Key for the regulation of glucose uptake is the sequestering of GLUT4 intracellularly in the absence of insulin (often referred to as the basal state). The basal state retention is achieved by a kinetic mechanism in which GLUT4-containing vesicles very slowly fuse with the plasma membrane and any GLUT4 on the cell surface is rapidly internalized and redelivered to the storage pool. In this kinetic retention, the amount of GLUT4 on the surface is dependent on the rates of internalization and return to the plasma membrane (exocytosis). Less than 5% of GLUT4 is on the surface in the basal state, indicating that GLUT4 is internalized 20 times faster than it is returned to the cell surface.