Development of hormone receptors and hormone responsiveness in vitro. Effect of prolonged insulin treatment on hexose uptake in 3T3-L1 adipocytes

Exposure of insulin-responsive, differentiated 3T3-L1 cells (adipocytes) to 0.1 to 1.0 μg/ml of insulin for 3 to 48 h resulted in a persistent state of enhanced 2-deoxy-D-glucose and 3-O-methyl-D-glucose uptake. Elevated basal transport activity was retained under conditions where ¹²⁵I-insulin binding activity remained unchanged and exchangeable insulin was dissociated from cell surface receptors. The appearance of enhanced hexose transport activity was prevented by cycloheximide and could be distinguished from the activation of the glucose transport system observed in these and other cells during glucose deprivation. Rigorously washed adipocytes, exhibiting insulin-induced elevations in basal transport activity, were refractory to further stimulation by insulin during hexose uptake assays. Insulin-unresponsive 3T3-L1 preadipocytes failed to increase hexose uptake activity when treated under conditions that elicited an optimal response in adipocytes.