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

Abstract

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 capacitance measurements. Suppression of Ca2+-dependent exocytosis was mediated via binding to P2Y1 purinoceptors but was not associated with inhibition of the voltage-dependent Ca2+ currents or adenylate cyclase activity. Inhibition of exocytosis by ATP resulted from G-protein-dependent activation of the serine/threonine protein phosphatase calcineurin and was abolished by cyclosporin A and deltamethrin. In contrast to the direct inhibitory action on exocytosis, ATP reduced the whole-cell ATP-sensitive K+ (K(ATP)) current by 30% (via activation of cytosolic phospholipase A2), leading to membrane depolarization and stimulation of electrical activity. The stimulatory effect of ATP also involved mobilization of Ca2+ from thapsigargin-sensitive intracellular stores. We propose that the inhibitory action of ATP, by interacting with the secretory machinery at a level downstream to an elevation in [Ca2+]i, is important for autocrine regulation of insulin secretion in mouse beta-cells.

ADP mediates inhibition of insulin secretion by activation of P2Y13 receptors in mice

“…To test whether endogenously released ADP regulates insulin release via P2Y 13 receptors, we added the P2Y 13 receptor antagonist MRS2211 (10 μmol/l). Interestingly, MRS2211 per se increased insulin secretion at 8.3 (p < 0.001) and 20 mmol/l glucose (p < 0.01, Fig.…”

“…To do so we quantified the mRNA levels for all the purinergic P2Y receptors, and based on these findings we did pharmacological studies on insulin and glucagon secretion in isolated mouse islets. We found an unanticipated role for ADP acting on P2Y 13 receptors as an autocrine inhibitor of insulin release both in vitro and in vivo.…”

“…The net pharmacological effects of extracellular ATP are difficult to predict since ATP by itself can stimulate P2Y 2 , P2Y 4 (in rodents), P2Y 11 and P2X 1 -P2X 7 receptors present on the cell surface [6]. Furthermore, ATP is rapidly degraded by ectonucleotidases to ADP [7], which can act on P2Y 1 , P2Y 12 and P2Y 13 receptors. ADP is then further degraded by ecto-5′-nucleotidase to adenosine, which in turn can activate four different adenosine receptors [8].…”

“…A large number of studies indicate that extracellular ATP and ADP have a key role in regulating insulin secretion by purinoreceptors [9][10][11][12][13]. Insulin-secretory granules contain 3.5 mmol/l ATP and 5 mmol/l ADP [14], and with a novel biosensor it has been demonstrated that glucose stimulation releases ATP from a single pancreatic beta cell to a local extracellular ATP concentration exceeding 25 µmol/l [4].…”

“…However, ADP has also been shown to decrease insulin release [12,13]. These discrepancies are probably in part due to involvement of several different purinoreceptors [13,[15][16][17][18][19][20][21][22]. Therefore, we wanted to examine whether endogenous release of purines may regulate insulin secretion and to determine the P2Y receptors involved.…”