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Am J Physiol Endocrinol Metab 277: E259-E267, 1999;
0193-1849/99 $5.00
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Vol. 277, Issue 2, E259-E267, August 1999

Mobilization of GLUT-4 from intracellular vesicles by insulin and K+ depolarization in cultured H9c2 myotubes

Bo Yu, Laurie A. Poirier, and Laura E. Nagy

Department of Nutrition, Case Western Reserve University, Cleveland, Ohio 44106-4906

The insulin-responsive glucose transporter, GLUT-4, moves from an intracellular compartment to the cell surface in response to insulin and/or muscle contraction. Treatment of H9c2 myotubes with insulin significantly increased uptake of 2-deoxyglucose. Depolarization of the myotubes by increasing extracellular [K+], which mimics the initial phases of excitation-contraction coupling, also increased 2-deoxyglucose uptake. The K+- but not insulin-evoked increase was blocked by dantrolene, an inhibitor of Ca2+ release from the sarcoplasmic reticulum. In contrast, wortmannin, an inhibitor of phosphatidylinositol 3-kinase, blocked insulin- but not K+-stimulated 2-deoxyglucose uptake. Increased glucose uptake in response to insulin or K+ depolarization was associated with increased GLUT-4 in plasma membranes and depletion of a population of small intracellular GLUT-4-containing vesicles. Similarly, in H9c2 cells transfected with c-myc-tagged GLUT-4, translocation of c-myc GLUT-4 to the cell surface was increased after stimulation with insulin or K+ depolarization. Taken together, these data demonstrate that insulin and K+ depolarization increase glucose uptake by recruiting GLUT-4 from intracellular vesicles to the plasma membrane of H9c2 myotubes via distinct signaling mechanisms.

skeletal muscle; vesicle trafficking; phosphatidylinositol 3-kinase; calcium


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