Temporal separation of insulin-stimulated GLUT4/IRAP vesicle plasma membrane docking and fusion in 3T3L1 adipocytes

Examination of the time and temperature dependence of insulin-stimulated GL UT4/IRAP-containing vesicle trafficking demonstrated an approximate 7-fold increase in the half-time for plasma membrane translocation at 23 degrees C (t(1/2) = similar to 30 min) compared with 37 degrees C (t(1/2) = similar to 4 min) without a significant change in the extent of either GLUT4 or IRA P translocation. Localization of the endogenous GLUT4 and expressed GLUT4-e nhanced green fluorescent protein fusion protein in intact 3T3L1 adipocytes demonstrated that at 23 degrees C there was a time-dependent accumulation of discrete GLUT4-containing vesicles adjacent to the inner face of the cel l surface membrane but that was not contiguous and/or physically incorporat ed into the plasma membrane. Together, these data demonstrate that the temp erature-dependent decrease in the rate of GLUT4 and IRAP translocation resu lts from a reduction in GLUT4/IRAP-containing vesicle fusion and not traffi cking or docking to the plasma membrane.