Endothelial potassium channels, endothelium-dependent hyperpolarization and the regulation of vascular tone in health and disease

Preeclampsia and transport of ions and small molecules: A literature review

Preeclampsia (PE) is a prevalent obstetric complication affecting approximately 3-5% of pregnancies worldwide and is a major cause of maternal and perinatal morbidity and mortality. Preeclampsia is considered a disease of the endothelial system that can progress to eclampsia, characterized by seizures. Early diagnosis and appropriate management are crucial to improving maternal and fetal outcomes, as preeclampsia can lead to severe complications such as placental abruption, fetal growth restriction, and stroke. The pathophysiology of PE is complex, involving a combination of genetic, acquired, and immunological factors. A central feature of the condition is inadequate placentation and impaired uteroplacental perfusion, leading to local hypoxia, endothelial dysfunction, vasoconstriction, and immunological dysregulation. Recent evidence suggests that dysregulation of ion transporters may play a significant role in the adaptation of uterine circulation during placentation. These transporters are essential for maintaining maternal-fetal homeostasis, influencing processes such as nutrient exchange, hormone synthesis, trophoblast cell migration, and the function of smooth muscle cells in blood vessels. In preeclampsia, adverse conditions like hypoxia and oxidative stress result in the downregulation of ion, solute, and water transporters, impairing their function. This review focuses on membrane transporters involved in PE, discussing functional alterations and their physiological implications. The goal of this investigation is to enhance understanding of how dysregulation of ion and small molecule transporters contributes to the development and progression of preeclampsia, underscoring the importance of exploring these signaling pathways for potential therapeutic interventions.

Renal Endothelial Single-Cell Transcriptomics Reveals Spatiotemporal Regulation and Divergent Roles of Differential Gene Transcription and Alternative Splicing in Murine Diabetic Nephropathy

Endothelial cell (EC) injury is a crucial contributor to the progression of diabetic kidney disease (DKD), but the specific EC populations and mechanisms involved remain elusive. Kidney ECs (n = 5464) were collected at three timepoints from diabetic BTBRob/ob mice and non-diabetic littermates. Their heterogeneity, transcriptional changes, and alternative splicing during DKD progression were mapped using SmartSeq2 single-cell RNA sequencing (scRNAseq) and elucidated through pathway, network, and gene ontology enrichment analyses. We identified 13 distinct transcriptional EC phenotypes corresponding to different kidney vessel subtypes, confirmed through in situ hybridization and immunofluorescence. EC subtypes along nephrons displayed extensive zonation related to their functions. Differential gene expression analyses in peritubular and glomerular ECs in DKD underlined the regulation of DKD-relevant pathways including EIF2 signaling, oxidative phosphorylation, and IGF1 signaling. Importantly, this revealed the differential alteration of these pathways between the two EC subtypes and changes during disease progression. Furthermore, glomerular and peritubular ECs also displayed aberrant and dynamic alterations in alternative splicing (AS), which is strongly associated with DNA repair. Strikingly, genes displaying differential transcription or alternative splicing participate in divergent biological processes. Our study reveals the spatiotemporal regulation of gene transcription and AS linked to DKD progression, providing insight into pathomechanisms and clues to novel therapeutic targets for DKD treatment.

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.

Pathophysiology and Outcomes of Endothelium Function in Coronary Microvascular Diseases: A Systematic Review of Randomized Controlled Trials and Multicenter Study

BACKGROUND

Coronary macrovascular disease is a concept that has been well-studied within the literature and has long been the subject of debates surrounding coronary artery bypass grafting (CABG) vs. Percutaneous Coronary Intervention (PCI). ISCHEMIA trial reported no statistical difference in the primary clinical endpoint between initial invasive management and initial conservative management, while in the ORBITA trial PCI did not improve angina frequency score significantly more than placebo, albeit PCI resulted in more patient-reported freedom from angina than placebo. However, these results did not prove the superiority of the PCI against OMT, therefore do not indicate the benefit of PCI vs. the OMT. Please rephrase the sentence. We reviewed the role of different factors responsible for endothelial dysfunction from recent randomized clinical trials (RCTs) and multicentre studies.

METHODS

A detailed search strategy was performed using a dataset that has previously been published. Data of pooled analysis include research articles (human and animal models), CABG, and PCI randomized controlled trials (RCTs). Details of the search strategy and the methods used for data pooling have been published previously and registered with Open-Source Framework.

RESULTS

The roles of nitric oxide (NO), endothelium-derived contracting factors (EDCFs), and vasodilator prostaglandins (e.g., prostacyclin), as well as endothelium-dependent hyperpolarization (EDH) factors, are crucial for the maintenance of vasomotor tone within the coronary vasculature. These homeostatic mechanisms are affected by sheer forces and other several factors that are currently being studied, such as vaping. The role of intracoronary testing is crucial when determining the effects of therapeutic medications with further studies on the horizon.

CONCLUSION

The true impact of coronary microvascular dysfunction (CMD) is perhaps underappreciated, which supports the role of medical therapy in determining outcomes. Ongoing trials are underway to further investigate the role of therapeutic agents in secondary prevention.

Mechanisms and Physiological Implications of Cooperative Gating of Ion Channels Clusters

Ion channels play a central role in the regulation of nearly every cellular process. Dating back to the classic 1952 Hodgkin-Huxley model of the generation of the action potential, ion channels have always been thought of as independent agents. A myriad of recent experimental findings exploiting advances in electrophysiology, structural biology, and imaging techniques, however, have posed a serious challenge to this long-held axiom as several classes of ion channels appear to open and close in a coordinated, cooperative manner. Ion channel cooperativity ranges from variable-sized oligomeric cooperative gating in voltage-gated, dihydropyridine-sensitive Ca_v1.2 and Ca_v1.3 channels to obligatory dimeric assembly and gating of voltage-gated Na_v1.5 channels. Potassium channels, transient receptor potential channels, hyperpolarization cyclic nucleotide-activated channels, ryanodine receptors (RyRs), and inositol trisphosphate receptors (IP₃Rs) have also been shown to gate cooperatively. The implications of cooperative gating of these ion channels range from fine tuning excitation-contraction coupling in muscle cells to regulating cardiac function and vascular tone, to modulation of action potential and conduction velocity in neurons and cardiac cells, and to control of pace-making activity in the heart. In this review, we discuss the mechanisms leading to cooperative gating of ion channels, their physiological consequences and how alterations in cooperative gating of ion channels may induce a range of clinically significant pathologies.

Coronary vasodilation mediated by T cells expressing choline acetyltransferase

CD4⁺ T cells expressing choline acetyltransferase (ChAT) have recently been shown to cause a drop in systemic blood pressure when infused into mice. The aim of this study was to determine if ChAT-expressing T cells could regulate coronary vascular reactivity. Preconstricted segments of epicardial and intramyocardial porcine coronary arteries relaxed in response to Jurkat T cells (JT) that overexpressed ChAT (JT_ChAT cells). The efficacy of the JT_ChAT cells was similar in epicardial and intramyocardial vessels with a maximum dilator response to 3 × 10⁵ cells/mL of 38.0 ± 6.7% and 38.7 ± 7.25%, respectively. In contrast, nontransfected JT cells elicited a weak dilator response, followed by a weak contraction. The response of JT_ChAT cells was dependent on the presence of the endothelial cells. In addition, the response could be significantly reduced by N^ω-nitro-l-arginine methyl ester (l-NAME) and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) in the presence of indomethacin. JT_ChAT cells, but not JT cells, increased the expression of phosphorylated endothelial nitric oxide synthase (eNOS). JT_ChAT cells contained significantly greater levels of acetylcholine compared with JT cells; however, the nonselective muscarinic antagonist atropine and the M₁ receptor antagonist pirenzepine both failed to block the dilator effect of JT_ChAT cells. Exogenously added acetylcholine induced only a weak relaxation (∼10%) at low concentrations, which became a contractile response at higher concentrations. These data illustrate the capacity for cells that express ChAT to regulate coronary vascular reactivity, via mechanisms that are dependent on interaction with the endothelium and in part mediated by the release of nitric oxide.NEW & NOTEWORTHY This study shows ChAT-expressing T cells can induce vasodilation of the blood vessel in the coronary circulation and that this effect relies on a direct interaction between T cells and the coronary vascular endothelium. The study establishes a potential immunomodulatory role for T cells in the coronary circulation. The present findings offer an additional possibility that a deficiency of ChAT-expressing T cells could contribute to reduced coronary blood flow and ischemic events in the myocardium.

Estrogen and Preeclampsia: Potential of Estrogens as Therapeutic Agents in Preeclampsia

There is a significant decline in the estrogen levels in preeclampsia, and exogenous administration of estradiol normalizes blood pressure and other associated symptoms of preeclampsia. The decrease in estrogen levels may be due to changes in enzyme activities of hydroxysteroid (17-β) dehydrogenase 1, aromatase, and COMT. There is also a decrease in the novel, estrogenic G-protein-coupled receptor 30 (GPR30) in the placental trophoblast cells in preeclampsia. The activation of GPR30 protects the placenta from hypoxia-reoxygenation injury, decreases apoptosis and increases proliferation through eNOS and PI3K-Akt signaling pathways. Estrogens may also increase Ca²⁺-activated K⁺ channel function, decrease the release of inflammatory cytokines, and oxidative stress to improve placental perfusion. Both preclinical and clinical studies show the decrease in the 2-methoxyestradiol levels in preeclampsia, which may be due to a decrease in estradiol itself along with a decrease in the enzymatic actions of the COMT enzyme. 2-Methoxyestradiol activates HIF1α and vascular endothelial growth factor receptors (VEGFR-2) to maintain placental perfusion by increasing angiogenesis. The present review discusses the preclinical and clinical studies describing the role of estrogen in preeclampsia along with possible mechanisms.

The protective effect of tanshinone IIa on endothelial cells: a generalist among clinical therapeutics

INTRODUCTION

Tanshinone IIa (TSA) has been approved to treat cardiovascular diseases by the China State Food and Drug Administration. TSA has exhibited a variety of pharmacological effects, including vasodilator, antioxidant, anti-inflammatory, and anti-tumor properties. Endothelial cells play an important physiological role in vascular homeostasis and control inflammation, coagulation, and thrombosis. Accumulating studies have shown that TSA can improve endothelial function through various pathways.

AREAS COVERED

The PubMed database was reviewed for relevant papers published up to 2020. This review summarizes the current clinical and pharmaceutical studies to provide a systemic overview of the pharmacological and therapeutic effects of TSA on endothelial cells.

EXPERT OPINION

TSA is a representative monomeric compound extracted from Danshen and it exhibits significant pharmacological and therapeutic properties to improve endothelial cell function, including alleviating oxidative stress, attenuating inflammatory injury, modulating ion channels and so on. TSA represents a spectrum of agents that are extracted from plants and can restore the endothelial function to establish the beneficial and harmless molecular therapeutics. This also suggests the possible detection of endothelial cells for very early diagnosis of diseases. In future, precise therapeutic methods will be developed to repair endothelial cells injury and recover endothelial dysfunction.

Prevention of Endothelial Dysfunction and Cardiovascular Disease by n-3 Fatty Acids-Inhibiting Action on Oxidative Stress and Inflammation

BACKGROUND

Prospective cohort studies and randomized controlled trials have shown the protective effect of n-3 fatty acids against cardiovascular disease (CVD). The effect of n-3 fatty acids on vascular endothelial cells indicates their possible role in CVD prevention.

OBJECTIVE

Here, we describe the effect of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) on endothelial dysfunction-caused by inflammation and oxidative stress-and their role in the development of CVD.

METHODS

We reviewed epidemiological studies done on n-3 fatty acids in CVD. The effect of DHA and EPA on vascular endothelial cells was examined with regard to changes in various markers, such as arteriosclerosis, inflammation, and oxidative stress, using cell and animal models.

RESULTS

Epidemiological studies revealed that dietary intake of EPA and DHA was associated with a reduced risk of various CVDs. EPA and DHA inhibited various events involved in arteriosclerosis development by preventing oxidative stress and inflammation associated with endothelial cell damage. In particular, EPA and DHA prevented endothelial cell dysfunction mediated by inflammatory responses and oxidative stress induced by events related to CVD. DHA and EPA also increased eNOS activity and induced nitric oxide production.

CONCLUSION

The effects of DHA and EPA on vascular endothelial cell damage and dysfunction may involve the induction of nitric oxide, in addition to antioxidant and anti-inflammatory effects. n-3 fatty acids inhibit endothelial dysfunction and prevent arteriosclerosis. Therefore, the intake of n-3 fatty acids may prevent CVDs, like myocardial infarction and stroke.

Trimethylamine-N-oxide Specifically Impairs Endothelium-Derived Hyperpolarizing Factor-Type Relaxation in Rat Femoral Artery

Although substantial evidence suggests that an increase in the level of trimethylamine-N-oxide (TMAO) is associated with the risk of cardiovascular diseases, including atherosclerosis, chronic kidney diseases, and hypertension, the direct effect of TMAO on vascular endothelial function remains unclear. Therefore, we investigated the acute effects of TMAO on endothelium-dependent relaxation induced by acetylcholine (ACh) in the superior mesenteric arteries and femoral arteries of rat. In endothelium-intact preparations, it was observed that TMAO (300 µmol/L for 60 min) did not affect ACh-induced relaxation in either of the two arteries. In endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation under nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibitions by N^ω-nitro-L-arginine (L-NNA) and indomethacin, respectively, TMAO specifically impairs the relaxation in femoral arteries but not in the superior mesenteric arteries. Under the inhibitory actions of NOS and as well as blockade of intermediate-conductance calcium-activated potassium channel (IK_Ca) (by TRAM-34) and small-conductance calcium-activated potassium channel (SK_Ca) (by apamin), which are putative sources of EDHF, ACh-induced relaxation was low, and there were no differences between the control and TMAO-treated groups with respect to both arteries. In femoral arteries, TMAO slightly reduces ACh-induced relaxation in the presence of indomethacin (preserved NO and EDHF signals) but does not affect ACh-induced NO-mediated relaxation under the combined presence of indomethacin, TRAM-34, and apamin. These results suggest that acute treatment with TMAO specifically impairs EDHF-mediated relaxation in the femoral arteries but not in the superior mesenteric arteries. These novel observations show that TMAO is a causative factor in the development of peripheral arterial disease.

Vascular mechanisms and molecular targets in hypertensive pregnancy and preeclampsia

Preeclampsia is a major complication of pregnancy manifested as hypertension and often intrauterine growth restriction, but the underlying pathophysiological mechanisms are unclear. Predisposing genetic and environmental factors cause placental maladaptations leading to defective placentation, apoptosis of invasive cytotrophoblasts, inadequate expansive remodeling of the spiral arteries, reduced uteroplacental perfusion pressure, and placental ischemia. Placental ischemia promotes the release of bioactive factors into the maternal circulation, causing an imbalance between antiangiogenic soluble fms-like tyrosine kinase-1 and soluble endoglin and proangiogenic vascular endothelial growth factor, placental growth factor, and transforming growth factor-β. Placental ischemia also stimulates the release of proinflammatory cytokines, hypoxia-inducible factor, reactive oxygen species, and angiotensin type 1 receptor agonistic autoantibodies. These circulating factors target the vascular endothelium, causing generalized endotheliosis in systemic, renal, cerebral, and hepatic vessels, leading to decreases in endothelium-derived vasodilators such as nitric oxide, prostacyclin, and hyperpolarization factor and increases in vasoconstrictors such as endothelin-1 and thromboxane A₂. The bioactive factors also target vascular smooth muscle and enhance the mechanisms of vascular contraction, including cytosolic Ca²⁺, protein kinase C, and Rho-kinase. The bioactive factors could also target matrix metalloproteinases and the extracellular matrix, causing inadequate vascular remodeling, increased arterial stiffening, and further increases in vascular resistance and hypertension. As therapeutic options are limited, understanding the underlying vascular mechanisms and molecular targets should help design new tools for the detection and management of hypertension in pregnancy and preeclampsia.

Vascular tone and angiogenesis modulation by catecholamine coordinated to ruthenium

Catecholamines participate in angiogenesis, an important tumor development process. However, the way catecholamines interact with their receptors has not been completely elucidated, and doubts still remain as to whether these interactions occur between catechol and/or amine sites and particular amino acid residues on the catecholamine receptors. To evaluate how catechol and amine groups contribute to angiogenesis, we immobilized the catechol site through ruthenium ion (Ru) coordination, to obtain species with the general formula [Ru(NH₃)₄(catecholamine-R)]Cl. We then assessed the angiogenic activity of the complexes in a chorioallantoic membrane model (CAM) and examined vascular reactivity and calcium mobilization in rat aortas and vascular cells. [Ru(NH₃)₄(catecholamine-R)]Cl acted as partial agonists and/or antagonists of their respective receptors and induced calcium mobilization. [Ru(NH₃)₄(isoproterenol)]⁺ [Ru(NH₃)₄(noradrenaline)]⁺, and [Ru(NH₃)₄(adrenaline)]⁺ behaved as antiangiogenic complexes, whereas [Ru(NH₃)₄(dopamine)]⁺ proved to be a proangiogenic complex. In conclusion, catecholamines and [Ru(NH₃)₄(catecholamine-R)]Cl can modulate angiogenesis, and catechol group availability can modify the way these complexes impact the vascular tone, suggesting that catecholamines and their receptors interact differently after catecholamine coordination to ruthenium.

Direct Impairment of the Endothelial Function by Acute Indoxyl Sulfate through Declined Nitric Oxide and Not Endothelium-Derived Hyperpolarizing Factor or Vasodilator Prostaglandins in the Rat Superior Mesenteric Artery

Upon stimulation, endothelial cells release various factors to regulate the vascular tone. In particular, vasorelaxing factors, called endothelium-derived relaxing factors (EDRFs), are altered in the production and/or release, as well as their signaling every vessel and under pathophysiological states, including cardiovascular, kidney, and metabolic diseases. Although indoxyl sulfate is known as a protein-bound uremic toxin and circulating levels are elevated in the impaired kidney functions, direct impact on the vascular function, especially EDRF's signaling, remains unclear. In this study, we hypothesize that acute exposure to indoxyl sulfate could alter vascular relaxation in the rat superior mesenteric artery. Accordingly, we measured acetylcholine (ACh)-induced endothelium-dependent relaxation in the absence and presence of several inhibitors to divide into each EDRF, including nitric oxide (NO), vasodilator prostaglandins (PGs), and endothelium-derived hyperpolarizing factor (EDHF). Indoxyl sulfate reduced the sensitivity to ACh but not sodium nitroprusside. Under cyclooxygenase (COX) inhibition or inhibitions of COX plus source of EDHF, such as small (SK_Ca)- and intermediate (IK_Ca)-conductance calcium-activated K⁺ channels, the decreased sensitivity to ACh in indoxyl sulfate exposed vessel was still preserved. However, under inhibition of NO synthase (NOS) or inhibitions of NOS and COX, the difference of sensitivity to ACh between vehicle and indoxyl sulfate was eliminated. These findings indicated that acute exposure of indoxyl sulfate in the rat superior mesenteric artery specifically explicitly impaired NO signaling but not EDHF or vasodilator PGs.

Ethanol enhances endothelial ionic currents and nitric oxide release via intermediate-conductance calcium-activated potassium channel

AIMS

Ethanol is known to induce NO release and coronary vasorelaxation. Evidence suggests that K⁺ channels, especially a Ca²⁺-activated K⁺ channel (K_Ca), may regulate endothelial NO production. We aimed to investigate the ethanol effect on K⁺ currents in human coronary artery endothelial cells (HCAECs), identify the K⁺ channel type/subtype and signaling pathway involved, and demonstrate the relevance to ethanol-induced NO release.

MAIN METHODS

Ionic currents of cultured HCAECs were studied using whole-cell patch clamp technique. NO production were measured using the fluorescent probe, 2,3-diaminonaphthalene.

KEY FINDINGS

We found that ethanol significantly potentiated HCAEC current (maximal increase to 155.68 ± 18.93%, 20 mM ethanol, +80 mV; mean ± SEM, n = 9). Ethanol-induced current was significantly inhibited by blockers of IK_Ca or SK_Ca (intermediate- or small-conductance K_Ca), but not by blocking other K⁺ channels. When other known HCAEC channels were inhibited except IK_Ca, 20 mM ethanol significantly increased IK_Ca current to 198 ± 25.11% (n = 6), but it could not enhance SK_Ca current that was similarly isolated. Moreover, ethanol-induced NO release was prevented by blocking IK_Ca channel, adenosine A_2A receptor (A_2AR), G_s protein, or protein kinase A (PKA).

SIGNIFICANCE

This study was the first to demonstrate that acute ethanol exposure could activate endothelial IK_Ca channel, via A_2AR-G_s-PKA signaling, leading to increased whole-cell current and NO release, which could be an important mechanism underlying ethanol-induced NO release and vasodilation.

Moringa oleifera Seeds Improve Aging-Related Endothelial Dysfunction in Wistar Rats

Vascular aging is characterized by functional and structural changes of the vessel wall, including endothelial dysfunction, with decreased endothelial NO^· bioavailability and elevated vasoconstrictor and inflammatory mediator production, vascular rigidity, and tone impairment. Moringa oleifera (MOI) is a little tree, and different parts of which are used in traditional medicine in tropical Africa, America, and Asia for therapeutic applications in several disorders including cardiovascular disease. The present study is aimed at assessing the effect of MOI on aging-associated alteration of the endothelial function in Wistar rats. Middle-aged Wistar rats (46-week-old males) have been fed with food containing or not 750 mg/kg/day of MOI seed powder for 4 weeks. A group of young Wistar rats (16-week-old) was used as control. Measurement of isometric contraction, western blot analysis, and immunostaining has then been performed in the aortas and mesenteric arteries to assess the endothelium function. MOI treatment improved carbachol-induced relaxation in both aortas and mesenteric arteries of middle-aged rats. In the aortas, this was associated with an increased Akt signalling and endothelial NO synthase activation and a downregulation of arginase-1. In the mesenteric arteries, the improvement of the endothelial-dependent relaxation was related to an EDHF-dependent mechanism. These results suggest a vascular protective effect of MOI seeds against the vascular dysfunction that develops during aging through different mechanisms in conductance and resistance arteries.

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.

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.

Molecular determinants of microvascular dysfunction in hypertensive pregnancy and preeclampsia

Preeclampsia is a pregnancy-related disorder characterized by hypertension and often fetal intrauterine growth restriction, but the underlying mechanisms are unclear. Defective placentation and apoptosis of invasive cytotrophoblasts cause inadequate remodeling of spiral arteries, placental ischemia, and reduced uterine perfusion pressure (RUPP). RUPP causes imbalance between the anti-angiogenic factors soluble fms-like tyrosine kinase-1 and soluble endoglin and the pro-angiogenic vascular endothelial growth factor and placental growth factor, and stimulates the release of proinflammatory cytokines, hypoxia-inducible factor, reactive oxygen species, and angiotensin AT1 receptor agonistic autoantibodies. These circulating factors target the vascular endothelium, smooth muscle and various components of the extracellular matrix. Generalized endotheliosis in systemic, renal, cerebral, and hepatic vessels causes decreases in endothelium-derived vasodilators such as nitric oxide, prostacyclin and hyperpolarization factor, and increases in vasoconstrictors such as endothelin-1 and thromboxane A2. Enhanced mechanisms of vascular smooth muscle contraction, such as intracellular Ca2+ , protein kinase C, and Rho-kinase cause further increases in vasoconstriction. Changes in matrix metalloproteinases and extracellular matrix cause inadequate vascular remodeling and increased arterial stiffening, leading to further increases in vascular resistance and hypertension. Therapeutic options are currently limited, but understanding the molecular determinants of microvascular dysfunction could help in the design of new approaches for the prediction and management of preeclampsia.

Cystathionine γ-Lyase-Produced Hydrogen Sulfide Controls Endothelial NO Bioavailability and Blood Pressure

Hydrogen sulfide (H₂S) and NO are important gasotransmitters, but how endogenous H₂S affects the circulatory system has remained incompletely understood. Here, we show that CTH or CSE (cystathionine γ-lyase)-produced H₂S scavenges vascular NO and controls its endogenous levels in peripheral arteries, which contribute to blood pressure regulation. Furthermore, eNOS (endothelial NO synthase) and phospho-eNOS protein levels were unaffected, but levels of nitroxyl were low in CTH-deficient arteries, demonstrating reduced direct chemical interaction between H₂S and NO. Pretreatment of arterial rings from CTH-deficient mice with exogenous H₂S donor rescued the endothelial vasorelaxant response and decreased tissue NO levels. Our discovery that CTH-produced H₂S inhibits endogenous endothelial NO bioavailability and vascular tone is novel and fundamentally important for understanding how regulation of vascular tone is tailored for endogenous H₂S to contribute to systemic blood pressure function.

Experimental preeclampsia in rats affects vascular gene expression patterns

Normal pregnancy requires adaptations of the maternal vasculature. During preeclampsia these adaptations are not well established, which may be related to maternal hypertension and proteinuria. The effects of preeclampsia on the maternal vasculature are not yet fully understood. We aimed to evaluate gene expression in aortas of pregnant rats with experimental preeclampsia using a genome wide microarray. Aortas were isolated from pregnant Wistar outbred rats with low-dose LPS-induced preeclampsia (ExpPE), healthy pregnant (Pr), non-pregnant and low-dose LPS-infused non-pregnant rats. Gene expression was measured by microarray and validated by real-time quantitative PCR. Gene Set Enrichment Analysis was performed to compare the groups. Functional analysis of the aorta was done by isotonic contraction measurements while stimulating aortic rings with potassium chloride. 526 genes were differentially expressed, and positive enrichment of “potassium channels”, “striated muscle contraction”, and “neuronal system” gene sets were found in ExpPE vs. Pr. The potassium chloride-induced contractile response of ExpPE aortic rings was significantly decreased compared to this response in Pr animals. Our data suggest that potassium channels, neuronal system and (striated) muscle contraction in the aorta may play a role in the pathophysiology of experimental preeclampsia. Whether these changes are also present in preeclamptic women needs further investigation.

Role of renal vascular potassium channels in physiology and pathophysiology

The control of renal vascular tone is important for the regulation of salt and water balance, blood pressure and the protection against damaging elevated glomerular pressure. The K⁺ conductance is a major factor in the regulation of the membrane potential (V_m ) in vascular smooth muscle (VSMC) and endothelial cells (EC). The vascular tone is controlled by V_m via its effect on the opening probability of voltage-operated Ca²⁺ channels (VOCC) in VSMC. When K⁺ conductance increases V_m becomes more negative and vasodilation follows, while deactivation of K⁺ channels leads to depolarization and vasoconstriction. K⁺ channels in EC indirectly participate in the control of vascular tone by endothelium-derived vasodilation. Therefore, by regulating the tone of renal resistance vessels, K⁺ channels have a potential role in the control of fluid homoeostasis and blood pressure as well as in the protection of the renal parenchyma. The main classes of K⁺ channels (calcium activated (K_Ca ), inward rectifier (K_ir ), voltage activated (K_v ) and ATP sensitive (K_ATP )) have been found in the renal vessels. In this review, we summarize results available in the literature and our own studies in the field. We compare the ambiguous in vitro and in vivo results. We discuss the role of single types of K⁺ channels and the integrated function of several classes. We also deal with the possible role of renal vascular K⁺ channels in the pathophysiology of hypertension, diabetes mellitus and sepsis.

Matrix Metalloproteinases in Normal Pregnancy and Preeclampsia

Normal pregnancy is associated with marked hemodynamic and uterine changes that allow adequate uteroplacental blood flow and uterine expansion for the growing fetus. These pregnancy-associated changes involve significant uteroplacental and vascular remodeling. Matrix metalloproteinases (MMPs) are important regulators of vascular and uterine remodeling. Increases in MMP-2 and MMP-9 have been implicated in vasodilation, placentation, and uterine expansion during normal pregnancy. The increases in MMPs could be induced by the increased production of estrogen and progesterone during pregnancy. MMP expression/activity may be altered during complications of pregnancy. Decreased vascular MMP-2 and MMP-9 may lead to decreased vasodilation, increased vasoconstriction, hypertensive pregnancy, and preeclampsia. Abnormal expression of uteroplacental integrins, cytokines, and MMPs may lead to decreased maternal tolerance, apoptosis of invasive trophoblast cells, inadequate remodeling of spiral arteries, and reduced uterine perfusion pressure (RUPP). RUPP may cause imbalance between the antiangiogenic factors soluble fms-like tyrosine kinase-1 and soluble endoglin and the proangiogenic vascular endothelial growth factor and placental growth factor, or stimulate the release of inflammatory cytokines, hypoxia-inducible factor, reactive oxygen species, and angiotensin AT1 receptor agonistic autoantibodies. These circulating factors could target MMPs in the extracellular matrix as well as endothelial and vascular smooth muscle cells, causing generalized vascular dysfunction, increased vasoconstriction and hypertension in pregnancy. MMP activity can also be altered by endogenous tissue inhibitors of metalloproteinases (TIMPs) and changes in the MMP/TIMP ratio. In addition to their vascular effects, decreases in expression/activity of MMP-2 and MMP-9 in the uterus could impede uterine growth and expansion and lead to premature labor. Understanding the role of MMPs in uteroplacental and vascular remodeling and function could help design new approaches for prediction and management of preeclampsia and premature labor.

The NOX2-derived reactive oxygen species damaged endothelial nitric oxide system via suppressed BKCa/SKCa in preeclampsia

The endothelial nitric oxide (NO) system may be damaged in preeclampsia; however, the involved mechanisms are unclear. In this study, we used primary human umbilical vein endothelial cells (HUVECs) to evaluate the endothelial NO system in preeclampsia and to determine the underlying mechanisms that are involved. We isolated and cultured HUVECs from normal and preeclamptic pregnancies and evaluated endothelial NO synthase enzyme (eNOS) expression and NO production. Whole-cell K⁺ currents and oxidative stress were also determined in normal and preeclamptic HUVECs. Compared with normal HUVECs, eNOS expression, NO production and whole-cell K⁺ currents in preeclamptic HUVECs were markedly decreased, whereas oxidative stress was significantly increased. The decreased K⁺ currents were associated with damaged Ca²⁺-activated K⁺ (KCa) channels, especially the large (BKCa) and small (SKCa) conductance KCa channels, and were involved in the downregulated eNOS expression in preeclamptic HUVECs. Moreover, the increased oxidative stress detected in preeclamptic HUVECs was mediated by NADPH (nicotinamide adenine dinucleotide phosphate) oxidase 2 (NOX2)-dependent reactive oxygen species overproduction that could downregulate whole-cell K⁺ currents, eNOS expression and NO production. Taken together, our study indicated that the increased oxidative stress in preeclamptic HUVECs could downregulate the NO system by suppressing BKCa and SKCa channels. Because the damaged NO system was closely related to endothelial dysfunction, this study provides important information to further understand the pathological process of endothelial cell dysfunction in preeclampsia.

Nonlinear effects of potassium channel blockers on endothelium-dependent hyperpolarization

In a number of published studies on endothelium-dependent hyperpolarization and relaxation, the results of the effects of K⁺ blockers have been difficult to interpret. When the effects of two blockers have been studied, often either blocker by itself had little effect, whereas the two blockers combined tended to abolish the responses. Explanations suggested in the literature include an unusual pharmacology of the K⁺ channels, and possible blocker binding interactions. In contrast, when we applied the same blockers to segments of small blood vessels under voltage clamp, the blockers reduced the endothelium-dependent K⁺ current in a linearly additive manner. Resolution of these contrasting results is important as endothelium-derived hyperpolarization (EDH) makes its greatest contribution to vasorelaxation in arterioles and small resistance arteries, where it can exert a significant role in tissue perfusion and blood pressure regulation. Furthermore, EDH is impaired in various diseases. Here, we consider why the voltage-clamp results differ from earlier free-running membrane potential and contractility studies. We fitted voltage-clamp-derived current-voltage relationships with mathematical functions and considered theoretically the effects of partial and total block of endothelium-derived K⁺ -currents on the membrane potential of small blood vessels. When the K⁺ -conductance was partially reduced, equivalent to applying a single blocker, the effect on EDH was small. Total block of the endothelium-dependent K⁺ conductance abolished the hyperpolarization, in agreement with various published studies. We conclude that nonlinear summation of the hyperpolarizing response evoked by endothelial stimulation can explain the variable effectiveness of individual K⁺ channel blockers on endothelium-dependent hyperpolarization and resulting relaxation.

Effect of potassium supplementation on vascular function: A meta-analysis of randomized controlled trials

BACKGROUND

Effects of potassium supplementation on vascular function remain conflicting. This meta-analysis aimed to summarized current literature to fill the gaps in knowledge.

METHODS

A literature search was performed on PubMed database through April, 2016. The measurements of vascular function included pulse wave velocity (PWV), augmentation index (AI), pulse pressure (PP), flow mediated dilatation (FMD), glycerol trinitrate responses (GTN), and intercellular cell adhesion molecule-1 (ICAM-1). Data were pooled as standardized mean difference (SMD) with 95% confidence intervals.

RESULTS

Seven randomized controlled trials examining 409 participants were included, with dosage of potassium ranging from 40 to 150mmol/day, and duration of intervention from 6days to 12months. Pooling results revealed a significant improvement in PP (SMD -0.280, 95% CI -0.493 to -0.067, p=0.010), but no improvement in PWV (SMD -0.342, 95% CI -1.123 to 0·440, p=0.391), AI (SMD -0.114, 95% CI -0.282 to 0.054, p=0.184), FMD (SMD 0·278, 95% CI -0.321 to 0.877, p=0.363), GTN (SMD -0.009, 95% CI -0.949 to 0.930, p=0.984), and ICAM-1 (SMD -0.238, 95% CI -0.720 to 0.244, p=0.333).

CONCLUSIONS

Potassium supplementation was associated with significant improvement of PP, rather than other measurements of vascular function. However, the small number of researches and wide variation of evidences make it difficult to make a definitive conclusion.

Mechanisms of Endothelial Dysfunction in Hypertensive Pregnancy and Preeclampsia

Preeclampsia is a pregnancy-related disorder characterized by hypertension and could lead to maternal and fetal morbidity and mortality. Although the causative factors and pathophysiological mechanisms are unclear, endothelial dysfunction is a major hallmark of preeclampsia. Clinical tests and experimental research have suggested that generalized endotheliosis in the systemic, renal, cerebral, and hepatic circulation could decrease endothelium-derived vasodilators such as nitric oxide, prostacyclin, and hyperpolarization factor and increase vasoconstrictors such as endothelin-1 and thromboxane A2, leading to increased vasoconstriction, hypertension, and other manifestation of preeclampsia. In search for the upstream mechanisms that could cause endothelial dysfunction, certain genetic, demographic, and environmental risk factors have been suggested to cause abnormal expression of uteroplacental integrins, cytokines, and matrix metalloproteinases, leading to decreased maternal tolerance, apoptosis of invasive trophoblast cells, inadequate spiral arteries remodeling, reduced uterine perfusion pressure (RUPP), and placental ischemia/hypoxia. RUPP may cause imbalance between the antiangiogenic factors soluble fms-like tyrosine kinase-1 and soluble endoglin and the proangiogenic factors vascular endothelial growth factor and placental growth factor, or stimulate the release of other circulating bioactive factors such as inflammatory cytokines, hypoxia-inducible factor-1, reactive oxygen species, and angiotensin AT1 receptor agonistic autoantibodies. These circulating factors could then target endothelial cells and cause generalized endothelial dysfunction. Therapeutic options are currently limited, but understanding the factors involved in endothelial dysfunction could help design new approaches for prediction and management of preeclampsia.

Specialized Functional Diversity and Interactions of the Na,K-ATPase

Na,K-ATPase is a protein ubiquitously expressed in the plasma membrane of all animal cells and vitally essential for their functions. A specialized functional diversity of the Na,K-ATPase isozymes is provided by molecular heterogeneity, distinct subcellular localizations, and functional interactions with molecular environment. Studies over the last decades clearly demonstrated complex and isoform-specific reciprocal functional interactions between the Na,K-ATPase and neighboring proteins and lipids. These interactions are enabled by a spatially restricted ion homeostasis, direct protein-protein/lipid interactions, and protein kinase signaling pathways. In addition to its "classical" function in ion translocation, the Na,K-ATPase is now considered as one of the most important signaling molecules in neuronal, epithelial, skeletal, cardiac and vascular tissues. Accordingly, the Na,K-ATPase forms specialized sub-cellular multimolecular microdomains which act as receptors to circulating endogenous cardiotonic steroids (CTS) triggering a number of signaling pathways. Changes in these endogenous cardiotonic steroid levels and initiated signaling responses have significant adaptive values for tissues and whole organisms under numerous physiological and pathophysiological conditions. This review discusses recent progress in the studies of functional interactions between the Na,K-ATPase and molecular microenvironment, the Na,K-ATPase-dependent signaling pathways and their significance for diversity of cell function.

Adenosine relaxation in isolated rat aortic rings and possible roles of smooth muscle Kv channels, KATP channels and A2a receptors

BACKGROUND

An area of ongoing controversy is the role adenosine to regulate vascular tone in conduit vessels that regulate compliance, and the role of nitric oxide (NO), potassium channels and receptor subtypes involved. The aim of our study was to investigate adenosine relaxation in rat thoracic aortic rings, and the effect of inhibitors of NO, prostanoids, Kv, KATP channels, and A2a and A2b receptors.

METHODS

Aortic rings were freshly harvested from adult male Sprague Dawley rats and equilibrated in an organ bath containing oxygenated, modified Krebs-Henseleit solution, 11 mM glucose, pH 7.4, 37 °C. Isolated rings were pre-contracted sub-maximally with 0.3 μM norepinephrine (NE), and the effect of increasing concentrations of adenosine (1 to 1000 μM) were examined. The drugs L-NAME, indomethacin, 4-aminopyridine (4-AP), glibenclamide, 5-hydroxydecanoate, ouabain, 8-(3-chlorostyryl) caffeine and PSB-0788 were examined in intact and denuded rings. Rings were tested for viability after each experiment.

RESULTS

Adenosine induced a dose-dependent, triphasic relaxation response, and the mechanical removal of the endothelium significantly deceased adenosine relaxation above 10 μM. Interestingly, endothelial removal significantly decreased the responsiveness (defined as % relaxation per μM adenosine) by two-thirds between 10 and 100 μM, but not in the lower (1-10 μM) or higher (>100 μM) ranges. In intact rings, L-NAME significantly reduced relaxation, but not indomethacin. Antagonists of voltage-dependent Kv (4-AP), sarcolemma KATP (glibenclamide) and mitochondrial KATP channels (5-HD) led to significant reductions in relaxation in both intact and denuded rings, with ouabain having little or no effect. Adenosine-induced relaxation appeared to involve the A2a receptor, but not the A2b subtype.

CONCLUSIONS

It was concluded that adenosine relaxation in NE-precontracted rat aortic rings was triphasic and endothelium-dependent above 10 μM, and relaxation involved endothelial nitric oxide (not prostanoids) and a complex interplay between smooth muscle A2a subtype and voltage-dependent Kv, SarcKATP and MitoKATP channels. The possible in vivo significance of the regulation of arterial compliance to left ventricular function coupling is discussed.

Differential regulation of TRPV1 channels by H2O2: implications for diabetic microvascular dysfunction

We demonstrated previously that TRPV1-dependent coupling of coronary blood flow (CBF) to metabolism is disrupted in diabetes. A critical amount of H2O2 contributes to CBF regulation; however, excessive H2O2 impairs responses. We sought to determine the extent to which differential regulation of TRPV1 by H2O2 modulates CBF and vascular reactivity in diabetes. We used contrast echocardiography to study TRPV1 knockout (V1KO), db/db diabetic, and wild type C57BKS/J (WT) mice. H2O2 dose-dependently increased CBF in WT mice, a response blocked by the TRPV1 antagonist SB366791. H2O2-induced vasodilation was significantly inhibited in db/db and V1KO mice. H2O2 caused robust SB366791-sensitive dilation in WT coronary microvessels; however, this response was attenuated in vessels from db/db and V1KO mice, suggesting H2O2-induced vasodilation occurs, in part, via TRPV1. Acute H2O2 exposure potentiated capsaicin-induced CBF responses and capsaicin-mediated vasodilation in WT mice, whereas prolonged luminal H2O2 exposure blunted capsaicin-induced vasodilation. Electrophysiology studies re-confirms acute H2O2 exposure activated TRPV1 in HEK293A and bovine aortic endothelial cells while establishing that H2O2 potentiate capsaicin-activated TRPV1 currents, whereas prolonged H2O2 exposure attenuated TRPV1 currents. Verification of H2O2-mediated activation of intrinsic TRPV1 specific currents were found in isolated mouse coronary endothelial cells from WT mice and decreased in endothelial cells from V1KO mice. These data suggest prolonged H2O2 exposure impairs TRPV1-dependent coronary vascular signaling. This may contribute to microvascular dysfunction and tissue perfusion deficits characteristic of diabetes.

Unitary TRPV3 channel Ca2+ influx events elicit endothelium-dependent dilation of cerebral parenchymal arterioles

Cerebral parenchymal arterioles (PA) regulate blood flow between pial arteries on the surface of the brain and the deeper microcirculation. Regulation of PA contractility differs from that of pial arteries and is not completely understood. Here, we investigated the hypothesis that the Ca(2+) permeable vanilloid transient receptor potential (TRPV) channel TRPV3 can mediate endothelium-dependent dilation of cerebral PA. Using total internal reflection fluorescence microscopy (TIRFM), we found that carvacrol, a monoterpenoid compound derived from oregano, increased the frequency of unitary Ca(2+) influx events through TRPV3 channels (TRPV3 sparklets) in endothelial cells from pial arteries and PAs. Carvacrol-induced TRPV3 sparklets were inhibited by the selective TRPV3 blocker isopentenyl pyrophosphate (IPP). TRPV3 sparklets have a greater unitary amplitude (ΔF/F0 = 0.20) than previously characterized TRPV4 (ΔF/F0 = 0.06) or TRPA1 (ΔF/F0 = 0.13) sparklets, suggesting that TRPV3-mediated Ca(2+) influx could have a robust influence on cerebrovascular tone. In pressure myography experiments, carvacrol caused dilation of cerebral PA that was blocked by IPP. Carvacrol-induced dilation was nearly abolished by removal of the endothelium and block of intermediate (IK) and small-conductance Ca(2+)-activated K(+) (SK) channels. Together, these data suggest that TRPV3 sparklets cause dilation of cerebral parenchymal arterioles by activating IK and SK channels in the endothelium.

Effect of sodium and potassium supplementation on vascular and endothelial function: a randomized controlled trial

BACKGROUND

It is known that increased potassium and reduced sodium intakes can improve postprandial endothelial function. However, the effect of increasing potassium in the presence of high sodium in the postprandial state is not known.

OBJECTIVE

We aimed to determine the effect of high potassium and high sodium on postprandial endothelial function as assessed by using flow-mediated dilatation (FMD) and arterial compliance as assessed by using pulse wave velocity (PWV) and central augmentation index (AIx).

DESIGN

Thirty-nine healthy, normotensive volunteers [21 women and 18 men; mean ± SD age: 37 ± 15 y; BMI (in kg/m(2)): 23.0 ± 2.8] received a meal with 3 mmol K and 65 mmol Na (low-potassium, high-sodium meal (LKHN)], a meal with 38 mmol K and 65 mmol Na [high-potassium, high-sodium meal (HKHN)], and a control meal with 3 mmol K and 6 mmol Na (low-potassium, low-sodium meal) on 3 separate occasions in a randomized crossover trial. Brachial artery FMD, carotid-femoral PWV, central AIx, and blood pressure (BP) were measured while participants were fasting and at 30, 60, 90, and 120 min after meals.

RESULTS

Compared with the LKHN, the addition of potassium (HKHN) significantly attenuated the postmeal decrease in FMD (P-meal by time interaction < 0.05). FMD was significantly lower after the LKHN than after the HKHN at 30 min (P < 0.01). AIx decreased after all meals (P < 0.05). There were no significant differences in AIx, PWV, or BP between treatments over time.

CONCLUSION

The addition of potassium to a high-sodium meal attenuates the sodium-induced postmeal reduction in endothelial function as assessed by FMD. This trial was registered at http://www.anzctr.org.au/ as ACTRN12613000772741.

A systematic review of vascular and endothelial function: effects of fruit, vegetable and potassium intake

AIM

To review the relationships between: 1) Potassium and endothelial function; 2) Fruits and vegetables and endothelial function; 3) Potassium and other measures of vascular function; 4) Fruits and vegetables and other measures of vascular function.

DATA SYNTHESIS

An electronic search for intervention trials investigating the effect of potassium, fruits and vegetables on vascular function was performed in MEDLINE, EMBASE and the Cochrane Library. Potassium appears to improve endothelial function with a dose of >40 mmol/d, however the mechanisms for this effect remain unclear. Potassium may improve measures of vascular function however this effect may be dependent on the effect of potassium on blood pressure. The effect of fruit and vegetables on endothelial function independent of confounding variables is less clear. Increased fruit and vegetable intake may improve vascular function only in high risk populations.

CONCLUSION

Increasing dietary potassium appears to improve vascular function but the effect of increasing fruit and vegetable intake per se on vascular function is less clear.

Contribution of endothelium-derived hyperpolarizing factor to exercise-induced vasodilation in health and hypercholesterolemia

The role of endothelium-derived hyperpolarizing factor (EDHF) in either the healthy circulation or in those with hypercholesterolemia is unknown. In healthy and hypercholesterolemic subjects, we measured forearm blood flow (FBF) using strain-gauge plethysmography at rest, during graded handgrip exercise, and after sodium nitroprusside infusion. Measurements were repeated after l-NMMA, tetraethylammonium (TEA), and combined infusions. At rest, l-NMMA infusion reduced FBF in healthy but not hypercholesterolemic subjects. At peak exercise, vasodilation was lower in hypercholesterolemic compared to healthy subjects (274% vs 438% increase in FBF, p=0.017). TEA infusion reduced exercise-induced vasodilation in both healthy and hypercholesterolemic subjects (27%, p<0.0001 and -20%, p<0.0001, respectively). The addition of l-NMMA to TEA further reduced FBF in healthy (-14%, p=0.012) but not in hypercholesterolemic subjects, indicating a reduced nitric oxide and greater EDHF-mediated contribution to exercise-induced vasodilation in hypercholesterolemia. In conclusion, exercise-induced vasodilation is impaired and predominantly mediated by EDHF in hypercholesterolemic subjects. CLINICAL TRIAL REGISTRATION IDENTIFIER NCT00166166:

Gap junction regulation of vascular tone: implications of modulatory intercellular communication during gestation

In the vasculature, gap junctions (GJ) play a multifaceted role by serving as direct conduits for cell-cell intercellular communication via the facilitated diffusion of signaling molecules. GJs are essential for the control of gene expression and coordinated vascular development in addition to vascular function. The coupling of endothelial cells to each other, as well as with vascular smooth muscle cells via GJs, plays a relevant role in the control of vasomotor tone, tissue perfusion and arterial blood pressure. The regulation of cell-signaling is paramount to cardiovascular adaptations of pregnancy. Pregnancy requires highly developed cell-to-cell coupling, which is affected partly through the formation of intercellular GJs by Cx43, a gap junction protein, within adjacent cell membranes to help facilitate the increase of uterine blood flow (UBF) in order to ensure adequate perfusion for nutrient and oxygen delivery to the placenta and thus the fetus. One mode of communication that plays a critical role in regulating Cx43 is the release of endothelial-derived vasodilators such as prostacyclin (PGI2) and nitric oxide (NO) and their respective signaling mechanisms involving second messengers (cAMP and cGMP, respectively) that are likely to be important in maintaining UBF. Therefore, the assertion we present in this review is that GJs play an integral if not a central role in maintaining UBF by controlling rises in vasodilators (PGI2 and NO) via cyclic nucleotides. In this review, we discuss: (1) GJ structure and regulation; (2) second messenger regulation of GJ phosphorylation and formation; (3) pregnancy-induced changes in cell-signaling; and (4) the role of uterine arterial endothelial GJs during gestation. These topics integrate the current knowledge of this scientific field with interpretations and hypotheses regarding the vascular effects that are mediated by GJs and their relationship with vasodilatory vascular adaptations required for modulating the dramatic physiological rises in uteroplacental perfusion and blood flow observed during normal pregnancy.

A vasoactive role for endogenous relaxin in mesenteric arteries of male mice

The peptide hormone relaxin has striking effects on the vascular system. Specifically, endogenous relaxin treatment reduces myogenic reactivity through nitric oxide (NO)-mediated vasorelaxation and increases arterial compliance in small resistance arteries. However, less is known about the vascular roles of endogenous relaxin, particularly in males. Therefore, we used male wild-type (Rln^+/+) and relaxin knockout (Rln^−/−) mice to test the hypothesis that passive wall properties and vascular reactivity in mesenteric arteries would be compromised in Rln^−/− mice. Passive compliance was determined in arteries (n = 8–9) mounted on a pressure myograph and in Ca²⁺-free Krebs containing 2 mM EGTA. Passive volume compliance was significantly (P = 0.01) decreased in the mesenteric arteries of Rln^−/− mice. Vascular reactivity was assessed using wire myography. In mesenteric arteries (n = 5) of Rln^−/− mice, there was a significant (P<0.03) increase in sensitivity to the vasoconstrictors phenylephrine and thromboxane-mimetic U41669. This enhanced responsiveness to vasoconstrictors was abolished by endothelial denudation, and attributed to impaired NO and prostanoid pathways in Rln^−/− mice. Sensitivity to the endothelial agonist acetylcholine was significantly (n = 7–9, P≤0.03) decreased, and this was abolished in the presence of the cyclooxygenase inhibitor, indomethacin (2 µM). This indicates that prostanoid vasoconstrictor pathways were upregulated in the mesenteric arteries of Rln^−/− mice. In summary, we demonstrate endothelial dysfunction and impaired arterial wall remodeling in male mice deficient in relaxin. Thus, our results highlight a role for endogenous relaxin in the maintenance of normal mesenteric artery structure and function in males.

Effect of high potassium diet on endothelial function

BACKGROUND AND AIMS

Increased potassium intake is related to reduced blood pressure (BP) and reduced stroke rate. The effect of increased dietary potassium on endothelial function remains unknown. The aim was to determine the effect of increased dietary potassium from fruit and vegetables on endothelial function.

METHODS AND RESULTS

Thirty five healthy men and women (age 32 ± 12 y) successfully completed a randomised cross-over study of 2 × 6 day diets either high or low in potassium. Flow mediated dilatation (FMD), BP, pulse wave velocity (PWV), augmentation index (AI) and a fasting blood sample for analysis of Intercellular Adhesion Molecule-1 (ICAM-1), E-selectin, asymmetric dimethylarginine (ADMA) and endothelin-1 were taken on completion of each intervention. Dietary change was achieved by including bananas and potatoes in the high potassium and apples and rice/pasta in the low potassium diet. Dietary adherence was assessed using 6 day weighed food diaries and a 24 h urine sample. The difference in potassium excretion between the two diets was 48 ± 32 mmol/d (P = 0.000). Fasting FMD was significantly improved by 0.6% ± 1.5% following the high compared to the low potassium diet (P = 0.03). There were no significant differences in BP, PWV, AI, ICAM-1, ADMA or endothelin-1 between the interventions. There was a significant reduction in E-selectin following the high (Median = 5.96 ng/ml) vs the low potassium diet (Median = 6.24 ng/ml), z = -2.49, P = 0.013.

CONCLUSION

Increased dietary potassium from fruit and vegetables improves FMD within 1 week in healthy men and women but the mechanisms for this effect remain unclear.

CLINICAL TRIAL REGISTRY

ACTRN12612000822886.

AKAP150-dependent cooperative TRPV4 channel gating is central to endothelium-dependent vasodilation and is disrupted in hypertension

Endothelial cell dysfunction, characterized by a diminished response to endothelial cell-dependent vasodilators, is a hallmark of hypertension. TRPV4 channels play a major role in endothelial-dependent vasodilation, a function mediated by local Ca(2+) influx through clusters of functionally coupled TRPV4 channels rather than by a global increase in endothelial cell Ca(2+). We showed that stimulation of muscarinic acetylcholine receptors on endothelial cells of mouse arteries exclusively activated TRPV4 channels that were localized at myoendothelial projections (MEPs), specialized regions of endothelial cells that contact smooth muscle cells. Muscarinic receptor-mediated activation of TRPV4 depended on protein kinase C (PKC) and the PKC-anchoring protein AKAP150, which was concentrated at MEPs. Cooperative opening of clustered TRPV4 channels specifically amplified Ca(2+) influx at MEPs. Cooperativity of TRPV4 channels at non-MEP sites was much lower, and cooperativity at MEPs was greatly reduced by chelation of intracellular Ca(2+) or AKAP150 knockout, suggesting that Ca(2+) entering through adjacent channels underlies the AKAP150-dependent potentiation of TRPV4 activity. In a mouse model of angiotensin II-induced hypertension, MEP localization of AKAP150 was disrupted, muscarinic receptor stimulation did not activate TRPV4 channels, cooperativity among TRPV4 channels at MEPs was weaker, and vasodilation in response to muscarinic receptor stimulation was reduced. Thus, endothelial-dependent dilation of resistance arteries is enabled by MEP-localized AKAP150, which ensures the proximity of PKC to TRPV4 channels and the coupled channel gating necessary for efficient communication from endothelial to smooth muscle cells in arteries. Disruption of this molecular assembly may contribute to altered blood flow in hypertension.

Endothelium-derived hyperpolarizing factor mediates bradykinin-stimulated tissue plasminogen activator release in humans

AIMS

Bradykinin (BK) stimulates tissue plasminogen activator (t-PA) release from human endothelium. Although BK stimulates both nitric oxide and endothelium-derived hyperpolarizing factor (EDHF) release, the role of EDHF in t-PA release remains unexplored. This study sought to determine the mechanisms of BK-stimulated t-PA release in the forearm vasculature of healthy human subjects.

METHODS

In 33 healthy subjects (age 40.3 ± 1.9 years), forearm blood flow (FBF) and t-PA release were measured at rest and after intra-arterial infusions of BK (400 ng/min) and sodium nitroprusside (3.2 mg/min). Measurements were repeated after intra-arterial infusion of tetraethylammonium chloride (TEA; 1 µmol/min), fluconazole (0.4 µmol·min(-1)·l(-1)), and N(G)-monomethyl-L-arginine (L-NMMA, 8 µmol/min) to block nitric oxide, and their combination in separate studies.

RESULTS

BK significantly increased net t-PA release across the forearm (p < 0.0001). Fluconazole attenuated both BK-mediated vasodilation (-23.3 ± 2.7% FBF, p < 0.0001) and t-PA release (from 50.9 ± 9.0 to 21.3 ± 8.9 ng/min/100 ml, p = 0.02). TEA attenuated FBF (-14.7 ± 3.2%, p = 0.002) and abolished BK-stimulated t-PA release (from 22.9 ± 5.7 to -0.8 ± 3.6 ng/min/100 ml, p = 0.0002). L-NMMA attenuated FBF (p < 0.0001), but did not inhibit BK-induced t-PA release (nonsignificant).

CONCLUSION

BK-stimulated t-PA release is partly due to cytochrome P450-derived epoxides and is inhibited by K(+)Ca channel blockade. Thus, BK stimulates both EDHF-dependent vasodilation and t-PA release.

Hydrogen peroxide induces vasorelaxation by enhancing 4-aminopyridine-sensitive Kv currents through S-glutathionylation

Hydrogen peroxide (H₂O₂) is an endothelium-derived hyperpolarizing factor. Since opposing vasoactive effects have been reported for H₂O₂ depending on the vascular bed and experimental conditions, this study was performed to assess whether H₂O₂ acts as a vasodilator in the rat mesenteric artery and, if so, to determine the underlying mechanisms. H₂O₂ elicited concentration-dependent relaxation in mesenteric arteries precontracted with norepinephrine. The vasodilatory effect of H₂O₂ was reversed by treatment with dithiothreitol. H₂O₂-elicited vasodilation was significantly reduced by blocking 4-aminopyridine (4-AP)-sensitive Kv channels, but it was resistant to blockers of big-conductance Ca²⁺-activated K⁺ channels and inward rectifier K⁺ channels. A patch-clamp study in mesenteric arterial smooth muscle cells (MASMCs) showed that H₂O₂ increased Kv currents in a concentration-dependent manner. H₂O₂ speeded up Kv channel activation and shifted steady state activation to hyperpolarizing potentials. Similar channel activation was seen with oxidized glutathione (GSSG). The H₂O₂-mediated channel activation was prevented by glutathione reductase. Consistent with S-glutathionylation, streptavidin pull-down assays with biotinylated glutathione ethyl ester showed incorporation of glutathione (GSH) in the Kv channel proteins in the presence of H₂O₂. Interestingly, conditions of increased oxidative stress within MASMCs impaired the capacity of H₂O₂ to stimulate Kv channels. Not only was the H₂O₂ stimulatory effect much weaker, but the inhibitory effect of H₂O₂ was unmasked. These data suggest that H₂O₂ activates 4-AP-sensitive Kv channels, possibly through S-glutathionylation, which elicits smooth muscle relaxation in rat mesenteric arteries. Furthermore, our results support the idea that the basal redox status of MASMCs determines the response of Kv currents to H₂O₂.

Role of different types of potassium channels in the relaxation of corpus cavernosum induced by resveratrol

Background:

Resveratrol (RVT), one of the most commonly employed dietary polyphenol, is used in traditional Japanese and Chinese medicine for treatment of cardiovascular diseases. Recently, we have shown that RVT has a potent relaxant effect on rat corpus cavernosum via endothelium-dependent and -independent mechanisms.

Objective:

The present study addressed the question whether different types of potassium channels are involved in the endothelium-dependent and -independent mechanism of corpus cavernosum relaxation induced by RVT.

Materials and Methods:

Strips of corpus cavernosum from rats were mounted in an organ-bath system for isometric tension studies.

Results:

RVT (1-100 μmol/L) produced concentration-dependent relaxation responses in rat corpus cavernosum pre-contracted by phenylephrine. The non-selective potassium channels blocker tetraethylammonium chloride (TEA, 10 mmol/L), ATP-sensitive potassium (K_ATP) channels blocker glibenclamide (10 μmol/L), and inward rectifier potassium (Kir) channels inhibitor barium chloride (BaCl₂, 30 μmol/L) caused a significant inhibition on the relaxation response to RVT, whereas voltage-dependent potassium channels inhibitor 4-aminopyridine (4-AP, 1 mmol/L), and large conductance calcium-activated potassium (BK_Ca) channels inhibitor iberiotoxin (IbTX, 0.1 μmol/L) did not significantly alter relaxant responses of corpus cavernosum strips to RVT. In addition, relaxant responses to RVT did not significantly inhibited by the combination of selective inhibitors of small and intermediate conductance BK_Ca channels (0.1 μmol/L charybdotoxin and 1 μmol/L apamin, respectively).

Conclusion:

These results demonstrated that endothelial small and intermediate conductance BK_Ca channels are not thought to be an important role in RVT-induced endothelium-dependent relaxation of corpus cavernosum. The endothelium-independent corpus cavernosum relaxation induced by RVT is seems to largely depend on Kir channels and K_ATP channels in corporal tissue.

Local effects of pregnancy on connexin proteins that mediate Ca2+-associated uterine endothelial NO synthesis

Uterine artery adaptations during gestation facilitate increases in uterine blood flow and fetal growth.

HYPOTHESIS

local expression and distribution of uterine artery connexins play roles in mediating in vivo gestational eNOS activation and NO production. We established an ovine model restricting pregnancy to a single uterine horn and measured uterine blood flow, uterine artery shear stress, connexins 37/43, and P(635)eNOS protein levels in uterine artery and systemic artery (omental and renal) endothelium and connexins in vascular smooth muscle. Uterine blood flow and shear stress were locally (unilaterally) and substantially elevated by gestation. During pregnancy, uterine artery endothelial gap junction proteins connexins 37/43 were locally regulated in the gravid horn and elevated 10.3- and 25.6-fold; uterine artery endothelial P(635)eNOS and total eNOS were elevated 3.3- and 2.9-fold; whereas uterine artery vascular smooth muscle connexins 37/43 were locally elevated 12.5- and 5.9-fold, respectively. Less pronounced changes were observed in systemic vasculature except for significant pregnancy-associated increases in omental artery vascular smooth muscle connexin 43 and omental artery endothelial P(635)eNOS and total eNOS. Gap junction blockade using connexin 43, but not connexin 37-specific Gap peptides, abrogated uterine artery endothelial ATP-induced Ca(2+)-mediated NO production. Thus, uterine artery endothelial connexin 43, but not connexin 37, regulates Ca(2+)-mediated NO production required for the vasodilation to accommodate increases in uterine blood flow and shear stress during healthy pregnancies.

TRP channel Ca(2+) sparklets: fundamental signals underlying endothelium-dependent hyperpolarization

Important functions of the vascular endothelium, including permeability, production of antithrombotic factors, and control of vascular tone, are regulated by changes in intracellular Ca(2+). The molecular identities and regulation of Ca(2+) influx channels in the endothelium are incompletely understood, in part because of experimental difficulties associated with application of patch-clamp electrophysiology to native endothelial cells. However, advances in confocal and total internal reflection fluorescence microscopy and the development of fast, high-affinity Ca(2+)-binding fluorophores have recently allowed for direct visualization and characterization of single-channel transient receptor potential (TRP) channel Ca(2+) influx events in endothelial cells. These events, called "TRP channel Ca(2+) sparklets," have been optically recorded from primary endothelial cells and the intact endothelium, and the biophysical properties and fundamental significance of these Ca(2+) signals in vasomotor regulation have been characterized. This review will first briefly discuss the role of endothelial cell TRP channel Ca(2+) influx in endothelium-dependent vasodilation, describe improved methods for recording unitary TRP channel activity using optical methods, and highlight discoveries regarding the regulation and physiological significance of TRPV4 Ca(2+) sparklets in the vascular endothelium enabled by this new technology. Perspectives on the potential use of these techniques to evaluate changes in TRP channel Ca(2+) influx activity associated with endothelial dysfunction are offered.

Hyperkalemic cardioplegia for adult and pediatric surgery: end of an era?

Despite surgical proficiency and innovation driving low mortality rates in cardiac surgery, the disease severity, comorbidity rate, and operative procedural difficulty have increased. Today's cardiac surgery patient is older, has a "sicker" heart and often presents with multiple comorbidities; a scenario that was relatively rare 20 years ago. The global challenge has been to find new ways to make surgery safer for the patient and more predictable for the surgeon. A confounding factor that may influence clinical outcome is high K(+) cardioplegia. For over 40 years, potassium depolarization has been linked to transmembrane ionic imbalances, arrhythmias and conduction disturbances, vasoconstriction, coronary spasm, contractile stunning, and low output syndrome. Other than inducing rapid electrochemical arrest, high K(+) cardioplegia offers little or no inherent protection to adult or pediatric patients. This review provides a brief history of high K(+) cardioplegia, five areas of increasing concern with prolonged membrane K(+) depolarization, and the basic science and clinical data underpinning a new normokalemic, "polarizing" cardioplegia comprising adenosine and lidocaine (AL) with magnesium (Mg(2+)) (ALM™). We argue that improved cardioprotection, better outcomes, faster recoveries and lower healthcare costs are achievable and, despite the early predictions from the stent industry and cardiology, the "cath lab" may not be the place where the new wave of high-risk morbid patients are best served.

KATP channels and cardiovascular disease: suddenly a syndrome

ATP-sensitive potassium (KATP) channels were first discovered in the heart 30 years ago. Reconstitution of KATP channel activity by coexpression of members of the pore-forming inward rectifier gene family (Kir6.1, KCNJ8, and Kir6.2 KCNJ11) with sulfonylurea receptors (SUR1, ABCC8, and SUR2, ABCC9) of the ABCC protein subfamily has led to the elucidation of many details of channel gating and pore properties. In addition, the essential roles of Kir6.x and SURx subunits in generating cardiac and vascular KATP(2) and the detrimental consequences of genetic deletions or mutations in mice have been recognized. However, despite this extensive body of knowledge, there has been a paucity of defined roles of KATP subunits in human cardiovascular diseases, although there are reports of association of a single Kir6.1 variant with the J-wave syndrome in the ECG, and 2 isolated studies have reported association of loss of function mutations in SUR2 with atrial fibrillation and heart failure. Two new studies convincingly demonstrate that mutations in the SUR2 gene are associated with Cantu syndrome, a complex multi-organ disorder characterized by hypertrichosis, craniofacial dysmorphology, osteochondrodysplasia, patent ductus arteriosus, cardiomegaly, pericardial effusion, and lymphoedema. This realization of previously unconsidered consequences provides significant insight into the roles of the KATP channel in the cardiovascular system and suggests novel therapeutic possibilities.

Reduced hyperpolarization of endothelial cells following high dietary Na+: effects of enalapril and tempol

1. High dietary Na(+) is associated with impaired vascular endothelial function. However, the underlying mechanisms are not completely understood. In the present study, we investigated whether the endothelial hyperpolarization response to acetylcholine (ACh) exhibited any abnormalities in Wistar rats fed a high-salt diet (HSD) for 1 month and, if so, whether chronic treatment with the angiotensin-converting enzyme inhibitor enalapril or the anti-oxidant tempol could normalize the response. Membrane potential was recorded using the perforated patch-clamp technique on the endothelium of rat aorta. 2. Acetylcholine (2 μmol/L) produced a hyperpolarization sensitive to TRAM-34, a blocker of intermediate-conductance Ca(2+) -sensitive K(+) channels (IK(Ca)), but not to apamin, a blocker of small-conductance Ca(2+)-sensitive K(+) channels (SK(Ca)). NS309 (3 μmol/L), an activator of SK(Ca) and IK(Ca) channels, produced a hyperpolarization of similar magnitude as ACh. 3. In the HSD group, the ACh-evoked hyperpolarization was significantly attenuated compared with that in the control group, which was fed normal chow rather than an HSD. Similarly, the hyperpolarization produced by NS309 was weaker in tissues from HSD-fed rats. 4. Combination of HSD with chronic enalapril treatment (20 mg/kg per day for 1 month) normalized endothelial hyperpolarizing responses to ACh. Chronic tempol treatment (1 mmol/L in tap water for 1 month) prevented the reduced hyperpolarization to ACh. 5. The results of the present study indicate that excess in dietary Na(+) results in a failure of endothelial cells to generate normal IK(Ca) channel-mediated hyperpolarizing responses. Our observations implicate oxidative stress mediated by increased angiotensin II signalling as a mechanism underlying altered endothelial hyperpolarization during dietary salt loading.

Characterization of endothelium-dependent relaxations in the mesenteric vasculature: a comparative study with potential pathophysiological relevance

BACKGROUND

Endothelium-dependent relaxations in human adult mesenteric microvessels involve 3 different main mechanisms: cyclooxygenase (COX)-derived prostanoids, nitric oxide (NO), and endothelium-derived hyperpolarizing factor (EDHF), which elicits vascular smooth muscle hyperpolarization and relaxation. There are some pathological conditions with an abnormal balance between mesenteric vasoconstriction and vasodilatation inputs leading to endothelial dysfunction and tissue injury.

PURPOSE

The purpose was to characterize the mechanisms mediating endothelium-dependent relaxation and differences in children and adult mesenteric microvessels.

METHODS

Microvessels were dissected from omentum obtained from children (3-6 years old) and adults (25-41 years old) and mounted as ring preparations in a small vessel myograph.

RESULTS

In microvessels precontracted with a thromboxane analogue, the endothelium-dependent relaxations to bradykinin (10 nmol/L to 30 μmol/L) mediated by EDHF, that is, nonsensitive to COX (10 μmol/L indomethacin) and NO synthase blockade (100 μmol/L N-nitro-L-arginine methyl ester), were higher in children than in adults. When EDHF was blunted by a depolarizing precontraction with KCl, the remaining COX- and NO-dependent relaxations were significantly lower in children.

CONCLUSIONS

The EDHF's role in the endothelium-dependent relaxations is higher in children's vasculature. This suggests that endothelial dysfunction in mesenteric microvessels in children is likely more dependent on EDHF-related mechanisms rather than on NO- or COX-derived prostanoids.

Mechanisms for vascular effects of androgens in normotensive and hypertensive rats

Castration had no effect on baseline BP and vascular sensitivity to acetylcholine and deficiency of nitric oxide and prostacyclin in normotensive specimens. Castration of hypertensive specimens decreased BP and potentiated the hypotensive effects of acetylcholine, but did not modulate vascular sensitivity to the blockade of nitric oxide and prostacyclin synthesis. The removal of the testicles abolished the pressor influence of glybenclamide in hypertensive and, particularly, in normotensive males. These data indicate that the non-endothelial vascular effects of androgens (i.e., stimulation of K(ATP) channels) predominate under normal conditions. The activating effects of androgens on K(ATP) channels decrease during hypertension, which is accompanied by inhibition of endothelium-dependent vasorelaxation. The production of nitric oxide and prostacyclin remains unchanged under these conditions. Our results suggest that endothelium-derived hyperpolarizing factor is involved in these processes.

Elementary Ca2+ signals through endothelial TRPV4 channels regulate vascular function

Major features of the transcellular signaling mechanism responsible for endothelium-dependent regulation of vascular smooth muscle tone are unresolved. We identified local calcium (Ca(2+)) signals ("sparklets") in the vascular endothelium of resistance arteries that represent Ca(2+) influx through single TRPV4 cation channels. Gating of individual TRPV4 channels within a four-channel cluster was cooperative, with activation of as few as three channels per cell causing maximal dilation through activation of endothelial cell intermediate (IK)- and small (SK)-conductance, Ca(2+)-sensitive potassium (K(+)) channels. Endothelial-dependent muscarinic receptor signaling also acted largely through TRPV4 sparklet-mediated stimulation of IK and SK channels to promote vasodilation. These results support the concept that Ca(2+) influx through single TRPV4 channels is leveraged by the amplifier effect of cooperative channel gating and the high Ca(2+) sensitivity of IK and SK channels to cause vasodilation.

The α2 isoform of the Na,K-pump is important for intercellular communication, agonist-induced contraction, and EDHF-like response in rat mesenteric arteries

The specific role of different isoforms of the Na,K-pump in the vascular wall is still under debate. We have previously suggested that the α(2) isoform of the Na,K-pump (α(2)), Na(+), Ca(2+)-exchange (NCX), and connexin43 form a regulatory microdomain in smooth muscle cells (SMCs), which controls intercellular communication and contractile properties of the vascular wall. We have tested this hypothesis by downregulating α(2) in cultured SMCs and in small arteries with siRNA in vivo. Intercellular communication was assessed by using membrane capacitance measurements. Arteries transfected in vivo were tested for isometric and isobaric force development in vitro; [Ca(2+)](i) was measured simultaneously. Cultured rat SMCs were well-coupled electrically, but 10 μM ouabain uncoupled them. Downregulation of α(2) reduced electrical coupling between SMCs and made them insensitive to ouabain. Downregulation of α(2) in small arteries was accompanied with significant reduction in NCX expression. Acetylcholine-induced relaxation was not different between the groups, but the endothelium-dependent hyperpolarizing factor-like component of the response was significantly diminished in α(2)-downregulated arteries. Micromolar ouabain reduced in a concentration-dependent manner the amplitude of norepinephrine (NE)-induced vasomotion. Sixty percent of the α(2)-downregulated arteries did not have vasomotion, and vasomotion in the remaining 40% was ouabain insensitive. Although ouabain increased the sensitivity to NE in the control arteries, it had no effect on α(2)-downregulated arteries. In the presence of a low NE concentration the α(2)-downregulated arteries had higher [Ca(2+)](i) and tone. However, the NE EC50 was reduced under isometric conditions, and maximal contraction was reduced under isometric and isobaric conditions. The latter was caused by a reduced Ca(2+)-sensitivity. The α(2)-downregulated arteries also had reduced contraction to vasopressin, whereas the contractile response to high K(+) was not affected. Our results demonstrate the importance of α(2) for intercellular coupling in the vascular wall and its involvement in the regulation of vascular tone.