Blood pressure regulation by smooth muscle cell ion channels

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Systemic blood pressure is regulated by smooth muscle cells (myocytes) of small (resistance-size) arteries and arterioles. A key regulator of arterial myocyte contractility is membrane potential, which is controlled by plasma membrane ion channels. Arteries from hypertensive subjects are depolarized, leading to vasoconstriction, but mechanisms involved in this pathological alteration are unclear. Arterial myocytes express several different transient receptor potential (TRP) channels, but physiological systemic blood pressure regulation and involvement of these proteins during hypertension is unclear. This lack of knowledge exists largely because TRP subfamily expression, regulation and function in myocytes of arteries that control blood pressure is unclear, there are no specific TRP channel modulators and global TRP channel knockout mice produced confusing effects on blood pressure. Arterial myocytes express TRP polycystin 1 (TRPP1) channels, but blood pressure regulation by these proteins, signaling mechanisms involved and the concept that targeting of these proteins alleviates hypertension have not been studied. For this proposal, we created the first conditional, myocyte-specific TRPP1 knockout (TRPP1sm-/-) mice to test these hypotheses. Cellular current (I) generated by a membrane ion channel population is determined by number (N), open probability (Po) and single channel current (i), such that I=N.Po.i. Previous studies have primarily examined cell currents (I) generated by TRP channels in myocytes. In contrast, contributions of N and Po to currents are poorly understood. This application stems from novel preliminary data suggesting that regulation of myocyte TRPP1 channel surface N and Po controls arterial contractility and blood pressure, TRPP1 channels are upregulated during hypertension, and myocyte-specific TRPP1 knockout alleviates hypertension. Three specific aims will be investigated. Aim 1 will examine the hypothesis that myocyte TRPP1 channels control arterial contractility and systemic blood pressure using novel, inducible, myocyte-specific TRPP1 knockout mice. Aim 2 will investigate the hypothesis that physiological stimuli regulate both TRPP1 channel surface abundance and open probability in myocytes to control arterial contractility. Aim 3 will explore the hypothesis that systemic hypertension is associated with an increase in arterial myocyte TRPP1 channel surface expression that contributes to vasoconstriction and that myocyte-specific TRPP1 ablation attenuates hypertension. Methods used to test these hypotheses will include arterial biotinylation, FRET, co-IP, immunofluorescence, patch-clamp electrophysiology, membrane potential recording, intracellular Ca2+ imaging, arterial myography and blood pressure telemetry. This proposal will provide significant novel information concerning blood pressure regulation by arterial myocyte TRPP1 channels.