Evidence for two different types of P2 receptors stimulating insulin secretion from pancreatic B cell

Abstract

1 Adenine nucleotides have been shown to stimulate insulin secretion by acting on P2 receptors of the P2Y type. Since there have been some discrepancies in the insulin response of di erent analogues of ATP and ADP, we investigated whether two di erent types of P2 receptors exist on pancreatic B cells. The e ects of a,b-methylene ATP, which is more speci®c for the P2X subtype, were studied in vitro in pancreatic islets and isolated perfused pancreas from rats, in comparison with the potent P2Y receptor agonist ADPbS. 2 In isolated islets, incubated with a slightly stimulating glucose concentration (8.3 mM), a,b-me ATP (200 mM) and ADPbS (50 mM) similarly stimulated insulin secretion; by contrast, under a non stimulating glucose concentration (3 mM), a,b-me ATP was still e ective whereas ADPbS was not. In the same way, in islets perifused with 3 mM glucose, a,b-me ATP but not ADPbS induced a partial but signi®cant reduction in the peak 86 Rb e ux induced by the ATP-dependent potassium channel opener diazoxide. 3 In the isolated pancreas, perfused with a non stimulating glucose concentration (4.2 mM), ADPbS and a,b-me ATP (5 ± 50 mM), administered for 10 min, induced an immediate, transient and concentration-dependent increase in the insulin secretion; their relative potency was not signi®cantly di erent. In contrast, with a slightly stimulating glucose concentration (8.3 mM), ADPbS was previously shown to be 100 fold more potent than a,b-me ATP. Furthermore, at 4.2 mM glucose a second administration of a,b-me ATP was ine ective. In the same way, ADPbS was also able to desensitize its own insulin response. At 3 mM glucose, a,b-me ATP as well as ADPbS (50 mM) induced a transient stimulation of insulin secretion and down regulated the action of each other. 4 These results give evidence that pancreatic B cells, in addition to P2Y receptors, which potentiate glucose-induced insulin secretion, are provided with P2X receptors, which transiently stimulate insulin release at low non-stimulating glucose concentration and slightly a ect the potassium conductance of the membrane.

Purinergic receptors in the endocrine and exocrine pancreas

“…ATP and its analogues (e.g. 2-methylthio ATP, ATPγS) induced insulin secretion, but ADP and its analogues (α,β-methylene ADP, ADPβS, ADPγS) were more potent and they required at least slightly stimulating glucose concentrations (8.3 mM) [8][9][10][11][12]. These findings indicated presence of an ADP-preferring receptor, such as the P2Y 1 receptor [13].…”

“…Although the P2Y 1 receptor may be the most important P2Y receptor in regulating insulin secretion, there is also evidence for other P2Y receptors [19][20][21], and also P2X receptors [12,[22][23][24], and indeed the P2X 4 receptor was cloned from rat pancreatic islets [25]. Evidence for P2X-type receptors was provided by intracellular Ca 2+ measurements.…”

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

“…As a consequence, extracellularly released ATP can only stimulate islet P2Y receptors after conversion into ADP and can then act on P2Y 1 or P2Y 13 receptors. ATP could still stimulate ionotropic P2X receptors on beta cells, but activation of P2X receptors has been shown to mediate only small and transient increases in insulin secretion at low glucose concentrations [39].…”

Purinergic signalling in endocrine organs

“…ATP increases [Ca 2+ ] i in clonal insulin-producing RINm5F cells [15]. ATP action was found to be glucose-dependent and was exerted via two different types of P2 receptors: P2X receptors on rat pancreatic β-cells transiently stimulated insulin release at low glucose concentrations and P2Y receptors potentiated glucose-stimulated insulin secretion ( [410]; see [479]). Electrophysiological and immunocytochemical evidence has been presented that P2X1 and P2X3 receptors are expressed by mouse pancreatic β-cells [484].…”

“…Extracellular ATP increases [Ca 2+ ] i in β-cells, mainly by triggering Ca 2+ release from intracellular stores [196,597], implicating P2Y receptors. Adenosine-5′-(β-thio)-diphosphate (ADPβS) was a potent agonist mediating insulin secretion from perfused rat pancreas and isolated islets [34,410], indicating that P2Y 1 , P2Y 12 or P2Y 13 receptors might be involved. This ADP analogue also enhanced insulin secretion and reduced hyperglycemia after oral administration to rats and dogs [227].…”