Influence of thiol groups, calcium, and glucose metabolism on cholinergic-induced insulin release and on methylscopolamine binding to muscarinic receptors in pancreatic islets of the rat.

Short-term regulation of [3H]methylscopolamine binding to muscarinic receptors and acetylcholine-induced stimulation of insulin release was investigated in pancreatic islets of the rat. Binding of methylscopolamine was reversible; 47% of label was displaced 10 min and 70% 30 min after addition of unlabelled substance. 0.1 mM chloromercuribenzoic acid, when present during binding incubations, inhibited binding by 54%, whereas acetylcholine-induced insulin release was unaffected by the presence of the thiol reactant. Pre-incubation for 60 min in a calcium-deprived medium or in the presence of 50 microM trifluoroperazine likewise inhibited binding. Pre-incubation with 1.0 mM 3-isobutyl-l-methylxanthine or 16.7 M glucose failed to influence subsequent binding although acetylcholine-induced insulin release was 4-fold enhanced by priming with glucose. We conclude that 1) binding to muscarinic receptors is influenced by thiol interaction, 2) short-term alterations in calcium fluxes influence binding, whereas short-term changes in cyclic AMP (cAMP) or glucose metabolism do not, 3) a priming effect of glucose on insulin secretion is not mediated by changes in receptor binding.