Is Ca2+ the second messenger in the response to melatonin in cuckoo wrasse melanophores?
2000 (English)In: Life Sciences, ISSN 0024-3205, Vol. 66, no 11, 1003-1010 p.Article in journal (Refereed) Published
Pigment aggregation in melanophores of Labrus ossifagus is controlled by an a2-adrenoceptor and is somehow modulated by melatonin. The signal transduction mechanisms seem to involve both an attenuation of cAMP and an increase in intracellular Ca2+, inhibiting protein kinase A or activating a phosphatase, respectively. These effects result in dephosphorylation, which in turn induces aggregation. Various a2-adrenoceptor agonists attenuate cAMP levels or increase the concentration of intracellular Ca2+. Noradrenaline, for example, lowers cAMP but does not affect the calcium signal whereas B-HT 920, an a2-adrenoceptor specific agonist, does not induce a cAMP decrease but does appear to induce an increase in intracellular Ca2+. This later inference is drawn from experiments with BAPTA/AM, an intracellular calcium chelator, which counteracts the aggregation induced by B-HT 920. Interestingly, the very potent a2-adrenoceptor agonist medetomidine apparently activates both signal transduction pathways, which could explain its high efficacy in producing aggregation. Melatonin itself does not cause pigment aggregation, but it potentiates noradrenaline-induced aggregation. It has been suggested that melatonin receptors and a2- adrenoceptors follow the same signal transduction pathway, i.e. an attenuation of cAMP. In our experiments, melatonin did not reduce cAMP levels, instead it appears to increase Ca2+ concentration, since melatonin- potentiated aggregation was inhibited by BAPTA/AM. Thus, aggregation amplified by melatonin is probably not mediated by a further decrease in cAMP, but by the same signal transduction mechanism as B-HT 920, i.e. an increase in Ca2+. This further strengthens the suggestion that melatonin and B-HT 920 bind to the same site, but it is unclear if that particular site is on the melatonin receptor or the a2-adrenoceptor.
Place, publisher, year, edition, pages
2000. Vol. 66, no 11, 1003-1010 p.
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:liu:diva-47731DOI: 10.1016/S0024-3205(99)00665-7OAI: oai:DiVA.org:liu-47731DiVA: diva2:268627