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 ins ulin sensitivity of skeletal muscle glucose transport induced by a sin gle bout of exercise is mediated by enhanced translocation of the GLUT -4 glucose transporter to the cell surface. The rate of 3-O-[H-3]methy l-D-glucose transport stimulated by a submaximally effective concentra tion of insulin (30 mu U/ml) was approximately twofold greater in the muscles studied 3.5 h after exercise than in those of the sedentary co ntrols (0.89 +/- 0.10 vs. 0.43 +/- 0.05 mu mol . ml(-1) . 10 min(-1); means +/- SE for n = 6/group). GLUT-4 translocation was assessed by us ing the ATB-[2-H-3]BMPA exofacial photolabeling technique. Prior exerc ise resulted in greater cell surface GLUT-4 labeling in response to su bmaximal insulin treatment (5.36 +/- 0.45 dpm x 10(3)/g in exercised v s. 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 signa l generated by the insulin receptor, as reflected in the extent of ins ulin receptor substrate-1 tyrosine phosphorylation, was unchanged afte r the exercise. We conclude that the increase in muscle insulin sensit ivity of glucose transport after exercise is due to translocation of m ore GLUT-4 to the cell surface and that this effect is not due to pote ntiation of insulin-stimulated tyrosine phosphorylation.