P2Y purinergic potentiation of glucose-induced insulin secretion and pancreatic β-cell metabolism

Purine nucleotides and their analogs increase insulin secretion through activation of pancreatic beta-cell P2Y receptors. The present study aimed at determining the role of glucose metabolism in the response to P2Y agonists and whether ATP-activated K+ channels (K-ATP channels) are involved in this response. The experiments were performed in the rat isolated pancreas, perfused with a Krebs-bicarbonate buffer supplemented with 2 g/l bovine serum albumin under dynamic glucose conditions from 5 mmol/l baseline to 11 mmol/l. ADPbetaS (0.5 mumol/l) was selected as a stable and selective P2Y agonist. This compound, ineffective on the 5 mmol/l glucose background, induced a significant threefold increase in insulin release triggered by the glucose challenge. The effect of ADPbetaS was markedly reduced (P < 0.001) in the presence of an inhibitor of glucose metabolism. In addition to glucose, the ADP analog also amplified the P-cell insulin response to 15 mmol/l methyl pyruvate (P < 0.05), but it was ineffective on the insulin response to 2.5 mmol/l methyl succinate. A nonmetabolic stimulus was applied using tolbutamide (185 mumol/l). Insulin secretion induced by the K-ATP channel blocker was strongly reinforced by ADPbetaS (P < 0.001), which prompted us to check a possible interplay of K-ATP channels in the effect of ADPbetaS. In the presence of diazoxide 250 mumol/l and 21 mmol/l KCl, ADPbetaS still amplified the second phase of glucose-induced insulin secretion (P < 0.001). We conclude that P2Y receptor activation is able to promote insulin secretion through a mechanism, involving beta-cell metabolism and a rise in intracellular calcium; this effect does not result from a direct inhibitory effect on K-ATP channels.