Coupling mechanisms in airway smooth muscle.

Coupling

mechanisms

in airway smooth muscle

R. F. COBURN AND C. B. BARON Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104

COBURN, R. F., AND C. B. BARON. Coupling mechanisms in airway smooth muscle. Am. J. Physiol. 258 (Lung Cell. Mol. Physiol. 2): L119L133, 1990.-This review documents available information about coupling mechanisms involved in airway smooth muscle force development and maintenance and relaxation of force. Basic concepts, obtained from experiments performed on many different mammalian cell types, are in place regarding coupling between surface membrane receptors and cell function; these concepts are considered as a framework for understanding coupling between receptors and contractile proteins in smooth muscles and in airway smooth muscles. We have divided various components of coupling mechanisms into those dependent on changes in the surface membrane potential (electromechanical coupling) and those independent of the surface membrane potential (pharmacomechanical coupling). We have, to some degree, emphasized modulation of coupling mechanisms by intrasurface membrane microprocessing or by second messengers. A challenge for the future is to obtain a better understanding of how coupling mechanisms are altered or modulated during different phases of contractions evoked by a single agonist and under conditions of multiple agonist exposure to airway smooth muscle cells. electromechanical coupling; pharmacomechanical inosital phospholipids; airway smooth muscle

IN THIS REVIEW is to document available information about coupling mechanisms involved in force generation, maintenance, and relaxation of airway smooth muscles. Neurotransmitters and other mediators bind to receptors initiating signals directed to ion channels and second messenger-generating mechanisms that control cross-bridge function. In this review we are concerned primarily with airway smooth muscle, but will also review pertinent data obtained from other smooth muscle and other cell types. We will divide the topic into coupling mechanisms dependent on surface membrane potential changes (electromechanical coupling, EMC) and coupling mechanisms that utilize membrane potential-independent mechanisms (pharmacomechanical coupling, PMC). Our goal is to emphasize basic concepts, rather than cover details of effects of many different mediators. We have not discussed many areas of this topic in any detail, including the following: controversies regarding genesis of the latch state and control of crossbridge events, structure-function of receptors, guanine nucleotide regulatory proteins (G proteins) or ion channels, control of guanosine cyclic monophosphate (cGMP) OUR GOAL

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coupling;

ion channels;

and adenosine 3’,5’-cyclic monophosphate (CAMP) second messenger systems, or the role of the epithelium in controlling airway smooth muscle tone. Figures 1 and 2 illustrate, in skeleton form, events involved in coupling extracellular signals to contractile proteins inferred from data obtained using many different tissues (23, 129). These schema indicate EMC and PMC mechanisms that deliver Ca”+ into the cell cytosolic compartment. Increases in intracellular Ca2+ ( [Ca2+]J activate myosin light chain kinase that catalyzes phosphorylation of the myosin light chain, activation of actomyosin ATPase, and contraction (122). Surface membrane mechanisms operating during EMC include apparent G protein-mediated activation of channels effecting surface membrane depolarization, activation of voltagedependent Ca2+ channels, and influx of Ca2+ into the cell. Pharmacomechanical coupling is driven by G protein-activation of inositol phosphate metabolism with formation of the second messenger inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] that releases Ca2+ from the sarcoplasmic reticulum (S R). Thi .s mechanism also produces another established second messenger, 1J-diacyl-

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glycerol (DAG), an activator of protein kinase C. The schema shown in Figs. 1 and 2 serve as a framework of understanding possible mechanisms operative in airway smooth muscle to which details can be added with future studies. Not shown in Fig. 1 are other PMC mechanisms that provide the second messengers CAMP and cGMP and other possible coupling mechanisms discussed in this review. In contrast to skeletal muscle, which is largely controlled by nerve recruitment, airway smooth muscle is controlled by multiple neurotransmitters and mediators, perhaps explaining the complexity in coupling mechanisms. In addition, coupling mechanisms serve to amplify extracellular signals. The classification of smooth muscle coupling mechanisms into EMC and PMC is somewhat arbitrary. The development of the microelectrode measurement of the surface membrane potential led to the establishment of a role of membrane depolarization in muscle contraction, especially in smooth muscles, which show action potentials (30), and the concept that influx of Ca2+ across the plasma membrane can be dependent on membrane depolarization (65, 82). However, the finding that agonists could further contract smooth muscle almost completely depolarized in high extracellular K+-containing media (52) and the discovery that smooth muscles could contraci in Ca2+- $free media, or without membrane depolarization (49, 56, 156), established the concept that there is a membrane potential-independent process activating release of Ca2+ from intracellular stores. Early investigations using canine, or bovine trachealis muscle, described agonist-evoked membrane depolarization that is graded and does not evoke action potentials under normal conditions (39,42, 55, 100,108, 163). Over the last years, many different agonist-evoked contractions of various airway smooth muscles have been shown to be accompanied by membrane depolarization (3, 38, 39, 55, 100, 123, 125, 157, 163, 179). Larger ACh-induced contractions are produced in canine trachealis muscle for a given membrane depolarization than seen during K+-evoked contractions (39). K+-evoked contractions are completely reversed by current clamp reversal of membrane depolarization; however, during Ach-maintained force, current clamp-evoked

DAG

1(1,4,5>P3

FIG. 1, Schemata illustrating inositol phospholipid metabolism. PI, phosphatidylinositol; PIP, phosphatidylinositol-+phosphate; PIP2, phosphatidylinositol bisphosphate; PLC, phosphoinositide-specific phosphodiesterase; G, guanine nucleotide regulatory protein, I( 1,4,5)P3, inositol 1,4,5trisphosphate, DAG, l,%diacylglycerol.

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membrane hyperpolarization produced an initial contraction followed by a small relaxation; current clampevoked depolarization resulted in relaxation followed by a small contraction. These are inappropriate responses if membrane potential-gated surface membrane Ca2’ channels are the only potential-sensitive components that are determining force changes. It became established that Ca2+ originating in the extracellular space and in intracellular stores can both be utilized for force activation in airway smooth muscle (56, 100). The finding that Ach-evoked contractions are resistant to organic Ca2+ antagonist agents that block voltage-dependent Ca2’ channels, and that K+ contractions are completely inhibited by these drugs, has been used to support the operation of PMC mechanisms in various airway smooth muscles (2, 38). At the time of this review there have been major recent advances in our knowledge of coupling mechanisms in smooth muscle and airway smooth muscle, fueled by use of new technologies. These advances are the subject of this review. RECEPTORS

AND

G

PROTEINS

Discussion of coupling mechanisms can be subdivided into roles of receptors and G proteins and discussion of effector mechanisms. The reader is referred to a recent review by Gilman (63) for detailed information on G proteins. Heterotrimer G proteins that function in transmembrane signaling have a-, ,&, and y-subunits. The current state of knowledge in regard to coupling of receptors to effector mechanisms has been much influenced by work on the ,&adrenergic receptor, adenylate cyclase system (24). After receptor binding of agonist, a first step in transduction is dissociation of GDP from the cysubunit of the G protein followed by GTP binding to the same subunit. Loss of GDP is associated with receptor interaction with G protein. In the ,&adrenergic receptoradenylate cyclase system, GTP binding causes dissociation of G proteins into a- and P-7 subunits. GTP-bound G protein subunits can interact with appropriate effectors. Deactivation is controlled by GTP hydrolysis. Multiple G proteins, or forms of the same G protein, have been identified in various tissues. G, and Gi were identified as G proteins which activate or inactivate adenylate cyclase. Study of Gi function led to the concept that a G protein subunit produced as a result of agonist binding to one type of receptor could inhibit effector mechanisms not directly linked to this receptor, giving the first example of “cross talk.” The finding that G, can also activate surface membrane Ca2+ channels (180) introduced the concept that a single G protein can control more than one effector. Evidence of different G protein roles in activation of various ion channels and activation of inositol phospholipid-specific phospholipase C (PLC) are discussed in a later section of this review. A single receptor, or receptor subtype, can be coupled via different G proteins to multiple effector mechanisms (6). Different muscarinic receptor subtypes can couple to different effecters (137). There may be different affinities for binding of different muscarinic agonists to different muscarinic receptor subtypes (15). Muscarinic receptors with


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INTRACELLULAR C-KINASE A-KINASE G-KINASE Ca*+

SIGNALS:

FIG. 2. Electromechanical coupling; ion channels. A and B, basic mechanisms reflecting our present understanding of components of electromechanical coupling mechanisms: ion channels that are involved in depolarization the surface membrane and voltage-gated Ca2’ channels responsible for delivery of Ca2’ to cytosol. C and D, possible modulators of this system, including G protein modulation of voltage-gated Ca2+ channels and modulation by intracellular diffusable second messengers.

the same agonist affinity can interact with different efficiency with Gx and the G protein subunit which activates PLC (Gp) (29). An effector can be regulated by multiple G protein subunits (63, 181). G proteins can be visualized as an intrasurface membrane microprocessor (61) directing information between different receptors to ion channels and to enzymes that control production of diffusable, cytosolic second messengers, and release of Ca2+ from the SR. The receptor-G protein-effector interactions can be modified by phosphorylation of receptors (45, 90, 110, Ill, 114) or G proteins (144), adding further complexity to G protein microprocessing of receptor signals. Receptor phosphorylations have been reported to be mediated by CAMP-dependent protein kinase (111), protein kinase C (114), and endogenous kinase(s) (110). Phosphorylation of receptors, or associated structures, can alter agonist affinity, uncouple or desensitize, or change receptor density (11, 45, 111, 114). Little information is currently available about coupling of receptors to effector mechanisms in airway smooth muscle (or in smooth muscle, as well). A G protein has been identified in a vascular smooth muscle (98). A role of G proteins in activation of inositol phospholipid transduction system has been established using GTPyS in several different skinned smooth muscle preparations (101,129) and in an isolated membrane preparation (126). The established role of G protein subunits for control of surface membrane channels in other cells (180, 181) makes it very likely that similar mechanisms exist in airway smooth muscle and other smooth muscles. Probably the best studied contraction in airway smooth muscle is that evoked by

muscarinic agonists which activate 1) mechanisms that operate ion channels involved in membrane depolarization; 2) mechanisms that result in activation of inositol phospholipid metabolism; 3) mechanisms that elevate cGMP concentrations; 4) mechanisms that may operate or modulate surface membrane Ca2+ channels; 5) mechanisms that inhibit adenylate cyclase; and 6) mechanisms that release arachidonic acid and produce prostaglandins and other arachidonate metabolites (179). Much information is needed before we will be able to understand, in any detail, coupling between various muscarinic receptor subtypes, or other types of receptors, and effector mechanisms. Of the mechanisms listed here, only the study of cross talk between muscarinic receptors and adenylate cyclase has been studied in airway smooth muscle in any detail (74, 75, 92, 171, 172). PHARMACOMECHANICAL PHOSPHOLIPID

COUPLING: THE TRANSDUCTION SYSTEM

INOSITOL

We turn now to discussion of various effector mechanisms. The topic of PMC can be divided into agonistinduced mechanisms that contract smooth muscle and agonist-evoked mechanisms that relax smooth muscle. In this review, we concentrate on the inositol phospholipid transduction system (23, 99, 128, 177), which is activated by many different receptors as a major mechanism involved in effecting muscle contraction. Mechanisms that relax smooth muscle via formation of CAMP or cGMP appear to be membrane potential-independent mechanisms and, therefore, are classified under PMC. We will not cover extensive literature that relates to control of these mechanisms.


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Inositol phospholipid metabolism is activated in trachealis muscle during many different types of agonistinduced contractions (9, 11, 12, 33, 6’7-69, 78, 80). Although interactions between the surface membrane potential and inositol phospholipid metabolism have not been studied in detail, it appears the inositol phospholipid transduction mechanism is membrane potential independent (12, 67) and can be classified under PMC. Figure 1 illustrates the surface membrane inositol phospholipid reactions which produce Ins( 1,4,5)P3 and DAG. Phosphatidylinositol (PI) is unique among phospholipids in that the inositol head group has five hydroxyl groups and is the only phospholipid that can be further phosphorylated. The major components of this system include plasma membrane phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP), phosphatidylinositol 4,5bisphosphate ( PIP2), specific inositol phospholipid phosphodiesterase (phospholipase C, PLC), and a series of inositol phosphates, Ins(1,4,5)P3, Ins( 1,3,4)P3, Ins( 1,3,4,5)P4, Ins( 1,4)PZ, Ins(4)P, Ins( l)P, DAG, and others. Receptor-activated PIP2 hydrolysis is mediated by a G protein interaction with PLC (101, 115, 126, 129). The nature and characteristics of G protein or proteins (G,) that can activate PLC are unknown and thus, details are not known about coupling between receptors and PLC. Soluble phosphoinositide-specific PLC isoforms have been isolated (21, 116) that show greater specificity for PIP, than for PIP or PI at physiological [Ca”‘]. There is less information available on membrane bound PLC (8, 97) involved in receptor-mediated activation of PI metabolism. There is direct evidence of GTPyS-activation of a membrane-bound PLC in an airway smooth muscle (126). Increasing [Ca”+] can activate a membrane-bound PLC activity in isolated membrane preparations (126); however, in intact cells increases in [Ca2+]i evoked by increasing extracellular [K’] do not activate PLC (12). G protein subunits may activate PIP-kinase (160), and there may be receptor-mediated control of this reaction as well as PLC-mediated PIP2 hydrolysis. Ins(1,4,5)P3 is an established second messenger that releases Ca2+ from nonmitochondrial intracellular organelles. Ins(1,4,5)P3 binds to a Ca2+ channel protein (51, 57,162), which increases the probability of the open state of this channel with resultant Ca2+ efflux into the cytoplasm. This channel has a 10 pS conductance and uses K+ as a counter ion. It is apparently inhibited by ryanodine (121). Ins(1,4,5)P3 binding to the channel protein is markedly inhibited by Ca2+, 50% inhibition occurring at a [Ca”‘] of 300 nM (170). Ins(l,4,5)P3-mediated Ca2+ release is determined, in part, by the state of Ca2+ loading of these organelles (23, 62, 102, 104, 174). In smooth muscle, Ins(1,4,5)P3 releases Ca2+ from the SR (154). The superficial SR of smooth muscle may be loaded by Ca2+ originating in the extracellular space, which can be released by Ins(1,4,5)PZ (174). It is unknown if all of the Ca2+ released by Ins(1,4,5)P3 originates in the SR or if Ins(I,4,5)P3 can function in smooth muscle to mediate exchange of Ca2+ between different intracellular Ca2+ pools (62, 64). Low-molecular-weight heparin, which inhibits

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Ins( l,4,5)P3-mediated Ca2+ release from the SR, inhibits receptor-activated, Ins( 1,4,5)P3-mediated increases in [Ca2+]i and force development (35, 101). This finding suggests that the PMC component of muscle contraction may be entirely or largely triggered by increases in [Ins( 1,4,5)Ps]. After treatment of swine trachealis muscle with phorbol dibutyrate, which inhibits muscarinicactivation of inositol phospholipid metabolism and Ins( 1,4,5)P3 formation (7, lo), muscarinic-evoked contractions are entirely dependent on surface membrane depolarization and extracellular Ca2’, supporting the concept that in this muscle, as well, the PMC component of force involves second messengers provided by inositol phospholipid metabolism (7). Although the evidence is strong for the role of Ins(1,4,5)P3 as a second messenger, it has not been convincingly demonstrated in a receptor-evoked contraction that Ins(1,4,5)P3 levels increase before increases in cytosolic [ Ca2+]. Elevated Ins( I,4,5)P3 levels (34) have been detected in bovine trachealis muscle within one second of onset of stimulation. Miller et al. (122) demonstrated small increases in total InsPs in bovine trachealis strips 500 mS after initiation of field stimulation, a time before Ca2+ activation of glycogen phosphorylase and myosin light chain phosphorylation. Increases in InsP and InsP2 were also seen at 500 mS, a finding that in other airway smooth muscle only occurs after more prolonged stimulations (13, 33), weakening the InsPs data. It seems possible that in very short time periods after onset of PIP2 hydrolysis, there may be functional compartmentation of Ins(1,4,5)Ps in a space between the surface membrane and the superficial SR, which can be considered to be a membrane running roughly parallel to the surface membrane (155). Thus there may be a diffusion gradient between surface membrane and SR where the SR may function as an Ins(1,4,5)P3 sink. Since this compartment is only a small fraction of the total cell volume, it may not be possible to detect increases in whole tissue [ Ins( 1,4,5)P3] before increases in [ Ca2+];. Ins( 1,4,5)P3 activates surface membrane Ca2+ channels in mast cells (136), and there may be a similar function in airway smooth muscle cells or roles of this second messenger that have not yet been discovered. Mean tissue Ins(1,4,5)P3 levels depend on rates of formation and degradation. In liver cells Ins(l,4,5)P3 degradation occurs via two different pathways (94, 177): the first involves phosphorylation to Ins( 1,3,4,5)P4 utilizing Ins(l,4,5)P3-kinase (3-kinase), with subsequent dephosphorylation to Ins( 1,3,4)P3. Ins( 1,4,5)Ps is also degraded via 5-phosphatase to Ins(l,4)P2, and then dephosphorylated to Ins(4)P or Ins( l)P [in swine trachealis muscle the Ins(4)P isomer predominates (13)] followed by another phosphatase-mediated reaction giving free myo-inositol. The K, for the initial reactions in the different pathways are such that the 3-kinase reaction is favored. Increases in [Ca”‘] over the physiological range activate the 3-kinase reaction (177), and [Ca’+]; increases during contraction should stimulate the 3-kinase pathway. Increasing [Ca”‘] in a smooth muscle homogenate resulted in an increase in the rate of Ins(l,4,5)P3 degradation (146). Ins( 1,4,5)P3-phosphatase can be phos-


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phorylated via protein kinase C (PKC), suggesting the possibility of control at this step of inositol phosphate degradation, as well (94). It is still not established if Ins(1,3,4,5)P4 can function as a second messenger (87, 93), either alone or synergistically with Ins(l,4,5)Pz. In liver cells, Ins( 1,3,4,5)P4 inhibits Ins( 1,4,5)Pz degradation via by-product inhibition (93). InsP5 and InsPG have been identified in nonmuscle cells, but these compounds seem not to be coupled to agonist stimulation (177). In canine trachealis muscle, activation of inositol phospholipid metabolism occurs in two phases (11, 14). In the first phase, which occurs during development of force and before onset of PI resynthesis, inositol phospholipid metabolism, with resultant production of second messengers, is driven by decreases in inositol phospholipid pool sizes. The second phase, which occurs during force maintenance, is characterized by nearly constant total pool sizes of inositol phospholipids and a state where metabolic flux in inositol phospholipids is nearly equal to the rate of PI resynthesis. Metabolic flux rates in canine trachealis muscle in the unstimulated state, and during phase one and two, were 0.004, 0.42 and 0.14 nmol . 100 nmol total lipid inorganic phosphate-’ min-‘, respectively. These data allow prediction that if processes determining Ins( 1,4,5)P3 degradation remain unaltered, addition of a muscarinic agonist should result in an increase in cellular Ins( l,4,5)P3 concentration to high levels during force development, followed by decrease to a steady-state level larger than control level during the tonic phase of contraction. This was not confirmed in bovine trachealis muscle with Ins( 1,4,5)P3 measurements using radioimmunoassay (34). Ins( 1,4,5)P3 increased transiently and then decreased during maintained exposure to ACh to levels that were less than control unstimulated levels. In swine trachealis muscle, Ins( l,4,5)P3 pool sizes, measured as radioactivity, appear elevated during carbachol-evoked maintained force in that atropine resulted in a decrease. Decrease in Ins(l,4,5)P3 pool size preceded relaxation, PI resynthesis persisted, and PIP and PIP:! pool sizes increased (13). In bovine trachealis muscle slices, base-line, unstimulated rates of metabolic flux in inositol phospholipids were much greater (33) than the very low metabolic flux rates in inositol phospholipids seen in unstimulated canine trachealis muscle strips (14). There may be a species difference, or the cutting of the tissues into thin slices may alter control mechanisms for inositol phospholipid metabolism. Several investigators have shown augmented incorporation of labeled myo-inositol into inositol phospholipids in agonist-stimulated tissue (11, 14, 33, 166). Measurements of incorporation of isotope under conditions where the pool size of each inositol phospholipid was determined have given some insight into metabolic flux between PI, PIP, and PIP2 (Fig. 3). Increases in specific radioactivities were practically identical in the receptorlinked compartments of the three phospholipids (14), indicating that under the conditions of the experiments these pools were in near chemical equilibrium. This finding suggests rate constants for PI-, and PIP-kinase are rapid. Turnover times for PIP and PIP2 pools linked

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FIG. 3. Specific radioactivities in PI, PIP, and PIP2 in canine tracheal& muscle after activation with carbachol. Unstimulated canine trachealis muscle strips were loaded with myo-[“Hlinositol. After several washes, carbachol was added, activating inositol phospholipid metabolism. Specific radioactivities in PI, PIP, and PIP, are shown, which increase in parallel and achieve an apparent steady state within -100 min of continued carbachol stimulation. Interrupted lines, control data; dotted line, myoinositol specific radioactivity. [From Baron, Pring, and Coburn (14).]

to receptor activation were determined to be 1.6 and 4.0 min, respectively. Surprisingly, carbachol-evoked increases in specific radioactivities in PI, PIP, and PIP, pools involved in inositol phospholipid metabolism can be described by a model that assumes one homogenous compartment for each of the lipids (C. B. Baron, M. Pring, and R. F. Coburn, unpublished observations). Although there is only a limited literature related to study of control of pool sizes of the various inositol phospholipids in smooth muscle and other tissues, the area is important because of possibili ties that different pools of membrane phospholipids may be activated under different condition .s and various inositol phospholipids may be directly involved in smooth muscle function. There is evidence that PIP may control plasma membrane Ca2+ ATPase (176). Inositol phospholipid metabolism may be controlled, in part, by PI- and PIP-kinase, which could limit metabolic flux to PIP2 or control changes in PI, PIP, and PIP2 pool sizes (54,77,145,149). There is evidence PIP-kinase is under control of G proteins (160). The relative sizes of PIP to PIP2 and PI can be altered in canine trachealis muscle by treatment


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with phorbol esters, either at rest (u nstimulated by agonist) or with muscar inic stim ulation (10) . Small concentrations of phosphatidylinositol 3,4-bisphosphate have been measured i n a nonmuscle tissue, however, this compound may not be coupled to a receptor-activated metabolism (173). Inositol phospholipid-specific PLC has activity toward PI and PIP as well as PIP, in platelet (178) and in an airway smooth muscle isolated membrane preparation implying that inositol phospholipid metabolism w6), could provide DAG without forming Ins(l,4,5)P3. There have been several demonstrations of increases in IP3 before IP, or IP (540) in smooth muscle, arguing against the importance of this metabolic pathway during force development. Mechanisms by which PI resynthesis is initiated and controlled during activation of inositol phospholipid metabolism are not well understood. This is an important area because PI resynthesis rate influences production of Ins( l,4,5)P3 during prolonged activation of PLC. After incubation of a vascular smooth muscle in 5 mM Li’, which inhibits monophosphate phosphatases (79), rnyoinositol concentration decreased to 3O-50% of control levels (E. Labelle, personal communication). In the presence of Li+, rates of incorporation of labeled myo-inositol into PI are markedly decreased during prolonged carbachol presumably due to decrease in free myo-inositol (33). PI resynthesis occurs in the endoplasmic reticulum, utilizing CDP-diacyglycerol and myo-inositol. Possible roles in CDP-DAG levels, [Ca”‘], or one of the inositol phosphates as con trollers of PI resynthesis should be assessed. Decrease in [Ca”‘] can control PI resynthesis in a smooth muscle homogenate (50, 165). The factors that control Ins(l,4,5)Ps degradation are important as determinants of [Ins( 1,4,5)Ps] and because it is possible Ins(1,4,5)P3 by-products may play roles in cellular function. The 3-kinase reaction is operating in muscarinic-contracted swine trachealis muscle (13) and bovine trachealis muscle (33) [Ins( 1,3,4,5)P4 pool size increases], but it was not possible to clearly prove the importance of th .e 5-phosphatase pathway for Ins( l,4,5)P3 degradation because Ins( 1,3,4)P3 could be the precursor for the elevated levels of Ins(1,4)P2 and Ins(4)P detected after carbachol activation of this muscle. As with other steps in PMC and EMC mechanisms operating in smooth muscle, the inositol phospholipid transduction system can be modulated. Increases in CAMP (5, 78, 117, 164), and cGMP (138, 139) inhibit formation of IP3. Phorbol esters inhibit inositol phospholipid metabolic flux and formation of inositol phosphates (7, 10, 28, 107, 126), suggesting that PKC-mediated phosphorylations are involved. Possible mechanisms for these effects include phosphorylations of PLC (21, 126), PIP-kinase (IO), or receptors or G proteins as discussed above. There seems to be no convincing evidence that G protein cross talk produces an inhibitory, G;-like protein directed at PLC. The role in smooth muscle of the established second messenger produced by inositol phospholipid metabolism, DAG, is controversial and not well developed. DAG

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levels increase in canine trachealis muscle during muscarinic activation (12, 133) [also in cultured vascular smooth muscle cells (70)]. It seems important to determine the physiological consequences of DAG increases, since, as discussed above, there has been a broad spectrum of effects of phorbol ester activation of PKC on coupling mechanisms that show the potential for PKCmediated mechanisms to control various steps in EMC and PMC mechanisms. Information is also needed about metabolic reactions producing receptor-activated increases in cellular DAG, as has been studied in nonmuscle tissue (53). In canine trachealis muscle acutely contracted with carbachol, phosphatidic acid increases in an apparent molar relationship to decrease in PI, suggesting early DAG increases were a result of PIP2 hydrolysis (12) and not due to hydrolysis of other lipids or triglyceride. There is an increasing body of data that address questions about which receptors activate inositol phospholipid metabolism in various airway smooth muscles. Increases in rates of formation of inositol phosphates has been described for tachykinins (68), histamine (78, 107), leukotrienes (69), as well as muscarinic agonists, as discussed above. ELECTROMECHANICAL

COUPLING

Figure 2, A and B, divides the surface membrane components of EMC into receptor-mediated events resulting in membrane depolarization (A) and voltageoperated Ca2+ channels (B). Figure 2, A and B, depicts receptor-activated depolarization as being controlled by G proteins and that Ca2+ influx via voltage-gated channels is due only to membrane depolarization. This figure also shows (C and D) other possible factors that control both the mechanisms of membrane depolarization and Ca”+ influx. Since there is little evidence for the presence of receptor-operated surface membrane Ca2’ channels in an airway smooth muscle, we have not included these channels in this figure. Agonist-Evoked

Membrane

Depolarization

Agonist-evoked membrane depolarization is graded, does not evoke action potentials under normal conditions, and is associated with decreases in membrane resistance; current-voltage plots show marked rectification (39, 42, 55, 163). Agonist-induced membrane depolarization reflects both inward and outward currents. Single channel and whole cell patch-clamp studies have shown rather small inward and large outward currents. Studies of outward currents have helped explain some of the characteristics of agonist-induced membrane depolarization in airway smooth muscle. A Ca2+-activated outwardly rectifying, voltage-dependent K+ current, which has a very high single channel conductance (109,120) has been identified in canine and rabbit airway muscle. In addition, a low conductance, Ca2+ -independent, delayed rectifying K+ current has been described in canine trachealis muscle cells (106). These channels appear similar to those described in other smooth muscle (17). The Ca2+-activated K+ current seen in patch-attached rabbit trachealis myo-


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cytes was markedly augmented by isoproterenol added to the bathing solution, or CAMP-dependent protein kinase, or a phosphatase inhibitor (109). The marked rectification seen in current-voltage plots from airway smooth muscle, which limits the ability of inward currents to depolarize the membrane, is explained by the outward rectifying characteristics of surface membrane K+ channels. These data have added to, and explain, earlier findings of various K+ channel inhibitors, tetraand 4aminopyridine on electrical ethylammonium, properties of airway smooth muscle cells in intact strips (96, 108, 159). So far, the approach of dissecting the membrane EMC mechanism into its components using whole cell and single channel recording has not proven any explanation for the depolarization phase of activation of EMC. Likely possibilities to explain receptor-activated membrane depolarization are receptor activation of an inward current through a receptor-operated channel or receptor-mediated inhibition of an outward K+ current. It seems likely, as discussed above, that coupling between receptor and ion channels involved in activating currents that depolarize the plasma membrane is mediated via G proteins. It is also possible because of the relatively slow onset of depolarization that activation of these putative channels involves cytoplasmic second messengers. Receptor-operated channel (ROC) hypothesis. This topic will be discussed in greater detail in our discussion of channels involved in Ca2+ influx in airway smooth muscle. Data obtained in vascular smooth muscle (20, 31, 86, 140), and other tissue (136), suggest the presence of non-voltage-gated Ca2+ channels that can provide inward current which may depolarize the surface membrane to threshold for activation of voltage-gated Ca2+ channels. So far, there is little evidence to prove the presence of ROCs in any airway smooth muscle. Agonist-inhibition of outward K+ current. The prototype for a mechanism whereby agonist-induced depolarization is mediated by inhibiting outward K+ currents is the M current, a late K+ current described in frog gastric smooth muscle cells (152) and in colon smooth muscle cells (43,44), which is inactivated in the presence of Ach. So far, this current has not been found in any airway smooth muscle preparation. Other possible ion currents responsible for agonist-induced membrane depolarization. These have been studied in non-airway smooth muscle and include Na+ (131,161), Chl- (31, 134), and nonspecific cationic current (25).

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current is seen at positive potentials; it slowly inactivates during maintained voltage clamp and is sensitive to dihydropyridines. So far, no agonist-induced alterations in this current have been reported, and the possibilities that current-voltage characteristics of the channels carrying this current are modulated via G proteins or diffusible second messengers-mediated mechanisms is not supported. However, agonist-regulated or modulated inward, voltage-dependent Ca2’ currents have been described in other smooth muscles (18, 37, 135), and the use of the cell-attached mode to study agonist-regulated currents has not yet been reported for airway smooth muscle. Data obtained using GPTyS applied to the cytoplasmic face of the airway smooth muscle surface membrane to screen for roles of G protein-mediated coupling between receptor and effector have not yet been reported; such studies have been reported for a vascular smooth muscle Ca2’ channel (183). Patch-clamp recordings of Ca2+ currents in airway myocytes represent an important step to understanding processes by which external Ca2’ traverses the surface membrane. However, there remains some difficulties in extrapolating available data to data obtained using intact muscles. Measurements of membrane potentials in cells in canine or swine trachealis muscle strips during contraction evoked by K+ show a threshold for contraction of about -45 mV (7, 55); thus there seems to be a discrepancy between threshold data obtained in whole cell patch recordings and these data. In addition, in patch-clamped myocytes, Ca2+currents inactivate during a constant depolarizing step from holding potential, and steady-state inactivation curves obtained by varying the holding potential predict the probability of channel open times would be very low at membrane potentials as great as -20 mV, even considering a “window” from -20 to -10 mV where there is activation and steady-state inactivation is not complete. The K+-evoked contraction seemsto be a reasonable model for a pure EMC contraction, in that it is dependent on extracellular Ca”+, can be reversed by repolarizing the membrane using current injection (39), and is likely dependent on opening of slow or L Ca”+ channels. It seems unlikely that membrane potential-dependent release of Ca2’ from intracellular stores (102, 103) can explain discrepancies between data obtained in whole tissue and patch-clamp data. The concept of ROCs (26) stems from our understanding of the nicotinic-cholinergic receptor. Opening of ROCs is not directly determined by changes in membrane potential, however, ion fluxes in ROCs are dependent on Channels Involved in Calcium Influx the membrane potential altering the driving force for in Airway Smooth Muscle current flow. Using a pure definition, ROCs should be distinguished from agonist-modulated voltage-gated We will discuss data relevant to voltage-dependent channels where voltage-current relationships are altered. and receptor-operated Ca”’ channels. Whole cell patch Early studies of ROCs in vascular smooth muscle have recordings have defined characteristics of voltage-gated documented agonist-induced Ca”+ influx resistant to Ca2’ channels using canine trachealis (105) or bronchial dihydropyridine Ca2+ antagonists and agonist-induced myocytes (119). In both airway muscles [unlike other smooth muscles where at least two distinct types of Ca2+ Ca2+ influx in K+-depolarized muscle (86, 174). ROCs channels have been identified (16, 59, 135, 182)], there have been better defined using patch-clamp techniques. is a single Ca”+ inward current’ that has similarities to Benham and Tsien (20) used both cell-attached and slow or L Ca”+ currents recorded in cardiac muscle (16). outside-out patches to measure inward currents and docThis current activates at -30 to -15 mV, and maximum ument ATP-activated nonspecific cation ROCs in rabbit Downloaded from www.physiology.org/journal/ajplung at Glasgow Univ Lib (130.209.006.061) on February 12, 2019.

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ear artery. The open-closed state of this channel is not voltage dependent. This channel does not have the high specificity for Ca2+ seen with L or T Ca2’ channels (but has a greater affinity for Ca2+ than for Na+), is not inhibited by dihydropyridine compounds, and has many other differences from L and T voltage-dependent Ca2’ channels, which are also present in this muscle. Similar evidence has been obtained in other smooth muscle (31, 175). There is some evidence that a majority of activating Ca2+ can traverse ROCs in another vascular smooth muscle (140). Thus ROCs may supply Ca2+, which can activate myosin light chain kinase as well as depolarize the surface membrane to thresholds for voltage-gated Ca2+ channels, as discussed in the previous section of this review. The importance of changes in membrane potential in altering flux through activated receptor-operated Ca2’ channels has been nicely demonstrated in studies on mast cells (136), where influx of Ca2+ is augmented by a Ca2+-induced activation of a Cl- current, which hyperpolarizes the surface membrane potential and increases the driving force for Ca2+ influx. It may well be that a similar mechanism exists in vascular smooth muscle and other smooth muscles where Ca2+-activated K+ current functions to limit membrane depolarization that would inhibit Ca”+ flux via receptor-operated Ca2+ channels. A similar role of Ca2+-activated Chl- channels on norepinephrine-induced ROC Ca2’ currents has been postulated for rat anococcygeus muscle (31). It is unknown if ROCs exist in any airway smooth muscle. Our study (39) of canine trachealis muscle strips held in a double sucrose gap (41) showed that during ACh-maintained contraction, current clamp-induced surface membrane hyperpolarization evoked an initial contraction, and current clamp-induced depolarization evoked an initial relaxation. This finding is consistent with the existence of a receptor-operated Ca2+ channel, but could be explained by other mechanisms. During K+maintained contractions, hyperpolarization-evoked relaxations and depolarization-evoked contractions were as expected if voltage-gated Ca2+ channels were operating. Murray and Kotlikoff (127) have reported, using cultured human trachealis myocytes, agonist-evoked increases in fura[Ca2+]; dependent on external Ca2+ in the presence of large concentrations of dihydropyridine, a finding consistent with the presence of ROCs that pass Ca2+ across the surface membrane. Na+-K+

Pump, Na+-Ca2+

Exchanger

It is established that! inhibition or facilitation of the surface membrane Na+-K’ pump can have a major effect on the surface membrane potential (32) and on airway smooth muscle force (71, 148) and that the Na+-Ca2+ transporter is electrogenic (1). Whether these mechanisms of controlling the membrane potential are important in EMC deserves more study. Modulation

of EMC Mechanisms

There is an extensive literature in nonrespiratory smooth muscles and other tissues describing mechanisms

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that can modulate ion channels (113, 141, 180, 181, 183). Considering data obtained in airway smooth muscle, phorbol dibutyrate pretreatment causes a decrease in carbachol-induced membrane depolarization in swine trachealis muscle (7) [phorbol esters also cause membrane depolarization in unstimulated swine trachealis muscle (7)]. cGMP and CAMP alter action-potential amplitudes under conditions of TEA inhibition of K+ channels (142, 143). Calcium-activated K+ currents in rabbit trachealis muscle are augmented by CAMP-dependent protein kinase (109). A muscarinic-evoked contraction of swine trachealis muscle that utilizes only an EMC mechanism was developed (7) after the discovery that preincubation of airway smooth muscle with phorbol ester inhibited metabolic flux in inositol phospholipids and formation of inositol phosphates (10, 107). The use of this preparation has produced data that appear to show that there is marked PKC-induced amplification of EMC mechanisms (Fig. 4), that appears to be due to increased Ca2+ flux via a verapamil-sensitive channel. Arachidonic acid (132) and fatty acids (27, 132) alter characteristics of smooth muscle K+ channels. DAG activates surface membrane Ca2+ channels (36). These findings suggest there is a link between lipid metabolism and surface membrane channels. CYTOSOLIC

[CA2+]

Increases in [Ca2+]; trigger the initial activation of contraction by forming a Gag’-calmodulin complex that combines with and activates the catalytic subunit of myosin light chain kinase (47, 76, 88, 95). Myosin light chain kinase catalyzes phosphorylation of the myosin light chain and allows activation of myosin ATPase by actin. During maintenance of contraction the energy cost of contraction decreasesand there is a poorly understood Force (%) 1001

CCh (Control) r.I

CCh(PDB)

CCh(verapamil-sensitwe)

0’ Ii :’

4

50 -

u

-50

-40

-30

-20

Em (mV) 4. Membrane potential (E,,); force relationships, comparing different contractions that are entirely dependent on electromechanical coupling (EMC) mechanisms, i.e., carbachol-induced contraction in phorbol dibutyrate-treated muscle, CCh(PDB) and K+-evoked force. E, force relationships for carbachol-evoked force, which is dependent on pharmacomechanical coupling mechanisms (PMC) as well as EMC mechanisms and the verapamil component of carbachol-evoked force are also shown. Data plotted for steep portion of steady-state doseforce relationship. Major finding is marked amplification of force for a given membrane depolarization, comparing K’ and CCh(PDB) data. Data are plotted for the steep portion of E, force relationships. [From Baba, Baron, and Coburn (7).] FIG.


INVITED

change in cross bridge mechanisms for force development. Mean [Ca2+]; is a function of rates of Ca2’ delivery, removal, and buffering. Important known factors that influence [ Ca2+]; (174) include Ca2+ release and reuptake from the SR, Ca2+ influx across the surface membrane utilizing voltage-gated Ca2+ channels and ROCs, surface membrane Na’-Ca2’ exchange and Ca2’ ATPase pumps, and perhaps, mechanisms which translocate intracellular Ca2+ stores. Technologies have been developed for monitoring [Ca2+];, and our goal in this section of the review is to list information obtained with these technologies using airway smooth muscle. Data are available using aequorin (72, 167), fura- (107, 150), and glycogen phosphorylase (151). Data obtained on canine, bovine, and swine trachealis muscle are qualitatively similar using a muscarinic agonist, histamine, or during field stimulation. There is an initial rapid increase in [Ca2+];, which occurs before phosphorylation of the myosin light chain (151), followed by a slow decrease during maintained force to a nearly constant level that is still elevated compared with control [Ca2+]i. Data are similar with strips and with isolated myocytes (107) and are similar to data obtained on other smooth muscle (84). There is a well-documented change in the relationship of [ Ca2+]; to agonist-induced isometric force during the time of maintained force in both airway and nonairway smooth muscle and under conditions where agents are given that produce activation of PKC and increases in CAMP levels (72, 89, 91, 129). [Ca2+]i is larger and more maintained during KS‘-evoked contractions than seen for equivalent agonist-evoked force (72, 84, 167). The intriguing possibilities that oscillations of [Ca2+]i (22), as well as mean [ Ca2+];, determine steady-state force under some conditions, or that the contractile apparatus can differentiate Ca2+ delivered into the cytosol from the extracellular space, vs. that delivered from the SR (124), deserve further investigation. PMC

AND

EMC

INTERACTIONS

Separate or Additive of Muscle Force?

Mechanisms

for Control

So far in this review we have considered PMC and EMC as separate processes in smooth muscle and airway smooth muscle. This clearly is an oversimplification. A partial list of possible interactions between EMC and PMC mechanisms is given here. These data come from experiments performed on many different tissues, and there is little information about this topic derived from experiments utilizing airway smooth muscle. 1) Increase in [ Ca2+]; inhibits ion fluxes in voltage gated Ca”+ channels (130). The implication is that Ca2+ release from the SR may alter Ca2+ delivery to the cytosol via EMC mechanisms. 2) Increase in [Ca2+]; inhibits binding of Ins(l,4,5)P3 to receptors that activate Ca2’ release from intracellular organelles (170). The implication is that Ca”+ influx via EMC mechanisms may inhibit Ins(l,4,5)P3-induced SR Ca2+ release. 3) Ca2+ provided by influx across the surface membrane is involved in SR

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“loading”, one of the factors that determines the amplitude of Ins( 1,4,5)P3-evoked release (174). 4) Ins( l,4,5)P3 can activate a surface membrane Ca”+ channel (136). 5) The putative second messenger Ins(l,3,4,5)P4 may operate or modulate Ca2+ influx across the surface membrane (87, 93). 6) Ca2’ can control [Ins(l,4,5)Ps] by altering its degradation rate (146, 177). The implication is that Ca2+ delivered to the cytosol via EMC mechanisms can influence [Ins(l,4,5)PJ. 7) Protein kinase C activation can inhibit PMC and amplify EMC mechanisms (7). 8) Ca2+ can activate surface membrane K+ and Chlchannels (31, 109, 120). The implication is that Ca2’ released from the SR may alter EMC coupling mechanisms by modulating the membrane potential. PMC and EMC Components During Force Development, Maintenance, and During Relaxation Given the possibilities of interactions of EMC and PMC mechanisms discussed above and the lack of clean approaches to quantitate roles of EMC and PMC mechanisms in an intact cell, it is not surprising that it is difficult to quantitate PMC- and EMC-evoked force with a high degree of certainty. There is indirect evidence of the relative importance of PMC and EMC mechanisms during different phases of muscle contraction. Ins( 1,4,5)P3-mediated Ca”+ release appears to have an important role in airway smooth muscle, particularly during force development. Evidence includes 1) the high metabolic flux in inositol phospholipids at this time (14); 2) agonist-evoked large increases in [Ca2+]; and force, under conditions of nearly zero extracellular [Ca”‘] or during K+-evoked depolarization (84, 167); and 3) the observation that muscarinic-evoked force development is markedly prolonged under conditions where inositol phospholipid metabolism and Ins( 1,4,5)P3 formation is inhibited by phorbol dibutyrate, whereas prevention of agonist-evoked membrane depolarization by placing the tissue in low [Na+] media has no effect on rate of development of force (7). The concept, that both PMC and EMC mechanisms are operative in airway smooth muscle during maintained muscarinic contractions is based on effects on force or [ Ca2+];, of removing extracellular Ca2+ or giving voltagegated Ca2+ channel-blocking agents (84, 150, 167), and the finding that flux rates in inositol phospholipids are elevated during the maintained force phase of contraction (14). There is some evidence of differences in relative importance of PMC and EMC mechanisms in airway smooth muscle during maintained force with different agonists. There are different mechanical responses to reversal of agonist-induced membrane depolarization evoked by current injection during seratonin or AChevoked force (39, 42). There are different mechanical responses of muscle to the Ca2’ channel agonist BAY K 8644 (118) administered during histamine or AChevoked force. Elevating bathing solution [K+] or administration of tetraethylammonium ion has different effects on ACh and on histamine-evoked force (123). These differences probably reflect different coupling mechanisms between receptors and effector mechanisms or


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A

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lsoproterenol

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IOnM

t 20mVI B

VIP

10s

IOnM

different modulation of coupling mechanisms by diffusable second messengers. One can consider two different general types of relaxations. 1) Relaxation caused by removal or inhibition of an agonist (common approach, giving atropine during a muscarinic-evoked contraction or cessation of field stimulation). 2) Relaxation caused by administration of a relaxant agent during an agonist-evoked contraction (common approach, the use of a ,&adrenergic drug during a muscarinic-evoked contraction). [Ca2+]i (95), phosphorylation of the myosin light chain (48), and [Ins(l,4,5)P3] (13) decrease after reversal of agonist activation. Relaxations evoked by ,&adrenergic agents are accompanied by decreases in [Ca”‘] (5, 46, 60, 73) and by membrane hyperpolarization (4, 60,85, 153). There is evidence that one of the factors that may be involved in decreasing [Ca2+]; is inhibition of InsPs formation (5, 70, 78, 117). ,8-Adrenergic agonist concentrations for inhibition of InsPn formation are greater than is necessary for relaxation, but there is evidence of decreasesin InsPs before relaxation (164). The finding of p-adrenergicinduced membrane hyperpolarization suggests that inhibition of voltage-gated Ca2+ channels is a factor. We have discussed in a previous section evidence regarding effects of CAMP-dependent protein kinase on various surface membrane ion channels. Whether CAMP-dependent protein kinase-evoked phosphorylation of myosin light chain kinase, with a resultant decrease in Ca2+ sensitivity (47), is important during ,B-adrenergic-evoked relaxations is controversial (46, 73, 122, 129); there is no doubt that this mechanism becomes operative with large increases in CAMP evoked with forskolin (47). Druginduced relaxations have additional complexities in that Ca2+ ATPases can be controlled by CAMP-dependent protein kinase phosphorylations (61, 174) or by PKCmediated phosphorylations (112). There is evidence of involvement of the surface membrane Na+-K+ pump in ,&adrenergic-evoked relaxations (147). Figure 5 illustrates data that show some differences in coupling mechanisms involved in relaxation of the guinea pig trachealis muscle cells evoked by two different mediators, both of which increase CAMP levels. With VIP,

FIG. 5. Membrane potential measurements during VIP- and isoproterenolinduced relaxations of guinea pig trachealis muscle (giving equivalent relaxations). [From Coburn (unpublished data) .]

relaxation occurs without membrane hyperpolarization, but at an isoproterenol concentration resulting in an equivalent relaxation, membrane hyperpolarization occurs. These data suggest that during isoproterenol-induced relaxations, there are effects on membrane channels that control ion currents that determine the membrane potential, which may be absent in the VIP-evoked relaxation. Differences in the two relaxations could occur at the G protein microprocessor level, reflect different effects of CAMP-dependent phosphorylation on ion channels determining hyperpolarization, or be due to another mechanism. Data reviewed above suggest PMC and EMC mechanisms can be altered during different phases of contraction and relaxation of airway smooth muscle (and other smooth muscles as well). Processes that turn on, or off, various PMC and EMC mechanisms are not understood. Much of our existing data on various components of PMC and EMC mechanisms comes from reductionisttype experiments, and we have much evidence on modulation of these components by either intramembrane processing of signals or by diffusable second messengermediated mechanisms. A challenge for the future is to understand how this modulation can switch coupling mechanisms on and off. This could involve modulation at the receptor, G protein, or effector levels. There is some evidence that supports a hypothesis that PKC can exert control of various coupling mechanisms and might function during switching from PMC to EMC in the transition from force development to force maintenance (7) . The authors gratefully acknowledge the comments of our colleague Dr. M. I. Kotlikoff, which were useful in preparing this review. This work was supported in part by National Heart, Lung, and Blood Institute Grant R37 HL-37498. Address reprint requests to: R. F. Coburn, B203 Richards, Univ. of Pennsylvania, School of Medicine, Philadelphia, PA 19104. REFERENCES 1. AARONSON, P. I., AND C. D. BENHAM. Alterations in calcium mediated by sodium-calcium exchange in smooth muscle cells isolated from the guinea-pig ureter. J. Physiol. Lond. 416: l-18, 1989.


INVITED 2. AHMED, F., R. F. FOSTER, AND R. C. SMALL. Some effects of nifedipine in guinea pig isolated trachealis. Br. J. Pharmacol. 85: 861-864, 1985. 3. AHMED, F., R. F. FOSTER, R. C. SMALL, AND A. H. WESTON. Some features of the spasmogenic actions of acetylcholine and histamine in guinea-pig isolated trachealis. Br. J. Pharmacol. 83: 227-233,1984. 4. ALLEN, S. L., D. J. BEECH, R. W. FOSTER, G. P. MORGAN, AND R. C. SMALL. Electrophysiological and other aspects of the relaxant action of isoprenaline in guinea-pig isolated trachealis. Br. J. Pharmacol. 86: 843-854,1985. 5. ANSWER, K., J. A. HOVINGTON, AND B. M. SANBORN. Antagonism of contractants and relaxants at the level of intracellular calcium and phosphoinositide turnover in the rat uterus. Endocrinology 124: 2995-3002, 1989. 6. ASHKENAZI, A., J. W. WINSLOW, E. G. PERALTA, G. L. PETERSON, M. I. SCHIMERLIK, AND D. J. CAPON. A M2 muscarinic receptor subtype coupled to both adenylylcyclase and phosphoinositide turnover. Science Wash. DC 238: 672-675, 1987. 7. BABA, K., C. B. BARON, AND R. F. COBURN. Phorbol ester effects on coupling mechanisms during cholinergic contractions of swine tracheal smooth muscle. J. Physiol. Lond. 412: 23-42, 1989. 8. BANNO, Y., AND Y. NOZAWA. Characterization of partially purified phospholipase C from human platelet membranes. Biochem. J. 248: 95-101,1987. 9. BARNES, P. J. Cell-surface receptors in airway smooth muscle. In: Airway Smooth Muscle in Health and Disease, edited by R. F. Coburn. New York: Plenum, 1989, p. 77-97. 10. BARON, C. B., AND R. F. COBURN. Phorbol ester modulates inositol phospholipid metabolism in carbamylcholine-stimulated tracheal smooth muscle. Federation Proc. 46: 704, 1987. 11. BARON, C. B., AND R. F. COBURN. Inositol phospholipid turnover during contraction of canine trachealis muscle. Ann. NY Acad. Sci. 494: 80-83, 1987. 12. BARON, C. B., M. CUNNINGHAM, J. F. STRAUSS III, AND R. F. COBURN. Pharmacomechanical coupling in smooth muscle may involve phosphatidylinositol metabolism. Proc. Natl. Acad. Sci. USA 81: 6899-6903,1984. 13. BARON, C. B., J. POMPEO, AND R. F. COBURN. Decreases in Ins( 1,4,5)Ps pool precedes decrease in force evoked by atropine in carbachol-contracted porcine trachealis smooth muscle (Abstract). FASEB J. 4: A1116, 1990. 14. BARON, C. B., M. PRING, AND R. F. COBURN. Inositol lipid turnover and compartmentation in canine trachealis smooth muscle. Am. J. Physiol. 256 (Cell Physiol. 25): C375-C383, 1989. 15. BAUMGOLD, J., AND T. WHITE. Pharmacological differences between muscarinic receptors coupled to phosphoinositide turnover and those coupled to adenylate cyclase inhibition. Biochem. Pharmacol. 38: 1605-1616, 1989. 16. BEAN, B. P. Classes of calcium channels in vertebrate cells. Annu. Rev. Physiol. 51: 367-384, 1989. 17. BEECH, D. J., AND T. B. BOLTON. The effects of tetraethylammonium ion, 4 amino pyridine or quinidine on K-currents in single smooth muscle cells of the rabbit portal vein. Biomed. Biochem. Acta 46: S673-S676, 1987. 18. BENHAM, C. D., T. B. BOLTON, AND R. T. LANG. Acetylcholine activates an inward current in single mammalian smooth muscle cells. Nature Lond. 316: 345-347, 1985. 19. BENHAM, C. D., T. B. BOLTON, R. J. LANG, AND T. TAKEWAKI. Calcium activated potassium channels in single smooth muscle cells of rabbit jejunum and guinea pig mesenteric artery. J. Physiol. Lond. 371: 45-67, 1986. 20. BENHAM, C. D., AND R. W. TSIEN. A novel receptor-operated Capermeable channel activated by ATP in smooth muscle. Nature Lond. 328: 275-278,1987. 21. BENNETT, C. F., AND S. T. CROOKE. Purification and characterization of phosphoinositide-specific phospholipase C from guinea pig uterus: phosphorylation by protein kinase C in vitro. J. BioZ. Chem. 262: 13789-13795,1987. 22. BERRIDGE, M. J., AND A. GALIONE. Cytosolic calcium oscillators. FASEB J. 2: 3074-3080,1988. 23. BERRIDGE, M. J., AND R. F. IRVINE. Inositol phosphates and cell signalling. Nature Lond. 341: 197-205, 1989. 24. BIRNBAUMER, L., J. CODINA, R. MATTERA, R. A. CERIONE, J. D. HILDEBRANDT, T. SUNYER, F. J. ROJAS, M. C. CARON, R. J.

REVIEW

25.

26. 27.

28.

29.

30.

31.

32. 33.

34.

35.

36.

37.

38. 39.

40.

41.

42.

43.

44.

45.

L129

LEFKOWITZ, AND R. IYENGAR. Structural basis of adenylate cyclase stimulation and inhibition by distinct guanine nucleotide regulatory proteins. In: Molecular Mechanisms of Transmembrane Signalling, edited by P. C. Cohen and M. D. Hausay. New York: Elsevier, 1985, p. 131-182. BOLTON, T. B. The depolarizing action of acetylcholine or carbachol in intestinal smooth muscle. J. Physiol. Lond. 220: 647671,1972. BOLTON, T. B. Mechanism of action of transmitters and other substances on smooth muscle. Physiol. Rev. 59: 606-718, 1979. BREGESTOVSKI, P. D., V. M. BOLOTINA, AND V. N. SEREBRYAKOV. Fatty acid modifies Ca-dependent potassium channel activity in smooth muscle cells from the human aorta. Proc. R. Sot. Lond. B Biol. Sci. 237: 259-266, 1989. BROCK, T. A., S. E. RITTENHOUSE, C. W. POWERS, L. S. EKSTEIN, M. A. GIMBRONE, JR., AND R. W. ALEXANDER. Phorbol ester and l-oleoyl-2-acetylglycerol inhibit angiotensin activation of phospholipase C in cultured vascular smooth muscle cells. J. Biol. Chem. 260: 14158-14162,1985. BROWN, J. H., AND D. GOLDSTEIN. Differences in muscarinic receptor reserve for inhibition of adenylate cyclase and stimulation of phosphoinositide hydrolysis in chick heart cells. Mol. Pharmacol. 30: 566-570, 1986. BULBRING, E. Correlation between membrane potential, spike discharge and tension in smooth muscle. J. Physiol. Lond. 128: 220-221,1955. BYRNE, N. G., AND W. A. LARGE. Action of noradrenaline on single smooth muscle cells freshly dispersed from the rat anococcygeus muscle. J. Physiol. Lond. 389: 513-525, 1987. CASTEELS, R. The action of ouabain on the smooth muscle cell of the guinea-pig’s taenia coli. J. Physiol. Lond. 184: 131-142, 1966. CHILVERS, E. R., P. J. BARNES, AND S. R. NAHORSKI. Characterization of agonist-stimulated incorporation of [“Hlmyo-inositol into inositol phospholipids and [“H]inositol phosphate formation in tracheal smooth muscle. Biochem. J. 262: 739-746, 1989. CHILVERS, E. R., R. A. CHALLIS, P. J. BARNES, AND S. R. NAHORSKI. Mass changes of inositol (1,4,5) trisphosphate in trachealis muscle following agonist stimulation. Eur. J. Pharmacol. 164: 587-590, 1989. CHOPRA, L. C., C. H. C. TWORT, J. P. T. WARD, AND I. R. CAMERON. Effects of heparin on inositol 1,4,5-trisphosphate and guanosine triphosphate induced calcium release in cultured smooth muscle trachea. Biochem. Biophys. Res. Commun. 163: 262-268,1989. CLAPP, L. H., M. B. VIVANDON, J. J. SINGER, AND J. V. WALSH, JR. A diacylglycerol analogue mimics the action of acetylcholine and substance P on calcium currents in freshly dissocaited smooth muscle cells (Abstract). J. Gen. Physiol. 90: 13a, 1987. CLAPP, L. H., M. B. VIVAUDOU, J. V. WALSH, AND J. J. SINGER. Acetylcholine increases voltage-activated Ca current in freshly dissociated smooth muscle cells. Proc. Natl. Acad. Sci. USA 84: 1092-1096,1987. COBURN, R. F. The airway smooth muscle cell. Federation Proc. 36: 2692-2696,1977. COBURN, R. F. Electromechanical coupling in canine trachealis muscle: acetylcholine contractions. Am. J. Physiol. 236 (CeZl PhysioZ. 5): C177-C184, 1979. COBURN, R. F., C. B. BARON, AND M. T. PAPADOPOULOS. Phosphoinositide metabolism and metabolism-contraction couling in rabbit aorta. Am. J. Physiol. 255 (Heart Circ. Physiol. 24): H1476H1483,1988. COBURN, R. F., M. OHBA, AND T. TOMITA. Recording of intracellular electrical activity with the sucrose-gap method. In: Methods in Pharmacology, edited by E. E. Daniel and D. M. Paton. New York: Plenum, 1974, vol. 3, p. 231-245. COBURN, R. F., AND T. YAMAGUCHI. Membrane potential-dependent and -independent tension in the canine tracheal muscle. J. Pharmacol. Exp. Ther. 201: 276-284, 1977. COLE, W. S., A. CARL, AND K. M. SANDERS. Muscarinic suppression of Ca-dependent K current in colonic smooth muscle. Am. J. Physiol. 257 (Cell Physiol. 26): C480-C487, 1987. COLE, W. S., AND K. M. SANDERS. G proteins mediate suppression of Ca-activated K current by acetylcholine in smooth muscle cells. Am. J. Physiol. 257 (Cell Physiol. 26): C596-C600, 1989. COLUCCI, W. S. Adenosine 3’,5’-cyclic-monophosphate-depend-


L130

46.

47%

48.

49.

50.

51.

52.

53.

54.

55.

56.

57.

58.

59.

60.

61.

62.

63. 64.

65.

66.

67.

INVITED

ent regulation of alpha-adrenergic receptor number in rabbit aortic smooth muscle cells. Circ. Res. 58: 292-297, 1986. DEFEO, T. T., AND K. G. MORGAN. Calcium force coupling mechanisms during vasodilation-induced relaxations of ferret aorta. J. Physiol. Lond. 412: 123-133, 1989. DE LANEROLLE, P. CAMP, myosin dephosphorylation and isometric relaxations of airway smooth muscle. J. Appl. Physiol. 964: 705-709,1988. DE LANEROLLE, P. Myosin phosphorylation during contraction and relaxation of tracheal smooth muscle. J. BioZ. Chem. 255: 9993-10000,1980. DROOGMANS, G., L. RAEYMAEKERS, AND R. CASTEELS. Electra and pharmacomechanical coupling in the smooth muscle cells of the rabbit ear artery. J. Gen. Physiol. 70: 129-148, 1977. EGAWA, K., B. SACKTOR, AND T. TAKENAWA. Ca-dependent and Ca-independent degradation of phosphatidylinositol in rabbit vas deferens. Biochem. J. 194: 129-136, 1981. EHRLICH, B. E., AND J. WATRAS. Inositol 1,4,5-trisphosphate activates a channel from smooth muscle sarcoplasmic reticulum. Nature Lond. 336: 583-586, 1988. EVANS, D. H. L., H. 0. SCHILD, AND S. THESLEFF. Effects of drugs on depolarized plain muscle. J. Physiol. Lond. 143: 474-485, 1958. FARESE, R. B., T. S. KONDA, J. S. DAVIS, M. L. STANDAERT, R. J. POLLET, AND D. R. COOPER. Insulin rapidly increases diacylglycerol by activating de novo phosphatidic acid synthesis. Science Wash. DC 236: 586-589,1987. FARKAS, G., A. ENYEDI, B. SARKADI, AND A. FARAGO. Cyclic AMP-dependent protein kinase stimulates the phosphorylation of phosphatidylinositol to phosphatidylinositol-4-monophosphate in a plasma membrane preparation from pig granulocyte. Biochem. Biophys. Res. Commun. 125: 871-876,1984. FARLEY, J. M., AND P. R. MILES. Role of depolarization in acetylcholine-induced contractions of dog tracheal muscle. J. PharmacoZ. Exp. Ther. 201: 199-205, 1977. FARLEY, J. M., AND P. R. MILES. The sources of calcium for acetylcholine-induced contractions of dog tracheal smooth muscle. J. PharmacoZ. Exp. Ther. 206: 340-346, 1978. FERRIS, C. D., R. L. HUGANIR, S. SUPATTAPONE, AND S. H. SNYDER. Purified inositol 1,4,5 trisphosphate receptor mediates calcium flux in reconstituted lipid vesicles. Nature Lond. 342: 8789, 1989. FORDER, J., A. SCRIABINE, AND H. RASMUSSEN. Plasma membrane calcium flux, protein kinase C activation and smooth muscle contraction. J. PharmacoZ. Exp. Ther. 235: 267-273, 1985. FRIEDMAN, M. E., G. SUAREZ-KURTZ, G. J. KACZOROWSKI, G. M. KATZ, AND J. P. REUBEN. TWO calcium currents in a smooth muscle cell line. Am. J. Physiol. 250 (Heart Circ. Physiol. 19): H699-H703,1986. FUJIWARA, T., T. ITOH, H. SUZUKI, AND H. KURIYAMA. Relaxing actions of procaterol on smooth muscle cells of the dog trachea. Br. J. Pharmacol. 93: 199-209, 1988. FURUKAWA, K. I., Y. TAWADA, AND M. SHIGEKAWA. Regulation of the plasma membrane Ca pump by cyclic nucleotides in cultured vascular smooth muscle cells. J. BioZ. Chem. 263: 80588065,1988. GHOSH, T. K., J. M. MULLANEY, F. I. TARAZI, AND D. L. GILL. GTP-activated communication between distinct inositol 1,4,5trisphosphate-sensitive and -insensitive calcium pools. Nature Lond. 340: 236-239,1989. GILMAN, A. G. G proteins: transducers of receptor-operated signals. Annu. Rev. Biochem. 56: 615-649, 1987. GOLDMAN, W. F., W. G. WIER, AND M. P. BLAUSTEIN. Effects of activation on distribution of Ca in single arterial smooth muscle cells. Circ. Res. 64: 1019-1029, 1989. GOLENHOFEN, K., N. HERMSTEIN, AND E. LAMMEL. Membrane potential and contraction of vascular smooth muscle during application of noradrenaline and high potassium, and selective inhibitory effects of verapamil. Microvasc. Res. 5: 73-80, 1973. GOODMAN, R. F., AND G. B. WEISS. Effects of lanthanum on 45Ca movements in contractions induced by norepinephrine, histamine and potassium in vascular smooth muscle. J. Pharmacol. Exp. Ther. 177: 415-423, 1971. GRANDORDY, B. M., F. M. Cuss, A. S. SAMPSON, J. B. PALMER, AND P. J. BARNES. Phosphatidvlinositol response to cholinergic

REVIEW

68.

69.

70.

71.

72.

73.

74.

75.

76.

77.

78.

79.

80.

81.

82.

83.

84.

85.

86.

87.

88.

agonists in airway smooth muscle: relationship to contraction and muscarinic receptor occupancy. J. PharmacoZ. Exp. Ther. 238: 273-279,1986. GRANDORDY, B. M., N. FROSSARD, K. J. RHODEN, AND P. J. BARNES. Tachykinin-induced phosphoinositide breakdown in airway smooth muscle and epithelium: relationship to contraction. MOL. PharmacoZ. 33: 515-519, 1988. GRANDORDY, B. M., L. MELDRUM, R. G. STURTON, AND P. J. BARNES. Leukotriene C4 and D4 induce contractions and formation of inositol phosphates in airway lung parenchyma (Abstract). Am. Rev. Respir. Dis. 113: All3, 1986. GRIENDLING, K. K., S. E. RITTENHOUSE, T. A. BROCK, L. S. EKSTEIN, M. A. GIMBRONE, JR., AND R. W. ALEXANDER. Substantial diacylglycerol formation from inositol phospholipid in angiotensin II-stimulated vascular smooth muscle cells. J. BioZ. Chem. 261: 5901-5906,1986. GUNST, S. J. Effect of Na-K adenosine triphosphatase activity on relaxations of canine tracheal smooth muscle. J. AppZ. Physiol. 64: 635-643,1988. GUNST, S. J. Effects of muscle length and load on intracellular Ca in tracheal smooth muscle. Am. J. Physiol. 256 (Cell Physiol. 25): C807-C812,1989. GUNST, S. J., AND S. BANDYOPADAYAX. Contractile force and intracellular Ca2+ during relaxation of canine tracheal smooth muscle. Am. J. Physiol. 257 (Cell Physiol. 26): C355-C364, 1989. GUNST, S. J., J. Q. STROPP, AND N. R. FLAVAHAN. Muscarinic receptor reserve and ,&adrenergic sensitivity in tracheal smooth muscle. J. AppZ. Physiol. 67: 1294-1298, 1989. GUNST, S. J., J. Q. STROPP, AND N. A. FLAVAHAN. Analysis of receptor reserves in canine tracheal smooth muscle. J. AppZ. Physiol. 62: 1755-1758, 1987. HAEBERLE, J. R., D. R. HATHAWAY, AND A. A. DEPAOLI-ROACH. Dephosphorylation of myosin by the catalytic subunit of a type-2 phosphatase produces relaxation of chemically skinned uterine smooth muscle. J. BioZ. Chem. 260: 9965-9968, 1985. HALENDA, S., AND M. B. FEINSTEIN. Phorbol myristate acetate stimulates formation of phosphatidylinositol 4phosphate and phosphatidylinositol 4,5-bisphosphate in human platelets. Biochem. Biophys. Res. Commun. 1254: 507-513, 1984. HALL, I. P., J. DONALDSON, AND S. J. HILL. Inhibition of histamine-stimulated inositol phospholipid hydrolysis by agents which increase cyclic AMP levels in bovine tracheal smooth muscle. Br. J. PharmacoZ. 97: 603-613, 1989. HALLCHER, L. M., AND W. R. SHERMAN. The effects of lithium ion and other agents on the activity of myo-inositol-l-phosphatase from bovine brain. J. BioZ. Chem. 255: 10896-10901, 1980. HASHIMATO, T., M. HIRATA, AND Y. ITO. A role of inositol 1,4,5trisphosphate in the initiation of agonist-induced contractions of dog tracheal smooth muscle. Br. J. Pharmacol. 86: 191-199, 1985. HASHIMATO, T., M. HIRATA, T. ITOH, Y. KANMURA, AND H. KURIYAMA. Inositol 1,4,5-trisphosphate activates pharmacomechanical coupling in smooth muscle of the rabbit mesenteric artery. J. Physiol. Lond. 307: 605-618, 1986. HAUSLER, G. Differential effect of verapamil on excitation-contraction coupling in smooth muscle and on excitation-secretion coupling in adrenergic nerve terminals. J. PharmacoZ. Exp. Ther. 180: 672-682,1972. HESCHELER, J., W. ROSENTHAL, W. TRAUTWEIN, AND G. SCHULTZ. The GTP-binding protein, Go, regulates neuronal calcium channels. Nature Lond. 325: 445-447, 1987. HIMPENS, B., AND A. P. SOMLYO. Free calcium and force transients during depolarization and pharmacomechanical coupling in guinea-pig smooth muscle. J. Physiol. Lond. 395: 507-530,1988. HONDA, K., T. SATAKE, K. TAKAGI, AND T. TOMITA. Effects of relaxants on electrical and mechanical activities in the guinea-pig tracheal muscle. Br. J. PharmacoZ. 87: 665-671, 1986. HWANG, K. S., AND C. VAN BREEMEN. Effects of the Ca agonist Bay K8644 on 45Ca influx and net Ca uptake into rabbit aortic smooth muscle. Eur. J. PharmacoZ. 116: 299-305, 1985. IRVINE, R. F., AND R. M. MOOR. Micro-injection of inositol 1,3,4,5-tetrakisphosphate activates sea urchin eggs by a mechanism dependent on external Ca2’. Biochem. J. 240: 917-920, 1986. ITOH, T., M. IKEBE, G. J. KARGACIN, D. J. HARTSHORNE, B. E. KEMP, AND F. S. FAY. Effects of modulators of myosin light-chain


INVITED

89.

90.

91.

92.

93.

94.

95.

96.

97.

98.

99.

100. 101.

102.

103.

104.

105.

106.

107.

108.

109.

110.

kinase activity in single smooth muscle cells. Nature Lond. 338: 164-167, 1989. ITOH, T., Y. KUBOTA, AND H. KURIYAMA. Effects of phorbol ester on acetylcholine-induced Ca2+ mobilization and contraction in the porcine coronary artery. J. Physiol. Lond. 397: 401-419, 1988. JIA, W. G., C. SHAW, F. VANHUIZEN, AND M. S. CYNADER. Phorbol l&13-dibutryate regulates muscarinic receptors in rat cerebral cortical slices by activating protein kinase C. Biol. Brain Res. 4: 311-315, 1989. JIANG, M. J., AND K. G. MORGAN. Intracellular calcium levels in phorbol ester-induced contractions of vascular muscle. Am. J. Physiol. 253 (Heart Circ. Physiol. 22): H1365-H1371, 1987. JONES, C. A., J. M. MADISON, M. TOM-MOY, AND J. K. BROWN. Muscarinic cholinergic inhibition of adenylate cyclase in airway smooth muscle. Am. J. Physiol. 253 (Cell Physiol. 22): C97-C104, 1987. JOSEPH, S. K., C. A. HANSEN, AND J. R. WILLIAMSON. Inositol tetrakisphosphate mobilizes calcium from cerebellum microsomes. MOL. Pharmacol. 36: 391-397, 1989. JOSEPH, S. K., AND J. R. WILLIAMSON. Inositol polyphosphates and intracellular calcium release. Arch. Biochem. Biophys. 273: l15, 1989. KAMM, K. E., AND J. T. STULL. Myosin phosphorylation, force, and maximal shortening velocity in neurally stimulated tracheal smooth muscle. Am. J. Physiol. 249 (Cell Physiol. 18): C238-C247, 1985. KANNAN, M. S., L. P. JAGER, E. E. DANIEL, AND R. E. GARFIELD. Effects of 4aminopyridine and tetraethylammonium chloride on the electrical activity and cable properties of canine tracheal smooth muscle. J. Pharmacol. Exp. Ther. 227: 706-715, 1983. KATAN, M., AND P. J. PARKER. Purification of phosphoinositidespecific phospholipase C from a particulate fraction of bovine brain. Eur. J. Biochem. 168: 413-418, 1987. KAWATA, M., Y. KAWAHARA, S. ARAKI, M. SUNAKO, T. TSUDA, H. MIZUOOGUCHI, AND Y. TAKAI. Identification of a major GTPbinding protein in bovine aortic smooth muscle membranes as SMG-P21, a GTP-binding protein having the same effect for domain as RAS-P21S. Biochem. Biophys. Res. Commun. 163: 1418-1427,1989. KIKKAWA, U., Y. TAKAI, Y. TANAKA, R. MIYAKE, AND Y. NISHIZUKA. Protein kinase C as a possible receptor protein of tumorpromoting phorbol esters. J. Biol. Chem. 258: 11442-11445, 1983. KIRKPATRICK, C. T. Excitation and contraction in bovine tracheal smooth muscle. J. Physiol. Lond. 244: 263-281, 1975. KITAZAWA, T., S. KOBAYASHI, K. HORIUTI, A. V. SOMLYO, AND A. P. SOMLYO. Receptor-coupled, permeabilized smooth muscle. J. Biol. Chem. 264: 5339-5342, 1989. KOBAYASHI, S., H. KANAIDE, AND M. NAKAMURA. Complete overlap of caffeineand K depolarization-sensitive cellular calcium storage site in cultured rat arterial smooth muscle cells. J. BioZ. Chem. 261: 15709-15713,1986. KOBAYASHI, S., H. KANAIDE, AND M. NAKAMURA. K-depolarization induces a direct release of Ca2’ from intracellular storage sites in cultured vascular smooth muscle cells from rat aorta. Biochem. Biophys. Res. Commun. 129: 877-884, 1985. KOBAYASHI, S., T. KITAZAWA, A. V. SOMLYO, AND A. P. SOMLYO. Cytosolic heparin inhibits muscarinic and alfa adrenergic Ca release in smooth muscle. J. BioZ. Chem. 264: 17997-18004, 1989. KOTLIKOFF, M. I. Calcium current in isolated canine airway smooth muscle cells. Am. J. Physiol. 254 (Cell Physiol. 23): C793C801,1988. KOTLIKOFF, M. I. Ion channels in airway smooth muscle. In: Airway Smooth Muscle in Health and Disease, edited by R. F. Coburn. New York: Plenum, 1989, p. 169-182. KOTLIKOFF, M. I., R. K. MURRAY, AND E. E. REYNOLDS. Histamine-induced calcium release and phorbol antagonists in cultured airway smooth muscle cells. Am. J. Physiol. 253 (CeZZ Physiol. 22): C561-C565,1987. KROEGER, E. A., AND N. L. STEPHENS. Effect of tetraethylammonium on tonic airway smooth muscle: initiation of phasic electrical activity. Am. J. Physiol. 228: 633-636, 1975. KUME, H., A. TAKAI, H. TOKUNQ, AND T. TOMITA. Regulation of Ca-dependent K-channel activity in tracheal myocytes by phosphorylation. Nature Lond. 341: 152-154, 1989. KWATRA, M. M., E. LEUNG, A. C. MANN, K. K. MCMAHON, J.

REVIEW

111.

112.

113. 114.

115.

116.

117.

118.

119.

120.

121.

122.

123.

124.

125.

126.

127.

128.

129. 130.

131.

L131

PTASIENSKI, R. D. GREEN, AND M. M. HOSEY. Correlation of agonist-induced phosphorylation of chick heart muscarinic receptors with receptor desensitization. J. Biol. Chem. 262: 1631416321, 1987. LEEB-LUNDBERG, L. M., F. S. COTECCHIA, A. DIBLASI, M. G. CARON, AND R. J. LEFKOWITZ. Regulation of adrenergic receptor function by phosphorylation: agonist-promoted desensitization and phosphorylation of alfa-l-adrenergic receptors coupled to inositol phospholipid metabolism in DDT, MF-2 smooth muscle cells. J. Biol. Chem. 262: 3098-3105, 1987. LEGAST, H., T. POZZAN, F. A. WALDVOGEL, AND P. D. LEW. Phorbol myristate acetate stimulates ATP-dependent calcium transport by the plasma membrane of neutrophils. J. CZin. Inuest. 73: 878-883,1984. LEVITAN, B. C. Phosphorylation of ion channels. J. Membr. Biol. 87: 177-190,1985. LIMAS, C. T., AND C. LIMAS. Phorbol esters and diacylglycerol mediate desensitization of cardiac P-adrenergic receptors. Circ. Res. 57: 443-449, 1985. LITOSCH, I., C. WALLIS, AND J. N. FAIN. 5-Hydroxy tryptamine stimulates inositol phosphate production in a cell-free system from blowfly salivary gland: evidence for a role of GTP in coupling receptor activation to phosphoinositide breakdown. J. Biol. Chem. 260: 5464-5471, 1985. LOW, M. G., R. C. CARROLL, AND A. C. COX. Characterization of multiple forms of phosphonositide-specific phospholipase C purified from human platelets. Biochem. J. 237: 139-145, 1986. MADISON, J. M., AND J. K. BROWN. Differential inhibitory effects of forskolin, isoproterenol and dibutyryl cyclic adenosine monophosphate on phosphoinositide hydrolysis in canine tracheal smooth muscle. J. C/in. Inuest. 82: 1462-1465, 1988. MARFAN, R., C. L. ARMOUR, P. R. A. JOHNSON, AND J. L. BLACK. The calcium channel agonist BAY K8644 enhances the responsiveness of human airway muscle to KC1 and histamine but not to carbachol. Am. Rev. Respir. Dis. 135: 185-189, 1987. MARFAN, R., C. MARTIN, T. MADEDD, AND J. MIRONNEAU. Calcium channel currents in isolated smooth muscle cells from human bronchus. J. Appl. Physiol. 66: 1706-1714, 1989. MCCANN, J. D., AND M. J. WELSH. Calcium-activated potassium channels in canine airway smooth muscle. J. Physiol. Lond. 372: 113-126,1986. MIGNERY, G. A., T. C. SUDHOF, K. TAKEI, AND P. DE CAMILLE. Putative receptor for inositol 1,3,4-trisphosphate similar to ryanodine receptor. Nature Lond. 342: 192-195, 1989. MILLER, W. C., J. R. MILLER, L. N. WELLS, J. T. STULL, AND K. E. KAMM. Biochemical events associated with activation of smooth muscle contractions. J. BioZ. Chem. 263: 13979-13982, 1988. MITCHELL, H. W. Electromechanical effects of tetraethylammonium and K’ on histamine-induced contraction in pig isolated tracheal smooth muscle. Lung 165: 129-142, 1987. MORELAND, S., AND R. S. MORELAND. Effects of dihydropyridines on stress, myosin phosphorylation and Vo in smooth muscle. Am. J. Physiol. 252 (Heart Circ. Physiol. 21): H1049-H1058, 1987. MURLAS, C. G., AND C. A. DOUPNIK. Electromechanical coupling in ferret airway smooth muscle in response to leukotriene Cq. J. Appl. Physiol. 22: 2533-2538, 1989. MURRAY, R. K., C. S. BENNETT, S. J. FLUHARTY, AND M. KoTLIKOFF. Mechanisms of phorbol ester inhibition of histamineinduced IP3 formation. Am. J. Physiol. 257 (Lung Cell. Mol. Physiol. 1): L209-L216, 1989. MURRAY, R. K., AND M. I. KOTLIKOFF. Multiple agonists couple to calcium release in cultured airway smooth muscle cells (Abstract). Am. Rev. Respir. Dis. 139: A469, 1989. NISHIMURA, J., AND C. VANBREEMEN. Direct regulation of smooth muscle contractile elements by 2nd messengers. Biochem. Biophys. Res. Commun. 163: 929-935, 1989. NISHIZUKA, Y. Studies and perspectives of protein kinase C. Science Wash. DC 233: 305-312, 1986. OHYA, Y., K. KITAMURA, AND H. KURIYAMA. Regulation of calcium current by intracellular calcium in smooth muscle cells of rabbit portal vein. Circ. Res. 962: 375-383, 1988. OHYA, Y., AND N. SPERELAKIS. Fast Na’ and slow Ca2’ channels in single uterine muscle cells from pregnant rats. Am. J. Physiol. 257 (Cell Physiol. 26): C408-C412, 1989.


L132 132.

133.

134.

135.

136.

137.

138.

139.

140.

141.

142.

143.

144. 145.

146.

147.

148.

149.

150.

151.

152.

153.

INVITED

ORDWAY, R. W., J. V. WALSH, JR., AND J. J. SINGER. Arachidonic acid and other fatty acids directly activate potassium channels in smooth muscle cells. Science Wash. DC 244: 1176-1179, 1989. PARK, S., AND H. RASMUSSEN. Activation of tracheal smooth muscle contraction: Synergism between Ca and activators of protein kinase C. Proc. NatL. Acad. Sci. USA 82: 8835-8839,1985. PECAUD, P., G. LOIRAND, J. L. LAVIE, C. MIRONNEAU, AND J. MIRONNEAU. Calcium-activated chloride current in rat vascular smooth muscle cells in short-term primary culture. Pfluegers Arch. 413: 629-636,1989. PECAUD, P., G. LOIRAND, C. MIRONNEAU, AND J. MIRONNEAU. Opposing effects of noradrenaline on the two classes of voltagedependent calcium channels of single vascular smooth muscle cells in short term primary culture. Pfluegers Arch. 410: 557-559, 1987. PENNER, R., G. MATTHEWS, AND E. NEHER. Regulation of calcium influx by second messengers in rat mast cells. Nature Lond. 334: 499-504, 1988. PERALTA, E. G., A. ASHKENAZI, J. W. WINSLOW, J. R. PAMACHANDRAN, AND D. J. CAPON. Differential regulation of PI hydrolysis and adenylate cyclase by muscarinic receptor subtypes. Nature Lond. 334: 434-437, 1987. POPESCO, L. M., C. PANOIM, M. HINESCU, AND 0. NUTU. The mechanisms of cGMP-induced relaxation in vascular smooth muscle. Eur. J. Pharmacol. 107: 393-394, 1985. RAPOPORT, R. J. Cyclic guanosine monophosphate inhibition of contraction may be mediated through inhibition of phosphatidylinositol hydrolysis in rat aorta. Circ. Res. 58: 407-410, 1986. RUEGG, U. T., H. WALLNOFER, S. WEIR, AND C. CAUVIN. Receptor-operated calcium-permeable channels in vascular smooth muscle. J. Cardiovasc. Pharmacol. 14: S49-S58, 1989. REUTER, H. Localization of beta adrenergic receptors and effects of noradrenaline and cyclic nucleotides on action potentials, ionic currents and tension in mammalian cardiac muscle. J. Physiol. Lond. 242: 429-451,1974. RICHARDS, I. S., AND C. G. MURLAS. 8-bromo-cyclic GMP abolishes TEA-induced slow action potentials in canine trachealis muscle. Eur. J. PharmacoZ. 128: 299-302, 1987. RICHARDS, I. S., N. OUSTERHOLT, N. SPERELAKIS, AND C. G. MURLAS. CAMP suppresses Ca2+ -dependent electrical activity of airway smooth muscle induced by TEA. J. Appl. Physiol. 62: 175179,1987. SAGEISENBERG, R. GTP-binding proteins as possible targets for protein kinase-C action. Trends Biochem. Sci. 14: 355-357, 1989. SARDAKI, B., E. ENYEDI, A. FARAGO, G. MESZAROS, T. KREMMER, AND A. GARDOSA. Cyclic AMP-dependent protein kinase stimulates the formation of polyphosphoinositides in lymphocyte plasma membranes. FEBS Lett. 152: 195-198, 1983. SASAGURI, T., M. HIRATA, AND H. KURIYAMA. Dependence on calcium of the activities of phosphatidylinositol 4,5-bisphosphate phosphodiesterase and inositol 1,4,5-trisphosphate in smooth muscles of the porcine coronary artery. Biochemistry 231: 497503, 1985. SCHEID, C. R., T. W. HONEYMAN, AND F. S. FAY. Mechanisms of P-adrenergic relaxations of smooth muscle. Nature Lond. 277: 3236, 1979. SCHRAMM, C. M., AND M. M. GRUNSTEIN. Mechanisms of protein kinase C regulation of airway contractility. J. Appl. Physiol. 66: 1935-1941,1989. SEYFRED, M. A., AND W. W. WELLS. Subcellular sites and mechanisms of vasopressin-stimulated hydrolysis of phosphoinositides in rat hepatocytes. J. BioZ. Chem. 259: 7666-7672, 1984. SHIEH, C. C., AND J. M. FARLEY. Agonist-induced intracellular calcium changes in swine tracheal smooth muscle (Abstract). FASEB J. A257, 1989. SILVER, P. J., AND J. T. STULL. Regulation of myosin light chain and phosphorylase phosphorylation in tracheal smooth muscle. J. BioL. Chem. 257: 6145-6150,1982. SIMS,‘s. M., J. J. SINGER, AND J. V. WALSH, JR. Antagonistic adrenergic-muscarinic regulation of M current in smooth muscle cells. Science Wash. DC 239: 190-193, 1988. , SMALL, R. C., R. W. FOSTER, J. P. BOYLE, AND J. M. DAVIES. The relationship between electrophysiological and mechanical events in airways smooth muscle. In: Mechanisms in Asthma:

REVIEW

154.

155.

156.

157.

158.

159.

160.

161.

163.

164.

165. 166.

167.

168.

169.

170.

171.

172.

173.

Pharmacology, Physiology and Management. New York: Liss, 1988, p. 205-217. SOMLYO, A. V., M. BOND, A. P. SOMLYO, AND A. SCARPA. Inositol trisphosphate-induced calcium release and contraction in vascular smooth muscle. Proc. N&Z. Acad. Sci. USA 82: 5231-5235, 1985. SOMLYO, A. V., AND C. FRANZINI-ARMSTRONG. New views of smooth muscle structure using freezing, deep-etching and rotary shadowing. Experientia Base1 41: 841-856, 1985. SOMLYO, A. V., AND A. P. SOMLYO. Electromechanical and pharmacomechanical coupling in vascular smooth muscle. J. Pharmacol. Exp. Ther. 159: 129-145, 1968. SOUHRADA, M., AND J. F. SOUHRADA. Reassessment of electrophysiological and contractile characteristics of sensitized airway smooth muscle. Respir. Physiol. 46: 17-27, 1981. STANDEN, N. B., J. M. QUAYLE, N. W. DAVIES, J. E. BRAYDEN, Y. HUANG, AND M. T. NELSON. Hyperpolarizing vasodilators activate ATP-sensitive K channels in arterial smooth muscle. Science Wash. DC 245: 177-180, 1989. STEPHENS, N. S., E. A. KROEGER, AND U. KROMER. Induction of a myogenic response in tonic airway smooth muscle by tetraethylammonium. Am. J. Physiol. 228: 618-632, 1975. STROSZNAJDER, J., AND R. P. STROSZNAJDER. Stimulation of phosphoinositide degradation and phosphatidylinositol-4-phosphate phosphorylation by GTP exclusively in plasma membrane of rat brain. Neurochem. Res. 14: 707-723, 1989. STUREK, M., AND K. HERMSMEYER. Calcium and sodium channels in spontaneously contracting vascular muscle cells. Science Wash. DC 233: 475-478,1986. SUPATTAPONE, S., P. F. WORLEY, J. M. BARABAN, AND S. H. SNYDER. Solubilization, purification and characterization of an inositol trisphosphate receptor. J. Biol. Chem. 263: 1530-1534, 1988. SUZUKI, H., K. MORITA, AND H. KURIYAMA. Innervation and properties of the smooth muscle of the dog trachea. Jpn. J. Physiol. 26: 303-320, 1976. TACHADO, S. D., R. A. AKHTAR, AND A. A. ABDEL-LATIF. Activation of beta-adrenergic receptors causes stimulation of cyclic AMP, inhibition of inositol trisphosphate and relaxation of bovine iris sphincter smooth muscle. Invest. Ophthalmol. Visual Sci. 30: 2232-2239,1989. TAKENAWA, T., AND K. EGAWA. CDP-diglyceride: inositol transferase from rat liver. J. BioL. Chem. 252: 5429-5523, 1977. TAKUWA, Y., N. TAKUWA, AND H. RASMUSSEN. Carbachol-induced rapid and sustained hydrolysis of polyphosphoinositides in bovine tracheal smooth muscle, measurements of the mass of polyphosphoinositides and 1,2,diacylglycerol and phosphatidic acids. J. BioZ. Chem. 261: 14670-14675, 1986. TAKUWA, Y., N. TAKUWA, AND H. RASMUSSEN. Measurement of cytoplasmic free Ca2+ concentration in bovine tracheal smooth muscle using aequorin. Am. J. Physiol. 253 (Cell Physiol. 22): C817-C827,1987. TAKUWA, Y., N. TAKUWA, AND H. RASMUSSEN. The effects of isoproterenol on intracellular calcium concentration. J. Biol. Chem. 263: 762-768,1988. TAYLOR, C. W., AND J. E. MERRITT. Receptor coupling to polyphosphoinositide turnover: a parallel with the adenylate cyclase system. Trends Pharmacol. Sci. 7: 238-240, 1986. THEIBERT, A. B., S. SUPPATTAPONE, P. E. WORLEY, J. M. BARABAN, J. L. MEEK, AND S. H. SNYDER. Demonstration of inositol 1,3,4,5 tetrakisphosphate receptor binding. Biochem. Biophys. Res. Commun. 148: 1283-1289,1987. TORPHY, T. J., G. A. RINARD, M. G. RIETOW, AND S. E. MAYER. Functional antagonism in canine tracheal muscle: inhibition by methacholine of the mechanical and biochemical responses to isoproterenol. J. PharmacoZ. Exp. Ther. 227: 694-699, 1983. TORPHY, T. J., C. ZHENG, S. M. PETERSON, R. R. FISCUS, G. A. RINARD, AND S. E. MAYER. Inhibitory effect of methacholine on drug-induced relaxations, cyclic AMP accumulation and cyclic AMP-dependent protein kinase activation in canine tracheal smooth muscle. J. Pharmacol. Exp. Ther. 233: 409-417, 1985. TRAYNOR-KAPLAN, A. E., B. L. THOMPSON, A. L. HARRIS, P. TAYLOR, G. M. OMANN, AND L. A. SKLAR. Transient increase in phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol trisphosphate during activation of human neutrophils. J. Biol. Chem. 264: 15668-15673,1989.


INVITED 174. VAN BREEMAN, C., AND K. SAIDA. Cellular mechanisms regulating Ca2’ in smooth muscle. Annu. Reu. Physiol. 51: 315-330, 1989. 175. VAN RENTERGHEM, C., G. ROMEY, AND M. LAZDUNSOL. Vasopressin modulates the electrical activity of aortic cells by acting on three different types of ionic channels. Proc. Nutl. Acad. Sci. USA 85: 9365-9369, 1988. 176. VROLIX, M., L. RAEYMAEKERS, F. WUYTACK, F. HOFMANN, AND R. CASTEELS. Cyclic GMP-dependent protein kinase stimulates the plasmalemmal Ca2’ pump of smooth muscle via phosphorylation of phosphatidylinositol. Biochem. J. 255: 855-863, 1988. 177. WILLIAMSON, J. R., C. A. HANSEN, A. VERHOEVEN, K. E. COLL, R. JOHANSON, M. T. WILLIAMSON, AND C. FILBURN. In: CelZuZar Calcium and Membrane Transport, edited by P. C. Eaton and L. J. Mandel. New York: Rockefeller, 1987, p. 93-116. 178. WILSON, D. B., E. J. NEUFELD, AND P. W. MAJERUS. Phosphoinositide interconversion in thrombin-stimulated human platelets. J. BioL. Chem. 260: 1046-1051, 1985.

REVIEW

L133

179. YAMAGUCHI, T., B. HITZIG, AND R. F. COBURN. Endogenous prostaglandins and mechanical tension in canine trachealis muscle. Am. J. Physiol. 230: 1737-1743, 1976. 180. YATANI, A., J. CODINA, Y. IMOTO, J. P. REEVES, L. BRINBAUMER, AND A. M. BROWN. A G protein directly regulates mammalian cardiac calcium channels. Science Wash. DC 238: 1288-1292,1988. 181. YATANI, A., R. MALLERA, J. CODINA, L. BIRNBAUMER, AND A. M. BROWN. The G protein gated atria1 K channel is stimulated by three distinct Gi alfa subunits. Nature Lond. 336: 600-682, 1988. 182. YOSHINO, M., T. TOMEYA, A. NISHIO, K. YAZAWA, T. USUKI, AND H. YABU. Multiple types of voltage-dependent Ca channels in mammalian intestinal smooth muscle cells. Pfluegers Arch. 414: 401-405,1989. 183. ZENG, Y. P., C. G. BENESH, AND P. K. PANG. Guanine nucleotide binding protein may modulate gating of Ca channels in vascular smooth muscle. J. PharmacoZ. Exp. Ther. 250: 343-351, 1989.


Assessment of signal transduction mechanisms regulating airway smooth muscle contractility.

Adrenoceptors in airway smooth muscle.

Airway smooth muscle and asthma.

Contraction coupling in colonic smooth muscle.

Phosphoinositide metabolism in airway smooth muscle.

Cellular Na+ handling mechanisms involved in airway smooth muscle contraction (Review).

The proliferative response of airway smooth muscle.

Airway blood flow modifies allergic airway smooth muscle contraction.

Control of human airway smooth muscle.

Cortex phellodendri Extract Relaxes Airway Smooth Muscle.

Nicotine-induced airway smooth muscle contraction: neural mechanisms involving the airway epithelium. Functional and histologic studies in vitro.

Abnormalities in airway smooth muscle in fatal asthma.

Airway epithelial cells regulate membrane potential, neurotransmission and muscle tone of the dog airway smooth muscle.

Effect of frusemide on airway smooth muscle contractility in vitro.

Receptor-activated calcium influx in human airway smooth muscle cells.

Cigarette Smoke and Estrogen Signaling in Human Airway Smooth Muscle.

Isometric and isotonic contractions in airway smooth muscle.

Maturational changes in airway smooth muscle structure-function relationships.

Changes of airway smooth muscle in experimental asthma.

Airway smooth muscle mechanics and biochemistry in experimental asthma.

Strain-related differences in airway smooth muscle and airway responsiveness in the rat.

Mechanisms of Vascular Smooth Muscle Contraction and the Basis for Pharmacologic Treatment of Smooth Muscle Disorders.

CF airway smooth muscle transcriptome reveals a role for PYK2.

Mechanism of H2O2-induced modulation of airway smooth muscle.