Melatonin synchronizes protein synthesis rhythm in hepatocyte cultures as an agonist of intercellular calcium and protein kinases

Melatonin in nanomolar concentrations synchronizes protein synthesis in primary cultures of hepatocytes through calcium-dependent activation of protein kinases. The synchronizing effect of melatonin is blocked by the cytoplasmic calcium chelating agent BAPTA-AM (20 μM) as well as by the inhibitor of protein kinases 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine dihydrochloride (40 μM). Thus, protein phosphorylation is the key event in hepatocyte synchronization by melatonin, as we have demonstrated previously for gangliosides and biogenic amines. The antagonist of melatonin receptors luzindole (20 nM) blocks the synchronizing function of melatonin.