Insulin release, cGMP, cAMP, and membrane potential in acetylcholine-stimulated islets

Acetylcholine potentiated the glucose-induced insulin release from microdissected mouse islets of Langerhans but had no effect on basal insulin release. Significant potentiation was obtained with 0.1 micron acetylcholine in the presence of 10 micron eserine and with 1 micron or more acetylcholine in the absence of a choline esterase inhibitor. Carbamylcholine, too, potentiated insulin release. Potentiation was blocked by methylatropine, whereas methylatropine alone had no effect on insulin release. Acetylcholine or carbamylcholine (5-500 micron) had no obvious effect on cyclic GMP or cyclic AMP in the islets. In the presence of 11.1 mM D-glucose, the membrane potential of beta-cells oscillated slowly between a polarized silent state of -50 to -55 mV and a depolarized active state of -33 to -39 mV, at which a fast spike activity occurred. Acetylcholine made the potential stay at the plateau and induced a continuous spike activity pattern. Atropine inhibited the electrical effects of acetylcholine but not those of glucose alone. It is suggested that cholinergic potentiation of insulin release is mediated by changes of transmembrane ionic fluxes, probably without the intervention of cyclic GMP or cyclic AMP.