Effect of training and detraining on skeletal muscle glucose transporter (GLUT41 content in rats p. D. NEUFER,'M. H. SHIWEBAWGEW, AND G. L. DOHM Department of Biocherazbtry, School sf Medicifze, East Carolina klniversi~,Greenville, MC 27858, UoI.S.A.

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Received February 12, 1982

M. He, and DOHM,G. L. 1992. Effect of training and detraining on skeletal muscle g l ~ c s s e NEWFER, D., SWINBBARGER, transporter (GLUT4) content in rats. Can. J. Physiol. Bharrnacol. 70: 1286- 1290. The aim of the present study was to examine the effects of treadmill exercise training and detraining on the skeletal muscle fiber type specific expression of the insulin-regulated glucose transpogeer protein (GLUT4) in rats. GLUT4 protein content was determined by Western and dot-blot analysis, using a polyclonal antibody raised against the carboxy-terminal peptide. Rats were sacrificed 24 h after the last training session. There were no significant changes in muscle GLUT4 afier 1 day or 1 week of training. Six weeks of training increased GLUT4 protein content 1.4- to 1.7-fold ( p < 0.05) over controls in the soleus and red vastus lateralis, whereas no significant change was evident in the white vastus lateralis muscle. GLUT4 protein content in both soleus and red vastus lateralis muscle returned to near control values after 7 days of detraining. Similar to GLUT4, citrate synthase activity showed no change after 1 day or B week of training, increased I .$-fold over controls after 6 weeks of training, but returned to control values after 7 days detraining. These findings demonstrate that muscle GLUT4 protein is increased in rats with as little as 6 weeks of treadmill exercise training but that the adaptation is lost within I week of detraining. It is suggested that expression of the GLUT4 protein is coordinated with the well-documented adaptations in oxidative enzyme activity with endurance training and detraining. Key words: insulin-regulated glucose transporter protein, citrate synthase. NEUFER, P. D., SHINESARGER, M. H.,et DOHM,G. L. 1892. Effect of training and detraining on skeletal muscle glucose transporter (GLUT4) content in rats. Can. J. Physiol. Bharmacol. 70 : I284 - 1290. Le but de la prksente 6tude a CtC d'examiner les eifets d'un entrainernent en endurance sur tapis roulant et ceux du rapss sur l'expressisn spdcifique type de la p r o t h e de transport. du glucose rCgul6e par l'insuline (GLUT4) dans la fibre msculaire squelettique du rat. On a dCterminC la teneur en proteine GLUT4 par les techniques de buvardage en taches et de Western, en utilisant un anticorps polyclonal montd contre le peptide en terminaison carboxy. On a sacrifiC les rats 24 h aprks la dernikre seance d'exercices. I1 n'y a pas eu de variations significatives de la GLUT4 aprks 1 jour ou 1 sernains d'entrainement. Six semaines d'entrainernent ont augment6 la teneur en protkine GLUT4 d9unfacteur 1,4- 1,7 ( p < 0,05) plus Clevt que celle des tkmoins dans le ssleaire et le muscle vaste externe rouge, alors qu'aucune variation significative n9a 6t6 obsewCe dans He muscle vaste externe blanc. La teneur en p r o t h e GLUT4 dans les muscles vaste externe rouge et solCaire est presque retournke aux valeurs tCrnoins aprbs '9 jours de repos. Comme pour Ia GLUT4, l'activite de citrate synthase n'a montrC aucune variation aprks 1 jour ou 1 semaine d'entrainement, elle a augment6 d'un facteur 1,8 au-dessus des valeurs tkrnoins aprks 6 semaines d'entrafnernent, mais est retournee aux valeurs t h o i n s aprks 7 jours de repos. Ces rtsuleats demoratrent que la teneur en p r o t h e GLUT4 musculaire est augment& chez les rats au plus avec 6 semaines daentraPnementen endurance sur tapis roulant, mais que 19adaptabionest perdue aprks moins d 91 semaine de repos. On suggkre que %'expressionde la protCine GLUT4 est coordonnee avec les adaptations bien connues de l'activitC enzyrnatique oxyddive avec I'entrainemene en endurance et le repss. Mots cb6s : prsteine de transport du glucose rCgu%Cepar %'insuline, citrate synthase. [Traduit par la rCdaction]

Introduction Glucose transport in skeletal muscle occurs via facilitated diffusion mediated primarily by a tissue-specific (adipose and skeletal muscle), insulin-sensitive transporter protein referred to as GLUT4 (Bisnbaum 1989; Charron et a&. 1989; James et a&.1989; Kaestner et al. 1989)- Both insulin and contractile activity stimulate glucose transport by invoking the translocation of GLUT4 from an intracellular membrane to the cell surface (Douen et al. 2989, 1990; Fkashiki ut a&.1989; Hirshman et a%.1990; Klip et a&. 198'9, 1990). Thus, the total GLUT4 protein available for translocation may be an important determinant of maximal glucose transport in skeletal muscle. In rats, maximal gglracse transport is increased in skeletal muscle with endurance exercise training (Ivy et a&.1989; J m e s et a&.1984, 1985; PIsug et a&.1987, 1990). This suggests that GLUT4 protein content and (or) intrinsic activity is increased with endurance exercise training. The effect of exercise training on GLUT4 expression was first reported in the genetically obese Zucker (fa&) rat, in which nearly a 2.5-fold increase in GLUT4 protein content was found in the gastrocnemius 'Author for correspondence. Printed in Canada !FrnprimC au Canada

muscle after 18-30 weeks s f treadmill exercise training (Friedman et al. 1990). A number s f recent studies have confirmed these findings in normal nsnsbese animals, using a variety of training modes (Ploug et al. 1998; Rodnick et a&. 1998; Wake et al. 1991). Collectively, these data indicate that changes in muscle GLUT4 expression may represent a primary adaptation to endurance exercise training, allowing for an enhmced glucose transport capacity. Whether the cellular stirnulus regdating GLUT4 expression is similar to that governing the training-induced adaptations in muscle oxidative enzyme activity is not known. As an initial step to address this question, we sought to determine in more detail the influence of endurance training on GLUT4 expression in skeletal muscle. Specifically, our aim was to determine the time course over which GLUT4 protein content is altered in response to training 41 day, 1 week, 6 weeks) and detraining (1 week) relative to changes in oxidative enzyme activity.

Methods Four-week-old female BF9lish-i~rats (75 - 100 g) were purchased from Charles River Laboratories and housed and maintained on standard

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FIG. 1 . Autoradiogram obtained from Western blot analysis of the GLUT4 glucose transporter protein in rat red vasms lateralis muscle. Muscle membranes were isolated, and total membrane protein (50 pgllane) was separated by %IDS-polyacrylamide gel electrophoresis, electropkoretically transferred to Imobolin membrane, and immunoblof ed with anti-GLUT4 antibody (raised in rabbits against the carboxyl-terminal region of GLUT4) and anti-rabbit t25~-labeled IgG. STD, rat heart standard; 6WCTL, 6 weeks control; IBTR, 1 day trained; IWTR, 1 week trained; 6WTR, 6 weeks trained; 7WCTL, 7 weeks control; IWDT, 1 week detrained.

f d (Brarina Rat Chow) and water in accordance with the Guide to the! Care o d Use of&peBjmentaCk&Animals. The animals were randomly assigned to one of four exercise training groups (1 day, I week, 6 weeks, or 6 weeks 1 week detraining) or one of two control groups (6 weeks or 7 weeks). Training for the 6 week trained animals began at 5 weeks of age and consisted of treadmill running at 15 d m i n , 0 % grade, for 2 Alday. Training demand was progressively increased during the initial 2 weeks to achieve a final intensity of 25 mlmin, 15% grade, for 2 hlday, 6 dayslweek. Afer 6 weeks, one group of animals was sacrificed, while a second group remained sedentary for an additional week (1 week detraining). Control rats were sacrificed corresponding to either the 6 week trained or 6 week trained + 1 week detrained groups. To eliminate any possible effects of aging, training of the 1-day and 1-week groups was delayed such that all animals were sacrificed at the same age (i.e., 1-week group delayed for 5 weeks). During the initial 5 -6 weeks, these rats were familiarized with treadmill running for 1 -2 minlday. The training protocol for the 1-day and 1-week groups consisted of treadmill running at 25 mlmin, 0 % grade, 2 hlday. All animals were sacrificed 24 h after the last training session. Soleus and portions of the red and white vastus lateralis muscle were excised and rapidly frozen with aluminum tongs cooled in liquid nitrogen. All samples were powdered using a cold steel mortar and pestle, mixed, and transferred to tubes for storage at -70°C until analysis. An aliquot (200 mg) of powdered muscle was homogenized (Pelytron) in 2 mL sf c d d (4°C) buffer (pH 7.4) containing 25 mM Hepes, 25 mM bemamidine, 4 mM EBTA, 0.5 mM phenylmethylsulfonyl fluoride (PMSF), and 1 pM each of leupeptin, pepstatin, and aprotiwin. To isolate total cdlular membranes, samples were centrifuged at 150 000 x g for 1 h at 4 "G. The resulting pellet was rinsed and resuspended (Polytron) in cold buffer. Triton was added to each resuspension to give a final concentration of 1%, The samples were allowed to sit on ice for 1.5 h to solubilize the membrane-bound protein. After a final spin (150 000 x g , 1 h, 4"@), the supernatant was removed, aliquoted, and stored at -70°C. For the quantification of GLUT4, 50 pg of protein (Pierce BCA) per sample was mixed with buffer containing 12.5 mM Tris, 4.6% sodium dodecyl sulfate (SBS), 20 % glycerol, and 2.5 9% ditkothreitol (DTT) and subjected to SBS -ptblyacrylamide gel electrophoresis on an 8 % resolving gel. Proteins were transferred to Immobilon membranes by dectrotransfer and incubated in a polyclonal antibody raised in rabbits against the carboxy-terminal region of the GLUT4

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protein (Kern ct wk. 1990) followed by 1251-labeledanti-rabbit IgG. Autoradiographs revealed only a single band, corresponding to a molecular mass of 45 kDa (Fig. 1). Owing to the large number of samples per muscle type and the high specificity of the plyclonal antibody, GLUT4 protein was also quantitated by direct blotting to nitrocellulose paper (dot blot) in a vacuum-filtration manifold (Schleicher and Schuell, Inc., Keene, N.M.). The dot-blot procedure permitted the simultaneous assessment of GLUT4 from all samples of a given muscle. The dot-blot procedure has been validated by comparing quantification of GLUT4 protein by repeated Western versus dot-blot analysis of six skeletal muscles composed of different fiber types (correlation coefficient >0.98, Kern ef a!. 1992)-To allow for comparison of GLUT4 protein between separate dot blots, a rat heart GLUT4 standard curve was generated on each blot by applying 10-50 pg of rat heart membrane protein. GLUT4 protein levels are expressed as microgram equivalents sf rat heart standard as determined from the corresponding regression equation for absorbance units versus micrograms of rat heart membrane protein loaded. Total rat heart membrane protein was prepared for Western and dot-blot analysis in the same manner as that described for skeletal muscle. For the determination of citrate synthase activity, 50 mg of muscle was homogenized (Polytron) in 2 mL of cold (4°C) buffer containing 175 mM KPO, and 2 m M EDTA, pH 7.5. Citrate synthase activity was measured in whole homogenates according to Srere (1969). All data were analyzed using one-way analysis of variance and are expressed as mean _+ SE. Differences between groups were detected using posthoc Newman-Keuls test with significance set at the P < 0.05 level.

Results Trakniag Figure 1 shows a representative autoradiograph obtained from Western blot analysis of red vastus lateralis muscle from each experimental group and a rat heart membrane standard. A 45-kDa protein was labeled with high specificity ((Fig. I). As such, GLUT4 protein was quan%itatedusing dot-blot maly sis . The level of GLUT4 protein in soleus muscle was 1.7-fold higher after 6 weeks of training relative to controls and 2-fold higher when compared with the 1 day trained group (Fig. 2). Mthough 1 day of braining appeared to decrease GLUT4 levels, no significant differences were present with 1 day or 1 week s f training as compared with csntro1s.

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FIG. 2. Effect of training on rat soleus muscle GLUT4 protein content, expressed as microgram equivalents s f rat heart standard (determined from regression andysis of absorbance units versus micrograms of rat heart protein loaded). Data represent mean f SE with N = 7 (1 day trained), N = 8 (esntrol), and N = 9 (1 and 6 weeks trained). "Significantly ( p < 0.05) different from all other groups.

In the red vastus lateralis muscle, training elicited a 1.4-fold increase in GLUT4 protein content compared with csntrsls and nearly a 1.7-fold increase relative to the 1 day trained animals (Fig. 3A). One day or I week of training did not produce any significant change in GLUT4 levels. GLUT4 protein in the white vastus lateralis muscle was not affected by 1 day, I week, or 6 weeks sf training (Fig. 3B). Detraining Shown in Fig. 4 are the GLUT4 levels after I week of detraining in the soleus and red vastus lateralis muscles. The levels sf GLUT4 protein after I week of detraining were no longer significantly different from control vdues in both the soleus and red vastus lateralis muscle. Oxidative enzyme activity To determine the extent to which changes in GLUT4 protein parallel adaptations in oxidative enzyme activity with training and detraining, citrate synthase activity was measured in red and white vastus lateralis muscle. Gitrate synthue activity followed a pattern similar to GLUT4 in response to training. In the red vastus lateralis muscle citrate sywthase activity was 1.$-fold higher after 6 weeks of training. No significant change was evident after 1 day or 1 week of training (Fig. 5). Similar to changes in muscle GLUT4, the tsaining-induced increase in citrate synthase activity was lost within 1 week of detraining (Fig. 59. As with GLUT4, no change in citrate synthase activity was found in the white vastus laterdis muscle with training (data not shown). Owing to limited tissue, citrate synthase activity was not determined in the soleus muscle.

Discussion The present findings demonstrate that GLUT4 transporter protein content is increased in skeletal muscle after 6 weeks of treadmill exercise training. This agrees with our data from the

0 FIG.3. Effect s f training on GLUT4 protein content, expressed as microgram equivalents of rat heart standard (see Fig. 2 ) , in red and white portions of the vastus lateralis muscle. "Significantly ( p < 0.05) different from all other groups.

obese Zucker rat after 18-30 weeks of training (Friedman et a!. 1990) and recent findings of others examining 6- 10 weeks of voluntary wheel cage exercise (Wodnick et al. 1990) or swim training (Ploug et sl. 1990). Ploug et al. (19%) also reported that the training-induced increase in GLUT4 protein was associated with a 1.5-fold higher GLUT4 mRNA level, suggesting that exercise training may regulate GLUT4 expression at the level of gene transcription. The training protocol employed in the present study required a training duration of 6 weeks to detect a significant increase in GLUT4 protein content and citrate synthase activity. However, within 1 week of detraining, both GLUT4 protein and citrate synthase activity decreased to levels no longer significantly different from control vdues. Bas4 on these findings, it appears

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FIG. 5. Effect of training and detraining on citrate synthase activity in the red portion of the vastus lateralis muscle. "Significantly ( p < 0.05) different from all other groups.

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FIG. 4. Effect of 1 week of detraining on GLUT4 protein content, expressed as microgram equivalents of rat heart standard (see Fig. 2), in the soleus and red portion of the vastus lateralis muscle. Data represent mean f SE with N = 7 (control) and N = 9 (6 weeks trained and 1 week detrained). *Significantly ( p < 0.05) different from all other groups. tSignificantly different from control.

that GLUT4 hiis a relatively short half-life, similar to that reported for oxidative enzymes (i.e., cytochrome c tin = 7 days; Booth 1977). Overall, our findings indicate that changes in GLUT4 protein content follow a similar time course to changes in mitochondrial protein in response to training and detraining (Holloszy and Coyle 1984; Neufer 1989). Two possibilities may account for the apparent fiber type specific adaptation of GLUT4 to training. One possibility is that control of GLUT4 expression may be regulated differently in red versus white muscle fiber types in response to exercise training. In rats, GLUT4 protein content and mRNA are inherently higher in muscles consisting of predominantly

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red oxidative (type I and IIa) compared with white glycolytic (type IIb) fibers (Henriksen et al. 1990; Kern et al. 1990). This difference in GLUT4 mRNA and protein corresponds to similar fiber type specific differences in maximally stimulated glucose transport (Hensiksen et al. 1990; Kern et al. 1990). Thus, the cellular dynamics governing GLUT4 gene expression appear to be very different between fiber types. However, the nature of reguHation in response to an exercise training stimulus is presently not h o w n . A second possibility is that gene expression in skeletal muscle is simply a function of muscle recruitment pattern. For example, chronic electrical stimulation of white glycslytic muscle for 10-2 1 days elicits a complete biochemical transformation to that of a red oxidative muscle, including up to a 3- to 4-fold increase in mitochondria1 enzyme activity (Pette 1984). Endurance training also results in a 2- to $-fold increase in oxidative enzyme activity but only in those muscles recruited during exercise (Holloszy and Coyle 1984; Terjung and Hood 1986). m e recruitment pattern for t r e a d d l running used in the present study typically elicits biochemical adaptations within the slow twitch oxidative (soleus) and fast twitch oxidative (red vastus) muscles (Dudley et al. 1982). This raises the possibility that GLUT4 expression may coincide with adaptations in oxidative enzyme activity according to the specific demand placed upon the muscle. In the present study, citrate synthase activity increased by 1 .$-fold in the red vastus lateralis but was unchanged in the white vastus lateralis muscle after 6 weeks of training (Fig. 5). Likewise, GLUT4 protein content increased in the red vastus lateralis, whereas no change occurred in the white vastus lateralis muscle. When training was stopped, both citrate synthase activity and GLUT4 protein content were no longer different from control levels after 1 week of detraining. These findings thus appear to support the concept that contractile activity per se may be a major factor involved in regulation of skeletal muscle GLUT4 expression in response to endurance training. In contrast to our data, Rodnick et al. (1990) recently

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reported a 60% increase in GLUT4 protein content in the plantaris (fast twitch mixed oxidative-glycolytic fibers) muscle and no change in the sosleus (slow twitch oxidative fibers) muscle after 6 weeks s f voluntary wheel cage running. Moreover, GLUT4 mRNA has been reported to be increased in the white vastus lateralis muscle of high fat fed animals undergoing a similar training protocol (Wake et a&. 1991). Muscle fiber recruitment, however, was likely limited to fast twitch oxidative and glycolytic fibers as a result of the intermittent, high-intensity nature of wheel cage exercise (Rodnick e$ al. 1989). Thus, the changes in GLUT4 protein content noted by these authors m y also have been governed by the muscle recruitment pattern dictzted by the made of training. The results presented in this study demonstrate thzt endusance exercise training produces marked increases in skeletal muscle GLUT4 protein content. Although GLUT4 levels are increased with as little as 6 weeks of training, the adaptation is lost within 1 week of detraining, Moreover, our findings suggest that the cellular stimulus regulating GLUT4 expression with training may be similar to that governing the traininginduced adaptations in muscle oxidative enzyme activity.

Acknowledgements The authors thank K. Jones for expert technical assistance. This work was supported by National Institutes of Hedth grant RQ1-DK-38416. Birnbaum, M. J. 1989. Identification of a novel gene encoding an insulin-responsive glucose transporter protein. Cell, 57: 305 - 3 15. Booth, F. W. 1977. Effects of endurance exercise on cytochrome c turnover in skeletal muscle. Hn The marathon: physiological, medical, epidemiological, and psychological studies. Ann. N oY. Acad. Sci. 301: 431-439. Charron, M. S., Brosius, F. C., Alper, S. k . , and Lsdish, M. F. 1989. A glucose transport protein expressed predominately in insulinresponsive tissues. Broc. Natl. Acad. Sci. U.S.A. $6: 2535 -2539. Douen, A. G o ,Ramlal, T., Klip, A., Young, D. A,, Cartee. G. B., and Holloszy, J. 0 . 1989. Exercise-induced increase in glucose transporters in plasma membranes of rat skeletal muscie. Endocrinology (Baltimore), 124: 449 -454. Douen, A. G . , R a d a l , T., Rastogi, S., Bilan, P. J., Cartee, G . D., Vranic, M., Holloszy , J. O., and Mip, A. 1990. Exercise induces recruitment sf the "insulin-responsive glucose transporter. " 9. Biol. Chem. 265: 13 427 - 13 430. Dudley, G . A., Abraham, W. A., and Terjung, R. L. 1982. Influence of exercise intensity and duration on biochemical adaptations in skeletal muscle. J. Appl. Physiol. 53: 844 - 850. Friedman, .I. E., Sherman. W. M., Weed, M. J., Elton, @. W., and Dohm, G. L. 1990. Exercise training increases glucose transporter protein GLUT4 in skeletal muscle of obese Zucker (falfa) rats. FEBS Lett. 268: 13-16. Fushiki, T., Wells, J. A., Tapcott, E. B., and Dohm, @. L. 1989. Changes in glucose transporters in muscle in response to exercise. Am. J. Bhysiol. 256: E580-E587. Henriksen, E. J., Bourney, hi. E., Wodnick, K. S . , Koranyi, k . , Permutt, M. A., and Holloszy, J. 0. 1990. Glucose transporter protein content and glucose transport capacity in rat skeletal muscles. Am. J. Physiol. 259: E593 -E598. Mirshman, M. F., Goodyear, L. J., Wardzala, L. J., Horton, E. D., and Horton, E. S. 1990. Identification of an intracellular p w l of glucose transporters from basal and insulin-stimulated rat skeletal muscle. 9. Biol. Chem. 265: 987-991.

Holloszy, S. 0., and Coyle, E. F. 1684. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J. Appl. Physiol. 56: $31-838. Ivy, J. E., Brozinick, J. T., Jr., Tsrgan, C. E., and Kastello, 6. M. 1989. Skeletal muscle glucose transport in obese Zueker rats after exercise training. B. Appl. Physiol. 66: 2635 - 264 1. James, D. E., Kraegen, E. W . , and Chisholm, D. J. 1984. The effect of exercise training on whole body insulin sensitivity and responsiveness. 5. Appl. Physiol. 56: 1%17- 1222. James, D. E., Kraegen, E. W., and Chisholm, D. J. 1985. Effects of exercise training on in vivo insulin action in individual tissues s f the rat. J. Clira. Invest. 76: 657 -666. James, D. E., Stmbe, M., and Mueckier, M. 1989. Molecular cloning and characterization of an insulin-regulatable glucose transporter. Nature (London), 33: 83 - 87. Kaestner, K. H., Christy, W. J., Mcknithan, J. C . , Braiterman, L. T.. Cornelius. P., Bekala, B. H e , and Lane, M. B . 1989. Sequence, tissue distribution, and differential expression of mRNA for a putative insulin-responsive glucose transporter in mouse 3T3-L1 adipocytes. Proc. Natl. Acad. Sci. U.S.A. 86: 3158-3154. Kern, M., Wells, 9. A., Stephens, J. M., Elton, C. W., Friedman, J. E., Tapscott, E. B., Pekala, P. H.: and Dohm, G. L. 1990. Insulin responsiveness in skeletal muscle is determined by glucose transporter (GLUT4) protein level. Biochem. J. 278: 397 -400. Kern, M., Dolan, P. E., Mazzeo, W. S., Wells, J. A., and Bshm, G. E. 1992. Effect of aging and exercise on glucose transporters (GEUT4) in muscle. Am. J. Physiol. 263: E362-E367. Klip, A., Ramlal, T., Young, D. A . , and Holloszy, 9. 0 . 1987. Insulin-induced translocation of glucose transporters in rat hindlimb muscles. FEBS Lett. 224: 224 -238. Klip, A., Ramlal, R., Bilan, P. F., Cartee, G. D.,Gulve, E. A . , and Holloszy, S. 1990. Recruitment of GLUT-4 glucose transporters by insulin in diabetic rat skeletal muscle. Biochem. Biophys. Res. Commun. 172: 728 -736. Neufer, B. D. 1989. The effect of detraining and reduced training on the physiological adaptations to aerobic exercise training. Sports Med. 8: 302-321. Pette, D. 1984. Activity-induced fast to slow transitions in mammalian muscle. Med. Sci. Sports Exercise. 16: 517-528. Ploug, T., Galbo, H., Vinten, J., Jorgensen, M., and Richter, E. A. 1987. Kinetics of glucose transport in rat muscle: effects of insulin and contractions. Am. J. Physiol. 253: E12 -E28. Ploug, T., Stdlhect, B. M., Pedersen, O., K&n, B. B., Ohkuwa, T., Vinten, J . , and Calbo, H. 1990. Effect s f endurance training on glucose transport capacity and glucose transporter expression in rat skeletal muscle. Am. J. Physiol. 259: E778 -E786, Rodnick, K. J., Reaven, G. M., Haskell, W. L., Sirns, C. W., and Msndon, C. E. 1989. Variations in mnning activity and enzymatic adaptations in voluntary mnning rats. J . Appl. Physiol. 66: 1258- 8257. Rodnick, K. J . , Holloszy, J. 0 . , Msndon, C. E., and James, D. E. 1990. Effects s f exercise training on insulin-regulatable glucosetransporter protein levels in rat skeletal muscle. Diabetes, 39: 8425- 8429. Srere, P. A. 1969. Methods of enzymology. Vsl. XIIT. Academic Press, New York. pp. 3 -5. Terjung, W. L., and Hood. D. A. 1986. Biochemical adaptations in skeletal muscle induced by exercise training. In Nutrition and aerobic Exercise. Edited by D. K. Layman. American Chemical Society, Washington, D.C. pp. 8-27. Wake, S. A., Sowden, J. A., Storlien, L. H., James, D. E., Clark, P. W., Shine, J., Chisholm, D. J., and Hgraegen, E. W. 1991. Effects sf exercise training and dietary manipulation on insulinregulatable glucose-transporter mRNA in rat muscie. Diabetes, 40: 275 -279.

Effect of training and detraining on skeletal muscle glucose transporter (GLUT4) content in rats.

The aim of the present study was to examine the effects of treadmill exercise training and detraining on the skeletal muscle fiber type specific expre...
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