The relationship between renal blood flow and glomerular filtration rate is well established. A decrease, in renal blood flow lowers glomerular filtration rate triggering water retention and increases in extracellular fluid volume and venous return. Following the Frank-Starling mechanism, increases in cardiac output and arterial pressure are observed. If both renal blood flow and glomerular filtration rate remain suppressed, the initial steps in the development of hypertension have taken place. In spite of the vast literature discussing renal circulation, the mechanisms underlying renal vascular disorders in various forms of hypertension are poorly understood. Since changes in renal blood flow have been implicated in certain vascular disorders, including hypertension and renal vasospasm, this research will help to fill the existing gap of knowledge regarding the relationship between ion channel regulation and vascular reactivity in the renal vasculature. This proposal seeks to obtain new information about the membrane abnormalities associated with renal vascular smooth muscle cells in rat models of genetic and nongenetic hypertension. The general hypothesis for this application is that ion channel function is altered in hypertension and that intracellular modulators, such as Ca2+, may play a role in altered regulation in the hypertensive models. Single smooth muscle cells will be enzymatically dispersed from Wistar-Kyoto (WKY), Sprague-Dawley (SD), Spontaneously Hypertensive (SHR), and DOCA (deoxycorticosterone acetate) hypertensive rat interlobar/arcuate artery of the kidney and the patch clamp technique will be utilized to characterize the properties of Ca2+ and K+ channels in these cells. Determining the pharmacological and biophysical properties of these ionic conductances will serve as a foundation to show the usefulness of isolated SHR and DOCA interlobar/arcuate arterial smooth muscle cells, when compared to control cells from SD and WKY rats, as a model of hypertension for studies involving ion channel regulation by various physiological stimuli. A number of circulating hormones, for example angiotensin II and arginine vasopressin produce significant vasoconstriction and changes in the levels of intracellular Ca2+ in renal arterial smooth muscle. The effects of these agents on membrane potential and whole-cell currents will be quantified. Simultaneously, changes in intracellular [Ca2+] in normo- and hypertensive cells will be measured with a PMT-based indo-1 microfluorometry system. The results provided from these studies should increase our knowledge of the mechanism of hormonal modulation of vascular tone in a clinically relevant tissue, the renal vascular bed and its role in the etiology of hypertension.
