EXERCISE INDUCES THE TRANSLOCATION OF GLUT4 TO TRANSVERSE TUBULES FROM AN INTRACELLULAR POOL IN RAT SKELETAL-MUSCLE

Exercise stimulates glucose transport in skeletal muscle by increasing the number of GLUT4 glucose transporters at the cell surface. The eff ect of exercise on GLUT4 content in transverse tubules, which are deep extensions of the plasma membrane involved in myofiber contraction, h as never been studied. In the present study, we have investigated whet her acute exercise induces translocation of GLUT4 to the transverse tu bules. Plasma membranes and transverse tubules were isolated from cont rol and exercised rats by a newly developed membrane fractionation pro cedure. As expected, acute exercise increased GLUT4 content in plasma membranes (95%; p < 0.01). Importantly, exercise also significantly in creased GLUT4 content in a transverse tubule-enriched fraction (60%; p < 0.05). Furthermore, acute exercise was found to decrease GLUT4 cont ent in an intracellular membrane fraction (-40%; p < 0.001). In conclu sion, this study demonstrates that GLUT4 is translocated not only to t he plasma membranes but also to the transverse tubules in acutely exer cized muscles. The results also indicate that GLUT4 is recruited from a novel intracellular membrane fraction. (C) 1996 Academic Press, Inc.