Intracellular Transport of Fatty Acids in Muscle

Abstract

Long-chain fatty acids represent a major substrate for energy production in striated muscles, especially in those muscles which have a high oxidative enzymatic capacity. Following their uptake from the extracellular compartment the fatty acids have to translocate through the aqueous cytoplasm of the myocytes to reach the mitochondria where they undergo oxidative degradation. This intracellular transport is assisted by cytoplasmic fatty acid-binding protein (FABP_c), a small (15 kD) protein which shows a high affinity for the non-covalent binding of long-chain fatty acids, and of which several types occur. So-called heart-type or muscle-type FABP_c is found in muscle cells, and is abundant especially in oxidative fibers. The muscular FABP_c content appears to relate to the rate of fatty acid utilization, and also changes in concert to modulations in fatty acid utilization induced by (patho)physiological stimuli (e. g. endurance training, diabetes). The facilitation of intracellular fatty acid transport by FABP_c is accomplished by increasing the concentration of the diffusing fatty acids in the aqueous cytoplasm and, most likely, also by interacting directly with membranes to promote transfer of fatty acids to and from the cytosolic binding protein.