The role of M(3)-muscarinic receptor signaling in insulin secretion.

Recently, M3-muscarinic receptor (M3R) has been identified as the bona fide receptor responsible for the cholinergic regulation of glucose-induced insulin release. The molecular mechanisms of such regulation have also begun to be unravelled. These include the conventional G protein-dependent pathways involving calcium mobilization and activation of protein kinase C. In addition, recent studies also provided evidence for G protein-independent pathways in the regulation of insulin secretion by M3R. These include phosphorylation/arrestin-dependent activation of protein kinase D1, Src family kinase-dependent activation of the sodium channel NALCN and the involvement of regulator of G protein signalling (RGS)-4. Time has now come to extend these studies which were done mainly in rodents to human and explore the potential for targeting such pathways at different levels for the treatment of diseases with impaired insulin secretion such as type II diabetes.