Glucose-, calcium- and concentration-dependence of acetylcholine stimulation of insulin release and ionic fluxes in mouse islets.
Mouse islets were used to define the glucose-dependence and extracellular Ca2+ requirement of muscarinic stimulation of pancreatic beta-cells. In the presence of a stimulatory concentration of glucose (10 mM) and of Ca2+, acetylcholine (0.1-100 microM) accelerated 3H efflux from islets preloaded with myo-[3H]inositol. It also stimulated 45Ca2+ influx and efflux, 86Rb+ efflux and insulin release. In the absence of Ca2+, only 10-100 microM-acetylcholine mobilized enough intracellular Ca2+ to trigger an early but brief peak of insulin release. At a non-stimulatory concentration of glucose (3 mM), 1 microM- and 100 microM-acetylcholine increased 45Ca2+ and 86Rb+ efflux in the presence and absence of extracellular Ca2+. However, only 100 microM-acetylcholine marginally increased 45Ca2+ influx and caused a small, delayed, stimulation of insulin release, which was abolished by omission of Ca2+. At a maximally effective concentration of glucose (30 mM), 1 microM- and 100 microM-acetylcholine increased 45Ca2+ influx and efflux only slightly, but markedly amplified insulin release. Again, only 100 microM-acetylcholine mobilized enough Ca2+ to trigger a peak of insulin release in the absence of Ca2+. The results thus show that only high concentrations of acetylcholine (greater than or equal to 10 microM) can induce release at low glucose or in a Ca2+-free medium. beta-Cells exhibit their highest sensitivity to acetylcholine in the presence of Ca2+ and stimulatory glucose. Under these physiological conditions, the large amplification of insulin release appears to be the result of combined effects of the neurotransmitter on Ca2+ influx, on intracellular Ca2+ stores and on the efficiency with which Ca2+ activates the releasing machinery.
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002132:Calcium Radioisotopes; D002217:Carbachol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D012414:Rubidium Radioisotopes; D013268:Stimulation, Chemical
D002132:Calcium Radioisotopes; D007328:Insulin; D012414:Rubidium Radioisotopes; D002217:Carbachol; D005947:Glucose; D000109:Acetylcholine; D002118:Calcium