CALCIPROTEINS REGULATE CYCLIC-AMP CONTENT AND MELATONIN SECRETION IN TROUT PINEAL PHOTORECEPTORS

PHOTORECEPTOR cells of the fish pineal transduce photoperiodic informa tion into the rhythmic secretion of melatonin. The nocturnal rise in m elatonin secretion has been associated with an increase in cyclic AMP (cAMP) production and with an entry of Ca2+ ions through L-type voltag e-dependent channels. It is shown here that two inhibitors of calcipro teins, W7 and calmidazolium, inhibit melatonin secretion and, to a les ser extent, cAMP levels in cultured trout pineal photoreceptors. Kinet ic studies indicated that melatonin secretion was affected earlier tha n cAMP in cells cultured in the presence of W7. The present results pr ovide evidence that Ca2+ acts through one or more calciproteins to reg ulate melatonin production. It is suggested that Ca2+/calciprotein com plexes might act at two different sites, one involving regulation of c AMP metabolism, and the other being independent from cAMP.