Insulin action on glucose transport in isolated rat adipocytes was assessed using the method originally reported by Whitesell et al. Insulin increased the Vmax of glucose transport without affecting the Km. So far as concentration dependence of insulin action it had pH and temperature dependency, and analogue specificity quite similar to previous reports.
The lag phase (time necessary for full exhibition) of insulin action has never been paid much attention, since suitable system for studying it has never been developed, and since only recently post receptor processes of insulin actions were interested in detecting insulin resistance. Insulin action on glucose transport reached the maximum in 3 min with half maximal response at 1.8 min. Lowering the pH or temperature of incubation medium prolonged the period for half maximal response.
On the other hand, various insulin analogues required comparable period with insulin for full exhibition of their actions. When isolated adipocytes were obtained from rats fasted for 48 hours, the period for half maximal response was markedly prolonged (12 min).
It might be suggested that in some insulin resistant conditions such as diabetic ketoacidosis and hunger, the delayed initiation of insulin action may be involved
