Muscle contractile activity increases fatty acid metabolism and transport and FAT/CD36
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We have examined whether 1) fatty acid (FA) uptake, 2) FA transporter expression, and 3) FA metabolism are increased when the oxidative capacity of skeletal muscle is increased. The oxidative capacities of red and white tibialis anterior and extensor digitorum longus muscles were increased via chronic stimulation (10 Hz, 24 h/day for 7 days). The contralateral muscles served as controls. After 7 days of increased muscle activity 1) palmitate uptake by giant sarcolemmal vesicles was increased twofold ( P < 0.05), 2) the expression of FA translocase (FAT)/CD36 was increased at both the mRNA (3.2- to 10-fold) and protein (3.4-fold) levels, and 3) palmitate oxidation and esterification into triacylglycerols and phospholipids were increased 1.5-, 2.7-, and 1.7-fold, respectively ( P < 0.05). These data show that when the oxidative capacity of muscle is increased, there is a parallel increase in the rate of FA transport and FA transporters at the sarcolemmal membrane, which is associated with the enhanced expression of the membrane transporter FAT/CD36.Keywords:
CD36
Sarcolemma
During muscle contraction the active transport of Na+ and K+ over the sarcolemma membrane is increased due to regulation of the Na+,K+-ATPase (NKA) activity. The FXYD1 protein, phospholemman (PLM), is expressed in skeletal muscle where it is known to regulate NKA activity. Our aim The purpose of the study was to investigate the influence of exercise on the concentration of PLM in the sarcolemma membrane. Method Rats were exposed to treadmill running. Immediately after exercise sarcolemma membrane were isolated as giant sarcolemma vesicles and analysed by Western blotting. Results Exercise increased the amount of PLM by 203 % (p < 0,05; n = 9) and caveolin-3 (Cav-3) by 21 % (p < 0,05; n = 8) in giant sarcolemma vesicles. Discussion During muscle contractions there is a change in the regulation of the NKA. Both hormones and intracellular alterations in [Na+] regulate the activity of the NKA. In muscle tissue interactions by PLM have shown to regulate the NKA activity. However, it is unknown to what extent PLM is involved in regulating NKA activity during exercise. The profound increase in the concentration of PLM found in giant sarcolemma vesicles indicates that PLM translocates from an internal compartment to the sarcolemma membrane during exercise. This translocation could increase the amount of PLM associated whit NKA, and thereby regulate the NKA activity. Alternatively: The increase in Cav-3 indicates that a structural change of the membrane may take place during exercise. This could also influence the distribution of PLM.
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Dysferlin
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CD36
Scavenger Receptor
Foam cell
Monocyte
Cholesteryl ester
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CD36
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Fatty acid transport proteins, including fatty acid translocase (FAT/CD36) and plasma membrane fatty acid binding protein (FABPpm) are responsible for protein-mediated uptake of long chain fatty acids (LCFA) into skeletal muscle. These proteins have been shown to exist in intracellular vesicles and translocate to the plasma membrane in response to acute electrical stimulation in rat skeletal muscle, however this has not been tested in exercising animals or humans. PURPOSE: To determine if prolonged moderate intensity exercise increases the content of fatty acid transport proteins at the sarcolemma in rat and human skeletal muscle and if this is accompanied by an increase in LCFA transport in rats. METHODS: Nine male and female subjects cycled for 120 min at ∼60 ± 2% VO2 max. Two skeletal muscle biopsies were taken at rest and again following 120 min of cycling and expired gases were sampled throughout exercise. Giant sarcolemmal vesicles were prepared from the muscle biopsies and the remaining muscle was used for whole muscle measurements. 4 male and 4 female Sprague-Dawley rats completed a 2 h treadmill run at 20 m/min while four male and four female rats acted as non-running controls. Giant sarcolemmal vesicles were prepared from the hindlimb muscles and palmitate uptake was measured. Protein content of FAT/CD36 and FABPpm were measured in both giant sarcolemmal vesicles and whole rat and human skeletal muscle homogenates. RESULTS: In human skeletal muscle, plasma membrane FAT/CD36 protein content increased by 40-300% following 120 min of exercise (p < 0.05), while whole muscle homogenate FAT/CD36 was unchanged. There was no change in FABPpm protein in human muscle. Transport increased 1.2-fold (p < 0.05) with exercise in rat muscle, which correlated with an increase in sarcolemmal FAT/CD36 (1.2-fold) and FABPpm (1.3-fold) protein. There was no change in sarcolemmal protein content in whole muscle. CONCLUSIONS: The rat and human data suggest that fat transport proteins are mobilized and translocated to the plasma membrane of skeletal muscle during prolonged endurance exercise to assist with increased LCFA uptake into the cell. The increase was restricted to FAT/CD36 in human skeletal muscle, and the increase was larger and more variable than found in rat skeletal muscle. Funded by CIHR and NSERC, Canada.
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Na+,K+-ATPase activity, phosphorylation, and [3H]ouabain binding in sarcolemma isolated from spontaneously hypertensive rat (SHR) hearts were compared to the same parameters in sarcolemma from normotensive rat (WKY) hearts. Sarcolemma prepared from SHR heart contained significantly less ouabain-inhibitable ATPase activity than sarcolemma from WKY heart. No significant differences in sarcolemmal protein content or recovery were noted between the two groups. The numbers of phosphorylation sites and ouabain binding sites were lower for SHR hearts than for WKY hearts. The KD values for ouabain binding were the same (0.30 muM) in cardiac sarcolemma of SHR and WKY. The I50 values for inhibition by ouabain of Na+,K+-ATPase were also the same for both groups (SHR = 49 microM; WKY = 44 microM). These data suggest that the decrease of cardiac sarcolemmal Na+,K+-ATPase activity in SHR hearts is due to a decrease in the number of active sites.
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The sarcolemma preparations isolated from the skeletal muscles of the normal rabbits and those with E-avitaminosis are characterized by electron microscopy according to the activity of 5-nucleotidase and different ATPase systems. As the data of electron microscopy evidence, the sarcolemma preparations of the normal and dystrophic muscles are deprived of admixtures of other subsellular structures. The 5-nucleotidase activity in the sarcolemma of dystrophic muscles is almost thrice as high as in the sarcolemma of normal muscles. On the basis of the results of studies in the kinetic parameters the optimal conditions are selected to investigate the Mg2+, Ca2+ and Na+, K+-ATPase activity. It is shown that under dystrophy the ATPase activity in the sarcolemma preparations in the presence of Ca2+ and Mg2+ does not change as compared to the norm. As to the Mg2+-dependent Na+, K+-ATPase system its activity in sarcolemma of muscles under dystrophy lowers noticeably. Ouabain-sensitive Na+, K+-ATPase of sarcolemma under dystrophy is considerably lower than at the normal level and is 4.1 and 12.1 mumol and phi n per 1 mg of protein for 1 h, respectively. Proceeding from the data on the changes in the lipid composition of sarcolemma of muscles with E-avitaminous dystrophy a problem is under discussion concerning dependence of the transport Na+, K+-ATPase activity on the structure of sarcolemma.
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Sarcolemma consists of plasma and basement membranes and constitutes the real permeability barrier to the heart cell. It is considered to provide high electrical resistance and capacitance to heart cell and its properties are essentially similar to those of the other excitable membranes. Methods are now available for isolating heart sarcolemma with high specific activities of adenylate cyclase, (Na(+)-K(+) ATPase, Ca(++) ATPase, and Mg(++) APTase. These enzymes are considered to play an important role in heart function by regulating ion movements across sarcolemma as well as by providing signals for various metabolic processes. Sarcolemma possesses different hormone and drug receptors and any alteration in its composition could result in abnormal responses of the myocardium. We believe that heart failure is associated with sarcolemmal defects which can be detected by monitoring the activities of different membrane-bound enzymes and other related processes.
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Scavenger Receptor
Foam cell
THP1 cell line
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Abstract Although Ca 2+ ‐dependent signaling pathways are important for skeletal muscle plasticity, the sources of Ca 2+ that activate these signaling pathways are not completely understood. Influx of Ca 2+ through surface membrane Ca 2+ channels may activate these pathways. We examined expression of two L‐type Ca 2+ channels in adult skeletal muscle, the Ca V 1.1 and Ca V 1.2, with isoform‐specific antibodies in Western blots and immunocytochemistry assays. Consistent with a large body of work, expression of the Ca V 1.1 was restricted to skeletal muscle where it was expressed in T‐tubules. Ca V 1.2 was also expressed in skeletal muscle, in the sarcolemma of type I and IIa myofibers. Exercise‐induced alterations in muscle fiber types cause a concomitant increase in the number of both Ca V 1.2 and type IIa–positive fibers. Taken together, these data suggest that the Ca V 1.2 Ca 2+ channel is expressed in adult skeletal muscle in a fiber type–specific manner, which may help to maintain oxidative muscle phenotype. Muscle Nerve, 2007
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