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

Perivascular Adipose Tissue and Uterine Artery Adaptations to Pregnancy

Pregnancy is characterized by longitudinal maternal, physiological adaptations to support the development of a fetus. One of the cardinal maternal adaptations during a healthy pregnancy is a progressive increase in uterine artery blood flow. This facilitates sufficient blood supply for the development of the placenta and the growing fetus. Regional hemodynamic changes in the uterine circulation, such as a vast reduction in uterine artery resistance, are mainly facilitated by changes in uterine artery reactivity and myogenic tone along with remodeling of the uterine arteries. These regional changes in vascular reactivity have been attributed to pregnancy-induced adaptations of cell-to-cell communication mechanisms, with an emphasis on the interaction between endothelial and vascular smooth muscle cells. Perivascular adipose tissue (PVAT) is considered the fourth layer of the vascular wall and contributes to the regulation of vascular reactivity in most vascular beds and most species. This review focuses on mechanisms of uterine artery reactivity and the role of PVAT in pregnancy-induced maternal vascular adaptations, with an emphasis on the uterine circulation.

α acid fraction from Hop extract exerts an endothelium-derived hyperpolarization vasorelaxant effect through TRPV4 employing the feedforward mechanism of PKCα

Until now, the beneficial vascular properties of Hop reported in the literature have been mainly attributed to specific compound classes, such as tannins and phenolic acids. However, the potential vascular action of a Hop subfraction containing a high amount of α or β acids remains completely understood. Therefore, this study aims to investigate the vascular effects of the entire Hop extract and to fraction the Hop extract to identify the main bioactive vascular compounds. A pressure myograph was used to perform vascular reactivity studies on mouse resistance arteries. Phytocomplex fractionation was performed on a semi-prep HPLC system and characterized by UHPLC-PDA-MS/MS coupled to mass spectrometry. Western blot analysis was performed to characterize the phosphorylation site enrolled. The entire Hop extract exerts a direct dose-dependent endothelial vascular action. The B1 subfraction, containing a high concentration of α acids, recapitulates the vascular effect of the crude extract. Its vasorelaxant action is mediated by the opening of Transient Receptor Potential Vanilloid type 4 (TRPV4), potentiated by PKCα, and subsequent involvement of endothelial small-conductance calcium-activated potassium channels (SKCa) and intermediate-conductance calcium-activated potassium channels (IKCa) that drives endothelium-dependent hyperpolarization (EDH) through heterocellular myoendothelial gap junctions (MEGJs). This is the first comprehensive investigation of the vascular function of Hop-derived α acids in resistance arteries. Overall, our data suggest that the B1 subfraction from Hop extracts, containing only α acids, has great potential to be translated into the useful armamentarium of natural bioactive compounds with cardiovascular benefits.

Calcium signaling in endothelial and vascular smooth muscle cells: sex differences and the influence of estrogens and androgens

Calcium signaling in vascular endothelial cells (ECs) and smooth muscle cells (VSMCs) is essential for the regulation of vascular tone. However, the changes to intracellular Ca2+ concentrations are often influenced by sex differences. Furthermore, a large body of evidence shows that sex hormone imbalance leads to dysregulation of Ca2+ signaling and this is a key factor in the pathogenesis of cardiovascular diseases. In this review, the effects of estrogens and androgens on vascular calcium-handling proteins are discussed, with emphasis on the associated genomic or nongenomic molecular mechanisms. The experimental models from which data were collected were also considered. The review highlights 1) in female ECs, transient receptor potential vanilloid 4 (TRPV4) and mitochondrial Ca2+ uniporter (MCU) enhance Ca2+-dependent nitric oxide (NO) generation. In males, only transient receptor potential canonical 3 (TRPC3) plays a fundamental role in this effect. 2) Female VSMCs have lower cytosolic Ca2+ levels than males due to differences in the activity and expression of stromal interaction molecule 1 (STIM1), calcium release-activated calcium modulator 1 (Orai1), calcium voltage-gated channel subunit-α1C (CaV1.2), Na+-K+-2Cl- symporter (NKCC1), and the Na+/K+-ATPase. 3) When compared with androgens, the influence of estrogens on Ca2+ homeostasis, vascular tone, and incidence of vascular disease is better documented. 4) Many studies use supraphysiological concentrations of sex hormones, which may limit the physiological relevance of outcomes. 5) Sex-dependent differences in Ca2+ signaling mean both sexes ought to be included in experimental design.

Nitric oxide, endothelium-derived hyperpolarizing factor, and smooth muscle-dependent mechanisms contribute to magnesium-dependent vascular relaxation in mouse arteries

AIM

Magnesium (Mg2+ ) is a vasorelaxant. The underlying physiological mechanisms driving this vasorelaxation remain unclear. Studies were designed to test the hypothesis that multiple signaling pathways including nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) in endothelial cells as well as Ca2+ antagonization and TRPM7 channels in vascular smooth muscle cells mediate Mg2+ -dependent vessel relaxation.

METHODS

To uncover these mechanisms, force development was measured ex vivo in aorta rings from mice using isometric wire myography. Concentration responses to Mg2+ were studied in intact and endothelium-denuded aortas. Key findings were confirmed in second-order mesenteric resistance arteries perfused ex vivo using pressure myography. Effects of Mg2+ on NO formation were measured in Chinese Hamster Ovary (CHO) cells, isolated mesenteric vessels, and mouse urine.

RESULTS

Mg2+ caused a significant concentration-dependent relaxation of aorta rings. This relaxation was attenuated significantly in endothelium-denuded aortas. The endothelium-dependent portion was inhibited by NO and cGMP blockade but not by cyclooxygenase inhibition. Mg2+ stimulated local NO formation in CHO cells and isolated mesenteric vessels without changing urinary NOx levels. High extracellular Mg2+ augmented acetylcholine-induced relaxation. SKCa and IKCa channel blockers apamin and TRAM34 inhibited Mg2+ -dependent relaxation. The endothelium-independent relaxation in aorta rings was inhibited by high extracellular Ca2+ . Combined blockade of NO, SKCa , and IKCa channels significantly reduced Mg2+ -dependent dilatation in mesenteric resistance vessels.

CONCLUSIONS

In mouse conductance and resistance arteries Mg2+ -induced relaxation is contributed by endothelial NO formation, EDHF pathways, antagonism of Ca2+ in smooth muscle cells, and additional unidentified mechanisms.

Coronary Microvascular Dysfunction and Hypertension: A Bond More Important than We Think

Coronary microvascular dysfunction (CMD) is a clinical entity linked with various risk factors that significantly affect cardiac morbidity and mortality. Hypertension, one of the most important, causes both functional and structural alterations in the microvasculature, promoting the occurrence and progression of microvascular angina. Endothelial dysfunction and capillary rarefaction play the most significant role in the development of CMD among patients with hypertension. CMD is also related to several hypertension-induced morphological and functional changes in the myocardium in the subclinical and early clinical stages, including left ventricular hypertrophy, interstitial myocardial fibrosis, and diastolic dysfunction. This indicates the fact that CMD, especially if associated with hypertension, is a subclinical marker of end-organ damage and heart failure, particularly that with preserved ejection fraction. This is why it is important to search for microvascular angina in every patient with hypertension and chest pain not associated with obstructive coronary artery disease. Several highly sensitive and specific non-invasive and invasive diagnostic modalities have been developed to evaluate the presence and severity of CMD and also to investigate and guide the treatment of additional complications that can affect further prognosis. This comprehensive review provides insight into the main pathophysiological mechanisms of CMD in hypertensive patients, offering an integrated diagnostic approach as well as an overview of currently available therapeutical modalities.

Hyperoside ameliorates cerebral ischaemic-reperfusion injury by opening the TRPV4 channel in vivo through the IP3-PKC signalling pathway

CONTEXT

Hyperoside (Hyp), one of the active flavones from Rhododendron (Ericaceae), has beneficial effects against cerebrovascular disease. However, the effect of Hyp on vasodilatation has not been elucidated.

OBJECTIVE

To explore the effect of Hyp on vasodilatation in the cerebral basilar artery (CBA) of Sprague-Dawley (SD) rats suffering with ischaemic-reperfusion (IR) injury.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly divided into sham, model, Hyp, Hyp + channel blocker and channel blocker groups. Hyp (50 mg/kg, IC₅₀ = 18.3 μg/mL) and channel blocker were administered via tail vein injection 30 min before ischaemic, followed by 20 min of ischaemic and 2 h of reperfusion. The vasodilation, hyperpolarization, ELISA assay, haematoxylin-eosin (HE), Nissl staining and channel-associated proteins and qPCR were analysed. Rat CBA smooth muscle cells were isolated to detect the Ca²⁺ concentration and endothelial cells were isolated to detect apoptosis rate.

RESULTS

Hyp treatment significantly ameliorated the brain damage induced by IR and evoked endothelium-dependent vasodilation rate (47.93 ± 3.09% vs. 2.99 ± 1.53%) and hyperpolarization (-8.15 ± 1.87 mV vs. -0.55 ± 0.42 mV) by increasing the expression of IP3R, PKC, transient receptor potential vanilloid channel 4 (TRPV4), IK_Ca and SK_Ca in the CBA. Moreover, Hyp administration significantly reduced the concentration of Ca²⁺ (49.08 ± 7.74% vs. 83.52 ± 6.93%) and apoptosis rate (11.27 ± 1.89% vs. 23.44 ± 2.19%) in CBA. Furthermore, these beneficial effects of Hyp were blocked by channel blocker.

DISCUSSION AND CONCLUSIONS

Although Hyp showed protective effect in ischaemic stroke, more clinical trial certification is needed due to the difference between animals and humans.

Effects of Mechanical Stress on Endothelial Cells In Situ and In Vitro

Endothelial cells lining blood vessels are essential for maintaining vascular homeostasis and mediate several pathological and physiological processes. Mechanical stresses generated by blood flow and other biomechanical factors significantly affect endothelial cell activity. Here, we review how mechanical stresses, both in situ and in vitro, affect endothelial cells. We review the basic principles underlying the cellular response to mechanical stresses. We also consider the implications of these findings for understanding the mechanisms of mechanotransducer and mechano-signal transduction systems by cytoskeletal components.

A nomogramic model for predicting the left ventricular ejection fraction of STEMI patients after thrombolysis-transfer PCI

Background

The prognosis of ST-segment elevation myocardial infarction (STEMI) is closely linked to left ventricular ejection fraction (LVEF). In contrast to primary percutaneous coronary intervention (PPCI), thrombolysis-transfer PCI (TTPCI) is influenced by multiple factors that lead to heterogeneity in cardiac function and prognosis. The aim of this study is to develop a nomogram model for predicting early LVEF in STEMI patients with TTPCI, based on routine indicators at admission.

Method

We retrospectively reviewed data from patients diagnosed with STEMI at five network hospitals of our PCI center who performed TTPCI as door-to-balloon time (the interval between arrival at the hospital and intracoronary balloon inflation) over 120 min, from February 2018 to April 2022. Categorical variables were analyzed using Pearson χ2 tests or Fisher exact tests, while Student's t-test or Mann-Whitney U-test was used to compare continuous variables. Subsequently, independent risk factors associated with reduced LVEF one week after TTPCI were identified through comprehensive analysis by combining All-Subsets Regression with Logistic Regression. Based on these indicators, a nomogram model was developed, and validated using the area under the receiver operating characteristic (ROC) curve and the Bootstrap method.

Results

A total of 288 patients were analyzed, including 60 with LVEF < 50% and 228 with LVEF ≥ 50%. The nomogram model based on six independent risk factors including age, heart rate (HR), hypertension, smoking history, Alanine aminotransferase (ALT), and Killip class, demonstrated excellent discrimination with an AUC of 0.84 (95% CI: 0.78-0.89), predicted C-index of 0.84 and curve fit of 0.713.

Conclusions

The nomogram model incorporating age, HR, hypertension, smoking history, ALT and Killip class could accurately predict the early LVEF ≥ 50% probability of STEMI patients undergoing TTPCI, and enable clinicians' early evaluation of cardiac function in STEMI patients with TTPCI and early optimization of treatment.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Endothelium-Derived Relaxing Factors and Endothelial Function: A Systematic Review

BACKGROUND

The endothelium plays a pivotal role in homeostatic mechanisms. It specifically modulates vascular tone by releasing vasodilatory mediators, which act on the vascular smooth muscle. Large amounts of work have been dedicated towards identifying mediators of vasodilation and vasoconstriction alongside the deleterious effects of reactive oxygen species on the endothelium. We conducted a systematic review to study the role of the factors released by the endothelium and the effects on the vessels alongside its role in atherosclerosis.

METHODS

A search was conducted with appropriate search terms. Specific attention was offered to the effects of emerging modulators of endothelial functions focusing the analysis on studies that investigated the role of reactive oxygen species (ROS), perivascular adipose tissue, shear stress, AMP-activated protein kinase, potassium channels, bone morphogenic protein 4, and P2Y2 receptor.

RESULTS

530 citations were reviewed, with 35 studies included in the final systematic review. The endpoints were evaluated in these studies which offered an extensive discussion on emerging modulators of endothelial functions. Specific factors such as reactive oxygen species had deleterious effects, especially in the obese and elderly. Another important finding included the shear stress-induced endothelial nitric oxide (NO), which may delay development of atherosclerosis. Perivascular Adipose Tissue (PVAT) also contributes to reparative measures against atherosclerosis, although this may turn pathological in obese subjects. Some of these factors may be targets for pharmaceutical agents in the near future.

CONCLUSION

The complex role and function of the endothelium is vital for regular homeostasis. Dysregulation may drive atherogenesis; thus, efforts should be placed at considering therapeutic options by targeting some of the factors noted.

Chloride Ions, Vascular Function and Hypertension

Blood pressure is determined by cardiac output and systemic vascular resistance, and mediators that induce vasoconstriction will increase systemic vascular resistance and thus elevate blood pressure. While peripheral vascular resistance reflects a complex interaction of multiple factors, vascular ion channels and transporters play important roles in the regulation of vascular tone by modulating the membrane potential of vascular cells. In vascular smooth muscle cells, chloride ions (Cl⁻) are a type of anions accumulated by anion exchangers and the anion–proton cotransporter system, and efflux of Cl⁻ through Cl⁻ channels depolarizes the membrane and thereby triggers vasoconstriction. Among these Cl⁻ regulatory pathways, emerging evidence suggests that upregulation of the Ca²⁺-activated Cl⁻ channel TMEM16A in the vasculature contributes to the increased vascular contractility and elevated blood pressure in hypertension. A robust accumulation of intracellular Cl⁻ in vascular smooth muscle cells through the increased activity of Na⁺–K⁺–2Cl⁻ cotransporter 1 (NKCC1) during hypertension has also been reported. Thus, the enhanced activity of both TMEM16A and NKCC1 could act additively and sequentially to increase vascular contractility and hence blood pressure in hypertension. In this review, we discuss recent findings regarding the role of Cl⁻ in the regulation of vascular tone and arterial blood pressure and its association with hypertension, with a particular focus on TMEM16A and NKCC1.

Dyslipidemia Increases the Risk of Incident Hypertension in a Large Taiwanese Population Follow-Up Study

Dyslipidemia is an important risk factor for hypertension and is strongly associated with an elevated risk of cardiovascular diseases including atherosclerosis and stroke. In this study, we investigated correlations between lipid profiles, including triglycerides, total cholesterol (Chol), high-and low-density lipoprotein cholesterol (HDL-C/LDL-C), and Chol/HDL-C, and baseline and incident hypertension. A total of 26,965 subjects with 4 years of follow-up data were enrolled from the Taiwan Biobank. In the cross-sectional cohort, associations between the prevalence of hypertension and lipid profiles were examined in all study participants (n = 26,965). In the longitudinal cohort, these associations were further assessed in the participants without baseline hypertension (n = 21,454). Multivariable analysis revealed that those in the second quartile (Q2) of triglycerides (compared to Q1; odds ratio (OR), 1.402; p < 0.001); Q3 of triglycerides (compared to Q1; OR, 1.365; p < 0.001); Q4 of triglycerides (compared to Q1; OR, 1.617; p < 0.001); Q3 of HDL-C (compared to Q1; OR, 0.886; p = 0.042); Q4 of HDL-C (compared to Q1; OR, 0.819; p = 0.002); Q2 of Chol/HDL-C (compared to Q1; OR, 1.144; p = 0.042); Q3 of Chol/HDL-C (compared to Q1; OR, 1.149; p = 0.034); and Q4 of Chol/HDL-C (compared to Q1; OR, 1.225; p = 0.002) were significantly associated with incident hypertension. In summary, high Chol/HDL-C, low HDL-C, and high triglycerides were associated with a higher risk of incident hypertension in the enrolled Taiwanese participants.

Antihypertensive effect of Mali-Nil surin rice bran hydrolysate and its mechanisms related to the EDHF-mediated vasorelaxation and L-type Ca2+ channel-mediated vasoconstriction in L-NAME hypertensive rats

Mali-Nil Surin rice bran hydrolysate (MRH) contains highly nutritional proteins and beneficial phenolic compounds. This study investigated an antihypertensive effect of MRH and evaluated the mechanisms mediating this action in N^ω-nitro-L-arginine-methyl ester (L-NAME)-induced hypertensive rats. Antihypertensive activity was determined in male rats orally administered with MRH (100 or 300 mg/kg) or enalapril (15 mg/kg) daily together with L-NAME (50 mg/kg/day) in drinking water, for 21 days. Concurrent oral treatment with MRH lowered the high blood pressure in the L-NAME-induced hypertensive rats. MRH treatment improved endothelial function and increased the endothelium-derived hyperpolarizing factor-mediated vasorelaxation in L-NAME hypertensive rats. L-NAME rats treated with MRH had reduced adrenergic hypercontractility, which was associated with a decrease in L-type calcium channel-mediated vasoconstriction. In addition, MRH exhibited antioxidant activity in hypertensive rats, as indicated by suppression of vascular superoxide anion production and reduction of malondialdehyde levels, as well as magnification of superoxide dismutase and catalase activities in serum. This study demonstrated the nutraceutical potential of MRH to prevent oxidative stress-related vascular dysfunction in hypertension.

Increased contribution of KCa channels to muscle contraction induced vascular and blood flow responses in sedentary and exercise trained ZFDM rats

KEY POINTS

Microvascular dysfunction in type 2 diabetes impairs blood flow redistribution during exercise and limits the performance of skeletal muscle and may cause early fatigability. Endothelium-dependent hyperpolarization (EDH), which mediates vasodilation in resistance arteries is known to be depressed in animals with diabetes. Here we report that low-intensity exercise training in ZFDM rats increased KCa channel-derived component in the vasodilator responses to muscle contraction than in sedentary rats, partly due to the increase in KCNN3 expression. These results suggest that low-intensity exercise training improves blood flow redistribution in contracting skeletal muscle in metabolic disease with diabetes via upregulation of EDH.

ABSTRACT

In resistance arteries, endothelium-dependent hyperpolarization (EDH) mediated vasodilation is depressed in diabetes. We hypothesized that downregulation of KCa channel derived EDH reduces exercise-induced vasodilation and blood flow redistribution in diabetes. To test this hypothesis, we evaluated vascular function in response to hindlimb muscle contraction, and the contribution of KCa channels in anaesthetised ZFDM, metabolic disease rats with type 2 diabetes. We also tested whether exercise training ameliorated the vascular response. Using in vivo microangiography, the hindlimb vasculature was visualized before and after rhythmic muscle contraction (0.5 s tetanus every 3 sec, 20 times) evoked by sciatic nerve stimulation (40 Hz). Femoral blood flow of the contracting hindlimb was simultaneously measured by an ultrasonic flowmeter. The contribution of KCa channels was investigated in the presence and absence of apamin and charybdotoxin. We found that vascular and blood flow responses to muscle contraction were significantly impaired at the level of small artery segments in ZFDM fa/fa rats compared to its lean control fa/+ rats. The contribution of KCa channels was also smaller in fa/fa than in fa/+ rats. Low-intensity exercise training for 12 weeks in fa/fa rats demonstrated minor changes in the vascular and blood flow response to muscle contraction. However, KCa-derived component in the response to muscle contraction was much greater in exercise trained than in sedentary fa/fa rats. These data suggest that exercise training increases the contribution of KCa channels among endothelium-dependent vasodilatory mechanisms to maintain vascular and blood flow responses to muscle contraction in this metabolic disease rat model. Abstract figure legend Low-intensity exercise training in ZFDM, metabolic disease rats with type 2 diabetes increases KCa channel-derived component of endothelium-dependent hyperpolarization in the vascular and blood flow responses to skeletal muscle contraction than the responses in sedentary rats, partly due to upregulation of KCNN3 protein expression. This article is protected by copyright. All rights reserved.

Mechanisms and clinical implications of endothelium-dependent vasomotor dysfunction in coronary microvasculature

Coronary microvascular disease (CMD), which affects the arterioles and capillary endothelium that regulate myocardial perfusion, is an increasingly recognized source of morbidity and mortality, particularly in the setting of metabolic syndrome. The coronary endothelium plays a pivotal role in maintaining homeostasis, though factors such as diabetes, hypertension, hyperlipidemia, and obesity can contribute to endothelial injury and consequently arteriolar vasomotor dysfunction. These disturbances in the coronary microvasculature clinically manifest as diminished coronary flow reserve, which is a known independent risk factor for cardiac death, even in the absence of macrovascular atherosclerotic disease. Therefore, a growing body of literature has examined the molecular mechanisms by which coronary microvascular injury occurs at the level of the endothelium and the consequences on arteriolar vasomotor responses. This review will begin with an overview of normal coronary microvascular physiology, modalities of measuring coronary microvascular function, and clinical implications of CMD. These introductory topics will be followed by a discussion of recent advances in the understanding of the mechanisms by which inflammation, oxidative stress, insulin resistance, hyperlipidemia, hypertension, shear stress, endothelial cell senescence, and tissue ischemia dysregulate coronary endothelial homeostasis and arteriolar vasomotor function.

The Contribution of Gut Microbiota and Endothelial Dysfunction in the Development of Arterial Hypertension in Animal Models and in Humans

The maintenance of the physiological values of blood pressure is closely related to unchangeable factors (genetic predisposition or pathological alterations) but also to modifiable factors (dietary fat and salt, sedentary lifestyle, overweight, inappropriate combinations of drugs, alcohol abuse, smoking and use of psychogenic substances). Hypertension is usually characterized by the presence of a chronic increase in systemic blood pressure above the threshold value and is an important risk factor for cardiovascular disease, including myocardial infarction, stroke, micro- and macro-vascular diseases. Hypertension is closely related to functional changes in the endothelium, such as an altered production of vasoconstrictive and vasodilator substances, which lead to an increase in vascular resistance. These alterations make the endothelial tissue unresponsive to autocrine and paracrine stimuli, initially determining an adaptive response, which over time lead to an increase in risk or disease. The gut microbiota is composed of a highly diverse bacterial population of approximately 10¹⁴ bacteria. A balanced intestinal microbiota preserves the digestive and absorbent functions of the intestine, protecting from pathogens and toxic metabolites in the circulation and reducing the onset of various diseases. The gut microbiota has been shown to produce unique metabolites potentially important in the generation of hypertension and endothelial dysfunction. This review highlights the close connection between hypertension, endothelial dysfunction and gut microbiota.

Oxidative Stress-Induced Hypertension of Developmental Origins: Preventive Aspects of Antioxidant Therapy

Hypertension remains the leading cause of disease burden worldwide. Hypertension can originate in the early stages of life. A growing body of evidence suggests that oxidative stress, which is characterized as a reactive oxygen species (ROS)/nitric oxide (NO) disequilibrium, has a pivotal role in the hypertension of developmental origins. Results from animal studies support the idea that early-life oxidative stress causes developmental programming in prime blood pressure (BP)-controlled organs such as the brain, kidneys, heart, and blood vessels, leading to hypertension in adult offspring. Conversely, perinatal use of antioxidants can counteract oxidative stress and therefore lower BP. This review discusses the interaction between oxidative stress and developmental programming in hypertension. It will also discuss evidence from animal models, how oxidative stress connects with other core mechanisms, and the potential of antioxidant therapy as a novel preventive strategy to prevent the hypertension of developmental origins.

Omega-3 Polyunsaturated Fatty Acids-Vascular and Cardiac Effects on the Cellular and Molecular Level (Narrative Review)

In the prevention and treatment of cardiovascular disease, in addition to the already proven effective treatment of dyslipidemia, hypertension and diabetes mellitus, omega-3 polyunsaturated fatty acids (n-3 PUFAs) are considered as substances with additive effects on cardiovascular health. N-3 PUFAs combine their indirect effects on metabolic, inflammatory and thrombogenic parameters with direct effects on the cellular level. Eicosapentaenoic acid (EPA) seems to be more efficient than docosahexaenoic acid (DHA) in the favorable mitigation of atherothrombosis due to its specific molecular properties. The inferred mechanism is a more favorable effect on the cell membrane. In addition, the anti-fibrotic effects of n-3 PUFA were described, with potential impacts on heart failure with a preserved ejection fraction. Furthermore, n-3 PUFA can modify ion channels, with a favorable impact on arrhythmias. However, despite recent evidence in the prevention of cardiovascular disease by a relatively high dose of icosapent ethyl (EPA derivative), there is still a paucity of data describing the exact mechanisms of n-3 PUFAs, including the role of their particular metabolites. The purpose of this review is to discuss the effects of n-3 PUFAs at several levels of the cardiovascular system, including controversies.

The Transient Receptor Potential Vanilloid 4 Channel and Cardiovascular Disease Risk Factors

Vascular endothelial cells regulate arterial tone through the release of nitric oxide and other diffusible factors such as prostacyclin and endothelium derived hyperpolarizing factors. Alongside these diffusible factors, contact-mediated electrical propagation from endothelial cells to smooth muscle cells via myoendothelial gap junctions, termed endothelium-dependent hyperpolarization (EDH), plays a critical role in endothelium-dependent vasodilation in certain vascular beds. A rise in intracellular Ca²⁺ concentration in endothelial cells is a prerequisite for both the production of diffusible factors and the generation of EDH, and Ca²⁺ influx through the endothelial transient receptor potential vanilloid 4 (TRPV4) ion channel, a nonselective cation channel of the TRP family, plays a critical role in this process in various vascular beds. Emerging evidence suggests that the dysregulation of endothelial TRPV4 channels underpins endothelial dysfunction associated with cardiovascular disease (CVD) risk factors, including hypertension, obesity, diabetes, and aging. Because endothelial dysfunction is a precursor to CVD, a better understanding of the mechanisms underlying impaired TRPV4 channels could lead to novel therapeutic strategies for CVD prevention. In this mini review, we present the current knowledge of the pathophysiological changes in endothelial TRPV4 channels associated with CVD risk factors, and then explore the underlying mechanisms involved.

Vascular Ageing Features Caused by Selective DNA Damage in Smooth Muscle Cell

Persistently unrepaired DNA damage has been identified as a causative factor for vascular ageing. We have previously shown that a defect in the function or expression of the DNA repair endonuclease ERCC1 (excision repair cross complement 1) in mice leads to accelerated, nonatherosclerotic ageing of the vascular system from as early as 8 weeks after birth. Removal of ERCC1 from endothelial alone partly explains this ageing, as shown in endothelial-specific Ercc1 knockout mice. In this study, we determined vascular ageing due to DNA damage in vascular smooth muscle cells, as achieved by smooth muscle-selective genetic removal of ERCC1 DNA repair in mice (SMC-KO: SM22αCre+ Ercc1fl/-). Vascular ageing features in SMC-KO and their wild-type littermates (WT: SM22αCre+ Ercc1fl/+) were examined at the age of 14 weeks and 25 weeks. Both SMC-KO and WT mice were normotensive. Compared to WT, SMC-KO showed a reduced heart rate, fractional shortening, and cardiac output. SMC-KO showed progressive features of nonatherosclerotic vascular ageing as they aged from 14 to 25 weeks. Decreased subcutaneous microvascular dilatation and increased carotid artery stiffness were observed. Vasodilator responses measured in aortic rings in organ baths showed decreased endothelium-dependent and endothelium-independent responses, mostly due to decreased NO-cGMP signaling. NADPH oxidase 2 and phosphodiesterase 1 inhibition improved dilations. SMC-KO mice showed elevated levels of various cytokines that indicate a balance shift in pro- and anti-inflammatory pathways. In conclusion, SMC-KO mice showed a progressive vascular ageing phenotype in resistant and conduit arteries that is associated with cardiac remodeling and contractile dysfunction. The changes induced by DNA damage might be limited to VSMC but eventually affect EC-mediated responses. The fact that NADPH oxidase 2 as wells as phosphodiesterase 1 inhibition restores vasodilation suggests that both decreased NO bioavailability and cGMP degradation play a role in local vascular smooth muscle cell ageing induced by DNA damage.

Trimethylamine-N-oxide (TMAO) Selectively Disrupts Endothelium-Dependent Hyperpolarization-Type Relaxations in a Time-Dependent Manner in Rat Superior Mesenteric Artery

The vascular action of trimethylamine-N-oxide (TMAO)-the gut microbiota-derived metabolite-in contributing cardiovascular disease is a controversial topic. A recent study has shown that acute exposure of TMAO at moderate concentrations inhibits endothelium-dependent hyperpolarization (EDH)-type relaxations selectively in rat isolated femoral arteries, but not in mesenteric arteries. Here we determined the efficacy of higher TMAO concentrations with longer exposure times on vascular reactivity in rat isolated superior mesenteric arteries. Acetylcholine-induced EDH-type relaxations were examined before and after incubation with TMAO (0.1-10 mM) at increasing exposure times (1-24 h). One- and 4-h-incubations with TMAO at 0.1-3 mM did not cause any change in EDH-type relaxations. However, when the incubation time was increased to 24 h, responses to acetylcholine were reduced in arteries incubated with 1-3 mM TMAO. In addition, at higher TMAO concentration (10 mM) the decrease in EDH relaxations could be detected both in 4-h- and 24-h-incubations. The EDH-relaxations were preserved in rings incubated with 10 mM TMAO for 24 h in the presence of SKA-31 (10 µM), the small (SKCa)- and intermediate (IKCa)-conductance calcium-activated potassium channel activator. Contractile responses to phenylephrine increased in arteries exposed to 10 mM TMAO for 24 h. Interestingly, nitric oxide (NO)-mediated relaxations remained unchanged in arteries treated for 24 h at any TMAO concentration. Our study revealed that TMAO selectively disrupted EDH-type relaxations time-dependently without interfering with NO-induced vasodilation in rat isolated mesenteric arteries. Disruption of these relaxations may help explain the causal role of elevated TMAO levels in certain vascular diseases.

Characterization of endothelium-dependent and -independent processes in occipital artery of the rat: Relevance to control of blood flow to nodose sensory cells

Circulating factors access cell bodies of vagal afferents in nodose ganglia (NG) via the occipital artery (OA). Constrictor responses of OA segments closer in origin from the external carotid artery (ECA) differ from segments closer to NG. Our objective was to determine the role of endothelium in this differential vasoreactivity in rat OA segments. Vasoreactivity of OA segments (proximal segments closer to ECA, distal segments closer to NG) were examined in wire myographs. We evaluated (a) vasoconstrictor effects of 5-hydroxytryptamine (5-HT) in intact and endothelium-denuded OA segments in absence/presence of soluble guanylate cyclase (SGC) inhibitor ODQ, (b) vasodilator responses elicited by NO-donor MAHMA NONOate in intact or endothelium-denuded OA segments in absence/presence of ODQ, and (c) vasodilator responses elicited by endothelium-dependent vasodilator, acetylcholine (ACh), in intact OA segments in absence/presence of ODQ. Intact distal OA responded more to 5-HT than intact proximal OA. Endothelium denudation increased 5-HT potency in both OA segments, especially proximal OA. ODQ increased maximal responses of 5HT in both segments, particularly proximal OA. ACh similarly relaxed both OA segments, effects abolished by endothelial denudation and attenuated by ODQ. MAHMA NONOate elicited transient vasodilation in both segments. Effects of ODQ against ACh were segment-dependent whereas those against MAHMA NONOate were not. The endothelium regulates OA responsiveness in a segment-dependently fashion. Endothelial cells at the OA-ECA junction more strongly influence vascular tone than those closer to NG. Differential endothelial regulation of OA tone may play a role in controlling blood flow and access of circulating factors to NG.

Angiotensin II, ATP and high extracellular potassium induced intracellular calcium responses in primary rat brain endothelial cell cultures

The meninges shield the nervous system from diverse, rather harmful stimuli and pathogens from the periphery. This tissue is composed of brain endothelial cells (BECs) that express diverse ion channels and chemical-transmitter receptors also expressed by neurons and glial cells to communicate with each other. However, information about the effects of ATP and angiotensin II on BECs is scarce, despite their essential roles in blood physiology. This work investigated in vitro if BECs from the meninges from rat forebrain respond to ATP, angiotensin II and high extracellular potassium, with intracellular calcium mobilizations and its second messenger-associated pathways. We found that in primary BEC cultures, both ATP and angiotensin II produced intracellular calcium responses linked to the activation of inositol trisphosphate receptors and ryanodine receptors, which led to calcium release from intracellular stores. We also used RT-PCR to explore what potassium channel subunits are expressed by primary BEC cultures and freshly isolated meningeal tissue, and which might be linked to the observed effects. We found that BECs mainly expressed the inward rectifier potassium channel subunits Kir1.1, Kir3.3, Kir 4.1 and Kir6.2. This study contributes to the understanding of the functions elicited by ATP and angiotensin II in BECs from rat meninges. SIGNIFICANCE OF THE STUDY: Brain endothelial cells (BECs) express diverse ion channels and membrane receptors, which they might use to communicate with neurons and glia. This work investigated in vitro, if BECs from the rat forebrain respond to angiotensin II and ATP with intracellular calcium mobilizations. We found that these cells did respond to said substances with intracellular calcium mobilizations linked to inositol trisphosphate and ryanodine receptor activation, which led to calcium release from intracellular stores. These findings are important because they might uncover routes of active communication between brain cells and endothelial cells.

Relationship between casual serum triglyceride levels and the development of hypertension in Japanese

OBJECTIVE

The purpose of the present study was to investigate the effects of serum triglyceride levels on the risk of new-onset hypertension in Japanese.

METHODS

Five thousand nine hundred and thirty-three Japanese workers without hypertension at baseline, who participated in medical check-ups from 2006 to 2018, were followed retrospectively. The participants were divided into quartiles of casual serum triglyceride levels and were followed from the first to last visit of the study period. The outcome was development of hypertension. Risk estimates were computed using Cox's proportional hazards model.

RESULTS

During the follow-up period (average: 6.7 years), 946 individuals developed hypertension. The crude incidence rates of hypertension (per 1000 person-years) increased with rising serum triglyceride levels: 10.1 for quartile 1 (<0.76 mmol/l), 19.6 for quartile 2 (0.76-1.17 mmol/l), 26.0 for quartile 3 (1.18-1.84 mmol/l), and 36.5 for quartile 4 (>1.84 mmol/l) (P < 0.0001 for trend). These associations remained significant even after adjustment for other risk factors: the multivariable-adjusted hazard ratio was 1.29 (1.01-1.66) for the second quartile, 1.27 (0.99-1.63) for the third quartile, and 1.39 (1.09-1.77) for the highest quartile compared with the lowest. There were comparable effects of serum triglyceride levels for incidence of hypertension between subgroups defined by sex, obesity, and diabetes (all P > 0.1 for interaction), whereas stronger associations were observed for participants under 40 years of age than for those aged 40 or above (P = 0.002 for interaction).

CONCLUSION

Serum triglyceride levels were significantly associated with development of hypertension in a Japanese worksite population.

Regulation of ion channels in the microcirculation by mineralocorticoid receptor activation

The mineralocorticoid receptor (MR) has classically been studied in the renal epithelium for its role in regulating sodium and water balance and, subsequently, blood pressure. However, the MR also plays a critical role in the microvasculature by regulating ion channel expression and function. Activation of the MR by its endogenous agonist aldosterone results in translocation of the MR into the nucleus, where it can act as a transcription factor. Although most of the actions of the aldosterone can be attributed to its genomic activity though MR activation, it can also act by nongenomic mechanisms. Activation of this ubiquitous receptor increases the expression of epithelial sodium channels (ENaC) in both the endothelium and smooth muscle cells of peripheral and cerebral vessels. MR activation also regulates activity of calcium channels, calcium-activated potassium channels, and various transient receptor potential (TRP) channels. Modification of these ion channels results in a myriad of negative consequences, including impaired endothelium-dependent vasodilation, alterations in generation of myogenic tone, and increased inflammation and oxidative stress. Taken together, these studies demonstrate the importance of studying the impact of the MR on ion channel function in the vasculature. While research in this area has made advances in recent years, there are still many large gaps in knowledge that need to be filled. Crucial future directions of study include defining the molecular mechanisms involved in this interaction, as well as elucidating the potential sex differences that may exist, as these areas of understanding are currently lacking.

Targeting the Endothelial Ca2+ Toolkit to Rescue Endothelial Dysfunction in Obesity Associated-Hypertension

BACKGROUND

Obesity is a major cardiovascular risk factor which dramatically impairs endothelium- dependent vasodilation and leads to hypertension and vascular damage. The impairment of the vasomotor response to extracellular autacoids, e.g., acetylcholine, mainly depends on the reduced Nitric Oxide (NO) bioavailability, which hampers vasorelaxation in large conduit arteries. In addition, obesity may affect Endothelium-Dependent Hyperpolarization (EDH), which drives vasorelaxation in small resistance arteries and arterioles. Of note, endothelial Ca2+ signals drive NO release and trigger EDH.

METHODS

A structured search of bibliographic databases was carried out to retrieve the most influential, recent articles on the impairment of vasorelaxation in animal models of obesity, including obese Zucker rats, and on the remodeling of the endothelial Ca2+ toolkit under conditions that mimic obesity. Furthermore, we searched for articles discussing how dietary manipulation could be exploited to rescue Ca2+-dependent vasodilation.

RESULTS

We found evidence that the endothelial Ca2+ could be severely affected by obese vessels. This rearrangement could contribute to endothelial damage and is likely to be involved in the disruption of vasorelaxant mechanisms. However, several Ca2+-permeable channels, including Vanilloid Transient Receptor Potential (TRPV) 1, 3 and 4 could be stimulated by several food components to stimulate vasorelaxation in obese individuals.

CONCLUSION

The endothelial Ca2+ toolkit could be targeted to reduce vascular damage and rescue endothelium- dependent vasodilation in obese vessels. This hypothesis remains, however, to be probed on truly obese endothelial cells.

Heterocellular Contact Can Dictate Arterial Function

RATIONALE

Resistance arteries and conduit arteries rely on different relative contributions of endothelial-derived hyperpolarization versus nitric oxide to achieve dilatory heterocellular signaling. Anatomically, resistance arteries use myoendothelial junctions (MEJs), endothelial cell projections that make contact with smooth muscle cells. Conduit arteries have very few to no MEJs.

OBJECTIVE

Determine if the presence of MEJs in conduit arteries can alter heterocellular signaling.

METHODS AND RESULTS

We previously demonstrated that PAI-1 (plasminogen activator inhibitor-1) can regulate formation of MEJs. Thus, we applied pluronic gel containing PAI-1 directly to conduit arteries (carotid arteries) to determine if this could induce formation of MEJs. We found a significant increase in endothelial cell projections resembling MEJs that correlated with increased biocytin dye transfer from endothelial cells to smooth muscle cells. Next, we used pressure myography to investigate whether these structural changes were accompanied by a functional change in vasodilatory signaling. Interestingly, PAI-1-treated carotids underwent a switch from a conduit to resistance artery vasodilatory profile via diminished nitric oxide signaling and increased endothelial-derived hyperpolarization signaling in response to the endothelium-dependent agonists acetylcholine and NS309. After PAI-1 application, we also found a significant increase in carotid expression of endothelial alpha globin, a protein predominantly expressed in resistance arteries. Carotids from mice with PAI-1, but lacking alpha globin (Hba1^-/-), demonstrated that l-nitro-arginine methyl ester, an inhibitor of nitric oxide signaling, was able to prevent arterial relaxation.

CONCLUSIONS

The presence or absence of MEJs is an important determinant for influencing heterocellular communication in the arterial wall. In particular, alpha globin expression, induced within newly formed endothelial cell projections, may influence the balance between endothelial-derived hyperpolarization and nitric oxide-mediated vasodilation.

Long noncoding RNAs as novel players in the pathogenesis of hypertension

Long noncoding RNAs (lncRNAs) are non-(protein)-coding RNAs longer than ~200 nucleotides and have been reported to be involved in multiple human diseases by regulating gene expression. A growing body of evidence has demonstrated that lncRNAs are also widely implicated in mechanisms of hypertension, including regulation of the proliferation, migration, and apoptosis of VSMCs; the production of iNOS and NO; and the angiogenic function of endothelial cells. Several lncRNAs were also differentially expressed in the renal and cardiac tissues of hypertensive rats and even in placental samples from preeclampsia patients. In particular, several circulating lncRNAs have been identified as novel biomarkers of hypertension. In this review, we summarize the current studies of lncRNAs in the pathogenesis of hypertension in order to aid in better understanding the molecular mechanism of hypertension and provide a basis to explore new therapeutic targets.

Low-Dose Aspirin Treatment Attenuates Male Rat Salt-Sensitive Hypertension via Platelet Cyclooxygenase 1 and Complement Cascade Pathway

Background The role of platelets in the development of vascular inflammation and endothelial dysfunction in the pathogenesis of hypertension is well established at this time. Aspirin is known to relieve pain, decrease fever, reduce inflammation, impair platelet aggregation, and prevent clotting, yet its effect in the context of salt-sensitive hypertension remains unclear. The present study investigated the importance of aspirin in inhibiting the abnormal activation of platelets and promoting the normal function of the vascular endothelium in a rat model of salt-sensitive hypertension. Method and Results Dahl salt-sensitive rats and salt-resistant rats were fed a normal-salt diet (4% NaCl), a high-salt diet (8% NaCl), or a high-salt diet with aspirin gavage (10 mg/kg per day) for 8 weeks. Blood pressure, platelet activation, vascular function, inflammatory response, and potential mechanism were measured. Low-dose aspirin (10 mg/kg per day) decreased the high-salt diet-induced elevation of blood pressure, platelet activation, leukocyte infiltration, and leukocyte-platelet aggregation (CD45+CD61+), as well as vascular endothelial and renal damage. These effects were related to the ability of aspirin to prevent the adhesion of leukocytes to endothelial cells via inhibition of the platelet cyclooxygenase 1 but not the cyclooxygenase 2 pathway. Aspirin also reversed the high-salt diet-induced abnormal activation of complement and coagulation cascades in platelets. Conclusions These results highlight a new property of aspirin in ameliorating vascular endothelial dysfunction induced by platelet activation, which may be beneficial in the treatment of salt-sensitive hypertension.

Internalization and Transportation of Endothelial Cell Surface KCa2.3 and KCa3.1 in Normal Pregnancy and Preeclampsia

Altered redox state modulates the expression levels of endothelial K_Ca2.3 and K_Ca3.1 (K_Cas) in normal pregnancy (NP) and preeclampsia (PE), thereby regulating vascular contractility. The mechanisms underlying K_Cas endocytosis and transportation remain unknown. We investigated the regulation of K_Cas expression in plasma membrane (PM) during NP and PE. Cultured human uterine artery endothelial cells were incubated in serum from normal nonpregnant women and women with NP or PE, or in oxidized LDL-, or lysophosphatidylcholine- (LPC-) containing a medium for 24 hours. NP serum elevated PM levels of K_Cas and reduced caveolin-1 and clathrin levels. PE serum, oxidized LDL, or LPC reduced PM levels of K_Cas and elevated caveolin-1, clathrin, Rab5c, and early endosome antigen-1 (EEA1) levels. Reduced K_Cas levels by PE serum or LPC were reversed by inhibition of caveolin-1, clathrin, or EEA1. Catalase and glutathione peroxidase 1 (GPX1) knockdown elevated PM-localized K_Cas levels and reduced caveolin-1 and clathrin levels. Elevated K_Ca2.3 levels upon catalase and GPX1 knockdown were reversed by PEG-catalase treatment. An H₂O₂ donor reduced clathrin and Rab5c. In contrast, elevated clathrin, caveolin-1, or colocalization of caveolin-1 with K_Ca3.1 by PE serum or LPC was reversed by NADPH oxidase inhibitors or antioxidants. A superoxide donor xanthine+xanthine oxidase elevated caveolin-1 or Rab5c levels. We concluded that K_Cas are endocytosed in a caveola- or a clathrin-dependent manner and transported in a Rab5c- and EEA1-dependent manner during pregnancy. The endocytosis and transportation processes may slow down via H₂O₂-mediated pathways in NP and may be accelerated via superoxide-mediated pathways in PE.

The importance of the nitric oxide-cGMP pathway in age-related cardiovascular disease: Focus on phosphodiesterase-1 and soluble guanylate cyclase

Among ageing-related illnesses, cardiovascular disease (CVD) remains the leading cause of morbidity and mortality causing one-third of all deaths worldwide. Ageing evokes a number of functional, pharmacological and morphological changes in the vasculature, accompanied by a progressive failure of protective and homeostatic mechanisms, resulting in target organ damage. Impaired vasomotor, proliferation, migration, antithrombotic and anti-inflammatory function in both the endothelial and vascular smooth muscle cells are parts of the vascular ageing phenotype. The endothelium regulates these functions by the release of a wide variety of active molecules including endothelium-derived relaxing factors such as nitric oxide, prostacyclin (PGI₂ ) and endothelium-derived hyperpolarization (EDH). During ageing, a functional decay of the nitric oxide pathway takes place. Nitric oxide signals to VSMC and other important cell types for vascular homeostasis through the second messenger cyclic guanosine monophosphate (cGMP). Maintenance of proper cGMP levels is an important goal in sustainment of proper vascular function during ageing. For this purpose, different components can be targeted in this signalling system, and among them, phosphodiesterase-1 (PDE1) and soluble guanylate cyclase (sGC) are crucial. This review focuses on the role of PDE1 and sGC in conditions that are relevant for vascular ageing.

The Vicious Cycle of Arterial Stiffness and Arterial Media Calcification

Arterial media calcification and arterial stiffness are independent predictors of cardiovascular mortality. Both processes reinforce one another, creating a vicious cycle in which transdifferentiation of endothelial cells and vascular smooth muscle cells play a central role. Physiological functioning of vascular smooth muscle cells in the arterial medial layer greatly depends on normal endothelial cell behavior. Endothelial or intimal layer cells are the primary sensors of pathological triggers circulating in the blood during, for example, ageing or inflammation, and often can be seen as initiators of this vicious cycle. As such, the search for treatment of arterial media calcification, which until now has been mainly concentrated at the level of the vascular smooth cell, may need to be expanded to intimal layer targets.

Vascular Endothelial Cell Biology: An Update

The vascular endothelium, a monolayer of endothelial cells (EC), constitutes the inner cellular lining of arteries, veins and capillaries and therefore is in direct contact with the components and cells of blood. The endothelium is not only a mere barrier between blood and tissues but also an endocrine organ. It actively controls the degree of vascular relaxation and constriction, and the extravasation of solutes, fluid, macromolecules and hormones, as well as that of platelets and blood cells. Through control of vascular tone, EC regulate the regional blood flow. They also direct inflammatory cells to foreign materials, areas in need of repair or defense against infections. In addition, EC are important in controlling blood fluidity, platelet adhesion and aggregation, leukocyte activation, adhesion, and transmigration. They also tightly keep the balance between coagulation and fibrinolysis and play a major role in the regulation of immune responses, inflammation and angiogenesis. To fulfill these different tasks, EC are heterogeneous and perform distinctly in the various organs and along the vascular tree. Important morphological, physiological and phenotypic differences between EC in the different parts of the arterial tree as well as between arteries and veins optimally support their specified functions in these vascular areas. This review updates the current knowledge about the morphology and function of endothelial cells, particularly their differences in different localizations around the body paying attention specifically to their different responses to physical, biochemical and environmental stimuli considering the different origins of the EC.

Increased inward rectifier K+ current of coronary artery smooth muscle cells in spontaneously hypertensive rats; partial compensation of the attenuated endothelium-dependent relaxation via Ca2+ -activated K+ channels

Endothelium-dependent vasorelaxation is partly mediated by small-conductance (SK3) and intermediate-conductance Ca²⁺ -activated K⁺ channels (SK4) in the endothelium that results in endothelium-dependent hyperpolarization (EDH). Apart from the electrical propagation through myoendothelial gap junctions, the K⁺ released from the endothelium facilitates EDH by increasing inward rectifier K⁺ channel (Kir) conductance in smooth muscle cells. The EDH-dependent relaxation of coronary artery (CA) and Kir current in smooth muscle cells (CASMCs) of hypertensive animals are poorly understood despite the critical role of coronary flow in the hypertrophic heart. In spontaneously hypertensive (SHR) and control (WKY) rats, we found attenuation of the CA relaxation by activators of SK3 and SK4 (NS309 and 1-EBIO) in SHR. In isolated CASMCs, whole-cell patch-clamp study revealed larger I_Kir in SHR than WKY, whereas the myocytes of skeletal and cerebral arteries showed smaller I_Kir in SHR than WKY. While the treatment with I_Kir inhibitor (0.1 mmol/L Ba²⁺ ) alone did not affect the WKY-CA, the SHR-CA showed significant contractile response, suggesting relaxing influence of the higher I_{K ir} in the CASMCs of SHR. Furthermore, the attenuation of NS309-induced relaxation of CA by the combined treatment with 0.1 mmol/L Ba²⁺ was more prominent in SHR than WKY. Our study firstly shows a distinct increase of I_{K ir} in the CASMCs of SHR, which could partly compensate for the attenuated relaxation via endothelial SK3 and SK4.

Modulation of Cardiovascular Function in Primary Hypertension in Rat by SKA-31, an Activator of KCa2.x and KCa3.1 Channels

The aim of this study was to investigate the hemodynamic effects of SKA-31, an activator of the small (K_Ca2.x) and intermediate (K_Ca3.1) conductance calcium-activated potassium channels, and to evaluate its influence on endothelium-derived hyperpolarization (EDH)-K_Ca2.3/K_Ca3.1 type relaxation in isolated endothelium-intact small mesenteric arteries (sMAs) from spontaneously hypertensive rats (SHRs). Functional in vivo and in vitro experiments were performed on SHRs or their normotensive controls, Wistar-Kyoto rats (WKY). SKA-31 (1, 3 and 10 mg/kg) caused a brief decrease in blood pressure and bradycardia in both SHR and WKY rats. In phenylephrine-pre-constricted sMAs of SHRs, SKA-31 (0.01–10 µM)-mediated relaxation was reduced and SKA-31 potentiated acetylcholine-evoked endothelium-dependent relaxation. Endothelium denudation and inhibition of nitric oxide synthase (eNOS) and cyclooxygenase (COX) by the respective inhibitors l-NAME or indomethacin, attenuated SKA-31-mediated vasorelaxation. The inhibition of K_Ca3.1, K_Ca2.3, K_IR and Na⁺/K⁺-ATPase by TRAM-34, UCL1684, Ba²⁺ and ouabain, respectively, reduced the potency and efficacy of the EDH-response evoked by SKA-31. The mRNA expression of eNOS, prostacyclin synthase, K_Ca2.3, K_Ca3.1 and K_IR were decreased, while Na⁺/K⁺-ATPase expression was increased. Collectively, SKA-31 promoted hypotension and vasodilatation, potentiated agonist-stimulated vasodilation, and maintained K_Ca2.3/K_Ca3.1-EDH-response in sMAs of SHR with downstream signaling that involved K_IR and Na⁺/K⁺-ATPase channels. In view of the importance of the dysfunction of endothelium-mediated vasodilatation in the mechanism of hypertension, application of activators of K_Ca2.3/K_Ca3.1 channels such as SKA-31 seem to be a promising avenue in pharmacotherapy of hypertension.

Endothelium-Dependent Hyperpolarization (EDH) in Diabetes: Mechanistic Insights and Therapeutic Implications

Diabetes mellitus is one of the major risk factors for cardiovascular disease and is an important health issue worldwide. Long-term diabetes causes endothelial dysfunction, which in turn leads to diabetic vascular complications. Endothelium-derived nitric oxide is a major vasodilator in large-size vessels, and the hyperpolarization of vascular smooth muscle cells mediated by the endothelium plays a central role in agonist-mediated and flow-mediated vasodilation in resistance-size vessels. Although the mechanisms underlying diabetic vascular complications are multifactorial and complex, impairment of endothelium-dependent hyperpolarization (EDH) of vascular smooth muscle cells would contribute at least partly to the initiation and progression of microvascular complications of diabetes. In this review, we present the current knowledge about the pathophysiology and underlying mechanisms of impaired EDH in diabetes in animals and humans. We also discuss potential therapeutic approaches aimed at the prevention and restoration of EDH in diabetes.

Pharmacological Targeting of KCa Channels to Improve Endothelial Function in the Spontaneously Hypertensive Rat

Systemic hypertension is a major risk factor for the development of cardiovascular disease and is often associated with endothelial dysfunction. KCa2.3 and KCa3.1 channels are expressed in the vascular endothelium and contribute to stimulus-evoked vasodilation. We hypothesized that acute treatment with SKA-31, a selective activator of KCa2.x and KCa3.1 channels, would improve endothelium-dependent vasodilation and transiently lower mean arterial pressure (MAP) in male, spontaneously hypertensive rats (SHRs). Isolated vascular preparations exhibited impaired vasodilation in response to bradykinin (i.e., endothelial dysfunction) compared with Wistar controls, which was associated with decreased bradykinin receptor expression in mesenteric arteries. In contrast, similar levels of endothelial KCa channel expression were observed, and SKA-31 evoked vasodilation was comparable in vascular preparations from both strains. Addition of a low concentration of SKA-31 (i.e., 0.2–0.3 μM) failed to augment bradykinin-induced vasodilation in arteries from SHRs. However, responses to acetylcholine were enhanced. Surprisingly, acute bolus administration of SKA-31 in vivo (30 mg/kg, i.p. injection) modestly elevated MAP compared with vehicle injection. In summary, pharmacological targeting of endothelial KCa channels in SHRs did not readily reverse endothelial dysfunction in situ, or lower MAP in vivo. SHRs thus appear to be less responsive to endothelial KCa channel activators, which may be related to their vascular pathology.

S-amlodipine improves endothelial dysfunction via the RANK/RANKL/OPG system by regulating microRNA-155 in hypertension

S-amlodipine has been broadly used to treat hypertension, but its protective effects and underlying mechanism remain controversial. The purpose of our study was to investigate the mechanism by which S-amlodipine improves endothelial dysfunction. Specifically, we investigated if S-amlodipine regulates RANK/RANKL/OPG and micro-RNA 155 (miR-155) levels. Spontaneous hypertensive rats (SHR) were randomly divided into two groups: SHR (n = 12) and S-amlodipine (n = 12). We found that left ventricular ejection fraction (LVEF) increased significantly in the S-amlodipine group compared to the SHR group. After 10 weeks of S-amlodipine treatment, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels were significantly lower and eNOS and NO production was significantly higher in the S-amlodipine group compared to the SHR group. In human umbilical vein endothelial cells (HUVECs), miR-155, RANK, and RANKL levels were significantly decreased, while OPG mRNA levels were significantly increased in the S-amlodipine group. HUVECs were transfected with miR-155 mimics or an inhibitor to determine the relationship between miR-155 and RANK/RANKL/OPG and NF-κB signaling. OPG mRNA levels following miR-155 inhibition were significantly higher compared to levels following treatment with miR-155 mimics. S-amlodipine significantly inhibited RANKL expression and NF-κB phosphorylation, and there were no significant differences in response to the NF-κB inhibitor (Bay110785). RANKL expression and NF-κB phosphorylation significantly decreased in the miR-155 inhibitor group. Furthermore, OPG protein expression significantly increased in response to miR-155 inhibition and S-amlodipine treatment (all p < 0.05). Our results indicate that S-amlodipine inhibits inflammation and protects against endothelial dysfunction, likely via regulating the RANK/RANKL/OPG pathway, which appears to be downstream of miR-155.

Vasodilation Elicited by Isoxsuprine, Identified by High-Throughput Virtual Screening of Compound Libraries, Involves Activation of the NO/cGMP and H₂S/KATP Pathways and Blockade of α₁-Adrenoceptors and Calcium Channels

Recently, our research group demonstrated that uvaol and ursolic acid increase NO and H₂S production in aortic tissue. Molecular docking studies showed that both compounds bind with high affinity to endothelial NO synthase (eNOS) and cystathionine gamma-lyase (CSE). The aim of this study was to identify hits with high binding affinity for the triterpene binding-allosteric sites of eNOS and CSE and to evaluate their vasodilator effect. Additionally, the mechanism of action of the most potent compound was explored. A high-throughput virtual screening (HTVS) of 107,373 compounds, obtained from four ZINC database libraries, was performed employing the crystallographic structures of eNOS and CSE. Among the nine top-scoring ligands, isoxsuprine showed the most potent vasodilator effect. Pharmacological evaluation, employing the rat aorta model, indicated that the vasodilation produced by this compound involved activation of the NO/cGMP and H₂S/K_ATP signaling pathways and blockade of α₁-adrenoceptors and L-type voltage-dependent Ca²⁺ channels. Incubation of aorta homogenates in the presence of isoxsuprine caused 2-fold greater levels of H₂S, which supported our preliminary in silico data. This study provides evidence to propose that the vasodilator effect of isoxsuprine involves various mechanisms, which highlights its potential to treat a wide variety of cardiovascular diseases.

Downregulation of endothelial transient receptor potential vanilloid type 4 channel underlines impaired endothelial nitric oxide-mediated relaxation in the mesenteric arteries of hypertensive rats

The endothelium contributes to the maintenance of vasodilator tone by releasing endothelium-derived relaxing factors, including nitric oxide (NO). In hypertension, endothelial nitric oxide synthase (eNOS) produces less NO and could be one of the contributing factors to the increased peripheral vascular resistance. Agonist-induced Ca(2+) entry is essential for the activation of eNOS. The transient receptor potential vanilloid type 4 (TRPV4) channel, a Ca(2+)-permeant cation channel, is expressed in the endothelial cells and involved in the regulation of vascular tone. The present study aimed to investigate the role of TRPV4 channel in endothelium-dependent NO-mediated relaxation of the resistance artery in hypertensive rats. Using a wire myograph, relaxation response to the TRPV4 activator, 4alpha-phorbol-12,13-didecanoate (4alphaPDD) was assessed in mesenteric arteries obtained from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs). Compared to WKY, SHR demonstrated a significantly attenuated 4alphaPDD-induced endothelium-dependent NO-mediated relaxation. Immunohistochemical analysis revealed positive staining for TRPV4 in the endothelium of mesenteric artery sections in both WKY and SHR. Furthermore, TRPV4 mRNA and protein expressions in SHR were significantly lower than their expression levels in WKY rats. We conclude that 4alphaPDD-induced endothelium-dependent NO-mediated vasorelaxation is reduced in SHR and downregulation of TRPV4 could be one of the contributing mechanisms.

Rhus coriaria L. (Sumac) Evokes Endothelium-Dependent Vasorelaxation of Rat Aorta: Involvement of the cAMP and cGMP Pathways

Rhus coriaria L. (sumac) is widely used in traditional remedies and cuisine of countries of the Mediterranean as well as Central and South-West Asia. Administration of sumac to experimental models and patients with diverse pathological conditions generates multi-faceted propitious effects, including the quality as a vasodilator. Together, the effects are concertedly channeled toward cardiovasobolic protection. However, there is paucity of data on the mechanism of action for sumac’s vasodilatory effect, an attribute which is considered to be advantageous for unhealthy circulatory system. Accordingly, we sought to determine the mechanisms by which sumac elicits its vasorelaxatory effects. We deciphered the signaling networks by application of a range of pharmacological inhibitors, biochemical assays and including the quantification of cyclic nucleotide monophosphates. Herein, we provide evidence that an ethanolic extract of sumac fruit, dose-dependently, relaxes rat isolated aorta. The mechanistic effect is achieved via stimulation of multiple transducers namely PI3-K/Akt, eNOS, NO, guanylyl cyclase, cGMP, and PKG. Interestingly, the arachidonic acid pathway (cyclooxygenases), adenylyl cyclase/cAMP and ATP-dependent potassium channels appear to partake in this sumac-orchestrated attenuation of vascular tone. Clearly, our data support the favorable potential cardio-vasculoprotective action of sumac.