Insulin's rapid action to increase glucose transport is believed to occur primarily through the translocation of glucose transporters from an intracellular pool to the plasma membrane. To better understand the mechanism involved, we studied the role of protein synthesis in glucose transporter translocation by using the protein synthesis inhibitor, cycloheximide. The results suggest that insulin's stimulation of glucose transport and translocation of glucose transporters can occur without acute protein synthesis. The possible role of protein kinase C in the regulation of glucose transport in the rat adipose cell has been examined. While the results do not clarify the relationship between protein kinase C and the mechanism of insulin action, they do suggest that 1) protein kinase C activation induces the translocation of glucose transporters without a corresponding increase in glucose transport activity and 2) insulin and PMA appear to stimulate glucose transport in rat adipose cells through distinct but interactive mechanisms. In another separate study, the data suggest that 1) glucose transporters redistributed in response to PMA or vasopressin exhibit different intrinsic activities compared to glucose transporters from insulin-stimulated cells and 2) the phosphorylation state of glucose transporters may regulate their activity. The question of a long-term regulatory role of insulin on adipocyte glucose transporter content has been addressed using the differentiating or fully mature 3T3-F442A adipocytes. The results suggest that insulin plays a long-term regulatory role on cultured adipocyte glucose transporter content through a selective effect on the erythrocyte/HepG2/brain-type glucose transporter. A procedure for purification of the 45 kDa transport protein from rat brain has been developed. An (approximate) 5,000-fold purification of the rat brain glucose transporter has been achieved with a yield of 25%.
