Melatonin effects on the insulin secretion are mediated via cAMP-, cGMP- or IP3-linked signaling cascades

Abstract

Introduction: Melatonin receptors belong to the large class of G-protein coupled membrane receptors. Recently published data speak in favour of a coupling of MT1 melatonin receptors on G-proteins of the Gi, as well as of the Gq class. Activation of the former triggers a cascade which leads to a reduction of adenylate cyclase activity and subsequently to a reduction of intracellular cAMP concentrations. Through alternative coupling of the MT1 to Gq proteins the release of the second messenger IP3 is induced, leading, consecutively, to an increase in intracellular calcium concentration. Activation of MT2 receptors, however, results in a reduction of the guanylate cyclase activity and consecutively of cGMP concentrations due to coupling to inhibitory Gi-proteins. In the present study, these melatonin-evoked signaling pathways were analysed in a rat insulinoma b-cell line (INS1).