Sarcolemmal FAT/CD36 in human skeletal muscle colocalizes with caveolin-3 and is more abundant in type 1 than in type 2 fibers.

FAT/CD36 is a transmembrane protein that is thought to facilitate cellular long-chain fatty acid uptake. However, surprisingly little is known about the localization of FAT/CD36 in human skeletal muscle. By confocal immunofluorescence microscopy, we demonstrate high FAT/CD36 expression in endothelial cells and weaker but significant FAT/CD36 expression in sarcolemma in human skeletal muscle. No apparent intracellular staining was observed in the muscle cells. There are indications in the literature that caveolae may be involved in the uptake of fatty acids, possibly as regulators of FAT/CD36 or other fatty acid transporters. We show that in sarcolemma, FAT/CD36 colocalizes with the muscle-specific caveolae marker protein caveolin-3, suggesting that caveolae may regulate cellular fatty acid uptake by FAT/CD36. Furthermore, we provide evidence that FAT/CD36 expression is significantly higher in type 1 compared with type 2 fibers, whereas caveolin-3 expression is significantly higher in type 2 fibers than in type 1 fibers.