EXERCISE-INDUCED INCREASE IN GLUCOSE-TRANSPORT, GLUT-4, AND VAMP-2 INPLASMA-MEMBRANE FROM HUMAN MUSCLE

A major effect of muscle contractions is an increase in sarcolemmal gl ucose transport. We have used a recently developed technique to produc e sarcolemmal giant vesicles from human muscle biopsy samples obtained before and after exercise. Six men exercised fdr 10 min at 50% maxima l O-2 uptake (V over dot o(2max)) and then to fatigue at 100% V over d ot o(2max) (5.7 +/- 0.2 min). Vesicle glucose transport at 5 mM increa sed from 3.3 +/- 0.6 pmol . mu g(-1) . min(-1) at rest to 6.6 +/- 1.0 pmol . mu g(-1) . min(-1) at fatigue (mean +/- SE, n = 6, P < 0.05). T his increase in glucose transport was associated with a 1.6-fold incre ase in vesicle GLUT-4 protein content. Glucose transport normalized to GLUT-4 protein content also increased with exercise, suggesting incre ased intrinsic activity of GLUT-4. Furthermore, exercise resulted in a 1.4-fold increase in sarcolemmal vesicle-associated membrane protein (VAMP-2) content, suggesting that muscle contractions may induce traff icking of GLUT-4-containing vesicles via a mechanism similar to neurot ransmitter release. Our results demonstrate for the first time exercis e-induced translocation of GLUT-4 and VAMP-2 to the plasma membrane of human muscle and increased sarcolemmal glucose transport.