Time course of termination of the glucose transport action of insulin in adipocytes.

Rapid sequence measures of changes in the rate of 14CO2 production from [14C]glucose bathing the cells was abruptly reduced from 20 to 4 microunits/ml. Interpretation of the data in terms of glucose transport was based on calibration experiments that described the time course of change in 14CO2 production when [14C]glucose entry into adipocytes was slowed by reducing the specific activity of [14C]glucose in the incubation medium. All experiments were performed at 37 degrees in Krebs-Ringer bicarbonate buffer at pH 7.4. Termination of the glucose transport action of insulin (which includes insulin-receptor disassociation and all other steps leading to decelerated glucose entry) began within 2 min and was complete within 30 min. The transition from one steady state rate of glucose transport to the other could be approximated by an exponential process occurring with a half-time of 14 min. For comparison, the time course of initiation of the glucose transport action of insulin was measured under the same conditions. The transition curve was virtually identical.