Acetylcholine releases endothelium-derived hyperpolarizing factor and EDRF from rat blood vessels

CP55940-induced vasorelaxation is endothelial-dependent and mediated by the CB1R through NOS, COX and EDHF pathways in porcine cerebral arteries

Using swine as an experimental model, we chose to examine whether the cannabinoid receptors, e.g. CB1R and the CB2R, could affect vasomotor tone in isolated pial arteries. It was hypothesized that the CB1R would specifically mediate cerebral artery vasorelaxation in an endothelial-dependent manner. First-order pial arteries were isolated from female Landrace pigs (age = 2 months; N = 27) for wire and pressure myography. Arteries were pre-contracted with a thromboxane A₂ analogue (U-46619) and vasorelaxation in response to the CB1R and CB2R receptor mixed agonist CP55940 was examined in the following conditions: 1) untreated; 2) inhibition of the CB1R (AM251); or 3) inhibition of the CB2R receptor (AM630). The data revealed that CP55940 elicits a CB1R-dependent relaxation in pial arteries. CB1R expression was confirmed using immunoblot and immunohistochemical analyses. Subsequently, the role of different endothelial-dependent pathways in the CB1R-mediated vasorelaxation was examined using: 1) denudation (removal of the endothelium); 2) inhibition of cyclooxygenase (COX; Naproxen); 3) inhibition of nitric oxide synthase (NOS; L-NAME); 4) combined inhibition of COX + NOS. The data revealed CB1R-mediated vasorelaxation was endothelial-dependent, with contributions from COX-derived prostaglandins, NO, and endothelium-dependent hyperpolarizing factor (EDHF). Pressurized arteries underwent myogenic curves (20-100 mmHg) under the following conditions: 1) untreated; 2) inhibition of the CB1R. The data revealed CB1R inhibition increased basal myogenic tone, but not myogenic reactivity. As the vascular responses were assessed in isolated pial arteries, this work reveals that the CB1R modulates cerebrovascular tone independently of changes in brain metabolism.

17α-ethinylestradiol modulates endothelial function in ovariectomized rat carotid arteries

17α-ethinylestradiol (EE2), a derivative of 17β-estradiol (E2), is a potent estrogenic substance that is used as the estrogenic component of oral contraceptives (OCPs). However, women who take OCPs have an increased risk of cardiovascular events. Since few studies have examined EE2 endothelial effects, we explored the effects of EE2 on endothelial function in ovariectomized and isoflavone-free rats. After ovariectomy, 12-week-old female Sprague-Dawley rats were assigned to EE2, E2 or control groups. After 16 weeks, the EE2 and E2 groups were orally administered EE2 (8.3 μg/day) and E2 (12.6 μg/day) for 4 weeks, respectively. At 18 weeks, endothelial denudation of the left common carotid arteries was performed, and they were harvested at 20 weeks. The rats in the EE2 and E2 groups exhibited significantly decreased body weights and significantly increased uterine weights, respectively, but no differences were observed between the EE2 and E2 groups. The EE2 and E2 groups showed significantly enhanced acetylcholine-induced endothelium-dependent relaxation, with apamin plus charybdotoxin inhibiting only the EE2 group. Endothelial nitric oxide (NO) synthase expression was significantly higher in the EE2 group than in the control, but lower than in the E2 group. The intima-to-media ratio of denuded arteries was significantly lower in the E2 group than in the other groups, suggesting that NO decreased in the EE2 group compared to the E2 group. We conclude that EE2 has a weaker ability than E2 to produce NO and, for the first time, we demonstrate the ability of EE2 to enhance the activity of endothelial-derived hyperpolarizing factor.

Flipping Off and On the Redox Switch in the Microcirculation

Resistance arteries and arterioles evolved as specialized blood vessels serving two important functions: (a) regulating peripheral vascular resistance and blood pressure and (b) matching oxygen and nutrient delivery to metabolic demands of organs. These functions require control of vessel lumen cross-sectional area (vascular tone) via coordinated vascular cell responses governed by precise spatial-temporal communication between intracellular signaling pathways. Herein, we provide a contemporary overview of the significant roles that redox switches play in calcium signaling for orchestrated endothelial, smooth muscle, and red blood cell control of arterial vascular tone. Three interrelated themes are the focus: (a) smooth muscle to endothelial communication for vasoconstriction, (b) endothelial to smooth muscle cell cross talk for vasodilation, and (c) oxygen and red blood cell interregulation of vascular tone and blood flow. We intend for this thematic framework to highlight gaps in our current knowledge and potentially spark interest for cross-disciplinary studies moving forward.

The Functional Effects of Visfatin on Human Left Internal Mammary Artery

ABSTRACT

Visfatin may play a role in vascular dysfunction in metabolic disorders. Apart from its insulin-mimetic actions, it has divergent actions in the cardiovascular system with discordant results in the literature. Thus, we aimed to study the effects of visfatin on vascular responses of the human left internal mammary artery. Sections of redundant human left internal mammary artery were cut into 3-mm wide rings and hung in 20-mL organ baths containing physiologic salt solution and attached to an isometric force transducer connected to a computer-based data acquisition system. Removing endothelium caused an increase in pD2 values for visfatin-induced relaxation responses (10 -12 -10 -7 M) (9.06 ± 0.21 and 11.08 ± 0.92, respectively). Nicotinamide phosphoribosyltransferase inhibitor FK866 (10 µM) reversed the visfatin-induced relaxations (10 -12 -10 -7 M) ( P = 0.024). Incubations with nitric oxide synthase inhibitor nitro- l -arginine methylester and guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ) caused significant reductions in relaxation responses of visfatin ( P = 0.011 and 0.008, respectively). Visfatin incubations decreased relaxation responses to acetylcholine but not to sodium nitroprusside. Incubations with visfatin did not change contractile responses to angiotensin II, endothelin-1, noradrenalin, and phenylephrine. In this study, visfatin caused endothelium-dependent relaxations mediated by nitric oxide-cyclic guanosine monophosphate pathway and nicotinamide phosphoribosyltransferase activity. Furthermore, visfatin-induced decreases in relaxation responses were also related to endothelium-derived nitric oxide.

Characterization of hypotensive and vasorelaxant effects of PHAR-DBH-Me a new cannabinoid receptor agonist

The effect of PHAR-DBH-Me, a cannabinoid receptor agonist, on different cardiovascular responses in adult male rats was analyzed. The blood pressure was measured directly and indirectly. The coronary flow was measured by Langendorff preparation, and vasomotor responses induced by PHAR-DBH-Me in aortic rings pre-contracted with phenylephrine (PHEN) were analyzed. The intravenous injection of the compound PHAR-DBH-Me (0.018–185 µg/kg) resulted in decreased blood pressure; maximum effect was observed at the dose of 1,850 µg/kg. A concentration-dependent increase in the coronary flow was observed in a Langendorff preparation. In the aortic rings, with and without endothelium, pre-contracted with PHEN (10^–6 M), the addition of PHAR-DBH-Me to the superfusion solution (10^–12–10^–5 M), produced a vasodilator response, which depends on the concentration and presence of the endothelium. L-NAME inhibited these effects. Addition of CB₁ receptor antagonist (AM 251) did not modify the response, while CB₂ receptor antagonist (AM630) decreased the potency of relaxation elicited by PHAR-DBH-Me. Indomethacin shifted the curve concentration-response to the left and produced an increase in the magnitude of the maximum endothelium dependent response to this compound. The maximum effect of PHAR-DBH-Me was observed with the concentration of 10^–5 M. These results show that PHAR-DBH-Me has a concentration-dependent and endothelium-dependent vasodilator effect through CB₂ receptor. This vasodilation is probably mediated by the synthesis/release of NO. On the other hand, it is suggested that PHAR-DBH-Me also induces the release of a vasoconstrictor prostanoid.

Endothelium in Coronary Macrovascular and Microvascular Diseases

ABSTRACT

The endothelium plays a pivotal role in the regulation of vascular tone by synthesizing and liberating endothelium-derived relaxing factors inclusive of vasodilator prostaglandins (eg, prostacyclin), nitric oxide (NO), and endothelium-dependent hyperpolarization factors in a distinct blood vessel size-dependent manner. Large conduit arteries are predominantly regulated by NO and small resistance arteries by endothelium-dependent hyperpolarization factors. Accumulating evidence over the past few decades has demonstrated that endothelial dysfunction and coronary vasomotion abnormalities play crucial roles in the pathogenesis of various cardiovascular diseases. Structural and functional alterations of the coronary microvasculature have been coined as coronary microvascular dysfunction (CMD), which is highly prevalent and associated with adverse clinical outcomes in many clinical settings. The major mechanisms of coronary vasomotion abnormalities include enhanced coronary vasoconstrictive reactivity at epicardial and microvascular levels, impaired endothelium-dependent and endothelium-independent coronary vasodilator capacities, and elevated coronary microvascular resistance caused by structural factors. Recent experimental and clinical research has highlighted CMD as the systemic small artery disease beyond the heart, emerging modulators of vascular functions, novel insights into the pathogenesis of cardiovascular diseases associated with CMD, and potential therapeutic interventions to CMD with major clinical implications. In this article, we will summarize the current knowledge on the endothelial modulation of vascular tone and the pathogenesis of coronary macrovascular and microvascular diseases from bench to bedside, with a special emphasis placed on the mechanisms and clinical implications of CMD.

Endothelium-Dependent Hyperpolarization: The Evolution of Myoendothelial Microdomains

ABSTRACT

Endothelium-derived hyperpolarizing factor (EDHF) was envisaged as a chemical entity causing vasodilation by hyperpolarizing vascular smooth muscle (VSM) cells and distinct from nitric oxide (NO) ([aka endothelium-derived relaxing factor (EDRF)]) and prostacyclin. The search for an identity for EDHF unraveled the complexity of signaling within small arteries. Hyperpolarization originates within endothelial cells (ECs), spreading to the VSM by 2 branches, 1 chemical and 1 electrical, with the relative contribution varying with artery location, branch order, and prevailing profile of VSM activation. Chemical signals vary likewise and can involve potassium ion, lipid mediators, and hydrogen peroxide, whereas electrical signaling depends on physical contacts formed by homocellular and heterocellular (myoendothelial; MEJ) gap junctions, both able to conduct hyperpolarizing current. The discovery that chemical and electrical signals each arise within ECs resulted in an evolution of the single EDHF concept into the more inclusive, EDH signaling. Recognition of the importance of MEJs and particularly the fact they can support bidirectional signaling also informed the discovery that Ca2+ signals can pass from VSM to ECs during vasoconstriction. This signaling activates negative feedback mediated by NO and EDH forming a myoendothelial feedback circuit, which may also be responsible for basal or constitutive release of NO and EDH activity. The MEJs are housed in endothelial projections, and another spin-off from investigating EDH signaling was the discovery these fine structures contain clusters of signaling proteins to regulate both hyperpolarization and NO release. So, these tiny membrane bridges serve as a signaling superhighway or infobahn, which controls vasoreactivity by responding to signals flowing back and forth between the endothelium and VSM. By allowing bidirectional signaling, MEJs enable sinusoidal vasomotion, co-ordinated cycles of widespread vasoconstriction/vasodilation that optimize time-averaged blood flow. Cardiovascular disease disrupts EC signaling and as a result vasomotion changes to vasospasm.

A novel evaluation of endothelial dysfunction ex vivo: "Teaching an Old Drug a New Trick"

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide. Many CVDs begin with endothelium dysfunction (ED), including hypertension, thrombosis, and atherosclerosis. Our assay evaluated ED in isolated murine aorta by quantifying phenylephrine-induced contractions (PE) in the presence of L-NAME, which blocked acetylcholine-induced relaxation (ACh %; >99%). The "L-NAME PE Contraction Ratio" (PECR) was defined as: "PE Tension post-L-NAME" divided by "PE Tension pre-L-NAME." We hypothesized that our novel PE Contraction Ratio would strongly correlate with alterations in endothelium function. Validation 1: PECR and ACh % values of naïve aortas were strongly and positively correlated (PECR vs. ACh %, r2  = 0.91, n = 7). Validation 2: Retrospective analyses of published aortic PECR and ACh % data of female mice exposed to filtered air, propylene glycol:vegetable glycerin (PG:VG), formaldehyde (FA), or acetaldehyde (AA) for 4d showed that the PECR in air-exposed mice (PECR = 1.43 ± 0.05, n = 16) correlated positively with the ACh % (r2  = 0.40) as seen in naïve aortas. Similarly, PECR values were significantly decreased in aortas with ED yet retained positive regression coefficients with ACh % (PG:VG r2  = 0.54; FA r2  = 0.55). Unlike other toxicants, inhaled AA significantly increased both PECR and ACh % values yet diminished their correlation (r2  = 0.09). Validation 3: To assess species-specific dependence, we tested PECR in rat aorta, and found PECR correlated with ACh % relaxation albeit less well in this aged and dyslipidemic model. Because the PECR reflects NOS function directly, it is a robust measure of both ED and vascular dysfunction. Therefore, it is a complementary index of existing tests of ED that also provides insight into mechanisms of vascular toxicity.

Altered Vascular Adaptations to Pregnancy in a Rat Model of Advanced Maternal Age

Advanced maternal age (≥35 years old) increases the risk of pregnancy complications such as preeclampsia and fetal growth restriction. We previously demonstrated vascular dysfunction and abnormal pregnancy outcomes in a rat model of advanced maternal age. However, vascular adaptations to pregnancy in aging were not studied. We hypothesize that advanced maternal age is associated with a more vasoconstrictive phenotype due to reduced nitric oxide (NO) and increased activity of matrix metalloproteinases (MMPs), contributing to impaired vascular adaptations to pregnancy. A rat model of advanced maternal age was used: young (4 months) and aged (9.5 months; ∼35 years in humans) non-pregnant and pregnant rats. On gestational day 20 (term = 22 days; non-pregnant rats were aged-matched), blood pressure and heart rate were measured (tail cuff plethysmography) and vascular function was assessed in mesenteric arteries (wire myography). Endothelium-dependent relaxation to methylcholine (MCh) was assessed in the presence/absence of nitric oxide synthase inhibitor (L-NAME), or inhibitors of endothelium-dependent hyperpolarization (EDH; apamin and TRAM-34). Vasoconstriction responses to big endothelin-1 (bigET-1), in the presence/absence of MMPs-inhibitor (GM6001) or endothelin converting enzyme (ECE-1) inhibitor (CGS35066), in addition, ET-1 responsiveness, were measured. Blood pressure was elevated only in aged non-pregnant rats (p < 0.001) compared to all other groups. MCh responses were not different, however, L-NAME decreased maximum vasodilation in young (p < 0.01) and aged pregnant rats (p < 0.001), and decreased MCh sensitivity in young non-pregnant rats (p < 0.01), without effects in aged non-pregnant rats. EDH contribution to relaxation was similar in young non-pregnant, and aged non-pregnant and pregnant rats, while EDH-mediated relaxation was absent in young pregnant rats (p < 0.001). BigET-1 responses were enhanced in aged non-pregnant (p < 0.01) and pregnant rats (p < 0.05). No significant changes in bigET-1 conversion occurred in the presence of MMP-inhibitor, whereas ECE-1 inhibition reduced bigET-1 constriction in aged rats (p < 0.01). No differences in ET-1 sensitivity were observed. In conclusion, contrary to our hypothesis, reduced blood pressure, and an increased EDH-dependent contribution to vasodilation suggest a compensatory mechanism that may reflect beneficial adaptations in these aged rats that were able to maintain pregnancy. These data increase our understanding of how the vascular adaptive pathways in pregnancy compensate for advanced maternal age.

Evaluation of right coronary vascular dysfunction in severe pulmonary hypertensive rats using synchrotron radiation microangiography

Pulmonary hypertension (PH) causes cardiac hypertrophy in the right ventricle (RV) and eventually leads to RV failure due to persistently elevated ventricular afterload. We hypothesized that the mechanical stress on the RV associated with increased afterload impairs vasodilator function of the right coronary artery (RCA) in PH. Coronary vascular response was assessed using microangiography with synchrotron radiation (SR) in two well-established PH rat models, monocrotaline injection or the combined exposure to chronic hypoxia and vascular endothelial growth factor receptor blockade with Su5416 (SuHx model). In the SuHx model, the effect of the treatment with the nonselective endothelin-1 receptor antagonist (ERA), macitentan, was also examined. Myocardial viability was determined in SuHx model rats, using 18F-FDG Positron emission tomography (PET) and magnetic resonance imaging (MRI). Endothelium-dependent and endothelium-independent vasodilator responses were significantly attenuated in the medium and small arteries of severe PH rats. ERA treatment significantly improved RCA vascular function compared with the untreated group. ERA treatment improved both the decrease in ejection fraction and the increased glucose uptake, and reduced RV remodeling. In addition, the upregulation of inflammatory genes in the RV was almost suppressed by ERA treatment. We found impairment of vasodilator responses in the RCA of severe PH rat models. Endothelin-1 activation in the RCA plays a major role in impaired vascular function in PH rats and is partially restored by ERA treatment. Treatment of PH with ERA may improve RV function in part by indirectly attenuating right heart afterload and in part by associated improvements in right coronary endothelial function.NEW & NOTEWORTHY We demonstrated for the first time the impairment of vascular responses in the right coronary artery (RCA) of the dysfunctional right heart in pulmonary hypertensive rats in vivo. Treatment with an endothelin-1 receptor antagonist ameliorated vascular dysfunction in the RCA, enabled tissue remodeling of the right heart, and improved cardiac function. Our results suggest that impaired RCA function might also contribute to the early progression to heart failure in patients with severe pulmonary arterial hypertension (PAH). The endothelium of the coronary vasculature might be considered as a potential target in treatments to prevent heart failure in severe patients with PAH.

Nitric Oxide Donors as Potential Drugs for the Treatment of Vascular Diseases Due to Endothelium Dysfunction

Endothelial dysfunction and consequent vasoconstriction are a common condition in patients with hypertension and other cardiovascular diseases. Endothelial cells produce and release vasodilator substances that play a pivotal role in normal vascular tone. The mechanisms underlying endothelial dysfunction are multifactorial. However, enhanced reactive oxygen species (ROS) production and consequent vasoconstriction instead of endothelium-derived relaxant generation and consequent vasodilatation contribute to this dysfunction considerably. The main targets of the drugs that are currently used to treat vascular diseases concerning enzyme activities and protein functions that are impaired by endothelial nitric oxide synthase (eNOS) uncoupling and ROS production. Nitric oxide (NO) bioavailability can decrease due to deficient NO production by eNOS and/or NO release to vascular smooth muscle cells, which impairs endothelial function. Considering the NO cellular mechanisms, tackling the issue of eNOS uncoupling could avoid endothelial dysfunction: provision of the enzyme cofactor tetrahydrobiopterin (BH4) should elicit NO release from NO donors, to activate soluble guanylyl cyclase. This should increase cyclic guanosine-monophosphate (cGMP) generation and inhibit phosphodiesterases (especially PDE5) that selectively degrade cGMP. Consequently, protein kinase-G should be activated, and K+ channels should be phosphorylated and activated, which is crucial for cell membrane hyperpolarization and vasodilation and/or inhibition of ROS production. The present review summarizes the current concepts about the vascular cellular mechanisms that underlie endothelial dysfunction and which could be the target of drugs for the treatment of patients with cardiovascular disease.

Gender Differences in Endothelial Function and Coronary Vasomotion Abnormalities

Introduction:

Structural and functional abnormalities of coronary microvasculature, referred to as coronary microvascular dysfunction (CMD), have been implicated in a wide range of cardiovascular diseases and have gained growing attention in patients with chest pain with no obstructive coronary artery disease, especially in females. The central mechanisms of coronary vasomotion abnormalities encompass enhanced coronary vasoconstrictive reactivity (ie, coronary spasm), reduced endothelium-dependent and -independent coronary vasodilator capacities, and increased coronary microvascular resistance. The 2 major endothelium-derived relaxing factors, nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) factors, modulate vascular tone in a distinct vessel size–dependent manner; NO mainly mediates vasodilatation of relatively large, conduit vessels, while EDH factors in small resistance vessels. Endothelium-dependent hyperpolarization–mediated vasodilatation is more prominent in female resistance arteries, where estrogens exert beneficial effects on endothelium-dependent vasodilatation via multiple mechanisms. In the clinical settings, therapeutic approaches targeting NO are disappointing for the treatment of various cardiovascular diseases, where endothelial dysfunction and CMD are substantially involved.

Significance:

In this review, we will discuss the current knowledge on the pathophysiology and molecular mechanisms of endothelial function and coronary vasomotion abnormalities from bench to bedside, with a special reference to gender differences.

Results:

Recent experimental and clinical studies have demonstrated distinct gender differences in endothelial function and coronary vasomotion abnormalities with major clinical implications. Moreover, recent landmark clinical trials regarding the management of stable coronary artery disease have questioned the benefit of percutaneous coronary intervention, supporting the importance of the coronary microvascular physiology.

Conclusion:

Further characterization and a better understanding of the gender differences in basic vascular biology as well as those in cardiovascular diseases are indispensable to improve health care and patient outcomes in cardiovascular medicine.

Sex Differences in the Inflammatory Response: Pharmacological Opportunities for Therapeutics for Coronary Artery Disease

Coordinated molecular responses are key to effective initiation and resolution of both acute and chronic inflammation. Vascular inflammation plays an important role in initiating and perpetuating atherosclerotic disease, specifically at the site of plaque and subsequent fibrous cap rupture. Both men and women succumb to this disease process, and although management strategies have focused on revascularization and pharmacological therapies in the acute situation to reverse vessel closure and prevent thrombogenesis, data now suggest that regulation of host inflammation may improve both morbidity and mortality, thus supporting the notion that prevention is better than cure. There is a clear sex difference in the incidence of vascular disease, and data confirm biological differences in inflammatory initiation and resolution between men and women. This article reviews contemporary opinions describing the sex difference in the initiation and resolution of inflammatory responses, with a view to explore potential targets for pharmacological intervention.

Hydrogen sulfide signalling in the CNS - Comparison with NO

Hydrogen sulfide (H₂ S) together with polysulfides (H₂ S_n , n > 2) are signalling molecules like NO with various physiological roles including regulation of neuronal transmission, vascular tone, inflammation and oxygen sensing. H₂ S and H₂ S_n diffuse to the target proteins for S-sulfurating their cysteine residues that induces the conformational changes to alter the activity. On the other hand, 3-mercaptopyruvate sulfurtransferase transfers sulfur from a substrate 3-mercaptopyruvate to the cysteine residues of acceptor proteins. A similar mechanism has also been identified in S-nitrosylation. S-sulfuration and S-nitrosylation by enzymes proceed only inside the cell, while reactions induced by H₂ S, H₂ S_n and NO even extend to the surrounding cells. Disturbance of signalling by these molecules as well as S-sulfuration and S-nitrosylation causes many nervous system diseases. This review focuses on the signalling by H₂ S and H₂ S_n with S-sulfuration comparing to that of NO with S-nitrosylation and discusses on their roles in physiology and pathophysiology.

The Natural-Mineral-Based Novel Nanomaterial IFMC Increases Intravascular Nitric Oxide without Its Intake: Implications for COVID-19 and beyond

There are currently no promising therapy strategies for either the treatment or prevention of novel coronavirus disease 2019 (COVID-19), despite the urgent need. In addition to respiratory diseases, vascular complications are rapidly emerging as a key threat of COVID-19. Existing nitric oxide (NO) therapies have been shown to improve the vascular system; however, they have different limitations in terms of safety, usability and availability. In light of this, we hypothesise that a natural-mineral-based novel nanomaterial, which was developed based on NO therapy, might be a viable strategy for the treatment and prevention of COVID-19. The present study examined if it could induce an increase of intravascular NO, vasodilation and the consequent increase of blood flow rate and temperature in a living body. The intravascular NO concentration in the hepatic portal of rats was increased by 0.17 nM over 35.2 s on average after its application. An ultrasonic Doppler flow meter showed significant increases in the blood flow rate and vessel diameter, but no difference in the blood flow velocity. These were corroborated by measurements of human hand surface temperature. To our knowledge, this result is the first evidence where an increase of intravascular NO and vasodilation were induced by bringing a natural-mineral-based nanomaterial into contact with or close to a living body. The precise mechanisms remain a matter for further investigation; however, we may assume that endothelial NO synthase, haemoglobin and endothelium-derived hyperpolarising factor are deeply involved in the increase of intravascular NO.

Dysregulation of TRPV4, eNOS and caveolin-1 contribute to endothelial dysfunction in the streptozotocin rat model of diabetes

Endothelial dysfunction is a common complication in diabetes in which endothelium-dependent vasorelaxation is impaired. The aim of this study was to examine the involvement of the TRPV4 ion channel in type 1 diabetic endothelial dysfunction and the possible association of endothelial dysfunction with reduced expression of TRPV4, endothelial nitric oxide synthase (eNOS) and caveolin-1. Male Wistar rats (350-450 g) were injected with 65 mg/kg i.p. streptozotocin (STZ) or vehicle. Endothelial function was investigated in aortic rings and mesenteric arteries using organ bath and myograph, respectively. TRPV4 function was studied with fura-2 calcium imaging in endothelial cells cultured from aortas from control and STZ treated rats. TRPV4, caveolin-1 and eNOS expression was investigated in these cells using immunohistochemistry. STZ-treated diabetic rats showed significant endothelial dysfunction characterised by impaired muscarinic-induced vasorelaxation (aortic rings: STZ-diabetics: Emax = 29.6 ± 9.3%; control: Emax = 77.2 ± 2.5% P˂0.001), as well as significant impairment in TRPV4-induced vasorelaxation (aortic rings, 4αPDD STZ-diabetics: Emax = 56.0 ± 5.5%; control: Emax = 81.1 ± 2.1% P˂0.001). Furthermore, STZ-diabetic primary aortic endothelial cells showed a significant reduction in TRPV4-induced intracellular calcium elevation (P˂0.05) compared with the control group. This was associated with significantly lower expression of TRPV4, caveolin-1 and eNOS and this was reversed by insulin treatment of the endothelial cultures from STZ -diabetic rats. Taken together, these data are consistent with the hypothesis that signalling through TRPV4, caveolin-1, and eNOS is downregulated in STZ-diabetic aortic endothelial cells and restored by insulin treatment.

Endothelial Ca2+ signaling-dependent vasodilation through transient receptor potential channels

Ca²⁺ signaling of endothelial cells plays a critical role in controlling blood flow and pressure in small arteries and arterioles. As the impairment of endothelial function is closely associated with cardiovascular diseases (e.g., atherosclerosis, stroke, and hypertension), endothelial Ca²⁺ signaling mechanisms have received substantial attention. Increases in endothelial intracellular Ca²⁺ concentrations promote the synthesis and release of endothelial-derived hyperpolarizing factors (EDHFs, e.g., nitric oxide, prostacyclin, or K⁺ efflux) or directly result in endothelial-dependent hyperpolarization (EDH). These physiological alterations modulate vascular contractility and cause marked vasodilation in resistance arteries. Transient receptor potential (TRP) channels are nonselective cation channels that are present in the endothelium, vascular smooth muscle cells, or perivascular/sensory nerves. TRP channels are activated by diverse stimuli and are considered key biological apparatuses for the Ca²⁺ influx-dependent regulation of vasomotor reactivity in resistance arteries. Ca²⁺-permeable TRP channels, which are primarily found at spatially restricted microdomains in endothelial cells (e.g., myoendothelial projections), have a large unitary or binary conductance and contribute to EDHFs or EDH-induced vasodilation in concert with the activation of intermediate/small conductance Ca²⁺-sensitive K⁺ channels. It is likely that endothelial TRP channel dysfunction is related to the dysregulation of endothelial Ca²⁺ signaling and in turn gives rise to vascular-related diseases such as hypertension. Thus, investigations on the role of Ca²⁺ dynamics via TRP channels in endothelial cells are required to further comprehend how vascular tone or perfusion pressure are regulated in normal and pathophysiological conditions.

Reactive oxygen species in cardiovascular health and disease: special references to nitric oxide, hydrogen peroxide, and Rho-kinase

The interaction between endothelial cells and vascular smooth muscle cells (VSMC) plays an important role in regulating cardiovascular homeostasis. Endothelial cells synthesize and release endothelium-derived relaxing factors (EDRFs), including vasodilator prostaglandins, nitric oxide (NO), and endothelium-dependent hyperpolarization (EDH) factors. Importantly, the contribution of EDRFs to endothelium-dependent vasodilatation markedly varies in a vessel size-dependent manner; NO mainly mediates vasodilatation of relatively large vessels, while EDH factors in small resistance vessels. We have previously identified that endothelium-derived hydrogen peroxide (H₂O₂) is an EDH factor especially in microcirculation. Several lines of evidence indicate the importance of the physiological balance between NO and H₂O₂/EDH factor. Rho-kinase was identified as the effectors of the small GTP-binding protein, RhoA. Both endothelial NO production and NO-mediated signaling in VSMC are targets and effectors of the RhoA/Rho-kinase pathway. In endothelial cells, the RhoA/Rho-kinase pathway negatively regulates NO production. On the contrary, the pathway enhances VSMC contraction with resultant occurrence of coronary artery spasm and promotes the development of oxidative stress and vascular remodeling. In this review, I will briefly summarize the current knowledge on the regulatory roles of endothelium-derived relaxing factors, with special references to NO and H₂O₂/EDH factor, in relation to Rho-kinase, in cardiovascular health and disease.

Nitric oxide and endothelium-dependent hyperpolarization mediated by hydrogen peroxide in health and disease

The endothelium plays crucial roles in modulating vascular tone by synthesizing and releasing endothelium-derived relaxing factors (EDRFs), including vasodilator prostaglandins, nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) factors. Thus, endothelial dysfunction is the hallmark of atherosclerotic cardiovascular diseases. Importantly, the contribution of EDRFs to endothelium-dependent vasodilatation varies in a distinct vessel size-dependent manner; NO mainly mediates vasodilatation of relatively large, conduit vessels (eg epicardial coronary arteries), while EDH factors in small resistance vessels (eg coronary microvessels). Endothelium-derived hydrogen peroxide (H₂ O₂ ) is a physiological signalling molecule serving as one of the major EDH factors especially in microcirculations and has gained increasing attention in view of its emerging relevance for cardiovascular diseases. In the clinical settings, therapeutic approaches targeting NO (eg NO donors) or non-specific elimination of reactive oxygen species (eg antioxidant supplements) are disappointingly ineffective for the treatment of various cardiovascular diseases, in which endothelial dysfunction and coronary microvascular dysfunction are substantially involved. These lines of evidence indicate the potential importance of the physiological balance between NO and H₂ O₂ /EDH factor. Further characterization and better understanding of endothelium-dependent vasodilatations are important to develop novel therapeutic strategies in cardiovascular medicine. In this MiniReview, we will briefly summarize the current knowledge on the emerging regulatory roles of endothelium-dependent vasodilatations in the cardiovascular system, with a special reference to the two major EDRFs, NO and H₂ O₂ /EDH factor, in health and disease.

Chronic ethanol consumption enhances inducible endothelium-dependent hyperpolarizing factor-mediated relaxation in the rat artery

The inducible endothelium-dependent hyperpolarizing factor (iEDHF) pathway is activated as a compensatory response to adverse changes in the body. It causes vasorelaxation and maintains circulatory homeostasis in the organs. Small to moderate quantities of ethanol enhance vascular relaxation. However, its mechanism and the involvement of the iEDHF pathway in this process are unknown. Therefore, we studied iEDHF-mediated, acetylcholine-induced, endothelium-dependent relaxation in the superior mesenteric arteries (SMAs) of rats chronically fed ethanol. Rats were administered a standard diet (S-Control group), Lieber's control diet (L-Control group), or Lieber's ethanol diet (EtOH group). SMA relaxation was assessed by isometric tension measurements. Arachidonate 15-lipoxygenase (ALOX15) and soluble epoxide hydrolase (sEH) were determined by immunoblot. Acetylcholine-induced, endothelium-dependent relaxation was significantly greater in the EtOH than the control groups. These differences persisted after PGI2 and NO blockade. Thus, the increase in acetylcholine-induced relaxation was EDHF-mediated. In the EtOH group, however, it was prevented by iEDHF inhibitors. ALOX15 and sEH protein expression levels were higher in the EtOH than the L-Control group. The increase in acetylcholine-induced relaxation by chronic ethanol consumption was mediated by the iEDHF pathway. This mechanism may compensate for the blood pressure elevation induced by ethanol. This study suggests that iEDHF is induced during proper drinking and may help prevent the onset of cardiovascular conditions.

The Cyclitol L-(+)-Bornesitol as an Active Marker for the Cardiovascular Activity of the Brazilian Medicinal Plant Hancornia speciosa

The cyclitol bornesitol is the main constituent of the leaves from the antihypertensive medicinal plant Hancornia speciosa. This study aimed to investigate the ability of bornesitol to reduce blood pressure and its mechanism of action. Normotensive Wistar rats were divided into control group and bornesitol groups treated intravenously with bornesitol (0.1, 1.0 and 3.0 mg/kg). Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were recorded in non-anesthetized awake animals. Nitric oxide (NO) and angiotensin-converting enzyme (ACE) were measured in plasma by using colorimetric methods. Vascular reactivity study was performed in rat aorta rings and the involvement of nitric oxide synthase (NOS), calcium-calmodulin complex and phosphatidylinositol-3-kinase (PI3K)/Akt pathway in the vasodilator effect was investigated. Administration of bornesitol significantly reduced the SBP, increased the plasmatic level of nitrite, and decreased ACE activity in normotensive rats. In the rat aorta, bornesitol induced endothelium-dependent vasodilatation, which was abolished by NOS blockade. While calcium-calmodulin complex inhibition decreased the vasodilator effect of bornesitol, the inhibition of PI3K/Akt pathway did not alter it. Bornesitol reduced the blood pressure by a mechanism involving an increased production or bioavailability of NO, inhibition of ACE, and by an endothelium- and NO-dependent vasodilator effect. The present results support the use of bornesitol as an active marker for the cardiovascular activity of Hancornia speciosa.

Transient receptor potential ion-channel subfamily V member 4: a potential target for cancer treatment

The transient receptor potential ion-channel superfamily consists of nonselective cation channels located mostly on the plasma membranes of numerous animal cell types, which are closely related to sensory information transmission (e.g., vision, pain, and temperature perception), as well as regulation of intracellular Ca2+ balance and physiological activities of growth and development. Transient receptor potential ion channel subfamily V (TRPV) is one of the largest and most diverse subfamilies, including TRPV1-TRPV6 involved in the regulation of a variety of cellular functions. TRPV4 can be activated by various physical and chemical stimuli, such as heat, mechanical force, and phorbol ester derivatives participating in the maintenance of normal cellular functions. In recent years, the roles of TRPV4 in cell proliferation, differentiation, apoptosis, and migration have been extensively studied. Its abnormal expression has also been closely related to the onset and progression of multiple tumors, so TRPV4 may be a target for cancer diagnosis and treatment. In this review, we focused on the latest studies concerning the role of TRPV4 in tumorigenesis and the therapeutic potential. As evidenced by the effects on cancerogenesis, TRPV4 is a potential target for anticancer therapy.

Transient Receptor Potential Channels and Endothelial Cell Calcium Signaling

The vascular endothelium is a broadly distributed and highly specialized organ. The endothelium has a number of functions including the control of blood vessels diameter through the production and release of potent vasoactive substances or direct electrical communication with underlying smooth muscle cells, regulates the permeability of the vascular barrier, stimulates the formation of new blood vessels, and influences inflammatory and thrombotic processes. Endothelial cells that make up the endothelium express a variety of cell-surface receptors and ion channels on the plasma membrane that are capable of detecting circulating hormones, neurotransmitters, oxygen tension, and shear stress across the vascular wall. Changes in these stimuli activate signaling cascades that initiate an appropriate physiological response. Increases in the global intracellular Ca²⁺ concentration and localized Ca²⁺ signals that occur within specialized subcellular microdomains are fundamentally important components of many signaling pathways in the endothelium. The transient receptor potential (TRP) channels are a superfamily of cation-permeable ion channels that act as a primary means of increasing cytosolic Ca²⁺ in endothelial cells. Consequently, TRP channels are vitally important for the major functions of the endothelium. In this review, we provide an in-depth discussion of Ca²⁺ -permeable TRP channels in the endothelium and their role in vascular regulation. © 2019 American Physiological Society. Compr Physiol 9:1249-1277, 2019.

Role of K+ channels in maintaining the synchrony of spontaneous Ca2+ transients in the mural cells of rat rectal submucosal arterioles

Mural cells in precapillary arterioles (PCAs) generate spontaneous Ca²⁺ transients primarily arising from the periodic release of Ca²⁺ from sarcoendoplasmic reticulum (SR/ER). The Ca²⁺ release induces Ca²⁺-activated chloride channel (CaCC)-dependent depolarisations that spread to neighbouring mural cells to develop the synchrony of their Ca²⁺ transients. Here, we explored the roles of K⁺ channels in maintaining the synchrony of spontaneous Ca²⁺ transients. Intracellular Ca²⁺ dynamics in mural cells were visualised by Cal-520 fluorescence Ca²⁺ imaging in the submucosal PCAs of rat rectum. Increasing extracellular K⁺ concentration ([K⁺]_o) from 5.9 to 29.7 mM converted synchronous spontaneous Ca²⁺ transients into asynchronous, high-frequency Ca²⁺ transients. Similarly, the blockade of inward rectifier K⁺ (K_ir) channels with Ba²⁺ (50 μM) or K_v7 voltage-dependent K⁺ (K_v7) channels with XE 991 (10 μM) disrupted the synchrony of spontaneous Ca²⁺ transients, while the blockers for large-, intermediate- or small-conductance Ca²⁺-activated K⁺ channels had no effect. K_ir2.1 immunoreactivity was detected in the arteriolar endothelium but not mural cells. In the PCAs that had been pretreated with XE 991 or Ba²⁺, nifedipine (1 μM) attenuated the asynchronous Ca²⁺ transients but failed to restore their synchrony. In contrast, levcromakalim, an ATP-sensitive K⁺ channel opener, restored the synchronous Ca²⁺ transients. Thus, constitutively active K_v7 and K_ir channels appear to be involved in maintaining the relatively hyperpolarised membrane of mural cells. The hyperpolarised membrane prevents depolarisation-induced 'premature' Ca²⁺ transients to ensure sufficient SR/ER Ca²⁺ refilling that is required for regenerative Ca²⁺ release resulting in synchronous Ca²⁺ transients amongst the mural cells.

Important Role of Endothelial Caveolin-1 in the Protective Role of Endothelium-dependent Hyperpolarization Against Nitric Oxide-Mediated Nitrative Stress in Microcirculation in Mice

AIMS

Nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) play important roles in maintaining cardiovascular homeostasis. We have previously demonstrated that endothelial NO synthase (eNOS) plays diverse roles depending on vessel size, as a NO generating system in conduit arteries and an EDH-mediated system in resistance arteries, for which caveolin-1 (Cav-1) is involved. However, the physiological role of endothelial Cav-1 in microvessels remains to be elucidated.

METHODS AND RESULTS

We newly generated endothelium-specific Cav-1-knockout (eCav-1-KO) mice. eCav-1-KO mice showed loss of endothelial Cav-1/eNOS complex and had cardiac hypertrophy despite normal blood pressure. In eCav-1-KO mice, as compared to wild-type controls, the extent of eNOS phosphorylation at inhibitory Thr495 was significantly reduced in mesenteric arteries and the heart. Isometric tension and Langendorff-perfused heart experiments showed that NO-mediated responses were enhanced, whereas EDH-mediated responses were reduced in coronary microcirculation in eCav-1-KO mice. Immunohistochemistry showed increased level of 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), a marker of nitrative stress, in the heart from eCav-1-KO mice. S-guanylation of cardiac H-Ras in eCav-1-KO mice was also significantly increased compared with wild-type controls.

CONCLUSIONS

These results suggest that eCav-1 is involved in the protective role of EDH against nitrative stress caused by excessive NO to maintain cardiac microvascular homeostasis.

Phenolic analysis and erectogenic function of African Walnut (Tetracarpidium conophorum) seeds: The impact of the seed shell on biological activity

This study investigated the erectogenic potential of African walnut seed (AWS). The extract from AWS cooked with/without shell interacted with phosphodiesterase-5 (PDE-5), arginase, angiotensin-I converting enzymes (ACE), and acetylcholinesterase (AChE); enzymes associated with erectile dysfunction (ED) and Fe²⁺ -induced malonaldehyde (MDA) production in the isolated penile tissue. The results showed that the extracts inhibited the enzymes and MDA production, but Walnut cooked with shell had the highest effect. This agreed with increased phenolic acids and flavonoids, found in the AWS cooked with the shell, compared with that cooked without shell. The inhibition of enzymes and antioxidative potentials could be among the possible mechanisms of actions of AWS in the management/treatment of ED. However, cooking walnut seed with the shell seem to be a contributing factor, as this could prevent possible leaching out of the phytochemicals that could be responsible for these biological effects. PRACTICAL APPLICATIONS: Walnut seed possesses a high content of phenolic compounds and inhibit enzymes relevant to the management of erectile dysfunction. Traditionally, Walnut seed is being cooked with/without the shell and consumed for the purpose of alternative medicine in folklore. Our investigation revealed the possible mechanism underlying the therapeutic effect Walnut seed in the management of ED, but the impact of the shell during cooking contributes to this effect. This result will inform the consumers and food scientist on the importance of cooking Walnut seed with the shell in order to maximize its nutraceutical values.

Terminalia fagifolia Mart. & Zucc. elicits vasorelaxation of rat thoracic aorta through nitric oxide and K+ channels dependent mechanism

Terminalia fagifolia Mart. & Zucc. (Combretaceae) is a plant commonly found in the regions of the Brazilian cerrado, popularly used for the treatment of gastrointestinal disorders. There are no reports in the literature on the use of T. fagifolia for the treatment of the cardiovascular system conditions. Nevertheless, plants of the same genus, such as Terminaliaarjuna (Roxb.) Wight & Arn and Terminaliasuperba Engler & Diels, present cardioprotective, hypotensive and vasodilatating effects. In light of this, the aim of the study was to investigate the effect of the ethanolic extract (Tf-EE) and of its aqueous (Tf-AQF), hexanic (Tf-HEXF) and hydroethanolic (Tf-HAF) partition fractions obtained from the stem bark of T.fagifolia Mart. & Zucc. The effects of the extract and partition fractions of T. fagifolia were evaluated on isometric tensions in the thoracic aorta rings of Wistar rats (250–300 g). Tf-EE, Tf-HEXF and Tf-HAF presented a concentration-dependent vasorelaxant effect, and Tf-AQF presented a vasorelaxant effect that was more potent in the presence of endothelium. The relaxation curves of the aorta promoted by the fraction investigated were attenuated in the presence of the following pharmacological tools: L-NAME, ODQ or PTIO. The vasorelaxant effect of the aorta promoted by Tf-AQF was attenuated in the presence of TEA and 4-AP. Tf-EE induced a concentration-dependent and endothelium-independent vasorelaxation. Tf-HAF and Tf-HEXF presented concentration-dependent and vascular-endothelium-independent vasorelaxation, but did not obtain 100% of relaxation. On the other hand, Tf-AQF presented concentration-dependent vasorelaxation that was more potent in aorta rings with vascular endothelium. The relaxant mechanism induced by the Tf-AQF involves the NO/sGC/cGMP pathway and channels Kv.

Summary: The investigation of the relaxing effect of extract and fractions of the stem bark partition of Terminalia fagifolia on aortic rings is a pioneering study involving the participation of K⁺ channels, which demonstrates a potential alternative therapeutic method for the treatment of cardiovascular diseases.

Chenopodium ambrosioides induces an endothelium-dependent relaxation of rat isolated aorta

OBJECTIVE

This study aims to evaluate the vasodilatory effect of Chenopodium ambrosioides on the isolated rat aorta, and to explore its mechanism of action.

METHODS

The vasorelaxant effect and the mode of action of various extracts from the leaves of C. ambrosioides were evaluated on thoracic aortic rings isolated from Wistar rats. In addition, ethyl acetate and methanol fractions were analyzed, using thin-layer chromatography and high-performance liquid chromatography techniques, for their polyphenolic content.

RESULTS

The various active extracts of C. ambrosioides at four concentrations (10^-3, 10^-2, 10^-1 and 1 mg/mL) relaxed the contraction elicited by phenylephrine, in a concentration-dependent manner. This effect seems to be endothelium-dependent, since the vasodilatory effect was entirely absent in denuded aortic rings. The vasorelaxant effect of the methanol fraction (MF) of C. ambrosioides at 1 mg/mL was also inhibited by atropine and tetraethylammonium. This effect remained unchanged by Nω-nitro-l-arginine methyl ester hydrochloride and glibenclamide. The preliminary phytochemical analysis showed that the leaves of C. ambrosioides are rich in phenolic and flavonoid derivatives.

CONCLUSION

These results suggest that the MF of C. ambrosioides produces an endothelium-dependent relaxation of the isolated rat aorta, which is thought to be mediated mainly through stimulation of the muscarinic receptors, and probably involving the opening of Ca²⁺-activated potassium channels.

Mechanisms of vascular dysfunction evoked by ionizing radiation and possible targets for its pharmacological correction

Ionizing radiation (IR) leads to a variety of the cardiovascular diseases, including the arterial hypertension. A number of studies have demonstrated that blood vessels represent important target for IR, and the endothelium is one of the most vulnerable components of the vascular wall. IR causes an inhibition of nitric oxide (NO)-mediated endothelium-dependent vasodilatation and generation of reactive oxygen (ROS) and nitrogen (RNS) species trigger this process. Inhibition of NO-mediated vasodilatation could be due to endothelial NO synthase (eNOS) down-regulation, inactivation of endothelium-derived NO, and abnormalities in diffusion of NO from the endothelial cells (ECs) leading to a decrease in NO bioavailability. Beside this, IR suppresses endothelial large conductance Ca²⁺-activated K⁺ channels (BK_Ca) activity, which control NO synthesis. IR also leads to inhibition of the BK_Ca current in vascular smooth muscle cells (SMCs) which is mediated by protein kinase C (PKC). On the other hand, IR-evoked enhanced vascular contractility may result from PKC-mediated increase in SMCs myofilament Ca²⁺ sensitivity. Also, IR evokes vascular wall inflammation and atherosclerosis development. Vascular function damaged by IR can be effectively restored by quercetin-filled phosphatidylcholine liposomes and mesenchymal stem cells injection. Using RNA-interference technique targeted to different PKC isoforms can also be a perspective approach for pharmacological treatment of IR-induced vascular dysfunction.

Total Flavones of Rhododendron simsii Planch Flower Protect against Cerebral Ischemia-Reperfusion Injury via the Mechanism of Cystathionine-γ-Lyase-Produced H2S

Total flavones of Rhododendron simsii Planch flower (TFR) have a significant protective effect against cerebral ischemia-reperfusion injury. However, its mechanism is unclear. This study investigated the protection of TFR against cerebral ischemia-reperfusion injury via cystathionine-γ-lyase- (CSE-) produced H2S mechanism. CSE-/- mice and CSE-siRNA-transfected rat were used. Relaxation of cerebral basilar artery (CBA), H2S, and CSE mRNA were measured. TFR significantly inhibited cerebral ischemia-reperfusion-induced abnormal neurological symptom and cerebral infarct in the normal rats and the CSE+/+ mice, but not in the CSE-/- mice, and the inhibition was markedly attenuated in CSE-siRNA-transfected rat; TFR elicited a significant vasorelaxation in rat CBA, and the relaxation was markedly attenuated by removal of endothelium or CSE-siRNA transfection or coapplication of NO synthase inhibitor L-NAME and PGI2 synthase inhibitor Indo. CSE inhibitor PPG drastically inhibited TFR-evoked vasodilatation resistant to L-NAME and Indo in endothelium-intact rat CBA. TFR significantly increased CSE mRNA expression in rat CBA endothelial cells and H2S production in rat endothelium-intact CBA. The increase of H2S production resistant to L-NAME and Indo was abolished by PPG. Our data indicate that TFR has a protective effect against the cerebral ischemia-reperfusion injury via CSE-produced H2S and endothelial NO and/or PGI2 to relax the cerebral artery.

Endothelium-Dependent Hyperpolarization (EDH) in Hypertension: The Role of Endothelial Ion Channels

Upon stimulation with agonists and shear stress, the vascular endothelium of different vessels selectively releases several vasodilator factors such as nitric oxide and prostacyclin. In addition, vascular endothelial cells of many vessels regulate the contractility of the vascular smooth muscle cells through the generation of endothelium-dependent hyperpolarization (EDH). There is a general consensus that the opening of small- and intermediate-conductance Ca2+-activated K⁺ channels (SKCa and IKCa) is the initial mechanistic step for the generation of EDH. In animal models and humans, EDH and EDH-mediated relaxations are impaired during hypertension, and anti-hypertensive treatments restore such impairments. However, the underlying mechanisms of reduced EDH and its improvement by lowering blood pressure are poorly understood. Emerging evidence suggests that alterations of endothelial ion channels such as SKCa channels, inward rectifier K⁺ channels, Ca2+-activated Cl- channels, and transient receptor potential vanilloid type 4 channels contribute to the impaired EDH during hypertension. In this review, we attempt to summarize the accumulating evidence regarding the pathophysiological role of endothelial ion channels, focusing on their relationship with EDH during hypertension.

Angiotensin II Receptor-Neprilysin Inhibitor Sacubitril/Valsartan Improves Endothelial Dysfunction in Spontaneously Hypertensive Rats

Background

We have previously demonstrated that antihypertensive treatment with renin‐angiotensin system inhibitors restores the impaired endothelium‐dependent hyperpolarization (EDH)–mediated responses in spontaneously hypertensive rats (SHRs). Herein, we investigated whether the angiotensin II receptor–neprilysin inhibitor sacubitril/valsartan (LCZ696) would improve reduced EDH‐mediated responses and whether LCZ696 would exert additional effects on endothelium‐dependent and endothelium‐independent vasorelaxation compared with an angiotensin II type 1 receptor blocker alone during hypertension.

Methods and Results

SHRs were treated for 3 months with either LCZ696 or valsartan, from the age of 8 to 11 months. Age‐matched, untreated SHRs and Wistar‐Kyoto rats served as controls. Membrane potentials and contractile responses were recorded from the isolated superior mesenteric arteries. Acetylcholine‐induced, EDH‐mediated responses were impaired in untreated SHRs compared with Wistar‐Kyoto rats. EDH‐mediated responses were similarly improved in the LCZ696‐ and valsartan‐treated SHRs. No difference was observed in acetylcholine‐induced, nitric oxide‐mediated relaxations among the 4 groups. Endothelium‐independent relaxations in response to a nitric oxide donor, sodium nitroprusside, and those to levcromakalim, an ATP‐sensitive K⁺‐channel opener, were similar among the 4 groups; however, the sensitivities to levcromakalim were significantly higher in both LCZ696‐ and valsartan‐treated SHRs.

Conclusions

LCZ696 appears to be as effective as valsartan in improving the impaired EDH‐mediated responses during hypertension. LCZ696 and valsartan exert similar beneficial effects on endothelium‐independent relaxation via enhanced sensitivity of the ATP‐sensitive K⁺ channel. However, the dual blockade of renin‐angiotensin system and neutral endopeptidase with LCZ696 does not appear to provide additional benefit over valsartan alone on vasomotor function in mesenteric arteries of SHRs.

Diverse Functions of Endothelial NO Synthases System: NO and EDH

Endothelium-dependent relaxations are predominantly regulated by nitric oxide (NO) in large conduit arteries and by endothelium-dependent hyperpolarization (EDH) in small resistance vessels. Although the nature of EDH factors varies depending on species and vascular beds, we have previously demonstrated that endothelial NO synthases (eNOS)-derived hydrogen peroxide (H₂O₂) is an EDH factor in animals and humans. This vessel size-dependent contribution of NO and EDH is, at least in part, attributable to the diverse roles of endothelial NOSs system; in large conduit arteries, eNOS mainly serves as a NO-generating system to elicit soluble guanylate cyclase–cyclic guanosine monophosphate-mediated relaxations, whereas in small resistance vessels, it serves as a superoxide-generating system to cause EDH/H₂O₂-mediated relaxations. Endothelial caveolin-1 may play an important role for the diverse roles of NOSs. Although reactive oxygen species are generally regarded harmful, the physiological roles of H₂O₂ have attracted much attention as accumulating evidence has shown that endothelium-derived H₂O₂ contributes to cardiovascular homeostasis. The diverse functions of endothelial NOSs system with NO and EDH/H₂O₂ could account for a compensatory mechanism in the setting of endothelial dysfunction. In this review, we will briefly summarize the current knowledge on the diverse functions of endothelial NOSs system: NO and EDH/H₂O₂.

Possible mechanisms involved in the vasorelaxant effect produced by clobenzorex in aortic segments of rats

Clobenzorex is a metabolic precursor of amphetamine indicated for the treatment of obesity. Amphetamines have been involved with cardiovascular side effects such as hypertension and pulmonary arterial hypertension. The aim of the present study was to investigate whether the direct application of 10^–9–10^–5 M clobenzorex on isolated phenylephrine-precontracted rat aortic rings produces vascular effects, and if so, what mechanisms may be involved. Clobenzorex produced an immediate concentration-dependent vasorelaxant effect at the higher concentrations (10^–7.5–10^–5 M). The present outcome was not modified by 10^–6 M atropine (an antagonist of muscarinic acetylcholine receptors), 3.1×10^–7 M glibenclamide (an ATP-sensitive K⁺ channel blocker), 10^–3 M 4-aminopyridine (4-AP; a voltage-activated K⁺ channel blocker), 10^–5 M indomethacin (a prostaglandin synthesis inhibitor), 10^–5 M clotrimazole (a cytochrome P450 inhibitor) or 10^–5 M cycloheximide (a general protein synthesis inhibitor). Contrarily, the clobenzorex-induced vasorelaxation was significantly attenuated (P<0.05) by 10^–5 M L-NAME (a direct inhibitor of nitric oxide synthase), 10^–7 M ODQ (an inhibitor of nitric oxide-sensitive guanylyl cyclase), 10^–6 M KT 5823 (an inhibitor of protein kinase G), 10^–2 M TEA (a Ca²⁺-activated K⁺ channel blocker and non-specific voltage-activated K⁺ channel blocker) and 10^–7 M apamin plus 10^–7 M charybdotoxin (blockers of small- and large-conductance Ca²⁺-activated K⁺ channels, respectively), and was blocked by 8×10^–2 M potassium (a high concentration) and removal of the vascular endothelium. These results suggest that the direct vasorelaxant effect by clobenzorex on phenylephrine-precontracted rat aortic rings involved stimulation of the NO/cGMP/PKG/Ca²⁺-activated K⁺ channel pathway.

Divergent roles of endothelial nitric oxide synthases system in maintaining cardiovascular homeostasis

Accumulating evidence has demonstrated the importance of reactive oxygen species (ROS) as an essential second messenger in health and disease. Endothelial dysfunction is the hallmark of atherosclerotic cardiovascular diseases, in which pathological levels of ROS are substantially involved. The endothelium plays a crucial role in modulating tone of underlying vascular smooth muscle by synthesizing and releasing nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) factors in a distinct vessel size-dependent manner through the diverse roles of the endothelial NO synthases (NOSs) system. Endothelium-derived hydrogen peroxide (H₂O₂) is a physiological signaling molecule serving as one of the major EDH factors especially in microcirculations and has gained increasing attention in view of its emerging relevance for cardiovascular homeostasis. In the clinical settings, it has been reported that antioxidant supplements are unexpectedly ineffective to prevent cardiovascular events. These lines of evidence indicate the potential importance of the physiological balance between NO and H₂O₂/EDH through the diverse functions of endothelial NOSs system in maintaining cardiovascular homeostasis. A better understanding of cardiovascular redox signaling is certainly needed to develop novel therapeutic strategies in cardiovascular medicine. In this review, we will briefly summarize the current knowledge on the emerging regulatory roles of redox signaling pathways in cardiovascular homeostasis, with particular focus on the two endothelial NOSs-derived mediators, NO and H₂O₂/EDH.

Update on the role of endothelial cells in trauma

PURPOSE

This review gives an overview of physiological processes, mainly regarding vascular endothelial cells and their important role in hemostasis, information processing, and communication during trauma. An insight is given into molecules and cells involved in the first innate immune response through to the behavior of endothelial cells in developing trauma. The goal of this review is to show the overlap of crucial factors related to the endothelium and the development of trauma.

METHODS

A systemic literature search was performed using Google scholar and PubMed.

RESULTS

The results of the literature search showed that the endothelium, especially the vascular endothelium, is involved in various cellular and subcellular pathways of activation, suppression, and transfer of information. A variety of molecules and cells are orchestrated, subsequently the endothelium gets in contact with a traumatizing event.

CONCLUSION

The endothelium is one of the first barriers that comes into contact with exo- and endogenous trauma-related signals and is a pivotal point in activating subsequent pathways and cascades by transfer of information.

TRPV4: Molecular Conductor of a Diverse Orchestra

Transient receptor potential vanilloid type 4 (TRPV4) is a calcium-permeable nonselective cation channel, originally described in 2000 by research teams led by Schultz (Nat Cell Biol 2: 695-702, 2000) and Liedtke (Cell 103: 525-535, 2000). TRPV4 is now recognized as being a polymodal ionotropic receptor that is activated by a disparate array of stimuli, ranging from hypotonicity to heat and acidic pH. Importantly, this ion channel is constitutively expressed and capable of spontaneous activity in the absence of agonist stimulation, which suggests that it serves important physiological functions, as does its widespread dissemination throughout the body and its capacity to interact with other proteins. Not surprisingly, therefore, it has emerged more recently that TRPV4 fulfills a great number of important physiological roles and that various disease states are attributable to the absence, or abnormal functioning, of this ion channel. Here, we review the known characteristics of this ion channel's structure, localization and function, including its activators, and examine its functional importance in health and disease.

EDH: endothelium-dependent hyperpolarization and microvascular signalling

Endothelium-dependent hyperpolarizing factor (EDHF) is a powerful vasodilator influence in small resistance arteries and thus an important modulator of blood pressure and flow. As the name suggests, EDHF was thought to describe a diffusible factor stimulating smooth muscle hyperpolarization (and thus vasodilatation). However, this idea has evolved with the recognition that a factor can operate alongside the spread of hyperpolarizing current from the endothelium to the vascular smooth muscle (VSM). As such, the pathway is now termed endothelium-dependent hyperpolarization (EDH). EDH is activated by an increase in endothelial [Ca²⁺ ]_i , which stimulates two Ca²⁺ -sensitive K channels, SK_Ca and IK_Ca . This was discovered because apamin and charybdotoxin applied in combination blocked EDHF responses, but iberiotoxin - a blocker of BK_Ca - was not able to substitute for charybdotoxin. SK_Ca and IK_Ca channels are arranged in endothelial microdomains, particularly within projections towards the adjacent smooth muscle, which are rich in IK_Ca channels and close to interendothelial gap junctions where SK_Ca channels, are prevalent. K_Ca activation hyperpolarizes endothelial cells, and K⁺ efflux through them can act as a diffusible 'EDHF' by stimulating VSM Na⁺ ,K⁺ -ATPase and inwardly rectifying K channels (K_IR ). In parallel, hyperpolarizing current spreads from the endothelium to the smooth muscle through myoendothelial gap junctions located on endothelial projections. The resulting radial EDH is complemented by the spread of 'conducted' hyperpolarization along the endothelium of arteries and arterioles to affect conducted vasodilatation (CVD). Retrograde CVD effectively integrates blood flow within the microcirculation, but how the underlying hyperpolarization is sustained is unclear.

Endothelium-dependent hyperpolarization: age, gender and blood pressure, do they matter?

Under physiological conditions, the endothelium generates vasodilator signals [prostacyclin, nitric oxide NO and endothelium-dependent hyperpolarization (EDH)], for the regulation of vascular tone. The relative importance of these two signals depends on the diameter of the blood vessels: as the diameter of the arteries decreases, the contribution of EDH to the regulation of vascular tone increases. The mechanism involved in EDH varies with species and blood vessel types; nevertheless, activation of endothelial intermediate- and small-conductance calcium-activated potassium channels (IK_Ca and SK_Ca , respectively) is characteristic of the EDH pathway. IK_Ca - and SK_Ca -mediated EDH are reduced with endothelial dysfunction, which develops with ageing and hypertension, and is less pronounced in female than in age-matched male until after menopause. Impaired EDH-mediated relaxation is related to a reduced involvement of SK_Ca , so that the response becomes more dependent on IK_Ca . The latter depends on the activation of adenosine monophosphate-activated protein kinase (AMPK) and silent information regulator T1 (SIRT1), proteins associated with the process of cellular senescence and vascular signalling in response to the female hormone. An understanding of the role of AMPK and/or SIRT1 in EDH-like responses may help identifying effective pharmacological strategies to prevent the development of vascular complications of different aetiologies.

Downregulation of Endothelial Transient Receptor Potential Vanilloid Type 4 Channel and Small-Conductance of Ca2+-Activated K+ Channels Underpins Impaired Endothelium-Dependent Hyperpolarization in Hypertension

Endothelium-dependent hyperpolarization (EDH)-mediated responses are impaired in hypertension, but the underlying mechanisms have not yet been determined. The activation of small- and intermediate-conductance of Ca²⁺-activated K⁺ channels (SK_Ca and IK_Ca) underpins EDH-mediated responses. It was recently reported that Ca²⁺ influx through endothelial transient receptor potential vanilloid type 4 channel (TRPV4) is a prerequisite for the activation of SK_Ca/IK_Ca in endothelial cells in specific beds. Here, we attempted to determine whether the impairment of EDH in hypertension is attributable to the dysfunction of TRPV4 and S/IK_Ca, using isolated superior mesenteric arteries of 20-week-old stroke-prone spontaneously hypertensive rats (SHRSP) and age-matched Wistar-Kyoto (WKY) rats. In the WKY arteries, EDH-mediated responses were reduced by a combination of SK_Ca/IK_Ca blockers (apamin plus TRAM-34; 1-[(2-chlorophenyl)diphenylmethl]-1H-pyrazole) and by the blockade of TRPV4 with the selective antagonist RN-1734 or HC-067047. In the SHRSP arteries, EDH-mediated hyperpolarization and relaxation were significantly impaired when compared with WKY. GSK1016790A, a selective TRPV4 activator, evoked robust hyperpolarization and relaxation in WKY arteries. In contrast, in SHRSP arteries, the GSK1016790A-evoked hyperpolarization was small and relaxation was absent. Hyperpolarization and relaxation to cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine, a selective SK_Ca activator, were marginally decreased in SHRSP arteries compared with WKY arteries. The expression of endothelial TRPV4 and SK_Ca protein was significantly decreased in the SHRSP mesenteric arteries compared with those of WKY, whereas function and expression of IK_Ca were preserved in SHRSP arteries. These findings suggest that EDH-mediated responses are impaired in superior mesenteric arteries of SHRSP because of a reduction in both TRPV4 and SK_Ca input to EDH.

The paracrine control of vascular motion. A historical perspective

During the last quarter of the past century, the leading role the endocrine and nervous systems had on the regulation of vasomotion, shifted towards a more paracrine-based regulation. This begun with the recognition of endothelial cells as active players of vascular control, when the vessel's intimal layer was identified as the main source of prostacyclin and was followed by the discovery of an endothelium-derived smooth muscle cell relaxing factor (EDRF). The new position acquired by endothelial cells prompted the discovery of other endothelium-derived regulatory products: vasoconstrictors, generally known as EDCFs, endothelin, and other vasodilators with hyperpolarizing properties (EDHFs). While this research was taking place, a quest for the discovery of the nature of EDRF carried back to a research line commenced a decade earlier: the recently found intracellular messenger cGMP and nitrovasodilators. Both were smooth muscle relaxants and appeared to interact in a hormonal fashion. Prejudice against an unconventional gaseous molecule delayed the acceptance that EDRF was nitric oxide (NO). When this happened, a new era of research that exceeded the vascular field commenced. The discovery of the pathway for NO synthesis from L-arginine involved the clever assembling of numerous unrelated observations of different areas of knowledge. The last ten years of research on the paracrine regulation of the vascular wall has shifted to perivascular fat (PVAT), which is beginning to be regarded as the fourth layer of the vascular wall. Starting with the discovery of an adipose-derived relaxing substance (ADRF), the role that different adipokines have on the paracrine control of vasomotion is now filling the research activity of many vascular pharmacology labs, and surprising interactions between the endothelium, PVAT and smooth muscle are being unveiled.

Reactive oxygen species facilitate the EDH response in arterioles by potentiating intracellular endothelial Ca(2+) release

There is abundant evidence that H2O2 can act as an endothelium-derived hyperpolarizing factor in the resistance vasculature. However, whilst scavenging H2O2 can abolish endothelial dependent hyperpolarization (EDH) and the associated vascular relaxation in some arteries, EDH-dependent vasorelaxation can often be mimicked only by using relatively high concentrations of H2O2. We have examined the role of H2O2 in EDH-dependent vasodilatation by simultaneously measuring vascular diameter and changes in endothelial cell (EC) [Ca(2+)]i during the application of H2O2 or carbachol, which triggers EDH. Carbachol (10µM) induced dilatation of phenylephrine-preconstricted rat cremaster arterioles was largely (73%) preserved in the presence of indomethacin (3µM) and l-NAME (300µM). This residual NO- and prostacyclin-independent dilatation was reduced by 89% upon addition of apamin (0.5µM) and TRAM-34 (10µM), and by 74% when an extracellular ROS scavenging mixture of SOD and catalase (S&C; 100Uml(-1) each) was present. S&C also reduced the carbachol-induced EC [Ca(2+)]i increase by 74%. When applied in Ca(2+)-free external medium, carbachol caused a transient increase in EC [Ca(2+)]i. This was reduced by catalase, and was enhanced when 1µM H2O2 was present in the bath. H2O2 -induced dilatation, which occurred only at concentrations ≥100µM, was reduced by a blocking antibody to TRPM2, which had no effect on carbachol-induced responses. Similarly, iberotoxin and Rp-8bromo cGMP reduced the vasodilatation induced by H2O2, but not by carbachol. Inhibiting PLC, PLA2 or CYP450 2C9 each greatly reduced the carbachol-induced increase in EC [Ca(2+)]i and vasodilatation, but adding 10µM H2O2 during PLA2 or CYP450 2C9 inhibition completely restored both responses. The nature of the effective ROS species was investigated by using Fe(2+) chelators to block the formation of ∙OH. A cell permeant chelator was able to inhibit EC Ca(2+) store release, but cell impermeant chelators reduced both the vasodilatation and EC Ca(2+) influx, implying that ∙OH is required for these responses. The results indicate that rather than mediating EDH by acting directly on smooth muscle, H2O2 promotes EDH by acting within EC to enhance Ca(2+) release.

RhoA/Rho-Kinase in the Cardiovascular System

Twenty years ago, Rho-kinase was identified as an important downstream effector of the small GTP-binding protein, RhoA. Thereafter, a series of studies demonstrated the important roles of Rho-kinase in the cardiovascular system. The RhoA/Rho-kinase pathway is now widely known to play important roles in many cellular functions, including contraction, motility, proliferation, and apoptosis, and its excessive activity induces oxidative stress and promotes the development of cardiovascular diseases. Furthermore, the important role of Rho-kinase has been demonstrated in the pathogenesis of vasospasm, arteriosclerosis, ischemia/reperfusion injury, hypertension, pulmonary hypertension, and heart failure. Cyclophilin A is secreted by vascular smooth muscle cells and inflammatory cells and activated platelets in a Rho-kinase-dependent manner, playing important roles in a wide range of cardiovascular diseases. Thus, the RhoA/Rho-kinase pathway plays crucial roles under both physiological and pathological conditions and is an important therapeutic target in cardiovascular medicine. Recently, functional differences between ROCK1 and ROCK2 have been reported in vitro. ROCK1 is specifically cleaved by caspase-3, whereas granzyme B cleaves ROCK2. However, limited information is available on the functional differences and interactions between ROCK1 and ROCK2 in the cardiovascular system in vivo. Herein, we will review the recent advances about the importance of RhoA/Rho-kinase in the cardiovascular system.

Serelaxin: A Novel Therapeutic for Vascular Diseases

Vascular dysfunction is an important hallmark of cardiovascular disease. It is characterized by increased sensitivity to vasoconstrictors, decreases in the endothelium-derived vasodilators nitric oxide (NO) and prostacyclin (PGI2), and endothelium-derived hyperpolarization (EDH). Serelaxin (recombinant human relaxin) has gained considerable attention as a new vasoactive drug, largely through its beneficial therapeutic effects in acute heart failure. In this review we first describe the contribution of endogenous relaxin to vascular homeostasis. We then provide a comprehensive overview of the novel mechanisms of serelaxin action in blood vessels that differentiate it from other vasodilator drugs and explain how this peptide could be used more widely as a therapeutic to alleviate vascular dysfunction in several cardiovascular diseases.