Distribution of melatonin receptors in murine pancreatic islets.

Melatonin has multiple receptor-dependent and receptor-independent functions. At the cell membrane, melatonin interacts with its receptors MT1 and MT2, which are expressed in numerous tissues. Genome-wide association studies have recently shown that the MTNR1B/MT2 receptor may be involved in the pathogenesis of type 2 diabetes mellitus. In line with these findings, expression of melatonin receptors has been shown in mouse, rat, and human pancreatic islets. MT1 and MT2 are G-protein-coupled receptors and are proposed to exert inhibitory effects on insulin secretion. Here, we show by immunocytochemistry that these membrane melatonin receptors have distinct locations in the mouse islet. MT1 is expressed in α-cells while MT2 is located to the β-cells. These findings help to unravel the complex machinery underlying melatonin's role in the regulation of islet function.