Inhibition of purinoceptors amplifies glucose-stimulated insulin release with removal of its pulsatility.
External ATP has been proposed to be an autocrine regulator of glucose-stimulated insulin secretion and responsible for the synchronization of the Ca2+ rhythmicity in the beta-cells required for a pulsatile release of insulin from the pancreas. The importance of external ATP for glucose-stimulated insulin release was evaluated in rats with the aid of 2-deoxy-N-methyladenosine-3,5-bisphosphate (MRS 2179), an inhibitor of the purinoceptors known to affect the Ca2+ signaling in beta-cells. The concentration of cytoplasmic Ca2+ was measured in single beta-cells and small aggregates with ratiometric fura-2 technique and the release of insulin recorded from isolated islets and the perfused pancreas. Addition of 1 micromol/l ATP induced premature cytoplasmic Ca2+ concentration ([Ca2+]i) oscillations similar to those found in beta-cells exposed to 20 mmol/l glucose. In most experiments, the presence of 10 micromol/l MRS 2179 did not remove the glucose-induced [Ca2+]i rhythmicity in single beta-cells or the synchronization seen in coupled cells. Nevertheless, the same concentration of MRS 2179 promptly interrupted the pulsatility (frequency 0.22 +/- 0.01/min) of insulin secretion, raising the total amounts released from the pancreas. Prolonged exposure of islets to 1 and 10 micromol/l MRS 2179 enhanced insulin secretion at 20 mmol/l glucose 33% (P < 0.05) and 63% (P < 0.01), respectively, without affecting the release at 3 mmol/l glucose. The results support the idea that neural ATP signals entrain the islets into a common rhythm resulting in pulsatile release of insulin and that glucose stimulation of the secretory activity is counteracted by accumulation of inhibitory ATP around the beta-cells.
Salehi
Albert
A
Institute of Physiological Sciences, University of Lund, Lund, Sweden.
Qader
Saleem S
SS
Quader
Saleem S
SS
Grapengiesser
Eva
E
Hellman
Bo
B
D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D009991:Oscillometry; D058914:Purinergic Antagonists; D051381:Rats; D017207:Rats, Sprague-Dawley
D007328:Insulin; C111914:N(6)-methyl-2'-deoxyadenosine 3',5'-diphosphate; D058914:Purinergic Antagonists; D000244:Adenosine Diphosphate; D005947:Glucose