Effects of calcium on vasopressin-mediated cyclic adenosine monophosphate formation in cultured rat inner medullary collecting tubule cells. Evidence for the role of intracellular calcium.

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Abstract
We explored the effects of alterations in extracellular and intracellular calcium concentration on arginine vasopressin (AVP)-stimulated cAMP formation in cultured rat inner medullary collecting tubule cells. cAMP formation remains constant at extracellular calcium concentrations between 0.5 and 4.0 mM, which did not change intracellular calcium. Maneuvers that alter intracellular calcium concentration are associated with marked changes in cAMP generation. EGTA decreases intracellular calcium and enhances AVP-stimulated cAMP formation, while increasing cellular calcium with 2 microM A23187 decreases AVP-stimulated cAMP formation in the presence, but not in the absence, of extracellular calcium. The changes in cAMP formation observed when intracellular calcium is altered are associated with reciprocal changes in prostaglandin E2 (PGE2) synthesis. Despite greater than 95% inhibition of PGE2 synthesis with 5 microM meclofenamic acid, the changes in cAMP formation accompanying alterations in intracellular calcium concentration are still evident. These studies suggest that intracellular calcium critically influences AVP-stimulated cAMP formation. It does so by a mechanism independent of PG that is probably mediated by a direct effect of the cation on the adenylate cyclase complex.

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