The importance of protein‐mediated transport of fatty acids for migration in birds

Long distance migratory birds are a useful model system to study how diet, body composition and exercise affect metabolic fuel selection. In particular, they are exceptional in their ability to store large amounts of lipid (i.e. become obese) and subsequently use fatty acids to power intense exercise (flight) for extraordinary lengths of time. During exercise the rate of fatty acid delivery from adipose stores to sites of oxidation in mitochondria appears to be limited by transport across the muscle membranes. We are investigating seasonal patterns in the expression of proteins that mediate fatty acid uptake by flight muscles of migratory birds. We are using immunoassays and real‐time PCR to quantify protein and mRNA concentrations of fatty acid translocase (FAT/CD36), and the cytosolic and plasma membrane fatty acid binding proteins (FABPc and FABPpm). Past studies demonstrate that FABPc is highly abundant and up‐regulated dramatically during migration, and our recent data suggest that FAT/CD36 responds similarly. Two mammalian conditions where these proteins are up‐regulated in skeletal muscle are obesity and diabetes, and birds may provide clues to the mechanisms underlying these pathophysiologies.