PROGRESSIVE INCREASE IN GLUCOSE-TRANSPORT AND GLUT-4 IN HUMAN SARCOLEMMAL VESICLES DURING MODERATE EXERCISE

Muscle glucose uptake increases progressively during moderate-intensit y exercise. To elucidate whether this is due to a progressive increase in sarcolemmal glucose transport capacity, nine men exercised for 40 min at 75% maximal oxygen uptake on a bicycle ergometer. Muscle biopsi es were obtained from the vastus lateralis at rest (0 min) and after 5 and 40 min of exercise and used for production of sarcolemmal giant ( SG) vesicles. SG vesicle glucose transport at 5 mM increased (P < 0.05 ) by 38 and 93% after 5 and 40 min of exercise, respectively, compared with glucose transport at rest. The SG vesicle GLUT-4 protein content increased (P < 0.05) by 36 and 91% after 5 and 40 min of exercise, re spectively, compared with rest. Thus the increase in vesicle glucose t ransport was accompanied by a similar increase in SG vesicle GLUT-4 pr otein content. Muscle glucose and glucose 6-phosphate were low at rest , increased (P < 0.05) 2.2- and 2.3-fold, respectively, after 5 min of exercise, and returned to resting values after 40 min of exercise. It is concluded that the progressive increase in muscle glucose uptake d uring moderate-intensity exercise may be due at least in part to a pro gressive increase in sarcolemmal glucose transport and GLUT-4 protein content.