Increased GLUT-4 Translocation Mediates Enhanced Insulin Sensitivity of Muscle Glucose Transport After Exercise

The purpose of this study was to determine whether the increase in insulin sensitivity of skeletal muscle glucose transport induced by a single bout of exercise is mediated by enhanced translocation of the GLUT-4 glucose transporter to the cell surface. The rate of 3-O-[3H]methyl-D-glucose transport stimulated by a submaximally effective concentration of insulin (30 microU/ml) was approximately twofold greater in the muscles studied 3.5 h after exercise than in those of the sedentary controls (0.89 +/- 0.10 vs. 0.43 +/- 0.05 micromol . ml-1 . 10 min-1; means +/- SE for n = 6/group). GLUT-4 translocation was assessed by using the ATB-[2-3H]BMPA exofacial photolabeling technique. Prior exercise resulted in greater cell surface GLUT-4 labeling in response to submaximal insulin treatment (5.36 +/- 0.45 dpm x 10(3)/g in exercised vs. 3.00 +/- 0.38 dpm x 10(3)/g in sedentary group; n = 10/group) that closely mirrored the increase in glucose transport activity. The signal generated by the insulin receptor, as reflected in the extent of insulin receptor substrate-1 tyrosine phosphorylation, was unchanged after the exercise. We conclude that the increase in muscle insulin sensitivity of glucose transport after exercise is due to translocation of more GLUT-4 to the cell surface and that this effect is not due to potentiation of insulin-stimulated tyrosine phosphorylation.