Cytoplasmic fatty acid-binding protein facilitates fatty acid utilization by skeletal muscle

The intracellular transport of long-chain fatty acids in muscle cells is facilitated to a great extent by heart-type cytoplasmic fatty acid-binding protein (H-FABP). By virtue of the marked affinity of this 14.5-kDa protein for fatty acids H-FABP dramatically increases their concentration in the aqueous cytoplasm by non-covalent binding, thereby facilitating both the transition of fatty acids from membranes to the aqueous space and their diffusional transport from membranes (e.g. sarcolemma) to other cellular compartments (e.g. mitochondria). Striking features are the relative abundance of H-FABP in muscle, especially in oxidative muscle fibres, and the modulation of the muscular H-FABP content in concert with the modulation of other proteins and enzymes involved in fatty acid handling and utilization. Newer studies with mice carrying a homozygous or heterozygous deletion of the H-FABP gene show that, in comparison with wild-type mice, hindlimb muscles from heterozygous animals have a markedly lowered (-66%) H-FABP content but unaltered palmitate uptake rate, while in hindlimb muscles from homozygous animals (no H-FABP present) palmitate uptake was reduced by 45%. These findings indicate that H-FABP is present in relative excess and plays a substantial, but merely permissive role in fatty acid uptake by skeletal muscles.