Contribution of Kv7 channels to natriuretic peptide mediated vasodilation in normal and hypertensive rats

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.

KCNQ5 Controls Perivascular Adipose Tissue-Mediated Vasodilation

BACKGROUND

Small arteries exhibit resting tone, a partially contracted state that maintains arterial blood pressure. In arterial smooth muscle cells, potassium channels control contraction and relaxation. Perivascular adipose tissue (PVAT) has been shown to exert anticontractile effects on the blood vessels. However, the mechanisms by which PVAT signals small arteries, and their relevance remain largely unknown. We aimed to uncover key molecular components in adipose-vascular coupling.

METHODS

A wide spectrum of genetic mouse models targeting Kcnq3, Kcnq4, and Kcnq5 genes (Kcnq3-/-, Kcnq4-/-, Kcnq5-/-, Kcnq5dn/dn, Kcnq4-/-/Kcnq5dn/dn, and Kcnq4-/-/Kcnq5-/-), telemetry blood pressure measurements, targeted lipidomics, RNA-Seq profiling, wire-myography, patch-clamp, and sharp-electrode membrane potential measurements was used.

RESULTS

We show that PVAT causes smooth muscle cell KV7.5 family of voltage-gated potassium (K+) channels to hyperpolarize the membrane potential. This effect relaxes small arteries and regulates blood pressure. Oxygenation of polyunsaturated fats generates oxylipins, a superclass of lipid mediators. We identified numerous oxylipins released by PVAT, which potentiate vasodilatory action in small arteries by opening smooth muscle cell KV7.5 family of voltage-gated potassium (K+) channels.

CONCLUSIONS

Our results reveal a key molecular function of the KV7.5 family of voltage-gated potassium (K+) channels in the adipose-vascular coupling, translating PVAT signals, particularly oxylipins, to the central physiological function of vasoregulation. This novel pathway opens new therapeutic perspectives.

Cycling matters: Sex hormone regulation of vascular potassium channels

Sex hormones and the reproductive cycle (estrus in rodents and menstrual in humans) have a known impact on arterial function. In spite of this, sex hormones and the estrus/menstrual cycle are often neglected experimental factors in vascular basic preclinical scientific research. Recent research by our own laboratory indicates that cyclical changes in serum concentrations of sex -hormones across the rat estrus cycle, primary estradiol, have significant consequences for the subcellular trafficking and function of KV. Vascular potassium channels, including KV, are essential components of vascular reactivity. Our study represents a small part of a growing field of literature aimed at determining the role of sex hormones in regulating arterial ion channel function. This review covers key findings describing the current understanding of sex hormone regulation of vascular potassium channels, with a focus on KV channels. Further, we highlight areas of research where the estrus cycle should be considered in future studies to determine the consequences of physiological oscillations in concentrations of sex hormones on vascular potassium channel function.

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.

The novel KV7 channel activator URO-K10 exerts enhanced pulmonary vascular effects independent of the KCNE4 regulatory subunit

KV7 channels exert a pivotal role regulating vascular tone in several vascular beds. In this context, KV7 channel agonists represent an attractive strategy for the treatment of pulmonary arterial hypertension (PAH). Therefore, in this study, we have explored the pulmonary vascular effects of the novel KV7 channel agonist URO-K10. Consequently, the vasodilator and electrophysiological effects of URO-K10 were tested in rat and human pulmonary arteries (PA) and PA smooth muscle cells (PASMC) using myography and patch-clamp techniques. Protein expression was also determined by Western blot. Morpholino-induced knockdown of KCNE4 was assessed in isolated PA. PASMC proliferation was measured by BrdU incorporation assay. In summary, our data show that URO-K10 is a more effective relaxant of PA than the classical KV7 activators retigabine and flupirtine. URO-K10 enhanced KV currents in PASMC and its electrophysiological and relaxant effects were inhibited by the KV7 channel blocker XE991. The effects of URO-K10 were confirmed in human PA. URO-K10 also exhibited antiproliferative effects in human PASMC. Unlike retigabine and flupirtine, URO-K10-induced pulmonary vasodilation was not affected by morpholino-induced knockdown of the KCNE4 regulatory subunit. Noteworthy, the pulmonary vasodilator efficacy of this compound was considerably increased under conditions mimicking the ionic remodelling (as an in vitro model of PAH) and in PA from monocrotaline-induced pulmonary hypertensive rats. Taking all together, URO-K10 behaves as a KCNE4-independent KV7 channel activator with much increased pulmonary vascular effects compared to classical KV7 channel activators. Our study identifies a promising new drug in the context of PAH.

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.

Marked oestrous cycle-dependent regulation of rat arterial KV 7.4 channels driven by GPER1

BACKGROUND AND PURPOSE

Kcnq-encoded KV 7 channels (termed KV 7.1-5) regulate vascular smooth muscle cell (VSMC) contractility at rest and as targets of receptor-mediated responses. However, the current data are mostly derived from males. Considering the known effects of sex, the oestrous cycle and sex hormones on vascular reactivity, here we have characterised the molecular and functional properties of KV 7 channels from renal and mesenteric arteries from female Wistar rats separated into di-oestrus and met-oestrus (F-D/M) and pro-oestrus and oestrus (F-P/E).

EXPERIMENTAL APPROACH

RT-qPCR, immunocytochemistry, proximity ligation assay and wire myography were performed in renal and mesenteric arteries. Circulating sex hormone concentrations were determined by liquid chromatography-tandem mass spectrometry. Whole-cell electrophysiology was undertaken on cells expressing KV 7.4 channels in association with G-protein-coupled oestrogen receptor 1 (GPER1).

KEY RESULTS

The KV 7.2-5 activators S-1 and ML213 and the pan-KV 7 inhibitor linopirdine were more effective in arteries from F-D/M compared with F-P/E animals. In VSMCs isolated from F-P/E rats, exploratory evidence indicates reduced membrane abundance of KV 7.4 but not KV 7.1, KV 7.5 and Kcne4 when compared with cells from F-D/M. Plasma oestradiol was higher in F-P/E compared with F-D/M, and progesterone showed the converse pattern. Oestradiol/GPER1 agonist G-1 diminished KV 7.4 encoded currents and ML213 relaxations and reduced the membrane abundance of KV 7.4 and interaction between KV 7.4 and heat shock protein 90 (HSP90), in arteries from F-D/M but not F-P/E.

CONCLUSIONS AND IMPLICATIONS

GPER1 signalling decreased KV 7.4 membrane abundance in conjunction with diminished interaction with HSP90, giving rise to a 'pro-contractile state'.

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.

Dynein Coordinates β2-Adrenoceptor-Mediated Relaxation in Normotensive and Hypertensive Rat Mesenteric Arteries

BACKGROUND

The voltage-gated potassium channel (Kv)7.4 and Kv7.5 channels contribute to the β-adrenoceptor-mediated vasodilatation. In arteries from hypertensive rodents, the Kv7.4 channel is downregulated and function attenuated, which contributes to the reduced β-adrenoceptor-mediated vasodilatation observed in these arteries. Recently, we showed that disruption of the microtubule network, with colchicine, or inhibition of the microtubule motor protein, dynein, with ciliobrevin D, enhanced the membrane abundance and function of Kv7.4 channels in rat mesenteric arteries. This study aimed to determine whether these pharmacological compounds can improve Kv7.4 function in third-order mesenteric arteries from the spontaneously hypertensive rat, thereby restoring the β-adrenoceptor-mediated vasodilatation.

METHODS

Wire and intravital myography was performed on normotensive and hypertensive male rat mesenteric arteries and immunostaining was performed on isolated smooth muscle cells from the same arteries.

RESULTS

Using wire and intravital microscopy, we show that ciliobrevin D enhanced the β-adrenoceptor-mediated vasodilatation by isoprenaline. This effect was inhibited partially by the Kv7 channel blocker linopirdine and was dependent on an increased functional contribution of the β2-adrenoceptor to the isoprenaline-mediated relaxation. In mesenteric arteries from the spontaneously hypertensive rat, ciliobrevin D and colchicine both improved the isoprenaline-mediated vasorelaxation and relaxation to the Kv7.2 -7.5 activator, ML213. Immunostaining confirmed ciliobrevin D enhanced the membrane abundance of Kv7.4. As well as an increase in the function of Kv7.4, the functional changes were associated with an increase in the contribution of β2-adrenoceptor following isoprenaline treatment. Immunostaining experiments showed ciliobrevin D prevented isoprenaline-mediated internalizationof the β2-adrenoceptor.

CONCLUSIONS

Overall, these data show that colchicine and ciliobrevin D can induce a β2-adrenoceptor-mediated vasodilatation in arteries from the spontaneously hypertensive rat as well as reinstating Kv7.4 channel function.

Kv7 Channels in Cyclic-Nucleotide Dependent Relaxation of Rat Intra-Pulmonary Artery

Pulmonary hypertension is treated with drugs that stimulate cGMP or cAMP signalling. Both nucleotides can activate Kv7 channels, leading to smooth muscle hyperpolarisation, reduced Ca²⁺ influx and relaxation. Kv7 activation by cGMP contributes to the pulmonary vasodilator action of nitric oxide, but its contribution when dilation is evoked by the atrial natriuretic peptide (ANP) sensitive guanylate cyclase, or cAMP, is unknown. Small vessel myography was used to investigate the ability of Kv7 channel blockers to interfere with pulmonary artery relaxation when cyclic nucleotide pathways were stimulated in different ways. The pan-Kv7 blockers, linopirdine and XE991, caused substantial inhibition of relaxation evoked by NO donors and ANP, as well as endothelium-dependent dilators, the guanylate cyclase stimulator, riociguat, and the phosphodiesterase-5 inhibitor, sildenafil. Maximum relaxation was reduced without a change in sensitivity. The blockers had relatively little effect on cAMP-mediated relaxation evoked by forskolin, isoprenaline or treprostinil. The Kv7.1-selective blocker, HMR1556, had no effect on cGMP or cAMP-dependent relaxation. Western blot analysis demonstrated the presence of Kv7.1 and Kv7.4 proteins, while selective activators of Kv7.1 and Kv7.4 homomeric channels, but not Kv7.5, caused pulmonary artery relaxation. It is concluded that Kv7.4 channels contribute to endothelium-dependent dilation and the effects of drugs that act by stimulating cGMP, but not cAMP, signalling.

KV7.1 channel blockade inhibits neonatal renal autoregulation triggered by a step decrease in arterial pressure

K_V7 channels, the voltage-gated K⁺ channels encoded by KCNQ genes, mediate heterogeneous vascular responses in rodents. Postnatal changes in the functional expression of K_V7 channels have been reported in rodent saphenous arteries, but their physiological function in the neonatal renal vascular bed is unclear. Here, we report that, unlike adult pigs, only KCNQ1 (K_V7.1) out of the five members of KCNQ genes was detected in neonatal pig renal microvessels. KCNQ1 is present in fetal pig kidneys as early as day 50 of gestation, and the level of expression remains the same up to postnatal day 21. Activation of renal vascular smooth muscle cell (SMC) K_V7.1 stimulated whole cell currents, inhibited by HMR1556 (HMR), a selective K_V7.1 blocker. HMR did not change the steady-state diameter of isolated renal microvessels. Similarly, intrarenal artery infusion of HMR did not alter mean arterial pressure, renal blood flow, and renal vascular resistance in the pigs. An ∼20 mmHg reduction in mean arterial pressure evoked effective autoregulation of renal blood flow, which HMR inhibited. We conclude that 1) the expression of KCNQ isoforms in porcine renal microvessels is dependent on kidney maturation, 2) K_V7.1 is functionally expressed in neonatal pig renal vascular SMCs, 3) a decrease in arterial pressure up to 20 mmHg induces renal autoregulation in neonatal pigs, and 4) SMC K_V7.1 does not control basal renal vascular tone but contributes to neonatal renal autoregulation triggered by a step decrease in arterial pressure.NEW & NOTEWORTHY K_V7.1 is present in fetal pig kidneys as early as day 50 of gestation, and the level of expression remains the same up to postnatal day 21. K_V7.1 is functionally expressed in neonatal pig renal vascular smooth muscle cells (SMCs). A decrease in arterial pressure up to 20 mmHg induces renal autoregulation in neonatal pigs. Although SMC K_V7.1 does not control basal renal vascular resistance, its inhibition blunts neonatal renal autoregulation engendered by a step decrease in arterial pressure.

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.

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.

The Functional Availability of Arterial Kv7 Channels Is Suppressed Considerably by Large-Conductance Calcium-Activated Potassium Channels in 2- to 3-Month Old but Not in 10- to 15-Day Old Rats

Background

Voltage-gated potassium (Kv) channels, especially Kv7 channels, are major potassium channels identified in vascular smooth muscle cells with a great, albeit differential functional impact in various vessels. Vascular smooth muscle Kv7 channels always coexist with other K channels, in particular with BK channels. BK channels differ in the extent to which they influence vascular contractility. Whether this difference also causes the variability in the functional impact of Kv7 channels is unknown. Therefore, this study addressed the hypothesis that the functional impact of Kv7 channels depends on BK channels.

Experimental Approach

Experiments were performed on young and adult rat gracilis and saphenous arteries using real-time PCR as well as pressure and wire myography.

Key Results

Several subfamily members of Kv7 (KCNQ) and BK channels were expressed in saphenous and gracilis arteries: the highest expression was observed for BKα, BKβ1 and KCNQ4. Arterial contractility was assessed with methoxamine-induced contractions and pressure-induced myogenic responses. In vessels of adult rats, inhibition of Kv7 channels or BK channels by XE991 or IBTX, respectively enhanced arterial contractility to a similar degree, whereas activation of Kv7 channels or BK channels by retigabine or NS19504, respectively reduced arterial contractility to a similar degree. Further, IBTX increased both the contractile effect of XE991 and the anticontractile effect of retigabine, whereas NS19504 reduced the effect of retigabine and impaired the effect of XE991. In vessels of young rats, inhibition of Kv7 channels by XE991 enhanced arterial contractility much stronger than inhibition of BK channels by IBTX, whereas activation of Kv7 by retigabine reduced arterial contractility to a greater extent than activation of BK channels by NS19504. Further, IBTX increased the anticontractile effect of retigabine but not the contractile effect of XE991, whereas NS19504 reduced the effect of retigabine and impaired the effect of XE991.

Conclusion

Kv7 and BK channels are expressed in young and adult rat arteries and function as negative feedback modulators in the regulation of contractility of these arteries. Importantly, BK channels govern the extent of functional impact of Kv7 channels. This effect depends on the relationship between the functional activities of BK and Kv7 channels.

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.

Empagliflozin dilates the rabbit aorta by activating PKG and voltage-dependent K+ channels

We investigated the vasodilatory effects of empagliflozin (a sodium-glucose co-transporter 2 inhibitor) and the underlying mechanisms using rabbit aorta. Empagliflozin induced vasodilation in a concentration-dependent manner independently of the endothelium. Likewise, pretreatment with the nitric oxide synthase inhibitor L-NAME or the SKca inhibitor apamin together with the IKca inhibitor TRAM-34 did not impact the vasodilatory effects of empagliflozin. Pretreatment with the adenylyl cyclase inhibitor SQ22536 or a guanylyl cyclase inhibitor ODQ or a protein kinase A (PKA) inhibitor KT5720 also did not alter the vasodilatory response of empagliflozin. However, the vasodilatory effects of empagliflozin were significantly reduced by pretreatment with the protein kinase G (PKG) inhibitor KT5823. Although application of the ATP-sensitive K⁺ (K_ATP) channel inhibitor glibenclamide, large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel inhibitor paxilline, or inwardly rectifying K⁺ (Kir) channel inhibitor Ba²⁺ did not impact the vasodilatory effects of empagliflozin, pretreatment with the voltage-dependent K⁺ (Kv) channel inhibitor 4-AP reduced the vasodilatory effects of empagliflozin. Pretreatment with DPO-1 (Kv1.5 channel inhibitor), guangxitoxin (Kv2.1 channel inhibitor), or linopirdine (Kv7 channel inhibitor) had little effect on empagliflozin-induced vasodilation. Application of nifedipine (L-type Ca²⁺ channel inhibitor) or thapsigargin (sarco-endoplasmic reticulum Ca²⁺-ATPase pump inhibitor) did not impact empagliflozin-induced vasodilation. Therefore, empagliflozin induces vasodilation by activating PKG and Kv channels.

SMIT (Sodium-Myo-Inositol Transporter) 1 Regulates Arterial Contractility Through the Modulation of Vascular Kv7 Channels

Supplemental Digital Content is available in the text.

Objective:

The SMIT1 (sodium:myo-inositol transporter 1) regulates myo-inositol movement into cells and responses to hypertonic stimuli. Alteration of myo-inositol levels has been associated with several diseases, including hypertension, but there is no evidence of a functional role of SMIT1 in the vasculature. Recent evidence showed that in the nervous system SMIT1 interacted and modulated the function of members of the Kv7 family of voltage-gated potassium channels, which are also expressed in the vasculature where they regulate arterial contractility. Therefore, in this study, we evaluated whether SMIT1 was functionally relevant in arterial smooth muscle.

Approach and Results:

Immunofluorescence and polymerase chain reaction experiments revealed that SMIT1 was expressed in rat renal and mesenteric vascular smooth muscle cells. Isometric tension recordings showed that incubation of renal arteries with raffinose and myo-inositol (which increases SMIT1 expression) reduced the contractile responses to methoxamine, an effect that was abolished by preincubation with the pan-Kv7 blocker linopirdine and by molecular knockdown of Kv7.4 and Kv7.5. Knockdown of SMIT1 increased the contraction of renal arteries induced by methoxamine, impaired the response to the Kv7.2–Kv7.5 activator ML213 but did not interfere with the relaxant responses induced by openers of other potassium channels. Proximity ligation assay showed that SMIT1 interacted with heteromeric channels formed by Kv7.4 and Kv7.5 proteins in both renal and mesenteric vascular smooth muscle cells. Patch-clamp experiments showed that incubation with raffinose plus myo-inositol increased Kv7 currents in vascular smooth muscle cells.

Conclusions:

SMIT1 protein is expressed in vascular smooth muscle cells where it modulates arterial contractility through an association with Kv7.4/Kv7.5 heteromers.

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.

Kv7 Channels in Lung Diseases

Lung diseases constitute a global health concern causing disability. According to WHO in 2016, respiratory diseases accounted for 24% of world population mortality, the second cause of death after cardiovascular diseases. The Kv7 channels family is a group of voltage-dependent K⁺ channels (Kv) encoded by KCNQ genes that are involved in various physiological functions in numerous cell types, especially, cardiac myocytes, smooth muscle cells, neurons, and epithelial cells. Kv7 channel α-subunits are regulated by KCNE1–5 ancillary β-subunits, which modulate several characteristics of Kv7 channels such as biophysical properties, cell-location, channel trafficking, and pharmacological sensitivity. Kv7 channels are mainly expressed in two large groups of lung tissues: pulmonary arteries (PAs) and bronchial tubes. In PA, Kv7 channels are expressed in pulmonary artery smooth muscle cells (PASMCs); while in the airway (trachea, bronchus, and bronchioles), Kv7 channels are expressed in airway smooth muscle cells (ASMCs), airway epithelial cells (AEPs), and vagal airway C-fibers (VACFs). The functional role of Kv7 channels may vary depending on the cell type. Several studies have demonstrated that the impairment of Kv7 channel has a strong impact on pulmonary physiology contributing to the pathophysiology of different respiratory diseases such as cystic fibrosis, asthma, chronic obstructive pulmonary disease, chronic coughing, lung cancer, and pulmonary hypertension. Kv7 channels are now recognized as playing relevant physiological roles in many tissues, which have encouraged the search for Kv7 channel modulators with potential therapeutic use in many diseases including those affecting the lung. Modulation of Kv7 channels has been proposed to provide beneficial effects in a number of lung conditions. Therefore, Kv7 channel openers/enhancers or drugs acting partly through these channels have been proposed as bronchodilators, expectorants, antitussives, chemotherapeutics and pulmonary vasodilators.

GORK Channel: A Master Switch of Plant Metabolism?

Potassium regulates a plethora of metabolic and developmental response in plants, and upon exposure to biotic and abiotic stresses a substantial K⁺ loss occurs from plant cells. The outward-rectifying potassium efflux GORK channels are central to this stress-induced K⁺ loss from the cytosol. In the mammalian systems, signaling molecules such as gamma-aminobutyric acid, G-proteins, ATP, inositol, and protein phosphatases were shown to operate as ligands controlling many K⁺ efflux channels. Here we present the evidence that the same molecules may also regulate GORK channels in plants. This mechanism enables operation of the GORK channels as a master switch of the cell metabolism, thus adjusting intracellular K⁺ homeostasis to altered environmental conditions, to maximize plant adaptive potential.

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.

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.

Potassium channels in vascular smooth muscle: a pathophysiological and pharmacological perspective

Potassium (K⁺ ) ion channel activity is an important determinant of vascular tone by regulating cell membrane potential (MP). Activation of K⁺ channels leads to membrane hyperpolarization and subsequently vasodilatation, while inhibition of the channels causes membrane depolarization and then vasoconstriction. So far five distinct types of K⁺ channels have been identified in vascular smooth muscle cells (VSMCs): Ca⁺² -activated K⁺ channels (BK_{C a} ), voltage-dependent K⁺ channels (K_V ), ATP-sensitive K⁺ channels (K_ATP ), inward rectifier K⁺ channels (K_ir ), and tandem two-pore K⁺ channels (K₂ P). The activity and expression of vascular K⁺ channels are changed during major vascular diseases such as hypertension, pulmonary hypertension, hypercholesterolemia, atherosclerosis, and diabetes mellitus. The defective function of K⁺ channels is commonly associated with impaired vascular responses and is likely to become as a result of changes in K⁺ channels during vascular diseases. Increased K⁺ channel function and expression may also help to compensate for increased abnormal vascular tone. There are many pharmacological and genotypic studies which were carried out on the subtypes of K⁺ channels expressed in variable amounts in different vascular beds. Modulation of K⁺ channel activity by molecular approaches and selective drug development may be a novel treatment modality for vascular dysfunction in the future. This review presents the basic properties, physiological functions, pathophysiological, and pharmacological roles of the five major classes of K⁺ channels that have been determined in VSMCs.

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.

Perivascular adipose tissue and the dynamic regulation of Kv 7 and Kir channels: Implications for resistant hypertension

Resistant hypertension is defined as high blood pressure that remains uncontrolled despite treatment with at least three antihypertensive drugs at adequate doses. Resistant hypertension is an increasingly common clinical problem in older age, obesity, diabetes, sleep apnea, and chronic kidney disease. Although the direct vasodilator minoxidil was introduced in the early 1970s, only recently has this drug been shown to be particularly effective in a subgroup of patients with treatment-resistant or uncontrolled hypertension. This pharmacological approach is interesting from a mechanistic perspective as minoxidil is the only clinically used K⁺ channel opener today, which targets a subclass of K⁺ channels, namely K_ATP channels in VSMCs. Beside K_ATP channels, two other classes of VSMC K⁺ channels could represent novel effective targets for treatment of resistant hypertension, namely K_v 7 (KCNQ) and inward rectifier potassium (K_ir 2.1) channels. Interestingly, these channels are unique among VSMC potassium channels. First, both have been implicated in the control of microvascular tone by perivascular adipose tissue. Second, they exhibit biophysical properties strongly controlled and regulated by membrane voltage, but not intracellular calcium. This review focuses on K_v 7 (K_v 7.1-5) and K_ir (K_ir 2.1) channels in VSMCs as potential novel drug targets for treatment of resistant hypertension, particularly in comorbid conditions such as obesity and metabolic syndrome.

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.

Effects of the Kv7 voltage-activated potassium channel inhibitor linopirdine in rat models of haemorrhagic shock

Recently, we demonstrated that Kv7 voltage-activated potassium channel inhibitors reduce fluid resuscitation requirements in short-term rat models of haemorrhagic shock. The aim of the present study was to further delineate the therapeutic potential and side effect profile of the Kv7 channel blocker linopirdine in various rat models of severe haemorrhagic shock over clinically relevant time periods. Intravenous administration of linopirdine, either before (1 or 3 mg/kg) or after (3 mg/kg) a 40% blood volume haemorrhage, did not affect blood pressure and survival in lethal haemorrhage models without fluid resuscitation. A single bolus of linopirdine (3 mg/kg) at the beginning of fluid resuscitation after haemorrhagic shock transiently reduced early fluid requirements in spontaneously breathing animals that were resuscitated for 3.5 hours. When mechanically ventilated rats were resuscitated after haemorrhagic shock with normal saline (NS) or with linopirdine-supplemented (10, 25 or 50 μg/mL) NS for 4.5 hours, linopirdine significantly and dose-dependently reduced fluid requirements by 14%, 45% and 55%, respectively. Lung and colon wet/dry weight ratios were reduced with linopirdine (25/50 μg/mL). There was no evidence for toxicity or adverse effects based on measurements of routine laboratory parameters and inflammation markers in plasma and tissue homogenates. Our findings support the concept that linopirdine-supplementation of resuscitation fluids is a safe and effective approach to reduce fluid requirements and tissue oedema formation during resuscitation from haemorrhagic shock.

Centipedes subdue giant prey by blocking KCNQ channels

The work showed that centipede venom can cause disorders in cardiovascular, respiratory, and nervous systems. The cardiovascular toxicity of the venom comes mostly from a peptide toxin SsTx, which blocks the KCNQ family of potassium channels. Retigabine, a KCNQ channel opener, neutralizes centipede venom toxicity, and thus could be used to treat centipede envenomation.

Centipedes can subdue giant prey by using venom, which is metabolically expensive to synthesize and thus used frugally through efficiently disrupting essential physiological systems. Here, we show that a centipede (Scolopendra subspinipes mutilans, ∼3 g) can subdue a mouse (∼45 g) within 30 seconds. We found that this observation is largely due to a peptide toxin in the venom, SsTx, and further established that SsTx blocks KCNQ potassium channels to exert the lethal toxicity. We also demonstrated that a KCNQ opener, retigabine, neutralizes the toxicity of a centipede’s venom. The study indicates that centipedes’ venom has evolved to simultaneously disrupt cardiovascular, respiratory, muscular, and nervous systems by targeting the broadly distributed KCNQ channels, thus providing a therapeutic strategy for centipede envenomation.

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.

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.

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.

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.

Relaxation Induced by Atrial Natriuretic Peptide Is Impaired in Carotid but Not Renal Arteries from Spontaneously Hypertensive Rats Due to Reduced BKCa Channel Activity

Atrial natriuretic peptide (ANP) plays an important role in vascular functions such as blood pressure regulation and relaxant activity. Individual vascular beds exhibit differences in vascular reactivity to various ligands, however, the difference in responsiveness to ANP between carotid and renal arteries and the molecular mechanisms of its vasorelaxant activity in a pathophysiological state, including hypertension, remain unclear. We therefore investigated this issue by exposing carotid and renal artery rings obtained from spontaneously hypertensive rats (SHR) to ANP. In the SHR artery (vs. control WKY artery), the ANP-induced relaxations were reduced in carotid artery but not renal artery. Acetylcholine-induced relaxations were reduced in both arteries in SHR (vs. WKY). Sodium nitroprusside-induced relaxation was similar in both arteries between the groups. In carotid arteries, the ANP-induced relaxation was not affected by endothelial denudation or by treatment with inhibitors of nitric oxide synthase, cyclooxygenase, the voltage-dependent potassium channel, or ATP-sensitive potassium channel in arteries from both SHR and WKY. In the carotid artery from WKY but not SHR, the ANP-induced relaxation was significantly reduced by inhibition of the large-conductance calcium-activated potassium channel (BKCa). The BKCa activator-induced relaxation was reduced in the SHR artery (vs. WKY). These results suggest that ANP-induced relaxation is impaired in the carotid artery from SHR and this impairment may be at least in part due to the reduction of BKCa activity rather than endothelial components.

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.

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.

MicroRNA-153 targeting of KCNQ4 contributes to vascular dysfunction in hypertension

Aims

Kv7.4, a voltage-dependent potassium channel expressed throughout the vasculature, controls arterial contraction and is compromised in hypertension by an unknown mechanism. MicroRNAs (miRs) are post-transcriptional regulators of protein production and are altered in disease states such as hypertension. We investigated whether miRs regulate Kv7.4 expression.

Methods and results

In renal and mesenteric arteries (MAs) of the spontaneously hypertensive rat (SHR), Kv7.4 protein decreased compared with the normotensive (NT) rat without a decrease in KCNQ4 mRNA, inferring that Kv7.4 abundance was determined by post-transcriptional regulation. In silico analysis of the 3′ UTR of KCNQ4 revealed seed sequences for miR26a, miR133a, miR200b, miR153, miR214, miR218, and let-7d with quantitative polymerase chain reaction showing miR153 increased in those arteries from SHRs that exhibited decreased Kv7.4 levels. Luciferase reporter assays indicated a direct targeting effect of miR153 on the 3′ UTR of KCNQ4. Introduction of high levels of miR153 to MAs increased vascular wall thickening and reduced Kv7.4 expression/Kv7 channel function compared with vessels receiving a non-targeting miR, providing a proof of concept of Kv7.4 regulation by miR153.

Conclusion

This study is the first to define a role for aberrant miR153 contributing to the hypertensive state through targeting of KCNQ4 in an animal model of hypertension, raising the possibility of the use of miR153-related therapies in vascular disease.

Novel treatment strategies for smooth muscle disorders: Targeting Kv7 potassium channels

Smooth muscle cells provide crucial contractile functions in visceral, vascular, and lung tissues. The contractile state of smooth muscle is largely determined by their electrical excitability, which is in turn influenced by the activity of potassium channels. The activity of potassium channels sustains smooth muscle cell membrane hyperpolarization, reducing cellular excitability and thereby promoting smooth muscle relaxation. Research over the past decade has indicated an important role for Kv7 (KCNQ) voltage-gated potassium channels in the regulation of the excitability of smooth muscle cells. Expression of multiple Kv7 channel subtypes has been demonstrated in smooth muscle cells from viscera (gastrointestinal, bladder, myometrial), from the systemic and pulmonary vasculature, and from the airways of the lung, from multiple species, including humans. A number of clinically used drugs, some of which were developed to target Kv7 channels in other tissues, have been found to exert robust effects on smooth muscle Kv7 channels. Functional studies have indicated that Kv7 channel activators and inhibitors have the ability to relax and contact smooth muscle preparations, respectively, suggesting a wide range of novel applications for the pharmacological tool set. This review summarizes recent findings regarding the physiological functions of Kv7 channels in smooth muscle, and highlights potential therapeutic applications based on pharmacological targeting of smooth muscle Kv7 channels throughout the body.

Molecular and functional characterization of Kv 7 channels in penile arteries and corpus cavernosum of healthy and metabolic syndrome rats

BACKGROUND AND PURPOSE

KCNQ-encoded voltage-dependent potassium channels (Kv 7) are involved in the regulation of vascular tone. In this study we evaluated the influence of Kv 7 channel activation on smooth muscle relaxation in rat penile arteries and corpus cavernosum from normal and spontaneously hypertensive, heart failure-prone (SHHF) rats - a rat model of human metabolic syndrome.

EXPERIMENTAL APPROACH

Quantitative PCR and immunohistochemistry were used to determine the expression of KCNQ isoforms in penile tissue. Isometric tension was measured in intracavernous arterial rings and corpus cavernosum strips isolated from normal and SHHF rats.

KEY RESULTS

Transcripts for KCNQ3, KCNQ4 and KCNQ5 were detected in penile arteries and corpus cavernosum. KCNQ1 was only found in corpus cavernosum. Immunofluorescence signals to Kv 7.4 and Kv 7.5 were found in penile arteries, penile veins and corpus cavernosum. The Kv 7.2-7.5 activators, ML213 and BMS204352, relaxed pre-contracted penile arteries and corpus cavernosum independently of nitric oxide synthase or endothelium-derived hyperpolarization. Relaxations to sildenafil, a PDE5 inhibitor, and sodium nitroprusside (SNP), an nitric oxide donor, were reduced by blocking Kv 7 channels with linopirdine in penile arteries and corpus cavernosum. In SHHF rat penile arteries and corpus cavernosum, relaxations to ML213 and BMS204352 were attenuated, and the blocking effect of linopirdine on sildenafil-induced and SNP-induced relaxations reduced. KCNQ3, KCNQ4 and KCNQ5 were down-regulated, and KCNQ1 was up-regulated in corpus cavernosum from SHHF rats. KCNQ1-5 transcripts remained unchanged in penile arteries from SHHF rats.

CONCLUSIONS AND IMPLICATIONS

These data suggest that Kv 7 channels play a role in erectile function and contribute to the pathophysiology of erectile dysfunction, an early indicator of cardiovascular disease.

Novel Roles for Kv7 Channels in Shaping Histamine-Induced Contractions and Bradykinin-Dependent Relaxations in Pig Coronary Arteries

Voltage-gated Kv7 channels are inhibited by agonists of Gq-protein-coupled receptors, such as histamine. Recent works have provided evidence that inhibition of vascular Kv7 channels may trigger vessel contractions. In this study, we investigated how Kv7 activity modulates the histamine-induced contractions in "healthy" and metabolic syndrome (MetS) pig right coronary arteries (CAs). We performed isometric tension and immunohistochemical studies with domestic, lean Ossabaw, and MetS Ossabaw pig CAs. We found that neither the Kv7.2/Kv7.4/Kv7.5 activator ML213 nor the general Kv7 inhibitor XE991 altered the tension of CA rings under preload, indicating that vascular Kv7 channels are likely inactive in the preloaded rings. Conversely, ML213 potently dilated histamine-pre-contracted CAs, suggesting that Kv7 channels are activated during histamine applications and yet partially inhibited by histamine. Immunohistochemistry analysis revealed strong Kv7.4 immunostaining in the medial and intimal layers of the CA wall, whereas Kv7.5 immunostaining intensity was strong in the intimal but weak in the medial layers. The medial Kv7 immunostaining was significantly weaker in MetS Ossabaw CAs as compared to lean Ossabaw or domestic CAs. Consistently, histamine-pre-contracted MetS Ossabaw CAs exhibited attenuated ML213-dependent dilations. In domestic pig CAs, where medial Kv7 immunostaining intensity was stronger, histamine-induced contractions spontaneously decayed to ~31% of the peak amplitude within 4 minutes. Oppositely, in Ossabaw CAs, where Kv7 immunostaining intensity was weaker, the histamine-induced contractions were more sustained. XE991 pretreatment significantly slowed the decay rate of histamine-induced contractions in domestic CAs, supporting the hypothesis that increased Kv7 activity correlates with a faster rate of histamine-induced contraction decay. Alternatively, XE991 significantly decreased the amplitude of bradykinin-dependent dilations in pre-contracted CAs. We propose that in CAs, a decreased expression or a loss of function of Kv7 channels may lead to sustained histamine-induced contractions and reduced endothelium-dependent relaxation, both risk factors for coronary spasm.

Stimulation of calcium-sensing receptors induces endothelium-dependent vasorelaxations via nitric oxide production and activation of IKCa channels

Stimulation of vascular calcium-sensing receptors (CaSRs) is reported to induce both constrictions and relaxations. However, cellular mechanisms involved in these responses remain unclear. The present study investigates the effect of stimulating CaSRs on vascular contractility and focuses on the role of the endothelium, nitric oxide (NO) and K(+) channels in these responses. In wire myography studies, increasing [Ca(2+)]o from 1mM to 6mM induced concentration-dependent relaxations of methoxamine pre-contracted rabbit mesenteric arteries. [Ca(2+)]o-induced relaxations were dependent on a functional endothelium, and were inhibited by the negative allosteric CaSR modulator Calhex-231. [Ca(2+)]o-induced relaxations were reduced by inhibitors of endothelial NO synthase, guanylate cyclase, and protein kinase G. CaSR activation also induced NO production in freshly isolated endothelial cells (ECs) in experiments using the fluorescent NO indicator DAF-FM. Pre-treatment with inhibitors of large (BKCa) and intermediate (IKCa) Ca(2+)-activated K(+) channels (iberiotoxin and charybdotoxin), and Kv7 channels (linopirdine) also reduced [Ca(2+)]o-induced vasorelaxations. Increasing [Ca(2+)]o also activated IKCa currents in perforated-patch recordings of isolated mesenteric artery ECs. These findings indicate that stimulation of CaSRs induces endothelium-dependent vasorelaxations which are mediated by two separate pathways involving production of NO and activation of IKCa channels. NO stimulates PKG leading to BKCa activation in vascular smooth muscle cells, whereas IKCa activity contributes to endothelium-derived hyperpolarisations.

Fundamental role for the KCNE4 ancillary subunit in Kv7.4 regulation of arterial tone

KEY POINTS

KCNE4 alters the biophysical properties and cellular localization of voltage-gated potassium channel Kv7.4. KCNE4 is expressed in a variety of arteries and, in mesenteric arteries, co-localizes with Kv7.4, which is important in the control of vascular contractility. Knockdown of KCNE4 leads to reduced Kv7.4 membrane abundance, a depolarized membrane potential and an augmented response to vasoconstrictors. KCNE4 is a key regulator of the function and expression of Kv7.4 in vascular smooth muscle.

ABSTRACT

The KCNE ancillary subunits (KCNE1-5) significantly alter the expression and function of voltage-gated potassium channels; however, their role in the vasculature has yet to be determined. The present study aimed to investigate the expression and function of the KCNE4 subunit in rat mesenteric arteries and to determine whether it has a functional impact on the regulation of arterial tone by Kv7 channels. In HEK cells expressing Kv7.4, co-expression of KCNE4 increased the membrane expression of Kv7.4 and significantly altered Kv7.4 current properties. Quantitative PCR analysis of different rat arteries found that the KCNE4 isoform predominated and proximity ligation experiments showed that KCNE4 co-localized with Kv7.4 in mesenteric artery myocytes. Morpholino-induced knockdown of KCNE4 depolarized mesenteric artery smooth muscle cells and resulted in their increased sensitivity to methoxamine being attenuated (mean ± SEM EC50 decreased from 5.7 ± 0.63 μm to 1.6 ± 0.23 μm), which coincided with impaired effects of Kv7 modulators. When KCNE4 expression was reduced, less Kv7.4 expression was found in the membrane of the mesenteric artery myocytes. These data show that KCNE4 is consistently expressed in a variety of arteries, and knockdown of the expression product leads to reduced Kv7.4 membrane abundance, a depolarized membrane potential and an augmented response to vasoconstrictors. The present study is the first to demonstrate an integral role of KCNE4 in regulating the function and expression of Kv7.4 in vascular smooth muscle.

G-protein βγ subunits are positive regulators of Kv7.4 and native vascular Kv7 channel activity

Kv7.4 channels are a crucial determinant of arterial diameter both at rest and in response to endogenous vasodilators. However, nothing is known about the factors that ensure effective activity of these channels. We report that G-protein βγ subunits increase the amplitude and activation rate of whole-cell voltage-dependent K(+) currents sensitive to the Kv7 blocker linopirdine in HEK cells heterologously expressing Kv7.4, and in rat renal artery myocytes. In excised patch recordings, Gβγ subunits (2-250 ng /mL) enhanced the open probability of Kv7.4 channels without changing unitary conductance. Kv7 channel activity was also augmented by stimulation of G-protein-coupled receptors. Gallein, an inhibitor of Gβγ subunits, prevented these stimulatory effects. Moreover, gallein and two other structurally different Gβγ subunit inhibitors (GRK2i and a β-subunit antibody) abolished Kv7 channel currents in the absence of either Gβγ subunit enrichment or G-protein-coupled receptor stimulation. Proximity ligation assay revealed that Kv7.4 and Gβγ subunits colocalized in HEK cells and renal artery smooth muscle cells. Gallein disrupted this colocalization, contracted whole renal arteries to a similar degree as the Kv7 inhibitor linopirdine, and impaired isoproterenol-induced relaxations. Furthermore, mSIRK, which disassociates Gβγ subunits from α subunits without stimulating nucleotide exchange, relaxed precontracted arteries in a linopirdine-sensitive manner. These results reveal that Gβγ subunits are fundamental for Kv7.4 activation and crucial for vascular Kv7 channel activity, which has major consequences for the regulation of arterial tone.