Multiple sites of purinergic control of insulin secretion in mouse pancreatic beta-cells

In mouse pancreatic beta-cells, extracellular ATP (0.1 mmol/l) effectively reduced glucose-induced insulin secretion. This inhibitory action resulted from a direct interference with the secretory machinery, and ATP suppressed depolarization-induced exocytosis by 60% as revealed by high-resolution ca pacitance measurements. Suppression of Ca2+-dependent exocytosis was mediat ed via binding to P2Y(1) purinoceptors but was not associated with inhibiti on of the voltage-dependent Ca2+ currents or adenylate cyclase activity. In hibition of exocytosis by ATP resulted from G-protein-dependent activation of the serine/threonine protein phosphatase calcineurin and was abolished b y cyclosporin A and deltamethrin, In contrast to the direct inhibitory acti on on exocytosis, ATP reduced the whole-cell ATP-sensitive K+ (K-ATP) curre nt by 30% (via activation of cytosolic phospholipase A(2)), leading to memb rane depolarization and stimulation of electrical activity. The stimulatory effect of ATP also involved mobilization of Ca2+ from thapsigargin-sensiti ve intracellular stores. We propose that the inhibitory action of ATP, by i nteracting with the secretory machinery at a level downstream to an elevati on in [Ca2+](i), is important for autocrine regulation of insulin secretion in mouse beta-cells.