Stimulation of maximal intracellular insulin action on glycogen synthase by preincubation of adipocytes with adenosine 5'-triphosphate

Preincubation of rat adipocytes with ATP further stimulated maximal insulin action on glycogen synthase. Half-maximum concentration of ATP was 5 X 10(-5) M. ATP, ADP, adenosine, inosine, and GTP were effective, while beta-gamma-methylene ATP was without effect. ADP and GTP were less potent than ATP, adenosine, or inosine. Inosine was active without insulin but was without effect in the presence of insulin. The mechanism of action of adenosine was clearly different from ATP. While ATP required both Mg2+ and Ca2+ for effectiveness, adenosine required only Ca2+. The effect of ATP, but not of adenosine, was preserved after cells were washed. The adenosine effect was completely blocked by theophylline, but the ATP effect was inhibited only 40%. The ATP effect was thus not due to adenosine generated by ATP breakdown.