Mobilization of different intracellular calcium pools after activation of muscarinic receptors in pancreatic beta-cells.
Exposure to carbachol resulted in a biphasic stimulation of 45Ca efflux when beta-cell-rich pancreatic islets from ob/ob mice were perifused with a Ca2+-deficient medium. The pattern of stimulated 45Ca efflux was markedly modified by glucose. Whereas the initial carbachol-stimulated phase was conditional on previous exposure to glucose, the subsequent phase was completely suppressed by 20 mmol/l of the sugar. The stimulatory could be clearly separated also on the basis of a Na+ dependence. Removal of extracellular Na+ resulted in a disappearance of the second phase, but it was still possible to induce a prominent initial peak if depletion of intracellular K+ was prevented when Na+ was omitted. It is concluded that activation of muscarinic receptors in the pancreatic beta-cells results in mobilization of calcium from more than one intracellular pool. Whereas the second phase of stimulated efflux can be explained in terms of an increased entry of Na+ into the beta-cells, the initial stimulation may be due to receptor-mediated breakdown of polyphosphoinositides.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008820:Mice, Obese; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000502:physiology
D007328:Insulin; D011976:Receptors, Muscarinic; D004533:Egtazic Acid; D001285:Atropine; D002217:Carbachol; D012964:Sodium; D005947:Glucose; D002118:Calcium