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 effect of exercise on GLUT4 content in transverse tubules, which are deep extensions of the plasma membrane involved in myofiber contraction, has never been studied. In the present study, we have investigated whether acute exercise induces translocation of GLUT4 to the transverse tubules. Plasma membranes and transverse tubules were isolated from control and exercised rats by a newly developed membrane fractionation procedure. As expected, acute exercise increased GLUT4 content in plasma membranes (95%; p < 0.01). Importantly, exercise also significantly increased GLUT4 content in a transverse tubule-enriched fraction (60%; p < 0.05). Furthermore, acute exercise was found to decrease GLUT4 content in an intracellular membrane fraction (-40%; p < 0.001). In conclusion, this study demonstrates that GLUT4 is translocated not only to the plasma membranes but also to the transverse tubules in acutely exercised muscles. The results also indicate that GLUT4 is recruited from a novel intracellular membrane fraction.