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Doherty W, Benson S, Pepdjonovic L, Koppes AN, Koppes RA. Cell Line and Media Composition Influence the Production of Giant Plasma Membrane Vesicles. ACS Biomater Sci Eng 2024; 10:1880-1891. [PMID: 38374716 PMCID: PMC10934252 DOI: 10.1021/acsbiomaterials.3c01596] [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: 10/27/2023] [Revised: 02/07/2024] [Accepted: 02/08/2024] [Indexed: 02/21/2024]
Abstract
Giant plasma membrane vesicles (GPMVs) have been utilized as a model to study phase separation in the plasma membrane. Additionally, GPMVs have been employed as vehicle for delivering molecular cargo, including small molecule drugs and nanoparticles. Nearly all examples of GPMV production use a defined salt buffer that is a stark contrast to typical cell culture medium. In this study, we demonstrate that the addition of formaldehyde and dithiothreitol to a standard culture medium was capable of generating GPMVs at a concentration equal to or higher than the traditional production buffer. These methods were evaluated for two human cell lines: kidney endothelial and Schwann cells (SCs). Morphological properties of the resultant GPMVs exhibited no significant differences between the two formulations. Factors such as pH and seeding density significantly influenced the production of GPMVs in both mediums. The cell type and seeding density was shown to influence the number of GPMVs to the greatest extent. SCs yield more GPMVs at higher seeding densities compared to endothelial cells. Stability of the membrane of the GPMVs produced in both mediums was evaluated by monitoring passive diffusion of two fluorescently tagged dextrans (3 and 10 kDa). Regardless of the production formulation or cell type, approximately 85% GPMVs are impermeable to either dextran. Cold storage for on-demand use and shipping are essential for broader use of GPMVs. Toward this aim, we have evaluated the GMPV number and morphologies following storage at -80 °C and in liquid nitrogen. A significant loss of the GPMV number, ∼30%, was observed following storage across production formulations as well as cell types. Our results indicate that smaller GMPVs, <5 μm are more stable for preservation. In conclusion, GPMVs can be produced in a broad range of formulations, exhibit a high degree of stability, and can undergo cold storage for further adoption.
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Affiliation(s)
- William Doherty
- Department
of Chemical Engineering, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, United States
| | - Sarah Benson
- Department
of Chemical Engineering, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, United States
| | - Lisa Pepdjonovic
- Department
of Chemical Engineering, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, United States
| | - Abigail N. Koppes
- Department
of Chemical Engineering, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, United States
- Department
of Biology, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, United States
- Department
of Bioengineering, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, United States
| | - Ryan A. Koppes
- Department
of Chemical Engineering, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, United States
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2
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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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3
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Sanchez-Conde FG, Jimenez-Vazquez EN, Auerbach DS, Jones DK. The ERG1 K+ Channel and Its Role in Neuronal Health and Disease. Front Mol Neurosci 2022; 15:890368. [PMID: 35600076 PMCID: PMC9113952 DOI: 10.3389/fnmol.2022.890368] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2022] [Accepted: 04/11/2022] [Indexed: 11/30/2022] Open
Abstract
The ERG1 potassium channel, encoded by KCNH2, has long been associated with cardiac electrical excitability. Yet, a growing body of work suggests that ERG1 mediates physiology throughout the human body, including the brain. ERG1 is a regulator of neuronal excitability, ERG1 variants are associated with neuronal diseases (e.g., epilepsy and schizophrenia), and ERG1 serves as a potential therapeutic target for neuronal pathophysiology. This review summarizes the current state-of-the-field regarding the ERG1 channel structure and function, ERG1’s relationship to the mammalian brain and highlights key questions that have yet to be answered.
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Affiliation(s)
| | - Eric N. Jimenez-Vazquez
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, United States
| | - David S. Auerbach
- Department of Pharmacology, State University of New York Upstate Medical University, Syracuse, NY, United States
- *Correspondence: David S. Auerbach,
| | - David K. Jones
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, United States
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, United States
- David K. Jones,
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4
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Conformation-sensitive antibody reveals an altered cytosolic PAS/CNBh assembly during hERG channel gating. Proc Natl Acad Sci U S A 2021; 118:2108796118. [PMID: 34716268 DOI: 10.1073/pnas.2108796118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Accepted: 09/22/2021] [Indexed: 11/18/2022] Open
Abstract
The human ERG (hERG) K+ channel has a crucial function in cardiac repolarization, and mutations or channel block can give rise to long QT syndrome and catastrophic ventricular arrhythmias. The cytosolic assembly formed by the Per-Arnt-Sim (PAS) and cyclic nucleotide binding homology (CNBh) domains is the defining structural feature of hERG and related KCNH channels. However, the molecular role of these two domains in channel gating remains unclear. We have previously shown that single-chain variable fragment (scFv) antibodies can modulate hERG function by binding to the PAS domain. Here, we mapped the scFv2.12 epitope to a site overlapping with the PAS/CNBh domain interface using NMR spectroscopy and mutagenesis and show that scFv binding in vitro and in the cell is incompatible with the PAS interaction with CNBh. By generating a fluorescently labeled scFv2.12, we demonstrate that association with the full-length hERG channel is state dependent. We detect Förster resonance energy transfer (FRET) with scFv2.12 when the channel gate is open but not when it is closed. In addition, state dependence of scFv2.12 FRET signal disappears when the R56Q mutation, known to destabilize the PAS-CNBh interaction, is introduced in the channel. Altogether, these data are consistent with an extensive structural alteration of the PAS/CNBh assembly when the cytosolic gate opens, likely favoring PAS domain dissociation from the CNBh domain.
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5
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Ríos-Pérez EB, Liu F, Stevens-Sostre WA, Eichel CA, Silignavong J, Robertson GA. A stable cell line inducibly expressing hERG1a/1b heteromeric channels. J Pharmacol Toxicol Methods 2021; 110:107081. [PMID: 34058320 DOI: 10.1016/j.vascn.2021.107081] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Revised: 04/07/2021] [Accepted: 05/20/2021] [Indexed: 11/24/2022]
Abstract
Heterologously expressed hERG channels represent a mainstay of in vitro drug safety screens intended to mitigate risk of cardiac IKr block and sudden cardiac death. This is true even as more channel types are adopted as part of the Comprehensive in vitro Proarrhythmia Assay (CiPA) intended to elevate specificity and thus enhance throughput of promising lead drugs. Until now, hERG1a homomeric channels have been used as a proxy for IKr despite a wealth of evidence showing that hERG1a/1b heteromers better represent native channels in terms of protein abundance and channel biophysical and pharmacological properties. Past efforts to create a stable hERG1a/1b cell line were met with unpredictable silencing of hERG1b expression despite stable integration of the gene into the HEK293 cell genome. Here we report a new cell line stably expressing hERG1a, with hERG1b reliably controlled by an inducible promoter sensitive to doxycycline. Co-immunoprecipitation, Western blot analysis and patch-clamp electrophysiology confirm the heteromeric composition of the expressed channels. Association with hERG1b was found to promote hERG1a protein levels and enhance membrane current levels. Optimal conditions for drug screening and experimental investigation were achieved at 24 h exposure to 100 ng/ml doxycycline. Differences in pharmacological sensitivity between homomeric and heteromeric channels were observed for dofetilide and ebastine, but not fluoxetine, as evaluated by their IC50 values. Using these values in the O'Hara-Rudy-CiPA in silico model revealed discrepancies in pro-arrhythmia risk, implying the hERG1a homomeric platform overestimates risk for these two drugs. Dofetilide block was use-dependent and faster for hERG1a/1b than hERG1a channels, whereas ebastine showed considerable block at rest and had a slower progression for hERG1a/1b channels. The hERG1a/1b cell line thus represents an advanced model for contemporary drug safety screening assays such as CiPA that employ IC50 values to estimate risk of proarrhythmia in computational models of ventricular cardiomyocytes. This novel technology fulfills an unmet need to enhance specificity and foster a safe yet expanded drug development pipeline.
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Affiliation(s)
- Erick B Ríos-Pérez
- Dept. of Neuroscience and Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, 1111 Highland Ave. #5505, Madison, WI 53705, United States of America
| | - Fang Liu
- Dept. of Neuroscience and Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, 1111 Highland Ave. #5505, Madison, WI 53705, United States of America
| | - Whitney A Stevens-Sostre
- Dept. of Neuroscience and Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, 1111 Highland Ave. #5505, Madison, WI 53705, United States of America
| | - Catherine A Eichel
- Dept. of Neuroscience and Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, 1111 Highland Ave. #5505, Madison, WI 53705, United States of America
| | - Jonathan Silignavong
- Dept. of Neuroscience and Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, 1111 Highland Ave. #5505, Madison, WI 53705, United States of America
| | - Gail A Robertson
- Dept. of Neuroscience and Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, 1111 Highland Ave. #5505, Madison, WI 53705, United States of America.
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6
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Tschirhart JN, Zhang S. Fentanyl-Induced Block of hERG Channels Is Exacerbated by Hypoxia, Hypokalemia, Alkalosis, and the Presence of hERG1b. Mol Pharmacol 2020; 98:508-517. [PMID: 32321735 DOI: 10.1124/mol.119.119271] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Accepted: 04/08/2020] [Indexed: 01/19/2023] Open
Abstract
Human ether-a-go-go-related gene (hERG) encodes the pore-forming subunit of the rapidly activating delayed rectifier potassium current (IKr) important for repolarization of cardiac action potentials. Drug-induced disruption of hERG channel function is a main cause of acquired long QT syndrome, which can lead to ventricular arrhythmias and sudden death. Illicit fentanyl use is associated with sudden death. We have demonstrated that fentanyl blocks hERG current (IhERG) at concentrations that overlap with the upper range of postmortem blood concentrations in fentanyl-related deaths. Since fentanyl can cause respiratory depression and electrolyte imbalances, in the present study we investigated whether certain pathologic circumstances exacerbate fentanyl-induced block of IhERG Our results show that chronic hypoxia or hypokalemia additively reduced IhERG with fentanyl. As well, high pH potentiated the fentanyl-mediated block of hERG channels, with an IC50 at pH 8.4 being 7-fold lower than that at pH 7.4. Furthermore, although the full-length hERG variant, hERG1a, has been widely used to study hERG channels, coexpression with the short variant, hERG1b (which does not produce current when expressed alone), produces functional hERG1a/1b channels, which gate more closely resembling native IKr Our results showed that fentanyl blocked hERG1a/1b channels with a 3-fold greater potency than hERG1a channels. Thus, in addition to a greater susceptibility due to the presence of hERG1b in the human heart, hERG channel block by fentanyl can be exacerbated by certain conditions, such as hypoxia, hypokalemia, or alkalosis, which may increase the risk of fentanyl-induced ventricular arrhythmias and sudden death. SIGNIFICANCE STATEMENT: This work demonstrates that heterologously expressed human ether a-go-go-related gene (hERG) 1a/1b channels, which more closely resemble rapidly activating delayed rectifier potassium current in the human heart, are blocked by fentanyl with a 3-fold greater potency than the previously studied hERG1a expressed alone. Additionally, chronic hypoxia, hypokalemia, and alkalosis can increase the block of hERG current by fentanyl, potentially increasing the risk of cardiac arrhythmias and sudden death.
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Affiliation(s)
- Jared N Tschirhart
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Shetuan Zhang
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
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7
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Goversen B, Jonsson MK, van den Heuvel NH, Rijken R, Vos MA, van Veen TA, de Boer TP. The influence of hERG1a and hERG1b isoforms on drug safety screening in iPSC-CMs. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2019; 149:86-98. [PMID: 30826123 DOI: 10.1016/j.pbiomolbio.2019.02.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Revised: 01/14/2019] [Accepted: 02/08/2019] [Indexed: 01/03/2023]
Abstract
The human Ether-à-go-go Related Gene (hERG) encodes the pore forming subunit of the channel that conducts the rapid delayed rectifier potassium current IKr. IKr drives repolarization in the heart and when IKr is dysfunctional, cardiac repolarization delays, the QT interval on the electrocardiogram (ECG) prolongs and the risk of developing lethal arrhythmias such as Torsade de Pointes (TdP) increases. TdP risk is incorporated in drug safety screening for cardiotoxicity where hERG is the main target since the IKr channels appear highly sensitive to blockage. hERG block is also included as an important read-out in the Comprehensive in Vitro Proarrhythmia Assay (CiPA) initiative which aims to combine in vitro and in silico experiments on induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) to screen for cardiotoxicity. However, the hERG channel has some unique features to consider for drug safety screening, which we will discuss in this study. The hERG channel consists of different isoforms, hERG1a and hERG1b, which individually influence the kinetics of the channel and the drug response in the human heart and in iPSC-CMs. hERG1b is often underappreciated in iPSC-CM studies, drug screening assays and in silico models, and the fact that its contribution might substantially differ between iPSC-CM and healthy but also diseased human heart, adds to this problem. In this study we show that the activation kinetics in iPSC-CMs resemble hERG1b kinetics using Cs+ as a charge carrier. Not including hERG1b in drug safety testing might underestimate the actual role of hERG1b in repolarization and drug response, and might lead to inappropriate conclusions. We stress to focus more on including hERG1b in drug safety testing concerning IKr.
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Affiliation(s)
- Birgit Goversen
- Department of Medical Physiology, Division Heart & Lungs, University Medical Center Utrecht, the Netherlands
| | - Malin Kb Jonsson
- Department of Medical Physiology, Division Heart & Lungs, University Medical Center Utrecht, the Netherlands; Bioscience Heart Failure, Cardiovascular, Renal and Metabolic Diseases, IMED Biotech Unit, AstraZeneca, Gothenburg, Sweden
| | - Nikki Hl van den Heuvel
- Department of Medical Physiology, Division Heart & Lungs, University Medical Center Utrecht, the Netherlands
| | - Rianne Rijken
- Department of Medical Physiology, Division Heart & Lungs, University Medical Center Utrecht, the Netherlands
| | - Marc A Vos
- Department of Medical Physiology, Division Heart & Lungs, University Medical Center Utrecht, the Netherlands
| | - Toon Ab van Veen
- Department of Medical Physiology, Division Heart & Lungs, University Medical Center Utrecht, the Netherlands
| | - Teun P de Boer
- Department of Medical Physiology, Division Heart & Lungs, University Medical Center Utrecht, the Netherlands.
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8
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Perissinotti LL, De Biase PM, Guo J, Yang PC, Lee MC, Clancy CE, Duff HJ, Noskov SY. Determinants of Isoform-Specific Gating Kinetics of hERG1 Channel: Combined Experimental and Simulation Study. Front Physiol 2018; 9:207. [PMID: 29706893 PMCID: PMC5907531 DOI: 10.3389/fphys.2018.00207] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Accepted: 02/23/2018] [Indexed: 12/22/2022] Open
Abstract
IKr is the rapidly activating component of the delayed rectifier potassium current, the ion current largely responsible for the repolarization of the cardiac action potential. Inherited forms of long QT syndrome (LQTS) (Lees-Miller et al., 1997) in humans are linked to functional modifications in the Kv11.1 (hERG) ion channel and potentially life threatening arrhythmias. There is little doubt now that hERG-related component of IKr in the heart depends on the tetrameric (homo- or hetero-) channels formed by two alternatively processed isoforms of hERG, termed hERG1a and hERG1b. Isoform composition (hERG1a- vs. the b-isoform) has recently been reported to alter pharmacologic responses to some hERG blockers and was proposed to be an essential factor pre-disposing patients for drug-induced QT prolongation. Very little is known about the gating and pharmacological properties of two isoforms in heart membranes. For example, how gating mechanisms of the hERG1a channels differ from that of hERG1b is still unknown. The mechanisms by which hERG 1a/1b hetero-tetramers contribute to function in the heart, or what role hERG1b might play in disease are all questions to be answered. Structurally, the two isoforms differ only in the N-terminal region located in the cytoplasm: hERG1b is 340 residues shorter than hERG1a and the initial 36 residues of hERG1b are unique to this isoform. In this study, we combined electrophysiological measurements for HEK cells, kinetics and structural modeling to tease out the individual contributions of each isoform to Action Potential formation and then make predictions about the effects of having various mixture ratios of the two isoforms. By coupling electrophysiological data with computational kinetic modeling, two proposed mechanisms of hERG gating in two homo-tetramers were examined. Sets of data from various experimental stimulation protocols (HEK cells) were analyzed simultaneously and fitted to Markov-chain models (M-models). The minimization procedure presented here, allowed assessment of suitability of different Markov model topologies and the corresponding parameters that describe the channel kinetics. The kinetics modeling pointed to key differences in the gating kinetics that were linked to the full channel structure. Interactions between soluble domains and the transmembrane part of the channel appeared to be critical determinants of the gating kinetics. The structures of the full channel in the open and closed states were compared for the first time using the recent Cryo-EM resolved structure for full open hERG channel and an homology model for the closed state, based on the highly homolog EAG1 channel. Key potential interactions which emphasize the importance of electrostatic interactions between N-PAS cap, S4-S5, and C-linker are suggested based on the structural analysis. The derived kinetic parameters were later used in higher order models of cells and tissue to track down the effect of varying the ratios of hERG1a and hERG1b on cardiac action potentials and computed electrocardiograms. Simulations suggest that the recovery from inactivation of hERG1b may contribute to its physiologic role of this isoform in the action potential. Finally, the results presented here contribute to the growing body of evidence that hERG1b significantly affects the generation of the cardiac Ikr and plays an important role in cardiac electrophysiology. We highlight the importance of carefully revisiting the Markov models previously proposed in order to properly account for the relative abundance of the hERG1 a- and b- isoforms.
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Affiliation(s)
- Laura L Perissinotti
- Centre for Molecular Simulations, Department of Biological Sciences, Faculty of Science, University of Calgary, Calgary, AB, Canada
| | - Pablo M De Biase
- Centre for Molecular Simulations, Department of Biological Sciences, Faculty of Science, University of Calgary, Calgary, AB, Canada
| | - Jiqing Guo
- Libin Cardiovascular Institute of Alberta, Faculty of Medicine, University of Calgary, Calgary, AB, Canada
| | - Pei-Chi Yang
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States
| | - Miranda C Lee
- Centre for Molecular Simulations, Department of Biological Sciences, Faculty of Science, University of Calgary, Calgary, AB, Canada
| | - Colleen E Clancy
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States
| | - Henry J Duff
- Libin Cardiovascular Institute of Alberta, Faculty of Medicine, University of Calgary, Calgary, AB, Canada
| | - Sergei Y Noskov
- Centre for Molecular Simulations, Department of Biological Sciences, Faculty of Science, University of Calgary, Calgary, AB, Canada
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9
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Roy S, Mathew MK. Fluid flow modulates electrical activity in cardiac hERG potassium channels. J Biol Chem 2018; 293:4289-4303. [PMID: 29305421 DOI: 10.1074/jbc.ra117.000432] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Revised: 12/28/2017] [Indexed: 01/01/2023] Open
Abstract
Fluid movement within the heart generates substantial shear forces, but the effect of this mechanical stress on the electrical activity of the human heart has not been examined. The fast component of the delayed rectifier potassium currents responsible for repolarization of the cardiac action potential, Ikr, is encoded by the human ether-a-go-go related gene (hERG) channel. Here, we exposed hERG1a channel-expressing HEK293T cells to laminar shear stress (LSS) and observed that this mechanical stress increased the whole-cell current by 30-40%. LSS shifted the voltage dependence of steady-state activation of the hERG channel to the hyperpolarizing direction, accelerated the time course of activation and recovery from inactivation, slowed down deactivation, and shifted the steady-state inactivation to the positive direction, all of which favored the hERG open state. In contrast, the time course of inactivation was faster, favoring the closed state. Using specific inhibitors of focal adhesion kinase, a regulator of mechano-transduction via the integrin pathway, we also found that the LSS-induced modulation of the whole-cell current depended on the integrin pathway. The hERG1b channel variant, which lacks the Per-Arnt-Sim (PAS) domain, and long QT syndrome-associated variants having point mutations in the PAS domain were unaffected by LSS, suggesting that the PAS domain in hERG1a channel may be involved in sensing mechanical shear stress. We conclude that a mechano-electric feedback pathway modulates hERG channel activity through the integrin pathway, indicating that mechanical forces in the heart influence its electrical activity.
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Affiliation(s)
- Samrat Roy
- From the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560065.,the Biocon Bristol Myers Squibb Research Center, Bengaluru 560099, and.,the School of Biotechnology, Kalinga Institute of Industrial Technology (KIIT) University, Bhubaneswar 751024, India
| | - M K Mathew
- From the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560065,
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10
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McNally BA, Pendon ZD, Trudeau MC. hERG1a and hERG1b potassium channel subunits directly interact and preferentially form heteromeric channels. J Biol Chem 2017; 292:21548-21557. [PMID: 29089383 DOI: 10.1074/jbc.m117.816488] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Revised: 10/24/2017] [Indexed: 01/20/2023] Open
Abstract
Voltage-activated human ether-á-go-go-related gene (hERG) potassium channels are critical for the repolarization of cardiac action potentials and tune-spike frequency adaptation in neurons. Two isoforms of mammalian ERG1 channel subunits, ERG1a and ERG1b, are the principal subunits that conduct the IKr current in the heart and are also broadly expressed in the nervous system. However, there is little direct evidence that ERG1a and ERG1b form heteromeric channels. Here, using electrophysiology, biochemistry, and fluorescence approaches, we systematically tested for direct interactions between hERG1a and hERG1b subunits. We report 1) that hERG1a dominant-negative subunits suppress hERG1b currents (and vice versa), 2) that disulfide bonds form between single cysteine residues experimentally introduced into an extracellular loop of hERG1a and hERG1b subunits and produce hERG1a-hERG1b dimers, and 3) that hERG1a and hERG1b subunits tagged with fluorescent proteins that are FRET pairs exhibit robust energy transfer at the plasma membrane. Thus, multiple lines of evidence indicated a physical interaction between hERG1a and hERG1b, consistent with them forming heteromeric channels. Moreover, co-expression of variable ratios of hERG1a and hERG1b RNA yielded channels with deactivation kinetics that reached a plateau and were different from those of hERG1b channels, consistent with a preference of hERG1b subunits for hERG1a subunits. Cross-linking studies revealed that an equal input of hERG1a and hERG1b yields more hERG1a-hERG1a or hERG1a-hERG1b dimers than hERG1b-hERG1b dimers, also suggesting that hERG1b preferentially interacts with hERG1a. We conclude that hERG1b preferentially forms heteromeric ion channels with hERG1a at the plasma membrane.
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Affiliation(s)
- Beth A McNally
- From the Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201
| | - Zeus D Pendon
- From the Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201
| | - Matthew C Trudeau
- From the Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201
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11
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Sale H, Roy S, Warrier J, Thangathirupathy S, Vadari Y, Gopal SK, Krishnamurthy P, Ramarao M. Modulation of K v 11.1 (hERG) channels by 5-(((1H-indazol-5-yl)oxy)methyl)-N-(4-(trifluoromethoxy)phenyl)pyrimidin-2-amine (ITP-2), a novel small molecule activator. Br J Pharmacol 2017; 174:2484-2500. [PMID: 28500657 DOI: 10.1111/bph.13859] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Revised: 05/04/2017] [Accepted: 05/05/2017] [Indexed: 01/10/2023] Open
Abstract
BACKGROUND AND PURPOSE Activators of Kv 11.1 (hERG) channels have potential utility in the treatment of acquired and congenital long QT (LQT) syndrome. Here, we describe a new hERG channel activator, 5-(((1H-indazol-5-yl)oxy)methyl)-N-(4-(trifluoromethoxy)phenyl)pyrimidin-2-amine (ITP-2), with a chemical structure distinct from previously reported compounds. EXPERIMENTAL APPROACH Conventional electrophysiological methods were used to assess the effects of ITP-2 on hERG1a and hERG1a/1b channels expressed heterologously in HEK-293 cells. KEY RESULTS ITP-2 selectively increased test pulse currents (EC50 1.0 μM) and decreased tail currents. ITP-2 activated hERG1a homomeric channels primarily by causing large depolarizing shifts in the midpoint of voltage-dependent inactivation and hyperpolarizing shifts in the voltage-dependence of activation. In addition, ITP-2 slowed rates of inactivation and made recovery from inactivation faster. hERG1a/1b heteromeric channels showed reduced sensitivity to ITP-2 and their inactivation properties were differentially modulated. Effects on midpoint of voltage-dependent inactivation and rates of inactivation were less pronounced for hERG1a/1b channels. Effects on voltage-dependent activation and activation kinetics were not different from hERG1a channels. Interestingly, hERG1b channels were inhibited by ITP-2. Inactivation-impairing mutations abolished activation by ITP-2 and led to inhibition of hERG channels. ITP-2 exerted agonistic effect from extracellular side of the membrane and could activate one of the arrhythmia-associated trafficking-deficient LQT2 mutants. CONCLUSIONS AND IMPLICATIONS ITP-2 may serve as another novel lead molecule for designing robust activators of hERG channels. hERG1a/1b gating kinetics were differentially modulated by ITP-2 leading to altered sensitivity. ITP-2 is capable of activating an LQT2 mutant and may be potentially useful in the development of LQT2 therapeutics.
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Affiliation(s)
- Harinath Sale
- Disease Sciences and Technology, Biocon Bristol-Myers Squibb Research and Development Center, Syngene International Limited, Bangalore, India
| | - Samrat Roy
- Disease Sciences and Technology, Biocon Bristol-Myers Squibb Research and Development Center, Syngene International Limited, Bangalore, India
| | - Jayakumar Warrier
- Medicinal Chemistry, Biocon Bristol Myers-Squibb Research and Development Center, Syngene International Limited, Bangalore, India
| | - Srinivasan Thangathirupathy
- Medicinal Chemistry, Biocon Bristol Myers-Squibb Research and Development Center, Syngene International Limited, Bangalore, India
| | - Yoganand Vadari
- Disease Sciences and Technology, Biocon Bristol-Myers Squibb Research and Development Center, Syngene International Limited, Bangalore, India
| | - Shruthi K Gopal
- Disease Sciences and Technology, Biocon Bristol-Myers Squibb Research and Development Center, Syngene International Limited, Bangalore, India
| | - Prasad Krishnamurthy
- Disease Sciences and Technology, Biocon Bristol-Myers Squibb Research and Development Center, Syngene International Limited, Bangalore, India
| | - Manjunath Ramarao
- Disease Sciences and Technology, Biocon Bristol-Myers Squibb Research and Development Center, Syngene International Limited, Bangalore, India
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Gregers E, Ahlberg G, Christensen T, Jabbari J, Larsen KO, Herfelt CB, Henningsen KM, Andreasen L, Thiis JJ, Lund J, Holme S, Haunsø S, Bentzen BH, Schmitt N, Svendsen JH, Olesen MS. Deep sequencing of atrial fibrillation patients with mitral valve regurgitation shows no evidence of mosaicism but reveals novel rare germline variants. Heart Rhythm 2017; 14:1531-1538. [PMID: 28549997 DOI: 10.1016/j.hrthm.2017.05.027] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Indexed: 12/22/2022]
Abstract
BACKGROUND Atrial fibrillation (AF) is the most common cardiac arrhythmia. Valvular heart disease is a strong predictor, yet the underlying molecular mechanisms are unknown. OBJECTIVE The purpose of this study was to investigate the prevalence of somatic variants in AF candidate genes in an AF patient population undergoing surgery for mitral valve regurgitation (MVR) to determine whether these patients are genetically predisposed to AF. METHODS DNA was extracted from blood and left atrial tissue from 44 AF patients with MVR. Using next-generation sequencing, we investigated 110 genes using the HaloPlex Target Enrichment System. MuTect software was used for identification of somatic point variants. We functionally characterized selected variants using electrophysiologic techniques. RESULTS No somatic variants were identified in the cardiac tissue. Thirty-three patients (75%) had a rare germline variation in ≥1 candidate genes. Fourteen variants were novel. Fifteen variants were predicted damaging or likely damaging in ≥6 in silico predictions. We identified rare variants in genes never directly associated with AF: KCNE4, SCN4B, NEURL1, and CAND2. Interestingly, 7 patients (16%) had variants in genes involved in cellular potassium handling. The variants KCNQ1 (p.G272S) and KCNH2 (p.A913V) resulted in gain of function due to faster activation (KCNQ1) and slowed deactivation kinetics (KCNQ1, KCNH2). CONCLUSION We did not find any somatic variants in patients with AF and MVR. Surprisingly, we found that our cohort of non-lone AF patients might, like lone AF patients, be predisposed to AF by rare germline variants. Our findings emphasize the extent of still unknown factors in the pathogenesis of AF.
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Affiliation(s)
- Emilie Gregers
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Laboratory for Molecular Cardiology, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Gustav Ahlberg
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Laboratory for Molecular Cardiology, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Thea Christensen
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Department of Biomedical Science, University of Copenhagen, Copenhagen, Denmark
| | - Javad Jabbari
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Laboratory for Molecular Cardiology, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Kirstine O Larsen
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Department of Biomedical Science, University of Copenhagen, Copenhagen, Denmark
| | - Cecilie B Herfelt
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Laboratory for Molecular Cardiology, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Kristoffer M Henningsen
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Laboratory for Molecular Cardiology, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Laura Andreasen
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Laboratory for Molecular Cardiology, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jens J Thiis
- Department of Cardiothoracic Surgery, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Jens Lund
- Department of Cardiothoracic Surgery, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Susanne Holme
- Department of Cardiothoracic Surgery, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Stig Haunsø
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Laboratory for Molecular Cardiology, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Bo H Bentzen
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Department of Biomedical Science, University of Copenhagen, Copenhagen, Denmark
| | - Nicole Schmitt
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Department of Biomedical Science, University of Copenhagen, Copenhagen, Denmark
| | - Jesper H Svendsen
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Laboratory for Molecular Cardiology, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
| | - Morten S Olesen
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark; Laboratory for Molecular Cardiology, Department of Cardiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark; Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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Jones DK, Liu F, Dombrowski N, Joshi S, Robertson GA. Dominant negative consequences of a hERG 1b-specific mutation associated with intrauterine fetal death. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2016; 120:67-76. [PMID: 26772437 DOI: 10.1016/j.pbiomolbio.2016.01.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2015] [Revised: 12/07/2015] [Accepted: 01/04/2016] [Indexed: 12/16/2022]
Abstract
The human ether-a-go-go related gene (hERG) encodes two subunits, hERG 1a and hERG 1b, that combine in vivo to conduct the rapid delayed rectifier potassium current (IKr). Reduced IKr slows cardiac action potential (AP) repolarization and is an underlying cause of cardiac arrhythmias associated with long QT syndrome (LQTS). Although the physiological importance of hERG 1b has been elucidated, the effects of hERG 1b disease mutations on cardiac IKr and AP behavior have not been described. To explore the disease mechanism of a 1b-specific mutation associated with a case of intrauterine fetal death, we examined the effects of the 1b-R25W mutation on total protein, trafficking and membrane current levels in HEK293 cells at physiological temperatures. By all measures the 1b-R25W mutation conferred diminished expression, and exerted a temperature-sensitive, dominant-negative effect over the WT hERG 1a protein with which it was co-expressed. Membrane currents were reduced by 60% with no apparent effect on voltage dependence or deactivation kinetics. The dominant-negative effects of R25W were demonstrated in iPSC-CMs, where 1b-R25W transfection diminished native IKr compared to controls. R25W also slowed AP repolarization, and increased AP triangulation and variability in iPSC-CMs, reflecting cellular manifestations of pro-arrhythmia. These data demonstrate that R25W is a dominant-negative mutation with significant pathophysiological consequences, and provide the first direct link between hERG 1b mutation and cardiomyocyte dysfunction.
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Affiliation(s)
- David K Jones
- Dept. of Neuroscience, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison WI 53705, USA
| | - Fang Liu
- Dept. of Neuroscience, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison WI 53705, USA
| | - Natasha Dombrowski
- Dept. of Neuroscience, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison WI 53705, USA
| | - Sunita Joshi
- Dept. of Neuroscience, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison WI 53705, USA
| | - Gail A Robertson
- Dept. of Neuroscience, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison WI 53705, USA.
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14
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Arcangeli A, Becchetti A. Novel perspectives in cancer therapy: Targeting ion channels. Drug Resist Updat 2015; 21-22:11-9. [DOI: 10.1016/j.drup.2015.06.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Revised: 06/24/2015] [Accepted: 06/27/2015] [Indexed: 01/04/2023]
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15
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Wiśniowska B, Mendyk A, Fijorek K, Polak S. Computer-based prediction of the drug proarrhythmic effect: problems, issues, known and suspected challenges. Europace 2015; 16:724-35. [PMID: 24798962 DOI: 10.1093/europace/euu009] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
It is likely that computer modelling and simulations will become an element of comprehensive cardiac safety testing. Their role would be primarily the integration and the interpretation of previously gathered data. There are still unanswered questions and issues which we list and describe below. They include sources of data used for the development of the models as well as data utilized as input information, which can come from the in vitro studies and the quantitative structure-activity relationship models. The pharmacokinetics of the drugs in question play a crucial role as their active concentration should be considered, yet the question remains where is the right place to assess it. The pharmacodynamic angle includes complications coming from multiple drugs (i.e. active metabolites) acting in parallel as well as the type of interaction with (potentially) multiple affected channels. Once established, the model and the methodology of its use should be further validated, optimistically against individual data reported at the clinical level as the physiological, anatomical, and genetic parameters play a crucial role in the drug-triggered arrhythmia induction. All the abovementioned issues should be at least considered and-hopefully-resolved, to properly utilize the mathematical models for a cardiac safety assessment.
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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
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16
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Abstract
The human ether-à-go-go-related gene (hERG; or KCNH2) encodes the voltage-gated potassium channel underlying IKr, a repolarizing current in the heart. Mutations in KCNH2 or pharmacological agents that reduce IKr slow action potential (AP) repolarization and can trigger cardiac arrhythmias associated with long QT syndrome. Two channel-forming subunits encoded by KCNH2 (hERG 1a and 1b) are expressed in cardiac tissue. In heterologous expression systems, these subunits avidly coassemble and exhibit biophysical and pharmacological properties distinct from those of homomeric hERG 1a channels. Despite these findings, adoption of hERG 1a/1b heteromeric channels as a model for cardiac IKr has been hampered by the lack of evidence for a direct functional role for the 1b subunit in native tissue. In this study, we measured IKr and APs at physiological temperature in cardiomyocytes derived from human induced pluripotent stem cells (iPSC-CMs). We found that specific knockdown of the 1b subunit using shRNA caused reductions in 1b mRNA, 1b protein levels, and IKr magnitude by roughly one-half. AP duration was increased and AP variability was enhanced relative to controls. Early afterdepolarizations, considered cellular substrates for arrhythmia, were also observed in cells with reduced 1b expression. Similar behavior was elicited when channels were effectively converted from heteromers to 1a homomers by expressing a fragment corresponding to the 1a-specific N-terminal Per-Arnt-Sim domain, which is omitted from hERG 1b by alternate transcription. These findings establish that hERG 1b is critical for normal repolarization and that loss of 1b is proarrhythmic in human cardiac cells.
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17
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Thomson SJ, Hansen A, Sanguinetti MC. Concerted all-or-none subunit interactions mediate slow deactivation of human ether-à-go-go-related gene K+ channels. J Biol Chem 2014; 289:23428-36. [PMID: 25008322 DOI: 10.1074/jbc.m114.582437] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
During the repolarization phase of a cardiac action potential, hERG1 K(+) channels rapidly recover from an inactivated state then slowly deactivate to a closed state. The resulting resurgence of outward current terminates the plateau phase and is thus a key regulator of action potential duration of cardiomyocytes. The intracellular N-terminal domain of the hERG1 subunit is required for slow deactivation of the channel as its removal accelerates deactivation 10-fold. Here we investigate the stoichiometry of hERG1 channel deactivation by characterizing the kinetic properties of concatenated tetramers containing a variable number of wild-type and mutant subunits. Three mutations known to accelerate deactivation were investigated, including R56Q and R4A/R5A in the N terminus and F656I in the S6 transmembrane segment. In all cases, a single mutant subunit induced the same rapid deactivation of a concatenated channel as that observed for homotetrameric mutant channels. We conclude that slow deactivation gating of hERG1 channels involves a concerted, fully cooperative interaction between all four wild-type channel subunits.
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Affiliation(s)
- Steven J Thomson
- From the Nora Eccles Harrison Cardiovascular Research and Training Institute and
| | - Angela Hansen
- From the Nora Eccles Harrison Cardiovascular Research and Training Institute and
| | - Michael C Sanguinetti
- From the Nora Eccles Harrison Cardiovascular Research and Training Institute and Department of Internal Medicine and Division of Cardiovascular Medicine, University of Utah, Salt Lake City, Utah 84112
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18
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Erg potassium currents of neonatal mouse Purkinje cells exhibit fast gating kinetics and are inhibited by mGluR1 activation. J Neurosci 2013; 33:16729-40. [PMID: 24133274 DOI: 10.1523/jneurosci.5523-12.2013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
We investigated the subthreshold properties of an erg (ether-à-go-go-related gene) K(+) current in Purkinje cells of neonatal mice. Action potentials recorded from Purkinje cells in cerebellar slices exhibited a decreased threshold potential and increased frequency of spontaneous and repetitive activity following application of the specific erg channel blocker E-4031. Accommodation was absent before and after drug application. The erg current of these Purkinje cells activated at membrane potentials near -60 mV and exhibited fast gating kinetics. The functional importance of fast gating subthreshold erg channels in Purkinje cells was corroborated by comparing the results of action potential clamp experiments with erg1a, erg1b, erg2, and erg3 currents heterologously expressed in HEK cells. Computer simulations based on a NEURON model of Purkinje cells only reproduced the effects of the native erg current when an erg channel conductance like that of erg3 was included. Experiments with subunit-sensitive toxins (BeKm-1, APETx1) indicated that erg channels in Purkinje cells are presumably mediated by heteromeric erg1/erg3 or modified erg1 channels. Following mGluR1 activation, the native erg current was reduced by ∼70%, brought about by reduction of the maximal erg current and a shift of the activation curve to more positive potentials. The Purkinje cell erg current contributed to the sustained current component of the biphasic mGluR1 response. Activation of mGluR1 by the agonist 3,4-dihydroxyphenylglycol increased Purkinje cell excitability, similar to that induced by E-4031. The results indicated that erg currents can be modulated and may contribute to the mGluR1-induced plasticity changes in Purkinje cells.
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19
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Jost N, Virág L, Comtois P, Ordög B, Szuts V, Seprényi G, Bitay M, Kohajda Z, Koncz I, Nagy N, Szél T, Magyar J, Kovács M, Puskás LG, Lengyel C, Wettwer E, Ravens U, Nánási PP, Papp JG, Varró A, Nattel S. Ionic mechanisms limiting cardiac repolarization reserve in humans compared to dogs. J Physiol 2013; 591:4189-206. [PMID: 23878377 DOI: 10.1113/jphysiol.2013.261198] [Citation(s) in RCA: 106] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The species-specific determinants of repolarization are poorly understood. This study compared the contribution of various currents to cardiac repolarization in canine and human ventricle. Conventional microelectrode, whole-cell patch-clamp, molecular biological and mathematical modelling techniques were used. Selective IKr block (50-100 nmol l(-1) dofetilide) lengthened AP duration at 90% of repolarization (APD90) >3-fold more in human than dog, suggesting smaller repolarization reserve in humans. Selective IK1 block (10 μmol l(-1) BaCl2) and IKs block (1 μmol l(-1) HMR-1556) increased APD90 more in canine than human right ventricular papillary muscle. Ion current measurements in isolated cardiomyocytes showed that IK1 and IKs densities were 3- and 4.5-fold larger in dogs than humans, respectively. IKr density and kinetics were similar in human versus dog. ICa and Ito were respectively ~30% larger and ~29% smaller in human, and Na(+)-Ca(2+) exchange current was comparable. Cardiac mRNA levels for the main IK1 ion channel subunit Kir2.1 and the IKs accessory subunit minK were significantly lower, but mRNA expression of ERG and KvLQT1 (IKr and IKs α-subunits) were not significantly different, in human versus dog. Immunostaining suggested lower Kir2.1 and minK, and higher KvLQT1 protein expression in human versus canine cardiomyocytes. IK1 and IKs inhibition increased the APD-prolonging effect of IKr block more in dog (by 56% and 49%, respectively) than human (34 and 16%), indicating that both currents contribute to increased repolarization reserve in the dog. A mathematical model incorporating observed human-canine ion current differences confirmed the role of IK1 and IKs in repolarization reserve differences. Thus, humans show greater repolarization-delaying effects of IKr block than dogs, because of lower repolarization reserve contributions from IK1 and IKs, emphasizing species-specific determinants of repolarization and the limitations of animal models for human disease.
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Affiliation(s)
- Norbert Jost
- A. Varró: Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, H-6720 Szeged, Dóm tér 12, PO Box 427, Hungary.
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20
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Gustina AS, Trudeau MC. The eag domain regulates hERG channel inactivation gating via a direct interaction. ACTA ACUST UNITED AC 2013; 141:229-41. [PMID: 23319729 PMCID: PMC3557309 DOI: 10.1085/jgp.201210870] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Human ether-á-go-go (eag)-related gene (hERG) potassium channel kinetics are characterized by rapid inactivation upon depolarization, along with rapid recovery from inactivation and very slow closing (deactivation) upon repolarization. These factors combine to create a resurgent hERG current, where the current amplitude is paradoxically larger with repolarization than with depolarization. Previous data showed that the hERG N-terminal eag domain regulated deactivation kinetics by making a direct interaction with the C-terminal region of the channel. A primary mechanism for fast inactivation depends on residues in the channel pore; however, inactivation was also shown to be slower after deletion of a large N-terminal region. The mechanism for N-terminal region regulation of inactivation is unclear. Here, we investigated the contributions of the large N-terminal domains (amino acids 1-354), including the eag domain (amino acids 1-135), to hERG channel inactivation kinetics and steady-state inactivation properties. We found that N-deleted channels lacking just the eag domain (Δ2-135) or both the eag domain and the adjacent proximal domain (Δ2-354) had less rectifying current-voltage (I-V) relationships, slower inactivation, faster recovery from inactivation, and lessened steady-state inactivation. We coexpressed genetically encoded N-terminal fragments for the eag domain (N1-135) or the eag domain plus the proximal domain (N1-354) with N-deleted hERG Δ2-135 or hERG Δ2-354 channels and found that the resulting channels had more rectifying I-V relationships, faster inactivation, slower recovery from inactivation, and increased steady-state inactivation, similar to those properties measured for wild-type (WT) hERG. We also found that the eag domain-containing fragments regulated the time to peak and the voltage at the peak of a resurgent current elicited with a ramp voltage protocol. The eag domain-containing fragments effectively converted N-deleted channels into WT-like channels. Neither the addition of the proximal domain to the eag domain in N1-354 fragments nor the presence of the proximal domain in hERG Δ2-135 channels measurably affected inactivation properties; in contrast, the proximal region regulated steady-state activation in hERG Δ2-135 channels. The results show that N-terminal region-dependent regulation of channel inactivation and resurgent current properties are caused by a direct interaction of the eag domain with the rest of the hERG channel.
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Affiliation(s)
- Ahleah S Gustina
- Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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Jonsson MKB, van der Heyden MAG, van Veen TAB. Deciphering hERG channels: molecular basis of the rapid component of the delayed rectifier potassium current. J Mol Cell Cardiol 2012; 53:369-74. [PMID: 22742967 DOI: 10.1016/j.yjmcc.2012.06.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2012] [Revised: 06/07/2012] [Accepted: 06/19/2012] [Indexed: 12/23/2022]
Abstract
The rapid component of the delayed rectifier potassium current (I(Kr)), encoded by the ether-a-go-go-related gene (ERG1, officially denominated as KCNH2), is a major contributor to repolarization in the mammalian heart. Acute (e.g. drug-induced) and chronic (e.g. inherited genetic disorder) disruptions of this current can lead to prolongation of the action potential and potentiate occurrence of lethal arrhythmias. Many cardiac and non-cardiac drugs show high affinity for the I(Kr) channel and it is therefore extensively studied during safety pharmacology. The unique biophysical and pharmacological properties of the I(Kr) channel are largely recapitulated by expressing the human variant (hERG1a) in overexpressing systems. hERG1a channels are tetramers consisting of four 1159 amino acid long proteins and have electrophysiological properties similar, but not identical, to native I(Kr). In the search for an explanation to the discrepancies between I(Kr) and hERG1a channels, two alternative hERG1 proteins have been found. Alternative transcription of hERG1 leads to a protein with a 56 amino acid shorter N-terminus, known as hERG1b. hERG1b can form channels alone or coassemble with hERG1a. Alternative splicing leads to an alternate C-terminus and a protein known as hERGuso. hERGuso and hERG1b regulate hERG1a channel trafficking, functional expression and channel kinetics. Expression of hERGuso leads to a reduced number of channels at the plasma membrane and thereby reduces current density. On the contrary, co-assembly with hERG1b alters channel kinetics resulting in more available channels and a larger current. These findings have implication for understanding mechanisms of disease, acute and chronic drug effects, and potential gender differences.
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Affiliation(s)
- Malin K B Jonsson
- Department of Medical Physiology, Division Heart and Lungs, University Medical Center Utrecht, Utrecht, The Netherlands.
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Models of HERG gating. Biophys J 2011; 101:631-42. [PMID: 21806931 DOI: 10.1016/j.bpj.2011.06.050] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2011] [Revised: 06/22/2011] [Accepted: 06/27/2011] [Indexed: 11/21/2022] Open
Abstract
HERG (Kv11.1, KCNH2) is a voltage-gated potassium channel with unique gating characteristics. HERG has fast voltage-dependent inactivation, relatively slow deactivation, and fast recovery from inactivation. This combination of gating kinetics makes study of HERG difficult without using mathematical models. Several HERG models have been developed, with fundamentally different organization. HERG is the molecular basis of I(Kr), which plays a critical role in repolarization. We programmed and compared five distinct HERG models. HERG gating cannot be adequately replicated using Hodgkin-Huxley type formulation. Using Markov models, a five-state model is required with three closed, one open, and one inactivated state, and a voltage-independent step between some of the closed states. A fundamental difference between models is the presence/absence of a transition directly from the proximal closed state to the inactivated state. The only models that effectively reproduce HERG data have no direct closed-inactivated transition, or have a closed-inactivated transition that is effectively zero compared to the closed-open transition, rendering the closed-inactivation transition superfluous. Our single-channel model demonstrates that channels can inactivate without conducting with a flickering or bursting open-state. The various models have qualitative and quantitative differences that are critical to accurate predictions of HERG behavior during repolarization, tachycardia, and premature depolarizations.
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Du C, El Harchi A, McPate M, Orchard C, Hancox J. Enhanced inhibitory effect of acidosis on hERG potassium channels that incorporate the hERG1b isoform. Biochem Biophys Res Commun 2011; 405:222-7. [DOI: 10.1016/j.bbrc.2011.01.014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2010] [Accepted: 01/04/2011] [Indexed: 10/18/2022]
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Larsen AP, Bentzen BH, Grunnet M. Differential effects of Kv11.1 activators on Kv11.1a, Kv11.1b and Kv11.1a/Kv11.1b channels. Br J Pharmacol 2011; 161:614-28. [PMID: 20880400 DOI: 10.1111/j.1476-5381.2010.00897.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE K(v)11.1 channels are involved in regulating cellular excitability in various tissues including brain, heart and smooth muscle. In these tissues, at least two isoforms, K(v)11.1a and K(v)11.1b, with different kinetics, are expressed. K(v)11.1 activators are potential therapeutic agents, but their effects have only been tested on the K(v)11.1a isoform. In this study, the effects of two different K(v)11.1 activators, NS1643 and RPR260243, were characterized on K(v)11.1a and K(v)11.1b channels. EXPERIMENTAL APPROACH K(v)11.1a and K(v)11.1b channels were expressed in Xenopus laevis oocytes, and currents were measured using two-electrode voltage clamp. I/V curves and channel kinetics were measured before and after application of 30 µM NS1643 or 10 µM RPR260243. KEY RESULTS NS1643 increased steady-state currents through Kv11.1b several fold more than through K(v)11.1a channels, without affecting EC(50) values. NS1643 increased activation rates and decreased rates of inactivation, recovery from inactivation and deactivation for both channels. Except for activation, where effect of NS1643 was comparable, relative changes were greater for Kv11.1b than for K(v)11.1a. RPR260243 increased steady-state currents only through Kv11.1a channels, but slowed the process of deactivation for both channels primarily by decreasing time constant of slow deactivation. This effect was greater on K(v)11.1b than on K(v)11.1a. Effects of both compounds on heteromeric K(v)11.1a/K(v)11.1b channels were similar to those on K(v)11.1a. CONCLUSIONS AND IMPLICATIONS Both NS1643 and RPR260243 displayed differential effects on K(v)11.1a and K(v)11.1b channels, the effects being relatively more pronounced on K(v)11.1b channels. This affirms the importance of testing the effect of K(v)11.1 activators on different channel isoforms.
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Affiliation(s)
- A P Larsen
- The Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3, Copenhagen N, Denmark
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Role of ERG1 isoforms in modulation of ERG1 channel trafficking and function. Pflugers Arch 2010; 460:803-12. [DOI: 10.1007/s00424-010-0855-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2010] [Revised: 06/13/2010] [Accepted: 06/14/2010] [Indexed: 01/31/2023]
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