The gasotransmitters are a family of gaseous signaling molecules which are produced endogenously and act at specific receptors to play imperative roles in physiologic and pathophysiologic processes. As a well-known gasotransmitter along with hydrogen sulfide and carbon monoxide, nitric oxide (NO) has earned repute as a potent vasodilator also known as endothelium-derived vasorelaxant factor (EDRF). NO has been studied in greater detail, from its synthesis and mechanism of action to its physiologic, pathologic, and pharmacologic roles in different disease states. Different animal models have been applied to investigate the beneficial effects of NO as an antihypertensive, renoprotective, and antihypertrophic agent. NO and its interaction with different systems like the renin–angiotensin system, sympathetic nervous system, and other gaseous transmitters like hydrogen sulfide are also well studied. However, links that appear to exist between the endocannabinoid (EC) and NO systems remain to be fully explored. Experimental approaches using modulators of its synthesis including substrate, donors, and inhibitors of the synthesis of NO will be useful for establishing the relationship between the NO and EC systems in the cardiovascular and renal systems. Being a potent vasodilator, NO may be unique among therapeutic options for management of hypertension and resulting renal disease and left ventricular hypertrophy. Inclusion of NO modulators in clinical practice may be useful not only as curatives for particular diseases but also for arresting disease prognoses through its interactions with other systems.

Background: Impaired endothelium-dependent vasodilation is a hallmark of obesity-induced hypertension. The recognition that Ca 2+ signaling in endothelial cells promotes vasodilation has led to the hypothesis that endothelial Ca 2+ signaling is compromised during obesity, but the underlying abnormality is unknown. In this regard, transient receptor potential vanilloid 4 (TRPV4) ion channels are a major Ca 2+ influx pathway in endothelial cells, and regulatory protein AKAP150 (A-kinase anchoring protein 150) enhances the activity of TRPV4 channels. Methods: We used endothelium-specific knockout mice and high-fat diet–fed mice to assess the role of endothelial AKAP150-TRPV4 signaling in blood pressure regulation under normal and obese conditions. We further determined the role of peroxynitrite, an oxidant molecule generated from the reaction between nitric oxide and superoxide radicals, in impairing endothelial AKAP150-TRPV4 signaling in obesity and assessed the effectiveness of peroxynitrite inhibition in rescuing endothelial AKAP150-TRPV4 signaling in obesity. The clinical relevance of our findings was evaluated in arteries from nonobese and obese individuals. Results: We show that Ca 2+ influx through TRPV4 channels at myoendothelial projections to smooth muscle cells decreases resting blood pressure in nonobese mice, a response that is diminished in obese mice. Counterintuitively, release of the vasodilator molecule nitric oxide attenuated endothelial TRPV4 channel activity and vasodilation in obese animals. Increased activities of inducible nitric oxide synthase and NADPH oxidase 1 enzymes at myoendothelial projections in obese mice generated higher levels of nitric oxide and superoxide radicals, resulting in increased local peroxynitrite formation and subsequent oxidation of the regulatory protein AKAP150 at cysteine 36, to impair AKAP150-TRPV4 channel signaling at myoendothelial projections. Strategies that lowered peroxynitrite levels prevented cysteine 36 oxidation of AKAP150 and rescued endothelial AKAP150-TRPV4 signaling, vasodilation, and blood pressure in obesity. Peroxynitrite-dependent impairment of endothelial TRPV4 channel activity and vasodilation was also observed in the arteries from obese patients. Conclusions: These data suggest that a spatially restricted impairment of endothelial TRPV4 channels contributes to obesity-induced hypertension and imply that inhibiting peroxynitrite might represent a strategy for normalizing endothelial TRPV4 channel activity, vasodilation, and blood pressure in obesity.

Key points Endothelial cell TRPV4 (TRPV4EC) channels exert a dilatory effect on the resting diameter of resistance mesenteric and pulmonary arteries. Functional intermediate‐ and small‐conductance K+ (IK and SK) channels and endothelial nitric oxide synthase (eNOS) are present in the endothelium of mesenteric and pulmonary arteries. TRPV4EC sparklets preferentially couple with IK/SK channels in mesenteric arteries and with eNOS in pulmonary arteries. TRPV4EC channels co‐localize with IK/SK channels in mesenteric arteries but not in pulmonary arteries, which may explain TRPV4EC‐IK/SK channel coupling in mesenteric arteries and its absence in pulmonary arteries. The presence of the nitric oxide‐scavenging protein, haemoglobin α, limits TRPV4EC‐eNOS signalling in mesenteric arteries. Spatial proximity of TRPV4EC channels with eNOS and the absence of haemoglobin α favour TRPV4EC‐eNOS signalling in pulmonary arteries. Abstract Spatially localized Ca2+ signals activate Ca2+‐sensitive intermediate‐ and small‐conductance K+ (IK and SK) channels in some vascular beds and endothelial nitric oxide synthase (eNOS) in others. The present study aimed to uncover the signalling organization that determines selective Ca2+ signal to vasodilatory target coupling in the endothelium. Resistance‐sized mesenteric arteries (MAs) and pulmonary arteries (PAs) were used as prototypes for arteries with predominantly IK/SK channel‐ and eNOS‐dependent vasodilatation, respectively. Ca2+ influx signals through endothelial transient receptor potential vanilloid 4 (TRPV4EC) channels played an important role in controlling the baseline diameter of both MAs and PAs. TRPV4EC channel activity was similar in MAs and PAs. However, the TRPV4 channel agonist GSK1016790A (10 nm) selectively activated IK/SK channels in MAs and eNOS in PAs, revealing preferential TRPV4EC‐IK/SK channel coupling in MAs and TRPV4EC‐eNOS coupling in PAs. IK/SK channels co‐localized with TRPV4EC channels at myoendothelial projections (MEPs) in MAs, although they lacked the spatial proximity necessary for their activation by TRPV4EC channels in PAs. Additionally, the presence of the NO scavenging protein haemoglobin α (Hbα) within nanometer proximity to eNOS limits TRPV4EC‐eNOS signalling in MAs. By contrast, co‐localization of TRPV4EC channels and eNOS at MEPs, and the absence of Hbα, favour TRPV4EC‐eNOS coupling in PAs. Thus, our results reveal that differential spatial organization of signalling elements determines TRPV4EC‐IK/SK vs. TRPV4EC‐eNOS coupling in resistance arteries.

Pannexin 1 (Panx1), an ATP-efflux pathway, has been linked with inflammation in pulmonary capillaries. However, the physiological roles of endothelial Panx1 in the pulmonary vasculature are unknown. Endothelial transient receptor potential vanilloid 4 (TRPV4) channels lower pulmonary artery (PA) contractility and exogenous ATP activates of endothelial TRPV4 channels. We hypothesized that endothelial Panx1-ATP-TRPV4 channel signaling promotes vasodilation and lowers pulmonary arterial pressure (PAP). Endothelial, but not smooth muscle, knockout of Panx1 increased PA contractility and raised PAP in mice. Flow/shear stress increased ATP efflux through endothelial Panx1 in PAs. Panx1-effluxed extracellular ATP signaled through purinergic P2Y2 receptor (P2Y2R) to activate protein kinase Ca (PKCa), which in turn activated endothelial TRPV4 channels. Finally, caveolin-1 provided a signaling scaffold for endothelial Panx1, P2Y2R, PKCa, and TRPV4 channels in PAs, promoting their spatial proximity and enabling signaling interactions. These results indicate that endothelial Panx1-P2Y2R-TRPV4 channel signaling, facilitated by caveolin-1, reduces PA contractility and lowers PAP in mice.

Background: Ca 2+ 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 Ca 2+ signaling mechanisms. In this regard, transient receptor potential vanilloid 4 (TRPV4 SMC ) ion channels are a crucial Ca 2+ 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 α1 adrenergic receptor (α1AR) 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. α1AR stimulation activated TRPV4 SMC channels through PKCα (protein kinase Cα) signaling, which contributed significantly to vasoconstriction and blood pressure elevation. Intraluminal pressure–induced TRPV4 SMC channel activity opposed vasoconstriction through activation of Ca 2+ -sensitive K + (BK) channels, indicating functionally opposite pools of TRPV4 SMC channels. Superresolution imaging of SMCs revealed spatially separated α1AR:TRPV4 and TRPV4:BK nanodomains in SMCs. These data suggest that spatially separated α1AR–TRPV4 SMC and intraluminal pressure–TRPV4 SMC –BK channel signaling have opposite effects on blood pressure, with α1AR–TRPV4 SMC signaling dominating under resting conditions. Furthermore, in patients with hypertension and a mouse model of hypertension, constrictor α1AR–PKCα–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 Ca 2+ -signaling nanodomains that regulate blood pressure and demonstrate their impairment in hypertension.