Cardiovascular KCNQ (Kv7) potassium channels: physiological regulators and new targets for therapeutic intervention

The role of KCNQ channel activators in management of major depressive disorder

Depression, a complex disorder with significant treatment challenges, necessitates innovative therapeutic approaches to address its multifaceted nature and enhance treatment outcomes. The modulation of KCNQ potassium (K+) channels, pivotal regulators of neuronal excitability and neurotransmitter release, is a promising innovative therapeutic target in psychiatry. Widely expressed across various tissues, including the nervous and cardiovascular systems, KCNQ channels play a crucial role in modulating membrane potential and regulating neuronal activity. Recent preclinical evidence suggests that KCNQ channels, particularly KCNQ3, contribute to the regulation of neuronal excitability within the reward circuitry, offering a potential target for alleviating depressive symptoms, notably anhedonia. Studies using animal models demonstrate that interventions targeting KCNQ channels can restore dopaminergic firing balance and mitigate depressive symptoms. Human studies investigating the effects of KCNQ channel activators, such as ezogabine, have shown promising results in alleviating depressive symptoms and anhedonia. The aforementioned observations underscore the therapeutic potential of KCNQ channel modulation in depression management and highlight the need and justification for phase 2 and phase 3 dose-finding studies as well as studies prespecifying symptomatic targets in depression including anhedonia.

The renal vasodilatation from β-adrenergic activation in vivo in rats is not driven by KV7 and BKCa channels

The mechanisms behind renal vasodilatation elicited by stimulation of β-adrenergic receptors are not clarified. As several classes of K channels are potentially activated, we tested the hypothesis that KV7 and BKCa channels contribute to the decreased renal vascular tone in vivo and in vitro. Changes in renal blood flow (RBF) during β-adrenergic stimulation were measured in anaesthetized rats using an ultrasonic flow probe. The isometric tension of segmental arteries from normo- and hypertensive rats and segmental arteries from wild-type mice and mice lacking functional KV7.1 channels was examined in a wire-myograph. The β-adrenergic agonist isoprenaline increased RBF significantly in vivo. Neither activation nor inhibition of KV7 and BKCa channels affected the β-adrenergic RBF response. In segmental arteries from normo- and hypertensive rats, inhibition of KV7 channels significantly decreased the β-adrenergic vasorelaxation. However, inhibiting BKCa channels was equally effective in reducing the β-adrenergic vasorelaxation. The β-adrenergic vasorelaxation was not different between segmental arteries from wild-type mice and mice lacking KV7.1 channels. As opposed to rats, inhibition of KV7 channels did not affect the murine β-adrenergic vasorelaxation. Although inhibition and activation of KV7 channels or BKCa channels significantly changed baseline RBF in vivo, none of the treatments affected β-adrenergic vasodilatation. In isolated segmental arteries, however, inhibition of KV7 and BKCa channels significantly reduced the β-adrenergic vasorelaxation, indicating that the regulation of RBF in vivo is driven by several actors in order to maintain an adequate RBF. Our data illustrates the challenge in extrapolating results from in vitro to in vivo conditions.

Vitamin D Receptor Deficiency Upregulates Pulmonary Artery Kv7 Channel Activity

Recent evidence suggests that vitamin D is involved in the development of pulmonary arterial hypertension (PAH). The aim of this study was to analyze the electrophysiological and contractile properties of pulmonary arteries (PAs) in vitamin D receptor knockout mice (Vdr-/-). PAs were dissected and mounted in a wire myograph. Potassium membrane currents were recorded in freshly isolated PA smooth muscle cells (PASMCs) using the conventional whole-cell configuration of the patch-clamp technique. Potential vitamin D response elements (VDREs) in Kv7 channels coding genes were studied, and their protein expression was analyzed. Vdr-/- mice did not show a pulmonary hypertensive phenotype, as neither right ventricular hypertrophy nor endothelial dysfunction was apparent. However, resistance PA from these mice exhibited increased response to retigabine, a Kv7 activator, compared to controls and heterozygous mice. Furthermore, the current sensitive to XE991, a Kv7 inhibitor, was also higher in PASMCs from knockout mice. A possible VDRE was found in the gene coding for KCNE4, the regulatory subunit of Kv7.4. Accordingly, Vdr-/- mice showed an increased expression of KCNE4 in the lungs, with no changes in Kv7.1 and Kv7.4. These results indicate that the absence of Vdr in mice, as occurred with vitamin D deficient rats, is not sufficient to induce PAH. However, the contribution of Kv7 channel currents to the regulation of PA tone is increased in Vdr-/- mice, resembling animals and humans suffering from PAH.

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.

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.

Approaches for the discovery of drugs that target K Na 1.1 channels in KCNT1-associated epilepsy

INTRODUCTION

There are approximately 70 million people with epilepsy and about 30% of patients are not satisfactorily treated. A link between gene mutations and epilepsy is well documented. A number of pathological variants of KCNT1 gene (encoding the weakly voltage-dependent sodium-activated potassium channel - KNa 1.1) mutations has been found. For instance, epilepsy of infancy with migrating focal seizures, autosomal sleep-related hypermotor epilepsy or Ohtahara syndrome have been associated with KCNT1 gene mutations.

AREAS COVERED

Several methods for studies on KNa 1.1 channels have been reviewed - patch clamp analysis, Förster resonance energy transfer spectroscopy and whole-exome sequencing. The authors also review available drugs for the management of KCNT1 epilepsies.

EXPERT OPINION

The current methods enable deeper insights into electrophysiology of KNa 1.1 channels or its functioning in different activation states. It is also possible to identify a given KCNT1 mutation. Quinidine and cannabidiol show variable efficacy as add-on to baseline antiepileptic drugs so more effective treatments are required. A combined approach with the methods shown above, in silico methods and the animal model of KCNT1 epilepsies seems likely to create personalized treatment of patients with KCNT1 gene mutations.

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.

Linopirdine-supplemented resuscitation fluids reduce mortality in a model of ischemia-reperfusion injury induced acute respiratory distress syndrome

Previously, we demonstrated that supplementation of resuscitation fluids with the Kv7 voltage-activated potassium channel inhibitor linopirdine reduces fluid resuscitation requirements and stabilizes hemodynamics in various rat models of hemorrhagic shock. To further evaluate the therapeutic potential of linopirdine, we tested the effects of linopirdine-supplemented resuscitation fluids in a rat model of ischemia-reperfusion injury-induced acute respiratory distress syndrome (ARDS). Ventilated rats underwent unilateral lung ischemia from t=0-75 min, followed by lung reperfusion and fluid resuscitation to a mean arterial blood pressure of 60 mmHg with normal saline (NS, n=9) or NS supplemented with 50 µg/ml linopridine (NS-L), n=7) until t=360 min. As compared with NS, fluid resuscitation with NS-L stabilized blood pressure and reduced fluid requirements by 40% (p<0.05 vs. NS at t=240-360 min). While NS-L did not affect ARDS development, it reduced mortality from 66% with NS to 14% with NS-L (p=0.03, hazard ratio 0.14; 95% confidence interval of the hazard ratio: 0.03-0.65). Median survival time was 240 min with NS and >360 min with NS-L. As compared with NS treated animals that survived the observation period (n=3), however, plasma lactate and creatinine concentrations at t=360 min were higher with NS-L (n=6; p<0.05). Our findings extend therapeutic potential of NS-L from hypovolemic/hemorrhagic shock to hemodynamic instability under normovolemic conditions during organ ischemia-reperfusion injury. Possible adverse effects of NS-L, such as impairment of renal function and/or organ hypoperfusion, require further evaluation in long-term pre-clinical models.

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.

Chemical modulation of Kv7 potassium channels

The rising interest in Kv7 modulators originates from their ability to evoke fundamental electrophysiological perturbations in a tissue-specific manner. A large number of therapeutic applications are, in part, based on the clinical experience with two broad-spectrum Kv7 agonists, flupirtine and retigabine. Since precise molecular structures of human Kv7 channel subtypes in closed and open states have only very recently started to emerge, computational studies have traditionally been used to analyze binding modes and direct the development of more potent and selective Kv7 modulators with improved safety profiles. Herein, the synthetic and medicinal chemistry of small molecule modulators and the representative biological properties are summarized. Furthermore, new therapeutic applications supported by in vitro and in vivo assay data are suggested.

Vasopressin-stimulated ORAI1 expression and store-operated Ca2+ entry in aortic smooth muscle cells

Vascular calcification may result from stimulation of osteogenic signalling with upregulation of the transcription factors CBFA1, MSX2 and SOX9, as well as alkaline phosphatase (ALPL), which degrades and thus inactivates the calcification inhibitor pyrophosphate. Osteogenic signalling further involves upregulation of the Ca²⁺-channel ORAI1. The channel is activated by STIM1 and then accomplishes store-operated Ca²⁺ entry. ORAI1 and STIM1 are upregulated by the serum & glucocorticoid inducible kinase 1 (SGK1) which is critically important for osteogenic signalling. Stimulators of vascular calcification include vasopressin. The present study explored whether exposure of human aortic smooth muscle cells (HAoSMCs) to vasopressin upregulates ORAI1 and/or STIM1 expression, store-operated Ca²⁺ entry and osteogenic signalling. To this end, HAoSMCs were exposed to vasopressin (100 nM, 24 h) without or with additional exposure to ORAI1 blocker MRS1845 (10 μM) or SGK1 inhibitor GSK-650394 (1 μM). Transcript levels were measured using q-RT-PCR, cytosolic Ca²⁺-concentration ([Ca²⁺]_i) by Fura-2-fluorescence, and store-operated Ca²⁺ entry from increase of [Ca²⁺]_i following re-addition of extracellular Ca²⁺ after store depletion with thapsigargin (1 μM). As a result, vasopressin enhanced the transcript levels of ORAI1 and STIM1, store-operated Ca²⁺ entry, as well as the transcript levels of CBFA1, MSX2, SOX9 and ALPL. The effect of vasopressin on store-operated Ca²⁺ entry as well as on transcript levels of CBFA1, MSX2, SOX9 and ALPL was virtually abrogated by MRS1845 and GSK-650394. In conclusion, vasopressin stimulates expression of ORAI1/STIM1, thus augmenting store-operated Ca²⁺ entry and osteogenic signalling. In HAoSMCs, vasopressin (VP) upregulates Ca²⁺ channel ORAI1 and its activator STIM1. VP upregulates store-operated Ca²⁺ entry (SOCE) and osteogenic signalling (OS). VP-induced SOCE, OS and Ca²⁺-deposition are disrupted by ORAI1 inhibitor MRS1845. VP-induced SOCE, OS and Ca²⁺-deposition are disrupted by SGK1 blocker GSK-650394. KEY MESSAGES: • In HAoSMCs, vasopressin (VP) upregulates Ca²⁺ channel ORAI1 and its activator STIM1. • VP upregulates store-operated Ca²⁺ entry (SOCE) and osteogenic signalling (OS). • VP-induced SOCE, OS and Ca²⁺-deposition are disrupted by ORAI1 inhibitor MRS1845. • VP-induced SOCE, OS and Ca²⁺-deposition are disrupted by SGK1 blocker GSK-650394.

Vascular Kv7 channels control intracellular Ca2+ dynamics in smooth muscle

Voltage-gated Kv7 (or KCNQ) channels control activity of excitable cells, including vascular smooth muscle cells (VSMCs), by setting their resting membrane potential and controlling other excitability parameters. Excitation-contraction coupling in muscle cells is mediated by Ca2+ but until now, the exact role of Kv7 channels in cytosolic Ca2+ dynamics in VSMCs has not been fully elucidated. We utilised microfluorimetry to investigate the impact of Kv7 channel activity on intracellular Ca2+ levels and electrical activity of rat A7r5 VSMCs and primary human internal mammary artery (IMA) SMCs. Both, direct (XE991) and G protein coupled receptor mediated (vasopressin, AVP) Kv7 channel inhibition induced robust Ca2+ oscillations, which were significantly reduced in the presence of Kv7 channel activator, retigabine, L-type Ca2+ channel inhibitor, nifedipine, or T-type Ca2+ channel inhibitor, NNC 55-0396, in A7r5 cells. Membrane potential measured using FluoVolt exhibited a slow depolarisation followed by a burst of sharp spikes in response to XE991; spikes were temporally correlated with Ca2+ oscillations. Phospholipase C inhibitor (edelfosine) reduced AVP-induced, but not XE991-induced Ca2+ oscillations. AVP and XE991 induced a large increase of [Ca2+]i in human IMA, which was also attenuated with retigabine, nifedipine and NNC 55-0396. RT-PCR, immunohistochemistry and electrophysiology suggested that Kv7.5 was the predominant Kv7 subunit in both rat and human arterial SMCs; CACNA1C (Cav1.2; L-type) and CACNA1 G (Cav3.1; T-type) were the most abundant voltage-gated Ca2+ channel gene transcripts in both types of VSMCs. This study establishes Kv7 channels as key regulators of Ca2+ signalling in VSMCs with Kv7.5 playing a dominant role.

Hypoxia and metabolic inhibitors alter the intracellular ATP:ADP ratio and membrane potential in human coronary artery smooth muscle cells

ATP-sensitive potassium (K_ATP) channels couple cellular metabolism to excitability, making them ideal candidate sensors for hypoxic vasodilation. However, it is still unknown whether cellular nucleotide levels are affected sufficiently to activate vascular K_ATP channels during hypoxia. To address this fundamental issue, we measured changes in the intracellular ATP:ADP ratio using the biosensors Perceval/PercevalHR, and membrane potential using the fluorescent probe DiBAC₄(3) in human coronary artery smooth muscle cells (HCASMCs). ATP:ADP ratio was significantly reduced by exposure to hypoxia. Application of metabolic inhibitors for oxidative phosphorylation also reduced ATP:ADP ratio. Hyperpolarization caused by inhibiting oxidative phosphorylation was blocked by either 10 µM glibenclamide or 60 mM K⁺. Hyperpolarization caused by hypoxia was abolished by 60 mM K⁺ but not by individual K⁺ channel inhibitors. Taken together, these results suggest hypoxia causes hyperpolarization in part by modulating K⁺ channels in SMCs.

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.

Detrusor Smooth Muscle KV7 Channels: Emerging New Regulators of Urinary Bladder Function

Relaxation and contraction of the urinary bladder smooth muscle, also known as the detrusor smooth muscle (DSM), facilitate the micturition cycle. DSM contractility depends on cell excitability, which is established by the synchronized activity of multiple diverse ion channels. K+ channels, the largest family of channels, control DSM excitability by maintaining the resting membrane potential and shaping the action potentials that cause the phasic contractions. Among the members of the voltage-gated K+ (KV) channel superfamily, KV type 7 (KV7) channels - KV7.1-KV7.5 members encoded by KCNQ1-KCNQ5 genes - have been recently identified as functional regulators in various cell types including vascular, cardiac, and neuronal cells. Their regulatory roles in DSM, however, are just now emerging and remain to be elucidated. To address this gap, our research group has initiated the systematic investigation of human DSM KV7 channels in collaboration with clinical urologists. In this comprehensive review, we summarize the current understanding of DSM Kv7 channels and highlight recent discoveries in the field. We describe KV7 channel expression profiles at the mRNA and protein levels, and further elaborate on functional effects of KV7 channel selective modulators on DSM excitability, contractility, and intracellular Ca2+ dynamics in animal species along with in vivo studies and the limited data on human DSM. Within each topic, we highlight the main observations, current gaps in knowledge, and most pressing questions and concepts in need of resolution. We emphasize the lack of systematic studies on human DSM KV7 channels that are now actively ongoing in our laboratory.

Epileptic channelopathies caused by neuronal Kv7 (KCNQ) channel dysfunction

Seizures are the most common neurological manifestation in the newborn period, with an estimated incidence of 1.8-3.5 per 1000 live births. Prolonged or intractable seizures have a detrimental effect on cognition and brain function in experimental animals and are associated with adverse long-term neurodevelopmental sequelae and an increased risk of post-neonatal epilepsy in humans. The developing brain is particularly susceptible to the potentially severe effects of epilepsy, and epilepsy, especially when refractory to medications, often results in a developmental and epileptic encephalopathy (DEE) with developmental arrest or regression. DEEs can be primarily attributed to genetic causes. Given the critical role of potassium (K⁺) currents with distinct subcellular localization, biophysical properties, modulation, and pharmacological profile in regulating intrinsic electrical properties of neurons and their responsiveness to synaptic inputs, it is not too surprising that genetic research in the past two decades has identified several K⁺ channel genes as responsible for a large fraction of DEE. In the present article, we review the genetically determined epileptic channelopathies affecting three members of the Kv7 family, namely Kv7.2 (KCNQ2), Kv7.3 (KCNQ3), and Kv7.5 (KCNQ5); we review the phenotypic spectrum of Kv7-related epileptic channelopathies, the different genetic and pathogenetic mechanisms, and the emerging genotype-phenotype correlations which may prove crucial for prognostic predictions, disease management, parental counseling, and individually tailored therapeutic attempts.

Vasodilation of rat skeletal muscle arteries by the novel BK channel opener GoSlo is mediated by the simultaneous activation of BK and Kv 7 channels

Background and Purpose

BK channels play important roles in various physiological and pathophysiological processes and thus have been the target of several drug development programmes focused on creating new efficacious BK channel openers, such as the GoSlo‐SR compounds. However, the effect of GoSlo‐SR compounds on vascular smooth muscle has not been studied. Therefore, we tested the hypothesis that GoSlo‐SR compounds dilate arteries exclusively by activating BK channels.

Experimental Approach

Experiments were performed on rat Gracilis muscle, saphenous, mesenteric and tail arteries using isobaric and isometric myography, sharp microelectrodes, digital droplet PCR and the patch‐clamp technique.

Key Results

GoSlo‐SR compounds dilated isobaric and relaxed and hyperpolarised isometric vessel preparations and their effects were abolished after (a) functionally eliminating K⁺ channels by pre‐constriction with 50 mM KCl or (b) blocking all K⁺ channels known to be expressed in vascular smooth muscle. However, these effects were not blocked when BK channels were inhibited. Surprisingly, the K_v7 channel inhibitor XE991 reduced their effects considerably, but neither K_v1 nor K_v2 channel blockers altered the inhibitory effects of GoSlo‐SR. However, the combined blockade of BK and K_v7 channels abolished the GoSlo‐SR‐induced relaxation. GoSlo‐SR compounds also activated K_v7.4 and K_v7.5 channels expressed in HEK 293 cells.

Conclusion and Implications

This study shows that GoSlo‐SR compounds are effective relaxants in vascular smooth muscle and mediate their effects by a combined activation of BK and K_v7.4/K_v7.5 channels. Activation of K_v1, K_v2 or K_v7.1 channels or other vasodilator pathways seems not to be involved.

Structural Determinants of Kv7.5 Potassium Channels That Confer Changes in Phosphatidylinositol 4,5-Bisphosphate (PIP2) Affinity and Signaling Sensitivities in Smooth Muscle Cells

Smooth muscle cells express Kv7.4 and Kv7.5 voltage-dependent potassium channels, which have each been implicated as regulators of smooth muscle contractility, though they display different sensitivities to signaling via cAMP/protein kinase A (PKA) and protein kinase C (PKC). We expressed chimeric channels composed of different components of the Kv7.4 and Kv7.5 α-subunits in vascular smooth muscle cells to determine which components are essential for enhancement or inhibition of channel activity. Forskolin, an activator of the cAMP/PKA pathway, increased wild-type Kv7.5 but not wild-type Kv7.4 current amplitude. Replacing the amino terminus of Kv7.4 with the amino terminus of Kv7.5 conferred partial responsiveness to forskolin. In contrast, swapping carboxy-terminal phosphatidylinositol 4,5-bisphosphate (PIP₂) binding domains, or the entire C terminus, was without effect on the forskolin response, but the latter conferred responsiveness to arginine-vasopressin (an inhibitory PKC-dependent response). Serine-to-alanine mutation at position 53 of the Kv7.5 amino terminus abrogated its ability to confer forskolin sensitivity to Kv7.4. Forskolin treatment reduced the sensitivity of Kv7.5 channels to Ciona intestinalis voltage-sensing phosphatase (Ci-VSP)-induced PIP₂ depletion, whereas activation of PKC with phorbol-12-myristate-13-acetate potentiated the Ci-VSP-induced decline in Kv7.5 current amplitude. Our findings suggest that PKA-dependent phosphorylation of serine 53 on the amino terminus of Kv7.5 increases its affinity for PIP₂, whereas PKC-dependent phosphorylation of the Kv7.5 carboxy terminus is associated with a reduction in PIP₂ affinity; these changes in PIP₂ affinity have corresponding effects on channel activity. Resting affinities for PIP₂ differ for Kv7.4 and Kv7.5 based on differential responsiveness to Ci-VSP activation and different rates of current rundown in ruptured patch recordings. SIGNIFICANCE STATEMENT: Kv7.4 and Kv7.5 channels are known signal transduction intermediates and drug targets for regulation of smooth muscle tone. The present studies identify distinct functional domains that confer differential sensitivities of Kv7.4 and Kv7.5 to stimulatory and inhibitory signaling and reveal structural features of the channel subunits that determine their biophysical properties. These findings may improve our understanding of the roles of these channels in smooth muscle physiology and disease, particularly in conditions where Kv7.4 and Kv7.5 are differentially expressed.

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.

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.

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.

The KV 7 channel activator retigabine suppresses mouse urinary bladder afferent nerve activity without affecting detrusor smooth muscle K+ channel currents

KEY POINTS

K_V 7 channels are a family of voltage-dependent K⁺ channels expressed in many cell types, which open in response to membrane depolarization to regulate cell excitability. Drugs that target K_V 7 channels are used clinically to treat epilepsy. Interestingly, these drugs also cause urinary retention, but it was unclear how. In this study, we focused on two possible mechanisms by which retigabine could cause urinary retention: by decreasing smooth muscle excitability, or by decreasing sensory nerve outflow. Urinary bladder smooth muscle had no measurable K_V 7 channel currents. However, the K_V 7 channel agonist retigabine nearly abolished sensory nerve outflow from the urinary bladder during bladder filling. We conclude that K_V 7 channel activation likely affects urinary bladder function by blocking afferent nerve outflow to the brain, which is key to sensing bladder fullness.

ABSTRACT

K_V 7 channels are voltage-dependent K⁺ channels that open in response to membrane depolarization to regulate cell excitability. K_V 7 activators, such as retigabine, were used to treat epilepsy but caused urinary retention. Using electrophysiological recordings from freshly isolated mouse urinary bladder smooth muscle (UBSM) cells, isometric contractility of bladder strips, and ex vivo measurements of bladder afferent activity, we explored the role of K_V 7 channels as regulators of murine urinary bladder function. The K_V 7 activator retigabine (10 μM) had no effect on voltage-dependent K⁺ currents or resting membrane potential of UBSM cells, suggesting that these cells lacked retigabine-sensitive K_V 7 channels. The K_V 7 inhibitor XE-991 (10 μM) inhibited UBSM K⁺ currents; the properties of these currents, however, were typical of K_V 2 channels and not K_V 7 channels. Retigabine inhibited voltage-dependent Ca²⁺ channel (VDCC) currents and reduced steady-state contractions to 60 mM KCl in bladder strips, suggesting that reduction in VDCC current was sufficient to directly affect UBSM function. To determine if retigabine altered ex vivo bladder sensory outflow, we measured afferent activity during simulated transient contractions (TCs) of the bladder wall. Simulated TCs caused bursts of afferent activity that were nearly abolished by retigabine. The effects of retigabine were blocked by co-incubation with XE-991, suggesting specific activation of K_V 7 channels on afferent nerves. These results indicate that retigabine primarily affects urinary bladder function by inhibiting TC generation and afferent nerve activity, which are key to sensing bladder fullness. Any direct inhibition of UBSM contractility is likely to be from non-specific effects on VDCCs and K_V 2 channels.

Blood-Based Biomarkers for Predicting the Risk for Five-Year Incident Coronary Heart Disease in the Framingham Heart Study via Machine Learning

An improved approach for predicting the risk for incident coronary heart disease (CHD) could lead to substantial improvements in cardiovascular health. Previously, we have shown that genetic and epigenetic loci could predict CHD status more sensitively than conventional risk factors. Herein, we examine whether similar machine learning approaches could be used to develop a similar panel for predicting incident CHD. Training and test sets consisted of 1180 and 524 individuals, respectively. Data mining techniques were employed to mine for predictive biosignatures in the training set. An ensemble of Random Forest models consisting of four genetic and four epigenetic loci was trained on the training set and subsequently evaluated on the test set. The test sensitivity and specificity were 0.70 and 0.74, respectively. In contrast, the Framingham risk score and atherosclerotic cardiovascular disease (ASCVD) risk estimator performed with test sensitivities of 0.20 and 0.38, respectively. Notably, the integrated genetic-epigenetic model predicted risk better for both genders and very well in the three-year risk prediction window. We describe a novel DNA-based precision medicine tool capable of capturing the complex genetic and environmental relationships that contribute to the risk of CHD, and being mapped to actionable risk factors that may be leveraged to guide risk modification efforts.

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.

Pore- and voltage sensor-targeted KCNQ openers have distinct state-dependent actions

Ion channels encoded by KCNQ2-5 generate a prominent K⁺ conductance in the central nervous system, referred to as the M current, which is controlled by membrane voltage and PIP2. The KCNQ2-5 voltage-gated potassium channels are targeted by a variety of activating compounds that cause negative shifts in the voltage dependence of activation. The underlying pharmacology of these effects is of growing interest because of possible clinical applications. Recent studies have revealed multiple binding sites and mechanisms of action of KCNQ activators. For example, retigabine targets the pore domain, but several compounds have been shown to influence the voltage-sensing domain. An important unexplored feature of these compounds is the influence of channel gating on drug binding or effects. In the present study, we compare the state-dependent actions of retigabine and ICA-069673 (ICA73, a voltage sensor-targeted activator). We assess drug binding to preopen states by applying drugs to homomeric KCNQ2 channels at different holding voltages, demonstrating little or no association of ICA73 with resting states. Using rapid solution switching, we also demonstrate that the rate of onset of ICA73 correlates with the voltage dependence of channel activation. Retigabine actions differ significantly, with prominent drug effects seen at very negative holding voltages and distinct voltage dependences of drug binding versus channel activation. Using similar approaches, we investigate the mechanistic basis for attenuation of ICA73 actions by the voltage-sensing domain mutation KCNQ2[A181P]. Our findings demonstrate different state-dependent actions of pore- versus voltage sensor-targeted KCNQ channel activators, which highlight that subtypes of this drug class operate with distinct mechanisms.

Four drug-sensitive subunits are required for maximal effect of a voltage sensor-targeted KCNQ opener

KCNQ2-5 (Kv7.2-Kv7.5) channels are strongly influenced by an emerging class of small-molecule channel activators. Retigabine is the prototypical KCNQ activator that is thought to bind within the pore. It requires the presence of a Trp side chain that is conserved among retigabine-sensitive channels but absent in the retigabine-insensitive KCNQ1 subtype. Recent work has demonstrated that certain KCNQ openers are insensitive to mutations of this conserved Trp, and that their effects are instead abolished or attenuated by mutations in the voltage-sensing domain (VSD). In this study, we investigate the stoichiometry of a VSD-targeted KCNQ2 channel activator, ICA-069673, by forming concatenated channel constructs with varying numbers of drug-insensitive subunits. In homomeric WT KCNQ2 channels, ICA-069673 strongly stabilizes an activated channel conformation, which is reflected in the pronounced deceleration of deactivation and leftward shift of the conductance-voltage relationship. A full complement of four drug-sensitive subunits is required for maximal sensitivity to ICA-069673-even a single drug-insensitive subunit leads to significantly weakened effects. In a companion article (see Yau et al. in this issue), we demonstrate very different stoichiometry for the action of retigabine on KCNQ3, for which a single retigabine-sensitive subunit enables near-maximal effect. Together, these studies highlight fundamental differences in the site and mechanism of activation between retigabine and voltage sensor-targeted KCNQ openers.

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.

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.

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.

Role of renal vascular potassium channels in physiology and pathophysiology

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

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.

Kv7 voltage-activated potassium channel inhibitors reduce fluid resuscitation requirements after hemorrhagic shock in rats

Background

Recent evidence suggests that drugs targeting Kv7 channels could be used to modulate vascular function and blood pressure. Here, we studied whether Kv7 channel inhibitors can be utilized to stabilize hemodynamics and reduce resuscitation fluid requirements after hemorrhagic shock.

Methods

Anesthetized male Sprague-Dawley rats were instrumented with arterial and venous catheters for blood pressure monitoring, hemorrhage and fluid resuscitation. Series 1: Linopirdine (Kv7 channel blocker, 0.1–6 mg/kg) or retigabine (Kv7 channel activator, 0.1–12 mg/kg) were administered to normal animals. Series 2: Animals were hemorrhaged to a MAP of 25 mmHg for 30 min, followed by fluid resuscitation with normal saline (NS) to a MAP of 70 mmHg until t = 75 min. Animals were treated with single bolus injections of vehicle, linopirdine (1–6 mg/kg), XE-991 (structural analogue of linopirdine with higher potency for channel blockade, 1 mg/kg) prior to fluid resuscitation. Series 3: Animals were resuscitated with NS alone or NS supplemented with linopirdine (1.25–200 μg/mL). Data were analyzed with 2-way ANOVA/Bonferroni post-hoc testing.

Results

Series 1: Linopirdine transiently (10–15 min) and dose-dependently increased MAP by up to 15%. Retigabine dose-dependently reduced MAP by up to 60%, which could be reverted with linopirdine. Series 2: Fluid requirements to maintain MAP at 70 mmHg were 65 ± 34 mL/kg with vehicle, and 57 ± 13 mL/kg, 22 ± 8 mL/kg and 22 ± 11 mL/kg with intravenous bolus injection of 1, 3 and 6 mg/kg linopirdine, respectively. XE-991 (1 mg/kg), reduced resuscitation requirements comparable to 3 mg/kg linopirdine.

Series 3: When resuscitation was performed with linopirdine-supplemented normal saline (NS), fluid requirements to stabilize MAP were 73 ± 12 mL/kg with NS alone and 72 ± 24, 61 ± 20, 36 ± 9 and 31 ± 9 mL/kg with NS supplemented with 1.25, 6.25, 12.5 and 200 μg/mL linopirdine, respectively.

Conclusions

Our data suggest that Kv7 channel blockers could be used to stabilize blood pressure and reduce fluid resuscitation requirements after hemorrhagic shock.

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.

Interplay among distinct Ca2+ conductances drives Ca2+ sparks/spontaneous transient outward currents in rat cerebral arteries

KEY POINTS

Distinct Ca²⁺ channels work in a coordinated manner to grade Ca²⁺ spark/spontaneous transient outward currents (STOCs) in rat cerebral arteries. The relative contribution of each Ca²⁺ channel to Ca²⁺ spark/STOC production depends upon their biophysical properties and the resting membrane potential of smooth muscle. Na⁺ /Ca²⁺ exchanger, but not TRP channels, can also facilitate STOC production.

ABSTRACT

Ca²⁺ sparks are generated in a voltage-dependent manner to initiate spontaneous transient outward currents (STOCs), events that moderate arterial constriction. In this study, we defined the mechanisms by which membrane depolarization increases Ca²⁺ sparks and subsequent STOC production. Using perforated patch clamp electrophysiology and rat cerebral arterial myocytes, we monitored STOCs in the presence and absence of agents that modulate Ca²⁺ entry. Beginning with Ca_V 3.2 channel inhibition, Ni²⁺ was shown to decrease STOC frequency in cells held at hyperpolarized (-40 mV) but not depolarized (-20 mV) voltages. In contrast, nifedipine, a Ca_V 1.2 inhibitor, markedly suppressed STOC frequency at -20 mV but not -40 mV. These findings aligned with the voltage-dependent profiles of L- and T-type Ca²⁺ channels. Furthermore, computational and experimental observations illustrated that Ca²⁺ spark production is intimately tied to the activity of both conductances. Intriguingly, this study observed residual STOC production at depolarized voltages that was independent of Ca_V 1.2 and Ca_V 3.2. This residual component was insensitive to TRPV4 channel modulation and was abolished by Na⁺ /Ca²⁺ exchanger blockade. In summary, our work highlights that the voltage-dependent triggering of Ca²⁺ sparks/STOCs is not tied to a single conductance but rather reflects an interplay among multiple Ca²⁺ permeable pores with distinct electrophysiological properties. This integrated orchestration enables smooth muscle to grade Ca²⁺ spark/STOC production and thus precisely tune negative electrical feedback.

Lidocaine relaxation in isolated rat aortic rings is enhanced by endothelial removal: possible role of Kv, KATP channels and A2a receptor crosstalk

BACKGROUND

Lidocaine is an approved local anesthetic and Class 1B antiarrhythmic with a number of ancillary properties. Our aim was to investigate lidocaine's vasoreactivity properties in intact versus denuded rat thoracic aortic rings, and the effect of inhibitors of nitric oxide (NO), prostenoids, voltage-dependent Kv and KATP channels, membrane Na+/K+ pump, and A2a and A2b receptors.

METHODS

Aortic rings were harvested from adult male Sprague Dawley rats and equilibrated in an organ bath containing oxygenated, modified Krebs-Henseleit solution, pH 7.4, 37 °C. The rings were pre-contracted sub-maximally with 0.3 μM norepinephrine (NE), and the effect of increasing lidocaine concentrations was examined. Rings were tested for viability after each experiment with maximally dilating 100 μM papaverine. The drugs 4-aminopyridine (4-AP), glibenclamide, 5-hydroxydecanoate, ouabain, 8-(3-chlorostyryl) caffeine and PSB-0788 were examined.

RESULTS

All drugs tested had no significant effect on basal tension. Lidocaine relaxation in intact rings was biphasic between 1 and 10 μM (Phase 1) and 10 and 1000 μM (Phase 2). Mechanical removal of the endothelium resulted in further relaxation, and at lower concentrations ring sensitivity (% relaxation per μM lidocaine) significantly increased 3.5 times compared to intact rings. The relaxing factor(s) responsible for enhancing ring relaxation did not appear to be NO- or prostacyclin-dependent, as L-NAME and indomethacin had little or no effect on intact ring relaxation. In denuded rings, lidocaine relaxation was completely abolished by Kv channel inhibition and significantly reduced by antagonists of the MitoKATP channel, and to a lesser extent the SarcKATP channel. Curiously, A2a subtype receptor antagonism significantly inhibited lidocaine relaxation above 100 μM, but not the A2b receptor.

CONCLUSIONS

We show that lidocaine relaxation in rat thoracic aorta was biphasic and significantly enhanced by endothelial removal, which did not appear to be NO or prostacyclin dependent. The unknown factor(s) responsible for enhanced relaxation was significantly reduced by Kv inhibition, 5-HD inhibition, and A2a subtype inhibition indicating a potential role for crosstalk in lidocaine's vasoreactivity.

Comparison of Voltage Gated K+ Currents in Arterial Myocytes with Heterologously Expressed K v Subunits

We have shown that three components contribute to functional voltage gated K⁺ (K _v) currents in rat small mesenteric artery myocytes: (1) Kv1.2 plus Kv1.5 with Kvβ1.2 subunits, (2) Kv2.1 probably associated with Kv9.3 subunits, and (3) Kv7.4 subunits. To confirm and address subunit stoichiometry of the first two, we have compared the biophysical properties of K _v currents in small mesenteric artery myocytes with those of K_v subunits heterologously expressed in HEK293 cells using whole cell voltage clamp methods. Selective inhibitors of Kv1 (correolide, COR) and Kv2 (stromatoxin, ScTx) channels were used to separate these K _v current components. Conductance-voltage and steady state inactivation data along with time constants of activation, inactivation, and deactivation of native K _v components were generally well represented by those of Kv1.2-1.5-β1.2 and Kv2.1-9.3 channels. The slope of the steady state inactivation-voltage curve (availability slope) proved to be the most sensitive measure of accessory subunit presence. The availability slope curves exhibited a single peak for both native K _v components. Availability slope curves for Kv1.2-1.5-β1.2 and Kv2.1-9.3 channels expressed in human embryonic kidney cells also exhibited a single peak that shifted to more depolarized voltages with increasing accessory to α subunit transfection ratio. Availability slope curves for SxTc-insensitive currents were similar to those of Kv1.2-1.5 expressed with Kvβ1.2 at a 1:5 molar ratio while curves for COR-insensitive currents closely resembled those of Kv2.1 expressed with Kv9.3 at a 1:1 molar ratio. These results support the suggested K_v subunit combinations in small mesenteric artery, and further suggest that Kv1 α and Kvβ1.2 but not Kv2.1 and Kv9.3 subunits are present in a saturated (4:4) stoichiometry.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Tannic acid activates the Kv7.4 and Kv7.3/7.5 K+ channels expressed in HEK293 cells and reduces tension in the rat mesenteric arteries

Objectives

This study investigated the effect of tannic acid (TA), a plant-derived hydrolyzable polyphenol, on Kv7.4 and Kv7.5 K+ channels and rat mesenteric artery.

Methods

Whole-cell patch clamp experiments were used to record the Kv7.4 and Kv7.3/7.5 K+ currents expressed in HEK293 cells; and the tension changes of mesenteric arteries isolated from rats were recorded using small vessel myography apparatus.

Key findings

Tannic acid increases the Kv7.4 and Kv7.3/7.5 K+ currents in a concentration-dependent manner (median effective concentration (EC50) = 27.3 ± 3.6 μm and EC50 = 23.1 ± 3.9 μm, respectively). In addition, 30 μm TA shifts the G–V curve of Kv7.4 and Kv7.3/7.5 K+ currents to the left by 14.18 and 25.24 mV, respectively, and prolongs the deactivation time constants by 184.44 and 154.77 ms, respectively. Moreover, TA relaxes the vascular tension of rat mesenteric arteries in a concentration-dependent manner (half inhibitory concentration (IC50) = 148.7 ± 13.4 μm).

Conclusion

These results confirms the vasodilatory effects of TA on rat mesenteric artery and the activating effects on the Kv7.4 and Kv7.3/7.5 K+ channels, which may be a mechanism to explain the vasodilatory effect and this mechanism can be used in the research of antihypertension.

KV7 channels contribute to paracrine, but not metabolic or ischemic, regulation of coronary vascular reactivity in swine

Hydrogen peroxide (H2O2) and voltage-dependent K(+) (KV) channels play key roles in regulating coronary blood flow in response to metabolic, ischemic, and paracrine stimuli. The KV channels responsible have not been identified, but KV7 channels are possible candidates. Existing data regarding KV7 channel function in the coronary circulation (limited to ex vivo assessments) are mixed. Thus we examined the hypothesis that KV7 channels are present in cells of the coronary vascular wall and regulate vasodilation in swine. We performed a variety of molecular, biochemical, and functional (in vivo and ex vivo) studies. Coronary arteries expressed KCNQ genes (quantitative PCR) and KV7.4 protein (Western blot). Immunostaining demonstrated KV7.4 expression in conduit and resistance vessels, perhaps most prominently in the endothelial and adventitial layers. Flupirtine, a KV7 opener, relaxed coronary artery rings, and this was attenuated by linopirdine, a KV7 blocker. Endothelial denudation inhibited the flupirtine-induced and linopirdine-sensitive relaxation of coronary artery rings. Moreover, linopirdine diminished bradykinin-induced endothelial-dependent relaxation of coronary artery rings. There was no effect of intracoronary flupirtine or linopirdine on coronary blood flow at the resting heart rate in vivo. Linopirdine had no effect on coronary vasodilation in vivo elicited by ischemia, H2O2, or tachycardia. However, bradykinin increased coronary blood flow in vivo, and this was attenuated by linopirdine. These data indicate that KV7 channels are expressed in some coronary cell type(s) and influence endothelial function. Other physiological functions of coronary vascular KV7 channels remain unclear, but they do appear to contribute to endothelium-dependent responses to paracrine stimuli.

The Modulation of Potassium Channels in the Smooth Muscle as a Therapeutic Strategy for Disorders of the Gastrointestinal Tract

Alterations of smooth muscle contractility contribute to the pathophysiology of important functional gastrointestinal disorders (FGIDs) such as functional dyspepsia and irritable bowel syndrome. Consequently, drugs that decrease smooth muscle contractility are effective treatments for these diseases. Smooth muscle contraction is mainly triggered by Ca(2+) influx through voltage-dependent channels located in the plasma membrane. Thus, the modulation of the membrane potential results in the regulation of Ca(2+) influx and cytosolic levels. K(+) channels play fundamental roles in these processes. The open probability of K(+) channels increases in response to various stimuli, including membrane depolarization (voltage-gated K(+) [K(V)] channels) and the increase in cytosolic Ca(2+) levels (Ca(2+)-dependent K(+) [K(Ca)] channels). K(+) channel activation is mostly associated with outward K(+) currents that hyperpolarize the membrane and reduce cell excitability and contractility. In addition, some K(+) channels are open at the resting membrane potential values of the smooth muscle cells in some gut segments and contribute to set the resting membrane potential itself. The closure of these channels induces membrane depolarization and smooth muscle contraction. K(V)1.2, 1.5, 2.2, 4.3, 7.4 and 11.1, K(Ca)1.1 and 2.3, and inwardly rectifying type 6K(+) (K(ir)6) channels play the most important functional roles in the gastrointestinal smooth muscle. Activators of all these channels may theoretically relax the gastrointestinal smooth muscle and could therefore be promising new therapeutic options for FGID. The challenge of future drug research and development in this area will be to synthesize molecules selective for the channel assemblies expressed in the gastrointestinal smooth muscle.

Expression and function of Kv7.4 channels in rat cardiac mitochondria: possible targets for cardioprotection

AIMS

Plasmalemmal Kv7.1 (KCNQ1) channels are critical players in cardiac excitability; however, little is known on the functional role of additional Kv7 family members (Kv7.2-5) in cardiac cells. In this work, the expression, function, cellular and subcellular localization, and potential cardioprotective role against anoxic-ischaemic cardiac injury of Kv7.4 channels have been investigated.

METHODS AND RESULTS

Expression of Kv7.1 and Kv7.4 transcripts was found in rat heart tissue by quantitative polymerase chain reaction. Western blots detected Kv7.4 subunits in mitochondria from Kv7.4-transfected cells, H9c2 cardiomyoblasts, freshly isolated adult cardiomyocytes, and whole hearts. Immunofluorescence experiments revealed that Kv7.4 subunits co-localized with mitochondrial markers in cardiac cells, with ∼ 30-40% of cardiac mitochondria being labelled by Kv7.4 antibodies, a result also confirmed by immunogold electron microscopy experiments. In isolated cardiac (but not liver) mitochondria, retigabine (1-30 µM) and flupirtine (30 µM), two selective Kv7 activators, increased Tl(+) influx, depolarized the membrane potential, and inhibited calcium uptake; all these effects were antagonized by the Kv7 blocker XE991. In intact H9c2 cells, reducing Kv7.4 expression by RNA interference blunted retigabine-induced mitochondrial membrane depolarization; in these cells, retigabine decreased mitochondrial Ca(2+) levels and increased radical oxygen species production, both effects prevented by XE991. Finally, retigabine reduced cellular damage in H9c2 cells exposed to anoxia/re-oxygenation and largely prevented the functional and morphological changes triggered by global ischaemia/reperfusion (I/R) in Langendorff-perfused rat hearts.

CONCLUSION

Kv7.4 channels are present and functional in cardiac mitochondria; their activation exerts a significant cardioprotective role, making them potential therapeutic targets against I/R-induced cardiac injury.

Structural basis of a Kv7.1 potassium channel gating module: studies of the intracellular c-terminal domain in complex with calmodulin

Kv7 channels tune neuronal and cardiomyocyte excitability. In addition to the channel membrane domain, they also have a unique intracellular C-terminal (CT) domain, bound constitutively to calmodulin (CaM). This CT domain regulates gating and tetramerization. We investigated the structure of the membrane proximal CT module in complex with CaM by X-ray crystallography. The results show how the CaM intimately hugs a two-helical bundle, explaining many channelopathic mutations. Structure-based mutagenesis of this module in the context of concatemeric tetramer channels and functional analysis along with in vitro data lead us to propose that one CaM binds to one individual protomer, without crosslinking subunits and that this configuration is required for proper channel expression and function. Molecular modeling of the CT/CaM complex in conjunction with small-angle X-ray scattering suggests that the membrane proximal region, having a rigid lever arm, is a critical gating regulator.

Noise-induced plasticity of KCNQ2/3 and HCN channels underlies vulnerability and resilience to tinnitus

Vulnerability to noise-induced tinnitus is associated with increased spontaneous firing rate in dorsal cochlear nucleus principal neurons, fusiform cells. This hyperactivity is caused, at least in part, by decreased Kv7.2/3 (KCNQ2/3) potassium currents. However, the biophysical mechanisms underlying resilience to tinnitus, which is observed in noise-exposed mice that do not develop tinnitus (non-tinnitus mice), remain unknown. Our results show that noise exposure induces, on average, a reduction in KCNQ2/3 channel activity in fusiform cells in noise-exposed mice by 4 days after exposure. Tinnitus is developed in mice that do not compensate for this reduction within the next 3 days. Resilience to tinnitus is developed in mice that show a re-emergence of KCNQ2/3 channel activity and a reduction in HCN channel activity. Our results highlight KCNQ2/3 and HCN channels as potential targets for designing novel therapeutics that may promote resilience to tinnitus.

K(V)7.4 channels participate in the control of rodent renal vascular resting tone

AIM

We tested the hypothesis that K(V)7 channels contribute to basal renal vascular tone and that they participate in agonist-induced renal vasoconstriction or vasodilation.

METHODS

KV 7 channel subtypes in renal arterioles were characterized by immunofluorescence. Renal blood flow (RBF) was measured using an ultrasonic flow probe. The isometric tension of rat interlobar arteries was examined in a wire myograph. Mice afferent arteriolar diameter was assessed utilizing the perfused juxtamedullary nephron technique.

RESULTS

Immunofluorescence revealed that K(V)7.4 channels were expressed in rat afferent arterioles. The K(V)7 blocker XE991 dose-dependently increased the isometric tension of rat interlobar arteries and caused a small (approx. 4.5%) RBF reduction in vivo. Nifedipine abolished these effects. Likewise, XE991 reduced mouse afferent arteriolar diameter by approx. 5%. The K(V)7.2-5 stimulator flupirtine dose-dependently relaxed isolated rat interlobar arteries and increased (approx. 5%) RBF in vivo. The RBF responses to NE or Ang II administration were not affected by pre-treatment with XE991 or flupirtine. XE991 pre-treatment caused a minor augmentation of the acetylcholine-induced increase in RBF, while flupirtine pre-treatment did not affect this response.

CONCLUSION

It is concluded that K(V)7 channels, via nifedipine sensitive channels, have a role in the regulation of basal renal vascular tone. There is no indication that K(V)7 channels have an effect on agonist-induced renal vasoconstriction while there is a small effect on acetylcholine-induced vasodilation.