1
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Muhammad A, Calandranis ME, Li B, Yang T, Blackwell DJ, Harvey ML, Smith JE, Daniel ZA, Chew AE, Capra JA, Matreyek KA, Fowler DM, Roden DM, Glazer AM. High-throughput functional mapping of variants in an arrhythmia gene, KCNE1, reveals novel biology. Genome Med 2024; 16:73. [PMID: 38816749 PMCID: PMC11138074 DOI: 10.1186/s13073-024-01340-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Accepted: 04/26/2024] [Indexed: 06/01/2024] Open
Abstract
BACKGROUND KCNE1 encodes a 129-residue cardiac potassium channel (IKs) subunit. KCNE1 variants are associated with long QT syndrome and atrial fibrillation. However, most variants have insufficient evidence of clinical consequences and thus limited clinical utility. METHODS In this study, we leveraged the power of variant effect mapping, which couples saturation mutagenesis with high-throughput sequencing, to ascertain the function of thousands of protein-coding KCNE1 variants. RESULTS We comprehensively assayed KCNE1 variant cell surface expression (2554/2709 possible single-amino-acid variants) and function (2534 variants). Our study identified 470 loss- or partial loss-of-surface expression and 574 loss- or partial loss-of-function variants. Of the 574 loss- or partial loss-of-function variants, 152 (26.5%) had reduced cell surface expression, indicating that most functionally deleterious variants affect channel gating. Nonsense variants at residues 56-104 generally had WT-like trafficking scores but decreased functional scores, indicating that the latter half of the protein is dispensable for protein trafficking but essential for channel function. 22 of the 30 KCNE1 residues (73%) highly intolerant of variation (with > 70% loss-of-function variants) were in predicted close contact with binding partners KCNQ1 or calmodulin. Our functional assay data were consistent with gold standard electrophysiological data (ρ = - 0.64), population and patient cohorts (32/38 presumed benign or pathogenic variants with consistent scores), and computational predictors (ρ = - 0.62). Our data provide moderate-strength evidence for the American College of Medical Genetics/Association of Molecular Pathology functional criteria for benign and pathogenic variants. CONCLUSIONS Comprehensive variant effect maps of KCNE1 can both provide insight into I Ks channel biology and help reclassify variants of uncertain significance.
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Affiliation(s)
- Ayesha Muhammad
- Vanderbilt Genetics Institute, Vanderbilt University Medical Center, 1235 Medical Research Building IV, 2215B Garland Avenue, Nashville, TN, 37232, USA
- Medical Scientist Training Program, Vanderbilt University, Nashville, TN, 37232, USA
| | - Maria E Calandranis
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Bian Li
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
- Regeneron Pharmaceuticals Inc., Tarrytown, NY, USA
| | - Tao Yang
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Daniel J Blackwell
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - M Lorena Harvey
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Jeremy E Smith
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Zerubabell A Daniel
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Ashli E Chew
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - John A Capra
- Bakar Computational Health Sciences Institute and Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, 94143, USA
| | - Kenneth A Matreyek
- Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
| | - Douglas M Fowler
- Department of Genome Sciences, University of Washington, Seattle, WA, 98195, USA
| | - Dan M Roden
- Vanderbilt Genetics Institute, Vanderbilt University Medical Center, 1235 Medical Research Building IV, 2215B Garland Avenue, Nashville, TN, 37232, USA
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
- Department of Biomedical Informatics, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Andrew M Glazer
- Vanderbilt Genetics Institute, Vanderbilt University Medical Center, 1235 Medical Research Building IV, 2215B Garland Avenue, Nashville, TN, 37232, USA.
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA.
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2
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Muhammad A, Calandranis ME, Li B, Yang T, Blackwell DJ, Harvey ML, Smith JE, Chew AE, Capra JA, Matreyek KA, Fowler DM, Roden DM, Glazer AM. High-throughput functional mapping of variants in an arrhythmia gene, KCNE1, reveals novel biology. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.28.538612. [PMID: 37162834 PMCID: PMC10168370 DOI: 10.1101/2023.04.28.538612] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Background KCNE1 encodes a 129-residue cardiac potassium channel (IKs) subunit. KCNE1 variants are associated with long QT syndrome and atrial fibrillation. However, most variants have insufficient evidence of clinical consequences and thus limited clinical utility. Results Here, we demonstrate the power of variant effect mapping, which couples saturation mutagenesis with high-throughput sequencing, to ascertain the function of thousands of protein coding KCNE1 variants. We comprehensively assayed KCNE1 variant cell surface expression (2,554/2,709 possible single amino acid variants) and function (2,539 variants). We identified 470 loss-of-surface expression and 588 loss-of-function variants. Out of the 588 loss-of-function variants, only 155 had low cell surface expression. The latter half of the protein is dispensable for protein trafficking but essential for channel function. 22 of the 30 KCNE1 residues (73%) highly intolerant of variation were in predicted close contact with binding partners KCNQ1 or calmodulin. Our data were highly concordant with gold standard electrophysiological data (ρ = -0.65), population and patient cohorts (32/38 concordant variants), and computational metrics (ρ = -0.55). Our data provide moderate-strength evidence for the ACMG/AMP functional criteria for benign and pathogenic variants. Conclusions Comprehensive variant effect maps of KCNE1 can both provide insight into IKs channel biology and help reclassify variants of uncertain significance.
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Affiliation(s)
- Ayesha Muhammad
- Vanderbilt Genetics Institute, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Medical Scientist Training Program, Vanderbilt University, Nashville, TN 37232, USA
| | - Maria E. Calandranis
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Bian Li
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Tao Yang
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Daniel J. Blackwell
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - M. Lorena Harvey
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Jeremy E. Smith
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Ashli E. Chew
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - John A. Capra
- Bakar Computational Health Sciences Institute and Department of Epidemiology and Biostatistics, University of California, San Francisco, CA 94143, USA
| | - Kenneth A. Matreyek
- Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Douglas M. Fowler
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Dan M. Roden
- Vanderbilt Genetics Institute, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Department of Biomedical Informatics, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Andrew M. Glazer
- Vanderbilt Genetics Institute, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA
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3
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Ukachukwu CU, Jimenez-Vazquez EN, Jain A, Jones DK. hERG1 channel subunit composition mediates proton inhibition of rapid delayed rectifier potassium current (I Kr) in cardiomyocytes derived from hiPSCs. J Biol Chem 2023; 299:102778. [PMID: 36496073 PMCID: PMC9867984 DOI: 10.1016/j.jbc.2022.102778] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 11/29/2022] [Accepted: 12/04/2022] [Indexed: 12/13/2022] Open
Abstract
The voltage-gated channel, hERG1, conducts the rapid delayed rectifier potassium current (IKr) and is critical for human cardiac repolarization. Reduced IKr causes long QT syndrome and increases the risk for cardiac arrhythmia and sudden death. At least two subunits form functional hERG1 channels, hERG1a and hERG1b. Changes in hERG1a/1b abundance modulate IKr kinetics, magnitude, and drug sensitivity. Studies from native cardiac tissue suggest that hERG1 subunit abundance is dynamically regulated, but the impact of altered subunit abundance on IKr and its response to external stressors is not well understood. Here, we used a substrate-driven human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) maturation model to investigate how changes in relative hERG1a/1b subunit abundance impact the response of native IKr to extracellular acidosis, a known component of ischemic heart disease and sudden infant death syndrome. IKr recorded from immatured hiPSC-CMs displays a 2-fold greater inhibition by extracellular acidosis (pH 6.3) compared with matured hiPSC-CMs. Quantitative RT-PCR and immunocytochemistry demonstrated that hERG1a subunit mRNA and protein were upregulated and hERG1b subunit mRNA and protein were downregulated in matured hiPSC-CMs compared with immatured hiPSC-CMs. The shift in subunit abundance in matured hiPSC-CMs was accompanied by increased IKr. Silencing hERG1b's impact on native IKr kinetics by overexpressing a polypeptide identical to the hERG1a N-terminal Per-Arnt-Sim domain reduced the magnitude of IKr proton inhibition in immatured hiPSC-CMs to levels comparable to those observed in matured hiPSC-CMs. These data demonstrate that hERG1 subunit abundance is dynamically regulated and determines IKr proton sensitivity in hiPSC-CMs.
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Affiliation(s)
- Chiamaka U Ukachukwu
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Eric N Jimenez-Vazquez
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Abhilasha Jain
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - David K Jones
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, USA; Department of Internal Medicine, University of Michigan Medical School.
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4
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Lopez-Medina AI, Chahal CAA, Luzum JA. The genetics of drug-induced QT prolongation: evaluating the evidence for pharmacodynamic variants. Pharmacogenomics 2022; 23:543-557. [PMID: 35698903 DOI: 10.2217/pgs-2022-0027] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Drug-induced long QT syndrome (diLQTS) is an adverse effect of many commonly prescribed drugs, and it can increase the risk for lethal ventricular arrhythmias. Genetic variants in pharmacodynamic genes have been associated with diLQTS, but the strength of the evidence for each of those variants has not yet been evaluated. Therefore, the purpose of this review was to evaluate the strength of the evidence for pharmacodynamic genetic variants associated with diLQTS using a novel, semiquantitative scoring system modified from the approach used for congenital LQTS. KCNE1-D85N and KCNE2-T8A had definitive and strong evidence for diLQTS, respectively. The high level of evidence for these variants supports current consideration as risk factors for patients that will be prescribed a QT-prolonging drug.
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Affiliation(s)
- Ana I Lopez-Medina
- Department of Clinical Pharmacy, University of Michigan College of Pharmacy, Ann Arbor, MI 48109, USA
| | - Choudhary Anwar A Chahal
- Division of Cardiovascular Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA 19104, USA.,Department of Cardiovascular Diseases, Mayo Clinic, Rochester, MN 55905, USA.,Barts Heart Centre, St. Bartholomew's Hospital, West Smithfield, London, EC1A 7BE, UK.,WellSpan Health, Lancaster, PA 17607, USA
| | - Jasmine A Luzum
- Department of Clinical Pharmacy, University of Michigan College of Pharmacy, Ann Arbor, MI 48109, USA
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5
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Du C, Zhang H, Harmer SC, Hancox JC. Identification through action potential clamp of proarrhythmic consequences of the short QT syndrome T618I hERG 'hotspot' mutation. Biochem Biophys Res Commun 2022; 596:49-55. [PMID: 35114584 PMCID: PMC8865743 DOI: 10.1016/j.bbrc.2022.01.057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Accepted: 01/14/2022] [Indexed: 11/30/2022]
Abstract
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 (IhERG) elicited by APs from different cardiac regions. Whole-cell patch-clamp recordings were made at 37 °C of IhERG from hERG-transfected HEK-293 cells. Maximal IhERG during a ventricular AP command was increased ∼4-fold for T618I IhERG and occurred much earlier during AP repolarization. The mutation also increased peak repolarizing currents elicited by Purkinje fibre (PF) APs. Maximal wild-type (WT) IhERG 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 IhERG 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 IhERG 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. T618I is a ‘hotspot’ hERG potassium channel mutation in the congenital short QT syndrome. Differences in hERG current during ventricular and Purkinje fibre action potentials are exacerbated by the T618I mutation. T618I has more modest effects on current during atrial action potentials. T618I modifies the protective response of hERG to premature ventricular excitation. These alterations to hERG function help explain ECG changes reported in T618I-hERG carriers.
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Affiliation(s)
- Chunyun Du
- School of Physiology, Pharmacology and Neuroscience, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD, UK
| | - Henggui Zhang
- Biological Physics Group, Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
| | - Stephen C Harmer
- School of Physiology, Pharmacology and Neuroscience, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD, UK
| | - Jules C Hancox
- School of Physiology, Pharmacology and Neuroscience, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD, UK; Biological Physics Group, Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.
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6
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Kemp JM, Whittaker DG, Venkateshappa R, Pang Z, Johal R, Sergeev V, Tibbits GF, Mirams GR, Claydon TW. Electrophysiological characterization of the hERG R56Q LQTS variant and targeted rescue by the activator RPR260243. J Gen Physiol 2021; 153:212555. [PMID: 34398210 PMCID: PMC8493834 DOI: 10.1085/jgp.202112923] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Revised: 06/11/2021] [Accepted: 07/21/2021] [Indexed: 11/20/2022] Open
Abstract
Human Ether-à-go-go (hERG) channels contribute to cardiac repolarization, and inherited variants or drug block are associated with long QT syndrome type 2 (LQTS2) and arrhythmia. Therefore, hERG activator compounds present a therapeutic opportunity for targeted treatment of LQTS. However, a limiting concern is over-activation of hERG resurgent current during the action potential and abbreviated repolarization. Activators that slow deactivation gating (type I), such as RPR260243, may enhance repolarizing hERG current during the refractory period, thus ameliorating arrhythmogenicity with reduced early repolarization risk. Here, we show that, at physiological temperature, RPR260243 enhances hERG channel repolarizing currents conducted in the refractory period in response to premature depolarizations. This occurs with little effect on the resurgent hERG current during the action potential. The effects of RPR260243 were particularly evident in LQTS2-associated R56Q mutant channels, whereby RPR260243 restored WT-like repolarizing drive in the early refractory period and diastolic interval, combating attenuated protective currents. In silico kinetic modeling of channel gating predicted little effect of the R56Q mutation on hERG current conducted during the action potential and a reduced repolarizing protection against afterdepolarizations in the refractory period and diastolic interval, particularly at higher pacing rates. These simulations predicted partial rescue from the arrhythmic effects of R56Q by RPR260243 without risk of early repolarization. Our findings demonstrate that the pathogenicity of some hERG variants may result from reduced repolarizing protection during the refractory period and diastolic interval with limited effect on action potential duration, and that the hERG channel activator RPR260243 may provide targeted antiarrhythmic potential in these cases.
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Affiliation(s)
- Jacob M Kemp
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, Canada
| | - Dominic G Whittaker
- Centre for Mathematical Medicine & Biology, School of Mathematical Sciences, University of Nottingham, Nottingham, UK
| | | | - ZhaoKai Pang
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, Canada
| | - Raj Johal
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, Canada
| | - Valentine Sergeev
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, Canada
| | - Glen F Tibbits
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, Canada
| | - Gary R Mirams
- Centre for Mathematical Medicine & Biology, School of Mathematical Sciences, University of Nottingham, Nottingham, UK
| | - Thomas W Claydon
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, Canada
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7
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Kojima A, Mi X, Fukushima Y, Ding WG, Omatsu-Kanbe M, Matsuura H. Elevation of propofol sensitivity of cardiac I Ks channel by KCNE1 polymorphism D85N. Br J Pharmacol 2021; 178:2690-2708. [PMID: 33763865 DOI: 10.1111/bph.15460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 03/13/2021] [Accepted: 03/16/2021] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE The slowly activating delayed rectifier K+ channel (IKs ), composed of pore-forming KCNQ1 α-subunits and ancillary KCNE1 β-subunits, regulates ventricular repolarization in human heart. Propofol, at clinically used concentrations, modestly inhibits the intact (wild-type) IKs channels and is therefore unlikely to appreciably prolong QT interval in ECG during anaesthesia. However, little information is available concerning the inhibitory effect of propofol on IKs channel associated with its gene variants implicated in QT prolongation. The KCNE1 single nucleotide polymorphism leading to D85N is associated with drug-induced QT prolongation and therefore regarded as a clinically important genetic variant. This study examined whether KCNE1-D85N affects the sensitivity of IKs to inhibition by propofol. EXPERIMENTAL APPROACH Whole-cell patch-clamp and immunostaining experiments were conducted in HEK293 cells and/or mouse cardiomyocyte-derived HL-1 cells, transfected with wild-type KCNQ1, wild-type or variant KCNE1 cDNAs. KEY RESULTS Propofol inhibited KCNQ1/KCNE1-D85N current more potently than KCNQ1/KCNE1 current in HEK293 cells and HL-1 cells. Immunostaining experiments in HEK293 cells revealed that pretreatment with propofol (10 μM) did not appreciably affect cell membrane expression of KCNQ1 and KCNE1 proteins in KCNQ1/KCNE1 and KCNQ1/KCNE1-D85N channels. CONCLUSION AND IMPLICATIONS The KCNE1 polymorphism D85N significantly elevates the sensitivity of IKs to inhibition by propofol. This study detects a functionally important role of KCNE1-D85N polymorphism in conferring genetic susceptibility to propofol-induced QT prolongation and further suggests the possibility that the inhibitory action of anaesthetics on ionic currents becomes exaggerated in patients carrying variants in genes encoding ion channels.
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Affiliation(s)
- Akiko Kojima
- Department of Anesthesiology, Shiga University of Medical Science, Otsu, Japan
| | - Xinya Mi
- Department of Physiology, Shiga University of Medical Science, Otsu, Japan
| | - Yutaka Fukushima
- Department of Anesthesiology, Shiga University of Medical Science, Otsu, Japan
| | - Wei-Guang Ding
- Department of Physiology, Shiga University of Medical Science, Otsu, Japan
| | | | - Hiroshi Matsuura
- Department of Physiology, Shiga University of Medical Science, Otsu, Japan
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9
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Bennett JS, Bernhardt M, McBride KL, Reshmi SC, Zmuda E, Kertesz NJ, Garg V, Fitzgerald-Butt S, Kamp AN. Reclassification of Variants of Uncertain Significance in Children with Inherited Arrhythmia Syndromes is Predicted by Clinical Factors. Pediatr Cardiol 2019; 40:1679-1687. [PMID: 31535183 DOI: 10.1007/s00246-019-02203-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2019] [Accepted: 08/28/2019] [Indexed: 12/19/2022]
Abstract
Genetic testing is important to augment clinical diagnosis and inform management of inherited arrhythmias syndromes (IAS), but variants of uncertain significance (VUS) are common and remain a challenge in clinical practice. In 2015, American College of Medical Genetics (ACMG) published updated guidelines for interpretation of genetic results. Despite increasing understanding of human genomic variation, there are no guidelines for reinterpretation of prior genetic test results. Patients at a single tertiary children's hospital with genetic testing for an IAS that demonstrated a VUS were re-evaluated using 2015 ACMG guidelines, clinical information, and publically available databases. Search of the electronic medical record identified 116 patients with genetic testing results available, and 24/116 (21%) harbored a VUS for an IAS. 23 unique VUS were evaluated from 12 genes. Over half of the VUS (12/23 (52%)) were reclassified using 2015 criteria, and 8 (35%) changed to pathogenic and 4 (17%) to benign. Relative risk of reclassification of VUS to a pathogenic variant in a patient with confirmed clinical diagnosis was 4.1 (95% CI 1.23-15.4). Reclassification was not associated with initial testing year. These data demonstrate 52% of VUS in children with IAS are reclassified with application of 2015 ACMG guidelines. Strength of phenotyping is associated with eventual pathogenic classification of genetic variants and periodic re-evaluation of VUS identified on genetic testing for IAS is warranted.
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Affiliation(s)
- Jeffrey S Bennett
- Department of Pediatrics, The Ohio State University College of Medicine, Columbus, OH, USA.,The Heart Center, Nationwide Children's Hospital, 700 Children's Drive, Columbus, OH, 43205, USA
| | - Madison Bernhardt
- Department of Medical Genetics, St. Luke's Mountain States Tumor Institute, Boise, ID, USA
| | - Kim L McBride
- Department of Pediatrics, The Ohio State University College of Medicine, Columbus, OH, USA.,Division of Genetic and Genomic Medicine, Nationwide Children's Hospital, Columbus, OH, USA.,The Center for Cardiovascular Research, Nationwide Children's Hospital, Columbus, OH, USA
| | - Shalini C Reshmi
- Department of Pediatrics, The Ohio State University College of Medicine, Columbus, OH, USA.,Department of Pathology and Laboratory Medicine, Nationwide Children's Hospital, Columbus, OH, USA
| | - Erik Zmuda
- Department of Pediatrics, The Ohio State University College of Medicine, Columbus, OH, USA.,Department of Pathology and Laboratory Medicine, Nationwide Children's Hospital, Columbus, OH, USA
| | - Naomi J Kertesz
- Department of Pediatrics, The Ohio State University College of Medicine, Columbus, OH, USA.,The Heart Center, Nationwide Children's Hospital, 700 Children's Drive, Columbus, OH, 43205, USA
| | - Vidu Garg
- Department of Pediatrics, The Ohio State University College of Medicine, Columbus, OH, USA.,The Heart Center, Nationwide Children's Hospital, 700 Children's Drive, Columbus, OH, 43205, USA.,The Center for Cardiovascular Research, Nationwide Children's Hospital, Columbus, OH, USA
| | - Sara Fitzgerald-Butt
- Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Anna N Kamp
- Department of Pediatrics, The Ohio State University College of Medicine, Columbus, OH, USA. .,The Heart Center, Nationwide Children's Hospital, 700 Children's Drive, Columbus, OH, 43205, USA.
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10
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Haworth AS, Brackenbury WJ. Emerging roles for multifunctional ion channel auxiliary subunits in cancer. Cell Calcium 2019; 80:125-140. [PMID: 31071485 PMCID: PMC6553682 DOI: 10.1016/j.ceca.2019.04.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Revised: 04/16/2019] [Accepted: 04/16/2019] [Indexed: 02/07/2023]
Abstract
Several superfamilies of plasma membrane channels which regulate transmembrane ion flux have also been shown to regulate a multitude of cellular processes, including proliferation and migration. Ion channels are typically multimeric complexes consisting of conducting subunits and auxiliary, non-conducting subunits. Auxiliary subunits modulate the function of conducting subunits and have putative non-conducting roles, further expanding the repertoire of cellular processes governed by ion channel complexes to processes such as transcellular adhesion and gene transcription. Given this expansive influence of ion channels on cellular behaviour it is perhaps no surprise that aberrant ion channel expression is a common occurrence in cancer. This review will focus on the conducting and non-conducting roles of the auxiliary subunits of various Ca2+, K+, Na+ and Cl- channels and the burgeoning evidence linking such auxiliary subunits to cancer. Several subunits are upregulated (e.g. Cavβ, Cavγ) and downregulated (e.g. Kvβ) in cancer, while other subunits have been functionally implicated as oncogenes (e.g. Navβ1, Cavα2δ1) and tumour suppressor genes (e.g. CLCA2, KCNE2, BKγ1) based on in vivo studies. The strengthening link between ion channel auxiliary subunits and cancer has exposed these subunits as potential biomarkers and therapeutic targets. However further mechanistic understanding is required into how these subunits contribute to tumour progression before their therapeutic potential can be fully realised.
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Affiliation(s)
- Alexander S Haworth
- Department of Biology, University of York, Heslington, York, YO10 5DD, UK; York Biomedical Research Institute, University of York, Heslington, York, YO10 5DD, UK
| | - William J Brackenbury
- Department of Biology, University of York, Heslington, York, YO10 5DD, UK; York Biomedical Research Institute, University of York, Heslington, York, YO10 5DD, UK.
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11
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Hagen CM, Gonçalves VF, Hedley PL, Bybjerg-Grauholm J, Bækvad-Hansen M, Hansen CS, Kanters JK, Nielsen J, Mors O, Demur AB, Als TD, Nordentoft M, Børglum A, Mortensen PB, Kennedy J, Werge TM, Hougaard DM, Christiansen M. Schizophrenia-associated mt-DNA SNPs exhibit highly variable haplogroup affiliation and nuclear ancestry: Bi-genomic dependence raises major concerns for link to disease. PLoS One 2018; 13:e0208828. [PMID: 30532134 PMCID: PMC6287820 DOI: 10.1371/journal.pone.0208828] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Accepted: 11/23/2018] [Indexed: 11/19/2022] Open
Abstract
Mitochondria play a significant role in human diseases. However, disease associations with mitochondrial DNA (mtDNA) SNPs have proven difficult to replicate. An analysis of eight schizophrenia-associated mtDNA SNPs, in 23,743 Danes without a psychiatric diagnosis and 2,538 schizophrenia patients, revealed marked inter-allelic differences in mitochondrial haplogroup affiliation and nuclear ancestry. This bi-genomic dependence could entail population stratification. Only two mitochondrial SNPs, m.15043A and m.15218G, were significantly associated with schizophrenia. However, these associations disappeared when corrected for haplogroup affiliation and nuclear ancestry. The extensive bi-genomic dependence documented here is a major concern when interpreting historic, as well as designing future, mtDNA association studies.
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Affiliation(s)
- Christian M. Hagen
- Department for Congenital Disorders, Statens Serum Institut, Copenhagen, Denmark
| | | | - Paula L. Hedley
- Department for Congenital Disorders, Statens Serum Institut, Copenhagen, Denmark
| | | | - Marie Bækvad-Hansen
- Department for Congenital Disorders, Statens Serum Institut, Copenhagen, Denmark
| | - Christine S. Hansen
- Department for Congenital Disorders, Statens Serum Institut, Copenhagen, Denmark
| | - Jørgen K. Kanters
- Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jimmi Nielsen
- Aalborg Psychiatric Hospital, Aalborg University Hospital, Aalborg, Denmark
| | - Ole Mors
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Alfonso B. Demur
- Mental Health Centre, Sct Hans, Capital Region of Denmark, Denmark
| | - Thomas D. Als
- Institute of Medical Genetics, Aarhus University, Aarhus, Denmark
| | | | - Anders Børglum
- Institute of Medical Genetics, Aarhus University, Aarhus, Denmark
| | - Preben B. Mortensen
- Center for Register Research, Institute of Economics, Aarhus University, Aarhus, Denmark
| | - James Kennedy
- Centre for Addiction and Mental Health, University of Toronto, Toronto, Canada
| | - Thomas M. Werge
- Mental Health Centre, Sct Hans, Capital Region of Denmark, Denmark
| | - David M. Hougaard
- Department for Congenital Disorders, Statens Serum Institut, Copenhagen, Denmark
| | - Michael Christiansen
- Department for Congenital Disorders, Statens Serum Institut, Copenhagen, Denmark
- Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
- * E-mail:
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12
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Lainez S, Doray A, Hancox JC, Cannell MB. Regulation of Kv4.3 and hERG potassium channels by KChIP2 isoforms and DPP6 and response to the dual K + channel activator NS3623. Biochem Pharmacol 2018; 150:120-130. [PMID: 29378180 PMCID: PMC5906734 DOI: 10.1016/j.bcp.2018.01.036] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Accepted: 01/22/2018] [Indexed: 12/14/2022]
Abstract
Transient outward potassium current (Ito) contributes to early repolarization of many mammalian cardiac action potentials, including human, whilst the rapid delayed rectifier K+ current (IKr) contributes to later repolarization. Fast Ito channels can be produced from the Shal family KCNDE gene product Kv4.3s, although accessory subunits including KChIP2.x and DPP6 are also needed to produce a near physiological Ito. In this study, the effect of KChIP2.1 & KChIP2.2 (also known as KChIP2b and KChIP2c respectively), alone or in conjunction with the accessory subunit DPP6, on both Kv4.3 and hERG were evaluated. A dual Ito and IKr activator, NS3623, has been recently proposed to be beneficial in heart failure and the action of NS3623 on the two channels was also investigated. Whole-cell patch-clamp experiments were performed at 33 ± 1 °C on HEK293 cells expressing Kv4.3 or hERG in the absence or presence of these accessory subunits. Kv4.3 current magnitude was augmented by co-expression with either KChIP2.2 or KChIP2.1 and KChIP2/DPP6 with KChIP2.1 producing a greater effect than KChIP2.2. Adding DPP6 removed the difference in Kv4.3 augmentation between KChIP2.1 and KChIP2.2. The inactivation rate and recovery from inactivation were also altered by KChIP2 isoform co-expression. In contrast, hERG (Kv11.1) current was not altered by co-expression with KChIP2.1, KChIP2.2 or DPP6. NS3623 increased Kv4.3 amplitude to a similar extent with and without accessory subunit co-expression, however KChIP2 isoforms modulated the compound’s effect on inactivation time course. The agonist effect of NS3623 on hERG channels was not affected by KChIP2.1, KChIP2.2 or DPP6 co-expression.
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Affiliation(s)
- Sergio Lainez
- School of Physiology, Pharmacology and Neuroscience, Faculty of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
| | - Adélaïde Doray
- School of Physiology, Pharmacology and Neuroscience, Faculty of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
| | - Jules C Hancox
- School of Physiology, Pharmacology and Neuroscience, Faculty of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
| | - Mark B Cannell
- School of Physiology, Pharmacology and Neuroscience, Faculty of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
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13
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Wiśniowska B, Polak S. The Role of Interaction Model in Simulation of Drug Interactions and QT Prolongation. CURRENT PHARMACOLOGY REPORTS 2016; 2:339-344. [PMID: 27917367 PMCID: PMC5114317 DOI: 10.1007/s40495-016-0075-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Computational modelling is a cornerstone of Comprehensive In Vitro Proarrhythmia Assay and is re-increasingly being used in drug development. Electrophysiological effects of drug-drug interactions can be predicted in silico, e.g. with the use of in vitro cardiac ion channel data, PK profiles and human ventricular cardiomyocyte models. There are, however, several approaches with different assumptions used to assess the combined effect of multiple drugs, and there is no agreed standard interaction model. The aim of this study was to assess whether the choice of the drug-drug interaction (DDI) model (Bliss independence, Loewe additivity, or simple sum) influences the results of QT interval simulation trial. The Simcyp Simulator version 12.1 (Simcyp Ltd. [part of Certara], Sheffield, UK) and Cardiac Safety Simulator 2.0 (Simcyp Ltd. [part of Certara], Sheffield, UK) were used to simulate results of 8 virtual trials mimicking clinical studies and generate individual QTc data. The combined effect of inhibitory actions of drugs which were given simultaneously was calculated with use of three different interaction models. The PD effect of DDI was assessed and the differences between mean observed and mean predicted ΔQTcB values for terfenadine interactions were not statistically significant in all but one cases. Differences between the three DDI models are not statistically significant, implying that the choice of the DDI model, in the case of lack of synergy or antagonism, is irrelevant to the average predicted effect at the clinical level. However, in some cases, it can influence the verdict on combinatorial therapy safety for individual patients.
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Affiliation(s)
- Barbara Wiśniowska
- Unit of Pharmacoepidemiology and Pharmacoeconomics, Faculty of Pharmacy, Medical College, Jagiellonian University, Medyczna 9 Street, 30-688 Kraków, Poland
| | - Sebastian Polak
- Unit of Pharmacoepidemiology and Pharmacoeconomics, Faculty of Pharmacy, Medical College, Jagiellonian University, Medyczna 9 Street, 30-688 Kraków, Poland
- Simcyp (part of Certara), Blades Enterprise Centre John Street, Sheffield, S2 4SU UK
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14
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Cubeddu LX. Drug-induced Inhibition and Trafficking Disruption of ion Channels: Pathogenesis of QT Abnormalities and Drug-induced Fatal Arrhythmias. Curr Cardiol Rev 2016; 12:141-54. [PMID: 26926294 PMCID: PMC4861943 DOI: 10.2174/1573403x12666160301120217] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 02/29/2016] [Indexed: 01/11/2023] Open
Abstract
Risk of severe and fatal ventricular arrhythmias, presenting as Torsade de Pointes (TdP), is increased in congenital and acquired forms of long QT syndromes (LQTS). Drug-induced inhibition of K+ currents, IKs, IKr, IK1, and/or Ito, delay repolarization, prolong QT, and increase the risk of TdP. Drug-induced interference with IKr is the most common cause of acquired LQTS/TdP. Multiple drugs bind to KNCH2-hERG-K+ channels affecting IKr, including antiarrythmics, antibiotics, antivirals, azole-antifungals, antimalarials, anticancer, antiemetics, prokinetics, antipsychotics, and antidepressants. Azithromycin has been recently added to this list. In addition to direct channel inhibition, some drugs interfere with the traffic of channels from the endoplasmic reticulum to the cell membrane, decreasing mature channel membrane density; e.g., pentamidine, geldalamicin, arsenic trioxide, digoxin, and probucol. Other drugs, such as ketoconazole, fluoxetine, norfluoxetine, citalopram, escitalopram, donepezil, tamoxifen, endoxifen, atazanavir, and roxitromycin, induce both direct channel inhibition and impaired channel trafficking. Although many drugs prolong the QT interval, TdP is a rare event. The following conditions increase the risk of drug-induced TdP: a) Disease states/electrolyte levels (heart failure, structural cardiac disease, bradycardia, hypokalemia); b) Pharmacogenomic variables (presence of congenital LQTS, subclinical ion-channel mutations, history of or having a relative with history of drug-induced long QT/TdP); c) Pharmacodynamic and kinetic factors (high doses, women, elderly, metabolism inhibitors, combining two or more QT prolonging drugs, drugs that prolong the QT and increase QT dispersion, and drugs with multiple actions on ion channels). Because most of these conditions are preventable, careful evaluation of risk factors and increased knowledge of drug use associated with repolarization abnormalities are strongly recommended.
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Affiliation(s)
- Luigi X Cubeddu
- Division of Cardio-Metabolic Research, Department of Pharmaceutical Sciences, Health professions Division, Nova Southeastern University, 3200 S. University Dr., Davie, FL, 333218, USA.
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15
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Fermini B, Hancox JC, Abi-Gerges N, Bridgland-Taylor M, Chaudhary KW, Colatsky T, Correll K, Crumb W, Damiano B, Erdemli G, Gintant G, Imredy J, Koerner J, Kramer J, Levesque P, Li Z, Lindqvist A, Obejero-Paz CA, Rampe D, Sawada K, Strauss DG, Vandenberg JI. A New Perspective in the Field of Cardiac Safety Testing through the Comprehensive In Vitro Proarrhythmia Assay Paradigm. ACTA ACUST UNITED AC 2015; 21:1-11. [PMID: 26170255 DOI: 10.1177/1087057115594589] [Citation(s) in RCA: 198] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 06/11/2015] [Indexed: 12/31/2022]
Abstract
For the past decade, cardiac safety screening to evaluate the propensity of drugs to produce QT interval prolongation and Torsades de Pointes (TdP) arrhythmia has been conducted according to ICH S7B and ICH E14 guidelines. Central to the existing approach are hERG channel assays and in vivo QT measurements. Although effective, the present paradigm carries a risk of unnecessary compound attrition and high cost, especially when considering costly thorough QT (TQT) studies conducted later in drug development. The C: omprehensive I: n Vitro P: roarrhythmia A: ssay (CiPA) initiative is a public-private collaboration with the aim of updating the existing cardiac safety testing paradigm to better evaluate arrhythmia risk and remove the need for TQT studies. It is hoped that CiPA will produce a standardized ion channel assay approach, incorporating defined tests against major cardiac ion channels, the results of which then inform evaluation of proarrhythmic actions in silico, using human ventricular action potential reconstructions. Results are then to be confirmed using human (stem cell-derived) cardiomyocytes. This perspective article reviews the rationale, progress of, and challenges for the CiPA initiative, if this new paradigm is to replace existing practice and, in time, lead to improved and widely accepted cardiac safety testing guidelines.
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Affiliation(s)
| | - Jules C Hancox
- School of Physiology and Pharmacology, University of Bristol, Bristol, UK
| | - Najah Abi-Gerges
- Translational Safety, Drug Safety and Metabolism, Innovative Medicines and Early Development, AstraZeneca R&D, Macclesfield, UK AnaBios Corporation, San Diego, CA, USA
| | - Matthew Bridgland-Taylor
- Discovery Sciences, Innovative Medicines and Early Development, AstraZeneca R&D, Macclesfield, UK
| | | | - Thomas Colatsky
- Division of Applied Regulatory Science, CDER, US Food and Drug Administration, Silver Spring, MD, USA
| | | | | | - Bruce Damiano
- Global Safety Pharmacology, Discovery Sciences, Janssen Research & Development LLC, Spring House, PA, USA
| | - Gul Erdemli
- Center for Proteomic Chemistry, Novartis Institutes for BioMedical Research, Inc, Cambridge, MA, USA
| | - Gary Gintant
- Department of Integrative Pharmacology, Integrated Sciences & Technology, AbbVie, North Chicago, IL, USA
| | - John Imredy
- Department of Safety Assessment, Merck & Co, Kenilworth, NJ, USA
| | - John Koerner
- Division of Cardiovascular and Renal Products, CDER, U.S. Food and Drug Administration, Silver Spring, MD, USA
| | - James Kramer
- ChanTest, A Charles River Company, Cleveland, OH, USA
| | - Paul Levesque
- Bristol Myers Squibb Research & Development, Princeton, NJ, USA
| | - Zhihua Li
- Division of Applied Regulatory Science, CDER, US Food and Drug Administration, Silver Spring, MD, USA
| | | | | | - David Rampe
- Preclinical Safety, Sanofi, Bridgewater, NJ, USA
| | - Kohei Sawada
- Global Cardiovascular Assessment, Eisai Co., Ltd., Ibaraki, Japan
| | - David G Strauss
- Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD, USA
| | - Jamie I Vandenberg
- Victor Chang Cardiac Research Institute, St Vincent's Clinical School, University of NSW, Darlinghurst, NSW, Australia
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16
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Vatta M, Spoonamore KG. Use of genetic testing to identify sudden cardiac death syndromes. Trends Cardiovasc Med 2015; 25:738-48. [PMID: 25864170 DOI: 10.1016/j.tcm.2015.03.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Revised: 03/06/2015] [Accepted: 03/07/2015] [Indexed: 01/25/2023]
Abstract
Sudden cardiac death (SCD) is a leading cause of mortality worldwide. Although coronary artery disease remains the most common substrate for SCD, primary cardiac genetic diseases, presenting with or without structural heart abnormalities, play a significant role. In the last 30 years, the study of large family pedigrees allowed the discovery of causative genes unveiling the genetic basis of diseases such as primary cardiomyopathies and arrhythmia syndromes, which are known to increase the risk of SCD. However, recent technological advancement with the ability to perform massive parallel sequencing and analyze the entire genome has uncovered a higher level of complexity in the genetic predisposition for cardiac diseases, which are usually characterized by Mendelian inheritance patterns. Clinical genetic testing, historically shaped around a monogenic Mendelian disorder paradigm, is now facing the challenge to adopt and adapt to a more complex model in which a significant portion of subjects may present with multi-allelic inheritance involving additional genes that could modulate the severity and type of disease-related phenotypes. Here, we will try to provide a viewpoint that will hopefully foster further debate in the field.
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Affiliation(s)
- Matteo Vatta
- Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, IN; Department of Medicine, Krannert Institute of Cardiology, Indiana University School of Medicine, Indianapolis, IN.
| | - Katherine G Spoonamore
- Department of Medicine, Krannert Institute of Cardiology, Indiana University School of Medicine, Indianapolis, IN
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17
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Melgari D, Du C, El Harchi A, Zhang Y, Hancox JC. Suppression of the hERG potassium channel response to premature stimulation by reduction in extracellular potassium concentration. Physiol Rep 2014; 2:2/10/e12165. [PMID: 25318749 PMCID: PMC4254092 DOI: 10.14814/phy2.12165] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Potassium channels encoded by human ether‐à‐go‐go‐related gene (hERG) mediate the cardiac rapid delayed rectifier K+ current (IKr), which participates in ventricular repolarization and has a protective role against unwanted premature stimuli late in repolarization and early in diastole. Ionic current carried by hERG channels (IhERG) is known to exhibit a paradoxical dependence on external potassium concentration ([K+]e), but effects of acute [K+]e changes on the response of IhERG to premature stimulation have not been characterized. Whole‐cell patch‐clamp measurements of hERG current were made at 37°C from hERG channels expressed in HEK293 cells. Under conventional voltage‐clamp, both wild‐type (WT) and S624A pore‐mutant IhERG during depolarization to +20 mV and subsequent repolarization to −40 mV were decreased when superfusate [K+]e was decreased from 4 to 1 mmol/L. When [K+]e was increased from 4 to 10 mmol/L, pulse current was increased and tail IhERG was decreased. Increasing [K+]e produced a +10 mV shift in voltage‐dependent inactivation of WT IhERG and slowed inactivation time course, while lowering [K+]e from 4 to 1 mmol/L produced little change in inactivation voltage dependence, but accelerated inactivation time course. Under action potential (AP) voltage‐clamp, lowering [K+]e reduced the amplitude of IhERG during the AP and suppressed the maximal IhERG response to premature stimuli. Raising [K+]e increased IhERG early during the AP and augmented the IhERG response to premature stimuli. Our results are suggestive that during hypokalemia not only is the contribution of IKr to ventricular repolarization reduced but its ability to protect against unwanted premature stimuli also becomes impaired. hERG potassium channels are important for ventricular repolarization and for protecting the ventricles of the heart from unwanted premature stimuli. This study shows that, in addition to reducing the contribution of hERG channel current to ventricular repolarization, hypokalemia impairs the protective response of hERG to premature stimulation.
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Affiliation(s)
- Dario Melgari
- School of Physiology and Pharmacology and Cardiovascular Research Laboratories, University of Bristol, Medical Sciences Building, Bristol, BS8 1TD, UK
| | - Chunyun Du
- School of Physiology and Pharmacology and Cardiovascular Research Laboratories, University of Bristol, Medical Sciences Building, Bristol, BS8 1TD, UK
| | - Aziza El Harchi
- School of Physiology and Pharmacology and Cardiovascular Research Laboratories, University of Bristol, Medical Sciences Building, Bristol, BS8 1TD, UK
| | - Yihong Zhang
- School of Physiology and Pharmacology and Cardiovascular Research Laboratories, University of Bristol, Medical Sciences Building, Bristol, BS8 1TD, UK
| | - Jules C Hancox
- School of Physiology and Pharmacology and Cardiovascular Research Laboratories, University of Bristol, Medical Sciences Building, Bristol, BS8 1TD, UK
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18
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Hancox JC, Du C, Harchi AE, Baranchuk A, Zhang H. A novel genetic modifier for clarithromycin-related cardiac arrhythmia risk? Ther Adv Infect Dis 2014; 2:71-2. [PMID: 25165557 DOI: 10.1177/2049936114522996] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Affiliation(s)
- Jules C Hancox
- School of Physiology and Pharmacology and Cardiovascular Research Laboratories, Medical Sciences Building, University Walk, University of Bristol, Bristol, BS8 1TD
| | - Chunyun Du
- School of Physiology and Pharmacology and Cardiovascular Research Laboratories, Medical Sciences Building, University of Bristol, Bristol, UK
| | - Aziza El Harchi
- School of Physiology and Pharmacology and Cardiovascular Research Laboratories, Medical Sciences Building, University of Bristol, Bristol, UK
| | - Adrian Baranchuk
- Department of Cardiology, Kingston General Hospital, Queen's University, Kingston, Ontario, Canada
| | - Henggui Zhang
- Biological Physics Group, School of Physics and Astronomy, University of Manchester, Manchester, UK
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19
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Hancox JC, Du C, El Harchi A, Zhang H. Modification of KCNH2-encoded cardiac potassium channels by KCNE1 polymorphism. Circ J 2014; 78:2330. [PMID: 25008780 DOI: 10.1253/circj.cj-14-0513] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Jules C Hancox
- School of Physiology and Pharmacology and Cardiovascular Research Laboratories, Medical Sciences Building, University of Bristol
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20
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Tabata T, Yamaguchi Y, Hata Y, Ichida F, Mori H. Modification of <i>KCNH2</i>-Encoded Cardiac Potassium Channels by KCNE1 Polymorphism. Circ J 2014; 78:2331. [DOI: 10.1253/circj.cj-14-0654] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Toshihide Tabata
- Laboratory for Neural Information Technology, Graduate School of Sciences and Engineering, University of Toyama
| | | | - Yukiko Hata
- Department of Legal Medicine, University of Toyama
| | | | - Hisashi Mori
- Department of Molecular Neurosciences, University of Toyama
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