REGULATION OF WATER AND SALT TRANSPORT IN COLLECTING DUCT THROUGH CALCIUM-DEPENDENT SIGNALING MECHANISMS

The reabsorption of salt and water by the collecting duct is under complex hormonal control. Data are reviewed comparing the cellular signaling mechanisms of several hormones and autacoids with their effects on transport in this segment. These studies suggest antagonistic roles for adenosine 3',5'-cyclic monophosphate (cAMP)-dependent and calcium-dependent signaling mechanisms. Whereas vasopressin stimulates both water and sodium transport through cAMP generation, there is accumulating evidence that these stimulatory effects are offset by agonists that activate phosphatidylinositol hydrolysis. The cellular effects of prostaglandin E2, bradykinin, acetylcholine, and high concentrations of vasopressin itself may fall into this category. There is also evidence for an important interrelationship between hormonal modulation of sodium transport rate and intracellular calcium concentration through basolateral sodium-calcium exchange. These calcium-coupled signaling mechanisms and their linkage to protein kinase C activation and eicosanoid production constitute an important pathway resulting in inhibition of both basal and vasopressin-stimulated transport in the collecting duct.