Response of Sarcolemmal Fatty Acid Transport Proteins to Moderate Exercise in Human and Rat Muscle

Abstract

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.