[Evidence for a role of calmodulin in cellular cAMP production in response to vasopressin, prostaglandin E2 and forskolin in cultured rat renal papillary collecting tubule cells].

In the present study, the role of calmodulin in the cellular action of arginine vasopressin (AVP), prostaglandin (PG) E2 and forskolin on adenosine-3', 5'-monophosphate (cAMP) production was examined in cultured rat renal papillary collecting tubule cells. In the presence of the phosphodiesterase inhibitor, submaximal concentrations of 10(-9) M AVP, 2 X 10(-8) M PGE2 and 2.4 X 10(-7) M forskolin significantly increased cellular cAMP accumulation by 2.3, 6.0 and 8.4-fold, respectively. Two chemically dissimilar inhibitors of calmodulin, namely trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), attenuated the cellular production of cAMP in a dose-related manner in response to all three stimuli. A dose which inhibited the cellular production of cAMP by 50% (ID50) ranged from 1.6 X 10(-5) to 2.8 X 10(-5) M for trifluoperazine and from 3.5 X 10(-5) to 4.4 X 10(-5) M for W-7. Basal accumulation of cellular cAMP was also decreased by treatment with either trifluoperazine or W-7, but an effective dose was relatively higher than that which inhibited agents-stimulated cellular cAMP production. Since forskolin is recognized as activating adenylate cyclase at one step of the catalytic component and the cellular action of AVP to activate adenylate cyclase is mediated through receptor-catalytic component, the present study indicates calmodulin regulation of basal, AVP-, PGE2- and forskolin-activated adenylate cyclase in the papillary collecting tubule cells. Further study demonstrated the inhibition of AVP- or PGE2-induced cellular cAMP production by treatment with either a calcium-free medium or verapamil, a blocker of cellular calcium uptake, before and during the experiment. These findings suggest that an increase in cytosolic calcium, which interacts with calmodulin to form an active complex, is, at least in part, due to the increased cellular influx of calcium from the extracellular space.