Abstract
Examination of the time and temperature dependence of insulin-stimulated GLUT4/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)) = approximately 30 min) compared with 37 degrees C (t((1)/(2)) = approximately 4 min) without a significant change in the extent of either GLUT4 or IRAP translocation. Localization of the endogenous GLUT4 and expressed GLUT4-enhanced 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 cell surface membrane but that was not contiguous and/or physically incorporated into the plasma membrane. Together, these data demonstrate that the temperature-dependent decrease in the rate of GLUT4 and IRAP translocation results from a reduction in GLUT4/IRAP-containing vesicle fusion and not trafficking or docking to the plasma membrane.
Highlights
Based upon this paradigm, the insulin-stimulated translocation of the GLUT4/IRAP-containing compartments must necessarily require the trafficking of these vesicles to the cell surface, subsequent to docking to and ultimate fusion with the plasma membrane
The Rate of Insulin-stimulated GLUT4/IRAP Translocation Is Temperature-dependent—It has been well documented that the transfer of protein cargo from one membrane compartment to another requires the trafficking, docking, and fusion of carrier vesicles with the appropriate target membrane (10 –12)
The rate of insulin-stimulated IRAP translocation was reduced at 23 °C (Fig. 2A, panels 1, 3, 5, 7, 9, and 11) in comparison to 3T3L1 adipocytes maintained at 37 °C (Fig. 2B, panels 2, 4, 6, 8, 10, and 12)
Summary
The insulin-stimulated translocation of the GLUT4/IRAP-containing compartments must necessarily require the trafficking of these vesicles to the cell surface, subsequent to docking to and ultimate fusion with the plasma membrane. The Rate of Insulin-stimulated GLUT4/IRAP Translocation Is Temperature-dependent—It has been well documented that the transfer of protein cargo from one membrane compartment to another requires the trafficking, docking, and fusion of carrier vesicles with the appropriate target membrane (10 –12).
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