K7 channels are voltage-gated potassium channels encoded by KCNQ genes that have a considerable physiological impact in many cell types. This reliance upon K7 channels for normal cellular function, as well as the existence of hereditary disorders caused by mutations to KCNQ genes, means that pharmacological targeting of these channels has broad appeal. Consequently, a plethora of chemical entities that modulate K7 channel activity have been developed. Moreover, K7 channels are influenced by many disparate intracellular mediators and trafficking processes, making upstream targeting an appealing prospect for therapeutic development. This review covers the main characteristics of these multifunctional and versatile channels with the aim of providing insight into the therapeutic value of targeting these channels.

Objective-Middle cerebral artery (MCA) diameter is regulated by inherent myogenic activity and the effect of potent vasodilators such as calcitonin gene-related peptide (CGRP). Previous studies showed that MCAs express KCNQ1, 4, and 5 potassium channel genes, and the expression products (Kv7 channels) participate in the myogenic control of MCA diameter. The present study investigated the contribution of Kv7.4 and Kv7.5 isoforms to myogenic and CGRP regulation of MCA diameter and determined whether they were affected in hypertensive animals. Approach and Results-Isometric tension recordings performed on MCA from normotensive rats produced CGRP vasodilations that were inhibited by the pan-Kv7 channel blocker linopirdine (P<0.01) and after transfection of arteries with siRNA against KCNQ4 (P<0.01) but not KCNQ5. However, isobaric myography revealed that myogenic constriction in response to increases in intravascular pressure (20-80 mm Hg) was affected by both KCNQ4 and KCNQ5 siRNA. Proximity ligation assay signals were equally abundant for Kv7.4/Kv7.4 or Kv7.4/Kv7.5 antibody combinations but minimal for Kv7.5/Kv7.5 antibodies or Kv7.4/7.1 combinations. In contrast to systemic arteries, Kv7 function and Kv7.4 abundance in MCA were not altered in hypertensive rats. Conclusions-This study reveals, for the first time to our knowledge, that in cerebral arteries, Kv7.4 and Kv7.5 proteins exist predominantly as a functional heterotetramer, which regulates intrinsic myogenicity and vasodilation attributed to CGRP. Surprisingly, unlike systemic arteries, Kv7 activity in MCAs is not affected by the development of hypertension, and CGRP-mediated vasodilation is well maintained. As such, cerebrovascular Kv7 channels could be amenable for therapeutic targeting in conditions such as cerebral vasospasm. evidence demonstrated that Kv7.4 channels in systemic arteries, such as the mesenteric and renal, are severely compromised in hypertension. 2,4 A similar situation in cerebral circulation would lead to a predilection toward vasospasm and may underlie ischemic stroke. Here, we used a combination of molecular and functional approaches to define the interaction of different Kv7 channels in MCA and to ascertain the functional impact of individual Kv7 isoforms in the intrinsic and CGRP-mediated regulation of arterial diameter. Materials and MethodsMaterials and Methods are available in the online-only Supplement. ResultsInitial studies used a pharmacological approach to tease out a functional role for KCNQ1, 4, and 5 that are dominantly expressed in the MCA. 5 The application of a selective Kv7.1 channel blocker, HMR1556 (10 μmol/L), 12 had no effect on MCA tone, whereas the pan-Kv7 channel blocker, linopirdine, evoked robust contractions of MCAs under similar conditions ( Figure 1A). In MCAs precontracted with 0.1 μmol/L U46619, the application of Kv7.2 to Kv7.5 channel activators, retigabine and S-1, caused relaxation in a concentration-dependent manner with the latter being more potent ( Figure 1B). In contrast, the Kv7.1-selective...

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The Kv7 family of voltage-gated potassium channels are expressed within the vasculature where they are key regulators of vascular tone and mediate cAMP-linked endogenous vasodilator responses, a pathway that is compromised in hypertension. However, the role of Kv7 channels in non–cAMP-linked vasodilator pathways has not been investigated. Natriuretic peptides are potent vasodilators, which operate primarily through the activation of a cGMP-dependent signaling pathway. This study investigated the putative role of Kv7 channels in natriuretic peptide–dependent relaxations in the vasculature of normal and hypertensive animals. Relaxant responses of rat aorta to both atrial and C-type natriuretic peptides and the nitric oxide donor sodium nitroprusside were impaired by the Kv7 blocker linopirdine (10 μmol/L) but not by the Kv7.1-specific blocker HMR1556 (10 μmol/L) and other K + channel blockers. In contrast, only the atrial natriuretic peptide response was sensitive to linopirdine in the renal artery. These Kv7-mediated responses were attenuated in arteries from hypertensive rats. Quantitative polymerase chain reaction showed that A- and B-type natriuretic peptide receptors were expressed at high levels in the aorta and renal artery from normal and spontaneously hypertensive rats. This study provides the first evidence that natriuretic peptide responses are impaired in hypertension and that recruitment of Kv7 channels is a key component of natriuretic peptide–dependent vasodilations.

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

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.Kv7 channels | KCNQ genes | G-protein beta gamma subunits | electrophysiology | vascular biology

BACKGROUND AND PURPOSEThe KCNQ-encoded voltage-gated potassium channel family (Kv7.1-Kv7.5) are established regulators of smooth muscle contractility, where Kv7.4 and Kv7.5 predominate. Various Kv7.2-7.5 channel enhancers have been developed that have been shown to cause a vasorelaxation in both rodent and human blood vessels. Recently, two novel Kv7 channel enhancers have been identified, ML213 and NS15370, that show increased potency, particularly on Kv7.4 channels. The aim of this study was to characterize the effects of these novel enhancers in different rat blood vessels and compare them with Kv7 enhancers (S-1, BMS204352, retigabine) described previously. We also sought to determine the binding sites of the new Kv7 enhancers. KEY RESULTSBoth ML213 and NS15370 relaxed segments of rat thoracic aorta, renal artery and mesenteric artery in a concentration-dependent manner. In the mesenteric artery ML213 and NS15370 displayed EC50s that were far lower than other Kv7 enhancers tested. Current-clamp experiments revealed that both novel enhancers, at low concentrations, caused significant hyperpolarization in mesenteric artery smooth muscle cells. In addition, we determined that the stimulatory effect of these enhancers relied on a tryptophan residue located in the S5 domain, which is the same binding site for the other Kv7 enhancers tested in this study. CONCLUSIONS AND IMPLICATIONSThis study has identified and characterized ML213 and NS15370 as potent vasorelaxants in different blood vessels, thereby highlighting these new compounds as potential therapeutics for various smooth muscle disorders. Abbreviations

AimsKv7.4, 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 resultsIn 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.ConclusionThis 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.