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The T618I KCNH2-encoded hERG mutation is the most frequently observed mutation in genotyped cases of the congenital short QT syndrome (SQTS), a cardiac condition associated with ventricular fibrillation and sudden death. Most T618I hERG carriers exhibit a pronounced U wave on the electrocardiogram and appear vulnerable to ventricular, but not atrial fibrillation (AF). The basis for these effects is unclear. This study used the action potential (AP) voltage clamp technique to determine effects of the T618I mutation on hERG current (I hERG ) elicited by APs from different cardiac regions. Whole-cell patch-clamp recordings were made at 37 °C of I hERG from hERG-transfected HEK-293 cells. Maximal I hERG during a ventricular AP command was increased ∼4-fold for T618I I hERG and occurred much earlier during AP repolarization. The mutation also increased peak repolarizing currents elicited by Purkinje fibre (PF) APs. Maximal wild-type (WT) I hERG current during the PF waveform was 87.2 ± 4.5% of maximal ventricular repolarizing current whilst for the T618I mutant, the comparable value was 47.7 ± 2.7%. Thus, the T618I mutation exacerbated differences in repolarizing I hERG between PF and ventricular APs; this could contribute to heterogeneity of ventricular-PF repolarization and consequently to the U waves seen in T618I carriers. The comparatively shorter duration and lack of pronounced plateau of the atrial AP led to a smaller effect of the T618I mutation during the atrial AP, which may help account for the lack of reported AF in T618I carriers. Use of a paired ventricular AP protocol revealed an alteration to protective I hERG transients that affect susceptibility to premature excitation late in AP repolarization/early in diastole. These observations may help explain altered arrhythmia susceptibility in this form of the SQTS., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

The lipophilic polycyclic aromatic hydrocarbon (PAH) phenanthrene is relatively abundant in polluted air and water and can access and accumulate in human tissue. Phenanthrene has been reported to interact with cardiac ion channels in several fish species. This study was undertaken to investigate the ability of phenanthrene to interact with hERG (human Ether-à-go-go-Related Gene) encoded Kv11.1 K + channels, which play a central role in human ventricular repolarization. Pharmacological inhibition of hERG can be proarrhythmic. Whole-cell patch clamp recordings of hERG current (I hERG ) were made from HEK293 cells expressing wild-type (WT) and mutant hERG channels. WT I hERG1a was inhibited by phenanthrene with an IC 50 of 17.6 ± 1.7 µM, whilst I hERG1a/1b exhibited an IC 50 of 1.8 ± 0.3 µM. WT I hERG block showed marked voltage and time dependence, indicative of dependence of inhibition on channel gating. The inhibitory effect of phenanthrene was markedly impaired by the attenuated inactivation N588K mutation. Remarkably, mutations of S6 domain aromatic amino acids (Y652, F656) in the canonical drug binding site did not impair the inhibitory action of phenanthrene; the Y652A mutation augmented I hERG block. In contrast, the F557L (S5) and M651A (S6) mutations impaired the ability of phenanthrene to inhibit I hERG , as did the S624A mutation below the selectivity filter region. Computational docking using a cryo-EM derived hERG structure supported the mutagenesis data. Thus, phenanthrene acts as an inhibitor of the hERG K + channel by directly interacting with the channel, binding to a distinct site in the channel pore domain., (© 2021. The Author(s).)

Cardiac potassium channels encoded by human ether-à-go-go-related gene ( hERG ) are major targets for structurally diverse drugs associated with acquired long QT syndrome. This study characterized hERG channel inhibition by a minimally structured high-affinity hERG inhibitor, Cavalli-2, composed of three phenyl groups linked by polymethylene spacers around a central amino group, chosen to probe the spatial arrangement of side chain groups in the high-affinity drug-binding site of the hERG pore. hERG current ( I hERG ) recorded at physiological temperature from HEK293 cells was inhibited with an IC 50 of 35.6 nm with time and voltage dependence characteristic of blockade contingent upon channel gating. Potency of Cavalli-2 action was markedly reduced for attenuated inactivation mutants located near (S620T; 54-fold) and remote from (N588K; 15-fold) the channel pore. The S6 Y652A and F656A mutations decreased inhibitory potency 17- and 75-fold, respectively, whereas T623A and S624A at the base of the selectivity filter also decreased potency (16- and 7-fold, respectively). The S5 helix F557L mutation decreased potency 10-fold, and both F557L and Y652A mutations eliminated voltage dependence of inhibition. Computational docking using the recent cryo-EM structure of an open channel hERG construct could only partially recapitulate experimental data, and the high dependence of Cavalli-2 block on Phe-656 is not readily explainable in that structure. A small clockwise rotation of the inner (S6) helix of the hERG pore from its configuration in the cryo-EM structure may be required to optimize Phe-656 side chain orientations compatible with high-affinity block., (© 2018 by The American Society for Biochemistry and Molecular Biology, Inc.)