Effects of ethylene glycol tetraacetic acid, A23187 and calmodulin, calcium activated neutral proteinase antagonists on melatonin secretion in perifused chick pineal gland

We have recently described, using perifused pineal glands, that calcium influx participates in the activation of chick pineal gland. This study shows that the loss of perifused chick pineal gland activity is a complex process which seems to involve the release of calcium from intracellular stores, calmodulin and calcium-activated neutral protease (CANP). Pineal glands were perifused with Krebs medium (controls) or with Krebs medium plus the drugs ethylene glycol tetraacetic acid (EGTA; calcium chelator), A23187 (calcium ionophore), EGTA plus A23187 (extra-intra cellular calcium chelation), trifluoperazine and CGS9343B (calmodulin inhibitors), and E-64 (CANP inhibitor) at the time of the natural peak of melatonin release. When EGTA or A23187 were added to the perifusion medium, no effects were observed. On the other hand, when the calcium chelator EGTA plus A23187 (free extra and intracellular calcium levels were dramatically decreased), trifluoperazine, CGS 9343B or E-64 were added to the perifusion medium melatonin synthesis increased significantly and was sustained for 8 h. We propose a prominent role for calcium output from intracellular stores in regulating melatonin production primarily by acting on Ca-calmodulin and calcium-activated neutral protease.