title: Calcium channel blockers in vivo inhibit serotonin N-acetyltransferase (NAT) activity in chicken retina stimulated by darkness and not by agents elevating intracellular cyclic AMP level.
abstract: The molecular mechanism underlying the role of calcium influx in the regulation of retinal serotonin N-acetyltransferase (NAT) activity was studied in vivo in chickens. Systemic administration of organic antagonists of voltage-sensitive calcium channels (VSCC), i.e., nimodipine and nifedipine, resulted in a marked suppression of the nocturnal increase of NAT activity in chicken retina. In contrast, NAT activity stimulated by nonhydrolysable analogs of cyclic AMP (dibutyryl-cyclic AMP and 8-bromo-cyclic AMP), forskolin, a direct activator of adenylate cyclase, and by phosphodiesterase inhibitors (aminophylline and 3-isobutyl-1-methylxanthine), was not significantly affected by various tested VSCC antagonists. The inhibitory effect of nimodipine on the dark-dependent increase in NAT activity of chicken retina was abolished by Bay K 8644, a selective VSCC agonist. The results presented in this paper indicate an important role of calcium influx through L-type of VSCC in the induction of NAT activity in chicken retina, and suggest that a requirement of calcium ions in the process of NAT induction in the retina may be primarily at the level of cyclic AMP production.
authors.affiliation: Department of Pharmacodynamics, Medical University, Lodz, Poland.
authors.forename: J B
authors.initials: JB
authors.lastname: Zawilska
authors.forename: M
authors.initials: M
authors.lastname: Wawrocka
authors.forename: E
authors.initials: E
authors.lastname: Zurawska
authors.forename: J Z
authors.initials: JZ
authors.lastname: Nowak
mesh_terms: D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002645:Chickens; D002940:Circadian Rhythm; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D003624:Darkness; D008027:Light; D008297:Male; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D012160:Retina / Q000187:drug effects* / Q000201:enzymology
chemical_list: D002121:Calcium Channel Blockers; D010726:Phosphodiesterase Inhibitors; D005576:Colforsin; D000242:Cyclic AMP; D001191:Arylamine N-Acetyltransferase; D002118:Calcium