Ramraeheya, Reshma D., Muller, Danu S., Squires, Paul E., Brereten, Helen, Sugden, David, Huang, Guo Cai, Amiel, Stephanie A., Jones, Peter M. and Persaud, Shanta J.. (2008) Function and expression of melatonin receptors on human pancreatic islets. Journal of Pineal Research , Vol.44 (No.3). pp. 273-279. ISSN 0742-3098

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Abstract

Melatonin is known to inhibit insulin secretion from rodent beta-cells through interactions with cell-surface MT1 and/or MT2 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 ([Ca2+](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 MT1 and MT2 melatonin receptors, although MT2 mRNA expression was very low. Analysis of MT, receptor mRNA expression at the single cell level indicated that it was expressed by human islet alpha-cells, but not by beta-cells. Exogenous melatonin stimulated increases in intracellular calcium ([Ca2+](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 beta-cells as the MT, receptor was absent in beta-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) beta-cell line and it also inhibited glucose-stimulated insulin secretion from MINE cells. These data suggest that melatonin has direct stimulatory effects at human islet a-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 beta-cells and a stimulatory effect in human islets.

Item Type:	Journal Article
Subjects:	R Medicine > RC Internal medicine R Medicine > RC Internal medicine > RC0321 Neuroscience. Biological psychiatry. Neuropsychiatry Q Science > QP Physiology
Divisions:	Faculty of Science > Life Sciences (2010- )
Journal or Publication Title:	Journal of Pineal Research
Publisher:	Wiley-Blackwell Publishing, Inc.
ISSN:	0742-3098
Date:	April 2008
Volume:	Vol.44
Number:	No.3
Number of Pages:	7
Page Range:	pp. 273-279
Identification Number:	10.1111/j.1600-079X.2007.00523.x
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
URI:	http://wrap.warwick.ac.uk/id/eprint/30293

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