Contribution of Kv7 channels to basal coronary flow and active response to ischemia

G protein βγ regulation of KCNQ-encoded voltage-dependent K channels

The KCNQ family is comprised of five genes and the expression products form voltage-gated potassium channels (Kv7.1-7.5) that have a major impact upon cellular physiology in many cell types. Each functional Kv7 channel forms as a tetramer that often associates with proteins encoded by the KCNE gene family (KCNE1-5) and is critically reliant upon binding of phosphatidylinositol bisphosphate (PIP2) and calmodulin. Other modulators like A-kinase anchoring proteins, ubiquitin ligases and Ca-calmodulin kinase II alter Kv7 channel function and trafficking in an isoform specific manner. It has now been identified that for Kv7.4, G protein βγ subunits (Gβγ) can be added to the list of key regulators and is paramount for channel activity. This article provides an overview of this nascent field of research, highlighting themes and directions for future study.

Canagliflozin improves coronary microvascular vasodilation and increases absolute blood flow to the myocardium independent of angiogenesis

OBJECTIVES

Sodium-glucose cotransporter-2 inhibitor, canagliflozin, improves myocardial perfusion to ischemic territory without accompanying changes in vascular density. We aimed to (1) characterize effects on angiogenic pathways, (2) use multiomics to identify gene expression and metabolite profiles relevant to regulation of myocardial blood flow, and (3) investigate drug effect on coronary microvascular reactivity.

METHODS

A nondiabetic swine model of chronic myocardial ischemia and nondiabetic rat model were used to study functional and molecular effects of canagliflozin on myocardium and in vitro microvascular reactivity.

RESULTS

Canagliflozin resulted in increased coronary microvascular vasodilation and decreased vasoconstriction (P < .05) without changes in microvascular density (P > .3). Expression of the angiogenic modulator, endostatin, increased (P = .008), along with its precursor, collagen 18 (P < .001), and factors that increase its production, including cathepsin L (P = .004). Endostatin and collagen 18 levels trended toward an inverse correlation with blood flow to ischemic territory at rest. Proangiogenic fibroblast growth factor receptor was increased (P = .03) and matrix metalloproteinase-9 was decreased (P < .001) with canagliflozin treatment. Proangiogenic vascular endothelial growth factor A (P = .13), Tie-2 (P = .10), and Ras (P = .18) were not significantly altered. Gene expression related to the cardiac renin-angiotensin system was significantly decreased.

CONCLUSIONS

In chronic myocardial ischemia, canagliflozin increased absolute blood flow to the myocardium without robustly increasing vascular density or proangiogenic signaling. Canagliflozin resulted in altered coronary microvascular reactivity to favor vasodilation, likely through direct effect on vascular smooth muscle. Downregulation of cardiac renin-angiotensin system demonstrated local regulation of perfusion. VIDEO ABSTRACT.

Single cell and spatial transcriptomics analysis of kidney double negative T lymphocytes in normal and ischemic mouse kidneys

T cells are important in the pathogenesis of acute kidney injury (AKI), and TCR+CD4-CD8- (double negative-DN) are T cells that have regulatory properties. However, there is limited information on DN T cells compared to traditional CD4+ and CD8+ cells. To elucidate the molecular signature and spatial dynamics of DN T cells during AKI, we performed single-cell RNA sequencing (scRNA-seq) on sorted murine DN, CD4+, and CD8+ cells combined with spatial transcriptomic profiling of normal and post AKI mouse kidneys. scRNA-seq revealed distinct transcriptional profiles for DN, CD4+, and CD8+ T cells of mouse kidneys with enrichment of Kcnq5, Klrb1c, Fcer1g, and Klre1 expression in DN T cells compared to CD4+ and CD8+ T cells in normal kidney tissue. We validated the expression of these four genes in mouse kidney DN, CD4+ and CD8+ T cells using RT-PCR and Kcnq5, Klrb1, and Fcer1g genes with the NIH human kidney precision medicine project (KPMP). Spatial transcriptomics in normal and ischemic mouse kidney tissue showed a localized cluster of T cells in the outer medulla expressing DN T cell genes including Fcer1g. These results provide a template for future studies in DN T as well as CD4+ and CD8+ cells in normal and diseased kidneys.

Medicinal plant rosemary relaxes blood vessels by activating vascular smooth muscle KCNQ channels

The evergreen plant rosemary (Salvia rosmarinus) has been employed medicinally for centuries as a memory aid, analgesic, spasmolytic, vasorelaxant and antihypertensive, with recent preclinical and clinical evidence rationalizing some applications. Voltage-gated potassium (Kv) channels in the KCNQ (Kv7) subfamily are highly influential in the nervous system, muscle and epithelia. KCNQ4 and KCNQ5 regulate vascular smooth muscle excitability and contractility and are implicated as antihypertensive drug targets. Here, we found that rosemary extract potentiates homomeric and heteromeric KCNQ4 and KCNQ5 activity, resulting in membrane hyperpolarization. Two rosemary diterpenes, carnosol and carnosic acid, underlie the effects and, like rosemary, are efficacious KCNQ-dependent vasorelaxants, quantified by myography in rat mesenteric arteries. Sex- and estrous cycle stage-dependence of the vasorelaxation matches sex- and estrous cycle stage-dependent KCNQ expression. The results uncover a molecular mechanism underlying rosemary vasorelaxant effects and identify new chemical spaces for KCNQ-dependent vasorelaxants.

Colchicine enhances β adrenoceptor-mediated vasodilation in men with essential hypertension

AIMS

The aim of this study is to examine whether colchicine improves β adrenoceptor-mediated vasodilation in humans by conducting a double-blinded, placebo-controlled intervention study. Colchicine treatment has known beneficial effects on cardiovascular health and reduces the incidence of cardiovascular disease. Studies in isolated rodent arteries have shown that colchicine can enhance β adrenoceptor-mediated vasodilation, but this has not been determined in humans.

METHODS

Middle-aged men with essential hypertension were randomly assigned firstly to acute treatment with either 0.5 mg colchicine (n = 19) or placebo (n = 12). They were subsequently re-randomized for 3 weeks of treatment with either colchicine 0.5 mg twice daily (n = 16) or placebo (n = 15) followed by a washout period of 48-72 h. The vasodilator responses to isoprenaline, acetylcholine and sodium nitroprusside were determined as well as arterial pressure, arterial compliance and plasma inflammatory markers.

RESULTS

Acute colchicine treatment increased isoprenaline (by 38% for the highest dose) as well as sodium nitroprusside (by 29% main effect) -induced vasodilation but had no effect on the response to acetylcholine. The 3-week colchicine treatment followed by a washout period did not induce an accumulated or sustained effect on the β adrenoceptor response, and there was no effect on arterial pressure, arterial compliance or the level of measured inflammatory markers.

CONCLUSION

Colchicine acutely enhances β adrenoceptor- and nitric oxide-mediated changes in vascular conductance in humans, supporting that the mechanism previously demonstrated in rodents, translates to humans. The results provide novel translational evidence for a transient enhancing effect of colchicine on β adrenoceptor-mediated vasodilation in humans with essential hypertension.

CONDENSED ABSTRACT

Preclinical studies in isolated rodent arteries have shown that colchicine can enhance β adrenoceptor-mediated vasodilation. Here we show that this effect of colchicine can be translated to humans. Acute colchicine treatment was found to increase both isoprenaline- and sodium nitroprusside-induced vasodilation. The study provides the first translational evidence for a transient β adrenoceptor-mediated vasodilatory effect of colchicine in humans. The finding of an acute effect suggests that it may be clinically important to maintain an adequate bioavailability of colchicine.

The inhibitory effects of pimozide, an antipsychotic drug, on voltage-gated K+ channels in rabbit coronary arterial smooth muscle cells

Pimozide is an antipsychotic drug used to treat chronic psychosis, such as Tourette's syndrome. Despite its widespread clinical use, pimozide can cause unexpected adverse effects, including arrhythmias. However, the adverse effects of pimozide on vascular K⁺ channels have not yet been determined. Therefore, we investigated the effects of pimozide on voltage-gated K⁺ (Kv) channels in rabbit coronary arterial smooth muscle cells. Pimozide concentration-dependently inhibited the Kv currents with an IC₅₀ value of 1.78 ± 0.17 μM and a Hill coefficient of 0.90 ± 0.05. The inhibitory effect on the Kv current by pimozide was highly voltage-dependent in the voltage range of Kv channel activation, and additive inhibition of the Kv current by pimozide was observed in the full activation voltage range. The decay rate of inactivation was significantly accelerated by pimozide. Pimozide shifted the inactivation curve to a more negative potential. The recovery time constant from inactivation increased in the presence of pimozide. Furthermore, pimozide-induced inhibition of the Kv current was augmented by applying train pulses. Although pretreatment with the Kv2.1 subtype inhibitor guangxitoxin and the Kv7 subtype inhibitor linopirdine did not alter the degree of pimozide-induced inhibition of the Kv currents, pretreatment with the Kv1.5 channel inhibitor DPO-1 reduced the inhibitory effects of pimozide on Kv currents. Pimozide induced membrane depolarization. We conclude that pimozide inhibits Kv currents in voltage-, time-, and use (state)-dependent manners. Furthermore, the major Kv channel target of pimozide is the Kv1.5 channel.

Kv7-specific activators hyperpolarize resting membrane potential and modulate human iPSC-derived sensory neuron excitability

Chronic pain is highly prevalent and remains a significant unmet global medical need. As part of a search for modulatory genes that confer pain resilience, we have studied two family cohorts where one individual reported much less pain than other family members that share the same pathogenic gain-of-function Nav1.7 mutation that confers hyperexcitability on pain-signaling dorsal root ganglion (DRG) neurons. In each of these kindreds, the pain-resilient individual carried a gain-of-function variant in Kv7.2 or Kv7.3, two potassium channels that stabilize membrane potential and reduce excitability. Our observation in this molecular genetic study that these gain-of-function Kv7.2 and 7.3 variants reduce DRG neuron excitability suggests that agents that activate or open Kv7 channels should attenuate sensory neuron firing. In the present study, we assess the effects on sensory neuron excitability of three Kv7 modulators-retigabine (Kv7.2 thru Kv7.5 activator), ICA-110381 (Kv7.2/Kv7.3 specific activator), and as a comparator ML277 (Kv7.1 specific activator)-in a "human-pain-in-a-dish" model (human iPSC-derived sensory neurons, iPSC-SN). Multi-electrode-array (MEA) recordings demonstrated inhibition of firing with retigabine and ICA-110381 (but not with ML277), with the concentration-response curve indicating that retigabine can achieve a 50% reduction of firing with sub-micromolar concentrations. Current-clamp recording demonstrated that retigabine hyperpolarized iPSC-SN resting potential and increased threshold. This study implicates Kv7.2/Kv7.3 channels as effective modulators of sensory neuron excitability, and suggest that compounds that specifically target Kv7.2/Kv7.3 currents in sensory neurons, including human sensory neurons, might provide an effective approach toward pain relief.

Emerging mechanisms involving brain Kv7 channel in the pathogenesis of hypertension

Hypertension is a prevalent health problem inducing many organ damages. The pathogenesis of hypertension involves a complex integration of different organ systems including the brain. The elevated sympathetic nerve activity is closely related to the etiology of hypertension. Ion channels are critical regulators of neuronal excitability. Several mechanisms have been proposed to contribute to hypothalamic-driven elevated sympathetic activity, including altered ion channel function. Recent findings indicate one of the voltage-gated potassium channels, Kv7 channels (M channels), plays a vital role in regulating cardiovascular-related neurons activity, and the expression of Kv7 channels is downregulated in hypertension. This review highlights recent findings that the Kv7 channels in the brain, blood vessels, and kidneys are emerging targets involved in the pathogenesis of hypertension, suggesting new therapeutic targets for treating drug-resistant, neurogenic hypertension.

The KCNQ channel inhibitor XE991 suppresses nicotinic acetylcholine receptor-mediated responses in rat intracardiac ganglion neurons

BACKGROUND

XE991 (10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone) is reportedly a potent and selective Kv7 (KCNQ) channel inhibitor. This study aimed to evaluate how XE991 affects nicotinic responses in intracardiac ganglion neurons.

METHODS

We studied how the KCNQ channel inhibitor XE991 could affect nicotinic responses in acutely isolated rat intracardiac ganglion neurons using a perforated patch-clamp recording configuration and Ca²⁺ imaging.

RESULTS

XE991 reversibly and concentration-dependently inhibited the nicotine (10 μM)-induced current with an IC₅₀ of 14.4 μM. The EC₅₀ values for nicotine-induced currents in the absence and presence of 10 μM XE991 were 8.7 and 12.0 μM, respectively. Because XE991 suppressed the maximum response of the nicotine concentration-response curve, the inhibitory effect of this drug appears to be noncompetitive. In addition, linopirdine reduced the amplitude of 10 µM nicotine-induced currents with an IC₅₀ value of 16.9 μM. The inorganic KCNQ channel inhibitor Ba²⁺ affected neither the nicotine-induced current nor the inhibitory effect of XE991 on the nicotinic response. The KCNQ activator flupirtine at a concentration of 10 μM slightly but markedly inhibited the nicotine-induced current. Finally, XE991 inhibited the nicotine-induced elevation of intracellular calcium concentration and the nicotine-induced firing of action potentials.

CONCLUSION

We propose that XE991 inhibits nicotinic acetylcholine receptors in intracardiac ganglion neurons, which in turn attenuate nicotine-induced neuronal excitation.

KCNQ Potassium Channels as Targets of Botanical Folk Medicines

Since prehistory, human species have depended on plants for both food and medicine. Even in countries with ready access to modern medicines, alternative treatments are still highly regarded and commonly used. Unlike modern pharmaceuticals, many botanical medicines are in widespread use despite a lack of safety and efficacy data derived from controlled clinical trials and often unclear mechanisms of action. Contributing to this are the complex and undefined composition and likely multifactorial mechanisms of action and multiple targets of many botanical medicines. Here, we review the newfound importance of the ubiquitous KCNQ subfamily of voltage-gated potassium channels as targets for botanical medicines, including basil, capers, cilantro, lavender, fennel, chamomile, ginger, and Camellia, Sophora, and Mallotus species. We discuss the implications for the traditional use of these plants for disorders such as seizures, hypertension, and diabetes and the molecular mechanisms of plant secondary metabolite effects on KCNQ channels.

Sexual dimorphism in prostacyclin-mimetic responses within rat mesenteric arteries: A novel role for KV 7.1 in shaping IP-receptor mediated relaxation

Background and Purpose

Prostacyclin mimetics express potent vasoactive effects via prostanoid receptors that are not unequivocally defined, as to date no study has considered sex as a factor. The aim of this study was to determine the contribution of IP and EP₃ prostanoid receptors to prostacyclin mimetic iloprost‐mediated responses, whether K_V7.1–5 channels represent downstream targets of selective prostacyclin‐IP‐receptor agonist MRE‐269 and the impact of the oestrus cycle on vascular reactivity.

Experimental Approach

Within second‐order mesenteric arteries from male and female Wistar rats, we determined (1) relative mRNA transcripts for EP_1–4 (Ptger_1–4), IP (Ptgi) and TXA₂ (Tbxa) prostanoid receptors via RT‐qPCR; (2) the effect of iloprost, MRE‐269, isoprenaline and ML277 on precontracted arterial tone in the presence of inhibitors of prostanoid receptors, potassium channels and the molecular interference of K_V7.1 via wire‐myograph; (3) oestrus cycle stage via histological changes in cervical cell preparations.

Key Results

Iloprost evoked a biphasic response in male mesenteric arteries, at concentrations ≤100 nmol·L⁻¹ relaxing, then contracting the vessel at concentration ≥300 nmol·L⁻¹, a process attributed to IP and EP₃ receptors respectively. Secondary contraction was absent in the females, which was associated with a reduction in Ptger3. Pharmacological inhibition and molecular interference of K_V7.1 significantly attenuated relaxations produced by the selective IP receptor agonist MRE‐269 in male and female Wistar in dioestrus/metoestrus, but not pro‐oestrus/oestrus.

Conclusions and Implications

Stark sexual dimorphisms in iloprost‐mediated vasoactive responses are present within mesenteric arteries. K_V7.1 is implicated in IP receptor‐mediated vasorelaxation and is impaired by the oestrus cycle.

Kv7 channel trafficking by the microtubule network in vascular smooth muscle

In arterial smooth muscle cells, changes in availability of integral membrane proteins influence the regulation of blood flow and blood pressure, which is critical for human health. However, the mechanisms that coordinate the trafficking and membrane expression of specific receptors and ion channels in vascular smooth muscle are poorly understood. In the vasculature, very little is known about microtubules, which form a road network upon which proteins can be transported to and from the cell membrane. This review article summarizes the impact of the microtubule network on arterial contractility, highlighting the importance of the network, with an emphasis on our recent findings regarding the trafficking of the voltage‐dependent Kv7 channels.

Allisartan ameliorates vascular remodeling through regulation of voltage-gated potassium channels in hypertensive rats

BACKGROUND

The objective of the present study was to determine the effect of allisartan, a new angiotensin II type 1 receptor antagonist on vascular remodeling through voltage gated potassium channels (Kv7) in hypertensive rats.

METHODS

The study included a total of 47 Sprague Dawley (SD) rats. The animals were randomized to sham operation (n = 14), untreated hypertensive control group (n = 18) and allisartan treatment group (n = 15). Using renal artery stenosis, hypertension was induced in animals. Single dose of allisartan was administered intra-gastrically to animals in the allisartan treatment group and match placebo in the other 2 groups. Wire myography was used to measure the muscle tension in isolated mesenteric arteries from the animals. Real-time polymerase chain reaction was used to quantify the expression of Kv7 channel mRNA subunits.

RESULTS

After 4 weeks of treatment, a significant decrease in mean arterial, systolic and diastolic blood pressure (SBP and DBP) was observed in allisartan treatment group compared to hypertension control group. The median arterial wall thickness and area/diameter ratio reduced significantly in treatment group compared to untreated hypertension group (P < 0.05). Wire myography demonstrated increased relaxation of mesenteric artery with increase in concentration of ML213. A significant up-regulation in the expression of all Kv7 mRNA subunits was observed in allisartan group compared to untreated hypertension group.

CONCLUSIONS

From the results, allisartan was found to lower BP and preserve vascular remodeling through Kv7 channels.

Remodeling of Arterial Tone Regulation in Postnatal Development: Focus on Smooth Muscle Cell Potassium Channels

Maturation of the cardiovascular system is associated with crucial structural and functional remodeling. Thickening of the arterial wall, maturation of the sympathetic innervation, and switching of the mechanisms of arterial contraction from calcium-independent to calcium-dependent occur during postnatal development. All these processes promote an almost doubling of blood pressure from the moment of birth to reaching adulthood. This review focuses on the developmental alterations of potassium channels functioning as key smooth muscle membrane potential determinants and, consequently, vascular tone regulators. We present evidence that the pattern of potassium channel contribution to vascular control changes from K_ir2, K_v1, K_v7 and TASK-1 channels to BK_Ca channels with maturation. The differences in the contribution of potassium channels to vasomotor tone at different stages of postnatal life should be considered in treatment strategies of cardiovascular diseases associated with potassium channel malfunction.

Adenosine and adenosine receptor-mediated action in coronary microcirculation

Adenosine is an ubiquitous extracellular signaling molecule and plays a fundamental role in the regulation of coronary microcirculation through activation of adenosine receptors (ARs). Adenosine is regulated by various enzymes and nucleoside transporters for its balance between intra- and extracellular compartments. Adenosine-mediated coronary microvascular tone and reactive hyperemia are through receptors mainly involving A_2AR activation on both endothelial and smooth muscle cells, but also involving interaction among other ARs. Activation of ARs further stimulates downstream targets of H₂O₂, K_ATP, K_V and K_Ca2+ channels leading to coronary vasodilation. An altered adenosine-ARs signaling in coronary microcirculation has been observed in several cardiovascular diseases including hypertension, diabetes, atherosclerosis and ischemic heart disease. Adenosine as a metabolite and its receptors have been studied for its both therapeutic and diagnostic abilities. The present review summarizes important aspects of adenosine metabolism and AR-mediated actions in the coronary microcirculation.

Pirfenidone Is a Vasodilator: Involvement of KV7 Channels in the Effect on Endothelium-Dependent Vasodilatation in Type-2 Diabetic Mice

Endothelial cell dysfunction and fibrosis are associated with worsening of the prognosis in patients with cardiovascular disease. Pirfenidone has a direct antifibrotic effect, but vasodilatation may also contribute to the effects of pirfenidone. Therefore, in a first study we investigated the mechanisms involved in the relaxant effect of pirfenidone in rat intrapulmonary arteries and coronary arteries from normal mice. Then in a second study, we investigated whether pirfenidone restores endothelial function in the aorta and mesenteric arteries from diabetic animals. From 16–18-week old normal male C57BL/6 mice and normoglycemic (db/db+), and type 2 diabetic (db/db) male and female mice, arteries were mounted in microvascular isometric myographs for functional studies, and immunoblotting was performed. In rat pulmonary arteries and mouse coronary arteries, pirfenidone induced relaxations, which were inhibited in preparations without endothelium. In mouse coronary arteries, pirfenidone relaxation was inhibited in the presence of a nitric oxide (NO) synthase inhibitor, N^G-nitro-l-arginine (L-NOARG), a blocker of large-conductance calcium-activated potassium channels (BK_Ca), iberiotoxin, and a blocker of K_V7 channels, XE991. Patch clamp studies in vascular smooth muscle revealed pirfenidone increased iberiotoxin-sensitive current. In the aorta and mesenteric small arteries from diabetic db/db mice relaxations induced by the endothelium-dependent vasodilator, acetylcholine, were markedly reduced compared to db/db + mice. Pirfenidone enhanced the relaxations induced by acetylcholine in the aorta from diabetic male and female db/db mice. An opener of K_V7 channels, flupirtine, had the same effect as pirfenidone. XE991 reduced the effect of pirfenidone and flupirtine and further reduced acetylcholine relaxations in the aorta. In the presence of iberiotoxin, pirfenidone still increased acetylcholine relaxation in aorta from db/db mice. Immunoblotting for K_V7.4, K_V7.5, and BK_Ca channel subunits were unaltered in aorta from db/db mice. Pirfenidone failed to improve acetylcholine relaxation in mesenteric arteries, and neither changed acetylcholine-induced transient decreases in blood pressure in db/db+ and db/db mice. In conclusion, pirfenidone vasodilates pulmonary and coronary arteries. In coronary arteries from normal mice, pirfenidone induces NO-dependent vasodilatation involving BK_Ca and K_V7 channels. Pirfenidone improves endothelium-dependent vasodilatation in aorta from diabetic animals by a mechanism involving voltage-gated K_V7 channels, a mechanism that may contribute to the antifibrotic effect of pirfenidone.

Kv7 Channels and Excitability Disorders

Kv7.1-Kv7.5 (KCNQ1-5) K⁺ channels are voltage-gated K⁺ channels with major roles in neurons, muscle cells and epithelia where they underlie physiologically important K⁺ currents, such as neuronal M current and cardiac I_Ks. Specific biophysical properties of Kv7 channels make them particularly well placed to control the activity of excitable cells. Indeed, these channels often work as 'excitability breaks' and are targeted by various hormones and modulators to regulate cellular activity outputs. Genetic deficiencies in all five KCNQ genes result in human excitability disorders, including epilepsy, arrhythmias, deafness and some others. Not surprisingly, this channel family attracts considerable attention as potential drug targets. Here we will review biophysical properties and tissue expression profile of Kv7 channels, discuss recent advances in the understanding of their structure as well as their role in various neurological, cardiovascular and other diseases and pathologies. We will also consider a scope for therapeutic targeting of Kv7 channels for treatment of the above health conditions.

KV7 Channel Expression and Function Within Rat Mesenteric Endothelial Cells

Background and Purpose: Arterial diameter is dictated by the contractile state of the vascular smooth muscle cells (VSMCs), which is modulated by direct and indirect inputs from endothelial cells (ECs). Modulators of KCNQ-encoded k_V7 channels have considerable impact on arterial diameter and these channels are known to be expressed in VSMCs but not yet defined in ECs. However, expression of k_V7 channels in ECs would add an extra level of vascular control. This study aims to characterize the expression and function of K_V7 channels within rat mesenteric artery ECs. Experimental Approach: In rat mesenteric artery, KCNQ transcript and K_V7 channel protein expression were determined via RT-qPCR, immunocytochemistry, immunohistochemistry and immunoelectron microscopy. Wire myography was used to determine vascular reactivity. Key Results: KCNQ transcript was identified in isolated ECs and VSMCs. K_V7.1, K_V7.4 and K_V7.5 protein expression was determined in both isolated EC and VSMC and in whole vessels. Removal of ECs attenuated vasorelaxation to two structurally different K_V7.2-5 activators S-1 and ML213. K_IR2 blockers ML133, and BaCl₂ also attenuated S-1 or ML213-mediated vasorelaxation in an endothelium-dependent process. K_V7 inhibition attenuated receptor-dependent nitric oxide (NO)-mediated vasorelaxation to carbachol, but had no impact on relaxation to the NO donor, SNP. Conclusion and Implications: In rat mesenteric artery ECs, K_V7.4 and K_V7.5 channels are expressed, functionally interact with endothelial K_IR2.x channels and contribute to endogenous eNOS-mediated relaxation. This study identifies K_V7 channels as novel functional channels within rat mesenteric ECs and suggests that these channels are involved in NO release from the endothelium of these vessels.

Uncovered Contribution of Kv7 Channels to Pulmonary Vascular Tone in Pulmonary Arterial Hypertension

K + channels play a fundamental role regulating membrane potential of pulmonary artery (PA) smooth muscle cells and their impairment is a common feature in pulmonary arterial hypertension (PAH). K + voltage-gated channel subfamily Q ( KCNQ1-5 ) or Kv7 channels and their regulatory subunits subfamily E (KCNE) regulatory subunits are known to regulate vascular tone, but whether Kv7 channel function is impaired in PAH and how this can affect the rationale for targeting Kv7 channels in PAH remains unknown. Here, we have studied the role of Kv7/KCNE subunits in rat PA and their possible alteration in PAH. Using the patch-clamp technique, we found that the total K + current is reduced in PA smooth muscle cells from pulmonary hypertension animals (SU5416 plus hypoxia) and Kv7 currents made a higher contribution to the net K + current. Likewise, enhanced vascular responses to Kv7 channel modulators were found in pulmonary hypertension rats. Accordingly, KCNE4 subunit was highly upregulated in lungs from pulmonary hypertension animals and patients. Additionally, Kv7 channel activity was enhanced in the presence of Kv1.5 and TASK-1 channel inhibitors and this was associated with an increased KCNE4 membrane abundance. Compared with systemic arteries, PA showed a poor response to Kv7 channel modulators which was associated with reduced expression and membrane abundance of Kv7.4 and KCNE4. Our data indicate that Kv7 channel function is preserved and KCNE4 is upregulated in PAH. Therefore, compared with other downregulated channels, the contribution of Kv7 channels is increased in PAH resulting in an enhanced sensitivity to Kv7 channel modulators. This study provides insight into the potential usefulness of targeting Kv7 channels in PAH.

Ionic Channels as Potential Therapeutic Targets for Erectile Dysfunction: A Review

Erectile dysfunction (ED) is a prevalent condition, especially in men over 40 years old, characterized by the inability to obtain and/or maintain penile erection sufficient for satisfactory sexual intercourse. Several psychological and/or organic factors are involved in the etiopathogenesis of ED. In this context, we gathered evidence of the involvement of Large-conductance, Ca2+-activated K+ channels (BKCa), Small-conductance, Ca2+-activated K+ channels (SKCa), KCNQ-encoded voltage-dependent K+ channels (KV7), Transient Receptor Potential channels (TRP), and Calcium-activated Chloride channels (CaCC) dysfunctions on ED. In addition, the use of modulating agents of these channels are involved in relaxation of the cavernous smooth muscle cell and, consequent penile erection, suggesting that these channels are promising therapeutic targets for the treatment of erectile dysfunction.

Impact of Administration Time and Kv7 Subchannels on the Cardioprotective Efficacy of Kv7 Channel Inhibition

Purpose

The mechanism of cardioprotection by Kv7.1-5 (KCNQ1-5) channels inhibition by XE991 is unclear. We examined the impact of administration time on the cardioprotective efficacy of XE991, the involvement of key pro-survival kinases, and the importance of the Kv7 subchannels.

Methods

Isolated perfused rat hearts were divided into five groups: 1) vehicle, 2) pre-, 3) post- or 4) pre- and post-ischemic administration of XE991 or 5) chromanol 293B (Kv7.1 inhibitor) followed by infarct size quantification. HL-1 cells undergoing simulated ischemia/reperfusion were exposed to either a) vehicle, b) pre-, c) per-, d) post-ischemic administration of XE991 or pre-, per- and post-ischemic administration of e) XE991, f) Chromanol 293B or g) HMR1556 (Kv7.1 inhibitor). HL-1 cell injury was evaluated by propidium iodide/Hoechst staining. Pro-survival kinase activation of Akt, Erk and STAT3 in XE991-mediated HL-1 cell protection was evaluated using phosphokinase inhibitors. Kv7 subtype expression was examined by RT-PCR and qPCR.

Results

XE991, but not Chromanol 293B, reduced infarct size and improved hemodynamic recovery in all isolated heart groups. XE991 protected HL-1 cells when administered during simulated ischemia. Minor activation of the survival kinases was observed in cells exposed to XE991 but pharmacological inhibition of kinase activation did not reduce XE991-mediated protection. Kv7 subchannels 1-5 were all present in rat hearts but predominately Kv7.1 and Kv7.4 were present in HL-1 cells and selective Kv7.1 did not reduce ischemia/reperfusion injury.

Conclusion

The cardioprotective efficacy of XE991 seems to depend on its presence during ischemia and early reperfusion and do not rely on RISK (p-Akt and p-Erk) and SAFE (p-STAT3) pathway activation. The protective effect of XE991 seems mainly mediated through the Kv7.4 subchannel.

Cyclic AMP-Dependent Regulation of Kv7 Voltage-Gated Potassium Channels

Voltage-gated Kv7 potassium channels, encoded by KCNQ genes, have major physiological impacts cardiac myocytes, neurons, epithelial cells, and smooth muscle cells. Cyclic adenosine monophosphate (cAMP), a well-known intracellular secondary messenger, can activate numerous downstream effector proteins, generating downstream signaling pathways that regulate many functions in cells. A role for cAMP in ion channel regulation has been established, and recent findings show that cAMP signaling plays a role in Kv7 channel regulation. Although cAMP signaling is recognized to regulate Kv7 channels, the precise molecular mechanism behind the cAMP-dependent regulation of Kv7 channels is complex. This review will summarize recent research findings that support the mechanisms of cAMP-dependent regulation of Kv7 channels.

Acetaminophen (Paracetamol) Metabolites Induce Vasodilation and Hypotension by Activating Kv7 Potassium Channels Directly and Indirectly

OBJECTIVE

Intravenous acetaminophen/paracetamol (APAP) is well documented to cause hypotension. Since the patients receiving intravenous APAP are usually critically ill, any severe hemodynamic changes, as with those associated with APAP, can be life-threatening. The mechanism underlying this dangerous iatrogenic effect of APAP was unknown. Approach and Results: Here, we show that intravenous APAP caused transient hypotension in rats, which was attenuated by the Kv7 channel blocker, linopirdine. APAP metabolite N-acetyl-p-benzoquinone imine caused vasodilatation of rat mesenteric arteries ex vivo. This vasodilatation was sensitive to linopirdine and also the calcitonin gene-related peptide antagonist, BIBN 4096. Further investigation revealed N-acetyl-p-benzoquinone imine stimulates calcitonin gene-related peptide release from perivascular nerves, causing a cAMP-dependent activation of Kv7 channels. We also show that N-acetyl-p-benzoquinone imine enhances Kv7.4 and Kv7.5 channels overexpressed in oocytes, suggesting that it can activate Kv7.4 and Kv7.5 channels directly, to elicit vasodilatation.

CONCLUSIONS

Direct and indirect activation of Kv7 channels by the APAP metabolite N-acetyl-p-benzoquinone imine decreases arterial tone, which can lead to a drop in blood pressure. Our findings provide a molecular mechanism and potential preventive intervention for the clinical phenomenon of intravenous APAP-dependent transient hypotension.

Ion channels as effectors of cyclic nucleotide pathways: Functional relevance for arterial tone regulation

Numerous mediators and drugs regulate blood flow or arterial pressure by acting on vascular tone, involving cyclic nucleotide intracellular pathways. These signals lead to regulation of several cellular effectors, including ion channels that tune cell membrane potential, Ca²⁺ influx and vascular tone. The characterization of these vasocontrictive or vasodilating mechanisms has grown in complexity due to i) the variety of ion channels that are expressed in both vascular endothelial and smooth muscle cells, ii) the heterogeneity of responses among the various vascular beds, and iii) the number of molecular mechanisms involved in cyclic nucleotide signalling in health and disease. This review synthesizes key data from literature that highlight ion channels as physiologically relevant effectors of cyclic nucleotide pathways in the vasculature, including the characterization of the molecular mechanisms involved. In smooth muscle cells, cation influx or chloride efflux through ion channels are associated with vasoconstriction, whereas K⁺ efflux repolarizes the cell membrane potential and mediates vasodilatation. Both categories of ion currents are under the influence of cAMP and cGMP pathways. Evidence that some ion channels are influenced by CN signalling in endothelial cells will also be presented. Emphasis will also be put on recent data touching a variety of determinants such as phosphodiesterases, EPAC and kinase anchoring, that complicate or even challenge former paradigms.

Effect of ischemic preconditioning and a Kv7 channel blocker on cardiac ischemia-reperfusion injury in rats

Recently, we found cardioprotective effects of ischemic preconditioning (IPC), and from a blocker of KCNQ voltage-gated K⁺ channels (K_V7), XE991 (10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone), in isolated rat hearts. The purpose of the present study was to investigate the cardiovascular effects of IPC and XE991 and whether they are cardioprotective in intact rats. In conscious rats, we measured the effect of the K_V7 channel blocker XE991 on heart rate and blood pressure by use of telemetry. In anesthetized rats, cardiac ischemia was induced by occluding the left coronary artery, and the animals received IPC (2 × 5 min of occlusion), XE991, or a combination. After a 2 h reperfusion period, the hearts were excised, and the area at risk and infarct size were determined. In both anesthetized and conscious rats, XE991 increased blood pressure, and the highest dose (7.5 mg/kg) of XE991 also increased heart rate, and 44% of conscious rats died. XE991 induced marked changes in the electrocardiogram (e.g., increased PR interval and prolonged QT_C interval) without changing cardiac action potentials. The infarct size to area at risk ratio was reduced from 53 ± 2% (n = 8) in the vehicle compared to 36 ± 3% in the IPC group (P < 0.05, n = 9). XE991 (0.75 mg/kg) treatment alone or on top of IPC failed to reduce myocardial infarct size. Similar to the effect in isolated hearts, locally applied IPC was cardioprotective in intact animals exposed to ischemia-reperfusion. Systemic administration of XE991 failed to protect the heart against ischemia-reperfusion injury suggesting effects on the autonomic nervous system counteracting the cardioprotection in intact animals.

Investigating the Role of G Protein βγ in Kv7-Dependent Relaxations of the Rat Vasculature

Objective- In renal arteries, inhibitors of G protein βγ subunits (Gβγ) reduce Kv7 activity and inhibit Kv7-dependent receptor-mediated vasorelaxations. However, the mechanisms underlying receptor-mediated relaxation are artery specific. Consequently, the aim of this study was to ascertain the role of Gβγ in Kv7-dependent vasorelaxations of the rat vasculature. Approach and Results- Isometric tension recording was performed in isolated rat renal, mesenteric, and cerebral arteries to study isoproterenol and calcitonin gene-related peptide relaxations. Kv7.4 was knocked down via morpholino transfection while inhibition of Gβγ was investigated with gallein and M119K. Proximity ligation assay was performed on isolated myocytes to study the association between Kv7.4 and G protein β subunits or signaling intermediaries. Isoproterenol or calcitonin gene-related peptide-induced relaxations were attenuated by Kv7.4 knockdown in all arteries studied. Inhibition of Gβγ with gallein or M119K had no effect on isoproterenol-mediated relaxations in mesenteric artery but had a marked effect on calcitonin gene-related peptide-induced responses in mesenteric artery and cerebral artery and isoproterenol responses in renal artery. Isoproterenol increased association with Kv7.4 and Rap1a in mesenteric artery which were not sensitive to gallein, whereas in renal artery, isoproterenol increased Kv7.4-AKAP (A-kinase anchoring protein) associations in a gallein-sensitive manner. Conclusions- The Gβγ-Kv7 relationship differs between vessels and is an essential requirement for AKAP, but not Rap-mediated regulation of the channel.

Activation of Kv 7 channels as a novel mechanism for NO/cGMP-induced pulmonary vasodilation

BACKGROUND AND PURPOSE

The NO/cGMP pathway represents a major physiological signalling controlling tone in pulmonary arteries (PA), and drugs activating this pathway are used to treat pulmonary arterial hypertension. K_v channels expressed in PA smooth muscle cells (PASMCs) are key determinants of vascular tone. We aimed to analyse the contribution of K_v 1.5 and K_v 7 channels in the electrophysiological and vasodilating effects evoked by NO donors and the GC stimulator riociguat in PA.

EXPERIMENTAL APPROACH

K_v currents were recorded in isolated rat PASMCs using the patch-clamp technique. Vascular reactivity was assessed in a wire myograph.

KEY RESULTS

The NO donors diethylamine NONOate diethylammonium (DEA-NO) and sodium nitroprusside hyperpolarized the membrane potential and induced a bimodal effect on K_v currents (augmenting the current between -40 and -10 mV and decreasing it at more depolarized potentials). The hyperpolarization and the enhancement of the current were suppressed by K_v 7 channel inhibitors and by the GC inhibitor ODQ but preserved when K_v 1.5 channels were inhibited. Additionally, DEA-NO enhanced K_v 7.5 currents in COS7 cells expressing the KCNQ5 gene. Riociguat increased K_v currents at all potentials ≥-40 mV and induced membrane hyperpolarization. Both effects were prevented by K_v 7 inhibition. Likewise, PA relaxation induced by NO donors and riociguat was attenuated by K_v 7 inhibitors.

CONCLUSIONS AND IMPLICATIONS

NO donors and riociguat enhance K_v 7 currents, leading to PASMC hyperpolarization. This mechanism contributes to NO/cGMP-induced PA vasodilation. Our study identifies K_v 7 channels as a novel mechanism of action of vasodilator drugs used in the treatment of pulmonary arterial hypertension.

Marked Vascular Dysfunction in a Case of Peripartum Cardiomyopathy

Peripartum cardiomyopathy (PPCM) is a rare form of congestive heart failure characterized by left ventricular dysfunction that develops towards the end of pregnancy or during the early postpartum phase. Even though the majority of PPCM patients show partial or complete recovery of their heart functions, the mortality rate of PPCM remains high. Previous research has suggested that vascular dysfunction triggered by late-gestational hormones and potent anti-angiogenic factors play key roles in the pathogenesis of PPCM; however, the exact mechanisms remain elusive due to limited patient tissues for characterization. Here, we report a case of PPCM where the coronary vessels from the patient's explanted heart showed marked vascular dysfunction with impaired nitric oxide response. Importantly, these vessels exhibited deficient adenosine-mediated vasorelaxation when subjected to myograph studies, suggesting impaired Kv7 ion channels. Results from this work may lead to new therapeutic strategies for improving Kv7 function in PPCM patients.

Pharmacology and clinical applications of flupirtine: Current and future options

Flupirtine is the first representative in a class of triaminopyridines that exhibits pharmacological properties leading to the suppression of over-excitability of neuronal and non-neuronal cells. Consequently, this drug has been used as a centrally acting analgesic in patients with a range of acute and persistent pain conditions without the adverse effects characteristic of opioids and non-steroidal anti-inflammatory drug and is well tolerated. The pharmacological profile exhibited involves actions on several cellular targets, including Kv7 channels, G-protein-regulated inwardly rectifying K channels and γ-aminobutyric acid type A receptors, but also there is evidence of additional as yet unidentified mechanisms of action involved in the effects of flupirtine. Flupirtine has exhibited effects in a range of cells and tissues related to the locations of these targets. In additional to analgesia, flupirtine has demonstrated pharmacological properties consistent with use as an anticonvulsant, a neuroprotectant, skeletal and smooth muscle relaxant, in treatment of auditory and visual disorders, and treatment of memory and cognitive impairment. Flupirtine is providing important information and clues regarding novel mechanistic approaches to the treatment of a range of clinical conditions involving hyper-excitability of cells. Identification of molecules exhibiting specificity for the pharmacological targets (e.g., Kv7 isoforms) involved in the actions of flupirtine will provide further insight into clinical applications. Whether the broad-spectrum pharmacology of flupirtine or target-specific actions is preferential to gain benefit, especially in complex clinical conditions, requires further investigation. This review will consider recent advancement in understanding of the pharmacological profile and related clinical applications of flupirtine.

KV channels and the regulation of vascular smooth muscle tone

VSMCs in resistance arteries and arterioles express a diverse array of K_V channels with members of the K_V 1, K_V 2 and K_V 7 families being particularly important. Members of the K_V channel family: (i) are highly expressed in VSMCs; (ii) are active at the resting membrane potential of VSMCs in vivo (-45 to -30 mV); (iii) contribute to the negative feedback regulation of VSMC membrane potential and myogenic tone; (iv) are activated by cAMP-related vasodilators, hydrogen sulfide and hydrogen peroxide; (v) are inhibited by increases in intracellular Ca²⁺ and vasoconstrictors that signal through G_q -coupled receptors; (vi) are involved in the proliferative phenotype of VSMCs; and (vii) are modulated by diseases such as hypertension, obesity, the metabolic syndrome and diabetes. Thus, K_V channels participate in every aspect of the regulation of VSMC function in both health and disease.

Kv7 potassium channels as signal transduction intermediates in the control of microvascular tone

Potassium channels are recognized as important regulators of cellular functions in most, if not all cell types. These cellular proteins assemble to form gated pores in the plasma membrane, which serve to regulate the flow of potassium ions (K⁺ ) from the cytosol to the extracellular space. In VSMCs, the open state of potassium channels enables the efflux of K⁺ and thereby establishes a negative resting voltage across the plasma membrane that inhibits the opening of VSCCs. Under these conditions, cytosolic Ca²⁺ concentrations are relatively low and Ca²⁺ -dependent contraction is inhibited. Recent research has identified Kv7 family potassium channels as important contributors to resting membrane voltage in VSMCs, with much of the research focusing on the effects of drugs that specifically activate or block these channels to produce corresponding effects on VSMC contraction and vascular tone. Increasingly, evidence is emerging that these channels are not just good drug targets-they are also essential intermediates in vascular signal transduction, mediating vasoconstrictor or vasodilator responses to a variety of physiological stimuli. This review will summarize recent research findings that support a crucial function of Kv7 channels in both positive (vasoconstrictive) and negative (vasorelaxant) regulation of microvascular tone.

Contribution of BKCa channels to vascular tone regulation by PDE3 and PDE4 is lost in heart failure

Aims

Regulation of vascular tone by 3′,5′-cyclic adenosine monophosphate (cAMP) involves many effectors including the large conductance, Ca2+-activated, K+ (BKCa) channels. In arteries, cAMP is mainly hydrolyzed by type 3 and 4 phosphodiesterases (PDE3, PDE4). Here, we examined the specific contribution of BKCa channels to tone regulation by these PDEs in rat coronary arteries, and how this is altered in heart failure (HF).

Methods and results

Concomitant application of PDE3 (cilostamide) and PDE4 (Ro-20-1724) inhibitors increased BKCa unitary channel activity in isolated myocytes from rat coronary arteries. Myography was conducted in isolated, U46619-contracted coronary arteries. Cilostamide (Cil) or Ro-20-1724 induced a vasorelaxation that was greatly reduced by iberiotoxin (IBTX), a BKCa channel blocker. Ro-20-1724 and Cil potentiated the relaxation induced by the β-adrenergic agonist isoprenaline (ISO) or the adenylyl cyclase activator L-858051 (L85). IBTX abolished the effect of PDE inhibitors on ISO but did not on L85. In coronary arteries from rats with HF induced by aortic stenosis, contractility and response to acetylcholine were dramatically reduced compared with arteries from sham rats, but relaxation to PDE inhibitors was retained. Interestingly, however, IBTX had no effect on Ro-20-1724- and Cil-induced vasorelaxations in HF. Expression of the BKCa channel α-subunit, of a 98 kDa PDE3A and of a 80 kDa PDE4D were lower in HF compared with sham coronary arteries, while that of a 70 kDa PDE4B was increased. Proximity ligation assays demonstrated that PDE3 and PDE4 were localized in the vicinity of the channel.

Conclusion

BKCa channels mediate the relaxation of coronary artery induced by PDE3 and PDE4 inhibition. This is achieved by co-localization of both PDEs with BKCa channels, enabling tight control of cAMP available for channel opening. Contribution of the channel is prominent at rest and on β-adrenergic stimulation. This coupling is lost in HF.

The expression and function of KCNQ potassium channels in human chorionic plate arteries from women with normal pregnancies and pre-eclampsia

Pre-eclampsia is associated with altered maternal and placental vascular reactivity. Kv7 channels (encoded by KCNQ 1–5 genes) are a potential contributor to the regulation of vascular tone in CPAs (chorionic plate arteries) during normal pregnancy. The aim of this study is to establish the expression profile of KCNQ subunits in CPAs taken from women with preeclampsia or normotensive women and to examine the functional relevance of the Kv7 channels on an altered expression profile of KCNQ subunits. The effects of Kv7 channel modulators on CPAs were investigated by tension measurement. Quantitative PCR experiments were used to analyze the expression of KCNQ genes. Western blotting and immunofluorescence were both used to analyze the protein expression of Kv7 channels. Finally, in CPAs from normotensive women, the Kv7 channel blocker XE991 increased arterial basal tone and U46619-induced contraction, and pre-contracted CPAs (10⁻⁷ M U46619) exhibited significant relaxation following treatment with Retigabine(Kv7.2–7.5 activator) and BMS-204352(Kv7.2–7.5 activator). However, ICA-27243(selective KCNQ2 and KCNQ3 activator) and ML277(selective KV7.1 activator) had no significant effect on tension in the pre-contracted CPAs. Conversely, compared with CPAs from normotensive women, the effects of XE991 on basal tone and agonist (U46619)-induced contractions in CPAs from women with preeclampsia were markedly attenuated. Moreover, the relaxation effects of Retigabine and BMS-204352 on pre-contracted CPA vessels from women with pre-eclampsia were also markedly down-regulated. Interestingly, the relaxation ability of ICA-27243 in pre-contracted CPA vessels in women with pre-eclampsia was enhanced. The mRNA of KCNQ3 was specifically up-regulated, whereas those for KCNQ4 and KCNQ5 were down-regulated in CPAs from women with pre-eclampsia compared with those in normotensive women. Similar observations were found in a subsequent analysis of protein expression of KCNQ genes 3–5. Thus, down-regulated Kv7 channel function in tension regulation of CPAs in women with pre-eclampsia could be associated with considerably altered expression profiles of Kv7 subunits.

Regulation of voltage-gated potassium channels in vascular smooth muscle during hypertension and metabolic disorders

Voltage-gated potassium (KV ) channels are key regulators of vascular smooth muscle contractility and vascular tone, and thus have major influence on the microcirculation. KV channels are important determinants of vascular smooth muscle membrane potential (Em ). A number of KV subunits are expressed in the plasma membrane of smooth muscle cells. Each subunit confers distinct kinetics and regulatory properties that allow for fine control of Em to orchestrate vascular tone. Modifications in KV subunit expression and/or channel activity can contribute to changes in vascular smooth muscle contractility in response to different stimuli and in diverse pathological conditions. Consistent with this, a number of studies suggest alterations in KV subunit expression and/or function as underlying contributing mechanisms for small resistance artery dysfunction in pathologies such as hypertension and metabolic disorders, including diabetes. Here, we review our current knowledge on the effects of these pathologies on KV channel expression and function in vascular smooth muscle cells, and the repercussions on (micro)vascular function.

Microtubule Regulation of Kv7 Channels Orchestrates cAMP-Mediated Vasorelaxations in Rat Arterial Smooth Muscle

Microtubules can regulate GPCR (G protein-coupled receptor) signaling in various cell types. In vascular smooth muscle, activation of the β-adrenoceptor leads to production of cAMP to mediate a vasorelaxation. Little is known about the role of microtubules in smooth muscle, and given the importance of this pathway in vascular smooth muscle cells, we investigated the role of microtubule stability on β-adrenoceptor signaling in rat renal and mesenteric arteries. In isometric tension experiments, incubation with the microtubule inhibitors colchicine and nocodazole enhanced isoprenaline-mediated relaxations of renal and mesenteric arteries that the microtubule stabilizer, paclitaxel, prevented. Sharp microelectrode experiments showed that colchicine treatment caused increased hyperpolarization of mesenteric artery segments in response to isoprenaline. Application of the Kv7 channel blocker, XE991, attenuated the effect of colchicine on isoprenaline relaxations, whereas iberiotoxin-a BKCa channel blocker-had no effect. In addition, colchicine improved the relaxations to the Kv7.2 to 7.5 activator, S-1, in both renal and mesenteric artery segments compared with dimethyl sulfoxide incubation. We determined that increased mesenteric artery myocytes treated with colchicine showed increased Kv7.4 membrane expression, but Western blot analysis showed no change in total Kv7.4 protein. This study is the first to show microtubule disruption improves the β-adrenoceptor-mediated relaxations of mesenteric and renal arteries and determine this enhancement to be because of increased membrane expression of the Kv7 voltage-gated potassium channels.

The Kv7 Channel and Cardiovascular Risk Factors

Potassium channels play a pivotal role in the regulation of excitability in cells such as neurons, cardiac myocytes, and vascular smooth muscle cells. The KCNQ (Kv7) family of voltage-activated K⁺ channels hyperpolarizes the cell and stabilizes the membrane potential. Here, we outline how Kv7 channel activity may contribute to the development of the cardiovascular risk factors such as hypertension, diabetes, and obesity. Questions and hypotheses regarding previous and future research have been raised. Alterations in the Kv7 channel may contribute to the development of cardiovascular disease (CVD). Pharmacological modification of Kv7 channels may represent a possible treatment for CVD in the future.

Downregulation of KCNQ5 expression in the rat pulmonary vasculature of nitrofen-induced congenital diaphragmatic hernia

PURPOSE

Pulmonary hypertension (PH) is a common complication of congenital diaphragmatic hernia (CDH). Voltage-gated potassium channels KCNQ1, KCNQ4, and KCNQ5 are expressed by rodent pulmonary artery smooth muscle cells, contributing to their vascular tone. We hypothesized that KCNQ1, KCNQ4, and KCNQ5 expression is altered in the pulmonary vasculature of nitrofen-induced CDH rats.

METHODS

After ethical approval (REC913b), time-pregnant rats received nitrofen or vehicle on gestational day (D)9. D21 fetuses were divided into CDH and control group (n=22). QRT-PCR and western blotting were performed to determine gene and protein expression of KCNQ1, KCNQ4, and KCNQ5. Confocal microscopy was used to detect these proteins in the pulmonary vasculature.

RESULTS

Relative mRNA level of KCNQ5 (p=0.025) was significantly downregulated in CDH lungs compared to controls. KCNQ1 (p=0.052) and KCNQ4 (p=0.574) expression was not altered. Western blotting confirmed the decreased pulmonary KCNQ5 protein expression in CDH lungs. Confocal-microscopy detected a markedly diminished KCNQ5 expression in pulmonary vasculature of CDH fetuses.

CONCLUSIONS

Downregulated pulmonary expression of KCNQ5 in CDH lungs suggests that this potassium channel may play an important role in the development of PH in this model. KCNQ5 channel activator drugs may be a potential therapeutic target for the treatment of PH in CDH.

LEVEL OF EVIDENCE

2b (Centre for Evidence-Based Medicine, Oxford).

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

Expressions of adenosine A2A receptors in coronary arteries and peripheral blood mononuclear cells are correlated in coronary artery disease patients

BACKGROUND

Altered coronary blood flow occurs in patients with coronary artery disease (CAD). Adenosine strongly impacts blood flow mostly via adenosine A_2A receptor (A_2AR) expressed in coronary tissues. As part of a systemic regulation of the adenosinergic system, we compared A_2AR expression in situ, and on peripheral blood mononuclear cells (PBMC) in CAD patients.

METHODS AND RESULTS

Aortic and coronary tissues, and PBMC were sampled in 20 CAD patients undergoing coronary artery bypass surgery and consecutively included. Controls were PBMC obtained from 15 healthy subjects. Expression and activity of A_2AR were studied by Western blotting and cAMP measurement, respectively. A_2AR expression on PBMC was lower in patients than in controls (0.83±0.31 vs 1.2±0.35 arbitrary units; p<0.01), and correlated with A_2AR expression in coronary and aortic tissues (Pearson's r: 0.77 and 0.59, p<0.01, respectively). Basal and maximal cAMP productions following agonist stimulation of PBMC were significantly lower in patients than in controls (120±42 vs 191±65 and 360±113 vs 560±215pg/10⁶ cells, p<0.05, respectively). In CAD patients, the increase from basal to maximal cAMP production in PBMC and aortic tissues was similar (+300% and +246%, respectively).

CONCLUSION

Expression of A_2AR on PBMC correlated with those measured in coronary artery and aortic tissues in CAD patients, A_2AR activity of PBMC matched that observed in aorta, and A_2AR expression and activity in PBMC were found reduced as compared to controls. Measuring the expression level of A_2AR on PBMC represents a good tool to address in situ expression in coronary tissues of CAD patients.

Do KV 7.1 channels contribute to control of arterial vascular tone?

BACKGROUND AND PURPOSE

K_V 7.1 voltage-gated potassium channels are expressed in vascular smooth muscle cells (VSMC) of diverse arteries, including mesenteric arteries. Based on pharmacological evidence using R-L3 (K_V 7.1 channel opener), HMR1556, chromanol 293B (K_V 7.1 channel blockers), stimulation of these channels has been suggested to evoke profound relaxation in various vascular beds of rats. However, the specificity of these drugs in vivo is uncertain.

EXPERIMENTAL APPROACH

We used Kcnq1^-/- mice and pharmacological tools to determine whether K_V 7.1 channels play a role in the regulation of arterial tone.

KEY RESULTS

R-L3 produced similar concentration-dependent relaxations (EC₅₀  ~ 1.4 μM) of arteries from wild-type (Kcnq1^+/+ ) and Kcnq1^-/- mice, pre-contracted with either phenylephrine or 60 mM KCl. This relaxation was not affected by 10 μM chromanol 293B, 10 μM HMR1556 or 30 μM XE991 (pan-K_V 7 channel blocker). The anti-contractile effects of the perivascular adipose tissue (PVAT) were normal in Kcnq1^-/- arteries. Chromanol 293B and HMR1556 did not affect the anti-contractile effects of (PVAT). Isolated VSMCs from Kcnq1^-/- mice exhibited normal peak K_V currents. The K_V 7.2-5 channel opener retigabine caused similar relaxations in Kcnq1^-/- and wild-type vessels.

CONCLUSION AND IMPLICATIONS

We conclude that K_V 7.1 channels were apparently not involved in the control of arterial tone by α₁ -adrenoceptor agonists and PVAT. In addition, R-L3 is an inappropriate pharmacological tool for studying the function of native vascular K_V 7.1 channels in mice.

Kv7 Channel Activation Underpins EPAC-Dependent Relaxations of Rat Arteries

OBJECTIVE

To establish the role of Kv7 channels in EPAC (exchange protein directly activated by cAMP)-dependent relaxations of the rat vasculature and to investigate whether this contributes to β-adrenoceptor-mediated vasorelaxations.

APPROACH AND RESULTS

Isolated rat renal and mesenteric arteries (RA and MA, respectively) were used for isometric tension recording to study the relaxant effects of a specific EPAC activator and the β-adrenoceptor agonist isoproterenol in the presence of potassium channel inhibitors and cell signaling modulators. Isolated myocytes were used in proximity ligation assay studies to detect localization of signaling intermediaries with Kv7.4 before and after cell stimulation. Our studies showed that the EPAC activator (8-pCPT-2Me-cAMP-AM) produced relaxations and enhanced currents of MA and RA that were sensitive to linopirdine (Kv7 inhibitor). Linopirdine also inhibited isoproterenol-mediated relaxations in both RA and MA. In the MA, isoproterenol relaxations were sensitive to EPAC inhibition, but not protein kinase A inhibition. In contrast, isoproterenol relaxations in RA were attenuated by protein kinase A but not by EPAC inhibition. Proximity ligation assay showed a localization of Kv7.4 with A-kinase anchoring protein in both vessels in the basal state, which increased only in the RA with isoproterenol stimulation. In the MA, but not the RA, a localization of Kv7.4 with both Rap1a and Rap2 (downstream of EPAC) increased with isoproterenol stimulation.

CONCLUSIONS

EPAC-dependent vasorelaxations occur in part via activation of Kv7 channels. This contributes to the isoproterenol-mediated relaxation in mesenteric, but not renal, arteries.

Treatment of Serpiginous Choroiditis with Chlorambucil: A Report of 17 Patients

PURPOSE

To evaluate the efficacy of chlorambucil in the treatment of serpiginous choroiditis.

METHODS

Patient records from the Massachusetts Eye Research and Surgery Institution (MERSI) were reviewed from over the past 10 years. In total, 17 patients with the diagnosis of serpiginous choroiditis treated with chlorambucil were identified. QuantiFERON gold was negative in all of them. Chlorambucil was started at 0.15 mg/kg and dosage was titrated up using weekly white blood cell (WBC) count to achieve a target cell number of 3.0-4.5 × 10⁹ cells/L. The goal of therapy was to maintain this value for at least 6-9 months. Adverse effects, recurrence, rate of new choroidal neovascularization (CNVM), and visual acuity before and after treatment were recorded.

RESULTS

The mean age of the 17 patients with the diagnosis of serpiginous choroiditis treated with chlorambucil was 46 years, and six patients (35%) were male. The mean duration of treatment for chlorambucil was 8.4 months. None of them developed cancer or persistent side-effects, with a mean follow-up of 53 months. Of the patients, 12 (71%) achieved an average of 45 (5-120) months drug-free remission in their last follow-up. Visual acuity of 33 treated eyes remained within two lines of Snellen acuity in 27 eyes (82%), improved in one eye (3%), and deteriorated in five eyes (15%). Leukopenia was the most common side-effect, which was reversible in all cases.

CONCLUSIONS

Chlorambucil in a relatively short duration of time, with an escalating dose guided by weekly WBC was well tolerated, as well as effective in preventing recurrence and maintaining vision in patients with serpiginous choroiditis.

Kcne4 Deletion Sex-Dependently Alters Vascular Reactivity

Voltage-gated potassium (Kv) channels formed by Kv7 (KCNQ) α-subunits are recognized as crucial for vascular smooth muscle function, in addition to their established roles in the heart (Kv7.1) and the brain (Kv7.2-5). In vivo, Kv7 α-subunits are often regulated by KCNE subfamily ancillary (β) subunits. We investigated the effects of targeted germline Kcne4 deletion on mesenteric artery reactivity in adult male and female mice. Kcne4 deletion increased mesenteric artery contractility in response to α-adrenoceptor agonist methoxamine, and decreased responses to Kv7.2-7.5 channel activator ML213, in male but not female mice. In contrast, Kcne4 deletion markedly decreased vasorelaxation in response to isoprenaline in both male and female mice. Kcne4 expression was 2-fold lower in the female versus the male mouse mesenteric artery, and Kcne4 deletion elicited only moderate changes of other Kcne transcripts, with no striking sex-specific differences. However, Kv7.4 protein expression in females was twice that in males, and was reduced in both sexes by Kcne4 deletion. Our findings confirm a crucial role for KCNE4 in regulation of Kv7 channel activity to modulate vascular tone, and provide the first known molecular mechanism for sex-specificity of this modulation that has important implications for vascular reactivity and may underlie sex-specific susceptibility to cardiovascular diseases.

Vascular smooth muscle cell dysfunction in diabetes: nuclear receptors channel to relaxation

Endothelial dysfunction and impaired vascular relaxation represent a common cause of microvascular disease in patients with diabetes. Although multiple mechanisms underlying altered endothelial cell function in diabetes have been described, there is currently no specific and approved pharmacological treatment. In this edition of Clinical Science, Morales-Cano et al. characterize voltage-dependent K+ (Kv) channels as genes regulated by pharmacological activation of peroxisome proliferator-activated receptor-b/d (PPARb/d). Diabetes altered Kv channel function leading to impaired coronary artery relaxation, which was prevented by pharmacological activation of PPARb/d. These studies highlight an important mechanism of vascular dysfunction in diabetes and point to a potential approach for therapy, particularly considering that PPARb/d ligands have been developed and tested in small clinical trials.

Potassium Channels in Regulation of Vascular Smooth Muscle Contraction and Growth

Potassium channels importantly contribute to the regulation of vascular smooth muscle (VSM) contraction and growth. They are the dominant ion conductance of the VSM cell membrane and importantly determine and regulate membrane potential. Membrane potential, in turn, regulates the open-state probability of voltage-gated Ca²⁺ channels (VGCC), Ca²⁺ influx through VGCC, intracellular Ca²⁺, and VSM contraction. Membrane potential also affects release of Ca²⁺ from internal stores and the Ca²⁺ sensitivity of the contractile machinery such that K⁺ channels participate in all aspects of regulation of VSM contraction. Potassium channels also regulate proliferation of VSM cells through membrane potential-dependent and membrane potential-independent mechanisms. VSM cells express multiple isoforms of at least five classes of K⁺ channels that contribute to the regulation of contraction and cell proliferation (growth). This review will examine the structure, expression, and function of large conductance, Ca²⁺-activated K⁺ (BK_Ca) channels, intermediate-conductance Ca²⁺-activated K⁺ (K_Ca3.1) channels, multiple isoforms of voltage-gated K⁺ (K_V) channels, ATP-sensitive K⁺ (K_ATP) channels, and inward-rectifier K⁺ (K_IR) channels in both contractile and proliferating VSM cells.

Critical contribution of KV1 channels to the regulation of coronary blood flow

Ion channels in smooth muscle control coronary vascular tone, but the identity of the potassium channels involved requires further investigation. The purpose of this study was to evaluate the functional role of KV1 channels on porcine coronary blood flow using the selective antagonist correolide. KV1 channel gene transcripts were found in porcine coronary arteries, with KCNA5 (encoding KV1.5) being most abundant (P < 0.001). Immunohistochemical staining demonstrated KV1.5 protein in the vascular smooth muscle layer of both porcine and human coronary arteries, including microvessels. Whole-cell patch-clamp experiments demonstrated significant correolide-sensitive (1-10 µM) current in coronary smooth muscle. In vivo studies included direct intracoronary infusion of vehicle or correolide into a pressure-clamped left anterior descending artery of healthy swine (n = 5 in each group) with simultaneous measurement of coronary blood flow. Intracoronary correolide (~0.3-3 µM targeted plasma concentration) had no effect on heart rate or systemic pressure, but reduced coronary blood flow in a dose-dependent manner (P < 0.05). Dobutamine (0.3-10 µg/kg/min) elicited coronary metabolic vasodilation and intracoronary correolide (3 µM) significantly reduced coronary blood flow at any given level of myocardial oxygen consumption (P < 0.001). Coronary artery occlusions (15 s) elicited reactive hyperemia and correolide (3 µM) reduced the flow volume repayment by approximately 30 % (P < 0.05). Taken together, these data support a major role for KV1 channels in modulating baseline coronary vascular tone and, perhaps, vasodilation in response to increased metabolism and transient ischemia.

The Role of DPO-1 and XE991-Sensitive Potassium Channels in Perivascular Adipose Tissue-Mediated Regulation of Vascular Tone

The anti-contractile effect of perivascular adipose tissue (PVAT) is an important mechanism in the modulation of vascular tone in peripheral arteries. Recent evidence has implicated the XE991-sensitive voltage-gated KV (KCNQ) channels in the regulation of arterial tone by PVAT. However, until now the in vivo pharmacology of the involved vascular KV channels with regard to XE991 remains undetermined, since XE991 effects may involve Ca(2+) activated BKCa channels and/or voltage-dependent KV1.5 channels sensitive to diphenyl phosphine oxide-1 (DPO-1). In this study, we tested whether KV1.5 channels are involved in the control of mesenteric arterial tone and its regulation by PVAT. Our study was also aimed at extending our current knowledge on the in situ vascular pharmacology of DPO-1 and XE991 regarding KV1.5 and BKCa channels, in helping to identify the nature of K(+) channels that could contribute to PVAT-mediated relaxation. XE991 at 30 μM reduced the anti-contractile response of PVAT, but had no effects on vasocontraction induced by phenylephrine (PE) in the absence of PVAT. Similar effects were observed for XE991 at 0.3 μM, which is known to almost completely inhibit mesenteric artery VSMC KV currents. 30 μM XE991 did not affect BKCa currents in VSMCs. Kcna5 (-/-) arteries and wild-type arteries incubated with 1 μM DPO-1 showed normal vasocontractions in response to PE in the presence and absence of PVAT. KV current density and inhibition by 30 μM XE991 were normal in mesenteric artery VSMCs isolated from Kcna5 (-/-) mice. We conclude that KV channels are involved in the control of arterial vascular tone by PVAT. These channels are present in VSMCs and very potently inhibited by the KCNQ channel blocker XE991. BKCa channels and/or DPO-1 sensitive KV1.5 channels in VSMCs are not the downstream mediators of the XE991 effects on PVAT-dependent arterial vasorelaxation. Further studies will need to be undertaken to examine the role of other KV channels in the phenomenon.

Activation of PPARβ/δ prevents hyperglycaemia-induced impairment of Kv7 channels and cAMP-mediated relaxation in rat coronary arteries

PPARβ/δ activation protects against endothelial dysfunction in diabetic models. Elevated glucose is known to impair cAMP-induced relaxation and Kv channel function in coronary arteries (CA). Herein, we aimed to analyse the possible protective effects of the PPARβ/δ agonist GW0742 on the hyperglycaemic-induced impairment of cAMP-induced relaxation and Kv channel function in rat CA. As compared with low glucose (LG), incubation under high glucose (HG) conditions attenuated the relaxation induced by the adenylate cyclase activator forskolin in CA and this was prevented by GW0742. The protective effect of GW0742 was supressed by a PPARβ/δ antagonist. In myocytes isolated from CA under LG, forskolin enhanced Kv currents and induced hyperpolarization. In contrast, when CA were incubated with HG, Kv currents were diminished and the electrophysiological effects of forskolin were abolished. These deleterious effects were prevented by GW0742. The protective effects of GW0742 on forskolin-induced relaxation and Kv channel function were confirmed in CA from type-1 diabetic rats. In addition, the differences in the relaxation induced by forskolin in CA incubated under LG, HG or HG + GW0742 were abolished by the Kv7 channel inhibitor XE991. Accordingly, GW0742 prevented the down-regulation of Kv7 channels induced by HG. Finally, the preventive effect of GW0742 on oxidative stress and cAMP-induced relaxation were overcome by the pyruvate dehydrogenase kinase 4 (PDK4) inhibitor dichloroacetate (DCA). Our results reveal that the PPARβ/δ agonist GW0742 prevents the impairment of the cAMP-mediated relaxation in CA under HG. This protective effect was associated with induction of PDK4, attenuation of oxidative stress and preservation of Kv7 channel function.