Glucose-, calcium- and concentration-dependence of acetylcholine stimulation of insulin release and ionic fluxes in mouse islets

Abstract

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.

The muscarinic receptor subtype in mouse pancreatic B‐cells

“…Several, but not necessarily all effects brought about by ACh in B-cells are interconnected [17,18]. Slight differences in the potencies of the antagonists on ACh-induced insulin release and on 86Rb+ or 45Ca2+ efflux were noted.…”

“…This peak is due to Ca2+ mobilization (peak of 45Ca2+) by inositol trisphosphate. However, concentrationdependence studies have shown that the relationship between insulin release and the magnitude of Ca2+ mobilization is non-linear [18]. A small decrease in mobilization, as that produced by the lowest concentration of antagonists, is sufficient to cause a marked reduction in release.…”

Nuclear Factor-κB Activity in β-Cells Is Required for Glucose-Stimulated Insulin Secretion

“…Glybenclamide, a sulfonylurea drug, induces membrane depolarization and insulin secretion by directly blocking the SUR1/Kir6.2 K ATP channel (35). Carbachol, a cholinergic agonist, enhances GSIS via the phospholipase C/protein kinase C signaling pathway and is suggested to increase the transport of insulin vesicles to the secretory site (1,36,37). These secretagogues depend, at least partly, on intact glucose metabolism for their ability to stimulate insulin secretion (36 -42).…”

Type VIII adenylyl cyclase in rat beta cells: coincidence signal detector/generator for glucose and GLP-1

“…1) was completely suppressed by coincubation with 50 µmol/l of the L-type Ca 2+ -channel blocker verapamil, a well known inhibitor of glucoseinduced insulin release [33,34]. On the contrary, acetylcholine (Table 1), a neurotransmitter that mobilizes calcium ions from intracellular stores in beta cells [35] did not influence cAMP content in beta cells. However, potentiating effects of acetylcholine on insulin release from purified cells were observed (p<0.005; Table 1).…”