title: Melatonin modulates rat myotube-acetylcholine receptors by inhibiting calmodulin.
abstract: Melatonin, the pineal gland hormone, modulates alpha-bungarotoxin sensitive nicotinic acetylcholine receptors in sympathetic nerve terminals, cerebellum and chick retina imposing a diurnal variation in functional responses [Markus, R.P., Zago, W.M., Carneiro, R.C., 1996. Melatonin modulation of presynaptic nicotinic acetylcholine receptors in the rat vas deferens. J. Pharmacol. Exp. Ther. 279, 18-22; Markus, R.P., Santos, J.M., Zago, W., Reno, L.A., 2003. Melatonin nocturnal surge modulates nicotinic receptors and nicotine-induced [3HI] glutamate release in rat cerebellum slices. J. Pharmacol. Exp. Ther. 305, 525-530; Sampaio, L.F.S., Hamassaki-Britto, D.E., Markus, R.P., 2005. Influence of melatonin on the development of functional nicotinic acetylcholine receptors in cultured chick retinal cells. Braz. J. Med. Biol. Res. 38, 603-613]. Here we show that in rat myotubes forskolin and melatonin reduced the number of nicotinic acetylcholine receptors expressed in plasma membrane. In addition, these cells expressed melatonin MT1 receptors, which are known to be coupled to G(i)-protein. However, the pharmacological profile of melatonin analogs regarding the reduction in cyclic AMP accumulation and number of nicotinic acetylcholine receptors did not point to a mechanism mediated by activation of G(i)-protein coupled receptors. On the other hand, calmidazolium, a classical inhibitor of calmodulin, reduced in a similar manner both effects. Considering that one isoform of adenylyl cyclase present in rat myotubes is regulated by Ca2+/calmodulin, we propose that melatonin modulates the number of nicotinic acetylcholine receptors via reduction in cyclic AMP accumulation.
authors.affiliation: Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brasil.
authors.forename: Lidiana Duarte
authors.initials: LD
authors.lastname: de Almeida-Paula
authors.forename: Leticia V
authors.initials: LV
authors.lastname: Costa-Lotufo
authors.forename: Zulma
authors.initials: Z
authors.lastname: Silva Ferreira
authors.forename: Amanda Elisa G
authors.initials: AE
authors.lastname: Monteiro
authors.forename: Mauro Cesar
authors.initials: MC
authors.lastname: Isoldi
authors.forename: Rosely O
authors.initials: RO
authors.lastname: Godinho
authors.forename: Regina P
authors.initials: RP
authors.lastname: Markus
mesh_terms: D000818:Animals; D002147:Calmodulin / Q000037:antagonists & inhibitors*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D008550:Melatonin / Q000494:pharmacology*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D044122:Receptor, Melatonin, MT1 / Q000235:genetics / Q000378:metabolism; D044123:Receptor, Melatonin, MT2 / Q000235:genetics / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000378:metabolism
chemical_list: D002147:Calmodulin; D012333:RNA, Messenger; D044122:Receptor, Melatonin, MT1; D044123:Receptor, Melatonin, MT2; D011978:Receptors, Nicotinic; D000242:Cyclic AMP; D006152:Cyclic GMP; D008550:Melatonin