The long term objective of this project is to understand the cellular and molecular events in target epithelium by which aldosterone and glucocorticoid hormones modulate electrolyte transport. Although our experiments directly relate to renal epithelium, insights gained from these studies are likely to implicate broad areas in human biology since specific receptor sites for these classes of hormones are found in liver, brain, vascular endothelium and other tissues. In the proposed studies we plan to study cultured cells from distal nephron of frog kidney (A6) and the cortical collecting tubule (CCT) of the rabbit which are target sites for the action of vasopressin and aldosterone. These preparations have two advantages: 1) The A6 cell line is well defined and cultured CCT exhibits similar properties to intact CCT and 2) tissue culture offers a major advantage over fresh tissue because of greater accessibility for experimental manipulations. There are three specific aims: 1) Since induction of apical membrane conductance for Na+ and K+ represents the major cellular event that affects changes in ion transport in most target sites for hormone action, we plan to use the patch clamp technique to develop a model of Na+ and K+ channels, at rest and after hormone stimulation, explore factors that may, under physiological conditions, modulate conductance, and determine the messenger systems that link hormone-receptor interaction to channel gating. 2) Aldosterone decreases paracellular conductance for sodium. Since we have access to the first major protein isolated from the tight junction, we wish to determine how the cellular action of aldosterone regulates shunt conductance through changes in the ZO- 1 protein. 3) Aldosterone stimulates electrogenic acid secretion by intercalated cells in the renal tubule. Using a newly designed chamber to estimate H+/OH- transport and methods to control cellular pH, we plan to determine whether the hormone affects H+ transfer by directly causing cell acidification, inducing exocytosis of the intracellular pool of H+ pumps, or by affecting the kinetic properties of the pump. We anticipate that insights gained from these studies will have direct clinical implications in therapeutic strategies involved in reducing Na+ absorption in patients with volume-dependent hypertension, potassium wasting in metabolic alkalosis and primary hyperaldosteronism, and glucocorticoid induced hypertension.
