Voltage-dependent calcium channels regulate melatonin output from cultured chick pineal cells.
Chick pineal cells maintained in primary culture display a circadian rhythm of melatonin production and release, and the nocturnal increase in melatonin output is enhanced by elevating extracellular K+. The divalent cations, Co2+, Cd2+, and Mn2+, each reduce nocturnal melatonin output. Nitrendipine and nifedipine also prevent the nocturnal rise in melatonin output, while Bay K 8644 increases it, suggesting a role for voltage-dependent Ca2+ channels in regulating melatonin output. The whole-cell patch-clamp technique was used to record from individual chick pineal cells. Under conditions designed to isolate currents through voltage-dependent Ca2+ channels, biphasic inward currents are elicited by large depolarizing commands (e.g., to 0 mV) from a holding potential of -90 mV; from a holding potential of -40 mV, only a sustained inward current is elicited by steps to 0 mV. Both components of the inward current are blocked by Co2+ or Cd2+. The sustained current is increased in amplitude by Bay K 8644 and blocked by nifedipine, while the transient current is unaffected. Since there is no evidence for vesicular release of melatonin, the "L-type" calcium channels mediating the sustained calcium current appear to be involved in the pathways regulating melatonin synthesis in chick pineal cells.
Harrison
N L
NL
Laboratory of Neurophysiology, NINCDS, Bethesda, Maryland 20892.
Zatz
M
M
D000818:Animals; D000831:Animals, Newborn; D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D002645:Chickens; D004594:Electrophysiology; D008550:Melatonin / Q000378:metabolism*; D010870:Pineal Gland / Q000166:cytology / Q000378:metabolism*; D013997:Time Factors
D015220:Calcium Channels; D008550:Melatonin