Calcium influx through voltage-sensitive calcium channels regulates in vivo serotonin N-acetyltransferase (NAT) activity in hen retina and pineal gland.

The involvement of transmembrane transport of Ca2+ in regulation of retinal and pineal serotonin N-acetyltransferase (NAT) activity was studied in vivo in hens. Intramuscular administration to hens of organic antagonists of voltage-sensitive calcium channels (VSCC), nimodipine, nifedipine and verapamil, resulted in a marked inhibition of the nocturnal increase of NAT activity in retina and pineal gland. In both tissues the inhibitory effect of nimodipine on the night-time rise of NAT activity was abolished by Bay K 8644, a VSCC agonist. Bay K 8644 administered to hens at the end of the light phase of the light-dark cycle significantly enhanced the dark-dependent increase in retinal and pineal NAT activity. It is suggested that the nocturnal increase of NAT activity in hen retina and pineal gland is similarly regulated in vivo by Ca2+ influx through the VSCC.