This program is based on the hypothesis that salt-dependent hypertension involves the following sequence of events: Salt retention as a result of excessive intake or reduced renal excretion, leads to elevation of the endogenous ouabain (EO) level in plasma. EO, an adrenocortical hormone, selectively inhibits Na+ pumps with alpha2 or alpha3 subunits in neurons, artery myocytes and endothelial cells. Consequently, local intracellular Na+ concentrations rise at plasma membrane-sarco/endo-plasmic reticulum (PM-S/ER) junctions where these Na+ pumps are located. Then, via Na/Ca exchange (NCX), local Ca 2+signaling and Ca 2+storage are augmented; in the chronic state, however, endothelium-dependent vasodilation may be suppressed. The net result is an increase in vasoconstriction, peripheral vascular resistance (PVR) and blood pressure. This hypothesis will be tested on isolated small arteries and myocytes from rats and mice. The studies are designed to elucidate the detailed mechanism of action of acute and chronic low dose ouabain treatment. The ouabain-hypertensive (OH) rat model, several transgenic mouse lines with altered PM ion transporters and transmitter receptors, and novel anti-ouabain agents and NCX blockers will be used. There are 4 projects and 2 cores. Project 1 will characterize the physiology and pharmacology of several key steps in smooth muscle within intact arteries, in the pathway from ouabain to increased PVR. Project 2 will focus on store-operated Ca 2+ entry and storage mechanisms in freshly isolated myocytes, and the effects of acute and chronic ouabain on these mechanisms which appear to be altered in OH. Project 3 will employ novel measurements of quantal content and Ca 2+ signaling to characterize details of sympathetic neuromuscular transmission in small arteries, and will determine how acute and chronic ouabain treatment influences these parameters. Project 4 will elucidate the effects of acute and chronic ouabain treatment on Ca 2+signaling in endothelial cell and pericyte function in renal descending vasa recta and, based on preliminary data, will explore the apparent dysfunction of these signaling mechanisms in OH. The projects will be supported by animal model/analytic chemistry/biochemistry and imaging/electrophysiology/relational database cores. The results will elucidate the mechanism(s) by which ouabain alters Ca 2+ homeostasis, augments sympathetic neuromuscular transmission, influences endothelial feedback, and induces hypertension. This will provide insight into novel targets for anti-hypertensive therapy.
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