Effects of insulin receptor down-regulation on hexose transport in human erythrocytes.

D-Glucose and D-galactose influx and efflux rates in human erythrocytes were studied using infinite-cis and zero-trans assay methods. It was found that insulin decreased the infinite-cis Km for both D-glucose and D-galactose influx by 44 and 56%, respectively, while the Vmax was unchanged. The Km for D-glucose efflux in the presence of insulin decreased by 47% when compared to controls, and the change in Vmax was statistically insignificant. If insulin receptors were first down regulated, and then influx and efflux assays were performed, decreases in the infinite-cis and zero-trans Km values were also observed in the absence of exogenous insulin. These affinity changes were not due to persistent surface insulin receptor occupation by the insulin which was used to induce down-regulation. These affinity changes were comparable to those observed in non-down-regulated cells in the presence of insulin.