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The KCNQ1 gene encodes the α-subunit of the cardiac voltage-gated potassium (Kv) channel KCNQ1, also denoted as Kv7.1 or KvLQT1. The channel assembles with the ß-subunit KCNE1, also known as minK, to generate the slowly activating cardiac delayed rectifier current I Ks , a key regulator of the heart rate dependent adaptation of the cardiac action potential duration (APD). Loss-of-function variants in KCNQ1 cause the congenital Long QT1 (LQT1) syndrome, characterized by delayed cardiac repolarization and a QT interval prolongation in the surface electrocardiogram (ECG). Autosomal dominant loss-of-function variants in KCNQ1 result in the LQT syndrome called Romano-Ward syndrome (RWS), while autosomal recessive variants affecting function, lead to Jervell and Lange-Nielsen syndrome (JLNS), associated with deafness. The aim of this study was the characterization of novel KCNQ1 variants identified in patients with RWS to widen the spectrum of known LQT1 variants, and improve the interpretation of the clinical relevance of variants in the KCNQ1 gene. We functionally characterized nine human KCNQ1 variants using the voltage-clamp technique in Xenopus laevis oocytes, from which we report seven novel variants. The functional data was taken as input to model surface ECGs, to subsequently compare the functional changes with the clinically observed QTc times, allowing a further interpretation of the severity of the different LQTS variants. We found that the electrophysiological properties of the variants correlate with the severity of the clinically diagnosed phenotype in most cases, however, not in all. Electrophysiological studies combined with in silico modelling approaches are valuable components for the interpretation of the pathogenicity of KCNQ1 variants, but assessing the clinical severity demands the consideration of other factors that are included, for example in the Schwartz score.

KvLQT1 and hERG are the α-subunits of the voltage-gated K + channels which carry the cardiac repolarizing currents IKs and IKr, respectively. These currents function in vivo with some redundancy to maintain appropriate action potential durations (APDs) in cardiomyocytes. As such, protein-protein interactions between hERG and KvLQT1 may be important in normal cardiac electrophysiology, as well as in arrhythmia and sudden cardiac death. Previous phenomenological observations of functional, mutual downregulation between these complementary repolarizing currents in transgenic rabbit models and human cell culture motivate our investigations into protein-protein interactions between hERG and KvLQT1. Previous data suggest that a dynamic, physical interaction between hERG and KvLQT1 modulates the respective currents. However, the mechanism by which hERG-KvLQT1 interactions are regulated is still poorly understood. Phosphorylation is proposed to play a role since modifying the phosphorylation state of each protein has been shown to alter channel kinetics, and both hERG and KvLQT1 are targets of the Ser/Thr protein kinase PKA, activated by elevated intracellular cAMP. In this work, quantitative apFRET analyses of phosphonull and phosphomimetic hERG and KvLQT1 mutants indicate that unphosphorylated hERG does not interact with KvLQT1, suggesting that hERG phosphorylation is important for wild-type proteins to interact. For proteins already potentially interacting, phosphorylation of KvLQT1 appears to be the driving factor abrogating hERG-KvLQT1 interaction. This work increases our knowledge about hERG-KvLQT1 interactions, which may contribute to the efforts to elucidate mechanisms that underlie many types of arrhythmias, and also further characterizes novel protein-protein interactions between two distinct potassium channel families., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Abuse of the common anti-diarrheal loperamide is associated with QT interval prolongation as well as development of the potentially fatal arrhythmia torsades de pointes. The mechanism underlying this cardiotoxicity is high affinity inhibition of the human ether-a-go-go-related gene (hERG) cardiac K+ channel. N-Desmethyl loperamide is the major metabolite of loperamide and is a close structural relative of the parent molecule. To date no information is available regarding the affinity of N-desmethyl loperamide for human cardiac ion channels. The effects of N-desmethyl loperamide on various cloned human cardiac ion channels including hERG, KvLQT1/mink and Na v 1.5 were studied and compared to that of the parent. N-Desmethyl loperamide was a much weaker (7.5-fold) inhibitor of hERG compared to loperamide. However, given the higher plasma levels of the metabolite relative to the parent, it is likely that N-desmethyl loperamide can contribute, at least secondarily, to the cardiotoxicity observed with loperamide abuse. We used the recently solved cryo-EM structure of the hERG channel together with previously published inhibitors, to understand the basis of the interactions as well as the difference that a single methyl plays in the hERG channel blocking affinities of these two compounds., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

I Ks channels open in response to depolarization of the membrane voltage during the cardiac action potential, passing potassium ions outward to repolarize ventricular myocytes and end each beat. Here, we show that the voltage required to activate I Ks channels depends on their covalent modification by small ubiquitin-like modifier (SUMO) proteins. I Ks channels are comprised of four KCNQ1 pore-forming subunits, two KCNE1 accessory subunits, and up to four SUMOs, one on Lys 424 of each KCNQ1 subunit. Each SUMO shifts the half-maximal activation voltage (V 1/2 ) of I Ks ∼ +8 mV, producing a maximal +34-mV shift in neonatal mouse cardiac myocytes or Chinese hamster ovary (CHO) cells expressing the mouse or human subunits. Unexpectedly, channels formed without KCNE1 carry at most two SUMOs despite having four available KCNQ1-Lys 424 sites. SUMOylation of KCNQ1 is KCNE1 dependent and determines the native attributes of cardiac I Ks in vivo., Competing Interests: The authors declare no conflict of interest.

Background: The most common inherited cardiac arrhythmia, LQT1, is due to IKs potassium channel mutations and is linked to high risk of adrenergic-triggered cardiac events. We recently showed that although exercise-triggered events are very well treated by ß-blockers for these patients, acute arousal-triggered event rate were not significantly reduced after beta-blocker treatment, suggesting that the mechanisms underlying arousal-triggered arrhythmias may be different from those during exercise. IKs is strongly regulated by β-adrenergic receptor (β-AR) signaling, but little is known about the role of α1-AR-mediated regulation., Methods and Results: Here we show, using a combination of cellular electrophysiology and computational modeling, that IKs phosphorylation and α1-AR regulation via activation of calcium-dependent PKC isoforms (cPKC) may be a key mechanism to control channel voltage-dependent activation and consequently action potential duration (APD) in response to adrenergic-stimulus. We show that simulated mutation-specific combined adrenergic effects (β+α) on APD were strongly correlated to acute stress-triggered cardiac event rate for patients while β-AR effects alone were not., Conclusion: We were able to show that calcium-dependent PKC signaling is key to normal QT shortening during acute arousal and when impaired, correlates with increased rate of sudden arousal-triggered cardiac events. Our study suggests that the acute α1-AR-cPKC regulation of IKs is important for QT shortening in "fight-or-flight" response and is linked to decreased risk of sudden emotion/arousal-triggered cardiac events in LQT1 patients., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

KCNE1 (E1) β-subunits assemble with KCNQ1 (Q1) voltage-gated K(+) channel α-subunits to form IKslow (IKs) channels in the heart and ear. The number of E1 subunits in IKs channels has been an issue of ongoing debate. Here, we use single-molecule spectroscopy to demonstrate that surface IKs channels with human subunits contain two E1 and four Q1 subunits. This stoichiometry does not vary. Thus, IKs channels in cells with elevated levels of E1 carry no more than two E1 subunits. Cells with low levels of E1 produce IKs channels with two E1 subunits and Q1 channels with no E1 subunits--channels with one E1 do not appear to form or are restricted from surface expression. The plethora of models of cardiac function, transgenic animals, and drug screens based on variable E1 stoichiometry do not reflect physiology.