain a carnitine-dependent transport system for acyl-CoA esters. Peroxisomal ,&oxidation occurs similar to that of mitochondria, except that electrons are transferred directly to molecular oxygen to yield H20Z, which is then decomposed by catalase. Moreover, as a consequence of virtual inactivity of the system toward short-chain (C, and C,) acyl-CoA esters, peroxisomal ,&oxidation is incomplete. The accumulating intermediates are thought to be degraded further within the mitochondrial matrix (316,348). When assayed in vitro, the peroxisomal ,&oxidation reactions are insensitive to cyanide because they are not directly linked to the mitochondrial respiratory chain. The contribution of peroxisomal fatty acid oxidation to overall fatty acid oxidation in the heart is discussed in section IIIA~.


892

VAN

DER

VUSSE,

GLATZ,

4. Control of fatty acid oxidation The main factors controlling the rate of cardiac fatty acid oxidation are 1) the supply of fatty acids by the blood, 2) the level of high-energy phosphates, 3) the redox state of the mitochondria, and 4) the availability of CoA in both the mitochondrial compartment and the cytoplasmic space (254,371, 416). Kohn (297) and Kohn and Garfinkel(298,299) have developed a computer simulation of fatty acid oxidation in rat heart. Their findings also indicate that, among others, the rate of fatty acid utilization is regulated by the mitochondrial redox potential and the cellular distribution of acyl-CoA esters. Under normoxic conditions the transport system for acyl units across the mitochondrial inner membrane may function as the primary regulatory site for fatty acid oxidation (36,254,314,441), although modulation of 3-ketoacyl-CoA thiolase, catalyzing one of the steps in the P-oxidative pathway, may also play a role (404). Studies of Fournier and Richard (148, 149) suggest an active participation of FABP, in the transport of fatty acyl moieties across the mitochondrial membrane and hence in the overall rate of fatty acid oxidation. They propose that the process of self-aggregation produces multispecies of FABP,. These multispecies, intracellularly existing at ~70 and 140 PM, of FABP, may act as specific translocators, delivering acylcarnitine to the mitochondrial ,&oxidative system. Myocardial energy production from fatty acids may thus depend on optimized local concentrations of FABP,. However, the existance of self-aggregation of FABP, could not yet be confirmed by other investigators (185). An increase in cardiac work enhances the uptake of fatty acids and their oxidation rate (92, 389, 392, 416). Increased intracellular degradation of fatty acids is caused by an increased rate of oxidative phosphorylation to meet the enhanced ATP requirement associated with lower NADH levels and acceleration of tricarboxylic acid cycling. As a consequence the contents of acetyl-CoA, acyl-CoA, and acetylcarnitine fall while the concentrations of CoA, carnitine, and acylcarnitine increase. These changes are considered to stimulate the rate of fatty acyl-CoA formation and mitochondrial oxidation of the fatty acyl chain (392). Because elevation of cardiac work causes an increase in cardiac coronary blood flow, the supply of molecular oxygen, required for mitochondrial oxidative phosphorylation, and fatty acids, needed as oxidizable substrates, is enhanced concomitantly. Because the increase in blood flow is proportional to the rise in workload, fatty acid uptake from the vascular compartment most likely keeps pace with the enhanced intracellular need of oxidizable compounds. 5. Oxidation

versus estericfication

STAM,

AND

RENEMAN

Volume

7.2

plasmic carnitine-to-CoA ratio in this tissue. IdellWenger and Neely (254) have shown that in the rat heart 95% of cellular CoA resides in the mitochondria and 90% of cellular carnitine is in the cytoplasm. In addition, the total cellular content of carnitine was at least IO-fold greater than that of CoA. The intracellular distribution of these cofactors and the predominant presence of acyl-CoA synthetases on the mitochondrial outer membrane would tend to channel the extracted fatty acyl moieties directly into the mitochondrial oxidative pathway, leaving little cytoplasmic acyl-CoA available for esterification reactions. However, both pulse-chase autoradiographic (558, 621, 622) and other uptake studies with radioactively labeled (189,428,484, 513), deuterium-labeled (250), or positron-emitting (295) fatty acids indicate that a notable portion of the fatty acids entering the cells is immediately esterified to triacylglycerols and phospholipids. Together with the observations that the rate of 14C0, production from 14Clabeled fatty acids shows a lag time of lo-20 min (323, 416) but that the final myocardial production of 14C02 represents ‘70-90% of totally extracted label (361, 597, 651), this led to the concept that a major pathway in fatty acid metabolism is initial incorporation into an intracellular triacylglycerol pool followed by hydrolysis by endogenous lipases and subsequent oxidation (cf. Ref. 321). However, it cannot be excluded that (part of) the time lag between radiolabeled fatty acid uptake and release of 14C02 is caused by dilution of label in the intracellular pool of metabolic intermediates. Hence the precise dynamic participation of the intracellular lipid pool in the oxidation of exogenous fatty acids remains to be established. It is noteworthy that in forearm muscle a delay time of ~30 min was observed between the uptake of radiolabeled oleic acid and the release of 14C0, suggesting that in skeletal muscle no plasma fatty acids are oxidized directly and all of them are first esterified (662). 6. Cardiac

capacity for oxidation

of fatty acids

The capacity for fatty acid oxidation in rat heart homogenates is ~750 nmol min-l .g wet wt-’ (182) for both the commonly present saturated and (poly)unsaturated fatty acids of 16 and 18 carbon atoms, but it is much less for fatty acids exceeding this chain length (458). For dog hearts an in vitro oxidation rate of ~160 nmol min-l .g-’ was monitored (583). In rats the relative contribution of peroxisomes to the total oxidation capacity is estimated to be lo-30% for common fatty acids but up to 45% for some fatty acids with a chain length exceeding 22 carbon atoms (397, 458, 601). Whether the ratio between the actual rates of peroxisoma1 and mitochondrial P-oxidation varies in relation to changes in cardiac workload is not known. In the normoxic in situ dog heart the fatty acid oxidation rate is ~100 nmol min-l . g-l (591), indicating that ~60% of the available capacity to oxidize fatty acyl moieties is actually utilized. This proportion will obvil

l

l

. The corn .parati vely low rate of synthesis of complex 11.pids by the heart is thought to relate to the high cyto-


October

19%

MYOCARDIAL

FATTY

ously be augmented when workload is enhanced, resulting in an increased demand of cellular energy. C. Interrelationship Between Carbohydrate Metabolism

Fatty

Acid and

Although long-chain fatty acids are important substrates for the heart (39, 40, 321), other nonlipid substrates are also avidly extracted and metabolized by cardiac cells. In this sense, the heart can be considered an “omnivorous” organ (566). In addition to long- and short-chain fatty acids, glucose, lactate, pyruvate, and ketone bodies can serve as oxidizable substrates (390, 391). Under normal conditions fatty acid oxidation accounts for 30-70% of the energy produced (22,194,321). Current evidence favors the notion that the supply of a substrate is the major factor regulating its contribution to overall energy production. Blood levels of fatty acids are on the order of 0.2-0.5 mmol/l plasma, whereas the plasma concentrations of the main two carbohydrate substrates, glucose and lactate, are on the order of 5 and 1 mmol/l plasma, respectively. During one single capillary passage, ~50% of both fatty acids and lactate are extracted. Only a minor proportion of glucose is taken up at first passage (591). At normal cardiac workload, uptake of glucose is hormonally regulated. Circulating insulin governs the extraction rate of glucose by cardiomyocytes (566). Increased workload accelerates cellular glucose uptake in an insulin-independent manner. The mechanism of this process is incompletely understood. Conversely, lactate extraction is mainly dominated by the concentration of this substance in the extracellular compartment (122, 291,334,539,540). There are indications that the various substrates mutually modulate their transport from the vascular to the intracellular compartment (389). Inside the cell the substrates supplied by the blood can interfere with each other through their specific routes of intermediary metabolism (315,392). When the supply of fatty acids is sufficiently high to keep intracellular ATP at its normal physiological level, enzymatic degradation of glucose, blood-borne or derived from endogenous glycogen stores, is depressed (93,392). Phosphofructokinase, one of the enzymes controlling the glycolytic rate, is modulated by cytoplasmic ATP levels. High concentrations of ATP depress phosphofructokinase activity (392). Direct inhibitory effects of fatty acids on glycolytic enzymes have been reported (3‘17, 451), but it is doubtful whether the cytoplasmic fatty acid concentration is sufficiently high to exert a direct negative effect on the rate of the glycolytic pathway under physiological conditions (591). Other metabolic intermediates, such as citrate, acetyl-CoA, and NADH, may also contribute to preferential utilization of fatty acids in cardiac tissue. Extraction and subsequent oxidation of fatty acids result in enhanced production of citric acid, elevated NADH/ NAD+ ratio, and acetyl-CoA formation in the mitochondrial matrix (169, 392). Although citrate modulates

ACID

HOMEOSTASIS

893

phosphofructokinase activity in vitro, it is doubtful whether this metabolic intermediate interferes with the glycolytic enzyme in vivo as citrate release from cardiac mitochondria is minimal (523). High NADH and acetylCoA levels in the mitochondria depress the oxidation of pyruvate at the level of pyruvate dehydrogenase (392). This contributes to reduced utilization of glucose in the presence of excess fatty acids (405,532, 636). Lactate is capable of competing successfully with fatty acids for mitochondrial oxidation (122, 291, 334, 539). At normal plasma lactate concentrations (i.e., on the order of 0.5-1.0 mmol/l) the amount of lactate extracted and subsequently oxidized by the heart is insufficient to generate all energy required for proper electromechanical performance. At higher extracellular lactate levels, on the order of 5 mmol/l, a level readily reached during physical exercise, lactate oxidation appears to account for >85% of the energy generated by substrate oxidation (122,539). These findings in anesthetized animals are in line with earlier observations in awake human volunteers and dogs (290,291,334). The molecular mechanism underlying lactate-induced inhibition of cardiac fatty acid oxidation is partly elucidated. Rose and Goresky (467) proposed that increased lactate utilization leads to inhibition of the activity of acyl-CoA synthetase. More recent experiments showing that lactate increases the incorporation of fatty acyl moieties in the endogenous triacylglycerol pool do not support this hypothesis (36, 125, 612, 613). Increased incorporation of exogenous fatty acids in the cellular neutral fat stores with a concomitant inhi bition of fatty acid oxidation can be explained by impairment of the activity of carnitine acyl-CoA transferase I (36). It has been hypothesized that lactate stimulates acetylCoA carboxylase, which results in enhanced cytoplasmic levels of malonyl-CoA. The latter compound is an inhibitor of carnitine acyl-CoA transferase I activity. The finding that acylcarnitine levels are decreased in lactate-perfused hearts is in line with this notion (36). Additional evidence for inhibition of a carnitine-dependent step is the observation that oxidation of octanoate, a medium-chain fatty acid not requiring carnitine for transport into the mitochondrial matrix, is not influenced by high concentrations of lactate in the cardiac perfusion buffer (36,146). In addition, lactate will most likely increase the sarcoplasmic NADH/NAD+ ratio. A concomitant increase in mitochondrial redox state will result in decreased activity of the ,&oxidation pathway. Lactate-induced inhibition of cardiac fatty acid oxidation was found to be associated with enhanced backdiffusion of radiolabeled fatty acids into the venous system after extraction from the microvascular compartment (126, 467). Other exogenous substrates, such as pyruvate, usually present in blood in minor quantities, have been found to compete effectively with fatty acids for oxidative degradation in cardiac muscle (38,136,146). An increased supply of pyruvate inhibits fatty acid ,&oxidation most likely at the level of intramitochondrial CoA. Reduced CoA is used in the conversion of pyruvate to


894

VAN DER VUSSE, GLATZ,

acetyl-CoA, catalyzed by the pyruvate dehydrogenase complex (392). In isolated rat hearts oxidation of oleate and octanoate is hampered by a concomitant supply of ketones, such as acetoacetate and P-hydroxybutyrate (146). Because the oxidative degradation of both longchain and medium-chain fatty acids is diminished, it follows that the locus of inhibition must be in @-oxidation itself or the subsequent oxidative conversion of acetyl-CoA. D. Fatty Acids in Cardiac Lipid Pools

Phospholipids and triacylglycerols are the main storage forms of fatty acyl moieties in the heart. Phospholipids are essential constituents of the sarcolemma and intracellular membranes. It is uncertain whether fatty acyl moieties incorporated in this lipid pool also serve as internal sources of substrates for oxidative energy production. This role is most likely reserved for triacylglycerol fatty acids. Studies in isolated rat hearts perfused in the absence of exogenous substrates underline this notion (406, 512). Endogenous triacylglycerols are also the primary storage pool of such fatty acids as arachidonic acid after extraction from the extracellular compartment (213). Thereafter arachidonic acid is most likely transferred to the endogenous phospholipid pool, as this pool contains, on a quantitative basis, almost all arachidonic acid moieties present in the heart (see sect. IIIA). 1. Cardiac triacylglycerols

Triacylglycerols are localized at various sites in the heart. Part of this lipid pool is present in cardiac adipocytes. With the naked eye, clusters of adipocytes are visible in the vicinity of the superficial epicardial coronary arteries of dog and rat hearts. In humans, fat cells sometimes completely cover the epicardium (588). In addition to fat deposition in the interstitial space (471), triacylglycerols are stored inside the cardiomyocytes and, to some extent, in the endothelial cells (141). Part of the endogenous triacylglycerols is present as free-floating cytoplasmic lipid droplets, easily visible on electron micrographs. These lipid aggregates, the diameter of which varies from 0.5 to 1.0 pm, are found in close vicinity of mitochondria. These droplets may represent a relatively inert form of triacylglycerol in the cardiomyocyte, since they are not associated with membranes containing lipid-hydrolyzing enzymes (554). An additional portion of intracellular triacylglycerols is associated with lysosomal-like particles (554). Some triacylglycerols may be integral parts of cellular membranes or attached to membranes in the form of small lipid spheres. Biochemical studies have revealed that the microsomal fraction of heart homogenates, enriched in fragments of sarcoplasmic reticulum, contains significant amounts of triacylglycerol (75). The latter lipid pool may represent newly synthetized triacylglycerol,

STAM, AND RENEMAN

Volume

72

since the key enzymes in the formation of triacylglycer01s are of sarcoplasmic reticular origin (489). The intracellular triacylglycerol pools are in a dynamic state (90, 91). Both intracellular transport of triacylglycerols and enzymatic synthesis and degradation occur in the cardiomyocytes (see sect. III, D2 and 03). In a number of tissues transfer of triacylglycerols between intracellular membranes is mediated by an endoplasmic reticular protein complex with a molecular mass of 220 kDa (641, 642). Because the amount of this protein in the cardiomyocyte is rather low, other mechanisms for intracellular triacylglycerol transfer may prevail (554). The turnover of the various triacylglycerol pools in the heart may depend on the site of localization. In this respect it is worthwhile to note that autophagy of the metabolically inert, cytoplasmic lipid droplets by lysosomes most likely renders this lipid pool relatively more susceptible to triacylglycerol hydrolysis (490,554). 2. Enx ymes involved in triac ylgl ycerol synthesis

In 1961 Kennedy (288) described the complete pathway of the synthesis of triacylglycerols in mammalian tissue. The overall reaction of glycolytically derived glycerol 3-phosphate with 3 mol fatty acyl-CoA is accomplished by a set of enzymes situated in various loci in the cell (29). In cardiac cells glycerol 3-phosphate is the product of a NADH-driven reduction of dihydroxyacetone phosphate, an intermediate of the glycolysis (Fig. 3). This reaction is catalyzed by glycerol-3-phosphate glucose,

glycogen I

I dihydroxyaceton-P

NADH a n.

NAD+ glycerol-3-P

02 c 1-acyl

lycerol-3-P

CoA

03

acylCoA

-A

phosphatidic

phospholipids

acid -

PiA@

f

1,2-diacylglycerol acylCoA CoA

7

0’

t riacylglycerol

m / 7-h

fatty

acid

fatty

acid

fatty

acid

diacylglycerol @// monoacylglycerol @/L

/

glycerol

FIG. 3. Synthesis and degradation of triacylglycerols in myocardial tissue. Numbers refer to enzymes involved: 1) glycerol-3-phosphate dehydrogenase, 2) glycerol-3-phosphate acyltransferase, 3) lacylglycerol-phosphate acyltransferase, 4) phosphatidic acid phosphatase, 5) diacylglycerol acyltransferase, 6) triacylglycerol lipase, 7) diacylglycerol lipase, 8) monoacylglycerol lipase. P, phosphate.


October

1992

MYOCARDIAL

FATTY

dehydrogenase, present in both the mitochondrial and cytoplasmic compartments of the cardiomyocyte. Direct phosphorylation of free glycerol contributes to the formation of myocytal glycerol 3-phosphate to a minor extent, because in cardiac tissue the activity of glycerol kinase has been reported to be relatively low (464). Binding of fatty acyl chains to the glycerol backbone occurs by condensation of glycerol 3-phosphate, with one molecule of fatty acyl-CoA yielding l-acylglycerol-3-phosphate (catalyzed by glycerol-3-phosphate acyltransferase), followed by a second condensation step, i.e., the reaction of 1-acylglycerol-3-phosphate with fatty acyl-CoA to form phosphatidic acid (catalyzed by 1-acylglycerol-phosphate acyltransferase). Phosphatidic acid can serve as substrate for either phospholipid synthesis or the formation of triacylglycerol (Fig. 3). In the latter case, the end-standing phosphate group is removed by phosphatidic acid phosphatase yielding 1,2-diacylglycerol. This enzyme is present in the microsomal, lysosomal, and mitochondrial fractions of heart homogenates (554). Interestingly, in vitro observations indicate that the enzyme phosphatidic acid phosphatase can translocate from the cytoplasmic space to intracellular membranes and vice versa (489). On the basis of the localization of the other lipogenic enzymes, in cardiac tissue phosphatidic acid phosphatase of microsomal origin is considered to be involved in cardiac neutral lipid formation (554). Condensation of I,%diacylglycerol with a third molecule of fatty acyl-CoA, catalyzed by diacylglycerol acyltransferase, forms triacylglycerol (Fig. 3). Because diacylglycerol acyltransferase is localized at the cytoplasmic leaflet of the sarcoplasmic reticulum, the final step in the formation of triacylglycerol occurs at the interface between the cytoplasmic compartment and the outer surface of the sarcoplasmic reticular membrane (29, 558). It is conceivable that lipid spheres are budded off from the sarcoplasmic reticulum or that fusion occurs with other intracellular membranes or particles. Both phosphatidic acid phosphatase and diacylglycerol acyltransferase from rat heart were recently characterized (489). 3. Enx ymatic hydrolysis

of cardiac

triacylglycerols

Degradation of triacylglycerols in cardiac tissue is mediated by a set of three distinct enzymes, operating in a successive way (503,504,507,544,545). Triacylglycerol lipase catalyses the removal of a fatty acyl chain attached to one of the end-standing carbon atoms of the glycerol backbone of triacylglycerol. The second and last fatty acyl chains are split off by diacylglycerol and monoacylglycerol lipase, respectively (Fig. 3). The latter two enzymes can be recovered in the microsomal fraction of cardiac homogenates, suggesting a localization in the endoplasmic reticulum of the cardiac cells (225,507, 544). Because the activity of both diacylglycerol lipase and monoacylglycerol lipase exceed by far the activity of triacylglycerol lipase in cardiac tissue, the latter en-

ACID

HOMEOSTASIS

895

zyme has been identified as catalysator of the ratelimiting step in overall tri .acylglycerol hydrolysis (503 9 507, 544, 545). The exact nature and localization of this key enzyme in triacylglycerol hydrolysis have been a matter of debate (19,243,303,318,362,417,425,503,504, 549, 554). Several distinct triacylglycerol lipases have been found in cardiac tissue. On the basis of pH activity curves of triacylglycerol hydrolysis in tissue homogenates, three lipases can be identified in the heart: alkaline lipoprotein lipase and neutral and acid triacylglycerol lipases (554). Acid lipase is most likely localized in the cardiac lysosomes and has been proposed to play a crucial role in endogenous triacylglycerol hydrolysis (490). Evidence collected during the past decade that favors this notion includes the presence of triacylglycerols in lysosomes (242,620), the depletion of the lysosomal triacylglycerol pool in isolated rat heart during in vitro perfusion (489, 490,545), the unimpeded hydrolysis of endogenous triacylglycerol in hearts depleted in neutral triacylglycerol lipase activity (545), the inhibition of lipolysis of endogenous triacylglycerols by drugs depressing lysosomal activity (242), and the observation that isolated cardiac lysosomes are capable of internalizing and degrading triacylglycerols (489, 490). However, the crucial role of lysosomes in endogenous triacylglycerol degradation has been seriouly challenged by others (303). It is uncertain whether, and to what extent, neutral lipases are involved in endogenous triacylglycerol hydrolysis. Substantial evidence indicates that the majority, if not all, of the neutral lipase in cardiac tissue represents lipoprotein lipase synthetized and processed in cardiomyocytes before transfer to their site of action at the luminal endothelial cell membrane (490). In homogenates prepared from heparin-perfused hearts from which vascular lipoprotein lipase is washed off, the residual lipoprotein lipase shows its highest activity at neutral pH, which hampers the unequivocal detection of another neutral lipase(s). After removal of vascular lipoprotein lipase by heparin perfusion and intracellular lipoprotein lipase by heparin sepharose-affinity chromatography, the presence of a low and labile neutral triacylglycerol lipase activity, insensitive to serum factors and polyclonal antibodies raised against lipoprotein lipase, could be demonstrated (191, 452). Recently Small et al. (524) were also able to show the existence of a neutral lipase activity in whole heart homogenates and in homogenates of isolated myocytes. This enzyme was purified, revealed an estimated molecular mass of 84 kDa, and showed sensitivity toward antibodies raised against hormone-sensitive lipase from adipose tissue. The CAMP-protein kinase system stimulated the lipolytic activity of this enzyme (524). The actual contribution of this enzyme to in vivo triacylglycerol hydrolysis remains to be established. Circumstantial evidence indicates that hydrolysis of long-chain polyunsaturated fatty acyl groups from cardiac triacylglycerol occurs at a lower rate than saturated and monounsaturated fatty acyl moieties (101). Various investigators have attempted to assess the


896

VAN

DER

VUSSE,

GLATZ,

maximal activity of neutral and acid triacylglycerol lipases in rat cardiac tissue (191, 221, 243, 352, 488, 490, 508, 544). Data obtained appear to vary appreciably. When expressed as nanomoles of fatty acids released per milligram of protein per minute the lowest and highest values of neutral lipase reported are 0.18 (222) and 12.2 (352), respectively. Acid lipase varied from 0.14 to 0.45 nmol fatty acid min-’ . mg protein-’ (508, 544). The differences may be caused by the fact that the actual lipase activity measured is largely dependent on the nature and the purity of the (artificial) triacylglycerol substrate, the presence of albumin and/or serum in the assay system, and the subcellular membrane preparations used. In addition, neutral lipase activity appears to be sensitive to freeze-thawing and prolonged storage at -20°C @tam et al., unpublished results). l

4. Regulation

of cardiac

triacylglycerol

formation

Short-term regulation of cardiac triacylglycerol formation is thought to be governed by the supply of substrates, cellular concentration of cofactors, and the phosphorylation state and subcellular localization of the anabolic enzymes involved. Increased tissue levels of glycerol 3-phosphate and fatty acyl-CoA promote the formation of neutral lipids (554). Although information on phosphorylation and dephosphorylation of glycerol3-phosphate acyltransferase, phosphatidic acid phosphatase, and diacylglycerol acyltransferase in cardiac tissue is limited, the apparent homology of these enzymes in mammalian tissues most likely allows extrapolation of observations in liver and adipose tissue to the heart (29,554). The activity of these lipogenic enzymes is depressed by phosphorylation of the enzyme, whereas dephosphorylation augments the catalytic activity. The CAMP-dependent protein kinases play an important role in this mechanism (29). In line with this notion is the observation that adrenergic agents decrease cardiac glycerol-3-phosphate acyltransferase activity. a,-Antagonists were found to stimulate the biosynthetic activity of this enzyme (222). In vitro studies indicate that such lipogenic enzymes as phosphatidic acid phosphatase have a dual intracellular localization. Conditions known to enhance cardiac neutral lipid formation are associated with increased amounts of the enzyme attached to the sarcoplasmic reticulum at the expense of the cytoplasmic content (489). This intracellular translocation is proposed to play an important role in the regulation of triacylglycerol synthesis, since this anabolic process is largely localized at the surface of the endoplasmic reticulum (29). A variety of intracellular cofactors and other metabolically active substances has been shown to influence the activity of the lipogenic enzymes in vitro. In general, FABP, polyamines, divalent cations, and fatty acids increase the biosynthetic activity, whereas acylcarnitine and probably also carnitine exert a depressive action (554). Enhanced fatty acid levels in plasma during recov-

STAM,

AND

RENEMAN

Volume

72

ery from exercise most likely play a key role in the resynthesis of the cardiac triacylglycerol pool (437). Long-term regulation of the cardiac capacity to synthesize triacylglycerol is determined by increased formation and hence an augmented cellular content of lipogenie enzymes. In this respect variations in the capacity to synthesize triacylglycerol during cell differentiation, corticosteroid, and thyroxine treatment, ethanol administration, fasting, and experimentally provoked diabetes are worth mentioning (29,52,270,271,383). 5. Regulation

of triacylglycerol

hydrolysis

As discussed in section IIID3, the rate-limiting step in hydrolysis of intracellular triacylglycerol is the conversion of triacylglycerol into diacylglycerol, a step catalyzed by enzymes commonly referred to as triglyceridases or triacylglycerol lipases (490,554). Long-term regulation of the rate of triacylglycerol hydrolysis most likely involves enzyme protein synthesis and degradation, resulting in an increased number of enzyme molecules in the cardiac cells (543,553). Neutral lipase activity was found to be increased after treatment with ACTH, corticosteroids, and thyroxine and after fasting. Diabetes depressed cardiac neutral lipase activity (553). Acid lipase activity was enhanced by fasting and in vivo thyroxine treatment, whereas ACTH treatment failed to modulate acid lipase activity. Diabetic animals showed depressed cardiac lysosomal lipase activity; corticosteroid treatment had a comparable effect on this enzyme (553). The mechanism underlying the acute regulation of intracellular cardiac lipase activity is far from clear. Theoretically, various modes of action can be responsible for acceleration of the conversion of triacylglycerol into diacylglycerol: 1) a direct activating effect on the enzyme by, for instance, chemical modification of the enzyme protein structure (phosphorylation, glycosylation) or physicochemical changes at the level of the active center of the enzyme (pH, Ca”‘); 2) mitigation of feedback inhibition by either (end)products of lipolytic activity, such as fatty acids, fatty acyl-CoA, and monoacylglycerols or by fatty acids extracted from extracellular sources; 3) translocation of the enzyme to the site of triacylglycerol storage; 4) translocation of triacylglycerol to the site of enzyme localization; 5) physicochemical modification of the triacylglycerol pool, rendering the triacylglycerol molecules more sensitive to the action of lipases; and 6) other regulating processes or compounds unknown until now. Stimulation of the hydrolysis of cardiac triacylglycerols by such hormones as catecholamines has been clearly established (94). Moreover, ,&adrenergic blockade prevents utilization of endogenous triacylglycerol in vivo (555). Hron et al. (232) have shown that both catecholamine- and glucagon-stimulated triacylglycerol hydrolysis is dependent on a threshold extracellular Ca2+ level. Cyclic AMP may mediate the lipolytic effect of catecholamines and glucagon (74,318,449), as the activ-


October

1992

MYOCARDIAL

FATTY

ity of a neutral triacylglycerol lipase in cell-free cardiac preparations is enhanced by the CAMP-protein kinase system (191, 222, 424, 524). These observations suggest phosphorylation of the lipase protein as the activating mechanism. Findings of Schoonderwoerd et al. (487) strongly suggest that the effect of the CAMP-protein kinase system on lipase activity is indirect, since the presence of glycogen or glycogen derivatives, such as glucose or glycerol 3-phosphate, is an absolute requirement for full expression of enhanced hydrolysis of triacylglycerol. Depletion of glycogen or glycolytic intermediates completely abolishes CAMP-protein kinase stimulation of triacylglycerol hydrolysis in cardiac homogenates. Therefore it has been suggested that the increased supply of intermediates, such as glycerol 3-phosphate, used for reesterification of fatty acids and their CoA derivatives may lead to the continuous removal of inhibitory fatty acids from the catalytic site of the enzyme and hence promote degradation of triacylglycerol (554). Feedback inhibition of triacylglycerol lipase by fatty acids and their CoA and carnitine derivatives has been found under various in vitro conditions (352, 508, 549). It remains to be established whether fatty acids and their esters exert feedback inhibition on triacylglycerol lipase in vivo because this modulating effect was observed at fatty acid levels not commonly present in the intact heart. Moreover, the effects of specific binding proteins and differences in intracellular compartmentalization of fatty acyl moieties and the lipase enzymes should be considered. Intracellular translocation of lipolytic enzymes to the site of triacylglycerol storage will theoretically enhance the actual rate of triacylglycerol degradation. Until now, no conclusive data were presented to support this possibility. On the contrary, engulfment of intracellular triacylglycerol by lysosomes, which implicates transfer of substrate to the enzymes, might play an important role in the regulation of cardiac triacylglycerol hydrolysis (490). Subtle alterations at the surface of intracellular lipid droplets may render this endogenous substrate pool more susceptible for the hydrolytic attack of lipases, since the latter enzymes operate at the waterlipid interface. These changes may include enlargement of the available surface of the lipid material by endogenous compounds with detergent action. In addition, newly synthetized triacylglycerol has been hypothesized to be more sensitive to hydrolytic enzymes than triacylglycerol molecules closely packed in the core of the endogenous lipid spheres (111). Phospholipids were found to influence cardiac triacylglycerol hydrolase in vitro (509). Phosphatidylethanolamine and its lyso form appreciably stimulated the hydrolytic activity of the enzyme. Phosphatidylcholine and cardiolipin were inhibitory. The myocardial lipase may have obligatory requirements for certain phospholipid species, since the activity was markedly reduced in acetone-ether powder preparations, virtually devoid of phospholipids. Activity was restored to near-control lev-

ACID

897

HOMEOSTASIS

els after addition mine (509). 6. Triacylglycerol-fatty

of

(lyso)phosphatidylethanola-

acid cycle in normal heart

Increased lipolysis can occur without net depletion of the intracellular triacylglycerol pool when resynthesis of neutral lipids speeds up to the same rate as hydrolysis. Under such conditions glycerol release will be augmented and a triacylglycerol-fatty acid cycle is operating. Enhanced turnover of the cardiac triacylglycerol pool by accelerated hydrolysis in concert with increased resynthesis of triacylglycerol has been demonstrated in hearts perfused with elevated concentrations of lactate (111,410). Similar to lactate, malate stimulates the turnover of the endogenous triacylglycerol pool (410). This effect of malate or lactate can be explained by inhibition of mitochondrial carnitine acyltransferase and hampering of P-oxidation due to an enhanced NADH/NAD+ ratio, leaving more cytoplasmic fatty acids available for the reesterification process (36). However, it is unlikely that in vivo the rate of triacylglycerol hydrolysis, the increase of which is required for a balanced turnover, is enhanced by mitigated feedback inhibition though fatty acids, since the tissue content of fatty acids was found to be increased in lactate perfused hearts (Ill). It has been hypothesized that in the latter hearts the newly synthetized triacylglycerol pool is more susceptible to cardiac lipase activity (111). Withdrawal of fatty acyl moieties from the resynthesis-degradation cycle, a situation that readily occurs when the metabolic need for these substrates is increased (enhanced workload) or the supply from exogenous sources is abolished (perfusion of isolated hearts in the absence of appropriate substrates), will unmask the activity of hydrolytic enzymes in the heart without really changing the actual flux of fatty acyl moieties through the catabolic pathway. During normoxic perfusion of isolated rat hearts triacylglycerol levels fall to -50% of control in 1 h of perfusion (406). However, when glucose was present as cosubstrate, net depletion of the endogenous triacylglycerol pool occurred at a lower rate (244). The latter investigators calculated that >50% of the fatty acids hydrolyzed from neutral lipids were reesterified during the course of the experiment. The consequences of enhanced triacylglycerol turnover for cardiac energy expenditure are discussed in section vA3. 7. Fatty acids in cardiac phospholipid pool

Like other mammalian organs, the heart contains a substantial amount of phospholipids. On the average the total content of phospholipids in the myocardium amounts to 20-25 pmol phosphorus/g wet wt cardiac tissue, accomodating on the order of 40-50 pmol fatty acyl


898

VAN phospholipase phospholipase

VUSSE,

GLATZ,

A1

I II

A2

DER

;0 I I II /I ti2c1-OiC-R, I ‘2

R*-40-C-H

phogpholipase

o

II

’

D

11 /’

I

H2C3-OTP-‘6-X 1I 1 I I 0 I I

I

I I I

phospholipase

C

FIG. 4. Schematic representation of chemical structure of diacylphospholipids. R,, R,, fatty acyl chains; X, commonly choline, ethanolamine, serine, inositol, or glycerol. Specific site of action of various phospholipases are indicated by arrow. Numbers refer to snl, sn2, and sn3 positions on glycerol backbone. [Modified from Achari et al. (4).]

moieties (595). This amount corresponds with -85% of the total endogenous cardiac fatty acid pool. Phospholipids consist of a variety of species differing in chemical composition of their hydrophilic headgroup. The phospholipid molecule possesses a hydrophobic tail that is composed of two long-chain fatty acyl chains covalently bound to the first (snl) and second (sn2) carbon atom of the glycerol backbone (Fig. 4). The third carbon atom (sn3) of glycerol is covalently bound via phosphate to an alcohol molecule. The nature of this hydrophilic headgroup is determined by the chemical composition of the alcohol moiety. The most common alcohols attached to the phosphate group at the sn3 position in cardiac tissue are choline, ethanolamine, serine, inositol, and glycerol. The latter alcohol component generally forms the bridge between two covalently bound phospholipids, as is the case in cardiolipin. The most abundant phospholipids in the heart are phosphatidylcholine and phosphatidylethanolamine. They comprise -40 and 30% of the total rat cardiac phospholipid pool, respectively. A significantly lower value of phosphatidylethanolamine has been monitored in human heart, i.e., ~20% of total phospholipids (465). Only small amounts of phosphatidylinositol, phosphatidylserine, and cardiolipin are found in cardisc tissue. Under normal conditions lysophospholipids, lacking one fatty acyl chain at either snl or sn2, are present in trace amounts (85,510). Sphingomyelin, present in the heart in relatively small amounts, does not possess glycerol as a backbone but is composed of one molecule of sphingosine to which one fatty acyl chain and one molecule of phosphocholine are covalently bound. The hydrophobic part of phospholipids is formed by the aliphatic fatty acyl chains. The number of carbon atoms in the aliphatic chain is even and commonly varies from 14 to 24. The number of unsaturated bonds in the acyl chain also varies. Up to six unsaturated bonds can be present in very long-chain fatty acyl chains. Fatty acids, such as arachidonic acid, are almost exclusively incorporated in the phospholipid pool. The rela-

STAM,

AND

RENEMAN

Volume

72

tive composition of the fatty acyl moieties greatly differs among the various phospholipid subclasses (587). It should be noted that the fatty acid composition of the various phospholipid species is dependent on a variety of factors, including composition of diet and animal speties (64-66). Three distinct types of choline-containing phospholipids have been identified (10, 217). They differ in nature of the bond of one of the aliphatic chains to the glycerol backbone. The most abundant form of cholinecontaining phospholipids in the heart is diacylphosphatidylcholine. Both aliphatic chains are attached to glycerol by ester linkages. In alkenylacylphosphatidylcholine the connection of the aliphatic chain at the snl position of glycerol is a vinyl ether bond rather than an ester linkage. This form is commonly referred to as choline plasmalogen. Substantial differences between animal species have been reported with respect to the proportions of plasmalogens in the cardiac phosphatidylcholine pool (15, 201, 217, 510, 579). In dog, rabbit, and guinea pig hearts it is present in rather high quantities (up to 40% of phosphatidylcholine), but in rat and hamster hearts it comprises only -3-5% of the phosphatidylcholine pool. Intermediate values were found in human hearts (465). The third type, alkylacylphosphatidylcholine, is present in cardiac tissue in trace amou nts (217). The plasmalogen form of phosphatidylethanolamine has also been identified in cardiac tissue (349). The rel .ative prevalen ce in rat hearts appears to be lower than that of the phosphatidylcholine form (579). 8. Phospholipids

in cardiac

membranes

Like other mammalian cells, cardiac myocytes and endothelial cells are enclosed in a plasmalemma. Organelles, such as mitochondria, lysosomes, and nuclei localized inside the cells, are surrounded by intracellular membranes. Phospholipids, cholesterol, and proteins are the main constituents of these cellular and subcellular membranes. Studies dealing with the subcellular localization of phospholipids have revealed that a relatively minor part of the cardiac phospholipids is located in the sarcolemma, i.e., on the order of 5-10% of the total phospholipid pool (85). Hence the majority of phospholipids are localized in the intracellular membranes. Cardiac myocyte membranes are composed of two leaflets. In the plasmalemma the hydrophilic head groups of the inner leaflet point toward the intracellular compartment and the hydrophilic head groups of the outer leaflet point toward the interstitial fluid. The hydrophobic part of the phospholipid molecules, mainly composed of the aliphatic fatty acyl chains, is buried in the inner region of the phospholipid bilayer. The various phospholipid subclasses are asymmetrically distributed over the inner and outer leaflet. The outer leaflet contains predominantly phosphatidylcholine in combination with sphingomyelin. The inner leaflet is relatively enriched in phosphatidylethanolamine and phosphatidylinositol. Phosphatidylserine is almost exclusively lo-


October

1992

MYOCARDIAL

FATTY

calized in the inner leaflet (438). To compensate for differences in fluidity between the inner and outer leaflet of the bilayer the cholesterol content of the outer exceeds that of the inner leaflet (144). Because membranes play a critical role in normal cellular functioning, a balanced synthesis and degradation of phospholipids and incorporation and release of fatty acids in and from the phospholipid pool is of paramount importance for adequate cellular performance. 9. Phospholipid turnover

The phospholipid components of cellular membranes are subject to a continuous turnover process, enabling the cell to regulate the intracellular phospholipid composition and the fatty acyl moieties forming the hydrophobic tail (581). It is generally considered that turnover of phospholipids is required to repair damaged phospholipid molecules and to adjust the biological properties of the phospholipid moieties in the membranes to changes in cellular conditions. The actual rate of turnover of the total cardiac phospholipid pool is unknown (217, 595). The turnover rate may depend on the phospholipid species and the nature of the (sub)cellular membrane in which they are incorporated (364). Theoretically, the rate of phospholipid turnover is determined by the rate of hydrolytic degradation of the phospholipid molecules and their energy-dependent resynthesis. Several metabolic routes for degradation and resynthesis of phospholipids are present in the cardiac cell (Fig. 5). Regarding the pathway of de novo synthesis of phosphatidylcholine, Zelinski et al. (661) determined in the isolated hamster heart, perfused with radiolabeled choline, a rate of phosphatidylcholine formation of -40 nmol . mine1 . g wet wt-? Recently, Lochner and

ACID HOMEOSTASIS

899

De Villiers (330) found in isolated rat hearts in a comparable experimental setup a formation rate of -0.8 nmol min-l g-l. Considering the total phosphatidylcholine content of ~8 pmol phosphorus/g wet wt and assuming that degradation of phospholipids keeps pace with resynthesis, complete turnover of the cardiac phosphatidylcholine pool will take 3.3 h and 7 days in hamsters and rats, respectively. No explanation can be offered for this species difference. The deacylation-reacylation cycle is an alternative pathway of phospholipid turnover. The acyl group at either the snl or sn2 position can be split off, yielding one lysophospholipid and one fatty acid molecule. The resultant lysophospholipid can be either further hydrolyzed to glycerophosphoalcohol and fatty acid or reacylated to the parent phospholipid (217,581). Deacylationreacylation offers the possibility to modulate the fatty acid composition of the endogenous phospholipid pool. The phosphate part of the molecule can be released from the glycerol backbone by hydrolytic action, a reaction step yielding phosphoalcohol and diacylglycerol. Lastly, the bond between the alcohol moiety of the hydrophilic headgroup and phosphate can be hydrolyzed. The latter two pathways are of crucial importance for the production of biologically active compounds. Both diacylglycerol and hydrolytic products of phosphatidylinositol have been identified to play a role in (intra)cellular signaling. For more detailed information on this subject the reader is referred to two recent reviews (105,453). l

l

10. Phospholipid hydrolyzing enzymes

Enzymes involved in the hydrolytic cleavage of the various components of the phospholipid molecule are referred to as phospholipases. A variety of phospholipases has been identified in cardiac tissue (217, 595). They differ in subcellular localization and nature of the acyl CoA chemical bond hydrolyzed by their catalytic action (Fig. 4). CoA palmitic arachidonic Phospholipases A, and A, catalyze the hydrolysis of acid acid the acylester bond at the snl and sn2 position of glycerol, respectively. Phospholipase C attacks the bond between the third carbon atom of glycerol and the phosphate component of the polar headgroup, whereas I CDP-choline phospholipase D catalyzes the hydrolysis of the phos16 I phoalcohol linkage (581). Phospholipase Al and A2 activ/- CTP arachidonic acid phosphorylity gives rise to the formation of lysophospholipids. The palmitic acid choline 1 1 remaining fatty acyl moiety of lysophospholipids can be phosphatidyldiacylglycerol A glycerol 5 removed by the action of lysophospholipase, abundantly choline a present in cardiac cells (202,207,208,386,506). Cardiac FIG. 5. Synthesis and degradation of phosphatidylcholine. Path- tissue contains enzymes that are specialized in cleaving way I: deacylation-reacylation pathway. In this example palmitic acid and arachidonic acid are bound to glycerol backbone at snl and sn2 the glycerol ether linkage and glycerol ester bonds in plasmalogens, i.e., plasmalogenase and plasmalogenpositions, respectively. Pathway II: turnover of hydrophylic headgroup phosphorylcholine. Numbers refer to enzymes involved: 1) specific phospholipase AZ, respectively (14, 16, 145, 219, phospholipase A,, 2) acyl-CoA synthetase, 3) lysophosphatidylcholine 385, 656). acyltransferase, 4) lysophospholipase, 5) phospholipase C, 6) Almost all subcellular compartments and memCTP:phosphocholine cytidylyltransferase, 7) phosphocholine transbrane structures have been found to possess phosphoferase, 8) diacylglycerol + monoacylglycerol lipases. [From van der lipid hydrolyzing activity. Part of the phospholipase Al Vusse et al. (594).]


900

VAN

DER

VUSSE,

GLATZ,

STAM,

AND

RENEMAN

Volume

72

and A, activity is localized in the cytoplasm (59,385,386, 567,656). The pH optimum of the soluble enzymes varies from 8.4 in rat hearts to 7.0 in bovine cardiac tissue. In some animal species phospholipase A,, displaying its maximal activity at a pH varying between 6 and 9, has been found to be associated with the sarcolemma (155, 630). Mitochondrial membranes contain both phospholipases A, and A2 (16,385,423,629). Cardiac endoplasmic reticulum also contains enzymes that are capable of hydrolyzing fatty acyl chains incorporated at the snl and sn2 position of phospholipids. The microsomal enzymes show their highest activity in vitro under mildly alkaline conditions (205, 567, 629, 656). Phospholipases A1 and AZ, associated with cardiac lysosomes, are active under acidic conditions, i.e., at a pH varying from 4 to 5 (157, 385). The maximal activity of phospholipase AZ, measured in cardiac homogenates in the presence of endogenous substrates, is found to be on the order of 0.25 hydrolyzed pmol g dry wt? min-’ of phospholipid (570). Recent studies performed on rat cardiac tissue, damaged by freeze-thawing and subsequently stored under anoxic conditions, show a degradation rate of phosphatidylcholine and phosphatidylethanolamine of ~0.16 pmol l g dry wt-’ min-’ (584). Because cardiac tissue contains -120 pmol/g dry wt of phosphatidylcholine and phosphatidylethanolamine (584), complete removal of the fatty acyl groups from the intracellular phospholipid pool of these phospholipids would take ~10 h. Plasmalogen-specific phospholipase AZ has been identified both in the cytosolic and membrane-rich fractions of cardiac homogenates (145,219). The activity of this novel class of calcium-independent phospholipases in cardiac tissue appears to be on the same order of magnitude as that of phospholipase A2 acting on diacylphospholipids. Interestingly, the cytosolic plasmalogen-phospholipase A2 is activated by ATP, suggesting a possible role of this high-energy phosphate in modulating the fatty acid composition of plasmalogen-type phospholipids and hence in modifying the physical properties of cellular membranes (220). Lysophospholipases are abundantly present in the soluble sarcoplasmic compartment (207, 385), but subcellular structures, such as mitochondria, sarcoplasmic reticulum, and lysosomes, also contain lysophospholipolytic activity (385). The activity of cardiac phospholipase C (230) is predominantly present in the soluble cytoplasmic compartment and lysosomes (153,497,656). Phospholipase C activity is also monitored in mitochondrial, microsomal, and sarcolemmal membrane fractions isolated from rabbit hearts (655). The presence of phospholipase D in cardiac tissue has recently been demonstrated (326).

ied and well documented (217). De novo synthesis of phosphatidylcholine is mainly accomplished by the CDP-choline pathway (217). In this pathway choline is converted into phosphocholine by choline kinase. Phosphocholine is activated at the expense of one molecule of CTP by cytidylyl transferase, resulting in the formation of CDPcholine. The condensation of 1,2=diacylglycerol and CDPcholine yields phosphatidylcholine. This step is catalyzed by phosphocholine transferase. Cytidylyl transferase catalyzes the rate-limiting step in the overall reaction (661). The contribution of methylation of phosphatidylethanolamine and base exchange of other phospholipids by choline to the formation of phosphatidylcholine was found to be limited (217, 661). In vivo studies indicate that phosphocholine transferase displays limited specificity for the fatty acyl composition of its substrate 1,2-diacylglycerol(l3). This suggests that the final fatty acyl composition of phosphatidylcholine is accomplished by extensive remodeling to attain the required acyl groups at the snl and sn2 positions of the glycerol backbone. Remodeling of the fatty acyl chain in phosphatidylcholine is largely achieved by the consecutive hydrolysis of one fatty acyl moiety by phospholipase A followed by a reacylation step catalyzed by lysophosphatidylcholine transferase. This process is commonly referred to as the deacylationreacylation cycle and has been extensively studied in guinea pig hearts by Arthur and co-workers (15,17). An alternative mechanism to achieve distinctive and nonrandom composition of fatty acyl moieties in phospholipids is transacylation. When two lysophosphatidylcholine molecules react, phosphatidylcholine and glycerophosphocholine are produced (204,206). Hatch et al. (217) have postulated that the acyl composition of cardiac membrane phospholipids is probably determined by the selectivity of both phospholipase A and acyltransferase and by the fatty acyl composition of acyl-CoA, required for resynthesis of the phospholipid molecule. In cardiac cells synthesis of phosphatidylethanolamine is accomplished in a comparable way as described for phosphatidylcholine (217). De novo synthesis of phosphatidylserine and phosphatidylinositol occurs via a different metabolic route. The formation of the latter two phospholipids starts with the synthesis of CDPdiacylglycerol from CTP and phosphatidic acid. Phosphatidylserine and phosphatidylinositol are produced when CDPdiacylglycerol reacts with serine or inositol, respectively (217). The site of phospholipid synthesis in the cardiac cell is most likely the sarcoplasmic reticulum. Specific phospholipid-binding proteins are involved in the transport of the newly formed phospholipids from the site of synthesis to the sites of incorporation into (sub)cellular membranes (649, 650).

1I. Biosynthesis

12. Regulation of synthesis of phospholipids

l

l

l

of cardiac

phospholipids

Synthesis of phospholipids in the cardiac cells occurs via a variety of metabolic routes. The biosynthesis of phosphatidylcholine in the heart is extensively stud-

and hydrolysis

In the normal heart synthesis must keep pace with their hydrolytic

of phospholipids degradation (and


October

1992

MYOCARDIAL

FATTY

vita versa) to prevent net loss or overproduction (phospholipidosis) of these lipid moieties. Although the details of the regulatory mechanisms of cardiac phospholipid biosynthesis and degradation, and the delicate interrelationship between them, have not been elucidated in full detail, a variety of potentially important factors has already been identified. De novo synthesis of phosphatidylcholine may be regulated on at least four different levels: I) uptake of choline and intracellular conversion into phosphocholine; Z) the tissue content of CTP; 3) activity of CTP:phosphocholine cytidylyltransferase, the enzyme catalyzing the rate-limiting step in the biosynthetic pathway; and 4) availability and selection of molecular species of diacylglycerol (217). In the heart modulation of cytidylyltransferase most likely plays a crucial role in the overall regulation of phosphatidylcholine biosynthesis. In this respect, it is noteworthy that exogenous stearic acid significantly stimulates the formation of phosphatidylcholine (368). This enhancement is caused by a severalfold increase in the activity of cytidylyltransferase in the microsomal fraction. Unlike liver, in hamster heart enhanced microsomal cytidylyltransferase activity cannot be attributed to a translocation of the enzyme from the cytosplasm to the endoplasmic reticulum (368, 434). As pointed out in the previous section, the final fatty acid composition of cardiac phospholipids is most likely obtained after de novo synthesis of the phospholipid molecule. A variety of factors is potentially involved in the regulation of phospholipase A-mediated release of fatty acids from the cardiac phospholipid pool: 1) synthesis and chemical modification of phospholipase A, 2) intracellular Ca2+ levels, 3) vitamin E (tocopherol) status, 4) intracellular nonenzymatic proteins, 5) hormones, 6) feedback inhibition by end prod ucts, and 7) physicochemical changes in membr anes, including the peroxidation state of membrane phospholipids. Chemical modification of an inactive form (zymogen) of phospholipase into a biologically active enzyme was conclusively demonstrated for the soluble pancreatic phospholipase 20 years ago (112). Activation of the zymogen was achieved by trypsin-mediated hydrolytic cleavage of an oligopeptide from the NH2 terminus of the proenzyme (581). Although studies performed on a variety of mammalian cell types, including hepatocytes a nd platelets, suggest the presence of a similar mechan ism to activate phos phol ipase A2, so far no definitive proof has been provided that conversion of a zymogen into an active enzyme is responsible for activation of cardiac phospholipase A2 (581). In vitro studies indicate that cardiac phospholipase A2 is activated by Ca2+, with the exception of phospholipases from lysosomal origin (385, 629) and hydrolytic enzymes acting on plasmalogens (220). However, it is unknown whether under normal conditions the basal level of and changes in cy toplasm .ic Ca2+ concentration are suffi ciently high to elicit increased ph ospholipase activity. Recent studies on platelets show that subtle changes in Ca2+ levels in the micromolar and hence phys-

ACID

HOMEOSTASIS

901

iological range strongly influence thrombocyte phospholipase A2 activity (336). When extrapolation of this finding to other mammalian cell types is allowed, fluctuations in cardiac levels of Ca2+ will modify the rate of hydrolysis of endogenous phospholipids. Calmodulin might be involved in the Ca2+-stimulated phospholipase activity, as in isolated rat hearts, trifluoroperazine, an inhibitor of Ca2+-calmodulin-mediated processes, was found to inhibit the release of lysophospholipids (547). The vitamin E status of the heart appears to have a regulatory influence on the phospholipase-mediated degradation of cardiac phospholipids (59, 73,217). This notion is based on the following findings. First, in hearts of rats fed with a vitamin E-deficient diet the lysophospholipid content was significantly increased, whereas with diets rich in vitamin E low cardiac lysophospholipid levels were observed. Second, vitamin E inhibited phospholipases A1 and A2 in a noncompetitive manner (217). These observations led Hatch et al. (217) to conclude that the vitamin E-regulated phospholipase A activity may constitute an important control mechanism in the catabolism of the cardiac phosphatidylcholine pool. Moreover, vitamin E likely has a regulatory role in the biosynthesis of cardiac phospholipids (63). The existence of nonenzymatic proteins with appreciable affinity for phospholipids was first described for BaciZZus subtdis (581). Subsequent studies in mammalian cells revealed a family of proteins, commonly referred to as annexins, with a molecular mass of 35-40 kDa and showing a relatively high affinity for phospholipids. Several members of this family possess phospholipase-inhibiting properties (104). In rat hearts, annexin-specific mRNA has been identified (617), whereas recently the presence of annexin V could be established in the heart of the same animal species (448,577). Conflicting data have been published on the cellular localization of annexin V in the heart. Van Bilsen et al. (577) found that this protein was exclusively present in the endothelial cells. In contrast, Giambanco et al. (178) reported a cardiomyocytal and endothelial localization. Annexin V partly prevents the Ca2+-s ti mulated hydrolysis of endogenou s phospholipids in a rat cardiac homogenate (577). Because the precise mode of action of annexins on phospholipase A, in the intact heart is incompletely elucidated, it remains to be established whether these intracellular proteins play a crucial role in the release of fatty acids from the endogenous phospholipid pool (103, 117). Clark et al. (76) have recently identified a protein antigenically and functionally related to m eli ttin with phospholipase A, stimulatory properties. It rem ains to be established whether this protein, named phospholipase A,-stimulatory peptide, is involved in cardiac phospholipid homeostasis. Circumstantial evidence has been provided that hormones, such as glucagon and norepinephrine, stimulate cardiac phospholipase A activity (156,547). The release of lysophospholipids from isolated rat hearts was significantly enhanced when the hormones were included in the perfusion medium. Earlier studies conducted by Hsueh et al. (233) indicate that bradykinin


902

VAN

DER

VUSSE,

GLATZ,

causes a severalfold increase in the release of arachidonic acid from isolated rat hearts. The latter effect seems to be specific for arachidonate-hydrolyzing phospholipases, since no increase in the efflux of fatty acids like linoleate, oleate, or palmitate was observed (233). The mechanism underlying hormone-induced phospholipid hydrolysis is incompletely understood. Degradation of phospholipids might be mediated by CAMP (156, 581). Cyclic AMP probably promotes phosphorylation of the phospholipase or a regulatory protein that enhances phospholipase activity on phosphorylation. In addition, CAMP may also interfere with cardiac Ca2+ levels, thereby increasing the concentration of this ion in the vicinity of Ca2+ -sensitive phospholipases. At present these mechanisms of action remain hypothetical and await experimental support. It is noteworthy that the findings by Stam and Hiilsmann (547) indicate that the site of localization of the hormone-induced phospholipid hydrolysis is the vascular wall. This observation suggests a close relationship between phospholipid degradation and eicosanoid production under such conditions, a notion in line with earlier observations made by Hsueh et al. (233; see sect. IIIG).

Recent in vitro studies delineated that arachidonic acid inhibits phospholipase A, partially purified from rat cardiac tissue. The mean inhibitory concentration was found to be 50 PM (154). It is unknown whether arachidonic acid in vivo also exerts this regulatory effect. Tissue analysis has shown that under normal conditions the cardiac content of arachidonic acid is on the order of 1.5 nmol/g wet wt (592), a value far below the level at which arachidonic acid displays its inhibitory action (154). In addition, in cardiac tissue damaged by freeze-thawing and stored under anoxic conditions, degradation of phospholipids proceeds unimpeded despite arachidonic acid levels up to 1,000 nmol/g wet wt (584). The obvious lack of inhibitory action does not favor the notion of feedback inhibition of phospholipase by degradation products. A decade ago Van den Bosch (581) pointed out that physicochemical alterations in phospholipid-containing membranes may lead to either a decreased or more vigorous attack of phospholipases. These alterations may be induced by changes in fluidity and packing of the phospholipid molecules in the membrane, interaction with detergents, the coexistence of solid and liquid phases in the phospholipid layer, and absorption of the enzyme molecules to the membrane. The latter process is strongly influenced by negatively charged compounds inserted in the membrane. A complicating factor is that a substantial portion of phospholipases in the heart is membrane bound, whereas most studies carried out on the interaction between membrane phospholipids and phospholipases are dealing with soluble enzymes (4). Therefore it remains to be established whether the activity of membrane-associated phospholipases can be augmented by any process that creates irregularities in the two-dimensional packing of phospholipids in the bilayer of biological membranes (581).

STAM,

AND

RENEMAN

Volume

72

Chemical modifications of membrane phospholipids can be caused by peroxidation of fatty acyl moieties with polyunsaturated aliphatic chains. It has been proposed that lipid peroxidation alters the physical characteristics of the membrane and renders the phospholipid molecules more susceptible to the attack of phospholipases A or C (166,626,627). Although the details of this process are unknown, enhanced phospholipolytic activity toward chemically altered phospholipids will guarantee the removal of damaged molecules from the lipid bilayer and, in doing so, maintain the integrity of the membrane. E. Spatial and Cellular Acid Metabolism

Diflerences

in Fatty

Spatial differences in cardiac fatty acid homeostasis can be anticipated, since the heart is a multifunctional and multicellular organ (285). On the one hand, the heart is composed of various discrete anatomic structures, such as the right and left ventricles mutually connected by the ventricular septum and the right and left atria, sharing the atria1 septum, with marked differences in function and workload. Transmural differences in, for instance, the free left ventricular wall have to be considered as well (583). From a cellular point of view it should be realized that the heart contains endothelial cells, fibroblasts, mast cells, macrophages, smooth muscle cells, adipocytes, nerve cells, and cardiomyocytes. As these cell types differ greatly in function, metabolic properties may differ as well. Transmural differences in lipid metabolism in the free wall of the left ventricle are most likely limited (583). The tissue content of fatty acids is similar in the subendocardial and subepicardial layers of the canine heart (446, 591). The content of triacylglycerol in the outer layers markedly exceeds the content in the inner layers of the ventricular wall. This difference is most likely caused by the presence of fat cells at the epicardium, because adipose tissue can readily be observed in the vicinity of large vessels at the epicardial surface (588). The content of phospholipids and the relative fatty acyl composition do not significantly differ between the various layers in the left ventricular wall of the dog heart (591). No direct information is available on transmural differences in the activity of individual enzymes involved in either fatty acid incorporation in or release from the endogenous fatty ester pools. The oxidation rate of palmitoylcarnitine and palmitic acid by mitochondria isolated from subendocardial layers of canine left ventricle appreciably exceeded the oxidation rates measured in mitochondria harvested from the subepicardial layers (57). However, with the current techniques used, only a small proportion of the total mitochondrial population is isolated. Therefore differences in recovery of mitochondria from subendocardial and subepicardial layers, due to differences in size and shape (647), may be responsible for the gradient in oxidative rate (583). This notion is substantiated by


October

1992

MYOCARDIAL

FATTY

the observation that the capacity to oxidize palmitate, when measured in homogenates of canine left ventricular wall, was slightly but significantly lower in the subendocardial layer than in the midwall and subepicardial regions (583). In addition, the oxidation rate of palmitic acid in homogenates of papillary muscle of rabbit heart was found to be considerably lower than that in the subepicardial preparation (180). Studies performed with radiolabeled fatty acids in anesthetized, open-chest dogs showed that the deposition of label was ~20% higher in the inner than in the outer layers (596). These findings, however, do not automatically imply that in vivo the actual rate of fatty acid utilization is different in the various regions of the left ventricular wall. It remains to be elucidated whether in the heart of conscious animals the oxidative utilization of fatty acids also shows uneven distribution across the left ventricular wall. This aspect of cardiac lipid metabolism relates to the question as to whether the workload of the subendocardial layer and hence utilization of oxidizable substrates exceed that of the more outer layers of the left ventricle wall. At present it may be concluded that there is no convincing evidence for significant transmural differences in energy metabolism in the left ventricle of intermediate-sized hearts of conscious animals (583). The fatty acid oxidation capacity resides principally in the cardiomyocytes as they occupy -75% of cardiac tissue volume. They show an oxidation capacity per milligram of tissue protein that is manifold higher than that of nonmyocyte cells (328). Assuming that -90% of cardiac protein is of cardiomyocyte origin, myocytes contribute by 98% to the total cardiac fatty acid oxidation capacity. Coronary endothelial cells, although capable of fatty acid oxidation, preferentially generate their metabolic energy from anaerobic breakdown of glucose (531). Regional differences in fatty acid oxidation capacity, e.g., between atria and ventricles, have not yet been reported. With respect to the content of cytoplasmic FABP, both the right and left ventricles of adult rat heart were found to contain -100 nmol immunoreactive FABP/g wet wt, whereas the atria contain approximately one-half of this content (96). F. E#ect of Maturation

ACID

903

HOMEOSTASIS

lated fetal pig hearts, it most likely does not represent the metabolic status of the fetal heart in situ, since the availability of fatty acids is limited due to low levels of these substrates in fetal plasma (639). It should be noted that major species differences may exist with respect to the development of the capacity to oxidize fatty acids. Rat hearts, for instance, do not oxidize fatty acids within the first 24 h after birth but acquire the capacity rapidly thereafter (652). Breuer et al. (51) could not detect in in vivo studies of neonatal dog hearts uptake of fatty acids during the first 14 days after birth. The mechanisms underlying the reduced capacity to oxidize fatty acids in immature hearts might relate to limitations in transport or a diminished mitochondrial capacity to oxidize fatty acids. The observation in pigs that carnitine levels are only slightly lower in fetal than in neon atal hearts (640) sluggests that the content of this CO facto r is unlikely to be a limiti ng factor for fatty acid oxidation during maturation. Studies of Lockwood and Bailey (335) favor the hypothesis that carnitine acyltransferase is a limiting factor in the utilization of fatty acyl moieties. This notion is supported by the observations by Warshaw (623) and Warshaw and Terry (624) that fetal rat and chicken hearts lack the capacity to produce acylcarnitine from acyl-CoA and carnitine. In contrast, Wolfe et al. (657) failed to detect an appreciable increase in carnitine acyltransferase activity in piglet heart homogenates with age. Results obtained in rat hearts indicate that changes during maturation also affeet the ,&oxidative pathway, as the activity of ,&hydroxyacyl-CoA dehydrogenase i ncreased during development (618). Detailed studies on the development of metabolic processes in hearts obtained from rats 3 wk of age revealed that the increase in the capacity to oxidize fatty acids is due to a rise of both mitochondrial activity and content of mitochondria per gram of tissue. The latter is caused by increased number and size of the mitochondria during maturation (599). Rosenthal and Warshaw (469) showed that the typical pattern of development of fatty acid oxidation is absent in cultured hear t cells of fetal and newborn rats. They concluded that the ob served differences between cultured cells and the intact heart may relate to decreased aerobic metabolism in cell culture.

on Cardiac Fatty Acid Oxidation

Although fatty acids are the primary energy source of the adult heart under normal physiological circumstances (321), immature hearts show a greater dependency on the metabolism of nonlipid substrates (142, 143,187, 599, 623, 640, 652). In pigs the rate of palmitate oxidation in intact neonatal hearts is ~35% higher than in fetal hearts (0.9 gestation) (639) and increases further during postnatal maturation. On days 6-12 after birth fatty acid oxidation (normal ized per gram tissue) is ~70% higher than in neonatal pig hearts (18). Comparable findings are reported in studies on the capacity to oxidize fatty acids in homogenates of maturing piglet hearts (355). Although the capacity to oxidize fatty acids is substantial in iso-

G. Production and Function of Arachidonic Metabolites in the Heart

Acid

Like most other mammalian organs, the heart can produce a family of lipid-derived, biologically active compounds commonly referred to as eicosanoids (106, 171,276,278,492,493,519). Arachidonic acid is the natural precursor of such eicosanoids as prostaglandins, thromboxane, leukotrienes, and other produ .cts of its enzymatic peroxidation. This indicates that polyunsaturated fatty acids not only serve as fatty acyl moieties of structural componen .ts of cellular membranes but also as substrates for biologically potent and versatile compounds that are thought to be involved in the modula-


VAN DER VUSSE, GLATZ,

904

tion of a host of (patho)physiological processes, such as tissue perfusion, immune response, thrombosis, inflammation, and atherosclerotic disease (278,519,550). However, in most of the studies reported, the production of eicosanoids by the heart was found to be rather limited under normal circumstances. I. Synthetic pathways

In the cascade of eicosanoid production from arachidonic acid, several enzymatically controlled steps are involved (Fig. 6). Lipoxygenases catalyze the formation of hydroperoxyeicosatetraenoic acid derivatives (HPETEs), whereas cyclooxygenase promotes the conversion of arachidonic acid into the endoperoxide-derivatives prostaglandins Gz and H, (PGGz and PGH2). In the lipoxygenase pathway 5-HPETE is metabolized into leukotriene A4 (LTA,). This compound serves as precursor for either LTB4 or the peptide LTC,. The latter substance is formed by coupling of the tripeptide glutathione to LTA,, a reaction catalyzed by glutathione S-transferase. Both LTD4 and LTE2 are subsequently produced by elimination of the glutamic acid and glytine part of the short peptide chain of the parent LTC, molecule, respectively. Both 120HPETE and 15-HPETE are transformed to their corresponding hydroxyeicosatetraenoic acids (HETEs). In the cyclooxygenase pathway the endoperoxide PGHz is enzymatically converted into either thromboxanes or prostaglandins. The former reaction is catalyzed by thromboxane synthase. The latter reaction is modulated by a set of isomerases and reductases, resulting in the formation of prostaglandins, such as prostacyclin (PGI,) and PGF,. Earlier studies performed on renal tissue have disclosed a third pathway of arachidonic acid metabolites (496). In this biosynthetic route, the so-called epoxygenase pathway, arachidonic acid is converted into epoxides and HETEs by the catalytic action of cytochrome P-4500dependent monooxygenases. Recently Abraham et al. (1) have shown that this enzymatic pathway is also present in cardiac tissue. arachidonic

HETE -

LTE4 +

LTD4 4-

72

2. Site of eicosanoid production

Although it has been shown in a variety of studies that the heart is able to produce eicosanoids, the site of production of these compounds in cardiac tissue is still the subject of debate (171,519). With the use of a differential labeling technique, the endothelial cells lining the vascular compartment have been identified as the major site of production of prostaglandins in the heart (234). In several studies on cultured endothelial cells it has been shown that these cells are indeed capable of producing prostaglandins (171,328,460). The main subtypes produced are PGE,, PGF%, and PGI,, but endothelial cells also produce small amounts of thromboxane A, (TxA,). The production of leukotrienes in endothelial cells is likely to be absent. Although the production of PGI, by isolated neonatal and adult cardiomyocytes devoid of vascular endothelium has been reported (43,132,133,278,459), it is generally accepted that under normal circumstances the production of eicosanoids by this cell type is very limited (7, 229,276,327). It is interesting to note that cultured myocardial smooth muscle cells and fibroblasts are also able to produce prostaglandins, mainly PGE, (81, 327). Stimulation of the intact heart with the calcium ionophore A23187 or through induction of the calcium paradox leads to the production of leukotrienes (130, 276,280). A likely source of these eicosanoids are macrophages and mas It cells present in cardiac tis sue (287), since production of leukotrienes by other cell types isolated from the hear It could not be demons trated (Li nssen et al. 9 unpublished results). It remains, however, to be seen whether this production is of physiological importance because the intracellular Ca2+ concentrati .ons reached under these circumstances are very high. In situations where blood platelets are activated, TxA, may be released from blood-perfused hearts (519). Because of the chemical unstability of TxA, and PGI,, their biological half-life is short, i.e., on the order of 0.5 and 5 min, respectively (388). This short half-life infers that the locus of production and biological action of TxA, and PGI, are most likely in proximity.

FIG. 6. Arachidonic acid (AA) cascade resulting in production of eicosanoids. EET, epoxyeicosatrienoic acid; GSH, reduced glutathione; HETE, hydroxyeicosatetraenoic acid; HPETE, hydroperoxyeicosatetraenoic acid; LT, leukotriene; PG, prostaglandin; TX, thromboxane. [Modified from van Bilsen et al. (5’75).]

[ PGG2 + PGH2 ]

L,

Volume

acid

HPETE

LTC4

STAM, AND RENEMAN

20-OH AA

PGFza

PGD;!


October

MYOCARDIAL

1992

3. Regulation

of cardiac

eicosanoid

FATTY

production

The rate of production of eicosanoids depends on a number of regulating factors: I) the activity of the enzymes involved; 2) the rate of supply of the substrate arachidonic acid; 3) the local concentration and availability of cofactors, such as molecular oxygen, calcium, glutathione, and peroxides; and 4) the peroxidative status of the tissue. Because the endogenous rate of eicosanoid production is far below the maximal activity of the enzymes involved, as measured under optimal in vitro conditions, the cellular content of the enzymes is most likely not rate limiting but merely determines the types of eicosanoids produced by the various cardiac cells (388, 575). This infers that the production rate is almost exclusively determined by the available amount of substrates and cofactors required for the synthesis of eicosanoids. The affinity of the oxygenases for molecular oxygen is very high, indicating that even under hypoxic conditions oxygen is most likely not a limiting factor (276). It has been established that lipid peroxides influence the activity of cyclooxygenase. Low concentrations of peroxides stimulate the enzyme, whereas elevated concentrations of these compounds exert a negative action (388, 550). The presence of sufficient amounts of glutathione is an absolute requirement for the synthesis of peptide leukotrienes, such as LTC, and its products LTD4 and LTE4. Calcium ions have been found to stimulate the activity of 5’-lipoxygenase (388). Current knowledge suggests that the supply of arachidonic acid, the main substrate for the lipoxygenase and cyclooxygenase pathways, determines the rate of eicosanoid production (256,480). Exogenous arachidonic acid supplied from either albumin-fatty acid complexes in the vascular space or from cellular sources in the vicinity of the actual site of production in the eicosanoid-producing cells may serve as a suitable substrate. The facts that t0.02% of tissue arachidonic acid is present in its nonesterified form (591) and that the supply from extracellular sources is limited due to low circulating levels of arachidonic acid suggest that the release rate of arachidonic acid from the main storage form, i.e., membrane phospholipids, is of paramount importance for the actual rate of endogenous eicosanoid production. Although the regulation of arachidonic acid incorporation into and release from the cellular phospholipid pool has not been elucidated in full detail, experiments performed with the calcium ionophore A23187 indicate that the intracellular calcium concentration may play a role in the availability of arachidonic acid as a substrate for eicosanoid formation (276). Activation of cellular phospholipases by Ca2+ most likely results in net degradation of part of the phospholipid pool leading to increased tissue levels of arachidonic acid (130,278). The observed depression of endothelial eicosanoid production by calcium antagonistic drugs is also in favor of a regulatory role of Ca2’ in the production rate of arachidonic acid metabolites (171). A number of interventions can enhance cardiac eicosanoid production. Reduced supply of oxygen stimu-

ACID

905

HOMEOSTASIS

lates the biosynthesis of prostaglandins (278; see sect. IvD). Treatment with hormones, such as catecholamines, angiotensin II, acetylcholine, and prolactin, is known to augment the production of prostaglandins in the heart (278). It is thought that these hormones stimulate cardiac eicosanoid production by acting on intracellular phospholipase activity. Physical manipulation, such as electrical stimulation of the heart, also activates the synthesis of prostaglandins (501). A variety of drugs, such as nicotine and nitroglycerin, are known to stimulate basal cardiac prostaglandin formation (374, 638). 4. Physiological role of eicosanoids cardiac tissue

in normal

Eicosanoids have been shown to exert a variety of actions on cardiac function, including inotropic and chronotropic effects, electrophysiological actions, modulation of coronary vascular resistance, subcellular metabolic effects, and modification of other externally applied stimuli. These properties of eicosanoids have been extensively reviewed by others (276, 278, 519) and are discussed only briefly here. Both PG12 and PG12 mimetics exert a dilating action on coronary vessels (278,493). However, it is uncertain whether this prostaglandin, when locally released, accumulates in a sufficiently high concentration to produce a vasodilating effect in the working heart. Vasoconstricting properties have been reported for TxA, and peptide leukotrienes, such as LTC, (278). Because under normal circumstances the production of these compounds is very low in intact hearts, it is doubtful that TxA,, produced either by activated platelets in the vascular space or in the cardiac endothelium, or LT&, released from circulating leukocytes or resident mast cells, exerts its biological activity under normal physiological conditions. Inotropic and chronotropic actions of prostaglandins have been established in both in vivo and in vitro experiments (278). The extent and nature of these effects on cardiac function appear to depend on the type of prostaglandin investigated, the concentration used, and the design of the experiment. In general, prostaglandins display antiarrhythmic effects in the heart. Administration of such prostaglandins as PGF, and PGE, suppressed dysrhythmic activity under a variety of conditions (278). However, studies performed by Karmazyn et al. (279) and Swift et al. (565) clearly established that this beneficial effect of prostaglandins is dose dependent. In addition, more recent studies (274,369) seriously challenge the notion that locally produced prostaglandins have antiarrhythmic properties during ischemia followed by reperfusion. On the contrary, their results suggest a causal relationship between prostaglandin release and the induction of arrhythmias during the reperfusion phase (see sect. IV@. A variety of effects of prostaglandins on cardiac metabolism and enzyme systems has been reported.


906

VAN

DER

VUSSE,

GLATZ,

Among others, the uptake of such substrates as fatty acids and glucose appears to be sensitive to the presence of circulating prostaglandins (188). The same study also revealed that prostaglandins stimulate the storage of neutral lipids in the heart. Although PGEl and PGF& were found to stimulate the activity of cardiac adenylate cyclase and the concentration of CAMP, no definite proof could be provided that the inotropic response to PGE, was established through CAMP-dependent protein kinase activity (278). Sarcolemmal Na+-K+-ATPase was found to be highly sensitive to PGE, and PGF2, (282), whereas the same prostaglandins stimulated the uptake of Ca2+ in cardiac tissue. However, other studies failed to disclose a specific effect on Ca2+ homeostasis in cultured cardiac cells (278). Prostaglandins PGE,, PGF,, and PGI, stimulated the Ca2+-dependent resting respiration of isolated cardiac mitochondria (275). This effect may be important when both the endogenous production of these autocoids is elevated and intracellular accumulation of Ca2’ occurs as in the reperfused heart. H. Platelet-Activating

Factor

The production and biological activity of plateletactivating factor (PAF) is considered to be closely related to that of eicosanoids (49, 339). The substrate for the production of PAF [1-alkyl-Z(R)-acetyl-glycero-3phosphorylcholine] is alkylacylglycerophosphocholine. In this phospholipid an aliphatic carbon chain is bound to the glycerol backbone at the snl position via an ether binding. At the sn2 position arachidonic acid is commonly present, bound to the glycerol molecule via an ester linkage. 1.

Biosynthesis

of platelet-activating

factor

The first step in the formation of PAF is hydrolytic removal of the arachidonoyl moiety by action of phospholipase A,, giving rise to the formation of lyso-PAF. Arachidonic acid may serve as precursor for eicosanoid production. The second step in the production process is the acetylation of the hydroxyl group at the sn2 position. This reaction is catalyzed by acetyltransferase, yielding PAF. Platelet-activating factor is degraded by acetylhydrolase, yielding acetate and lyso-PAF. Hence the latter compound is an obligatory intermediate in both biosynthesis and degradation of PAF (49). Evidence is accumulating that PAF is synthetized in platelets, leukocytes, and endothelial cells (339, 663). Recently, also, cardiomyocytes have been identified as cells capable of producing PAF in significant quantities (259). Synthesis of PAF is enhanced by agents whose actions lead to elevated intracellular levels of Ca2’ (49). Ischemia or hypoxia also results in increased PAF formation (33,370). It has been suggested that phosphorylation of endogenous lipocortins, resulting in stimulation of cellular phospholipase A, activity, plays an

STAM,

AND

important tion (49).

RENEMAN

Volume

role in regulating

2. E#ect of platelet-activating on cardiac functioning

72

the rate of PAF forma-

factor

Platelet-activating factor has been proposed to be a mediater in various kinds of cardiovascular shock, including endotoxin and anaphylactic shock (319,559). Administration of PAF to intact animals elicited a decline in arterial blood pressure, decreased cardiac output, and reduced peripheral resistance (559). Studies on isolated hearts revealed that this organ is one of the main targets of circulating PAF (138,479). Platelet-activating factor possesses marked vasoactive effects on the heart. In pig hearts in situ administration of PAF exerted a triphasic change in coronary blood flow. Severe coronary constriction was evoked after an initial brief phase of coronary dilation. In some animals a third phase of escape toward normal coronary perfusion could be observed (137). The same study suggested that the constrictory effects of PAF on coronary vasculature are mediated by TxA, (137). Marked vasodilatory effects of intracoronarily administered PAF have been observed in rabbits by Lucchesi et al. (339). Platelet-activating factor-induced vasodilation is most likely mediated by a not-yet-identified factor released by blood platelets (339). Data available suggest species differences in the effect of PAF on coronary circulation. In addition to circulatory effects, PAF was found to possess proarrhythmic properties in isolated guinea pig papillary muscles (568), whereas high doses of PAF exerted a direct depressant effect on cardiac output in conscious rats (520). IV.

FATTY AND

ACID

METABOLISM

REPERFUSED

IN THE

ISCHEMIC

HEART

During ischemia, a situation characterized by reduced coronary flow resulting in an inadequate supply of oxygen and substrates to and removal of waste products from the affected tissue, cardiac metabolism undergoes profound alterations. Oxidative degradation of carbohydrates shifts to anaerobic production of lactate, whereas oxidation of fatty acids becomes depressed (320,408). Prolonged ischemia results in increased turnover of the cardiac triacylglycerol pool and net degradation of membrane phospholipids. Various fatty acylcontaining intermediates accumulate in the oxygen-deprived cardiac tissue (85, 321, 371, 587). Some lipid intermediates are thought to exert a deleterious action on the jeopardized myocardium due to their amphipathic properties and, consequently, to aggravate the ischemic insult (85, 284, 286). Restoration of flow, with the intention to safeguard the heart cells against inevitable death, only partly results in normalization of fatty acid metabolism (67, 322,494, 579). The production and


October

MYOCARDIAL

1992

FATTY

subsequent release of eicosanoids appear to be enhanced in the ischemic and reperfused heart (129,276,277). A. Cardiac Fatty Acids and Reperfusion I. Depressed

fatty

and Esters

acid oxidation

During

Ischemia

in the ischemic

heart

During the initial phase of myocardial zero-flow ischemia, oxidative degradation of fatty acids is rapidly depressed due to the obligatory oxygen dependency of this metabolic process. Glucose was found to compete successfully with fatty acids for the residual oxygen extracted by the in situ low-flow ischemic dog heart (384, 413). However, the latter finding is at variance with the observation that in low-flow ischemic rat, rabbit, and pig hearts palmitate oxidation still accounts for the majority of residual oxygen consumption (152, 323, 646). Reduced supply of molecular oxygen to the mitochondria results in increased NADH/NAD+ ratios in both the cytoplasm and the mitochondrial matrix because of a decrease in transport flux of electrons in the mitochondrial respiratory chain (321). As a consequence of the enhanced mitochondrial NADH/NAD+ ratio, ,&oxidation of fatty acids becomes suppressed and accumulation of intermediates of the P-oxidative pathway readily occurs. Chronic low-flow ischemia of the heart, induced by the implantation of an ameroid constrictor around a coronary artery, results in enhanced capacity of peroxisoma1 fatty acid oxidation (272). This change has been interpreted as an intrinsic measure of the affected cells to cope with an increased fatty acid load (272). 2. Accumulation of fatty in the ischemic heart

acids and esters

In isolated palmitate-perfused rabbit hearts, lowflow ischemia results in a rapid accumulation of ,&hydroxypalmitate and P-hydroxystearate. In addition, hydroxyacylcarnitine and hydroxyacyl-CoA can be found in ischemic tissue (237, 373). Acyl-CoA hydrolase and acylcarnitine hydrolase, enzymes reported to be present in cardiac tissue (372), are most likely responsible for the formation of hydroxy fatty acids during oxygen deprivation. Originally produced in the mitochondrial matrix, a substantial part of the ,0-hydroxy fatty acids accumulates in the cytoplasmic compartment within 2 min after the onset of ischemia (237). Also, under hypoxic conditions hydroxy fatty acids were found to be rapidly released from the heart into the oxygen-lacking perfusate (450). Together with the accumulation of P-hydroxy fatty acids, increased cellular concentrations of fatty acylCoA and acylcarnitine can be anticipated. However, the experimental findings regarding accumulation of these acyl esters under oxygen-restricted circumstances are

ACID

HOMEOSTASIS

907

not consistent. The effect of ischemia on the tissue content of acyl-CoA and acylcarnitine appears to be species dependent and is strongly influenced by the presence of extracellular substrates during the low-flow ischemic period. In isolated hearts perfused with a fatty acidcontaining medium, the acylcarnitine content raises to high levels during low-flow ischemia. Acylcarnitine levels increase from 0.8 to 4.4 mmol/g dry wt tissue, while the acyl-CoA content shows an increase from 0.18 to 0.33 mmol/g dry wt tissue (390, 391). Unlike low-flow ischemia, complete cessation of flow prevents the increase in tissue acylcarnitine content and blunts the rise of acyl-CoA (429, 646). Accumulation of acyl-CoA and acylcarnitine is a rapid process occurring within 5 min after the onset of low-flow ischemia. In glucose-perfused rabbit hearts the content of acyl-CoA and acylcarnitine declined under low-flow conditions (372). However, in low-flow ischemic, glucose-perfused rat hearts a moderate accumulation of acylcarnitine was observed, whereas acyl-CoA levels increased to the same extent as in low-flow ischemic, palmitate-perfused rat hearts (390). Rabbit hearts subjected to low-flow ischemia in the absence of extracellular substrates showed a significant increase of acyl-CoA and carnitine esters (372). Occlusion of a coronary artery in dog hearts in situ resulted in a rapid, but relatively moderate, increase in the content of the fatty acyl esters in the flow-deprived area (517, 563). Studies of Idell-Wenger et al. (252) in isolated, palmitate-perfused rat hearts revealed an almost exclusive mitochondrial localization of acyl-CoA under normoxic and ischemic circumstances. Although acylcarnitine accumulated largely in the cytoplasmic compartment, appreciable amounts of this fatty acyl derivative could also be recovered in the mitochondrial fraction. The content of long-chain acylcarnitine increased from a control value of 0.22 to 1.05 and 1.88 nmol/mg mitochondrial protein in mild and severely ischemic cardiac tissue, respectively (252). Because accumulation of acyl-CoA and acylcarnitine in oxygen-deprived hearts reflects impaired degradation of fatty acyl moieties during mitochondrial p-oxidation, enhanced tissue levels of fatty acid can also be expected. Indeed, accumulation of fatty acids in ischemit cardiac tissue has been reported (69,102,151,363, 446, 579, 591, 628, 631, 632). Unlike acyl-CoA and acylcarnitine, accumulation of fatty acids is a relatively slow process. Studies in isolated, zero-flow ischemic rat hearts (579) and in regional ischemic dog hearts (69) indicate that fatty acid accumulation does not occur earlier than 20-45 min after the onset of ischemia. The accumulation of fatty acids was found to be most marked in the subendocardial layers of the ischemic region (591). Gas chromatographical analysis of the fatty acid pool revealed that the contents of palmitic, palmitoleic, stearic, oleic, linoleic, and arachidonic acids significantly increased. In dog hearts made ischemic for 120 min, the long-chain polyunsaturated linoleic and arachidonic acids showed the highest relative increase (-600 and l,OOO%, respectively) (591). The amount of


908

VAN

DER

VUSSE,

GLATZ,

fatty acids accumulated in dog hearts at 60 min of ischemia (446) was on the same order of magnitude as the quantity of acylcarnitine monitored in a comparable experimental preparation (517). 3. Origin

of fatty

acids in ischemic

cardiac

tissue

Although the precise origin of the fatty acids accumulating in flow-deprived cardiac tissue is incompletely known, various sources might be involved. First, in lowflow ischemic hearts, residual uptake of fatty acids from extracellular sources still occurs in the ischemic region (591) and hence may contribute to the intracellular fatty acid pool. This intracellular pool may increase because of reduced utilization of the fatty acyl moieties by mitochondrial oxidation due to lack of molecular oxygen. Although studies performed with labeled fatty acids indicate that during low-flow ischemia at least part of the intracellular fatty acids originates from extracellular sources (466,614), release of fatty acids from intracellular lipid pools has to be considered as well. In this respect it is noteworthy that in zero-flow ischemic rat hearts, preischemically perfused with a medium devoid of fatty acids, fatty acids accumulated to the same extent as in low-flow ischemic dog hearts in situ (586). In cardiac tissue, the phospholipid and triacylglycerol pools are the most likely candidates to release fatty acids and hence to contribute to an enhanced cellular fatty acid content. The observation that significant amounts of arachidonic acid are released from intracellular lipids indicates that degradation of endogenous phospholipids, practically the only pool of esterified arachidonyl moieties in the heart (69, 591), is involved in the accumulation of fatty acids during ischemia. In addition, because cardiac cells are capable of synthesizing fatty acids, albeit at a rather low rate (236,645), de novo formation of fatty acids under ischemic conditions has to be considered. Incorporation of labeled acetate in the cardiac fatty acid pool was found to be increased under hypoxic conditions (170, 190). Part of these de novo synthetized fatty acids were incorporated in triacylglycerol and phospholipids (190). Because no information is available about the actual rate of synthesis under ischemit conditions, no conclusions can be drawn regarding the quantitative contribution of de novo formation to the accumulation of fatty acids in the flow-deprived heart. 4. Fatty

acid metabolism

in the reperfused

heart

In 1985 Schwaiger et al. (495) published a detailed study on uptake and metabolic fate of [%]palmitic acid in reperfused dog hearts. Their findings indicate that restoration of metabolism after 3 h of ischemia is slow in the reperfused canine heart and is paralleled by retarded recovery of mechanical function. Moreover, metabolic recovery shows significant heterogeneity. At 24 h of reperfusion, areas that still lacked flow (no-reflow

STAM,

AND

RENEMAN

volume

72

phenomenon) were extensively necrotic and failed to extract labeled palmitic acid, whereas reversibly injured regions were capable of extracting palmitic acid, be it with a delayed clearance of label from the affected cells. Conversely, uptake of labeled deoxyglucose was increased in these cells. This led the authors to the conclusion that in reperfused cardiac tissue a shift of fatty acid to glucose utilization occurs to meet the energy requirements of the surviving cells (495). When the duration of ischemia was shortened to 20 min, derangements of fatty acid metabolism were partly mitigated, as monitored at 180 min of reperfusion. Detailed analysis of tracer kinetics suggests that normalization occurs of the fraction of labeled palmitic acid that is oxidized immediately following uptake in the cells. However, the late, slow clearance of labeled palmitate remained depressed during 180 min of reperfusion. This finding most likely indicates enhanced deposition of labeled fatty acids in a relatively inert esterified lipid pool in the reperfused heart. In dog hearts with a transiently occluded coronary artery for 60 min, Myears et al. (384) showed that, despite diminished net uptake of fatty acids, oxidation of these substrates accounted for 63% of total oxygen consumption in the reperfused area, indicating that preference of fatty acids as oxidizable substrates was restored on reperfusion. This conclusion is in agreement with earlier observations reported by Mickle et al. (360), who showed that, in contrast to normal hearts (122), reperfused hearts prefer fatty acids as substrates despite elevated circulating levels of lactate. Isolated rat hearts rendered ischemic for 25-60 min preferentially consumed fatty acids during reperfusion (195,337). Palmitate oxidation provided over 90% of the ATP produced from exogenous substrates. Recent studies conducted by Liedtke et al. (322) on adolescent swine subjected to regional low-flow ischemia of the heart in situ for 45 min revealed that moderate ischemia results in a strong preference for and aerobic use of fatty acids during reperfusion, to such an extent that the production of CO2 from labeled palmitic acid exceeded preischemit levels. Similar results were obtained when circulating fatty acid levels were increased from 0.55 to 1.50 mmol/l plasma. The latter findings indicate that fatty acid uptake and oxidation per se is not impaired in hearts reperfused after a period of moderate ischemia. Their observations also indicate that fatty acid metabolism and energy production are partially uncoupled, because mechanical activity was appreciably impaired and total oxygen consumption only slightly depressed (322). This phenomenon was further substantiated by observations made in mitochondria isolated from reperfused myocardial tissue showing significantly increased basal respiration and decreased production of ATP per molecule of oxygen consumed (235), a principle known as respiratory chain uncoupling. 5. Tissue levels of fatty

acids on reperfusion

The tissue content of fatty acids consistently increases on reperfusion (55, 579, 586). This change al-


October

MYOCARDIAL

1992

- 5000 7

•3 normoxia Cl ischemia

1

>. %

FATTY

1

ES7 reperfusion

En 1 g 3000. 5 .s mo ElOOOf;

l

IL

o-

czzi

N

cIizBi# 30

I

45

I

60

I

FIG. 7. Effect of ischemia of variable duration (I) and 30 min of reperfusion on cardiac content of fatty acids. Experiments were performed on isolated adult rat hearts. Duration of ischemia is given at bottom in minutes. Data are means + SD. *Significantly different from preischemic value (N). [From van Bilsen et al. (579).]

ready occurs after a short period of ischemia (e.g., 30min zero-flow ischemia in isolated rat hearts), whereas postischemic mechanical function is hardly affected (579). The fact that fatty acids accumulate in hearts perfused with a medium devoid of fatty acids indicates that these compounds originate from intracellular sources (579). Because arachidonic acid appreciably contributes to fatty acids accumulating in reperfused tissue, net degradation of the cardiac phospholipid pool likely takes place. The finding that saturated and monosaturated fatty acids, such as palmitic, stearic, and oleic acid, accumulate as well suggests that endogenous triacylglycerols also contribute to the elevated fatty acid level. With the techniques used, no definite statement can be made about the intracellular origin of tissue fatty acids under these circumstances. Net reduction of the content of triacylglycerols and phospholipids was not observed but also was not expected, since the quantity of fatty acids accumulating in postischemic cardiac tissue is relatively small compared with the overall esterified lipid pool (579). When the preceding period of ischemia is prolonged from 30 to 60 min the accumulation of fatty acids in the reperfused heart shows a significant further increase (Fig. 7). Cardiac fatty acid levels at 30 min of reperfusion after 60 min of ischemia were found to be on the order of 4,000 nmol/g dry wt (preischemic values being 250 nmol/g dry wt) (579). These levels were associated with a reduction of stroke volume of -40% (579). This indicates that limited functional recovery is still possible at these high levels of endogenous fatty acids and that the reperfused heart to some extent tolerates these levels. In vitro studies with isolated mitochondria indicate that fatty acid concentrations corresponding with >l,OOO nmol fatty acids/g dry wt tissue completely block mitochondrial energy production (435). Therefore the findings of Van Bilsen et al. (579) infer that either accumulation of fatty acids is compartmentalized or that agents protecting against the detrimental effect of fatty acids normally present in the cardiac cell are lost during isolation of mitochondria. In favor of the compartmentalization of fatty acids that accumulate in reperfused hearts is the observation made by Liedtke et al. (322) that under moderate ischemit conditions oxidation of exogenous fatty acids is

909

ACID HOMEOSTASIS

hardly affected after restoration of flow. Fatty acids, released from endogenous sources, may accumulate in only a small number of heavily damaged cells, forming a pool that does not exchange with fatty acids available for oxidative degradation. The latter notion is supported by the finding that the content of acyl-CoA and acylcarnitine appreciably declines after restoration of flow (251,322,429). The return to normal tissue values of acyl derivatives most likely indicates that the impediment of fatty acid oxidation during ischemia is relieved on reperfusion. An additional argument in favor of compartmentalization is the close relationship between tissue fatty acid levels in and the release of lactate dehydrogenase from the reperfused hearts (579). This finding suggests accumulation of fatty acids in a subpopulation of irreversibly injured cells. These fatty acids apparently do not reach the mitochondria and contractile machinery of the surviving cells in the heart. An additional argument in favor of compartmentalization is the discrepancy between the amount of arachidonic acid accumulating in reperfused cardiac tissue and PGI, produced, indicating that arachidonate is not readily available for the formation of eicosanoids (see sect. IV@. In summary, ischemia results in severe impairment of cardiac fatty acid metabolism. Lack of oxygen is associated with a rapid accumulation of fatty acyl-CoA, acylcarnitine, and ,&hydroxy fatty acids. Increasing the tissue content of fatty acids is a relatively slow process. In addition to extracellular sources, endogenous esterified fatty acyl pools, such as phospholipids, contribute to the rise of fatty acids in ischemic cardiac tissue. On reperfusion cardiac fatty acid metabolism is partly restored. After relatively short periods of ischemia fatty acid oxidation returns to normal levels. Reperfusion after prolonged ischemia results in sustained abnormalities of fatty acid oxidation. It is proposed that enhanced accumulation of fatty acids in postischemic hearts probably occurs in a subpopulation of heavily damaged cells. B. Endogenous Triacylglycerols and Reperfusion I. Changes in triacylglycerol

During Ischemia

levels during ischemia

Accumulation of lipid droplets in hypoxic and ischemit cardiac tissue in humans and in laboratory animals has been known for years (37, 55, 56, 94, 124, 197, 262, 263, 343, 387, 478, 483, 625). Biochemical analysis indicates that the lipid droplets most likely consist of triacylglycerols (95). Accumulation is moderate in the core of the ischemic region (263) and predominant around the rim of the infarct zone or the lateral border zones of the subepicardial and subendocardial regions (162,574). Surviving Purkinje fibers in the infarcted regions also show a striking accumulation of lipid droplets. This accumulation is most pronounced between 24 h and 3 days after the onset of ischemia (162). Jesmok et al. (262) observed an appreciable trans-


910

VAN

DER

VUSSE,

GLATZ,

mural difference in triacylglycerols, accumulating in the ischemic region in the dog heart. The epicardial layers of the left ventricles showed the highest relative increase. Changes in the endocardial layers were virtually absent (262). Contrasting results were reported by Crass and Sterrett (95), who observed a significant increase in the inner layers of the affected myocardium. In the heart, endogenous triacylglycerols are subject to continuous turnover (see sect. IIID6). Hence elevated levels of triacylglycerols can be caused by increased rate of synthesis or diminished hydrolysis of this esterified lipid pool (see sect. IVB3). 2. Synthesis of triacylglycerols

in the ischemic heart

Neutral lipid sequestration in the ischemic and peri-ischemic regions is most likely caused by a multitude of factors. In areas with residual blood flow, there is still supply of exogenous fatty acids. This is especially the case in the border zone surrounding the core of the ischemic region. Inside the ischemic cell fatty acid oxidation is impaired due to a diminished supply of molecular oxygen. Part of the fatty acids will diffuse back into the extracellular compartment and part will be converted into acyl-CoA by fatty acyl-CoA synthetase. Increased intracellular levels of glycerol 3=phosphate, as a consequence of an elevated tissue NADH/NAD+ ratio, which promotes the conversion of glycolytically derived dihydroxyacetone phosphate into glycerol 3-phosphate, favors the incorporation of the acyl chains in the neutral lipid pool. Because myocardial infarction is generally associated with elevated plasma catecholamine levels due to stress reactions, plasma fatty acids will readily increase and hence so will the supply of these substrates to the underperfused myocardial region, which in turn favors enhanced synthesis of neutral lipid in the oxygen-deprived heart. Theoretically, in the ischemic heart direct stimulation of enzymes involved in triacylglycerol synthesis can also contribute to enhanced formation of triacylglycer01s. The activity of glycerol-3-phosphate acyltransferase, catalyzing the rate-limiting step in overall triacylglycerol synthesis, was found to be declined (222) or unchanged (490) under ischemic conditions. The small decrease of glycerol-3-phosphate acyltransferase activity could be prevented by preperfusion with ,&antagonists or by injection of 6-hydroxydopamine 24 h before the ischemic insult (222). The latter findings indicate that an increased P-adrenergic drive by endogenous catecholamines modulates the activity of glycerol-3-phosphate acyltransferase. It is interesting to note that, despite decreased activity of this key enzyme, net triacylglycerol formation occurs in prolonged hypoperfused cardiac tissue. Most likely in vivo other factors are overruling the in vitro observed reduced activity of this anabolic enzyme. In vitro studies with isolated rat hearts failed to show accumulation of triacylglycerol in the ischemic tissue (488, 572, 579). This observation, apparently de-

STAM,

AND

RENEMAN

Volume

72

viant from in vivo findings, can be explained by differences in time scale, residual flow (low-flow vs. zero-flow ischemia), and availability of extracellular substrates. Studies on isolated rat hearts are commonly dealing with periods of ischemia too short to induce net increases in the cellular triacylglycerol pool. Complete cessation of flow will entirely block the supply of circulating fatty acids to the ischemic area and hence prevent net synthesis of triacylglycerols. This notion is in line with the observation of Jodalen et al. (263) that the increase of neutral lipids in the core of the ischemic region is significantly less than in the surrounding areas. It should be noted that, in addition to reduced availability of exogenous fatty acids, under prolonged severe ischemit conditions the production of glycerol 3-phosphate will be impaired due to exhaustion of the cellular glycogen pool and inhibition of glycolysis (410). Finally, isolated rat hearts are generally perfused with a glucosecontaining buffer, devoid of fatty acids, which in addition makes net synthesis of triacylglycerols very unlikely. 3. Hydrolysis of endogenous triacylglycerols during ischemia

Biochemical studies performed on ischemic dog hearts in situ and rat hearts ex vivo have revealed that the endogenous triacylglycerol pool is subject to enhanced hydrolytic degradation. The production rate of glycerol, assumed to originate exclusively from the cardiac neutral lipid pool, was found to be increased under ischemic circumstances (488, 572, 579, 611). The precise mechanism underlying enhanced lipolysis under ischemic but also hypoxic conditions is incompletely understood (488). The following factors may be involved. First is the activation of triacylglycerol lipase. Heathers and Brunt (222) found that in ischemic rat heart tissue the activity of triacylglycerol lipase was increased by 50% within 10 min after coronary occlusion. Endogenous catecholamines are most likely involved, since depletion of norepinephrine from the sympathetic nerve terminals by injection with 6-hydroxydopamine 24 h before the onset of ischemia prevents the rise in triacylglycerol lipase activity. Preperfusion with ,&antagonists also prevents the enhancement of enzymatic activity (222). The involvement of endogenous catecholamines in the stimulation of cardiac lipolysis is substantiated by earlier studies (231,283). Second is the relieving of feedback inhibition of triacylglycerol lipase. Although relieving of feedback inhibition offers an attractive explanation for increased lipolytic activity, it is doubtful whether the negative effect of fatty acids and their derivatives on cardiac lipase (352, 508, 549) has a physiological meaning in acutely ischemic myocytes, as numerous observations indicate enhanced rather than decreased levels of these substances in oxygen- and flow-deprived cardiac tissue (391,586). Third is the activation of lysosomal activity. Recent observations strongly support the notion that lysosomes are involved


October 1992

MYOCARDIAL

FATTY

in lipolysis of cardiac intracellular triacylglycerols (488). In the ischemic heart, enhanced engulfment of lipid material by activated lysosomes seems to occur readily. The mechanism responsible for this process is unknown, but increased H+ and Ca” levels in the cytoplasm might provoke a greater rate of lysosomal phagocytosis (488). The importance of lysosomal degradation of triacylglycerol under ischemic conditions is also evidenced by the finding that in the flow-deprived heart the rate of lipolysis is diminished by methylamine, a well-known lysomotropic agent (488). Fourth is the synthesis of a metabolically active triacylglycerol pool. The observed augmented release of glycerol in the absence of any measurable decline in the endogenous triacylglycerol pool in some experimental preparations strongly suggests that in the ischemic heart resynthesis of neutral fat keeps pace with triacyglycerol hydrolysis (572, 579). As pointed out in section IIIDZ, several metabolic changes in the oxygen-deprived cell, such as enhanced contents of glycerol 3-phosphate and acyl-CoA, might favor the synthesis of triacylglycerol (659). Assuming that at least part of the acyl moieties of acyl-CoA originates from the preexisting neutral lipid pool, it can be envisaged that the newly formed triacylglycerol pool is more accessible to hydrolytic enzymes than the “old” triacylglycerol pool. If this is the case, ischemia leads to the synthesis of a small but distinct triacylglycerol pool with a relatively high turnover rate, resulting in increased release rates of glycerol from the affected cells. It should be noted that this hypothetical shift in the neutral lipid pool awaits experimental verification. 4. Triacylglycerol-fatt cardiac tissue

y acid cycle in ischemic

The inference of a simultaneous augmentation of hydrolysis and resynthesis of triacylglycerol under ischemit conditions is the creation of the so-called triacylglycerol-fatty acid cycle. It has been speculated that rapid reesterification of fatty acids in this cycle during ischemia may well be a protective mechanism that counteracts the putative deleterious effects of increased tissue levels of fatty acids and their derivatives (572). However, the triacylglycerol-fatty acid cycle consumes energy in the form of ATP. Seven molecules of ATP are consumed for each molecule of triacylglycerol hydrolyzed into three fatty acids and resynthetized at the expense of one molecule glycerol 3-phosphate and three molecules fatty acyl-CoA. Recent calculations estimated the loss of energy by this cycle to be only 3-4% of the total amount produced in the glycolytic pathway under ischemic conditions (490). This number suggests that the negative consequences of an operative triacylglycerol-fatty acid cycle might be minimal under such circumstances. However, it cannot be excluded that in low-flow ischemic hearts in situ exposed to a continuous, and probably elevated, supply of extracellular fatty acids, incorporation of newly extracted fatty acyl moieties in the cardiac triacylglycerol pools proceeds at a higher rate than in isolated underperfused rat hearts.

ACID

911

HOMEOSTASIS

In such conditions the extra drain on cardiac ATP, the production of which is already diminished due to lack of a sufficient supply of oxygen, could well attribute to impairment of cardiac function (461). If this is the case, beneficial effects of lowering circulating fatty acid levels on ischemic cardiac function by ,&antagonists or elevated plasma concentrations of glucose might be caused (in part) by a lower rate of endogenous triacylglycerolfatty acid cycling (409, 461). 5. Turnover of triacylglycerol

in reperfused hearts

Normally, reperfusion of isolated rat hearts leads to an abrupt cessation of the release of newly formed glycerol (110,579). Diminution of triacylglycerol hydrolysis during the postischemic phase is in line with normalization of the activity of triacylglycerol lipase, assayed in tissue specimens obtained from reperfused rat hearts (222). However, return of the augmented glycerol production in the ischemic heart to normoxic values after readmission of flow was found to be strongly dependent on the type of substrate supplied to the heart. When hearts were reperfused with a lactate- instead of pyruvate-containing perfusion medium the release of glycerol was markedly enhanced on reperfusion (110). Because no decline in the tissue content of triacylglycerol could be observed, the triacylglycerol-fatty acid cycle most likely operates at a higher rate under such circumstances. Reperfusion of previously ischemic cardiac tissue resulted in a further fall in the activity of glycerol-3phosphate acyltransferase (222). The reperfusion-induced decline in enzymatic activity is *mostlikely caused by an increased cu,-adrenergic stimulus, since preperfusion with the cu,-antagonist doxazosin prevented the effect of reinstallation of flow on the activity of glycerol3-phosphate acyltransferase (222). 6. Lipoprotein lipase in the ischemic heart In rats the heparin-releasable portion of lipoprotein lipase activity decreases markedly during myocardial ischemia and anoxia (245, 610). In the ischemic rat heart this reduction in releasable lipase activity is followed by an increase in nonfunctional, non-heparin-releasable lipase activity in the tissue. A defective transport mechanism and/or enzyme secretion has therefore been suggested as possible cause of this phenomenon. Unlike the ischemic situation, in anoxic hearts the nonfunctional tissue lipoprotein lipase activity falls as well (367). A satisfactory explanation for the differences between ischemic and anoxic heart preparations is not available at present. C. Impairment of Phospholipid Metabolism During Ischemia and Reperfusion I. Phospholipid degradation during ischemia The association between progressive degradation of membrane phospholipids and the development of irre-


912

VAN

DER

VUSSE,

GLATZ,

versible myocardial ischemic damage has been well established (595). The pioneering study of Weglicki et al. (628) indicates that linoleic and arachidonic acids are released from endogenous lipid stores in isolated canine hearts made ischemic for 30 min. Because arachidonic acid is almost exclusively incorporated in the cellular phospholipid pool, their findings show net degradation of phospholipids under flow-restricted conditions. However, controversial and inconsistent findings have been reported concerning the time scale and amount of cardiac phospholipids degraded during ischemia. In rat hearts Chiariello et al. (68) observed a depletion of the total cardiac phospholipid pool to 47% of control within 2 h of ischemia. Chien and co-workers (69-71) reported that in dog hearts the total phospholipid pool decreased by 10 and 33% following 3 and 12 h of regional ischemia, respectively. Loss of phospholipids was mainly caused by reduced levels of phosphatidylcholine and phosphatidylethanolamine (69, 71). In ischemic pig hearts, a smaller but significant decrease of -115% was found after 24 h of flow cessation (510). No decrease in the cardiac phospholipid pool could be observed after 1 h of ischemia in pig (102, 419) and rat hearts (420, 579). Schwertz et al. (497) failed to observe a decrease in phospholipids in rat hearts made ischemic for 3 h. In tissue specimens of dog hearts the content of total phospholipids and the major individual phospholipids did not change after 7 h of complete ischemia (556). Extension of the duration of ischemia to 24 h did not lead to changes in total phospholipid content either (292). Interestingly, Man et al. (346) found that in canine hearts ischemic for 24 h the relatively small loss of phosphatidylcholine and phosphatidylethanolamine was compensated by increased levels of phosphatidylinositol, phosphatidylserine, phosphatidylglycerol, and cardiolipin. In rat hearts the enhancement of the phosphatidylinosito1 content was also found by Schwertz et al. (497) after prolonged cessation of flow. The observation of Man et al. (346) that edema rapidly occurred in the ischemic region might partly explain the inconsistency in the above results. The corollary of their observation is that when phospholipid content is expressed per gram wet weight, too low tissue levels of lipids will be monitored. The release of arachidonic acid, among other fatty acids, from the endogenous esterified lipid pool was found to be a sensitive measure of disturbances in cardiac phospholipid metabolism (69, 159, 258, 591). It has been shown that in the in situ dog heart arachidonic acid predominantly accumulates in the subendocardial layers of the ischemic area. The amount of arachidonic acid accumulated was found to be related to the extent of flow reduction in the affected region. Substantial accumulation occurs when coronary flow falls below 0.1 ml min-l . g tissue-l, i.e., 50% of the membrane phospholipids were degraded (353). When extrapolation from the phospholipase-treated erythrocyte preparation to the in vitro ischemic cardiomyocyte is allowed and the assumption is correct that the plasmalemma is the only site of phospholipid hydrolysis (which is rather unlikely; see sect. IvCZ), the mere loss of membrane phospholipid is insufficient to account for cardiomyocyte damage under flow-restricted conditions. However, it cannot be excluded that relatively minor changes in one or more phospholipid species in the cardiac membrane disturb the balanced fluidity between the inner and outer leaflet of the sarcolemma, resulting in destabilization of the membrane and subsequent loss of cellular integrity. Indeed, under oxygen-restricted conditions, subtle changes in the (phospho)lipid composition of the sarcolemma have been observed (602).

STAM,

AND

RENEMAN

Volume

72

Degradation of phospholipids results in accumulation of products with biological activity. Depending on the route of hydrolysis, compounds such as fatty acids, lysophospholipids, diacylglycerol, phosphocholine and related substances, and glycerol are produced. Because of impaired fatty acid oxidation (see sect. IvAZ) the contents of acyl-CoA and acylcarnitine also rise under ischemit conditions. Lipids and lipid derivatives, such as fatty acids, acyl-CoA, acylcarnitine, and lysophospholipids, have amphiphilic properties, i.e., their molecules have both hydrophobic and hydrophilic constituents. This particular property facilitates insertion of these compounds into cellular membranes. In doing so, lipid amphiphiles are thought to modulate the basic characteristics of biological membranes (85, 286). The effects of lipid amphiphiles on cardiac functioning under normal and pathophysiological conditions have been extensively reviewed in the past (85,286). In section v the potential involvement of lysophospholipids and fatty acids and esters in disturbances of cardiac function are discussed, with special reference to the ischemit and reperfused heart. D. Eicosanoid Production Cardiac Tissue

in Ischemic

and Reperfused

During ischemia and reperfusion the degradation of phospholipids in cardiac membranes results in the accumulation of arachidonic acid (69,446,579,594), the main substrate for eicosanoid production (see sects. IIIG~ and IvAR). The ability of the heart to produce eicosanoids is well established (106, 276, 576), and the release of arachidonic acid metabolites from the heart during ischemia and reperfusion has been reported by several investigators (129, 274, 576). The production of eicosanoids has attracted special attention because locally produced eicosanoids may exert both beneficial and detrimental effects on the ischemic and reperfused heart (32, 274, 276, 277, 493). The availability of nonesterified arachidonic acid is generally considered to be the rate-limiting step in cardiac eicosanoid synthesis (257, 442, 492). Because arachidonic acid accumulates in the myocardium during ischemia and an additional increase in myocardial content of this fatty acid is observed during reperfusion (579), it is tempting to assume that there is a direct relation between substrate accumulation and eicosanoid production under these circumstances. This assumption, however, implies that substrate accumulation occurs in cells that contain the enzymes cyclooxygenase and lipoxygenase, which are essential for the production of eicosanoids. Recent studies have shown that eicosanoids are mainly produced on reinstallation of flow. Production in zero-flow ischemic hearts is minimal (129); the amount of eicosanoids produced during ischemia and reperfusion is only a fraction of the amount of substrate available. Less than 1% of the accumulated arachidonic acid is converted into 6-keto-PGF,,, the stable metabolite of


October

1992

ifs -w

MYOCARDIAL

80

-5

: 0 al

FATTY

60

0

90

30 25

60

Ischemia

YU

Reperfusion time(min)

FIG. 9. Time course of changes in tissue content of arachidonic acid (fop) during 60 min of total ischemia followed by 30 min of reperfusion of isolated rat hearts. Release of 6-keto-PGF,, during reperfusion is also depicted. Means ~fi SD are shown. Weight of hearts used was on average 1 g. *Significantly different from preischemic value. C, normoxic control period. [From van Bilsen et al. (575).]

prostacyclin, during reperfusion following periods of ischemia up to 60 min (129). The disparity between substrate availability and the production of eicosanoids is further illustrated by the finding that during reperfusion arachidonic acid release from the heart gradually and substantially increases during the period of observation (up to 30 min), whereas the production of prostacyclin reaches its maximum immediately on reperfusion (Fig. 9). In addition to prostacyclin, TxB,, the stable metabolite of TxA,, is released from the heart during reperfusion, albeit in very small amounts [x0.03% of the available substrate (129)]. Cardiac cells can be considered to be the source of this prostanoid because the experiments were performed on isolated rat hearts perfused with a blood-free buffer. Without excessive stimulation, for example, through treatment with the Ca2+ ionophore A23187, in this model no other eicosanoids are produced by the myocardium during ischemia and reperfusion. This does not imply that under these circumstances no other eicosanoids can be collected in the hearts because durcoronary effluent of blood-perfused ing myocardial inju ry due to ischemia and/or reperfusion leukotrienes can be produced by activated neutrophils and TxA, by activated platelets (276, 427). The observation that in the heart endothelial cells are most likely the exclusive site for the conversion of exogenous and endogenous arachidonic acid into eicosanoids (171,172,229, 327,521) implies that the bulk of arachidonic acid accumulating in ischemic and reperfused cardiac tissue is localized in nonvascular cells and cannot readily be transported to the site of conversion.

ACID

HOMEOSTASIS

917

The most likely candidates for accumulation are the irreversibly damaged cardiomyocytes (see sect. IVAN). Whether prostanoids exert a beneficial or a disadvantageous effect on cardiac function is still matter of debate (276, 277). Depending on the type of prostanoid, the concentration, and/or the experimental model used, these eicosanoids have been shown to increase or decrease myocardial contraction force, to dilate or constrict coronary arteries, and to induce various electrical effects (276). Evidence is accumulating that prostaglandins are involved in myocardial reperfusion injury (277). As discussed, prostaglandins are released from the heart during the early reperfusion phase (129, 276), although short periods of ischemia did not result in enhanced production of prostaglandins (79). Drugs capable of inhibiting postischemic PG12 synthesis have been shown to exert a protective action against ischemia/reperfusion-induced damage (277). Moreover, addition of PGI, to the perfusion buffer resulted in a significant reversal of the protective effect of the inhibitors of prostaglandin synthesis (274). It should be stressed that the negative effects of prostaglandins on functional recovery of the postischemic heart were found to be concentration dependent. The findings obtained with unphysiologically high prostaglandin levels, while exerting salutary effects on the postischemic heart, are not in favor of a protective role of endogenously produced PG12 under normal and pathological conditions. The mechanism underlying the adverse effect of prostaglandins on postischemic cardiac function may relate to prostaglandin-evoked intramitochondrial Ca2’ overload resulting in depressed oxidative phosphorylation and enhanced lactate production due to activation of phosphorylase A activity in the affected heart (277). Conflicting results have been reported on the involvement of locally produced thromboxane in the precipitation of reperfusion arrhythmias. Coker et al. (80) provided evidence that thromboxane, most likely orginating from blood platelets, contributes to ventricular fibrillation during the postischemic phase. Burke et al. (54), though, failed to detect a causal relationship between enhanced postischemic thromboxane production and the generation of arrhythmias. The effect of leukotrienes, particularly LTC, and LTD,, on cardiac function appears also to depend on the concentration of the eicosanoid in the coronary fluid (277). Contractile depression and coronary vasoconstriction was generally seen at relatively high levels of leukotrienes (380). Treatment of the heart with antagonists or drugs capable of inhibiting leukotriene synthesis was found to be either salutary or without effect (277). Studies performed by Karmazyn and Moffat (281) revealed that in the normoxic heart leukotrienes at low physiological concentrations exert a significant positive inotropic effect. This stimulating effect was accompanied by constriction of the coronary vasculature. High concentrations of leukotrienes in the perfusion medium resulted in depressed contractility of the heart (281). Interestingly, no adverse effects on ischemic and reperfused hearts were observed when low concentrations


918

VAN

DER

VUSSE,

GLATZ,

of leukotrienes were supplied to the perfusion medium (277). For further details on this subject matter the reader is referred to surveys of Schrijr (493), Karmazyn (276, 277), and Van Bilsen et al. (575). E. Platelet-Activating Factor and Reperfused Heart

in the Ischemic

Reperfusion of ischemic cardiac tissue results in a significant release of PAF into the vascular compartment (33, 370). The highest release rate was observed during the first 5 min of reinstallation of coronary flow. Although the precise site of PAF production and release has not been identified, coronary endothelium is a likely candidate. It has been proposed that endogenously released PAF influences recovery of the postischemic heart in a negative way (33,359,370). Studies performed by Berti et al. (33) suggest that PAF and PG12 exert opposite effects on the reperfused, previously ischemic rabbit myocardium. In addition, administration of the PAF receptor antagonist BN-52021 significantly prevented myocardial contracture and electrical instability in the same experimental model (33). These findings also indicate that PAF exerts a direct effect on the postischemic heart. Other authors, however, propose that the detrimental action of PAF is mediated by either platelets or leukocytes trapped in the ischemic region (339, 359, 370). According to Montrucchio et al. (370), PAF-induced release of histamine and TxA, from blood cells contributes to postischemic loss of function in isolated rabbit hearts. A drug capable of binding to the PAF receptor on the platelet membrane, SDZ 63-675, was found to increase the resistance of the heart toward ischemia- and reperfusion-provoked damage (370). Alternatively, Lucchesi et al. (339) hypothesize that PAF enhances the release of vasoconstrictory factors from leukocytes infiltrated in the flow-deprived area. As a consequence proper restoration of function of the reperfused heart is substantially hampered. During longterm ischemia, administration of PAF antagonists significantly reduced cardiac infarct size in anesthetized rats (542), underlining the potential negative influence of PAF on the outcome of deprivation of flow in the heart. V.

EFFECTS

OF LIPID

AMPHIPHILES

ON CARDIAC

FUNCTIONING

A. Fatty

Acids and Heart

Function

Fatty acids are amphiphilic molecules containing a polar, hydrophilic carboxylate group and a nonpolar, hydrophobic hydrocarbon chain. Esterification of the carboxylate group with either CoA or with carnitine, which results in the formation of acyl-CoA and acylcarnitine, respectively, conserves the hydrophilic nature of

STAM,

AND

RENEMAN

Volume

72

that part of the molecule. At low concentrations in aqueous solution fatty acyl amphiphiles exist in the form of monomers. Incorporation of the monomers into biological membranes readily occurs and may lead to membrane stabilization (286). High concentrations of fatty acyl moieties give rise to the formation of micelles. Incorporation of large amounts of fatty acyl groups in membranes, either as micelles or as monomers, may induce mixed micelles with membrane phospholipids, which in turn strongly interfere with the physiological function of membranes and ultimately may lead to membrane instability and disruption (286). The latter effect is often referred to as the detergent action of fatty acyl moieties. During the past 20 years numerous studies have been published showing biological effects of fatty acids and their CoA and carnitine esters on the heart. These effects vary from modulation of metabolic pathways to severe depression of cardiac energy production and aggravation of ischemia-induced loss of cellular function. Other studies, however, failed to show detrimental effects of fatty acids or challenge the mechanisms proposed to explain the regulatory or noxious effects of fatty acyl moieties. Despite these deviant reports, it is generally believed that fatty acids and fatty acyl esters are potentially harmful for the heart when their extracellular or intracellular concentration rises above critical levels (85, 286, 325). Moveover, differences in the number of unsatured bonds and in cis/trans-configuration of the fatty acyl molecule may result in different degrees of the perturbing activity of these compounds on cardiac function. I. Electrophysiological

eflects of fatty

acids

Since the early publications of Oliver, Kurien, and co-workers (304,403) in which they suggested a possible relationship between elevated plasma levels of fatty acids and the occurrence of arrhythmias in patients with acute myocardial infarction, the putative noxious effect of exogenous fatty acids on myocardial function has been the subject of numerous studies. Oliver et al. (403) reported that serious arrhythmias and both early and late deaths were relatively more common in patients with acute myocardial infarction in whom plasma levels of fatty acids were considerably enhanced. According to the emerging “fatty acid hypothesis,” myocardial ischemia and pain could provoke the rise of plasma fatty acids by stimulating the release of catecholamines from the affected heart and postganglionic sympathic nerve endings. These hormones are known to release fatty acids from adipose tissue (304, 604). Fatty acids alone or in combination with increased catecholamine levels would precipitate myocardial arrhythmias. Although the clinical observations of Oliver et al. (403) were confirmed by others (211,306,443), the results obtained in a variety of other studies argue against it (212, 455,473). Interestingly, one group of investigators found that patients who developed ventricular tachycardia


October 1992

MYOCARDIAL

FATTY

had exceptionally low circulating fatty acid levels before the onset of arrthythmias (212). In addition, no significant relationship between arrhythmias and heparin-induced enhanced plasma fatty acid levels could be observed in noncardiac patients (393). Deliberately enhanced plasma fatty acid concentrations, exceeding those reported in patients with acute myocardial infarction, were well tolerated by the heart of healthy fasting volunteers (619). In this regard, it is worth mentioning that more recent studies dealing with the methodology of measuring fatty acids in biological fluids have revealed that the extremely high levels of circulating fatty acids, as reported in some earlier studies, are very rare and most likely caused by imperfections in the procedure of blood handling and analytical techniques to measure fatty acids (461, 462). The assumption that in the ischemic heart elevated plasma fatty acid levels and the occurrence of arrhythmias are causally related has been supported by studies with antilipolytic agents, such as sodium salicylate and nicotinic acid (85,342,461,470,472). Antilipolytic drugs mitigate cardiac electrical instability induced by ischemia (342,472) with a concomitant fall in plasma fatty acid levels. The incidence of ventricular fibrillation was reduced to zero in patients in whom plasma fatty acid levels were significantly decreased after administration of an antilipolytic drug. In patients in whom the drug failed to reduce the plasma fatty acid concentration, the incidence of ventricular fibrillation was high (470). Findings in animal studies either support or refute the fatty acid-arrhythmias hypothesis. Artificially raised fatty acid levels and elevated fatty acid-to-albumin ratios in plasma promoted the precipitation of cardiac arrhythmias (305, 306, 528, 648). In contrast to these confirmative findings, other studies failed to reveal a significant effect of elevated fatty acids on cardiac electrical behavior (83, 89, 300, 376, 377, 412, 447). Opie et al. (412) observed that in regional ischemic canine hearts in vivo ectopic activity was only enhanced at high levels of fatty acids when circulating epinephrine was concomitantly increased. Moreover, recent studies conducted by Riemersma (461), in which the continuous flow centrifugation technique was employed to specifically enhance blood fatty acid levels (196), indicate that raising the plasma concentration of oleate from -0.5 to 1.5 mM does not provoke cardiac electrical instability during the early vulnerable phase of ischemia. Despite the fact that both clinical and experimental studies do not allow an unequivocal conclusion regarding a causal relationship between plasma fatty acids and cardiac arrhythmias, several investigators have searched for a possible mechanism underlying the putative arrhythmogenic effect of fatty acids. Changes in the physicochemical properties of cellular membranes, due to accumulation of large amounts of fatty acids in the membranes, might cause or contribute to electrical instability. In addition, inhibition of Na+-K+-ATPase by fatty acids (308) might also be responsible for the arrhythmogenic effects elicited by some fatty acids. Fatty acid-induced shortening of the action poten-

ACID

HOMEOSTASIS

919

tial duration and the refractory period has been observed in hypoxic and ischemic cardiac tissue (89, 341, 456). In isolated rabbit hearts the threshold for ventricular arrhythmias was found to be significantly lowered during hypoxia. Saturated and monounsaturated fatty acids with chain lengths varying from 14 to 20 carbon atoms potentiated this effect. Long-chain polyunsaturated fatty acids counteracted both the threshold lowering effect of hypoxia and the potentiation of saturated and monounsaturated fatty acids (381). Antiarrhythmic effects of polyunsaturated fatty acids, like arachidonic and linoleic acid, in ouabain-induced arrhythmias have also been reported (358). In addition, linoleic and palmitic acid inhibited K+-induced slow potentials in hypoxic young chicken hearts (214). The latter effect was considered as antiarrhythmic. Other studies failed to demonstrate a significant effect of high concentrations of fatty acids on transmembrane action potentials in isolated ventricular tissue, Purkinje fibers, or isolated hearts when glucose was available as a substrate (83,89). However, when the isolated heart was made hypoxic or ischemit, palmitic acid considerably potentiated the shortening of the action potential duration (89). At present, no definite conclusion can be drawn about the potential arrhythmogenic effect of fatty acids on the normoxic and ischemic heart. The type of fatty acid accumulating in blood and/or tissue, the ratio of fatty acids to their carrier albumin, and the presence of circulating or locally released catecholamines, among others, seem to influence the outcome of the findings reported until now. 2. Fatty acids and infarct size Opie et al. (414) have reported a close relationship between peak plasma fatty acid levels and enzymatitally estimated infarct size in patients with acute myocardial infarction. This finding suggests the ability of fatty acids to aggravate the severity of myocardial infarction. Experimental support for this clinical observation was provided by experiments on isolated working rat hearts with regional ischemia. Significantly more enzyme was released from the infarcted area when the hearts were perfused with a palmitate-containing solution (115,116). Moreover, lowering fatty acid uptake and consumption in the hypoperfused heart by a variety of pharmaceutical compounds has been reported to decrease the extent of ischemic injury in experimental animal models (366, 608, 609, 611). To explain the clinical observation, the following metabolic vicious cycle was proposed (414). Myocardial infarction augments the plasma level of fatty acids due to an increased sympathetic drive. An enhanced supply of fatty acids subsequently decreased myocardial glucose utilization, which augments the amount of myocardial tissue damaged due to reduced anaerobic production of ATP. Extension of the ischemic injury causes a higher incidence of complications and hence further increases sympathetic drive. This hypothesis implicates a


920

VAN

DER

VUSSE,

GLATZ,

direct noxious effect of circulating fatty acids alone or in combination with increased levels of catecholamines on ischemic cardiac tissue. 3. Fatty

acids and mechanical

function

Negative effects of fatty acids on cardiac mechanical performance have been observed in isolated rabbit hearts perfused with a normoxic solution (502). These effects could be prevented by addition of equimolar amounts of albumin to the perfusion medium. Fatty acids depressed contractility of cardiac muscle preparations under hypoxic conditions but not under normal circumstances (226, 227). Conversely, palmitic acid in the presence of albumin (molar ratio 51) significantly improved mechanical performance of isolated hypoxic rat hearts (11), whereas high fatty acid-to-albumin molar ratios in the perfusion medium were found to depress the mechanical activity of isolated rat hearts under normoxic conditions (648). Stam and Hiilsmann (546) have shown th .at part of the negative effects of fatty acids might be mediated by endogenous catech olamines. Ichihara and Neely (2X), however, failed to demonstrate a detrimental effect of 1.2 mM palmitate on the mechanical function of isolated rat hearts exposed to relatively short periods of transient ischemia. Conflicting results were also obtained in studies on animal hearts in situ. When plasma fatty acid levels were raised by simultaneous administration of intralipid (i.e., triacylglycerols obtained from fractionated soy bean oil) and heparin the hemodynamic and metabolic functions of regionally ischemic pig hearts were significantly depressed (324). A similar treatment, however, did not affect the degree of cardiac injury following acute coronary occlusion (377). In dog hearts in situ, fatty acid levels raised by intralipid and heparin infusion significantly depressed residual blood flow in the ischemic region but left the overall hemodynamic function of the partly ischemic heart unaffected (447). Interestingly, a similar treatment in cardiac patients did not influence the overall mechanical function of the heart, despite highly elevated levels of plasma fatty acids (422). Apparent differences regarding the effects of circulating fatty acids on cardiac function might be due to variable effects of locally released or circulating catecholamines in the experimental preparations (546, 582, 607). Epinephrine infusion markedly impaired mechanical activity in isolated, normoxic, or ischemic rat (53, 415) and dog hearts in situ (293), whereas endogenous lipolysis was found to be enhanced under these circumstances. Administration of antilipolytic agents reduced both the depression of mechanical performance and the hydrolysis of the intracellular triacylglycerol pool (53, 293). Results obtained in other studies indicate that endogenous catecholamines are also involved in the depressant action of extracellular fatty acids on cardiac performance (294,546). In regional ischemic dog hearts, infusion of nicotinic acid, a well-known antilipolyticum, significantly improved mechanical function of the affected area on reperfusion (310).

STAM,

AND

RENEMAN

Volume

72

The molecular basis of the putative noxious effects of high circulating levels of fatty acids and/or enhanced release of fatty acids from intracellular stores on cardiac performance under normoxic and oxygen-deprived circumstances is incompletely understood. Fatty acids can directly affect the activity of enzymes involved in the glycolytic pathway (317,451). Under normal conditions this effect might reflect a physiological mechanism to regulate intracellular energy metabolism. However, under oxygen-restricted circumstances it may result in a depression of anaerobic production of high-energy phosphates. An alternative explanation is the oxygen- and hence energy-wasting effect of fatty acids (249). Theoretically, oxidation of fatty acids requires ~10% more molecular oxygen to produce the same amount of ATP than does the oxidation of glucose or lactate. One study with isolated rat hearts revealed that fatty acids can increase oxygen consumption by -40% (62), although this oxygen-wasting effect could not be confirmed by studies performed by other investigators (119,1.23,378). Fatty acids have been reported to stimulate ATPase activity in isolated mitochondria and to reduce coupling of oxidative phosphorylation (48, 240, 331, 332, 445, 613). The resulting impaired efficiency of cellular energy production might be the basis of increased cardiac oxygen consumption as observed by some investigators (62). Although fatty acids at relatively low concentrations act as uncoupling agents, at higher concentrations they are capable of inhibiting mitochondrial respiration (27, 435). An increased supply of fatty acids most likely results in an elevated incorporation in the cellular triacylglycerol pool. This event may especially occur in oxygen-restricted cells in which glycerol 3-phosphate levels are elevated due to enhanced glycogen and/or glucose degradation. When increased triacylglycerol formation is associated with stimulated triacylglycerol hydrolysis, an energy-wasting metabolic cycle is created. As discussed in section 1vB4, in this cycle seven ATP molecules are consumed to produce one molecule of triacylglycerol. To date no data are available to estimate the precise quantitative contribution of the triacylglycerol-fatty acid cycle in cardiac ATP consumption in oxygen-deprived cardiomyocytes. Conservative estimates indicate a number of ~10% (572). Depressed cardiac mechanical performance might also be caused by the interference of fatty acids with cellular Ca2+ handling because sequestration of Ca2+ in the isolated sarcoplasmic reticulum by fatty acids has been observed (286,356). When extrapolation of these in vitro findings to the intact heart is allowed, fatty acidinduced reticular sequestration of Ca2+ finally results in decreased cytoplasmic Ca2+ levels and depressed contractile behavior of the myocardium. Fatty acid-induced damage of mitochondria in flow-deprived cardiac tissue may also add to depressed mechanical function. In this respect, the striking changes in mitochondrial morphology in isolated, ischemic rat hearts supplied with exogenous palmitate are worth mentioning (139,140).


October

1992

MYOCARDIAL

FATTY

The effect of postischemic return of coronary flow on the cardiac tissue content of fatty acids has extensively been studied by Van Bilsen et al. (579). They found that fatty acids released from endogenous esterified lipid stores appreciably accumulate on reperfusion. Values up to 4 mmol fatty acid/g dry wt could be monitored after 30 min of reperfusion following 60 min of ischemia. Despite the highly elevated fatty acid levels, restoration of mechanical function was 40% of control. Interestingly, Piper et al. (435) estimated, on the basis of experiments with isolated cardiac mitochondria incubated in the presence of albumin-bound fatty acids, that a tissue fatty acid content >O.l mmol/g wet wt (corresponding with 0.5-1.0 mmol/g dry wt) would completely block mitochondrial energy production. Because substantially higher tissue fatty acid levels were monitored in reperfused hearts with significant residual mechanical function (579), the conclusion has to be drawn that fatty acids do not accumulate homogeneously but are compartmentalized at either the cellular or the subcellular level (see sect. IVAN). In addition, the relatively high intracellular content of FABP (see sect. IICS) may also contribute to prevent elevated fatty acid levels from detrimental actions (184). B. Fatty Acyl-Coenxyme A and Acylcarnitine and Cardiac Performance In addition to fatty acids, derivatives such as acylCoA and carnitine esters are potential modulators of cellular functioning in normal and oxygen-deprived hearts. As discussed in section 1vA.2, ischemia results in enhanced tissue levels of fatty acyl-CoA and acylcarnitine provided exogenous fatty acids are delivered to the cardiomyocytes through residual coronary circulation. These fatty acyl derivatives are suggested to modulate or impair cardiac functioning. I. Fatty

acylcarnitine

and cardiac

electrical

stability

A variety of electrophysiological effects of fatty acylcarnitine has been reported (85). Corr et al. (86) observed specific effects of exogenous palmitoylcarnitine on Purkinje fibers isolated from dog hearts and superfused under normoxic conditions. Maximum diastolic potential, amplitude, maximum rate of phase 0, and action potential duration were significantly depressed by palmitoylcarnitine at concentrations comparable to those monitored in ischemic cardiac tissue (324). The hydrolytic products carnitine and palmitic acid failed to provoke these changes in electrophysiological parameters of the isolated Purkinje fibers (86). Lowering the pH of the superfusion medium from physiological values to a value known to be present in ischemic tissue considerably increased the sensitivity of the Purkinje cells to exogenously applied palmitoylcarnitine (86). In studies on chicken ventricular tissue the rate of rise of phase 0 depolarization was found to be depressed, and

ACID

HOMEOSTASIS

921

the duration of the action potential increased following the administration of palmitoylcarnitine. Diastolic membrane potential appeared to be insensitive to extracellular palmitoylcarnitine (255). The lack of agreement on the effect of fatty acylcarnitine esters on the electrophysiological properties of the heart can be explained by differences in cell types and species investigated. Fatty acylcarnitines are not confined to the intracellular compartment. Normally the plasma concentration is on the order of lo-15 mmol/l (164). Therefore changes in the extracellular concentration of acylcarnitines may contribute to the impaired electrophysiological behavior of cardiac cells. This might especially be true under ischemic conditions, since a low pH increases the sensitivity of cardiac structures to the effects of acylcarnitine (86). Acylcarnitine may elicit cardiac arrhythmias in an indirect way. First, exposure of normoxic cardiomyocytes to low concentrations of acylcarnitine induces a substantial increase in the number of membrane cyladrenoceptors (223). Cardiomyocytes exposed to conditions of hypoxia, which are sufficiently severe to induce enhanced cellular acylcarnitine levels, also exhibit a severalfold increase of cu,-adrenoceptors (223). A causal relationship between density of cw,-adrenoceptors and electrical instability should be considered because blockade of the receptors was found to be antiarrhythmic (224). Moreover, POCA, a potent inhibitor of carnitine acyltransferase I, prevents both the accumulation of acylcarnitine and the increase of a,-adrenoceptor density (223). Recent studies by Corr et al. (84) show that in cat hearts POCA treatment also abolishes arrhythmias during the early phase of ischemia. These findings suggest a role of acylcarnitine in q-adrenoceptor-mediated loss of electrical stability of the oxygendeprived heart (85). Second, increased intracellular levels of acylcarnitine may give rise to enhanced lysophospholipid contents in the ischemic tissue (84). This effect is caused by the inhibitory action of acylcarnitine on two key enzymes involved in lysophospholipid degradation, i.e., lysophospholipase and lysophospholipase transacylase (204,207). 2. Effect of acylcarnitine and acyl-coenxyme A on cardiac ion transport and energy metabolism A host of effects of acylcarnitine and acyl-CoA on intracellular metabolic processes and membrane properties have been reported. Cellular handling of Ca2+ is most likely modulated by the carnitine and CoA esters of fatty acids. Enhanced membrane permeability to Ca2+ (255), increased Ca2’ release from vesicles enriched in sarcoplasmic reticulum (357, 436), depression of the Na+-Ca2+ antiporter in the sarcolemma (309), and alterations of Ca2+ pump activity of isolated sarcoplasmic reticulum (436) by acylcarnitine have been reported. Low concentrations of palmitoylcarnitine enhance the binding of Ca2+ to the sarcoplasmic reticulum and increase Ca2+ -ATPase activity (5). When the concentra-


922

VAN

DER

VUSSE,

GLATZ,

tion of palmitoylcarnitine was increased, opposite effects were observed (5, 436). Recent experiments by Lamers et al. (307) have provided evidence that in ischemic hearts the amount of acylcarnitine accumulated in the sarcolemma is insufficient to impair Ca2+ transport across cardiac membranes. This important observation makes acylcarnitine a less likely candidate to play a critical role in the disturbed sarcolemmal transport of Ca2+ in the ischemic myocyte. Fatty acylcarnitine may also modulate the cellular content of Na+ and K+, since sarcolemmal Na+-K+-ATPase activity appears to be sensitive to surrounding fatty acylcarnitine moieties (354). The lack of inhibitory action of palmitoylcarnitine on sarcolemmal vesicles, as used by Owens et al. (421), is most likely caused by the fact that the vesicles were primarily right-side out. As a consequence the initial Na+-K+-ATPase activity was low. Because of its detergent action, palmitoylcarnitine enhances the apparent Na+-K+-ATPase activity, on the one hand, and inhibits the activity of this enzyme, on the other hand, resulting in minor changes in overall enzyme activity (85). Inhibition of Na+-K+-ATPase in the sarcolemma by fatty acylcarnitine (5,308,354,418) may lead to loss of cellular K+ and accumulation of Na+ in the affected cell. Although long-chain fatty acyl-CoA can inhibit Na+-K+-ATPase (354,421), it is doubtful whether this in vitro phenomenon has pathophysiological implications. After all, accumulation of acyl-CoA moieties is largely confined to the mitochondrial matrix (252), and hence access to sarcolemmal Na+-K+-ATPase by these compounds will be limited or absent (325). Fatty acyl-CoA and fatty acylcarnitine moieties can potentially modulate cardiac energy metabolism. Increased concentrations of acylcarnitines inhibit carnitine-acylcarnitine translocase. This effect, which may be considered as feedback regulation under physiological conditions, will diminish transport of fatty acyl groups across the mitochondrial membrane and hence fatty acid oxidative degradation inside the mitochondria (658). Fatty acyl-CoA esters have been found to interfere with cellular energy metabolism mainly at the level of adenine nucleotide translocase (515). This membrane-associated system exchanges intramitochondrial ATP for cytoplasmic ADP and is thought to play an important role in the overall regulation of mitochondrial energy production. Fatty acyl-CoA inhibits the action of adenine nucleotide translocase with an apparent inhibitory constant of 0.3 ~mol/l(311,514). Because the tissue content of acyl-CoA esters is of the same order of magnitude, a physiological role of acyl-CoA in regulating cellular energy metabolism is feasible (85). Some debate has arisen about the site of action of acyl-CoA. Several investigators have reported that acyl-CoA can block translocase activity from both the matrix and cytoplasmic side of the mitochondrial inner membrane (516,654). Others have revealed that adenine nucleotide translocase is insensitive to acyl-CoA esters present on the mitochondrial matrix side (312). Because under nor-

STAM,

AND

RENEMAN

Volume

22

ma1 conditions the majority of acyl-CoA is localized inside the mitochondria and accumulation of acyl-CoA is thought to occur in this subcellular compartment during ischemia (254), a direct inhibitory effect of these compounds on adenine nucleotide translocase is only possible when acyl-CoA leaks from the mitochondrial matrix to the cytoplasmic compartment (85). This possibility cannot be excluded since ischemia might alter mitochondrial inner membrane permeability. C. Biological

Efects

of Lysophospholipids

1. Lysophospholipids and the ischemic heart

At low concentrations, i.e., below the critical micellar concentration, lysophospholipids exist as monomers. In this form lysophospholipids can be incorporated in the lipid bilayer of cellular membranes. At concentrations above the critical micellar concentration, lysophospholipids are forming micelles. These structures can either fuse with biological membranes or remove original lipid material from the membrane. Because of the wedge-shape structure of lysophospholipids, inclusion of these compounds in biological membranes might lead to an altered shape or curvature of the membrane (85, 340, 637), thereby possibly modifying its physical properties and physiological function. This may ultimately result in alteration of the biological activity of membrane proteins and impairment of membrane stability. In this respect it is noteworthy that the rate of lysophospholipid accumulation is more critical in perturbing sarcolemmal functioning than the quantity of amphiphiles accumulating in the cardiac membrane (500). The negative effects of lysophospholipids are probably related to an excessive Ca2+influx (333), impairment of oxidative phosphorylation as observed in isolated liver mitochondria (42), contracture of isolated hearts (31), and depressed activity of membrane-linked enzymes such as Na+-K+-ATPase (273). Enhancement of contractile force in isolated cardiac tissue (78) is most likely caused by increased cytoplasmic Ca2’ levels secondary to lysophospholipid-stimulated formation of CAMP (6). Inclusion of lysophospholipids in membranes may also cause severe electrophysiological derangements (85, 344). Elharrar et al. (128) have shown that alterations in excitability of cardiac tissue in vivo include a transient rise for l-3 min after the onset of ischemia followed by an appreciable decline. Interestingly, similar effects of lysophospholipids on cardiac electrophysiological functioning have been reported by Arnsdorf and Sawicki (12). The biphasic effects of lysophospholipid are characterized by an initial enhancement of excitability and a subsequent fall in excitability of the affected membranes. These changes are related to alterations in passive and active properties of the membrane (85). Earlier studies revealed that lysophospholipids ac-


Ocfo~x?r-

1922

MYOCARDIAL

FATTY

cumulate in myocardial tissue within 8-10 min after cessation of flow (88, 510). Snyder et al. (526) reported significantly elevated lysophospholipid levels in venous blood draining the ischemic area within the same time domain. However, others failed to observe an enhanced release of lysophospholipids from the ischemic heart (463). Later studies conducted by Corr et al. (88) showed that in cat hearts lysophospholipid accumulation occurs as early as 5 min after the onset of ischemia. Increase of lysophospholipids was absent in hearts without manifest signs of ventricular arrhythmias. The increase of lysophospholipids was higher in hearts with spontaneous fibrillation than in hearts showing less severe forms of arrhythmias (88). In addition to a close correlation between endogenous levels of lysophospholipids and electrophysiological alterations soon after the onset of ischemia, the effect of administration of exogenous lysophospholipids to all kinds of cardiac tissue preparations underlines the notion that lysophospholipids may cause electrical instability (85,345). Media containing lysophospholipids at a concentration of 1.2 mM in the presence of albumin induced appreciable electrophysiological alterations (83). In protein-free solutions significantly lower concentrations (i.e., lo-50 PM) of lysophospholipids elicited profound electrophysiological disturbances (l&78,86). The electrophysiological alterations were observed for both lysophosphatidylcholine and lysophosphatidylethanolamine (85), whereas other degradation products of phospholipids, such as fatty acids and glycerophosphorylcholine, were without effect (84). The sensitivity of Purkinje fibers to the electrophysiological effects of lysophospholipids was enhanced threefold when the pH of the medium was reduced to 6.7, a value corresponding with the pH of ischemic cardiac tissue (85, 86). The detergent effect of lysophospholipids might play an important role in the precipitation of arrhythmias (346, 347). Analysis of the effect of lysophospholipids on cardiac electrophysiological properties revealed its complex nature. Because lysophospholipids significantly slow down the rapid sodium-carried outward current and the slow calcium-carried inward current, the conclusion may be drawn that they are nonspecific inhibitors of cardiac ion channels (85). Ventricular muscle and Purkinje fibers are rapidly depolarized by exogenous lysophospholipids, changes also seen in ischemic tissue (85). Low concentrations of lysophosphatidylcholine shorten cardiac refractoriness, whereas high concentrations of this amphiphile lengthen the refractory period (83). These opposite effects may lead to conditions favorable for the occurrence of unidirectional block. As lysophospholipids also reduce conduction velocity (12, 83, 86), these changes in electrophysiological properties may favor the induction of reentry pathways, resulting in cardiac fibrillation. The similarity of lysophospholipid-induced and ischemia-provoked changes in cardiac electrophysiology (128) suggests a causal relationship between the accumulation of lysophospholipids and electrophysiological alterations soon after cessation of flow.

ACID

923

HOMEOSTASIS

Recent studies conducted by Corr et al. (88) revealed that purposely induced fibrillation lowers the tissue content of lysophospholipids. This finding favors the idea that electrophysiological perturbations are the result rather than the cause of the enhanced tissue levels of lysophospholipids during ischemia. It remains to be elucidated as to whether lysophospholipids are also involved in alterations of the electrophysiological properties of the heart during prolonged ischemia. In search for the critical level of lysophospholipids in the cardiac membranes, Corr et al. (85) observed that replacement of 1% of the total cardiac phospholipid pool by lysophospholipids causes electrophysiological derangements. Selective incorporation of lysophospholipids into the sarcolemma results in significant changes in electrical properties of the membrane when at least 2% of sarcolemmal phospholipids is in the lyso form (476). From these findings a threshold value for the induction of electrophysiological effects of ~0.2 nmol lysophospholipid/mg tissue protein could be calculated (85). Removal of lysophospholipids from the membrane structures results in the reversal of the electrophysiological derangements (203). Factors other than lysophospholipids may also contribute to the induction of electrical instability of the ischemic heart. These factors exert their action either independently of lysophospholipids or in concert with the hydrolytic products of phospholipids. Interestingly, fatty acylcarnitines, amphiphilic compounds known to accumulate in ischemic cardiac tissue with residual supply of fatty acids (391), are required to induce the accumulation of lysophospholipids in underperfused cat heart (84). This conclusion is based on the finding that inhibition of carnitine acyltransferase I with POCA prevented the accumulation of both acylcarnitine and lysophosphatidylcholine in the acute phase of cardiac ischemia (see sect. vBI). The fact that acylcarnitines are potent inhibitors of two key enzymes of lysophospholipid catabolism, i.e., lysophospholipase and lysophospholipase transacylase (200,204), offers a feasible explanation for the POCA-prevented rise of lysophospholipids in the ischemic heart. The concomitant reduction of lethal arrhythmias induced early after the onset of ischemia in POCA-treated hearts supports the notion of a causal relationship between elevated tissue levels of lipid amphiphiles and destabilization of electrical properties of the flow-deprived heart (84). 2. Lysophospholipids

during

reperfusion

The two most prominent features of reinstallation of coronary flow through ischemic cardiac tissue are impaired contractile force and reperfusion arrhythmias (325). Recent studies of Van Bilsen et al. (579) showed that in isolated rat hearts reperfusion following 45 min of global ischemia resulted in increased tissue content of lysophosphatidylethanolamine. Tissue levels of lysophosphatidylcholine appeared to be insensitive to the restoration of flow. No correlation was found between


924

VAN

DER

VUSSE,

GLATZ,

reperfusion-induced arrhythmias and changes in the content of lysophosphatidylethanolamine on reperfusion (579). These findings suggest that factors other than endogenous lysophospholipids are responsible for the reperfusion arrhythmias in rat hearts. The possible relationships between the formation of lysophospholipid and impairment of contractile force remain to be established. D. Uncertainties Regarding Detrimental Eflects of Lipid Amphiphiles on the In Situ Heart The pathogenetic activity of amphiphiles in cardiac ischemic cells in situ has not been unequivocally demonstrated. Amphiphiles, such as fatty acids, acyl-CoA, acylcarnitines, and lysophospholipids, accumulate in flow- and oxygen-deprived tissue. However, the exact cellular and subcellular site of accumulation remains to be elucidated. To investigate the (sub)cellular sites of accumulation, techniques are required that avoid intrapreparative hydrolysis of parent phospholipids and triacylglycerols and further degradation of the hydrolytic products. Exchange of amphiphiles between subcellular sites during the preparation procedure should also be avoided. The quantity of lipid amphiphiles accumulating in cardiac membranes employed in in vitro studies should be precisely known. The same holds for the amount of amphiphiles present in cardiac membranes in vivo. Detailed knowledge of quantities involved will make extrapolation of in vitro findings to the in vivo situation meaningful. Moreover, the presence of specific lipid-binding proteins in the proximity of the membrane should also be taken into account. On the other hand, studies designed to delineate a possible modulating or detrimental effect of lipid amphiphiles on cardiac function should take into account the specific changes that take place in oxygen-deprived cells, such as disturbed ion homeostasis, increased cellular acidity, and depressed levels of high-energy phosphates. All these changes may modulate the sensitivity of cardiac membranes to amphiphiles. VI.

CONCLUDING

REMARKS

During the past decades considerable progress has been made in our understanding of the homeostasis of fatty acids in cardiac tissue. Despite this progress, a variety of questions remains unresolved and warrants further investigation. Among others, these questions pertain to the role of endogenous esterified lipid pools in cardiac fatty acid metabolism. In particular, the rate of incorporation and subsequent release of extracellularly derived fatty acids in cardiac triacylglycerols and phospholipids and the factors governing the balance between synthesis and degradation await further clarification. Currently obtained evidence indicates that uptake and inter- and intracellular transport of fatty acids are multistep processes, the details of which are still frag-

STAM,

AND

RENEMAN

Volume

72

mentarily elucidated. Moreover, the physiological role and mutual relationship of various FABPs, such as FABP,, acyl-CoA-binding protein, and FABP,,, are incompletely understood. It is expected that advanced molecular biological techniques will help to unravel the significance of these intriguing proteins in cardiac fatty acid handling. Cardiac lipid homeostasis is severely disturbed under conditions of inadequate supply of blood to this organ. Ischemia and reperfusion have been shown to enhance the cellular content of lipid amphiphiles. Although in vitro findings suggest an additional detrimental effect of these amphiphiles on cardiac functioning, several uncertainties remain regarding their (patho) physiological role in the in situ heart. Further investigations are required to clarify the significance of membrane phospholipid degradation in the chain of events of ischemia- and reperfusion-induced irreversible damage of cardiac cells. Clarification of the precise significance of phospholipid hydrolysis under flow-restricted conditions and subsequent reperfusion is of utmost importance. In the ischemic heart, impaired resynthesis of phospholipids seems to contribute considerably to the net loss of these lipid moieties. On reperfusion, a more prominent role of phospholipase-mediated degradation of phosphlipids is foreseen. On the basis of this knowledge application of specific phospholipase-inhibiting agents might offer a valuable tool to reduce ischemiaand reperfusion-induced damage. The rapid and impressive development of noninvasive techniques, such as positron emission tomography and single photon emission computer tomography, to monitor the metabolic behavior of the healthy and diseased heart requires detailed information about cardiac fatty acid metabolism to properly interpret the data obtained with radiolabeled lipid substrates. This particular application of basic knowledge of fatty acid homeostasis in the heart is an additional stimulus to proceed with studies on the features of cardiac fatty acid uptake, storage, and conversion and the regulatory mechanism underlying these intricate metabolic processes. We are greatly indebted to Karlijn Dickison and Emmy van Roosmalen for their help in the preparation of the manuscript.

REFERENCES ABRAHAM, N. G., A. PINIO, R. D. LEVERE, AND K. MULLANE. Identification of hemo oxygenase and cytochrome P-450 in the rabbit heart. J. Mol. CeLZ. CardioZ. 19: 73-81, 1987. ABUMRAD, N. A., J. H. PARK, AND C. R. PARK. Permeation of long-chain fatty acid into adipocytes. Kinetics, specificity, and evidence for involvement of a membrane protein. J. BioL Chem. 259: 89458953, 1984. ABUMRAD, N. A., R. C. PERKINS, J. H. PARK, AND C. R. PARK. Mechanism of long chain fatty acid permeation in the isolated adipocyte. J. Biol. Chem. 256: 9183-9191,198l. ACHARI, A., D. SCOTT, P. GARLOW, J. C. VIDAL, A. OTWINOWSKI, S. BRUNIE, AND P. B. SIGLER. Facing up to membranes: structure/function relationships in phospholipases. Cold Spring Harbor Symp. Quad. Biol. 52: 441-452,198X


October

19%

MYOCARDIAL

FATTY

5. ADAMS, R. J., D. W. COHEN, S. GUPTA, J. D. JOHNSON, E. T. WALLICK, T. WANG, AND A. SCHWARTZ. In vitro effects of palmitoylcarnitine on cardiac plasma membrane Na,K-ATPase, and sarcoplasmic reticulum Ca’+-ATPase and Ca2+ transport. J. Biol. Ch,em. 254: 12404-12410, 1979. 6. AHUMADA, G. G., S. R. BERGMANN, E. CARLSON, P. B. CORR, AND B. E. SOBEL. Augmentation of cyclic AMP content induced by lysophosphatidyl choline in rabbit hearts. Cardiovasc. Res. 13: 377-382, 1979 7. AHUMADA, G. G., B. E. SOBEL, AND P. NEEDLEMAN. Synthesis of prostaglandins by cultured rat heart myocytes and cardiac mesenchymal cells. J. Mol. CeZZ. CardioZ. 12: 685-700, 1980. 8. AKITA, H., M. H. CREER, K. A. YAMADA, B. E. SOBEL, AND P. B. CORR. The electrophysiological effects of intracellular lysophosphoglycerides and their accumulation in cardiac lymph with myocardial ischemia in dogs. J. Clin. Invest. 78: 271-286, 1986. 9. AMRI, E. Z., C. VANNIER, J. ETIENNE, AND G. AILHAUD. Maturation and secretion of lipoprotein lipase in cultured adipose cells. II. Effects of tunicamycin on activation and secretion of the enzyme. Biochim. Biophys. Acta 875: 334-343,1986. 10. ANSELL, G. B., AND S. SPANNER. Phosphatidylserine, phosphatidylethanolamine and phosphatidylcholine. In: Phospholipids, edited by J. M. Hawthorne and G. B. Ansell. Amsterdam: Elsevier, 1982, p. l-49. 11. APSTEIN, C. S., R. B. GMEINER, AND N. BRACHFELD. Effect of palmitate on hypoxic myocardial metabolism and contractility. Recent Adv. Stud. Card. Struct. Metab. 1: 136-146, 1972. 12. ARNSDORF, M. F., AND G. J. SAWICKI. The effects of lysophosphatidyl choline, a toxic metabolite of ischemia, on the components of cardiac excitability in sheep Purkinje fibers. Circ. Res. 49: 16-30,198l. 13. ARTHUR, G., AND P. C. CHOY. Acyl specificity of hamster heart CDPcholine:l,2-diacylglycerol phosphocholine transferase in phosphatidylcholine biosynthesis. Biochim. Biophys. Acta 795: 221-229, 1984. 14. ARTHUR, G., L. COVIC, M. WIENTZEK, AND P. C. CHOY. Plasmalogenase in hamster heart. Biochim. Biophys. Acta 833: 189195,1985. 15. ARTHUR, G., T. MOCK, C. ZABORNIAK, AND P. C. CHOY. The distribution and acyl composition of plasmalogens in guinea pig heart. Lipids 20: 693-698, 1985. 16. ARTHUR, G., L. PAGE, T. MOCK, AND P. C. CHOY. The catabolism of plasmenylcholine in guinea pig heart. Biochem. J. 236: 475-480,1986. 17. ARTHUR, G., L. PAGE, C. ZABORNIAK, AND P. C. CHOY. The acylation of lysophosphatidylglycerocholines in guinea pig heart mitochondria. Biochem. J. 242: 171-175, 1987. 18. ASCUITTO, R. J., N. T. ROSS-ASCUITTO, V. CHEN, AND W. E. DOWNING. Ventricular function and fatty acid metabolism in neonatal piglet heart. Am. J. PhysioZ. 256 (Heart Circ. Physiol. 25): H9-H15, 1989. 19. AUPECLE, P., AND A. PINSON. The role of cardial lysosomal lipases in triacylglycerol cleavage. FEBS Lett. 144: 93-96, 1982. 20. BAGBY, G. J. Heparin-independent release of lipoprotein lipase activity from perfused rat hearts. Biochim. Biophys. Acta 753: 47-52, 1983. 21. BAGBY, G. J., AND C. B. CORLL. Comparison of lipoprotein lipase activity in heart myocytes and perfused hearts. J. Mol. Cell. Cardiol. 21: 253-262, 1989. 22. BALLARD, F. B., W. H. DANFORTH, S. NAEGLE, AND R. J. BING. Myocardial metabolism of fatty acids. J. Clin. Invest. 39: 717-730,196O. 23. BASS, N. M. The cellular fatty acid binding proteins: aspect of structure regulation and function. ht. Rev. Cytol. 3: 143-184, 1988. 24. BASSINGTHWAIGHTE, J. B., AND C. A. GORESKY. Modeling in the analysis of solute and water exchange in the microvasculature. In: Handbook of Physiology. The Cardiovascular System. Microcirculation. Bethesda, MD: Am. Physiol. Sot., 1984, sect. 2, vol. IV, pt. 1, chapt. 13, p. 549-626. 25. BASSINGTHWAIGHTE, J. B., L. NOODLEMAN, G. J. VAN

ACID

26.

27.

28. 29.

30.

31.

32.

33.

34.

35. 36.

37.

38. 39.

40. 41.

42.

43.

44.

45. 46.

47.

HOMEOSTASIS

925

DER VUSSE, AND J. F. C. GLATZ. Modeling of palmitate transport in the heart. Mol. CeZZ. Biochem. 88: 51-59, 1989. BASSINGTHWAIGHTE, J. B., AND H. V. SPARKS. Indicator dilution estimation of capillary endothelial transport. Annu. Rev. Physiol. 48: 321-334, 1986. BATAYNEH, N., S. J. KOPACZ, AND C. P. LEE. The modes of action of long chain alkyl compounds on the respiratory chainlinked energy transducing system in submitochondrial particles. Arch. Biochem. Biophys. 250: 476-478, 1986. BAUER, J. E. Substrate specificity studies of partially purified rabbit heart lipoprotein lipase. Artery 15: 272-291, 1988. BELL, R. M., AND R. A. COLEMAN. Enzymes of triacylglycerol formation in mammals. In: The Enzymes, edited by P. D. Boyer. New York: Academic, 1983, vol. 16, p. 87-111. BENTHAM, J. M., A. J. HIGGINS, AND B. WOODWARD. The effects of ischaemia, lysophosphatidylcholine and palmitoylcarnitine on rat heart phospholipase A, activity. Basic Res. CardioZ. 82, Suppl. II: 127-137, 1987. BERGMANN, S. R., T. B. FERGUSON, JR., AND B. E. SOBEL. Effects of amphiphiles on erythrocytes, coronary arteries, and perfused heart. Am. J. Physiol. 240 (Heart Circ. Physiol. 9): H229H237, 1981. BERTI, F., F. MAGNI, D. CARUSO, C. OMINI, L. PUGLISI, AND G. GALLI. Nonsteroidal anti-inflammatory drugs aggravate acute myocardial ischemia in the perfused rabbit heart; a role for prostacyclin. J. Cardiovasc. Pharmacol. 12: 438-444,1988. BERTI, F., F. MAGNI, G. ROSSONI, L. DE ANGELIS, AND G. GALLI. Production and biological interactions of prostacyclin and platelet-activating factor in acute myocardial ischemia in the perfused rabbit heart. J. Cardiovasc. Pharmacol. 16: 727-732, 1990. BESTER, R., AND A. LOCHNER. Sarcolemmal phospholipid fatty acid composition and permeability. Biochim. Biophys. Acta 941: 176-186, 1988. BIEBER, L. L. Carnitine. Annu. Rev. Biochem. 57: 261-283,1988. BIELEFELD, D. R., T. C. VARY, AND J. R. NEELY. Inhibition of carnitine palmitoyl-CoA transferase activity and fatty acid oxidation by lactate and oxfenicine in cardiac muscle. J. MoZ. Cell. Cardiol. 17: 619-625, 1985. BILHEIMER, D. W., L. M. BUJA, R. W. PARKEY, F. J. BONTE, AND J. T. WILLERSON. Fatty acid accumulation and abnormal lipid deposition in peripheral and border zones of experimental myocardial infarcts. J. Nucl. Med. 19: 276-283, 1978. BING, R. J. Cardiac metabolism. Physiol. Rev. 45: 171-213,1965. BING, R. J., A. SIEGEL, I. UNGAR, AND M. GILBERT. Metabolism of the human heart. II. Studies on fat, ketone and amino acid metabolism. Am. J. Med. 16: 504-515,1954. BLAIN, J., H. SCHAEFFER, A. SIEGEL, AND R. J. BING. Studies of myocardial metabolism. Am. J. Med. 20: 820-833,1956. BLANCHETTE-MACKIE, E. J., H. MASUNO, N. K. DWYER, T. OLIVECRONA, AND R. 0. SCOW. Lipoprotein lipase in myocytes and capillary endothelium of heart: immunocytochemical study. Am. J. PhysioZ. 256 (Endocrinol. Metab. 19): E818-E828, 1989. BOIME, I., E. E. SMITH, AND F. E. HUNTER, JR. The role of fatty acids in mitochondrial changes during liver ischemia. Arch. Biochem. Biophys. 139: 425-443,197O. BOLTON, H. S., R. CHANDERBHAN, R. W. BRYANT, J. M. BAILEY, W. B. WEGLICKI, AND G. V. VAHOUNY. Prostaglandin synthesis by adult heart myocytes. J. Mol. CeZl. Cardiol 12: 1287-1298,198O. BORCHERS, T., C. UNTERBERG, H. RUDEL, H. ROBENEK, AND F. SPENER. Subcellular distribution of cardiac fatty acidbinding protein in bovine heart muscle and quantitation with an enzyme-linked immunosorbent assay. Biochim. Biophys. Acta 1002: 54-61, 1989. BORENSZTAJN, J. Lipoprotein Lipase. Chicago, IL: Evener, 1987. BORENSZTAJN, J., S. OTWAY, AND D. S. ROBINSON. Effect of fasting on the clearing factor lipase (lipoprotein lipase) activity of fresh and defatted preparations of rat heart muscle. J. Lipid Res. 11: 102-110, 1970. BORENSZTAJN, J., D. R. SAMOLS, AND A. H. RUBENSTEIN.


926

VAN

DER

VUSSE,

GLATZ,

Effects of insulin on lipoprotein lipase activity in the rat heart and adipose tissue. Am. J. PhysioZ. 223: 1271-1275, 1975. 48. BORST, P., J. A. LOOS, E. J. CHRIST, AND E. C. SLATER. Uncoupling activity of long-chain fatty acids. Biochim. Biophys. Acta 62: 509-518, 1962. 49. BRAQUET, P., L. TOUQUI, Y. SHEN, AND B. B. VARGAFTIG. Perspectives in platelet-activating factor research. Pharmacol. Rev. 39: 97-145, 1987. 50. BREMER, J. Carnitine-metabolism and functions. Physiol. Rev.

STAM,

67.

68.

63:1420-1480,1983.

51. BREUER, E., E. BARTA, L. ZLATOS, AND E. PAPPOVA. Developmental changes of myocardial metabolism. II. Myocardial metabolism of fatty acids in the early postnatal period in dogs. Biol. Neonate 12: 54-64, 1968. 52. BRINDLEY, D. N. Some aspects of the physiological and pharmacological control of the synthesis of triacylglycerol and phospholipids. Int. J. Obesity 2: 7-26, 1978. 53. BROWNSEY, R. W., AND R. V. BRUNT. The effect of adrenalineinduced endogenous lipolysis upon the mechanical and metabolic performances of ischaemically perfused rat hearts. CZin. Sci. Mol. Med. 53: 513-521,1977. 54. BURKE, S. E., M. J. ANTONACCIO, AND M. A. LEFER. Lack of thromboxane A, involvement in the arrhythmias occurring during acute myocardial ischemia in dogs. Basic Res. Cardiob 77: 411-422,1982.

55. BURTON, K. P., L. M. BUJA, A. SEN, J. T. WILLERSON, AND K. R. CHIEN. Accumulation of arachidonate in triacylglycerols and unesterified fatty acids during ischemia and reflow in the isolated rat heart. Correlation with the loss of contractile function and the development of calcium overload. Am. J. Pathol. 124:

69.

70.

71.

72.

73.

238-245,1986.

56. BURTON, K. P., G. H. TEMPLETON, H. K. HAGLER, J. T. WILLERSON, AND L. M. BUJA. Effect of glucose availability on functional membrane integrity, ultrastructure, and contractile performance following hypoxia and reoxygenation in isolated feline cardiac muscle. J. Mol. Cell. CardioZ. 12: 109-133, 1980. 57. CAMICI, P., F. URSINI, F. GALIAZZO, L. BELLITTO, G. ELOSI, M. LARZILLI, A. L’ABBATE, AND R. BARSACCHI. Different respiratory activities in mitochondria isolated from the subendocardium and subepicardium of the canine heart. Basic Res. Cardial. 79: 454-460, 1984. 58. CAMPS, L., M. REINA, M. LOBERA, S. VILARD, ANDT. OLIVECRONA. Lipoprotein lipase: cellular origin and functional distribution. Am. J. Physiol. 258 (CeLZ Physiol. 27): C673-C681, 1990. 59. CAO, Y. A., S. W. TAM, G. ARTHUR, H. CHEN, AND P. C. CHOY. The purification and characterization of a phospholipase A in hamster heart cytosol for the hydrolysis of phosphatidylcholine. J Biol. Chem. 262: 16927-16935,1987. 60. CARLSON, L. A., L. KAYSER, AND B. W. LASSERS. Myocardial metabolism of plasma triglycerides in man. J. MoC Cell. Cardiol. 1: 467-475, 1970. 61. CARLSON, L. A., L. KAYSER, S. RijSSNER, AND M. L. WAHLQVIST. Myocardial metabolism of exogenous plasma triglycerides in resting man. Acta Med. Stand. 193: 233-245, 1973. 62. CHALLONER, D. R., AND D. STEINBERG. Effect of free fatty acid on the oxygen consumption of perfused rat heart. Am. J. Ph ysiol. 210: 280-286, 1966. 63. CHAN, A. C., B. FRAGISKOS, C. E. DOUGLAS, AND P. C. CHOY. Increased arachidonate incorporation in perfused heart phospholipids from vitamin E-deficient rats. Lipids 20: 328-330, 1985. 64. CHARNOCK, J. S., M. Y. ABEYWARDENA, AND P. L. McLENNAN. Comparative changes in the fatty-acid composition of rat cardiac phospholipids after long-term feeding of sunflower seed oil- or tuna fish oil-supplemented diets. Ann. Nutr. Metab. 30: 393-406,1986. 65. CHARNOCK, J. S., W. F. DRYDEN, E. J. McMURCHIE, M. Y. ABEYWARDENA, AND G. R. RUSSELL. Differences in the fatty acid composition of atria1 and ventricular phospholipids in rat heart following standard and lipid-supplemented diets. Comp. Biochem. Physiol. B Camp. Biochem. 75: 47-52,1983. 66 CHARNOCK, J. S., W. F. DRYDEN, E. J. McMURCHIE, M. Y. ABEYWARDENA, AND G. R. RUSSELL. Difference in the fatty

74.

75.

76.

AND

RENEMAN

Volume

72

acid composition of atria1 and ventricular phospholipids in rats fed different lipid supplements. Lipids 19: 206-213,1984. CHATELAIN, P., I. PAPAGEORGIOU, P. LUTHY, J. P. MELCHIOR, W. RUTISHAUSER, AND R. LERCH. Free fatty acid metabolism in “stunned” myocardium. Basic Res. CardioZ. 82, Suppl. 1: 169-176, 1987. CHIARIELLO, O., G. AMBROSIO, M. CAPPELLI-BIGAZZI, E. NEVOL, P. PERRONE-FILARDI, G. MANONE, AND M. CONDORELLI. Inhibition of ischemia induced phospholipase activation by quinacrine protects jeopardized myocardium in rats with coronary artery occlusion. J. Pharmacol. Exp. Ther. 241: 560-568, 1987. CHIEN, K. R., A. HAN, A. SEN, L. M. BUJA, AND J. T. WILLERSON. Accumulation of unesterified arachidonic acid in ischemic canine myocardium. Circ. Res. 54: 313-322,1984. CHIEN, K. R., R. G. PFAU, AND J. L. FARBER. Ischemic myocardial cell injury. Prevention by chlorpromazine of an accelerated phospholipid degradation and associated membrane dysfunction. Am. J. Pathol. 97: 505-529, 1979. CHIEN, K. R., J. P. REEVES, L. M. BUJA, F. BONTE, R. W. PARKEY, AND J. T. WILLERSON. Phospholipid alterations in canine ischemic myocardium. Temporal and topographical correlations with Tc-99m-PPi accumulation and an in vitro sarcolemma1 Ca2+ permeability defect. Circ. Rex 48: 711-719, 1981. CHIEN, K. R., A. SEN, R. REYNOLDS, A. CHANG, Y. KIM, M. D. GUNN, L. M. BUJA, AND J. T. WILLERSON. Release of arachidonate from membrane phospholipids in cultured neonatal rat myocardial cells during adenosine triphosphate depletion. J. C&n. Invest. 75: 1770-1780, 1985. CHOY, P. C., K. 0, R. Y. K. MAN, AND A. C. CHAN. Phosphatidyl-choline metabolism in isolated rat heart: modulation by ethanol and vitamin E. Biochim. Biophys. Acta 1005: 225-232, 1989. CHRISTIAN, D. R., G. S. KILSHEIMER, G. PETTETT, R. PARADISE, AND J. ASHMORE. Regulation of lipolysis in cardiac muscle: a system similar to the hormone-sensitive lipase of adipose tissue. Adv. Enzyme Regul. 7: 71-82, 1969. CHRISTIANSEN, K. Membrane-bounded lipid particles from beef heart. Acylglycerol synthesis. Biochim. Biophys. Acta 380: 390-402,1975. CLARK, M. A., T. M. CONWAY, R. G. L. SHORR, AND S. T. CROOKE. Identification and isolation of a mammalian protein which is antigenically and functionally related to the phospholipase A, stimulatory peptide melittin. J. Biol. Chem. 262: 44024406,1987.

77. CLARKE, S. D., AND M. K. ARMSTRONG. Cellular lipid binding proteins: expression, function, and nutritional regulation. FASEB J. 3: 2480-2487,1989. 78. CLARKSON, C. W., AND R. E. TEN EICK. On the mechanism of lysophosphatidylcholine-induced depolarization of cat ventricular myocardium. Circ. Res. 52: 543-556,1983. 79. COKER, S. J., R. J. MARSHALL, J. R. PARRATT, AND I. J. ZEITLIN. Does local myocardial release of prostaglandins E, or F, contribute to the early consequences of acute myocardial ischemia? J. Mol. Cell. Cardiol. 13: 425-434, 1981. 80. COKER, S. J., J. R. PARRATT, I. M. LEDDINGHAM, AND I. J. ZEITLIN. Evidence that thromboxane contributes to ventricular fibrillation induced by reperfusion of the ischemic myocardium. J. Mol. CelZ. CardioZ. 14: 483-485, 1982. 81. COLE, 0. F., T. P. D. FAN, AND G. P. LEWIS. Release of eicosanoids from cultured rat aortic endothelial cells; studies with arachidonic acid and calcium ionophore. CeLZ BioZ. Int. Rep. 10: 407413,1986. 82. COOPER, R. B., N. NOY, AND D. ZAKIM. Mechanism for binding of fatty acids to hepatocyte plasma membranes. J. Lipid Res. 30: 1719-1726,1989. 83. CORR, P. B., M. E. CAIN, F. X. WITKOWSKI, D. A. PRICE, AND B. E. SOBEL. Potential arhythmogenic electrophysiological derangements in canine Purkinje fibers induced by lysophosphoglycerides. Circ. Res. 44: 822-832, 1979. 84. CORR, P. B., M. H. CREER, K. A. YAMADA, J. E. SAFFITZ, AND B. E. SOBEL. Prophylaxis of early ventricular fibrillation by inhibition of acyl carnitine accumulation. J. Clin. Invest. 83: 927-936, 1989.


October

1992

MYOCARDIAL

FATTY

85. CORR, P. B., R. W. GROSS, AND B. E. SOBEL. Amphipathic metabolites and membrane dysfunction in ischemic myocardium. Circ. Res. 55: 135-154, 1984. 86. CORR, P. B., D. W. SNYDER, M. E. CAIN, W. A. CRAFFORD, JR., R. W. GROSS, AND B. E. SOBEL. Electrophysiological effects of amphiphiles on canine Purkinje fibers: implications for dysrhythmia secondary to ischemia. Circ. Res. 49: 354-363, 1981. 87. CORR, P. B., D. W. SNYDER, B. I. LEE, R. W. GROSS, C. R. KEIM, AND B. E. SOBEL. Pathophysiological concentrations of lysophosphatides and the slow response. Am. J. Physiol. 243 (Heart Circ. Physiol. 12): H187-H195, 1982. 88. CORR, P. B., K. A. YAMADA, M. H. CREER, A. D. SHARMA, AND B. E. SOBEL. Lysophosphoglycerides and ventricular fibrillation early after onset of ischemia. J. Mol. CeLL Cardiol. 19, Suppl. V: 45-53,1987. 89. COWAN, J. C., AND E. M. VAUGHAN WILLIAMS. The effect of palmitate on intracellular potentials recorded from Langendorff-perfused guinea-pig hearts in normoxia and hypoxia, and during perfusion and reduced rate of flow. J. Mob Cell. Cardiol. 9: 327-342, 1977. 90. CRASS, M. F., III. Regulation of triglyceride metabolism in the isotopically prelabeled perfused heart. Federation Proc. 36: 19951999,1977. 91. CRASS, M. F., III. Myocardial triacylglycerol metabolism in ischemia. Texas Rep. BioC Med. 39: 439-452, 1979. AND J. C. SHIPP. Effects of 92. CRASS, M. F., III, E. S. McCASKILL, pressure development on glucose and palmitate metabolism in perfused heart. Am. J. Physiol. 216: 1569-1576, 1969. AND J. C. SHIPP. Glucose93. CRASS, M. F., III, E. S. McCASKILL, free fatty acid interactions in the working heart. J. Appl. PhysioZ. 29: 87-91,197o. Lipid and glycogen metab94. CRASS, M. F., III, AND G. M. PIEPER. olism in the hypoxic heart. Effects of epinephrine. Am. J. Physioz. 229: 885-889, 1975. Distribution of glyco95. CRASS, M. F., III, AND P. R. STERRETT. gen and lipids in the ischemic canine left ventricle: biochemical and light and electron microscopic correlates. Recent Adv. Stud. Card. Struct. Metab. 10: 251-263, 1975. 96. CRISMAN, T. S., K. P. CLAFFEY, R. SAOUAF, J. HANSPAL, AND P. BRECHER. Measurement of rat heart fatty acid binding protein by ELISA. Tissue distribution, developmental changes and subcellular distribution. J. Mol. CeZC Curdiol. 19: 423-431, 1987. 97. CRUICKSHANK, E. W. H. Cardiac metabolism. Physiol. Rev. 16: 597-639, 1936. 98. CRYER, A. Tissue lipoprotein lipase activity and its action in lipoprotein metabolism. Int. J. Biochem. 13: 525-541,198l. 99. CRYER, A. The role of the endothelium in myocardial lipoprotein dynamics. Mol. Cell Biochem. 88: 7-15, 1989. 100. CRYER, A., P. CHOHAN, AND J. J. SMITH. Effecters of lipoprotein lipase secretion from isolated cardiac muscle cells incubated in vitro. Life Sci. 29: 923-929, 1981. 101. CUNNANE, S. C., AND M. KARMAZYN. Differential utilization of long chain fatty acids during triacylglycerol depletion. I. Rat heart after ischemic perfusion. Lipids 23: 62-64, 1988. 102. DAS, D. K., R. M. ENGELMAN, J. A. ROUSOU, R. H. BREYER, H. OTANI, AND S. LEMESHOW. Role of membrane phospholipids in myocardial injury induced by ischemia and reperfusion. Am. J. Physiol. 251 (Heart Circ. Physiol. 20): H?l-H79, 1986. F. F., AND E. A. DENNIS. Biological relevance of 103. DAVIDSON, lipocortins and related proteins as inhibitors of phospholipase A,. Biochem. Pharmacol. 38: 3645-3651,1989. F., E. DENNIS, M. POWELL, AND J. R. GLENNEY. 104. DAVIDSON, Inhibition of phospholipase A, by lipocortins and calpactins. J. Biol. Chem. 262: 1695-1705, 1987. DE COURCELLES, D. Is there evidence of a role 105. DE CHAFFOY of the phosphoinositol-cycle in the myocardium? lMoL CeLI. Biothem. 88: 65-72, 1989. E. A. M., D. H. NUGTEREN, AND F. TEN HOOR. 106. DE DECKERE, Prostacyclin is the major prostaglandin released from the isolated rabbit and rat heart. Nature Land. 268: 160-163,1977. C. Peroxisomes and related particles in historical 107. DE DUVE, perspective. Ann. NYAcad. Sci. 386: l-4, 1982.

ACID

HOMEOSTASIS

927

108. DEGRELLA, R., AND R. J. LIGHT. Uptake and metabolism of fatty acids by dispersed adult rat heart myocytes. I. Kinetics of homologous fatty acids. J. BioZ. Chem. 255: 9731-9738,198O. 109. DEGRELLA, R., AND R. J. LIGHT. Uptake and metabolism of fatty acids by dispersed adult rat heart myocytes. II. Inhibition by albumin and fatty acid homologues, and the effect of temperature and metabolic reagents. J. Biol. Chem. 255: 9739-9745,198O. 110. DE GROOT, M. J. M., AND G. J. VAN DER VUSSE. The effect of lactate on triacylglycerol (TG) metabolism in ischemic and reperfused hearts (Abstract). J. Mol. Cell Cardiol. 22, Suppl. III: s114, 1990. 111. DE GROOT, M. J. M., P. H. M. WILLEMSEN, W. A. COUMANS, M. VAN BILSEN, AND G. J. VAN DER VUSSE. Lactate-induced stimulation of myocardial triacylglycerol turnover. Biochim. Biophys. Acta 1006: ill-115,1989. 112. DE HAAS, G. H., N. M. POSTMA, W. NIEUWENHUIZEN, AND L. L. M. VAN DEENEN. Purification and properties of an anionic zymogen of phospholipase A from porcine pancreas. Biochim. Biophys. Acta 159: 118-129, 1968. 113. DE JONG, J. W., AND W. C. HULSMANN. Effects of Nagarse, adenosine and hexokinase on palmitate activation and oxidation. Biochim. Biophys. Acta 210: 499-501,197O. 114. DELCHER, H., M. FRIED, AND J. C. SHIPP. Metabolism of lipoprotein lipid in the isolated perfused rat heart. Biochim. Biophys. Acta 106: 10-18, 1965. 115. DE LEIRIS, J., AND L. H. OPIE. Effect of substrates and coronary artery ligation on mechanical performance and on release of lactate dehydrogenase and creatine phosphokinase in isolated working rat hearts. Cardiovasc. Res. 12: 585-596, 1978. 116. DE LEIRIS, J., L. H. OPIE, AND 0. BRICKNELL. Effect of substrate on enzyme release after coronary artery ligation in isolated rat heart. Recent Adv. Stud. Card. Struct. Metab. 10: 291-293, 1975. 117. DENNIS, E. A. Regulation of eicosanoid production: role of phospholipases and inhibitors. Biotechnology 5: 1294-1300, 1987. 118. DICKENS, B. F., I. T. MAK, AND W. B. WEGLICKI. Lysosomal lipolytic enzymes, lipid peroxidation, and injury. Mol. CeZL Biothem. 82: 119-123,1988. 119. DIDIER, J. P., D. MOREAU, AND L. H. OPIE. Effect of glucose and of fatty acid on rhythm, enzyme release and oxygen uptake in isolated perfused working rat heart with coronary artery ligation. J. Mol. Cell. Cardiol. 12: 1191-1206, 1980. 120. DOLE, V. P. A relation between non-esterified fatty acids in plasma and the metabolism of glucose. J. CZin. Invest. 35: 150-154, 1956. 121. DOLPHIN, P. J. Lipoprotein metabolism and the role of apolipoproteins as metabolic programmers. Can. J. Biochem. CeU BioC 63: 850-869,1985. 122. DRAKE, A. J., J. R. HAINES, AND M. I. M. NOBLE. Preferential uptake of lactate by the normal myocardium in dogs. Cardiovasc. Res. 14: 65-72, 1980. 123. DRAKE-HOLLAND, A. J., G. ELZINGA, M. I. M. NOBLE, H. E. D. J. TER KEURS, AND F. N. WEMPE. The effect of palmitate and lactate on mechanical performance and metabolism of cat and rat myocardium. J. Physiol. Lond. 339: l-15,1983. 124. DUSEK, J., G. ROUS, AND D. S. KAHN. Healing process in the original zone of an experimental myocardial infarct. Findings in the surviving cardiac muscle cells. Am. J. Pathol. 62: 321-338, 1971. 125. DUWEL, C. M. B., F. C. VISSER, M. J. VAN EENIGE, W. DEN HOLLANDER, AND J. P. ROOS. The fate of 17-I-131-iodoheptadecanoic acid during lactate loading: its oxidation is strongly inhibited in favor of its esterification. A radio-chemical study in the normal canine heart. Nucl. Med. 29: 24-27,199O. 126. DUWEL, C. M. B., F. C. VISSER, M. J. VAN EENIGE, AND J. P. ROOS. Variables of myocardial backdiffusion, determined with 17-iodo-131 heptadecanoic acid in the normal dog heart. Mol. Cell Biochem. 88: 191-194,1989. 127. ECKEL, R. H. Lipoprotein lipase: a multifunctional enzyme relevant to common metabolic diseases. N. Engh J. Med. 320: 10601068, 1989. 128. ELHARRAR, V., P. R. FOSTER, T. L. JIRAK, W. E. GAUM, AND


928

129.

130.

131.

132.

133.

134. 135. 136.

137.

138.

VAN

DER

VUSSE,

GLATZ,

P. D. ZIPES. Alterations in canine myocardial excitability during &hernia. Circ. Res. 40: 98-104, 1977. ENGELS, W., M. VAN BILSEN, M. J. M. DE GROOT, R. S. RENEMAN, AND G. J. VAN DER VUSSE. Ischemia and reperfusion induced formation of eicosanoids in isolated rat hearts. Am. J. Physiol. 258 (Heart Circ. Physiol. 27): Hl865-Hl871, 1990. ENGELS, W., M. VAN BILSEN, G. J. VAN DER VUSSE, P. H. M. WILLEMSEN, W. A. COUMANS, M. A. F. KAMPS, J. ENDERT, AND R. S. RENEMAN. Influence of intracellular Ca2+-overload on eicosanoid synthesis of the myocardium. Basic Res. Cardiol. 82, Suppl. 1: 245-252, 1987. ENSER, M. B., F. KUNZ, J. BORENSZTAJN, L. H. OPIE, AND D. S. ROBINSON. Metabolism of triglyceride fatty acid by the perfused rat heart. Biochem. J. 104: 306-317, 1967. ESCOUBET, B., G. GRIFFATION, AND P. LECHAT. Verapamil depresses the synthesis of lipoxygenase products by hypoxic cardiac rat fibroblasts in culture. Biochem. Phczrmacol. 35: 18791882, 1986. ESCOUBET, B., G. GRIFFATION, J. E. SAMUEL, AND P. LECHAT. Calcium antagonists stimulate prostaglandin synthesis by cultured rat cardiac myocytes and prevent the effects of hypoxia. Bioch,em. Ph,armacol. 35: 4401-4407, 1986. EVANS, J. R. Cellular transport of long chain fatty acids. Can. J. Biochem. 42: 955-969, 1964. EVANS, J. R. Importance of fatty acid in myocardial metabolism. Circ. Res. 14/15, Suppl. 2: 96-106, 1964. EVANS, J. R., L. H. OPIE, AND J. C. SHIPP. Metabolism of palmitic acid in perfused rat heart. Am. J. Physiol. 205: 766-770, 1963. EZRA, D., F. R. M. LAURINDO, J. F. CZAJA, F. SNYDER, R. E. GOLDSTEIN, AND G. FEUERSTEIN. Cardiac and coronary consequences of intracoronary platelet activating factor infusion in the domestic pig. Prostaglandins 34: 41-57, 1987. FELIX, S. B., G. BAUMANN, Z. AHMAD, T. HASHEMI, M. NIEMCZYK, AND W. E. BERDEL. Effects of platelet-activating factor on myocardial contraction and myocardial relaxation of isolated perfused guinea pig hearts. J. Curdiovasc. PhurmacoZ. 16: 750-756,199O.

139. FEUVRAY, D. Structural, functional, and metabolic correlates in ischemic hearts: effects of substrates. Am. J. Physiol. 240 (Heart Circ. Physiol. 9): H391-H398, 1981. 140. FEUVRAY, D., AND J. PLOUET. Relationship between structure and fatty acid metabolism in mitochondria isolated from ischemit rat hearts. Circ. Res. 48: 740-747, 1981. 141. FIGARD, P. H., D. P. HEJLIK, T. L. KADUSE, L. L. STOLL, AND A. A. SPECTOR. Free fatty acid release from endothelial cells. J. Lipid Res. 27: 771-780, 1986. 142. FISHER, D. J., M. A. HEYMANN, AND A. M. RUDOLPH. Myocardial oxygen and carbohydrate consumption in fetal lams in utero and in adult sheep. Aw2. J. Ph,ysioZ. 238 (Heart Circ. Physiol. 7): H399-H405,1980. 143. FISHER, D. H., M. A. HEYMANN, AND A. M. RUDOLPH. Myocardial consumption of oxygen and carbohydrates in newborn sheep. Pediatr. Res. 15: 843-846, 1981. 144. FISHER, K. A. Analysis of membrane halves: cholesterol. Proc. Nat!. Acad. Sci. USA 73: 173-177, 1976. 145. FORD, D. A., S. L. HAZEN, J. E. SAFFITZ, AND R. W. GROSS. The rapid and reversible activation of a calcium-independent plasmalogen-selective phospholipase A, during myocardial ischemia. J. Clin. Invest. 88: 331-335, 1991. 146. FORSEY, R. G. P., K. REID, AND J. T. BROSNAN. Competition between fatty acids and carbohydrate or ketone bodies as metabolic fuels for the isolated perfused heart. Can. J. Physiol. Pharn2ucd. 65: 401-406, 1987. N. C., AND M. RAHIM. Control of energy production 147. FOURNIER, in the heart: a new function for fatty acid binding protein. Bioch,emistry 24: 2387-2396, 1985. 148. FOURNIER, N. C., AND M. A. RICHARD. Fatty acid-binding protein, a potential regulator of energy production in the heart. Investigation of mechanisms by electron spin resonance. J. Biol. Chem. 263: 14471-14479,1988. 149. FOURNIER. N. C.. AND M. A. RICHARD. Role of fatty acid-bind-

STAM,

150.

151.

152.

153.

154.

155.

156.

157.

158.

159.

160.

161.

162.

163.

164.

165.

166.

167.

168.

AND

RENEMAN

Volume

72

ing protein in cardiac fatty acid oxidation. Mol. CeU Biochem. 98: 149-159, 1990. FOURNIER, N. C., M. ZUKER, R. E. WILLIAMS, AND I. C. P. SMITH. Self-association of the cardiac fatty acid binding protein. Influence on membrane-bound, fatty acid dependent enzymes. Biochemistry 22: 1863-1872, 1983. FOX, K. A. A., D. R. ABENDSCHEIN, H. D. AMBOS, B. E. SOBEL, AND S. R. BERGMANN. Efflux of metabolized and nonmetabolized fatty acid from canine myocardium. Circ. Res. 57: 232243, 1985. FOX, K. A. A., H. NOMURA, B. E. SOBEL, AND S. R. BERGMANN. Consistent substrate utilization despite reduced flow in hearts with maintained work. Am. J. Physiol. 244 (Heart Circ. Physioh 13): H799-H806, 1983. FRANSON, R. C., D. GAMACHE, W. BLACKWELL, D. EISEN, AND M. L. HESS. Sarcoplasmic reticulum dysfunction: phospholipid alterations induced by lysosomal phospholipase C. Am. J. Physiol. 254 (Heart Circ. Physiol. 23): Hl017-H1023, 1986. FRANSON, R. C., L. K. HARRIS, AND R. RHAGUPATHI. Fatty acid oxidation and myocardial phospholipase A, activity. Mol. Cell. Biochem. 88: 155-159,1989. FRANSON, R. C., D. C. PANG, P. W. TOWLE, AND W. B. WEGLICKI. Phospholipase A activity of highly enriched preparations of cardiac sarcolemma from hamster and dog. J. MoZ. Cell. Cardial. 10: 921-930, 1978. FRANSON, R. C., D. C. PANG, AND W. B. WEGLICKI. Modulation of lipolytic activity in isolated canine cardiac sarcolemma by isoproterenol and propranolol. Biochem. Biophys. Res. Commun. 90: 956-961, 1979. FRANSON, R. C., M. WAITE, AND W. B. WEGLICKI. Phospholipase A activity of lysosomes of fat myocardial tissue. Biochemistry 11: 472-476, 1972. FREDERICKSON, D. S., AND R. S. GORDON. Transport of fatty acids. Physiol. Rev. 38: 585-630, 1958. FREYSS-BEGUIN, M., E. MIILANVOYE-VAN BRUSSEL, AND D. DUVAL. Effect of oxygen deprivation on metabolism of arachidonic acid by cultures of rat heart cells. Am. J. PhysioZ. 257 (Heurt Circ. PhysioZ. 26): H444-H451, 1989. FRIEDMAN, G., T. CHAJEK-SHAUL, T. OLIVECRONA, 0. STEIN, AND Y. STEIN. Fate of milk ‘%I-labeled lipoprotein lipase in cells in culture: comparison of lipoprotein lipase and nonlipoprotein lipase-synthesizing cells. Biochim. Biophys. Acta 711: 114-122, 1982. FRIEDMAN, G., 0. STEIN, AND Y. STEIN. Lipoprotein lipase activity in cultured mesenchymal rat heart cells. Part 5. Effect on enzyme activity of the glycosylation inhibitors, Z-deoxyglucase and tunicamycin. AtheroscZerosis 36: 289-298, 1980. FRIEDMAN, P. L., J. J. FENOGLIO, AND A. L. WIT. Time course for reversal of electrophysiological and ultrastructural abnormalities in subendocardial Purkinje fibers surviving extensive myocardial infarction in dogs. Circ. Res. 36: 127-144, 1975. FRITZ, I. B., AND K. T. N. YUE. Long-chain carnitine acyl transferase and the role of acylcarnitine derivatives in the catalytic increase of fatty acid oxidation induced by carnitine. J. Lipid Res. 4: 279-288,1963. FROHLICH, J., D. W. SECCOMBE, P. HAHN, P. DODEK, AND I. HYNIE. Effect of fasting on free and esterified carnitine levels in human serum and urine: correlation with serum levels of free fatty acids and ,&hydroxybutyrate. Metubolism 27: 555-561,1978. FUJII, S., H. KAWAGUCHI, AND Y. HISAKAZU. Purification of high affinity fatty acid receptors in rat myocardial sarcolemmal membranes. Lipids 22: 544-546, 1987. GAMACHE, D. A., A. FAWZY, AND R. FRANSON. Preferential hydrolysis of peroxidized phospholipid by lysosomal phospholipase C. Biochim. Biophys. Actu 958: 116-124, 1988. GAMACHE, D. A., M. L. HESS, AND R. C. FRANSON. Phospholipid alterations in canine cardiac sarcoplasmic reticulum induced by an acid-active phospholipase C. Basic Res. CardioZ. 82, Suppl. 1: 107-112,1987. GARFINKEL, A. S., E. S. KEMPNER, 0. BEN-ZEEV, J. NIKAZY, S. J. JAMES, AND M. C. SCHOTZ. Lipoprotein lipase; size of the functional unit determined by radiation inactivation. J. Lipid Res. 24: 775-780,1983.


October

199.2

MYOCARDIAL

FATTY

169. GARLAND, P. B., P. J. RANDLE, AND E. A. NEWSHOLME. Citrate as an intermediary in the inhibition of phosphofructokinase in rat heart muscle by fatty acids, ketone bodies, pyruvate, diabetes and starvation. Nature Lond. ZOO: 169-170, 1963. 170. GERCKEN, G., AND M. TROTZ. Fatty acid synthesis in the arrested rabbit heart during ischemia. PJEuegers Arch. 398: 6972, 1983. 171. GERRITSEN, M. E. Eicosanoid production by the coronary microvascular endothelium. Federation Proc. 46: 47-53,1987. 172. GERRITSEN, M. E., AND M. P. PRINTZ. Sites of prostaglandin synthesis in the bovine heart and isolated coronary microvessels. Circ. Res. 49: 1152-1163, 1981. 173. GERSHON, N. D., K. R. PORTER, AND B. L. TRUS. The cytoplasmic matrix: its volume and surface area and the diffusion of molecules through it. Proc. Natl. Acad. Sci. USA 82: 5030-5034, 1985. 174. GEVERS, W. Generation of protons by metabolic processes in heart cells. J. Mol. Cell Cardiol. 9: 867-873, 1977. 175. GHINEA, N., M. ESKENASY, M. SIMIONESCU, AND N. SIMIONESCU. Endothelial albumin binding proteins are membrane-associated components exposed on the cell surface. J. Biol. Chew, 264: 4755-4758,1989. 176. GHINEA, N., A. FIXMAN, D. ALEXANDRU, D. POPOV, M. HASU, L. GHITESCU, M. ESKENASY, M. SIMIONESCU, AND N. SIMIONESCU. Identification of albumin binding proteins in capillary endothelial cells. J. CeLZ BioL 107: 231-239, 1988. 177. GHITESCU, L., A. FIXMAN, M. SIMIONESCU, AND N. SIMIONESCU. Specific binding sites for albumin restricted to plasmalemma1 vesicles of continuous capillary endothelium: receptormediated transcytosis. J. Cell Biol. 102: 1304-1311, 1986. 178. GIAMBANCO, I., G. PULA, P. CECCARELLI, R. BIANCHI, AND R. DONATO. Immunohistochemical localization of Annexin V (CaBP33) in rat organs. J. Histochem. Cytochem. 39: 1189-1198, 1991. 179. GILBERTSON, J. R. Cardiac muscle. In: Lipid iMetaboLism in Mamm.als, edited by F. Snyder. New York: Plenum, 1977, vol. 1, p. 367-397. 180. GINGELL, R. L., T. POZEFSKY, AND R. D. ROWE. Regional differences in fatty acid oxidation by the adult rabbit myocardium. Recent Adv. Stud. Card. Struct. Metab. 10: 47-50,1975. 181. GLATZ, J. F. C., C. C. F. BAERWALDT, J. H. VEERKAMP, AND H. J. M. KEMPEN. Diurnal variation of cytosolic fatty acid-binding protein content and of palmitate oxidation in rat liver and heart. J. BioZ. Chem. 259: 4295-4300,1984. 182. GLATZ, J. F. C., A. E. M. JACOBS, AND J. H. VEERKAMP. Fatty acid oxidation in human and rat heart; comparison of cell-free and cellular systems. Biochim. Biophys. Acta 794: 454-465, 1984. 183. GLATZ, J. F. C., AND G. J. VAN DER VUSSE. Lipid terminology: “free” fatty acid is ambiguous. Trends Biochem. Sci. 13: 167-168, 1988. J. F. C., AND G. J. VAN DER VUSSE. Intracellular trans184. GLATZ, port of lipids. Mol. CeZZ. Biochem. 88: 37-44, 1989. 185. GLATZ, J. F. C., AND G. J. VAN DER VUSSE. Cellular fatty acid-binding proteins: current concepts and future directions. Mol. Cell. Biochem. 98: 247-251, 1990. 186. GLATZ, J. F. C., G. J. VAN DER VUSSE, AND J. H. VEERKAMP. Fatty acid-binding proteins and their physiological significance. News Physiol. Sci. 3: 41-43, 1988. 187. GLATZ, J. F. C., AND J. H. VEERKAMP. Postnatal development of palmitate oxidation and mitochondrial enzyme activities in rat cardiac and skeletal muscle. Biochim. Biophys. Acta 711: 327335,1982. 188. GLAVIANO, K., AND T. MASTERS. Inhibitory actions of intracoronary protaglandin E, on myocardial lipolysis. Am. J. Physioh 220: 1187-1193,197l. 189. GLOSTER, J., M. ACHILLEA, AND P. HARRIS. Subcellular distribution of (1-14C)palmitate and (1-14C)oleate incorporated into lipids in the perfused rat heart: a comparison under isothermal and hypothermic conditions. J. MoZ. Cell. CardioZ. 10: 439-448, 1978. 190. GLOSTER, J., AND P. HARRIS. Effects of anaerobiosis on the incorporation of (‘“C) acetate into lipid in the perfused rat heart. J. Mol. Cell. Cardiol. 4: 213-228, 1972. 191. GOLDBERG, D. I., AND J. C. KHOO. Activation of myocardial

ACID

192.

193.

194. 195.

196.

197.

198.

199.

200.

201.

202.

203.

204.

205.

206.

207.

208.

209.

210.

211.

HOMEOSTASIS

929

neutral triglyceride lipase and neutral cholesterol esterase by CAMP-dependent protein kinase. J. BioZ. Chem. 260: 5879-5882, 1985. GOODMAN, D. S. The interaction of human serum albumin with long-chain fatty acid anions. J. Am. Chem. Sot. 80: 3892-3898, 1958. GORDON, R. S. Unesterified fatty acid in human blood plasma. II. The transport function of unesterified fatty acid. J. CZin. Invest. 36: 810-815, 1957. GORDON, R. S., AND A. CHERKES. Unesterified fatty acids in human blood plasma. J. Clin. Invest. 35: 206-212, 1956. GORGE, G., P. CHATELAIN, J. SCHAPER, AND R. LERCH. Effect of increasing degrees of ischemic injury on myocardial oxidative metabolism early after reperfusion in isolated rat hearts. Circ. Res. 68: 1681-1692, 1991. GREENOUGH, W. B., S. R. CRESPIN, AND D. STEINBERG. Infusion of long-chain fatty acids anions by continuous flow centrifugation. J. Clin. Invest. 48: 1923-1933, 1969. GRONG, K., H. JODALEN, L. STRANGELAND, H. VIK-MO, AND J. LEKVEN. Cellular lipid accumulation in different regions of myocardial infarcts in cat during beta adrenergic blockade with timolol. Cardiovasc. Res. 20: 248-255, 1986. GROOT, P. H. E., M. C. OERLEMANS, AND L. M. SCHEEK. Triglyceridase and phospholipase A, activities of rat heart lipoprotein lipase. Influence of apolipoprotein C-II and C-III. Biochim. Biophys. Acta 530: 91-98, 1979. GROOT, P. H. E., H. R. SCHOLTE, AND W. C. HULSMANN. Fatty acid localization: specificity, localization and function. In: Advances in Lipid Research, edited by R. Paoletti and D. Kritchevsky. New York: Academic, 1976, vol. 14, p. 75-119. GROSS, R. W. Purification of rabbit myocardial cytosolic acyl CoA hydrolase, identity with lysophospholipase, and modulation of enzymic activity by endogenous cardiac amphiphiles. Biochemistry 22: 5641-5646, 1983. GROSS, R. W. Identification of plasmalogen as the major phospholipid constituent of cardiac sarcoplasmic reticulum. Biochemistry 24: 1662-1668, 1985. GROSS, R. W., G. G. AHUMADA, AND B. E. SOBEL. Cytosolic lysophospholipase in cardiac myocytes and its inhibition by Lpalmitoyl carnitine. Am. J Physiol. 245 (CeU PhysioL 14): C266C270,1984. GROSS, R. W., P. B. CORR, B. I. LEE, J. E. SAFFITZ, W. A. CRAFFORD, JR., AND B. E. SOBEL. Incorporation of radiolabeled lysophosphatidyl choline into canine Purkinje fibers and ventricular muscle: electrophysiological, biochemical, and autoradiographic correlations. Circ. Res. 51: 27-36, 1982. GROSS, R. W., R. C. DRISDEL, AND B. E. SOBEL. Rabbit myocardial lysophospholipase-transacylase. Purification, characterization and inhibition by endogenous cardiac amphiphiles. J. BioC Chem. 258: 15165-15172,1983. GROSS, R. W., AND B. E. SOBEL. Augmentation of cardiac phospholipase activity induced with negative liposomes. Trans. Assoc. Am. Phys. 92: 136-174,1979. GROSS, R. W., AND B. E. SOBEL. Lysophosphatidylcholine metabolism in the rabbit heart: characterization of metabolic pathways and the partial purification of myocardial lysophospholipase-transacylase. J. Biol. Chem. 257: 6702-6708,1982. GROSS, R. W., AND B. E. SOBEL. Rabbit myocardial cytosolic lysophospholipase. Purification, characterization, and competitive inhibition by L-palmitoyl carnitine. J. Bio,l Chem. 258: 52215226,1983. GRYNBERG, A., G. NALBONE, M. DEGOIS, J. LEONARDI, P. ALTHIAS, AND H. LAFONT. Activities of some enzymes of phospholipid metabolism in cultured rat ventricular myocytes in normoxie and hypoxic conditions. Biochim. Biophys. Acta 958: 24-30, 1988. GUDBJARNASON, S., AND J. HALLGRIMSON. The role of myocardial membrane lipids in the development of cardiac necrosis. Acta Med. Stand. 587, Suppl.: 17-27, 1976. GUDBJARNASON, S., AND G. OSKARSDOTTIR. Modification of fatty acid composition of rat heart lipids by feeding cod liver oil. Biochim. Biophys. Acta 487: 10-15, 1977. GUPTA, D. K., D. E. JEWITT, R. YOUNG, AND M. HARTOG.


930

212.

213.

214.

215.

216. 217.

218.

219.

220.

221.

222.

223.

224.

225.

226.

227.

228.

229.

230. 231.

232.

VAN

DER

VUSSE,

GLATZ,

Increased plasma-free-fatty-acid concentrations and their significance in patients with acute myocardial infarction. Lancet 2: 1209-1213,1969. HAGENFELDT, L., AND P. 0. WESTER. Plasma levels of individual free fatty acids in patients with acute myocardial infarction. Acfa Med. Stand. 194: 357-362, 1973. HAGVE, T.-A., AND H. SPRECHER. Metabolism of long-chain polyunsaturated fatty acids in isolated cardiac myocytes. Biochim. Biophys. Acta 1001: 338-344, 1989. HARADA, J., J. AZUMA, H. HASEGAWA, H. OHTA, K. YAMAUCHI, K. OGURA, N. AWATA, A. SAWAMURA, N. SPERELAKIS, AND S. KISHIMOTO. Enhanced suppression of myocardial slow action potentials during hypoxia by free fatty acids. J. Mol. Cell. CardioZ. 16: 261-276, 1984. HARRIS, P., C. CHLOUVERAKIS, J. GLOSTER, AND J. HOWEL JONES. Arterio-venous differences in the composition of plasma free fatty acids in various regions of the body. Clin. Sci. Lond. 22: 113-118, 1962. HARRIS, P., J. A. GLOSTER, AND B. J. WARD. Transport of fatty acids in the heart. Arch. Mab Coeur Vaiss. 73: 593-598,198O. HATCH, G. M., K. 0, AND P. C. CHOY. Regulation of phosphatidyl-choline metabolism in mammalian hearts. Biochem. CeZl. Biol. 67: 67-77, 1989. HATTORI, M., K. OWAGA, T. SATAKE, S. SUGIYAMA, AND T. OZAWA. Depletion of membrane phospholipid and mitochondrial dysfunction associated with coronary reperfusion. Basic Res. Curdiol. 80: 241-250, 1985. HAZEN, S. L., D. A. FORD, AND R. W. GROSS. Activation of a membrane associated phospholipase A, during rabbit myocardial ischemia which is highly selective for plasmalogen substrate. J. Biol. Chem. 266: 5629-5633, 1991. HAZEN, S. L., AND R. W. GROSS. ATP-dependent regulation of rabbit myocardial cytosolic calcium-independent phospholipase A,. J. Biol. Chem. 266: 14526-14534, 1991. HEATHERS, G. P., N. AL-MUTHASEB, AND R. V. BRUNT. The effect of adrenergic agents on the activities of glycerol-3-phosphate acyltransferase and triglyceride lipase in the isolated rat heart. J. Mol. Cell. Curdiol. 17: 785-796, 1985. HEATHERS, G. P., AND P. V. BRUNT. The effect of coronary artery occlusion and reperfusion on the activation of triglyceride lipase and glycerol-3-phosphate acyl transferase in the isolated perfused rat heart. J. Mol. Cell Curdiol. 17: 907-916, 1985. HEATHERS, G. P., K. A. YAMADA, E. M. KATER, AND P. B. CORR. Long-chain acylcarnitines mediate the hypoxia-induced increase in alpha-adrenergic receptors on adult canine myocytes. Circ. Rea. 61: 735-746, 1987. HEATHERS, G. P., K. A. YAMADA, S. M. POGWIZD, AND P. B. CORR. The contribution of N- and ,&adrenergic mechanisms in the genesis of arrhythmias during myocardial ischemia and reperfusion. In: Newocardiology, edited by H. E. Kulbertus and G. Franck. Mount Kisco, NY: Futura, 1988, p. 143-178. HEE-CHEONG, M., AND D. L. SEVERSON. Metabolism of dioctanoylglycerol by isolated cardiac myocytes. J. Mob Cell Cardiol. 21: 829-837, 1989. HENDERSON, A. H., R. J. GRAIG, R. GORLIN, AND E. H. SONNENBLICK. Free fatty acids and myocardial function in perfused rat hearts. Curdiovusc. Res. 4: 466-472, 1970. HENDERSON, A. H., A. S. MOST, W. W. PARMLEY, R. GORLIN, AND E. H. SONNENBLICK. Depression of myocardial contractility in rats by free fatty acids during hypoxia. Circ. Res. 26: 439-449,197o. HENSON, L. C., M. C. SCHOTZ, AND I. HARARY. Lipoprotein in cultured heart cells: characteristics and cellular location. Bioch.im. Biophya. Actu 487: 212-221, 1977. HOHL, C. M., AND P. ROESEN. The role of arachidonic acid in rat heart cell metabolism. Biochim. Biophys. Actu 921: 356-363, 1987. HOSTETLER, K. Y., AND L. B. HALL. Phospholipase C activity of fat tissues. Biochem. Biophys. Res. Commun. 96: 388-393,198O. HOUGH, F. S., AND W. GEVERS. Catecholamine release as mediator of intracellular enzyme activation in ischaemic perfused rat hearts. S. Afr. Med. J. 49: 538-543, 1975. HRON, W. T., G. J. JESMOK, Y. B. LOMGARDO, L. A. MENA-

STAM,

233.

234.

235.

236.

237.

238.

239.

240.

241.

242.

243.

244.

245.

246.

247.

248.

249.

250.

251.

252.

AND

RENEMAN

Volume

72

HAN, AND J. J. LECH. Calcium dependency of hormone stimulated lipolysis in the perfused rat heart. J. Mol. Cell Curdiol. 9: 733-748,1977. HSUEH, W., P. C. ISAKSON, AND P. NEEDLEMAN. Hormone selective lipase activation in the isolated rabbit heart. Prostaglundins 13: 1073-1091,1977. HSUEH, W., AND P. NEEDLEMAN. Sites of lipase activation and prostaglandin synthesis in isolated, perfused hearts and hydronephrotic kidneys. Prostuglundins 16: 661-681, 1978. HUANG, X. Q., AND A. J. LIEDTKE. Alterations in fatty acid oxidation in ischemic and reperfused myocardium. MoZ. CeZZ. Biothem. 88: 145-153,1989. HULL, F. E., H. CHENEY, AND L. BAKER. Fatty acid synthesis and Krebs’ cycle activity in heart mitochondria. J. MoZ. CeZZ. CurdioZ. 5: 319-339, 1973. HULL, F. E., J. F. RADLOFF, AND C. C. SWEELEY. Fatty acid oxidation by ischemic myocardium. Recent Adv. Stud. Curd. Struct. Metub. 8: 153-165, 1975. HULSMANN, W. C., AND M. L. DUBELAAR. Aspects of fatty acid metabolism in vascular endothelial cells. Biochemie 70: 681686,1988. HULSMANN, W. C., M. L. DUBELAAR, E. A. DE WIT, AND N. L. M. PERSOON. Cardiac lipoprotein lipase: effects of lipopolysaccharide and tumor necrosis factor. MoZ. CelZ. Biochem. 79: 137145,1988. HULSMANN, W. C., W. B. ELLIOT, AND E. C. SLATER. The nature and mechanisms of action of incoupling agents present in mitochrome preparations. Biochim. Biophys. Acta 39: 267-276, 1960. HULSMANN, W. C., M. M. GEELHOED-MIERAS, H. JANSSEN, AND U. M. T. HOUTSMULLER. Alteration of the lipase activities of muscle, adipose tissue and liver by rapeseed oil feeding of rats. Biochim. Biophys. Actu 572: 183-187, 1979. HULSMANN, W. C., AND H. STAM. On the regulation of triglyceride hydrolysis in heart. In: Lipoprotein Metabolism and Endocrine Regulation, edited by L. W. Hessel and H. M. J. Krans. Amsterdam: Elseviers/North-Holland, 1979, p. 289-297. HULSMANN, W. C., H. STAM, AND W. A. P. BREEMAN. Acidand neutral lipases involved in endogenous lipolysis in small intestine and heart. Biochem. Biophys. Res. Commun. 102: 440-448, 1981. HULSMANN, W. C., H. STAM, AND H. JANSSEN. Localization and function of myocardial lipolysis. Basic Res. Curdiol. 79: 268273,1984. HULSMANN, W. C., H. STAM, AND J. M. J. LAMERS. Localization and function of lipases and their reaction products in rat heart. In: Myocardial Ischemiu and Lipid Metabolism, edited by R. Ferrari, A. M. Katz, A. Shrug, and 0. Visioli. New York: Plenum, 1984, p. 27-37. HUNNEMAN, D. H., AND C. SCHWEICKHARDT. Mass fragmentographic determination of myocardial free fatty acids. J. Mol. CeZZ. Cardiol. 14: 339-351, 1982. HUTTER, J. F., H. M. PIPER, AND P. G. SPIECKERMANN. Kinetic analysis of myocardial fatty acid oxidation suggesting an albumin receptor mediated uptake process. J. Mol. CeZL Cardiol. 16: 219-226, 1984. HUTTER, J. F., H. M. PIPER, AND P. G. SPIECKERMANN. Myocardial fatty acid oxidation: evidence for an albumin-receptor-mediated membrane transfer of fatty acids. Basic Res. Curdiol. 79: 274-282, 1984. HUTTER, J. F., M. PIPER, AND P. G. SPIECKERMANN. Effect of fatty acid oxidation of efficiency of energy production in rat heart. Am. J. Physiol. 249 (Heart Circ. Physiol. 18): H723-H728, 1985. HUTTER, J. F., C. SCHWEICKHARDT, D. H. HUNNEMAN, H. M. PIPER, AND P. G. SPIECKERMANN. A new method for studying the incorporation of nonesterified fatty acids into cardiac lipids by using deuterium-labelled palmitate. Basic Res. Curdiol. 83: 87-93, 1988. ICHIHARA, K., AND J. R. NEELY. Recovery of ventricular function in reperfused ischemic rat hearts exposed to fatty acids. Am. J. Physiol. 249 (Heart Circ. Physiol. 18): H492-H497, 1985. IDELL-WENGER, J. A., L. W. GROTYOHANN, AND J. R.


October

253.

254.

255.

256. 257.

258.

259.

260.

261.

262.

263.

264.

265.

266.

267. 268.

269. 270.

271.

272.

273.

1,992

MYOCARDIAL

FATTY

NEELY. Coenzyme A and carnitine distribution in normal and ischemic hearts. J. BioC Chem. 253: 4310-4318, 1978. IDELL-WENGER, J. A., L. W. GROTYOHANN, AND J. R. NEELY. Regulation of fatty acid utilization in heart. Role of the carnitine-acetyl-CoA transferase and carnitine-acetyl-carnitine translocase system. J. Mol. CeLZ. Curdiol. 14: 413-417, 1982. IDELL-WENGER, J. A., AND J. R. NEELY. Regulation of uptake and metabolism of fatty acids by muscle. In: Disturbances in Lipid and Lipoprotein Metabolism, edited by J. M. Dietschy, A. M. Gotto, and J. A. Ontko. Bethesda, MD: Am. Physiol. Sot., 1978, p. 269-285. INOUE, D., AND A. J. PAPPANO. L-Palmitylcarnitine and calcium ions act similarly on excitatory ionic currents in avian ventricular muscle. Circ. Res. 52: 625-634, 1983. IRVINE, R. I. How is the level of free arachidonic acid controlled in mammalian cells? Biochem. J. 204: 3-16, 1982. ISAKSON, P. C., A. RAZ, W. HSUEH, AND P. NEEDLEMAN. Lipases and prostaglandin synthesis. Adv. Prostaglandin Thromboxane Res. 3: 113-120, 1978. JANERO, D. R., AND C. BURGHARDT. Nonesterified fatty acid accumulation and release during heart muscle-cell (myocyte) injury: modulation by extracellular “acceptor.” J. Cell. Physiol. 140: 150-160, 1989. JANERO, D. R., AND C. BURGHARDT. Production and release of platelet-activating factor by the injured heart-muscle cell (cardiomyocyte). Res. Commun. Chem. Pathol. Pharmacol. 67: 201218, 1990. JANSEN, H., AND W. C. HULSMANN. On hepatic and extrahepatic postheparin serum lipase activities and the influence of experimental hypercortisolism and diabetes on these activities. Bioch,im. Biophys. Acta 398: 337-346, 1975. JANSEN, H., W. C. HULSMANN, A. VAN ZUYLEN-VAN WIGGEN, C. B. STRUYK, AND U. M. T. HOUTSMULLER. Influence of rapeseed oil feeding on the lipase activities of rat heart. Biothem. Biophys. Res. Commun. 64: 747-751, 1975. JESMOK, G. J., D. C. WARLTIER, G. J. GROSS, AND H. F. HARDMAN. Transmural triglycerides in acute myocardial ischemia. Curdiovasc. Res. 12: 659-665, 1978. JODALEN, H., L. STANGELAND, K. GRONG, H. VIK-MO, AND J. LEKVEN. Lipid accumulation in the myocardium during acute regional ischaemia in rats. J. Mol. Cell Cardiob 17: 973-980,1985. JONES, R. L., J. C. MILLER, H. K. HAGLER, K. R. CHIEN, J. T. WILLERSON, AND L. M. BUJA. Association between inhibition of arachidonic acid release and prevention of calcium loading during ATP depletion in cultured rat cardiac myocytes. Am. J. Pa.th,oZ. 135: 541-556, 1989. JULIEN, P., P. R. DAGENAIS, L. GAILIS, AND P. E. ROY. Role of cardiac lymph and interstitial fluid in lipid metabolism of canine heart. Can. J. Physiol. Pharmacol. 56: 1041-1046, 1978. JULIEN, P., L. GAILLIS, M. LEPAGE, AND P. E. ROY. A comparison of fatty acid patterns of arterial plasma, pericardial fluid and cardiac lymph in dog. Artery 5: 37-44,1979. KAIKAUS, R. M., N. M. BASS, AND R. K. OCKNER. Functions of fatty acid binding proteins. Experientia Basel46: 617-630, 1990. KAJIYAMA, K. J., D. F. PAULY, H. HUGHES, S. B. YOON, M. L. ENTMAN, AND J. B. McMILLIN-WOOD. Protection by verapamil of mitochondrial glutathione equilibrium and phospholipid changes during reperfusion of ischemic canine myocardium. Circ. Res. 61: 301-310, 1987. KAKO, K. J., AND M. KATO. Phospholipid metabolism in heart membranes. Dev. Cardiovasc. Med. 67: 99-112, 1987. KAKO, K. J., AND T. KIKUCHI. Mechanism of ethanol-induced triglyceride accumulation in the rabbit heart. Recent Adv. Stud. Card. Struct. Metab. 1: 596-604, 1972. KAKO, K. J., AND M. S. LIU. Acylation of glycerol-3-phosphate by rabbit heart mitochondria and microsomes: triiodothyronineinduced increase in its activity. FEBS Lett. 39: 243-246, 1974. KANG, E. S., AND D. M. MIRVIS. Reversible, highly localized alterations in fatty acid metabolism in the chronically ischemic canine myocardium. Am. J. CardioL 54: 411-414, 1984. KARLI, J. N., G. A. KARIKAS, P. K. HATZIPAVLOU, G. M. LEVIS, AND S. N. MOULOPOULOS. The inhibition of Na+ and

ACID

274.

275.

276.

277.

278.

279.

280.

281.

282.

283.

284.

285. 286.

287.

289.

291.

292.

293.

294.

295.

HOMEOSTASIS

931

K+ stimulated ATPase activity of rabbit and dog heart sarcolemma by lysophosphatidyl choline. Life Sci. 24: 1868-1876,1979. KARMAZYN, M. Contribution of prostaglandins to reperfusioninduced ventricular failure in isolated rat hearts. Am. J. Physiol. 251 (Heart Circ. Physiol. 20): Hl33-H140, 1986. KARMAZYN, M. Prostaglandins stimulate calcium-linked changes in heart mitochondrial respiration. Am. J. Physioh 251 (Heart Circ. Physiol. 20): Hl41-H147, 1986. KARMAZYN, M. Synthesis and relevance of cardiac eicosanoids with particular emphasis on ischemia and reperfusion. Can. J. Physiol. Pharmacol. 67: 912-921, 1989. KARMAZYN, M. The 1990 Merck Frost Award. Ischemic and reperfusion injury in the heart. Cellular mechanisms and pharmacological interventions. Can. J. Physiol. Phurmacol. 69: 719730,199l. KARMAZYN, M., AND N. S. DHALLA. Physiological and pathophysiological aspects of cardiac prostaglandins. Can. J. Physiol. Ph,armacol. 61: 1207-1225, 1983. KARMAZYN, M., D. F. HORROBIN, M. S. MANKU, S. C. CUNNANE, A. KARMALI, A. I. ALLY, R. 0. MORGAN, K. L. NICOLAOU, AND W. E. BARNETTE. Effects of prostacyclin on perfusion pressure electrical activity, rate of force of contraction in isolated rat and rabbit heart. Life Sci. 22: 2079-2086, 1978. KARMAZYN, M., AND M. P. MOFFAT. Calcium ionophore stimulated release of leukotriene C,-like immunoreactive material from cardiac tissue. J. Mol. Cell. Cardiol. 16: 1071-1073, 1984. KARMAZYN, M., AND M. P. MOFFAT. Positive inotropic effects of low concentrations of leukotrienes C, and D, in rat heart. Am. J. Physiol. 259 (Heart Circ. Physiol. 28): Hl239-H1246, 1990. KARMAZYN, M., B. S. TUANA, AND N. S. DHALLA. Effect of prostaglandins on rat sarcolemmal ATPases. Can. J. Physiol. Pharmacol. 59: 1122-1127, 1981. KARWATOWSKA-KRYNSKA, E., AND A. BERESEWICZ. Effect of locally released catecholamines on lipolysis and injury of the hypoxic isolated rabbit heart. J. Mol. Cell. Cardiol. 15: 523536, 1983. KATZ, A. M. Membrane derived lipids and the pathogenesis of ischemic myocardial damage. J. Mol. CeZl. Curdiol. 14: 627-632, 1982. KATZ, A. M., AND P. B. KATZ. Homogeneity out of heterogeneity. Circulation 79: 712-717, 1989. KATZ, A. M., AND F. C. MESSINEO. Lipid-membrane interactions and the pathogenesis of ischemic damage in the myocardium. Circ. Res. 48: l-16, 1981. KELLER, A. M., R. M. CLANCY, M. L. BARR, C. C. MARBOE, AND P. J. CANNON. Acute reoxygenation injury in the isolated rat heart: role of resident cardiac mast cells. Circ. Res. 63: 10441053, 1988. KENNEDY, E. P. Biosynthesis of complex lipids. Federation Proc. 20: 934-940, 1961. KESSLER, J. I. Effect of diabetes and insulin on the activity of myocardial and adipose tissue lipoprotein lipase of rats. J. C&n. Invest. 42: 362-367, 1963. KEUL, J., E. DOLL, H. STEIM, U. FLEER, AND H. REINDELL. Uber den Stoffwechsel des menschlichen Herzens. III. Der oxydative Stoffwechsel des menschlichen Herzens unter verschiedenen Arbeitsbedingungen. Pfluegers Arch. 282: 43-53,1965. KEUL, J., E. DOLL, H. STEIM, H. HOMBURGER, H. KERN, AND H. REINDELL. Uber den Stoffwechsel des menschlichen Herzens. I. Die Substrat versorgung des gesundes menschlichen Herzens in Ruhe, wahrend und nach korperlichen Arbeit. Pfluegers Arch. 282: I-27, 1965. KINNAIRD, A. A. A., P. C. CHOY, AND R. Y. K. MAN. Lysophosphatidylcholine accumulation in the ischemic canine heart. Lipids 23: 32-35, 1988. KJEKSHUS, J. K. Effects of lipolytic and inotropic stimulation on myocardial ischemic injury. Acta Med. Stand. Supph 378: 3546, 1976. KJEKSHUS, J. K. Effect of inhibition of lipolysis on acute myocardial injury during coronary occlusion in normal and reserpinized dogs. Acta Med. Stand. 645: 85-91, 1981. KLEIN, M. S., R. A. GOLDSTEIN, AND M. J. WELCH. External assessment of mvocardial metabolism with llC-nalmitate in rab-


932

296.

297.

298.

299.

300.

301. 302.

303.

304.

305.

306.

307.

308.

309.

310.

311. 312.

313.

314.

315.

316. 317.

VAN

DER

VUSSE,

GLATZ,

bit heart. Am. J. Physiol. 237 (Heart Circ. Physiol. 6): H51-H58, 1979. KNUDSEN, J., P. HOJRUP, H. 0. HANSEN, H. F. HANSEN, AND P. ROEPSTORFF. Acyl-CoA-binding protein in the rat: purification, binding characteristics and amino acid sequence. Biothem. J. 262: 513-519,1989. KOHN, M. C. Computer stimulation of metabolism in palmitateperfused rat heart. III. Sensitivity analysis. Ann. Biomed. Eng. 11: 533-549,1983. KOHN, M. C., AND D. GARFINKEL. Computer stimulation of metabolism in palmitate-perfused rat heart. I. Palmitate oxidation. Ann. Biomed. Eng. 11: 361-384, 1983. KOHN, M. C., AND D. GARFINKEL. Computer stimulation of metabolism in palmitate-perfused rat heart. II. Behavior of complete model. Ann. Biomed. En,g. 11: 511-531, 1983. KOSTIS, J. B., E. A. MAVROGEORGIS, E. HORSTMANN, AND S. GOTZOYANNIS. Effect of high concentration of free fatty acids on the ventricular fibrillation threshold of normal dogs and dogs with acute myocardial infarction. CardioZogy 58: 89-98,1973. KRAGH-HANSEN, U. Molecular aspects of ligand binding to serum albumin. Pharmacol. Rev. 33: 17-53, 1981. KRONQUIST, K. E., M. E. PEDERSEN, AND M. C. SCHOTZ. Mechanism of alteration of the functional fraction of lipoprotein lipase in rat heart. Life Sci. 27: 1153-1158,198O. KRYSKI, A., JR., T. S. LARSEN, I. RAMIREZ, ANDD. L. SEVERSON. Methylamine does not inhibit rates of endogenous lipolysis in isolated myocardial cells from rat heart. Can. J. Physiol. Pharmacol. 65: 226-229, 1987. KURIEN, V. A., AND M. F. OLIVER. A metabolic cause for arrhythmias during acute myocardial hypoxia. Lancet 1: 813-815, 1970. KURIEN, V. A., P. A. YATES, AND M. F. OLIVER. Free fatty acid, heparin, and arrhythmias during experimental myocardial infarction. Lancet 2: 185-187, 1969. KURIEN, V. A., P. A. YATES, AND M. F. OLIVER. The role of free fatty acids in the production of ventricular arrhythmias after acute coronary artery occlusion. Eur. J. CZin. Invest. 1: 225241, 1971. LAMERS, J..M. J., J. T. DE JONGE-STINIS, P. D. VERDOUW, AND W. C. HULSMANN. On the possible role of long chain fatty acyl carnitine accumulation in producing functional and calcium permeability changes in membranes during myocardial ischemia. Cardiovasc. Res. 21: 313-322,1987. LAMERS, J. M. J., AND W. C. HULSMANN. Inhibition of (Na+ + K+)-stimulated ATPase of heart by fatty acids. J. 1MoZ. CeZZ. Cardial. 9: 343-346, 1977. LAMERS, J. M. J., H. T. STINIS, A. MONTFOORT, AND W. C. HULSMANN. The effect of lipid intermediates on Ca++ and Na’ permeability and (Na+/K+)-ATPase of cardiac sarcolemma. Biochim. Biophys. Acta 774: 127-137, 1984. LAMPING, K. A., L. A. MENAHAN, AND G. J. GROSS. Nicotinic acid, free fatty acids and myocardial function during coronary occlusion and reperfusion in the dog. J. Pharmacol. Exp. Ther. 231: 532-538,1984. LANOUE, K. F., AND A. C. SCHOOLWERTH. Metabolite transport in mitochondria. Annu. Rev. Biochem. 48: 871-922, 1979. LANOUE, K. F., J. A. WATTS, AND C. D. KOCH. Adenine nucleotide transport during cardiac ischemia. Am. J. Physioh 241 (Heart Circ. PhysioL 10): H663-H671, 1981. LASSERS, B. W., M. L. WAHLQVIST, L. KAIJSER, AND L. A. CARLSON. Effect of nicotinic acid on myocardial metabolism in man at rest and during exercise. J Appl. Physiol. 33: 72-80,1972. LATIPAA, P. M. Energy-linked regulation of mitochondrial fatty acid oxidation in the isolated perfused rat heart. J. 1Mol. CeZL Cardiol. 21: 765-771, 1989. LATIPAA, P. M., K. J. PEUHKURINEN, J. K. HILTUNEN, AND I. E. HASSINEN. Regulation of pyruvate dehydrogenase during infusion of fatty acids of varying chain lengths in the perfused rat heart. J. Mol. CeZh CardioZ. 17: 1161-1171, 1985. LAZAROW, P. B. Rat liver peroxisomes catalyze the P-oxidation of fatty acids. J. Biol. Chem. 253: 1522-1528, 1978. LEA, M. A., AND G. WEBER. Role of enzymes in homeostasis. J. BioC Chem. 243: 1096-1102,1968.

STAM,

AND

RENEMAN

Volume

72

318. LECH, J. J., G. J. JESMOK, AND D. N. CALVERT. Effects of drugs and hormones lipolysis in heart. Federation Proc. 36: 20002008,1977. 319. LEFER, A. M. Induction of tissue injury and altered cardiovascular performance by platelet-activating factor: relevance to multiple systems organ failure. Crit. Care Clin. 5: 331-352, 1989. 320. LERCH, R. A., S. R. BERGMANN, H. D. AMBOS, M. J. WELCH, M. M. TER-POGOSSIAN, AND B. E. SOBEL. Effect of flow-independent reduction of metabolism on regional myocardial clearance of “C-palmitate. CircuZation 65: 731-738, 1985. 321. LIEDTKE, A. J. Alterations of carbohydrate and lipid metabolism in the acutely ischemic heart. Prog. Cardiovasc Dis. 23: 321336,198l. 322. LIEDTKE, A. J., L. DEMAISON, A. M. EGGLESTON, L. M. COHEN, AND S. H. NELLIS. Changes in substrate metabolism and effects of excess fatty acids in reperfused myocardium. Circ. Res. 62: 535-542, 1988. 323. LIEDTKE, A. J., H. C. HUGHES, AND J. R. NEELY. Metabolic responses to varying restrictions of coronary blood flow in swine. Am. J. Physiol. 228: 655-662, 1975. 324. LIEDTKE, A. J., S. NELLIS, AND J. R. NEELY. Effects of excess free fatty acids on mechanical and metabolic function in normal and ischemic myocardium in swine. Circ. Res. 43: 652-661, 1978. 325. LIEDTKE, A. J., AND E. SHRAGO. Detrimental effects of fatty acids and their derivatives in ischemic and reperfused myocardium. In: Pathophysiology of Severe Ischemic Myocardial Injury, edited by H. M. Piper. Dordrecht, The Netherlands: Kluwer, 1990, p. 149-166. 326. LINDMAR, R., K. LOFFELHOLZ, AND J. SANDMAN. On the mechanism of muscarinic hydrolysis of choline phospholipids in the heart. Biochem. Pharmacol. 37: 4689-4695,1988. 327. LINSSEN, M. C. J. G., W. ENGELS, P. J. M. R. LEMMENS, M. VAN BILSEN, G. J. VAN DER VUSSE, AND R. S. RENEMAN. Arachidonic acid metabolism in cells isolated from adult rat hearts (Abstract). FASEB J. 4: A418, 1990. 328. LINSSEN, M. C. J. G., M. M. VORK, Y. F. DE JONG, J. F. C. GLATZ, AND G. J. VAN DER VUSSE. Fatty acid oxidation capacity and fatty acid-binding protein content of different cell types isolated from rat heart. Mol. Cell Biochem. 89: 19-26, 1990. 329. LITTLE, S. E., G. J. VAN DER VUSSE, AND J. B. BASSINGTHWAIGHTE. Myocardial transcapillary transport of palmitate. J. Nucl. Med. 27: 966, 1986. 330. LOCHNER, A., AND M. DE VILLIERS. Phosphatidylcholine biosynthesis in myocardial ischaemia. J. Mol. Cell. Cardiol. 21: 151163, 1989. 331. LOCHNER, A., J. C. N. KOTZE, A. J. S. BENADE, AND W. GEVERS. Mitochondrial oxidative phosphorylation in low-flow hypoxia: role of free fatty acids. J. Mol. CeZZ. Cardiol. 10: 857-875, 1978. 332. LOCHNER, A., J. C. N. KOTZE, AND W. GEVERS. Mitochondrial oxidative phosphorylation in myocardial anoxia: effects of albumin. J. Mol. Cell. Cardiol. 8: 465-480, 1976. 333. LOCHNER, A., I. VAN NIEKERK, AND J. C. N. KOTZE. Normothermic ischaemic cardiac arrest of the isolated perfused rat heart: effets of trifluoperazine and lysolecithin on mechanical and metabolic recovery. Basic Res. CardioZ. 80: 363-376, 1985. 334. LOCHNER, W., AND M. NASSERI. Uber den veniisen Sauerstoffdruck, die Einstellung der Coronardurchblutung und den Kohlenhydrat-stoffwechsel des Herzens bei Muskelarbeit. PJuegers Arch. 269: 407-416,1959. 335. LOCKWOOD, E. A., AND E. BAILEY. Fatty acid utilization during development of the rat. Biochem. J. 120: 49-54,197O. 336. LOEB, L. A., AND R. W. GROSS. Identification and purification of sheep platelet phospholipase A, isoforms. J. BioZ. Chem. 261: 10467-10470,1986. 337. LOPASCHUK, G. D., M. A. APAFFORT, N. J. DAVIS, AND S. R. WALL. Glucose and palmitate oxidation in isolated working rat hearts reperfused after a period of transient global ischemia. Circ. Res. 66: 546-553, 1990. 338. LOPASCHUK, G. D., AND J. R. NEELY. Stimulation of myocardial coenzyme A degradation by fatty acids. Am. J. Physiol. 253 (Heart Circ. Physiol. 22): H41-H46, 1987. 339. LUCCHESI, B. R., J. K. MICKELSON, J. W. HOMEISTER, AND


October

340. 341.

342. 343.

344.

345. 346.

347.

348.

349. 350

351

352.

353.

354.

355.

356.

357.

358.

359.

360.

361.

362.

1992

MYOCARDIAL

FATTY

C. V. JACKSON. Interaction of the formed elements of blood with the coronary vasculature in vivo. Federation Proc. 46: 63-72, 1987. LUCY, J. A. The fusion of biological membranes. Nature Lond. 227: 815-817, 1970. LUDERITZ, B., C. N. D’ALNONCOURT, AND G. STEINBECK. Effects of free fatty acids on electrophysiological properties of ventricular myocardium. Klin. Wochenschr. 54: 309-313, 1976. LUXTON, M. R., N. E. MILLER, AND M. F. OLIVER. Antilipolytic therapy in angina pectoris. Br. Heart J. 38: 1204-1208, 1976. MALLORY, G. K., P. D. WHITE, AND J. SALCEDO-SAGAR. The speed of healing of myocardial infarction. Am. Heart J 18: 647671, 1939. MAN, R. Y. K. Lysophosphatidylcholine-induced arrhythmias and its accumulation in the rat perfused heart. Br. J PharmacoZ. 93: 412-416,1988. MAN, R. Y. K., AND P. C. CHOY. Lysophosphatidylcholine causes cardiac arrhythmia. J. Mol. Cell Cardiol. 14: 173-175, 1982. MAN, R. Y. K., T. L. SLATER, M. P. PELLETIER, AND P. C. CHOY. Alterations of phospholipids in ischemic canine myocardium during acute arrhythmia. Lipids 18: 677-681, 1983. MAN, R. Y. K., T. WONG, AND P. C. CHOY. Effects of lysophosphoglycerides on cardiac arrhythmias. Life Sci. 32: 1325-1330, 1983. MANNAERTS, G. P., AND L. DEBEER. Mitochondrial and peroxisomal o-oxidation of fatty acids in rat liver. Ann. NY Acad. Sci. 386: 30-39, 1982. MARINETTI, G. V., J. ERBLAND, AND E. STOTZ. The structure of beef heart plasmalogens. J. Am. Chem. Sot. 81: 861-864, 1959. MASSEY, K. D., AND K. P. BURTON. a-Tocopherol attenuates myocardial membrane-related alterations resulting from ischemia and reperfusion. Am. J PhysioZ. 256 (Heart Circ. Physiol. 25): Hll92-Hll99,1989. MATARESE, V., R. L. STONE, D. W. WAGGONER, AND D. A. BERNLOHR. Intracellular fatty acid trafficking and the role of cytosolic lipid binding proteins. Prog. Lipid Res. 28: 245-272,1989. McDONOUGH, K. H., AND J. R. NEELY. Inhibition of myocardial lipase by palmitoyl CoA. J. Mol. Celh CardioC 20, Suppl. II: 31-39,1988. McFARLANE, M. G. The biochemistry of bacterial toxins. Variations in haemolytic activity of immunologically distinct lecithinases toward erythrocytes from different species. Biochem. J 47: 270-279, 1950. McMILLIN-WOOD, J., W. E. TAYLOR, A. SCHWARTZ, AND C. CHANG. The effect of palmitoyl coenzyme A on rat heart and liver mitochondria. Biochim. Biophys. Acta 486: 331-340,1977. MERSMANN, H. J., AND G. PHINNEY. In vitro fatty acid oxidation in liver and heart from neonatal swine. Comp. Biochem. Physiol. B Comp. Biochem. 44: 219-223, 1973. MESSINEO, F. C., P. B. PINTO, AND A. M. KATZ. Palmitic acid enhances calcium sequestration by isolated sarcoplasmic reticulum. J. Mol. CeZZ. Cardiol. 12: 725-732, 1980. MESSINEO, F. C., M. RATHIER, C. FAVREAU, J. WATRAS, AND H. TAKENAKA. Mechanisms of fatty acid effects on sarcoplasmic reticulum. J. Biol. Chem. 259: 1336-1343, 1984. MEST, H. J., K. E. BLASS, AND W. FORSTER. Effects of arachidonic, linoleic, linolenic and oleic acid on experimental arrhythmias in cats, rabbits and guinea-pigs. Prostaglandins 14: 163-171, 1977. MICKELSON, J. K., P. J. SIMPSON, AND B. R. LUCCHESI. Myocardial dysfunction and coronary vasoconstriction induced by platelet-activating factor in the post-infarcted rabbit heart. J. Mol. Cell. Cardiol. 20: 547-561, 1988. MICKLE, D. A. G., P. J. DEL NIDO, G. J. WILSON, R. D. HARDING, AND A. D. ROMASCHIN. Exogenous substrate preference of the post-ischaemic myocardium. Cardiovasc. Res. 20: 256-263, 1986. MILLER, H. I., K. Y. YUM, AND B. C. DURHAM. Myocardial free fatty acid in unanesthetized dogs at rest and during exercise. Am. J. Physiol. 220: 589-596, 1971. MILLER, W. C., AND B. L. OSCAI. Relationship between type L hormone-sensitive lipase and endogenous triacvlglvcerol in rat

ACID

363.

364.

366.

367.

370.

371. 372.

373.

374.

375.

376.

377.

379. 380.

381.

HOMEOSTASIS

933

heart. Am. J. Physiol. 247 (Regulatory Integrative Comp. Physiol. 16): R621-R625, 1984. MIURA, I., H. HASHIZUME, H. AKUTSU, Y. HARA, AND Y. ABIKO. Accumulation of nonesterified fatty acids in the dog myocardium during coronary artery occlusion determined by a method using 9-anthryldiazomethane. Heart Vessels 3: 190-194, 1988. MIYAZAKI, Y., R. W. GROSS, B. E. SOBEL, AND J. E. SAFFITZ. Biochemical and subcellular distribution of arachidonic acid in rat myocardium. Am. J Physiol. 253 (Cell Physiol. 22): C846-C853, 1987. MIYAZAKI, Y., R. W. GROSS, B. E. SOBEL, AND J. E. SAFFITZ. Selective turnover of sarcolemmal phospholipids with lethal cardiac myocyte injury. Am. J Physiol. 259 (Cell Physiol. 28): C325c331,1990. MJOS, 0. D., N. E. MILLER, R. A. RIEMERSMA, AND M. F. OLIVER. Effects of p-chlorophenoxyisobutyrate on myocardial free fatty acid extraction, ventricular blood flow, and epicardial ST-segment elevation during coronary occlusion in dogs. Circulation 53: 494-500,1976. MOCHIZUKI, S., T. MURASE, H. YAMAOKA, M. ISHIKI, N. TADA, AND M. NAGANO. Lipoprotein lipase activity in ischaemic and anoxic myocardium. Basic Res. CardioZ. 82, Suppl. 1: 4553, 1987. MOCK, T., T. L. SLATER, G. ARTHUR, A. C. CHAN, AND P. C. CHOY. Effects of fatty acids on phosphatidylcholine biosynthesis in isolated hamster heart. Biochem. Cell. BioZ. 64: 413-417, 1986. MOFFAT, M. P. Concentration-dependent effects of prostacyclin on the response of the isolated guinea pig heart to ischemia and reperfusion: possible involvement of the slow inward current. J. Pharmacol. Exp. Ther. 242: 292-299,1987. MONTRUCCHIO, G., G. ALLOATTI, C. TETTA, R. DE LUCA, R. N. SAUNDERS, G. EMMANUELLI, AND G. CAMUSSI. Release of platelet-activating factor from ischemic-reperfused rabbit heart. Am. J Physiol. 256 (Heart Circ. Physiol. 25): Hl236H1246, 1989. MOORE, K. H. Fatty acid oxidation in ischemic heart. MoZ. Physiol. 8: 549-563, 1985. MOORE, K. H., J. D. BONEMA, AND F. J. SOLOMON. Long-chain acyl CoA and acylcarnitine hydrolase activities in normal and ischemic rabbit heart. J. Mol. CeZZ. Cardiol 16: 905-913, 1984. MOORE, K. H., J. R. RADLOFF, F. E. HULL, AND C. C. SWEELEY. Incomplete fatty acid oxidation by ischemic heart: beta-hydroxy fatty acid production. Am. J Physiol. 239 (Heart Circ. PhysioZ. 8): H257-H265, 1980. MORCILLIO, E., P. R. REILD, N. DUBIN, R. GHODGAONKOV, AND B. PITT. Myocardial prostaglandin E, release by nitroglycerin and modification by indomethacin. Am. J Cardiol. 45: 53-57, 1980. MOST, A. S., N. BRACHFELD, R. GORLIN, AND J. WAHREN. Free fatty acid metabolism of the human heart at rest. J. CZin. Invest. 48: 1177-1188,1969. MOST, A. S., R. J. CAPONE, AND P. A. MASTROFRACESCO. Free fatty acids and arrhythmias following acute coronary artery occlusion in pigs. Cardiovasc. Res. 11: 198-205, 1977. MOST, A. S., R. J. CAPONE, P. SZYDLIK, C. A. BRUNO, AND T. S. DEVONA. Failure of free fatty acids to influence degree of myocardial injury following acute coronary artery occlusion in pigs. Cardiology 59: 201-212, 1974. MOST, A. S., M. H. LIPSKY, P. SZYDLIK, AND C. A. BRUNO. Failure of free fatty acids to influence myocardial oxygen consumption in the intact, anesthetized dog. Cardiology 58: 220-228, 1973. MUIR, J. R. The regional production of lipoprotein lipase in man. Clin. Sci. Lond. 34: 261-270, 1968. MULLANE, K. M., W. WESTLIN, AND R. KRAEMER. Activated neutrophils release mediators that may contribute to myocardial injury and dysfunction associated with ischemia and reperfusion. Ann. NYAcad. Sci. 524: 103-121, 1988. MURNAGHAN, M. F. Effects of fatty acids on the ventricular arrhythmia threshold in the isolated heart of the rabbit. Br. J PharmacoZ. 73: 909-915, 1981.


934

VAN

DER

VUSSE,

GLATZ,

382. MURTHY, M. S. R., AND S. V. PANDE. Malonyl-CoA binding site and the overt carnitine palmitoyltransferase activity reside on the opposite sides of the outer mitochondrial membrane. Proc. Natl. Aca,d. Sci. USA 84: 378-382, 1987. 383. MURTHY, V. K., AND J. C. SHIPP. Accumulation of myocardial triglycerides in ketotic diabetes. Diabetes 26: 222-229, 1977. 384. MYEARS, D. W., B. E. SOBEL, AND S. R. BERGMANN. Substrate use in ischemic and reperfused canine myocardium: quantitative considerations. Am. J. Physiol. 253 (Heart Circ. Physiol. 22): H107-H114,1987. 385. NALBONE, G., AND K. Y. HOSTETLER. Subcellular localisation of the phospholipase A of rat hearts. Evidence for a cytosolic phospholipase A,. J. Lipid Res. 26: 104-114, 1985. 386. NALBONE, G., K. Y. HOSTETLER, J. LEONARDI, M. TROTZ, AND H. LAFONT. Partial characterization of rat heart cytosolic phospholipase A, and demonstration of essential sulfhydryl groups. Biochim. Biophys. Acta 877: 88-95, 1986. 387. NAYLER, W. Y., AND A. M. SLADE. The cardioprotective effect of verapamil. Clin. Exp. Pharmacol. Physiol. 6: 75-87, 1982. 388. NEEDLEMAN, P., J. TURK, B. A. JAKSCHIK, A. R. MORRISON, AND J. B. LEFKOWITCH. Arachidonic acid metabolism. An,nu. Rev. Biochem. 55: 69-102, 1986. 389. NEELY, J. R., R. H. BOWMAN, AND H. E. MORGAN. Effects of ventricular pressure development and palmitate on glucose transport. Am. J. Physiol. 216: 804-811, 1969. 390. NEELY, J. R., AND D. FEUVRAY. Metabolic products and myocardial ischemia. Am. J. Pathol. 102: 282-291, 1981. 391. NEELY, J. R., D. GARBER, K. McDONOUGH, AND J. IDELLWENGER. Relationship between ventricular function and intermediates of fatty acid metabolism during myocardial ischemia: effects of carnitine. In: Perspectives in Cardiovascular Research. Ischemic Myy0cardiu.m and Antianginal Drugs, edited by M. M. Winbury and Y. Abiko. New York: Raven, 1979, vol. 3. p. 225-239. 392. NEELY, J. R., AND H. E. MORGAN. Relationship between carbohydrate and lipid metabolism and the energy balance of heart muscle. Annu. Rev. Physiol. 36: 413-459, 1974. 393. NELSON, P. G. Effect of heparin on serum free-fatty-acids, plasma catecholamines, and the incidence of arrhythmias following acute myocardial infarction. Br. Med. J. 3: 735-737, 1970. 394. NIKKILA, E. A. Transport of free fatty acids. Prog. Biochem. Pharmncol. 6: 102-129, 1971. 395. NOEL, S. P. Instability of endothelium-bound lipoprotein lipase activity in perfused rat hearts. Can. J. Bioch,em. Cell Biol. 62: 89-93,1984. 396. NORMANN, P. T., J. NORSETH, AND T. FLATMARK. Acyl-CoA synthetase activity of rat heart mitochondria. Biochim. Biophys. Acta 752: 474-481, 1983. 397. NORSETH, J., AND M. S. THOMASSEN. Stimulation of microperoxisomal ,&oxidation in rat heart by high-fat diets. Biochim. Biophys. Acta 751: 312-320, 1983. 398. NOY, N., T. M. DONNELLY, R. B. COOPER, AND D. ZAKIM. The physicalchemical basis for sex-related differences on uptake of fatty acids by the liver. Bioch*im. Biophys. Acta 1003: 125-130, 1989. 399. OFFNER, G. D., R. F. TROXLER, AND P. BRECHER. Characterization of a fatty acid-binding protein from rat heart. J. Biol. Ch,em,. 261: 5584-5589, 1986. 400. OKANO, G., H. MATSUZAKA, AND T. SHIMOJO. A comparative study of the lipid composition of white intermediate, red and heart muscle in rats. Biochim. Bioph,ys. Acta 619: 167-175, 1980. 401. OLIVECRONA, T., AND G. BENGTSSON-OLIVECRONA. Lipoprotein lipase from milk. The model enzyme in lipoprotein lipase research. In: Lipoprotein Lipase, edited by J. Borensztajn. Chicago, IL: Evener, 1987, p. 15-58. 402. OLIVECRONA, T., S. S. CHEMICK, G. BENGTSSON-OLIVECRONA, M. GARRISON, AND R. 0. SCOW. Synthesis and secretion of lipoprotein lipase in 3T3-Ll adipocytes: demonstration of inactive forms of lipase in cells. J. Biol. Chem. 262: 10748-10759, 1987. 403. OLIVER, M. F., V. A. KURIEN, AND T. W. GREENWOOD. Relation between serum-free-fatty-acids and arrhythmias and death after acute myocardial infarction. Lancet 1: 710-715, 1968. 404. OLOWE, Y., AND H. SCHULZ. Regulation of thiolases from pig

STAM,

405.

406.

407.

408. 409.

410. 411. 412.

413.

414.

415.

416.

417.

AND

RENEMAN

Volume

72

heart. Control of fatty acid oxidation in heart. Eur. J. Biochem. 109: 425-429,198O. OLSON, M. S., S. C. DENNIS, C. A. ROUTH, AND M. S. DEBUYSERE. The regulation of pyruvate dehydrogenase by fatty acids in isolated rabbit heart mitochondria. Arch. Biochem. Biophys. 187: 121-131,1978. OLSON, R. E., AND R. J. HOESCHEN. Utilizaton of endogenous lipids by the isolated perfused rat heart. Biochem. J. 103: 791-801, 1967. ONG, J. M., T. G. KIRCHGESSNER, M. C. SCHOTZ, AND P. A. KERN. Insulin increases the synthetic rate and messenger RNA level of lipoprotein lipase in isolated rat adipocytes. J. Biol. Chem. 263: 12933-12938,1988. OPIE, L. H. Metabolism of the heart in health and disease. Part I. Am. Heart J. 76: 685-698,1968. OPIE, L. H. Metabolism of free fatty acids, glucose and catecholamines in acute myocardial infarction. Relation to myocardial ischemia and infarct size. Am. J. Cardiol. 36: 936-952, 1975. OPIE, L. H. Effects of regional ischemia on metabolism of glucose and fatty acids. Circ. Res. 38: 52-74, 1976. OPIE, L. H. Reperfusion injury and its pharmacologic modification. Circulation 80: 1049-1061, 1989. OPIE, L. H., R. NORRIS, M. THOMAS, A. HOLLAND, P. OWEN, AND M. VAN NOORDEN. Failure of high concentrations of circulating free fatty acids to provoke arrhythmias in experimental myocardial infarction. Lancet 1: 818-822, 1971. OPIE, L. H., P. OWEN, AND R. A. RIEMERSMA. Relative rates of oxidation of glucose and free fatty acids by ischaemic and non-ischaemic myocardium after coronary artery ligation in the dog. Eur. J. Clin. Invest. 3: 419-435, 1973. OPIE, L. H., M. TANSEY, AND B. M. KENNELLY. Proposed metabolic vicious circles in patients with large myocardial infarcts and high plasma-free-fatty-acid concentrations. Lancet 2: 890892,1977. OPIE, L. H., F. T. THANDROYEN, C. MULLER, AND 0. L. BRICKNELL. Adrenaline-induced “oxygen-wastage” and enzyme release from working rat heart. Effects of calcium antagonism, ,&blockade, nicotinic acid and coronary artery ligation. J. Mol. Cell. Cardiol. 11: 1073-1094, 1979. ORAM, J. F., S. L. BENNETCH, AND J. R. NEELY. Regulation of fatty acid utilization in isolated perfused rat hearts. J. Biol. Chem. 248: 5299-5309, 1973. OSCAI, B. L. Role of lipoprotein lipase in regulating endogenous triacylglycerols in rat heart. Biochem. Biophys. Res. Commun. 91: 227-232,1979.

418.

419.

420.

421.

422.

423.

424.

425. 426.

OSORNIO-VARGAS, A. R., I. K. BEREZESKY, AND B. F. TRUMP. Progression of ion movements during acute myocardial infarction in the rat. An X-ray microanalysis study. Scanning Electron Microsc. 2: 463-472, 1981. OTANI, H., R. M. ENGELMAN, R. H. BREYER, J. A. ROUSOU, S. LEMESHOW, AND D. K. DAS. Mepacrine, a phospholipase inhibitor. J. Thorac. Card&vase. Surg. 92: 247-254,1986. OTANI, H., M. R. PRASAD, R. M. JONES, ANDD. K. DAS. Mechanism of membrane phospholipid degradation in ischemic-reperfused rat hearts. Am. J. Physiol. 257 (Heart Circ. Physiol. 26): H252-H258, 1989. OWENS, K., F. F. KENNETT, AND W. B. WEGLICKI. Effects of fatty acid intermediates on Na+, K’-ATPase activity. Am. J. Physiol. 242 (Heart Circ. Physiol. 11): H456-H461, 1982. PACOLD, I., L. ACKERMAN, B. JOHNSON, R. W. REID, M. L. FREEMAN, H. S. LOEB, AND E. KAPLAN. The effects of acute hypertriglyceridemia and high levels of free fatty acids on left ventricular function. Am. Heart J. 110: 836-840, 1985. PALMER, J. W., P. C. SCHMID, D. R. PFEIFFER, AND H. H. 0. SCHMID. Lipids and lipolytic enzyme activities of rat heart mitochondria. Arch. Biochem. Biophys. 211: 674-682, 1981. PALMER, W. K., R. A. CARUSO, AND L. B. OSCAI. Cyclic AMP activation of a triglyceride lipase in broken cell preparations of rat heart. Arch. Biochem. Biophys. 249: 255-262, 1986. PALMER, W. K., AND T. A. KANE. Hormone-stimulated lipolysis in cardiac myocytes. Biochem. J. 216: 241-243, 1983. PARIS, S., D. SAMUEL, G. ROMEY, AND G. AILHAUD. Uptake of fatty acids by cultured cardiac cells from chick embryo: evi-


October

427.

428.

429.

430.

431.

432.

433.

434.

435.

436.

437.

438.

439.

440.

441.

442.

443.

444.

445.

446.

19%

MYOCARDIAL

FATTY

dence for a facilitation process without energy dependence. Bioch,imie 61: 361-367, 1979. PARRATT, J. R., AND S. J. COKER. Arachidonic acid cascade and the generation of ischemiaand reperfusion-induced ventricular arrhythmias. J. Cardiovasc. Pharmacol. 7: 65-70, 1985. PATTON, S., I. M. ZULAK, AND E. G. TRAMS. Fatty acid metabolism via triglyceride in the salmon heart. J. Mol. CeLC Cardiol. 7: 857-865, 1975. PAULSON, D. J., M. J. SCHMIDT, J. ROMANS, AND A. L. SHUG. Metabolic and physiological differences between zero-flow and low-flow myocardial ischemia: effects of L-acetyl carnitine. Basic Res. Cardiol. 79: 551-561, 1984. PAULUSSEN, R. J. A., M. J. H. GEELEN, A. C. BEYNEN, AND J. H. VEERKAMP. Immunochemical quantitation of fatty-acidbinding proteins. I. Tissue and intracellular distribution, postnatal development and influence of physiological conditions on rat heart and liver FABP. Biochim. Biophys. Acta 1001: 201-209, 1989. PEDERSEN, M. E., AND M. C. SCHOTZ. Changes in rat heart lipoprotein lipase activity after feeding carbohydrate. J. Nutr. 110: 481-487, 1980. PEDERSEN, M. E., L. E. WOLF, AND M. C. SCHOTZ. Hormonal mediation of rat heart lipoprotein lipase activity after fat feeding. Biochim. Biophys. Acta 666: 191-197, 1981. PEETERS, R. A., J. H. VEERKAMP, AND R. A. DEMEL. Are fatty acid-binding proteins involved in fatty acid transfer? Biochim. Biophys. Acta 1002: 8-13, 1989. PELECH, S. K., AND D. E. VANCE. Regulation of rat liver cytosolic CTP:phosphocholine cytidylyltransferase by phosphorylation and dephosphorylation. J. Biol. Chem. 257: 14198-14202,1982. PIPER, H. M., 0. SEZER, P. SCHWARTZ, J. F. HUTTER, AND P. G. SPIECKERMANN. Fatty acid-membrane interactions in isolated cardiac mitochondria and erythrocytes. Biochim. Bioph,ys. Acta 732: 193-203, 1983. PITTS, B. J. R., C. A. TATE, B. VAN WINKLE, J. M. WOOD, AND M. L. ENTMAN. Palmitylcarnitine inhibition of the calcium pump in cardiac sarcoplasmic reticulum: a possible role in myocardial ischemia. Lift! Sci. 23: 391-402, 1978. PODBIELSKI, B., AND W. K. PALMER. Cardiac triacylglycerol content and lipase activity during recovery from exercise. J. Appl. Ph ysiol. 66: 1099-1103, 1989. POST, J. A., G. A. LANGER, J. A. F. OP DEN KAMP, AND A. J. VERKLEY. Phospholipid asymmetry in cardiac sarcolemma. Analysis of intact cells and gas dissected membranes. Biochim. Biophgs. Acta 943: 256-266, 1988. POST, J. A., T. J. C. RUIGROK, AND A. J. VERKLEY. Phospholipid reorganisation and bilayer destabilization during myocardial ischemia and reperfusion: a hypothesis. J. Mol. Cell. CardioZ. 20, SuppL II: 107-111, 1988. POTTER, B. J., D. SORRENTINO, AND P. D. BERK. Mechanisms of cellular uptake of free fatty acids. Annu. Rev. Nutr. 9: 253-270, 1989. POWELL, G. L., P. S. TIPPETT, T. C. KIORPES, J. McMILLINWOOD, K. E. COLL, H. SCHULZ, K. TANAKA, E. S. KANG, AND E. SHRAGO. Fatty acyl-CoA as an effector molecule in metabolism. Federation Proc. 44: 81-84, 1985. POWELL, W., AND C. D. FUNK. Metabolism of arachidonic acid and other polyunsaturated fatty acids by blood vessels. Prog. Lipid Res. 26: 183-210, 1987. PRAKASH, R., W. W. PARMLEY, M. HORVAT, AND H. J. C. SWAN. Serum cortisol, plasma free fatty acids, and urinary catecholamines as indicators of complications in acute myocardial infarction. Circulation 45: 736-745, 1972. PRASAD, R. M., L. M. POPESCU, I. I. MORARU, X. LIU, S. MAITY, R. M. ENGELMAN, AND D. P. DAS. Role of phospholipases A, and C in myocardial ischemic reperfusion injury. Am. J. Ph, ysiol. 260 (Heart Circ. Physiol. 29) : H877-H883, 1991. PRESSMAN, B. C., AND H. A. LARDY. Effect of surface active agents on latent ATPase of mitochondria. Biochim. Biophys. Acta 21: 458-466, 1956. PRINZEN, F. W., G. J. VAN DER VUSSE, T. ARTS, T. H. M. ROEMEN, W. A. COUMANS, AND R. S. RENEMAN. Accumula-

ACID

447.

448.

449.

450.

451.

452.

453. 454.

455.

456.

457.

458.

459.

460.

461.

462.

463.

464. 465.

466.

HOMEOSTASIS

935

tion of nonesterified fatty acids in ischemic canine myocardium. Am. J. Physiol. 247 (Heart Circ. Physiol. 16): H264-H272, 1984. PRINZEN, F. W., G. J. VAN DER VUSSE, W. A. COUMANS, R. KRUGER, C. W. J. VERLAAN, AND R. S. RENEMAN. The effect of elevated arterial free fatty acid concentrations on hemodynamics and myocardial metabolism and blood flow during ischemia. Basic Res. Cardiol. 76: 197-210, 1981. PULA, G., R. BIANCHI, P. CECCARELLI, I. GIAMBIANCO, AND R. DONATO. Characterization of mammalian heart annexins with special reference to CaBP 33 (annexin V). FEBS Lett. 277: 53-58,199O. RABIN, R. A., AND D. 0. ALLEN. Role of protein kinase and contractile force in the regulation of myocardial lipolysis. Harm. Metab. Res. 16: 465-467, 1984. RABINOWITZ, J. L., AND E. S. HERCKER. Incomplete oxidation of palmitate and leakage of intermediary products during anoxia. Arch. Biochem. Biophys. 161: 621-627, 1974. RAMADOSS, C. S., R. 0. RUSSEL, W. J. ROGERS, J. A. MANTLE, AND H. G. MCDANIEL. Studies on the fatty acid inactivation of phosphofructokinase. J. BioZ. Chem. 251: 98407, 1976. RAMIREZ, I., A. J. KRYSKI, 0. BEN-ZEEV, M. C. SCHOTZ, AND D. L. SEVERSON. Characterization of triacylglycerol hydrolase activities in isolated cells from the heart. Biochem. J 232: 229236, 1985. RANA, R. S., AND L. E. HOKIN. Role of phosphoinositides in transmembrane signalling. Physiol. Rev. 70. 115-164, 1990. RAUCH, B., C. BODE, H. M. PIPER, J. F. HUTTER, R. ZIMMERMANN, E. BRAUNWELL, W. HASSELBACH, AND W. KUBLER. Palmitate uptake in calcium tolerant, adult rat myocardial single cells. Evidence for an albumin mediated transport across sarcolemma. J. Mol. Cell Cardiol. 19: 159-166, 1987. RAVENS, K. G., AND P. JIPP. Die freien Plasmafettsauren in der Fruhphase nach einem myocard Infarkt. Drug Res. 22: 1831-1833, 1972. RAVENS, K. G., AND U. RAVENS. The role of linoleic acid in hypoxia-induced changes of the action potentials and the force of concentration of isolated papillary muscles of the guinea pig. Recent Adv. Stud. Card. Struct. Metab. 7: 289-295, 1976. RENEMAN, R. S., F. W. PRINZEN, W. ENGELS, M. VAN BILSEN, AND G. J. VAN DER VUSSE. Arachidonic acid metabolism during myocardial ischemia. Prog. Appl. Microcirc. 12: 152-169, 1987. REUBSAET, F. A. G., J. H. VEERKAMP, J. M. F. TRIJBELS, AND L. A. H. MONNENS. Total and peroxisomal oxidation of various saturated and unsaturated fatty acids in rat liver, heart and m. quadriceps. Lipids 24: 945-950,1989. REVTYAK, G. E., L. M. BUJA, K. R. CHIEN, AND W. B. CAMPBELL. Reduced arachidonate metabolism in ATP-depleted myocardial cells occurs early in cell injury. Am. J. Physiol. 259 (Heart Circ. Physiol. 28): H582-H591, 1990. REVTYAK, G. E., A. R. JOHNSON, AND W. B. CAMPBELL. Cultured bovine coronary arterial endothelial cells synthesize HETEs and prostacyclin. Am. J. Physiol. 254 (CeZl. Physiol. 23): C8-C19,1988. RIEMERSMA, R. A. Raised plasma non-esterified fatty acid (NEFA) during ischaemia: implications for arrhythmias. Basic Res. Cardiol. 82, Suppl. 1: 177-186, 1987. RIEMERSMA, R. A., R. LOGAN, D. C. RUSSEL, H. J. SMITH, J. SIMPSON, AND M. F. OLIVER. Effect of heparin on plasma free fatty acid concentrations after acute myocardial infarction. Br. Heart J. 48: 134-139,1982. RIEMERSMA, R. A., AND B. MICHOROWSKI. Lysolecthin and acute coronary ligation in the anaesthetised dog. Cardiovasc. Res. 17: 505-508,1983. ROBINSON, J., AND E. A. NEWSHOLME. Glycerol kinase activities in rat heart and adipose tissue. Biochem. J. 104: 2c-4c, 1967. ROCQUELIN, G., L. GUENOT, P. 0. ASTORG, AND M. DAVID. Phospholipid content and fatty acid composition of human heart. Lipids 24: 775-780,1989. ROSAMOND, T. L., D. R. ABENSCHEIN, B. E. SOBEL, S. R. BERGMANN, AND K. A. A. FOX. Metabolic fate of radiolabeled palmitate in ischemic canine myocardium: implications for positron emission tomography. J. Nucl. Med. 28: 1322-1329, 1987.


936

VAN

DER

VUSSE,

GLATZ,

467. ROSE, C. P., AND C. A. GORESKY. Constraints on the uptake of labelled palmitate by the heart. The barriers at the capillary and sarcolemmal surfaces and the control of intracellular sequestration. Circ. Res. 41: 534-545, 1977. 468. ROSE, H., T. HENNECKE, AND H. KAMMERMEIER. Is fatty acid uptake in cardiomyocytes determined by physicochemical fatty acid partition between albumin and membranes? Mol. Cell. Biochem. 88: 31-36, 1989. M. D., AND J. B. WARSHAW. Fatty acid and glu469. ROSENTHAL, cose oxidation by cultured rat heart cells. J. Cell. PhysioZ. 93: 31-40, 1977. 470. ROWE, M. J., J. M. M. NEILSON, AND M. F. OLIVER. Control of ventricular arrhythmias during myocardial infarction by antilipolytic treatment using a nicotinic-acid analogue. Lancet 1: 295300,1975. 471. ROY, P.-E. Lipid droplets in the heart interstitium: concentration and distribution. Recent Adz?. Stud. Card. Struct. Metab. 10: 17-27, 1975. 472. RUSSELL, D. C., AND M. F. OLIVER. Effect of antilipolytic therapy on ST segment elevation during myocardial ischemia in man. Br. Heart J. 40: 117-123,1978. 473. RUTENBERG, H., J. C. PAMINTUAN, AND L. A. SOLOFF. Serum-free-fatty-acids and their relation to complications after acute myocardial infarction. Lancet 2: 559-564, 1969. 474. SACCHETTINI, J. C., J. I. GORDON, AND L. J. BANASZAK. Refined apoprotein structure of fat intestinal fatty acid-binding protein produced in Esch,erich.ia coli. Proc. Natl. Acad. Sci. USA 86: 7736-7740, 1989. 475. SADUR, C. N., AND R. H. ECKEL. Insulin stimulation of adipose tissue lipoprotein lipase: use of the euglycemic clamp technique. J. Cli32. Invest. 69: 1119-1125, 1982. 476. SAFFITZ, J. E., P. B. CORR, B. I. LEE, R. W. GROSS, E. K. WILLIAMSON, AND B. E. SOBEL. Pathophysiologic concentrations of lysophosphoglycerides quantified by electron microscopic autoradiography. Lab. Invest. 50: 278-286, 1984. 477. SAGE, H., C. JOHNSON, AND P. BORNSTEIN. Characterization of a novel serum albumin-binding glycoprotein secreted by endothelial cells in culture. J. Biol. Chem. 259: 3993-4007, 1984. 478. SAKURAI, I. Pathology of acute ischaemic myocardium. Acta Pathol. J~u. 27: 587-603, 1977. 479. SALARI, H., M. DEMOS, AND A. WONG. Comparative hemodynamics and cardiovascular effects of endotoxin and platelet-activating factor in rat. Circ. Sh,ock 32: 189-207, 1990. J. A. Inhibition of arachidonic acid metabolism. In: 480. SALMON, Cardiovascular Pharmacology of the Prostaglandins, edi ted by A. G. Herman, P. M. Vanhoutte, H. Denolin, and A. Goossens. New York: Raven, 1982, p. 7-22. 481. SAMANTA, A., M. R. PRASAD, R. M. ENGELMAN, AND D. K. DAS. Possible physiological role of myocardial fatty acid binding protein in phospholipid biosynthesis. J. Lipid Mediators 1: 243255,1989. 482. SAXENA, U., L. D. DE WITTE, AND I. J. GOLDBERG. Release of endothelial cell lipoprotein lipase by plasma lipoproteins and free fatty acids. J. Biob Chem. 15: 4349-4355, 1989. J. Structure characteristics in regional versus global 483. SCHAPER, ischemia. Adv. Myocardiol. 2: 311-314, 1980. 484. SCHEUER, J., AND N. BRACHFELD. Myocardial uptake and fractional distribution of palmitate-l-14C by the ischemic dog heart. Metabolism 15: 945-954, 1966. 485. SCHEUER, J., AND R. E. OLSON. Metabolism of exogenous triglyceride by the isolated perfused rat heart. Am. J. PhysioL 212: 301-307, 1967. 486. SCHNITZER, J. A., W. W. CARLEY, AND G. E. PALADE. Specific albumin binding to microvascular endothelium in culture. Am. J. Physiol. 254 (Heart Circ. Ph,ysiol. 23): H425-H437, 1988. 487. SCHOONDERWOERD, K., S. BROEKHOVEN-SCHOKKER, W. C. HULSMANN, AND H. STAM. Stimulation of neutral triglyceride lipase activity in isolated rat heart by adenosine-3’:5’monophosphate: involvement of glycogenolysis. Basic Res. Card,iol. 82, Suppl. 1: 29-35, 1987. 488. SCHOONDERWOERD, K., S. BROEKHOVEN-SCHOKKER, W. C. HULSMANN, AND H. STAM. Enhanced lipolvsis of myo-

STAM,

489.

490.

491.

492. 493. 494.

495.

496.

497.

498. 499.

500.

501.

502.

503. 504. 505.

506.

507.

508.

509.

AND

RENEMAN

Volume

7.2

cardial triglycerols during low-flow ischemia and anoxia in the isolated rat heart. Basic Res. Cardiob 84: 165-173, 1989. SCHOONDERWOERD, K., S. BROEKHOVEN-SCHOKKER, W. C. HULSMANN, AND H. STAM. Properties of phosphatidate phosphohydrolase and diacylglycerol acyltransferase activities in the isolated rat heart. Effect of glucagon, ischaemia and diabetes. Biochem. J. 268: l-6, 1990. SCHOONDERWOERD, K., T. VAN DER KRAAY, W. C. HULSMANN, AND H. STAM. Hormones and triacylglycerol metabolism under normoxic and ischemic conditions. Mol. Cell. Biothem. 88: 129-137,1989. SCHRIJVERS, A. H. G. J., M. J. M. DE GROOT, V. V. T. HEYNEN, G. J. VAN DER VUSSE, P. M. FREDERIK, AND R. S. RENEMAN. Ischemia and reperfusion induced multilamellar vesicles in isolated rabbit hearts: time correlation between morphometric data and metabolic alterations. J Mol. CeU. CardioC 22: 653-665, 1990. SCHROR, K. Prostaglandins, other eicosanoids and endothelial cells. Basic Res. Cardiol. 80: 502-514, 1985. SCHROR, K. Eicosanoids and myocardial ischaemia. Basic Res. Cardiol. 82, Suppl. 1: 235-243, 1987. SCHWAIGER, M., H. R. SCHELBERT, D. ELLISON, H. HANSEN, L. YEATMEN, J. VINTEN-JOHANSEN, C. SELIN, J. BARRIO, AND M. E. PHELPS. Sustained regional abnormalities in cardiac metabolism after transient ischemia in the chronic dog model. J Am. Colb Cardiol. 6: 336-347, 1985. SCHWAIGER, M., H. R. SCHELBERT, R. KEEN, J. VINTENJOHANSEN, H. HANSEN, C. SELIN, J. BARRIO, S. C. HUANG, AND M. E. PHELPS. Retention and clearance of C-11 palmitic acid in ischemic and reperfused canine myocardium. J. Am. ColZ. CardioC 6: 311-320, 1985. SCHWARTZMANN, M., M. A. CARROLL, N. G. IBRAHAM, N. R. FERRERI, E. SONGU-MIZE, AND J. C. McGIFF. Renal arachidonic acid metabolism. The third pathway. Hypertension Dallas 7, Suppl. 1: 136-144, 1985. SCHWERTZ, D., J. HALVERSON, T. ISAACSON, H. FEINBERG, AND J. W. PALMER. Alterations in phospholipid metabolism in the globally ischemic rat heart: emphasis on phosphoinositide specific phospholipase C activity. J. MoZ. CeZZ. Cardiol. 19: 685-697,1987 SCOW, R. O., AND E. J. BLANCHETTE-MACKIE. Why fatty acids flow in cell membranes. Prog. Lipid Res. 24: 197-241,1985. SCOW, R. O., E. J. BLANCHETTE-MACKIE, AND L. C. SMITH. Transport of lipid across capillary endothelium. Federation Proc. 39: 2610-2617,198O. SEDLIS, S. P., J. M. SEQUEIRA, G. G. AHUMADA, AND N. EL SHERIF. Effects of lysophosphatidylcholine on cultured heart cells: correlation of rate of uptake and extent of accumulation with cell injury. J. Lab. C&n. Med. 112: 745-754, 1988. SEN, A. K., F. A. SUNAHORA, AND J. TALESNIK. Prostaglandin E, and cyclic AMP in the coronary vasodilation due to cardiac hyperactivity. Can. J. Physiol. Pharmacol. 54: 128-159, 1976. SEVEREID, L., W. E. CONNER, AND J. P. LONG. The depressant effect of fatty acids on the isolated rabbit heart. Proc. Sot. Exp. Biol. Med. 131: 1239-1243, 1969. SEVERSON, D. L. Regulation of lipid metabolism in adipose tissue and heart. Can. J. Physiol. Pharmacol. 57: 923-937, 1979. SEVERSON, D. L. Characterization of triglyceride lipase activities in rat heart. J. MoZ. Cell. CardioZ. 11: 569-583, 1979. SEVERSON, D. L., AND R. CAROLL. Effect of taxol on the heparin-induced secrection of lipoprotein lipase from cardiac myocytes. Mol. Cell. Biochem. 88: 17-22, 1989. SEVERSON, D. L., AND T. FLETCHER. Regulation of lysophosphatidylcholine-metabolizing enzymes in isolated myocardial cells from rat heart. Can. J. Physiol. Pharmacol. 63: 944-952,1985. SEVERSON, D. L., AND M. HEE-CHEONG. Monoacylglycerol lipase activity in cardiac myocytes. Biochem. Cell Biol. 66: 10131018,1988. SEVERSON, D. L., AND B. HURLEY. Regulation of rat heart triacylglycerol ester hydrolases by free fatty acids, fatty acyl CoA and fatty acylcarnitine. J. Mol. CeZZ. Cardiol. 14: 467-474, 1982. SEVERSON, D. L., AND B. HURLEY. Stimulation of a neutral


October

510.

511.

512.

513.

514. 515.

516.

517. 518.

519. 520.

521. 522. 523. 524.

525.

526.

527.

528. 529.

530.

531.

532.

1,992

MYOCARDIAL

FATTY

triacylglycerol hydrolase from rat heart by phosphatidylethanolamine and lysophosphatidylethanolamine. Lipids 21: l-5, 1986. SHAIKH, N. A., AND E. DOWNAR. Time course of changes in porcine myocardial phospholipid levels during ischemia. Circ. Res. 49: 316-325, 1981. SHASBY, D. M., AND S. S. SHASBY. Active transendothelial transport of albumin. Interstitium to lumen. Circ. Res. 57: 903908,1985. SHIPP, J. C., L. A. MENAHAN, M. F. CRASS III, AND S. N. CHAUDHURI. Heart triglycerides in health and disease. Recent Adv. Stud. Curd. Struct. Metab. 3: 179-204, 1973. SHIPP, J. C., J. M. THOMAS, AND L. CREVASSE. Oxidation of carbon-14-labeled endogenous lipids by isolated perfused rat hearts. Science Wash. DC 143: 371-373, 1964. SHRAGO, E. Myocardial adenine nucleotide translocase. J. Mol. Cell. CurdioZ. 8: 497-500, 1976. SHRAGO, E. The effect of long chain fatty acyl CoA esters on the adenine nucleotide translocase in myocardial metabolism. Life Sci. 22: l-6, 1978. SHRAGO, E., AND G. WOLDEGIORGIS. Regulation of adenine nucleotide translocation by long chain fatty acyl CoA esters. Adv. Physiol. Sci. 8: 149-158, 1981. SHUG, A. L. Control of carnitine-related metabolism during myocardial &hernia. Tex. Rep. BioZ. Med. 39: 409-428, 1979. SIESS, M. Some aspects of the regulation of carbohydrate and lipid metabolism in cardiac tissue. Basic Res. CardioZ. 75: 47-55, 1980. SIMMET, T., AND B. A. PESKAR. Eicosanoids and the coronary circulation. Rev. Physiol. Biochem. Pharmacob 104: l-64, 1986. SIREN, A.-L., AND G. FEUERSTEIN. Effects of PAF and BN 52021 on cardiac function and regional blood flow in conscious rats. Am. J. Physiol. 257 (Heart Circ. Physiol. 26): H25-H32,1989. SIVAKOFF, M., W. HSUEH, E. PURE, AND P. NEEDLEMAN. Prostaglandins and the heart. Federation Proc. 38: 78-82,1979. SLEIGHT, R. G. Intracellular lipid transport in eukaryotes. Annu. Rev. Physiol. 49: 193-208, 1987. SLUSE, F. E., A. J. MEYER, AND J. M. TAGER. Anion translocators in rat-heart mitochondria. FEBS Lett. 18: 149-153,197l. SMALL, C. A., A. J. GARTON, AND S. J. YEAMAN. The presence and role of hormone-sensitive lipase in heart muscle. Biochem. J. 258: 67-72,1989. SMITH, L. C., AND R. 0. SCOW. Chylomicrons. Mechanisms of transfer of lipolytic products to cells. Prog. Biochem. PharmacoZ. 15: 109-138, 1979. SNYDER, D. W., W. A. CRAFFORD, JR., J. L. GLASHOW, D. RANKIN, B. E. SOBEL, AND P. B. CORR. Lysophosphoglycerides in ischemic myocardium effluents and potentiation of their arrhythmogenic effects. Am. J. Physiol. 241 (Heart Circ. PhysioL 10): H700-H707,1981. SOBEL, B. E., P. B. CORR, A. K. ROBISON, R. A. GOLDSTEIN, F. X. WITKOWSKI, AND M. S. KLEIN. Accumulation of lysophosphoglycerides with arrhythmogenic properties in ischemic myocardium. J. Clin. Invest. 62: 546-553,1978. SOLOFF, L. A. Arrhythmias following infusion of fatty acids. Am. Heart J. 80: 671-674, 1970. SORRENTINO, D., R. B. ROBINSON, C. L. KIANG, AND P. D. BERK. At physiological albumin/oleate concentrations oleate uptake by isolated hepatocytes, cardiac myocytes and adipocytes is a saturable function of the unbound oleate concentration. Uptake kinetics are consistent with the conventional theory. J. CZin. Invest. 84: 1325-1333,1989. SORRENTINO, D., D. STUMP, B. J. POTTER, R. B. ROBINSON, R. WHITE, C. L. KIANG, AND P. D. BERK. Oleate uptake by cardiac myocytes is carrier mediated and involves a 40-kD plasma membrane fatty acid binding protein similar to that in liver, adipose tissue and gut. J. Clin. Invest. 82: 928-935, 1988. SPAHR, R., A. KRUTZFELDT, S. MERTENS, B. SIEGMUND, AND H. M. PIPER. Fatty acids are not an important fuel for coronary microvascular endothelial cells. MoZ. Cell. Biochem. 88: 59-64,1989. SPAHR, R., I. PROBST, AND H. M. PIPER. Substrate utilization of adult cardiac myocytes. Basic Res. CurdioZ. 80: 53-56,1985.

ACID

533. 534. 535. 536.

537.

538.

539.

540.

541.

542.

543.

544.

545.

546.

547.

548.

549.

550.

551.

552.

553.

554.

555.

HOMEOSTASIS

937

SPECTOR, A. A. The transport and utilization of free fatty acid. Ann. NY Acad. Sci. 149: 768-783,1968. SPECTOR, A. A. Metabolism of free fatty acids. Prog. Biochem. Pharmacob 6: 130-176, 1971. SPECTOR, A. A. Plasma lipid transport. C&n. Physiol. Biochem. 2: 123-134, 1984. SPECTOR, A. A., AND J. E. FLETCHER. Transport of fatty acid in the circulation. In: Disturbances in Lipid and Lipoprotein Metabolism, edited by J. M. Dietschy, A. M. Gotto, and J. A. Ontko. Bethesda, MD: Am. Physiol. Sot., 1978, p. 229-249. SPECTOR, A. A., J. E. FLETCHER, AND J. D. ASHBROOK. Analysis of long-chain free fatty acid binding to bovine serum albumin by determination of stepwise equilibrium constants. Biochemistry 10: 3229-3232,197l. SPENER, R., T. BORCHERS, AND M. MURKERJEA. On the role of fatty acid binding proteins in fatty acid transport and metabolism. FEBS Lett. 244: l-5, 1989. SPITZER, J. J. Effect of lactate infusion on canine myocardial free fatty acid metabolism in vivo. Am. J. PhysioZ. 226: 213-217, 1974. SPITZER, J. J., AND J. A. SPITZER. Myocardial metabolism in dogs during hemorrhagic shock. Am. J. Physiol. 222: 101-105, 1972. SRIMANI, B. N., R. M. ENGELMAN, R. JONES, AND D. K. DAS. Protective role of intracoronary fatty acid binding protein in ischemit and reperfused myocardium. Circ. Res. 66: 1535-1543,199O. STAHL, G. L., Z.-I. TERASHITA, AND A. M. LEFER. Role of platelet activating factor in propagation of cardiac damage during myocardial ischemia. J. PharmacoZ. Exp. Ther. 244: 898-904, 1988. STAM, H., W. A. P. BREEMAN, AND W. C. HULSMANN. Neutral lipase of rat heart: an inducible enzyme? Biochem. Biophys. Res. Commun. 104: 333-339,1982. STAM, H., S. BROEKHOVEN-SCHOKKER, AND W. C. HULSMANN. Characterization of mono-, di- and triacylglycerol lipase activities in the isolated rat heart. Biochim. Biophys. Acta 875: 76-86,1986. STAM, H., S. BROEKHOVEN-SCHOKKER, AND W. C. HULSMANN. Studies on the involvement of lipolytic enzymes in endogenous lipolysis of the isolated rat heart. Biochim. Biophys. Acta 875: 87-96, 1986. STAM, H., AND W. C. HULSMANN. The role of endogenous catecholamine in the depressive effects of free fatty acids on isolated, perfused rat hearts. Basic Res. Curdiol. 73: 208-219, 1978. STAM, H., AND W. C. HULSMANN. Release of lipolytic products from rat heart. Hormonal stimulation, intracardial origin and pharmacological modification. Biochem. Intern. 2: 477-484,198l. STAM, H., AND W. C. HULSMANN. Effects of hormones, amino acids and specific inhibitors on rat heart during lipoprotein lipase and tissue lipase activities during long-term perfusion. Biochim. Biophys. Acta 794: 72-82,1984. STAM, H., AND W. C. HULSMANN. Regulation of lipases involved in the supply of substrate fatty acids for the heart. Eur. Heart J. 6: 158-167,1985. STAM, H., W. C. HULSMANN, J. F. JONGKIND, A. M. M. VAN DER KRAAIJ, AND J. F. KOSTER. Endothelial lesions, dietary composition and lipid peroxidation. Eicosanoids 2: 1-14, 1989. STAM, H., H. JANSSEN, AND W. C. HULSMANN. Distribution of chylomicron-degradation products in the isolated, perfused rat heart. Biochem. Biophys. Res. Commun. 96: 899-906,198O. STAM, H., AND J. F. KOSTER. Fatty acid peroxidation in ischemia. In: Prostaglandins and Other Eicosanoids in the CardiovascuZar System, edited by K. Schror. Basel: Karger, 1985, p. 131-148. STAM, H., K. SCHOONDERWOERD, W. BREEMAN, AND W. C. HULSMANN. Effects of hormones, fasting and diabetes on triglyceride lipase activities in rat heart and liver. Horm. Metab. Res. 16: 293-297, 1984. STAM, H., K. SCHOONDERWOERD, AND W. C. HULSMANN. Synthesis, storage and degradation of myocardial triglycerides. Basic Res. Cardiol. 82, SuppC 1: 19-28, 1987. STANKIEWICZ-CHOROSZUCHA, B., AND J. GORSKI. Effect of substrate supply and beta-adrenergic blockade on heart glycogen


938

VAN

DER

VUSSE,

GLATZ,

and triglyceride utilization during exercise in the rat. Eur. J. Appl. Ph ysiol. 43: 11-17, 1980. 556. STEENBERGEN, C., AND R. B. JENNINGS. Relationship between lysophospholipid accumulation and plasma membrane injury during total in vitro ischemia in dog heart. J. Mol. CeZZ. Cardial. 16: 605-621, 1984. 557. STEENBERGEN, C., E. MURPHY, L. LEVY, AND R. E. LONDON. Evaluation of cytosolic free calcium concentration early in myocardial ischemia in perfused rat heart. Circ. Res. 60: 700-707, 1987. 558. STEIN, O., AND Y. STEIN. Lipid synthesis, intracellular transport and storage. III. Electron microscopic radio-autographic study of the rat heart perfused with tritiated oleic acid. J. Cell BioZ. 36: 63-77, 1968. 559. STEWART, A. G., AND P. J. PIPER. Platelet-activating factor and the cardiovascular system: involvement in cardiac anaphylaxis. Prog. Biochem. Pharmucob 22: 132-140, 1988. 560. STORCH, J., AND N. M. BASS. Transfer of fluorescent fatty acids from liver and heart fatty acid-binding proteins to model membranes. J. Biol. Chem. 265: 7827-7831,199O. 561. STREMMEL, W. Fatty acid uptake by isolated rat heart myocytes represents a carrier-mediated transport process. J. Clin. Invest. 81: 844-852, 1988. 562. SUYATNA, F. D., P. P. VAN VELDHOVEN, M. BORGERS, AND G. P. MANNAERTS. Phospholipid composition and amphiphile content of isolated sarcolemma from normal and autolytic rat myocardium. J. Mol. Cell. Cardiol. 20: 47-62, 1988. 563. SUZUKI, Y., T. KAMIKAWA, A. KOBAYASHI, V. MASUMARA, AND N. YAMAZAKI. Effects of L-carnitine on tissue levels of acyl carnitine, acyl coenzyme A and high energy phosphate in ischemic dog heart. Jpn. Circ. J. 45: 687-694, 1981. 564. SWANSON, J. E., AND J. E. KINSELLA. Dietary n-3 polyunsaturated fatty acids: modification of rat cardiac lipids and fatty acid composition. J. Nutr. 116: 514-523, 1986. 565. SWIFT, A. M., M. KARMAZYN, D. F. HORROBIN, M. S. MANKU, R. A. KARMALI, R. 0. MORGAN, AND A. I. ALLY. Low prostaglandin concentration causes cardiac rhythm disturbances. Effects reversed by low levels of copper or chloroquine. Prosttsglundins 15: 651-657, 1978. 566. TAEGTMEYER, H. Carbohydrate interconversions and energy production. Circulation 72, Supple. IV: l-8, 1985. 567. TAM, S. W., R. Y. K. MAN, AND P. C. CHOY. The hydrolysis of phosphatidylcholine by phospholipase A, in hamster heart. C’uy~. J. Biochem. 62: 1269-1274, 1984. 568. TAMARGO, J., C. DELGADO, J. DIEZ, AND E. DELPON. Cardiac electrophysiology of PAF-acether and PAF-acether antagoBiology, Phurmucolog y und nists. In: GingolidesChemistry, CZi~~licctZ Perspectives, edited by P. Braquet. Barcelona, Spain: Prous, 1988, p. 417-431. 569. TAMBOLI, A., P. O’LOONEY, M. VANDERMATEN, AND G. V. VAHOUNY. Comparative metabolism of free and esterified fatty acids by the perfused rat heart and rat cardiac myocytes. Biochim. Biophys. Acta 750: 404-410, 1983. E., J. LEONARDI, H. LAFONT, AND G. NALBONE. 570. TERMINE, Intracellular phospholipase activity in rat heart. Comparison between endogenous and exogenous substrates. Bioch,emie 69: 245248,1987. 571.

572.

573.

574.

575

TIPPING, E., AND B. KETTERER. The influence of soluble binding proteins on lipophile transport and metabolism in hepatocytes. Biochem. J. 195: 441-452, 1981. TRACH, V., E. BUSCHMANS-DENKEL, AND W. SCHAPER. Relationship between lipolysis and glycolysis during ischemia in the isolated rat heart. Basic Res. Cardiol. 81: 454-464, 1986. TSCHUBAR, F., H. ROSE, AND H. KAMMERMEIER. The influence of the capillary wall and dissociation rate of fatty acid-albumin complex on myocardial uptake and release (Abstract). J. Mol. Cell. Ca,rdiol. 21, Suppl. IV: S71, 1989. URSELL, P. C., P. I. GARDNER, A. ARBALA, J. J. FENOGLIO, AND A. L. WIT. Structural and electrophysiological changes in the epicardial border zone of canine myocardial infarcts during infarct healing. Circ. Res. 56: 436-451, 1985. M., W. ENGELS, G. J. VAN DER VUSSE, AND . VAN BILSEN,

STAM,

576.

AND

RENEMAN

Volume

?Z

R. S. RENEMAN. Significance of myocardial eicosanoid production. Mol. Cell. Bioch,em. 88: 113-122, 1989. VAN BILSEN, M., W. ENGELS, P. H. M. WILLEMSEN, W. A. COUMANS, G. J. VAN DER VUSSE, AND R. S. RENEMAN. Arachidonic acid accumulation and eicosanoid synthesis during ischemia and reperfusion in isolated rat heart. Prog. AppI. Microcirc. 12:255-262,1987.

VAN BILSEN, M., C. P. M. REUTELINGSPERGER, AND G. J. VAN DER VUSSE. Are annexins involved in cardiac phospholipid metabolism? (Abstract). J Mol. Cell Curdiol. 23, Suppl. V: s51,1991. 578. VAN BILSEN, M., G. J. VAN DER VUSSE, W. A. COUMANS, M. J. M. DE GROOT, P. H. M. WILLEMSEN, AND R. S. RENEMAN. Degradation of adenine nucleotides in ischemic and reperfused rat heart. Am. J Physiol. 257 (Heart Circ. Physiol. 26): H47H54, 1989. 579. VAN BILSEN, M., G. J. VAN DER VUSSE, P. H. M. WILLEMSEN, W. A. COUMANS, T. H. M. ROEMEN, AND R. S. RENEMAN. Lipid alterations in isolated, working rat hearts during ischemia and reperfusion: its relation to myocardial damage. Circ. Res. 64: 304-314, 1989. 580. VAN BILSEN, M., G. J. VAN DER VUSSE, P. H. M. WILLEMSEN, W. A. COUMANS, T. H. M. ROEMEN, AND R. S. RENEMAN. Effects of nicotinic acid and mepacrine on fatty acid accumulation and myocardial damage during ischemia and reperfusion. J. Mol. Cell Curdiol. 22: 155-163, 1990. 581. VAN DEN BOSCH, H. Intracellular phospholipases A. Biochim. Biophys. Acta 604: 191-246, 1980. G. J. Myocardial free fatty acids under nor582. VAN DER VUSSE, moxie and ischemic circumstances. J. Drug Res. 8: 1578-1584, 1983. DER VUSSE, G. J., T. ARTS, J. F. C. GLATZ, AND R. S. 583. VAN RENEMAN. Transmural differences in energy metabolism of the left ventricular myocardium: fact or fiction. J. 1Mol. Cell. Cardiol. 22: 23-37, 1990. 584. VAN DER VUSSE, G. J., M. J. M. DE GROOT, P. H. M. WILLEMSEN, M. VAN BILSEN, A. H. G. J. SCHRIJVERS, AND R. S. RENEMAN. Degradation of phospholipids and triacylglycerol, and accumulation of fatty acids in anoxic myocardial tissue, disrupted by freeze-thawing. Mol. Cell. Biochem. 88: 83-90, 1989. 585. VAN DER VUSSE, G. J., S. E. LITTLE, AND J. B. BASSINGTHWAIGHTE. Transendothelial transport of arachidonic acid and palmitic acid in the isolated rabbit heart (Abstract). J. Mol. Cell. Cwdiol. 19, Suppl. III: SlOO, 1987. 586. VAN DER VUSSE, G. J., F. W. PRINZEN, AND R. S. RENEMAN. Disturbances in myocardial lipid homeostasis during ischemia and reperfusion. In: Activution, Metcdxdisnz and Reperfusion of the Heurt. Sirrmlution und Experimental Models, edited by S. Sideman and R. Beyar. Dordrecht, The Netherlands: Nijhoff, 1987, p. 577.

665-682.

VAN DER VUSSE, G. J., F. W. PRINZEN, M. VAN BILSEN, W. ENGELS, AND R. S. RENEMAN. Accumulation of lipids and lipid-intermediates in the heart during ischemia. Basic Res. Curdiol. 82, Suppl. 1: 157-167, 1987. 588. VAN DER VUSSE, G. J., AND R. S. RENEMAN. Glycogen and lipids (endogenous substrates). In: Cardiac Metabolism, edited by A. J. Drake-Holland and M. I. M. Noble. Chichester, UK: Wiley, 1983, p. 215-237. G. J., AND R. S. RENEMAN. The myocardial 589. VAN DER VUSSE, non-esterified fatty acid controversy. J. Mol. Cell. Cardiol. 16: 587.

677-682,1984.

590. VAN DER VUSSE, G. J., T. H. M. ROEMEN, W. FLAMENG, AND R. S. RENEMAN. Serum-myocardium gradients of non-esterified fatty acids in dog, rat and man. Biochim. Biophys. Acta 752: 361-370,1983.

591.

VAN DER VUSSE, G. J., T. H. M. ROEMEN, F. W. PRINZEN, W. A. COUMANS, AND R. S. RENEMAN. Uptake and tissue content of fatty acids in dog myocardium under normoxic and ischemic conditions. Circ. Res. 50: 538-546, 1982. G. J., T. H. M. ROEMEN, AND R. S. RENE592. VAN DER VUSSE, MAN. Assessment of fatty acids in dog left ventricular myocardium. Biochim. Biophys. Actu 617: 347-352, 1980. G. J., T. H. M. ROEMEN, AND R. S. RENE593. VAN DER VUSSE,


October

594.

595.

596.

597.

598.

599.

600.

1992

MYOCARDIAL

FATTY

MAN. The content of non-esterified fatty acids in rat myocardial tissue. A comparison between the Dole and Folch extraction procedures. J. Mol. Cell. Cardiol. 17: 527-531, 1985. VAN DER VUSSE, G. J., M. VAN BILSEN, AND R. S. RENEMAN. Is phospholipid degradation a critical event in ischemiaand reperfusion-induced damage? News Ph,ysioZ. Sci. 4: 49-53, 1989. VAN DER VUSSE, G. J., M. VAN BILSEN, T. SONDERKAMP, AND R. S. RENEMAN. Hydrolysis of phospholipids and cellular integrity. In: Path.ophysiology oj’severe Ischemic Myocardial Injury, edited by H. M. Piper. Dordrecht, The Netherlands: Kluwer, 1990, p. 167-193. VAN DER WALL, E. E., G. WESTRA, M. J. VAN EENIGE, S. SCHOLTABERS, F. C. VISSER, W. DEN HOLLANDER, AND J. P. ROOS. Influence of propranolol on uptake of radioiodinated heptadecanoic acid and thallium-201 in the dog heart. Eur. J Nucl. Med. 8: 454-457, 1983. VASDEV, S. C., AND K. J. KAKO. Incorporation of fatty acids into rat heart lipids. In vivo and in vitro studies. J. Mol. Cell. Cardiol. 9: 617-631, 1977. VASDEV, S. C., K. J. KAKO, AND G. P. BIRO. Phospholipid composition of cardiac mitochondria and lysosomes in experimental myocardial ischemia in the dog. J. Mol. Cell. Cardiol. 11: 11951200, 1979. VEERKAMP, J. H., J. F. C. GLATZ, AND A. J. M. WAGENMAKERS. Metabolic changes during cardiac maturation. Basic Res. Curdiol. 80, Szqpl. 2: 111-114, 1985. VEERKAMP, J. H., R. A. PEETERS, AND R. G. H. J. MAATMAN. Structural and functional features of different types of cytoplasmic fatty acid binding proteins. Biochim. Biophys. Acta 1081:1-24,199l.

VEERKAMP, J. H., AND H. T. B. VAN MOERKERK. Peroxisoma1 fatty acid oxidation in rat and human tissues. Effect of nutritional state, clofibrate treatment and postnatal development in the rat. Biochim. Biophys. Acta 875: 301-310, 1986. 602. VEMURI, R., M. MERSEL, M. HELLER, AND A. PINSON. Studies on oxygen and volume restriction in cultured cardiac cell: possible rearrangement of sarcolemmal lipid moieties during anoxia and ischemia-like states. Mol. Cell. Biochem. 79: 39-46,1988. A. J., AND J. A. POST. Physico-chemical properties 603. VERKLEY, and organization of lipids in membranes: their possible role in myocardial injury. Basic Rex Cardiol. 82, Suppl. 1: 85-91, 1987. N. J., W. ADAMS, R. C. STRANGE, AND M. F. 604. VETTER, OLIVER. Initial metabolic and hormonal response to acute myocardial infarction. Lancet 1: 284-288, 1974. 605. VICTOR, T., C. LA COCK, AND A. LOCHNER. Myocardial tissue free fatty acids. J. Mol. Cell. Cardiol. 16: 709-721, 1984. 606. VICTOR, T., N. VAN DER MERWE, A. J. S. BENADE, C. LA COCK, AND A. LOCHNER. Mitochondrial phospholipid composition and microviscosity in myocardial ischemia. Biochim. Bioph ya. Actn 834: 215-223, 1985. 607. VIK-MO, H., AND 0. D. MJ0S. Influence of free fatty acids on myocardial oxygen consumption and ischemic injury. Am. J. Cardial. 48: 361-365, 1981. 608. VIK-MO, H., 0. D. MJOS, M. D. JAMES, R. J. NEELY, P. R. MAROKO, AND L. G. T. RIBEIRO. Limitation of myocardial infarct size by metabolic interventions that reduce accumulation of fatty acid metabolites in ischemic myocardium. Am. Heart J. 111: 1048-1054,1986. 609. VIK-MO, H., 0. D. MJOS, R. A. RIEMERSMA, AND M. F. OLIVER. Importance of ischemic induced myocardial lipolysis in dogs. A&U. Physiol. Sci. 8: 121-128, 1980. 610. VIK-MO, H., P. MOEN, AND 0. D. MJ0S. Myocardial lipoprotein lipase activity during acute myocardial ischemia in dogs. Harm. Metab. Rex 14: 85-88, 1982. 611. VIK-MO, H., R. A. RIEMERSMA, 0. D. MJOS, AND M. F. OLIVER. Effect of myocardial ischaemia and antilipolytic agents on lipolysis and fatty acid metabolism in the in situ dog heart. Scnnd. J. Clin. Lab. Invest. 39: 559-568, 1979. 612. VISSER, F. C., C. M. B. DUWEL, M. J. VAN EENIGE, J. P. ROOS, F. F. KNAPP, AND G. J. VAN DER VUSSE. Biochemistry of radioiodinated non-esterified fatty acids. Mol. Cell. Biochem. 88: 185-190, 1989. 601.

ACID

613.

614.

615.

616.

HOMEOSTASIS

939

VISSER, F. C., M. J. VAN EENIGE, C. M. B. DUWEL, AND J. P. ROOS. Radio-iodinated free fatty acids: can we measure myocardial metabolism? Eur. J. Nucl. Med. 12, Suppl.: S20-S23, 1986. VISSER, F. C., G. WESTERA, M. J. EENIGE, AND E. E. VAN DER WAL. The myocardial elimination rate of radioiodinated heptadecanoic acid. Eur. J. Nucl. Med. 10: 118-122, 1985. VORK, M. M., J. F. C. GLATZ, D. A. M. SURTEL, H. J. M. KNUBBEN, AND G. J. VAN DER VUSSE. A sandwich enzyme linked immuno-sorbent assay for the determination of rat heart fatty acid-binding protein using the streptavidin-biotin system. Application to tissue and effluent samples from normoxic rat heart perfusion. Biochim. Biophys. Acta 1075: 199-205, 1991. VORK, M. M., J. F. C. GLATZ, D. A. M. SURTEL, AND G. J. VAN DER VUSSE. Assay of the binding of fatty acid by proteins: evaluation of the Lipidex 1000 procedure. Mol. CeU Biochem. 98: 113120,199o.

WALLNER, B. P., R. J. MATTALIANO, C. HESSION, R. L. CATE, R. TIZARD, L. K. SINCLAIR, C. FOELLER, E. P. CHOW, J. L. BROWNING, K. L. RAMCHANDRAN, AND R. B. PEPINKSY. Cloning and expression of human lipocortin, a phospholipase A, inhibitor with potential anti-inflammatory activity. Nature Lond. 320: 77-81,1986. 618. WALPURGER, G. Cytoplasmatische und mitochondrial Enzymen in der postnatelen Entwicklung des Rattenherzens. Klin. Wochenschr. 45: 239-244, 1967. 619. WANG, H., K. RASMUSSEN, H. VIK-MO, 0. D. MJOS, AND H. GRENDAHL. Influence of high plasma concentrations of free fatty acids on heart rhythm in healthy fasting men. Acta Med. Stand. 205: 299-301, 1979. 620. WANG, T. W., L. A. MENAHAN, AND J. J. LECH. Subcellular localization of enzymes, lipase and triglycerides in rat heart. J. Mol. Cell. Cardiol. 9: 25-38, 1977. 621. WARD, B., J. GLOSTER, AND P. HARRIS. The incorporation and distribution of 3H oleic acid in the isolated, perfused guinea-pig heart: a biochemical and EM autoradiographic study. Tissue CeZZ 11: 793-801, 1979. 622. WARD, B., AND P. HARRIS. Incorporation and distribution of 3H oleic acid in the isolated, perfused guinea-pig heart made hypoxic. J. Mol. Cell. Cardiol. 16: 765-770, 1984. 623. WARSHAW, J. B. Cellular energy metabolism during fetal development. IV. Fatty acid activation, acyl transfer and fatty acid oxidation during development of the chick and rat. Dev. Bioh 28: 617.

537-544,1972.

WARSHAW, J. B., AND M. L. TERRY. Cellular energy metabolism during fetal development. II. Fatty acid oxidation by the developing heart. J. Cell Biol. 44: 354-360, 1970. 625. WARTMAN, W. B., R. B. JENNINGS, H. 0. TOKOYAMA, AND G. F. CLABAUGH. Fatty change of the myocardium in early experimental infarction. Arch. Pathol. 62: 318-323,1956. 626. WEGLICKI, W. B., B. F. DICKENS, AND I. T. MAK. Enhanced lysosomal phospholipid degradation and lysophospholipid production due to free radicals. Biochem. Biophys. Res. Commun. 124: 229-235,1984. 627. WEGLICKI, W. B., AND M. G. LOW. Phospholipases of the myocardium. Basic Res. Cardiol. 87, Suppl. 1: 107-112, 1987. 628. WEGLICKI, W. B., K. OWENS, C. W. URSCHEL, J. R. SERUR, AND E. H. SONNENBLICK. Hydrolysis of myocardial lipids during acidosis and ischemia. Recent Adv. Stud. Card. Struct. Metab. 3: 781-793, 1973. 629. WEGLICKI, W. B., M. WAITE, P. SISSON, AND P. SHOLET. Myocardial phospholipase A of microsomal and mitochondrial fractions. Biochim. Biophys. Acta 231: 512-519,197l. 630. WEGLICKI, W. B., B. M. WAITE, AND A. C. STAM. Association of phospholipase A with a myocardial membrane preparation containing the (Na’-K+)-ATPase. J. Mol. Cell. Cardioh 4: 195-201, 1972 631. WEISHAAR, R. E., J. S. M. SARMA, Y. MARUYAMA, R. FISHER, AND R. J. BING. Regional blood flow, contractility and metabolism in early myocardial infarction. Cardiology 62: 2-20, 1977. 632. WEISHAAR, R. E., G. V. TSCHURTSCHENTHALER, K. ASHIKAWA, AND R. J. BING. The relationship of regional coronary 624.


940

633.

634.

635.

636.

637.

VAN DER VUSSE, GLATZ, blood flow to mitochondrial function during reperfusion of the ischemic myocardium. CardioZo~y 64: 350-365,1979. WEISIGER, R. A., J. GOLLAN, AND R. K. OCKNER. Receptor for albumin on the liver cell surface may mediate uptake of fatty acids and other albumin-bound substances. Science Wash. DC 211: 104%1051,198l. WEISIGER, R. A., AND W.-L. MA. Uptake of oleate from albumin solutions by rat liver. Failure to detect catalysis of the dissociation of oleate from albumin by an albumin receptor. J. Clin. Invest. 79: 1070-1077, 1987. WEISIGER, R. A., S. M. POND, AND L. BASS. Albumin enhances unidirectional fluxes of fatty acid across a lipid-water interface: theory and experiments. Am. J. Physiol. 257 (Gastrointest. Liver PhysioL. 20): G904-G916,1989. WEISS, R. G., V. P. CHACKO, AND G. GERSTENBLITH. Fatty acid regulation of glucose metabolism in the intact beating rat heart assessed by carbon-13 NMR spectroscopy: the critical role of pyruvate dehydrogenase. J. 2Mol. CeLI.CurdioZ. 21: 469-478,1989. WELTZIEN, H. U. Cytolytic and membrane-perturbing properties of lysophosphatidylcholine. Biochim. Biophys. Acta 559: 259-

STAM,

639. 640.

641.

642.

643.

644.

645. 646.

647.

WENNMALM, A. Nicotine stimulates prostaglandin formation in the rabbit heart. Br. J. PharmacoZ. 59: 95-100,1977. WERNER, J. C., R. E. SICARD, AND H. G. SCHULER. Palmitate oxidation by isolated working fetal and newborn pig hearts. Am. J Physiol. 256 (Endocrinol. Metab. 19): E315-E321,1989. WERNER, J. C., V. WHITMAN, R. R. FRIPP, H. G. SCHULER, J. MUSSELMAN, AND R. L. SHAM. Fatty acid and glucose utilization in isolated, working fetal pig hearts. Am. J. Physiol. 245 (Endocrinol. Metab. 8): El9-E23, 1983. WETTERAU, J. R., K. A. COMBS, S. N. SPINNER, AND B. J. JOINER. Protein disulfide isomerase is a component of the microsomal triglyceride transfer protein complex. J. BioZ. Chem. 262: 9800-9807,199O. WETTERAU, J. R., AND D. B. ZILVERSMIT. Localization of intracellular triacylglycerol and cholesterylester transfer activity in rat tissues. Biochim. Biophys. Acta 875: 610-617,1986. WETZEL, M. G., AND R. 0. SCOW. Lipolysis and fatty acid transport in rat heart: electron microscopic study. Am. J. Physiol. 246 (CeZZ Physiol. 15): C467-C485, 1984. WHEELDON, L., Z. SCHUMERT, AND D. A. TURNER. Lipid composition of heart muscle homogenate. J. Lipid Res. 6: 481-489, 1965. WHEREAT, A. F. Fatty acid biosynthesis in aorta and heart. Adv. Lipid Res. 9: 119-159, 1971. WHITMER, J. T., J. A. IDELL-WENGER, M. J. ROVETTO, AND J. R. NEELY. Control of fatty acid metabolism in ischemic and hypoxic hearts. J. BioL Chem. 251: 4305-4309, 1978. WHITTY, A. M., M. J. DOMINO, B. A. ELFONT, G. W. HUGHES, AND M. W. REPECK. Transmural mitochondrial differences in myocardium. Recent Adv. Stud. Card. Struck Metab. 11: 349-354,1978.

Volume

72

WILLEBRANDS, A. F., H. F. TER WELLE, AND S. J. A. TASSERON. The effect of a high molar FFA/albumin ratio in the perfusion medium on rhythm and contractility of the isolated rat heart. J. Mol. Cell. Cardiol. 5: 259-273, 1973. 649. WIRTZ, K. W. A. Phospholipid transfer proteins. In: Lipid-Protein Interactions, edited by P. C. Jost and 0. K. Griffith. New York: Wiley, 1982, vol. 1, p. 151-231. JR. Properties and 650. WIRTZ, K. W. A., AND T. W. J. GADELLA, modes of action of specific and non-specific phospholipid transfer proteins. Exiperientia BaseZ46: 592-599,199O. 651. WISNESKI, A. J., E. W. GERTZ, R. A. NEESE, AND M. MAYR. Myocardial metabolism of free fatty acids. J. Clin. Invest. 79: 359648.

366,1987.

WITTELS, B., AND R. BRESSLER. Lipid metabolism in the newborn heart. J. Clin. Invest. 44: 1639-1646,1965. 653. WOJTCZAK, L., AND A. B. WOJTCZAK. Uncoupling of oxidative phosphorylation and inhibition of ATP-Pi exchange by a substance from insect mitochondria. Biochim. Biophys. Acta 39: 277652.

286,196O. 654.

287,1979. 638.

AND RENEMAN

655.

656.

657.

658.

659. 660.

661. 662. 663.

WOLDEGIORGIS, G., AND E. SHRAGO. The recognition of two specific binding sites of the adenine nucleotide translocase by palmitoyl CoA in bovine heart mitochondria and submitochondrial particles. Biochem. Biophys. Res. Commun. 89: 837-844, 1979. WOLF, R. A. Cardiolipin-sensitive phospholipase C in subcellular fractions of rabbit myocardium. Am. J. Physioh 257 (Cell Physiol. 26): C926-C935, 1989. WOLF, R. A., AND R. W. GROSS. Identification of neutral active phospholipase C which hydrolyses choline glycerophospholipids and plasmalogen selective phospholipase A, in canine myocardium. J. Biol. Chem. 260: 7295-7303, 1985. WOLFE, R. G., C. V. MAXWELL, AND E. C. NELSON. Effect of age and dietary fat level on fatty acid oxidation in the neonatal pig. J. Nutr. 108: 1621-1634, 1978. WOLKOWICZ, P. E., H. J. POWNALL, AND J. B. McMILLINWOOD. (1-Pyrenebutyryl)carnitine and 1-pyrenebutyryl coenzyme A: fluorescent probes for lipid metabolite studies in artificial and natural membranes. Biochemistry 21: 2990-2996,1982. WOOD, J. M., A. E. HUTCHINGS, AND N. BRACHFELD. Lipid metabolism in myocardial cell-free homogenates. J. MoZ. Cell. CurdioZ. 4: 97-111, 1972. YANAGISHITA, T., N. KONNO, E. GOSHI, AND T. KATAGIRI. Alterations in phospholipids in acute ischemic myocardium. Jpn. Circ. J 5: 41-50, 1987. ZELINSKI, T. A., J. D. SAVARD, R. Y. K. MAN, AND P. C. CHOY. Phosphatidylcholine biosynthesis in isolated hamster hearts. J. Biol. Chem. 255: 11423-11428,198O. ZIERLER, K. L. Fatty acids as substrates for heart and skeletal muscle. Circ. Res. 38: 459-463, 1976. ZIMMERMAN, G. A., T. M. MCINTYRE, AND S. M. PRESCOTT. Production of platelet-activating factor by human vascular endothelial cells. Evidence for a requirement for specific agonists and modulation by prostacyclin. CircuZation 72: 718-727, 1985.


Release of fatty acid-binding protein from ischemic-reperfused rat heart and its prevention by mepacrine.

Plasma phospholipids indicate impaired fatty acid homeostasis in preterm infants.

Normoxic and hyperoxic cardiopulmonary bypass in congenital heart disease.

Fatty acid metabolism via triglyceride in the salmon heart.

Survivin expression pattern in the intestine of normoxic and ischemic rats.

Ischemic biomarker heart-type fatty acid binding protein (hFABP) in acute heart failure - diagnostic and prognostic insights compared to NT-proBNP and troponin I.

Fatty acid and glucose oxidation by cultured rat heart cells.

Cyp1b1 affects external control of mouse hepatocytes, fatty acid homeostasis and signaling involving HNF4α and PPARα.

Immunohistochemical studies on the localisation and ontogeny of heart fatty acid binding protein in the rat.

A sandwich enzyme linked immuno-sorbent assay for the determination of rat heart fatty acid-binding protein using the streptavidin-biotin system. Application to tissue and effluent samples from normoxic rat heart perfusion.

Electron microscopic observations and acid phosphatase activity in the ischemic rat heart.

Correction: Functional Analysis of Free Fatty Acid Receptor GPR120 in Human Eosinophils: Implications in Metabolic Homeostasis.

Functional analysis of free fatty acid receptor GPR120 in human eosinophils: implications in metabolic homeostasis.

Effects of carnitine in ischemic and fatty acid supplemented swine hearts.

Liver PPARα is crucial for whole-body fatty acid homeostasis and is protective against NAFLD.

Role of carnitine in fatty acid metabolism of normal and ischemic myocardium.

Revision of the amino acid sequence of human heart fatty acid-binding protein.

Heart-type fatty acid-binding protein (H-FABP) and coronary heart disease.

Contributions of colonic short-chain Fatty Acid receptors in energy homeostasis.

Chloroform and Fatty Heart.

Phosphorus nuclear magnetic resonance studies on normoxic and ischemic cardiac tissue.

A comparison of heart and liver fatty acid-binding proteins: interactions with fatty acids and possible functional differences studied with fluorescent fatty acid analogues.

Ischemic heart disease and the Mediterranean diet.

Targeting acid sphingomyelinase reduces cardiac ceramide accumulation in the post-ischemic heart.