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Function and expression of melatonin receptors on human pancreatic islets
Author(s) -
Ramracheya Reshma D.,
Muller Dany S.,
Squires Paul E.,
Brereton Helen,
Sugden David,
Huang Guo Cai,
Amiel Stephanie A.,
Jones Peter M.,
Persaud Shanta J.
Publication year - 2008
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.2007.00523.x
Subject(s) - medicine , endocrinology , melatonin , melatonin receptor , biology , glucagon , islet , receptor , paracrine signalling , insulin
Melatonin is known to inhibit insulin secretion from rodent β ‐cells through interactions with cell‐surface MT 1 and/or MT 2 receptors, but the function of this hormone in human islets of Langerhans is not known. In the current study, melatonin receptor expression by human islets was examined by reverse transcription‐polymerase chain reaction (RT‐PCR) and the effects of exogenous melatonin on intracellular calcium ([Ca 2+ ] i ) levels and islet hormone secretion were determined by single cell microfluorimetry and radioimmunoassay, respectively. RT‐PCR amplifications indicated that human islets express mRNAs coding for MT 1 and MT 2 melatonin receptors, although MT 2 mRNA expression was very low. Analysis of MT 1 receptor mRNA expression at the single cell level indicated that it was expressed by human islet α ‐cells, but not by β ‐cells. Exogenous melatonin stimulated increases in intracellular calcium ([Ca 2+ ] i ) in dissociated human islet cells, and stimulated glucagon secretion from perifused human islets. It also stimulated insulin secretion and this was most probably a consequence of glucagon acting in a paracrine fashion to stimulate β ‐cells as the MT 1 receptor was absent in β ‐cells. Melatonin did not decrease 3′, 5′‐cyclic adenosine monophosphate (cyclic AMP) levels in human islets, but it inhibited cyclic AMP in the mouse insulinoma (MIN6) β ‐cell line and it also inhibited glucose‐stimulated insulin secretion from MIN6 cells. These data suggest that melatonin has direct stimulatory effects at human islet α ‐cells and that it stimulates insulin secretion as a consequence of elevated glucagon release. This study also indicates that the effects of melatonin are species‐specific with primarily an inhibitory role in rodent β ‐cells and a stimulatory effect in human islets.