Novel Smooth Muscle Ca2+-Signaling Nanodomains in Blood Pressure Regulation

Background: Ca2+ signals in smooth muscle cells (SMCs) contribute to vascular resistance and control blood pressure. Increased vascular resistance in hypertension has been attributed to impaired SMC Ca2+ signaling mechanisms. In this regard, transient receptor potential vanilloid 4 (TRPV4(SMC)) ion channels are a crucial Ca2+ entry pathway in SMCs. However, their role in blood pressure regulation has not been identified. Methods: We used SMC-specific TRPV4(-/-) (TRPV4(SMC)(-/-)) mice to assess the role of TRPV4(SMC) channels in blood pressure regulation. We determined the contribution of TRPV4(SMC) channels to the constrictor effect of alpha 1 adrenergic receptor (alpha 1AR) stimulation and elevated intraluminal pressure: 2 main physiologic stimuli that constrict resistance-sized arteries. The contribution of spatially separated TRPV4(SMC) channel subpopulations to elevated blood pressure in hypertension was evaluated in angiotensin II-infused mice and patients with hypertension. Results: We provide first evidence that TRPV4(SMC) channel activity elevates resting blood pressure in normal mice. alpha 1AR stimulation activated TRPV4(SMC) channels through PKC alpha (protein kinase C alpha) signaling, which contributed significantly to vasoconstriction and blood pressure elevation. Intraluminal pressure-induced TRPV4(SMC) channel activity opposed vasoconstriction through activation of Ca2+-sensitive K+ (BK) channels, indicating functionally opposite pools of TRPV4(SMC) channels. Superresolution imaging of SMCs revealed spatially separated alpha 1AR:TRPV4 and TRPV4:BK nanodomains in SMCs. These data suggest that spatially separated alpha 1AR-TRPV4(SMC) and intraluminal pressure-TRPV4(SMC)-BK channel signaling have opposite effects on blood pressure, with alpha 1AR-TRPV4(SMC) signaling dominating under resting conditions. Furthermore, in patients with hypertension and a mouse model of hypertension, constrictor alpha 1AR-PKC alpha-TRPV4 signaling was upregulated, whereas dilator pressure-TRPV4-BK channel signaling was disrupted, thereby increasing vasoconstriction and elevating blood pressure. Conclusions: Our data identify novel smooth muscle Ca2+-signaling nanodomains that regulate blood pressure and demonstrate their impairment in hypertension.

Automated summary

This study demonstrates the role of TRPV4(SMC) channels in blood pressure regulation, showing that their activity increases resting blood pressure in normal mice. The study also reveals the opposite effects of α1AR-TRPV4(SMC) signaling and intraluminal pressure-TRPV4(SMC)-BK channel signaling on blood pressure. In hypertension, constrictor α1AR-PKCα-TRPV4 signaling is upregulated, while dilator pressure-TRPV4-BK channel signaling is disrupted, leading to increased vasoconstriction and elevated blood pressure.