EXPRESSION AND INSULIN-REGULATED DISTRIBUTION OF CAVEOLIN IN SKELETAL-MUSCLE - CAVEOLIN DOES NOT COLOCALIZE WITH GLUT4 IN INTRACELLULAR MEMBRANES

Caveolin is believed to play an important role in sorting processes, v esicular trafficking, transmembrane signaling, and molecular transport across membranes, In this study we have evaluated the expression and distribution of caveolin in skeletal muscle and its interaction with G LUT4 glucose carriers, Caveolin was expressed to substantial levels in muscle and its expression was regulated in muscle; aging and high fat diet enhanced caveolin expression in skeletal muscle and inversely, m yogenesis down-regulated caveolin in L6E9 cells. Under fasting conditi ons, most of caveolin was found in intracellular membranes and the cav eolin present in the cell surface was found in both sarcolemma and T-t ubules, Insulin administration led to a redistribution of caveolin fro m intracellular high density membrane fractions to intracellular light er density fractions and to the cell surface; this pattern of insulin- induced redistribution was different to what was shown by GLUT4. These results suggests that caveolin is a component of an insulin-regulated machinery of vesicular transport in muscle. Quantitative immunoisolat ion of GLUT4 vesicles obtained from different intracellular GLUT4 popu lations revealed the absence of caveolin which substantiates the lack of colocalization of intracellular GLUT4 and caveolin, This indicates that caveolin is not involved in intracellular GLUT4 trafficking in sk eletal muscle.