One transporter per vesicle: determination of the basis of the insulin effect on glucose transport.

The basis for insulin stimulation of glucose transport in rat adipocytes has been investigated by determining the relative number of functional glucose transporters in the plasma and microsomal membranes from basal and insulin-treated cells. Each fraction was solubilized with cholate and then reconstituted into vesicles of about 500 A in diameter through removal of the cholate by dialysis. This procedure distributed the glucose transporters into the vesicles at a density of either one or none per vesicle. Consequently the fraction of the intravesicular volume that rapidly equilibrated with D-glucose provided an estimate of the relative number of functional transporters. By means of this one-transporter-per-vesicle method, it was found that insulin increased the number of transporters in the plasma membrane by a factor of 2.4 and decreased the number in the microsomes to 68% of the original value. These results provide independent evidence for the hypothesis that insulin causes the translocation of functional transporters from an intracellular location to the plasma membrane.