[Calcium ion effects on cAMP system in cultured chick ciliary epithelial cells]

I investigated stimulation of cyclic adenosine 3': 5'-monophosphate (cAMP) production by vasoactive intestinal peptide (VIP), isoproterenol (ISO), sodium fluoride (NaF), and forskolin (FSK) in cultured chick embryo ciliary epithelium (CE). In order to clarify the influence of intracellular calcium ions on cAMP production when CE was activated by cAMP activating agents, I also studied the effects of calcium ionophore (A23187) on VIP, ISO NaF, and FSK stimulated cAMP production. After stimulation with VIP, ISO, NaF, and FSK, a concentration dependent increase in cAMP level was observed. Addition of A23187 activated VIP and ISO stimulated cAMP production. However, A23187 had no effect on the cAMP level when CE was stimulated by NaF and FSK. The activating effect of A23187 was inhibited by calcium/calmodulin-dependent protein kinase inhibitor (W-7). I speculate that calcium ions have different effects on receptor-mediated cAMP pathway and non-receptor-mediated cAMP pathway, and that calcium ions modulate the cAMP pathway through the calcium/calmodulin-dependent protein kinase.