title: Calcium and melatonin production in dissociated trout pineal photoreceptor cells in culture.
abstract: Trout pineal cells maintained in primary culture produce melatonin in high amounts during night time and low amounts during daytime. The dark-induced increase in melatonin production was enhanced, in a dose-dependent manner, by elevating extracellular calcium concentration. Low external calcium concentration reduced nocturnal and diurnal melatonin production. Bay K 8644 increased, in a dose-dependent manner, the dark-induced rise in melatonin output, and this effect was antagonized by nifedipine and verapamil. This suggests a role for the dihydropyridine calcium channels in the regulation of the melatonin output. To confirm this, patch-clamp recordings (whole-cell perforated) were run in a 20 mmol/l barium medium at different holding potentials from -80 mV. A voltage-dependent inward current was activated from -30 mV to +40 mV with a maximal amplitude being observed at 0 mV. This current was drastically increased in the presence of Bay K 8644. Nifedipine inhibited the current both in the absence or in the presence of Bay K 8644. Our results are consistent with the idea that extracellular calcium participates in the control of melatonin secretion by photoreceptor cells. It is suggested that activation of the voltage-dependent L-type channel may modulate this secretion.
authors.affiliation: Laboratoire de Neurobiologie et de Neuroendocrinologie Cellulaires, URA CNRS 1869, Poitiers, France.
authors.forename: V
authors.initials: V
authors.lastname: Bégay
authors.forename: P
authors.initials: P
authors.lastname: Bois
authors.forename: J P
authors.initials: JP
authors.lastname: Collin
authors.forename: J
authors.initials: J
authors.lastname: Lenfant
authors.forename: J
authors.initials: J
authors.lastname: Falcón
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002116:Calcitonin / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005260:Female; D008550:Melatonin / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D010786:Photoreceptor Cells / Q000166:cytology* / Q000378:metabolism*; D010870:Pineal Gland / Q000166:cytology* / Q000378:metabolism*; D013997:Time Factors; D014337:Trout / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D002116:Calcitonin; D014700:Verapamil; D009543:Nifedipine; D008550:Melatonin; D002118:Calcium