Inhibitory effect of amiloride on glucose transport in isolated rat adipocytes

The effect of amiloride on 3-O-methylglucose (3-O-MG) uptake was studied in isolated rat adipocytes to define to what extent amiloride inhibited the process of insulin action or glucose transport. Amiloride (1 mM), which did not change the intracellular water space of adipocytes, inhibited by 43.3% the insulin-stimulated uptake of 3-O-MG, while it did not appear to inhibit the basal uptake. To distinguish the inhibitory effect on glucose transport activity from that on the process of insulin action, the effect of amiloride was evaluated in the transport system using adipocytes deprived of ATP, in which glucose transporters were considered immobile. Amiloride (1 mM) inhibited this transport by 32.8% in an insulin-stimulated state, which was obtained using adipocytes that had been treated with 20 nM insulin and exposed to 2 mM KCN, whereas it did not inhibit the transport system at the basal state. In the inhibitory effect, 76% was thus attributable to the inhibition of glucose transport activity recruited by insulin and 24% to the inhibition of the action of 20 nM insulin itself. These results indicate that amiloride can not be used as a specific inhibitor of the insulin action itself.