The L-type Ca2+ (CaL) channels are multi-protein complexes that include a pore- forming 11C subunit and smaller ancillary subunits. The ancillary 2 subunits promote the expression of 11C subunits at the surface membrane to increase the number of functional CaL channels. In vascular smooth muscle cells (VSMCs), CaL channels are only sparsely expressed in order to tightly regulate voltage-gated Ca2+ influx and vascular contraction. However, during the development of hypertension, we have shown that CaL channels profoundly upregulate in the VSMCs to fuel abnormal vasoconstriction. The goal of this revised project is to determine the mechanism of CaL channel upregulation in response to rises in blood pressure. We have noted that a specific 2 subunit, 23, selectively and profoundly increases in the mesenteric circulation of angiotensin (Ang II) hypertensive mice. The resulting overabundance of CaL channel 11C23 complexes results in elevated Ca2+ influx and abnormal Ca2+-dependent tone in the small arteries of the affected animals. In fact, pharmacological block of CaL channels sharply reduces blood pressure in Ang II hypertensive mice in vivo, but has little antihypertensive effect in control mice, suggesting a central contribution of CaL channels to the pathogenesis of hypertension. At the reviewers'behest, this revised application is tightly focused on delineated the mechanism of vascular CaL channel abnormalities in hypertensive mice to take advantage of gene deletion models.
Aim 1 will determine if an increased number of CaL channel 11C23 complexes is associated with anomalous Ca2+ influx in VSMCs of two mouse models of hypertension.
Aim 2 will use 23 knockout mice to determine if the 23 subunit is a requisite contributor to CaL channel upregulation and the development of hypertension. We predict that vascular CaL channel 11C23 complexes will fail to upregulate in response to Ang II or norepinephrine infusion in 23 knockout mice, and that the development of hypertension will be severely blunted. Finally, Aim 3 will utilize a novel microvascular assay that we have developed to monitor CaL channel expression in the VSMCs of single, pressurized mouse mesenteric arteries. Using this unique assay, we will directly test the hypothesis that high intraluminal pressure inhibits the turnover of CaL channels, thereby increasing their expression at the VSMC surface membrane during hypertension.
Sixty million Americans have high blood pressure, which leads to heart attacks, kidney disease and stroke. This research project will determine if a specific molecule in the muscle cells of blood vessels is required for the abnormal appearance of membrane proteins that causes arteries to contract too much, thereby elevating blood pressure to dangerous levels.
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