The central hypothesis for this proposal is that the alterations in cellular Ca2+ handling that are observed in hypertension are mediated by a change in cellular pH or in the pH sensitivity of various membrane transport processes in vascular smooth muscle. Such a derangement could 1). alter the activtity of various memberane transport processes including Na+/H+ exchange, plasmalemmal ATP-dependent Ca2+ transport, or Na+/Ca2+ 2). alter the binding or permeability of the membrane to Ca2+ and/or 3). alter the mechanisms which mobilize Ca2+ within smooth muscle cells, particularly those related to the actions of inositol phosphates. To evaluate this hypthesis we have developed novel methods using fluorescent indicators to detect Ca2+ and H+ such that we can carry out a variety of biochemical studies on ion transport and release from membranes isolated from the small amounts of tissue that can be obtained from small blood vessels. Using these techniques we will utilize membranes from mesenteric arteries of both hypertensive and normotensive rats and examine 1). the magnitude and pH sensitivity of plasmalemmal ATP-dependent transport, 2). the magnitude and pH sensitivity of Na+/Ca2+ exchange, 3). the magnitude and pH senitivity of Na+/H+ exchange, 4). the magnitude and pH sensitivity of Ca2+ release with particular emphasis on that evoked by D-myo inositol 1,4,5,-trisphosphate and other biologically active inositol phosphate. These studies will provide information as to the kinetic constants and transport capacities of these porcesses that cannot be obtained using more conventional biochemical techniques. Thus, for the first time it will be possible to characterize the transport processes of small blood vessels from a well-established model of hypertension, the SHR rat, and to address a specific hypothesis as to the underlying etiology of hypertension.
