1
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Parallel Recordings of Transmembrane hERG Channel Currents Based on Solvent-Free Lipid Bilayer Microarray. MICROMACHINES 2021; 12:mi12010098. [PMID: 33478052 PMCID: PMC7835820 DOI: 10.3390/mi12010098] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/13/2020] [Revised: 01/15/2021] [Accepted: 01/18/2021] [Indexed: 12/23/2022]
Abstract
The reconstitution of ion-channel proteins in artificially formed bilayer lipid membranes (BLMs) forms a well-defined system for the functional analysis of ion channels and screening of the effects of drugs that act on these proteins. To improve the efficiency of the BLM reconstitution system, we report on a microarray of stable solvent-free BLMs formed in microfabricated silicon (Si) chips, where micro-apertures with well-defined nano- and micro-tapered edges were fabricated. Sixteen micro-wells were manufactured in a chamber made of Teflon®, and the Si chips were individually embedded in the respective wells as a recording site. Typically, 11 to 16 BLMs were simultaneously formed with an average BLM number of 13.1, which corresponded to a formation probability of 82%. Parallel recordings of ion-channel activities from multiple BLMs were successfully demonstrated using the human ether-a-go-go-related gene (hERG) potassium channel, of which the relation to arrhythmic side effects following drug treatment is well recognized.
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2
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Kabakov AY, Sengun E, Lu Y, Roder K, Bronk P, Baggett B, Turan NN, Moshal KS, Koren G. Three-Week-Old Rabbit Ventricular Cardiomyocytes as a Novel System to Study Cardiac Excitation and EC Coupling. Front Physiol 2021; 12:672360. [PMID: 34867432 PMCID: PMC8637404 DOI: 10.3389/fphys.2021.672360] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 10/06/2021] [Indexed: 01/14/2023] Open
Abstract
Cardiac arrhythmias significantly contribute to cardiovascular morbidity and mortality. The rabbit heart serves as an accepted model system for studying cardiac cell excitation and arrhythmogenicity. Accordingly, primary cultures of adult rabbit ventricular cardiomyocytes serve as a preferable model to study molecular mechanisms of human cardiac excitation. However, the use of adult rabbit cardiomyocytes is often regarded as excessively costly. Therefore, we developed and characterized a novel low-cost rabbit cardiomyocyte model, namely, 3-week-old ventricular cardiomyocytes (3wRbCMs). Ventricular myocytes were isolated from whole ventricles of 3-week-old New Zealand White rabbits of both sexes by standard enzymatic techniques. Using wheat germ agglutinin, we found a clear T-tubule structure in acutely isolated 3wRbCMs. Cells were adenovirally infected (multiplicity of infection of 10) to express Green Fluorescent Protein (GFP) and cultured for 48 h. The cells showed action potential duration (APD90 = 253 ± 24 ms) and calcium transients similar to adult rabbit cardiomyocytes. Freshly isolated and 48-h-old-cultured cells expressed critical ion channel proteins: calcium voltage-gated channel subunit alpha1 C (Cavα1c), sodium voltage-gated channel alpha subunit 5 (Nav1.5), potassium voltage-gated channel subfamily D member 3 (Kv4.3), and subfamily A member 4 (Kv1.4), and also subfamily H member 2 (RERG. Kv11.1), KvLQT1 (K7.1) protein and inward-rectifier potassium channel (Kir2.1). The cells displayed an appropriate electrophysiological phenotype, including fast sodium current (I Na), transient outward potassium current (I to), L-type calcium channel peak current (I Ca,L), rapid and slow components of the delayed rectifier potassium current (I Kr and I Ks), and inward rectifier (I K1). Although expression of the channel proteins and some currents decreased during the 48 h of culturing, we conclude that 3wRbCMs are a new, low-cost alternative to the adult-rabbit-cardiomyocytes system, which allows the investigation of molecular mechanisms of cardiac excitation on morphological, biochemical, genetic, physiological, and biophysical levels.
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Affiliation(s)
- Anatoli Y Kabakov
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Elif Sengun
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States.,Department of Pharmacology, Institute of Graduate Studies in Health Sciences, Istanbul University, Istanbul, Türkiye
| | - Yichun Lu
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Karim Roder
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Peter Bronk
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Brett Baggett
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Nilüfer N Turan
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Karni S Moshal
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Gideon Koren
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
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3
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Pueyo E, Dangerfield CE, Britton OJ, Virág L, Kistamás K, Szentandrássy N, Jost N, Varró A, Nánási PP, Burrage K, Rodríguez B. Experimentally-Based Computational Investigation into Beat-To-Beat Variability in Ventricular Repolarization and Its Response to Ionic Current Inhibition. PLoS One 2016; 11:e0151461. [PMID: 27019293 PMCID: PMC4809506 DOI: 10.1371/journal.pone.0151461] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2015] [Accepted: 02/29/2016] [Indexed: 11/18/2022] Open
Abstract
Beat-to-beat variability in repolarization (BVR) has been proposed as an arrhythmic risk marker for disease and pharmacological action. The mechanisms are unclear but BVR is thought to be a cell level manifestation of ion channel stochasticity, modulated by cell-to-cell differences in ionic conductances. In this study, we describe the construction of an experimentally-calibrated set of stochastic cardiac cell models that captures both BVR and cell-to-cell differences in BVR displayed in isolated canine action potential measurements using pharmacological agents. Simulated and experimental ranges of BVR are compared in control and under pharmacological inhibition, and the key ionic currents determining BVR under physiological and pharmacological conditions are identified. Results show that the 4-aminopyridine-sensitive transient outward potassium current, Ito1, is a fundamental driver of BVR in control and upon complete inhibition of the slow delayed rectifier potassium current, IKs. In contrast, IKs and the L-type calcium current, ICaL, become the major contributors to BVR upon inhibition of the fast delayed rectifier potassium current, IKr. This highlights both IKs and Ito1 as key contributors to repolarization reserve. Partial correlation analysis identifies the distribution of Ito1 channel numbers as an important independent determinant of the magnitude of BVR and drug-induced change in BVR in control and under pharmacological inhibition of ionic currents. Distributions in the number of IKs and ICaL channels only become independent determinants of the magnitude of BVR upon complete inhibition of IKr. These findings provide quantitative insights into the ionic causes of BVR as a marker for repolarization reserve, both under control condition and pharmacological inhibition.
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Affiliation(s)
- E. Pueyo
- Biomedical Research Networking Centre on Bioengineering, Biomaterials and Nanomedicine, University of Zaragoza, Zaragoza, Spain
- Biosignal Interpretation and Computational Simulation Group, I3A, IIS, Aragón, University of Zaragoza, Zaragoza, Spain
- * E-mail:
| | - C. E. Dangerfield
- Department of Computer Science, University of Oxford, Oxford, United Kingdom
| | - O. J. Britton
- Department of Computer Science, University of Oxford, Oxford, United Kingdom
| | - L. Virág
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
- MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary
| | - K. Kistamás
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - N. Szentandrássy
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
- Department of Dental Physiology and Pharmacology, Faculty of Dentistry, University of Debrecen, Debrecen, Hungary
| | - N. Jost
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
- MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary
| | - A. Varró
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
- MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary
| | - P. P. Nánási
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
- Department of Dental Physiology and Pharmacology, Faculty of Dentistry, University of Debrecen, Debrecen, Hungary
| | - K. Burrage
- Department of Computer Science, University of Oxford, Oxford, United Kingdom
- School of Mathematical Sciences, Queensland University of Technology, Brisbane, Queensland, Australia
- ARC Centre of Excellence for Mathematical and Statistical Frontiers, Queensland University of Technology, Brisbane, Queensland, Australia
| | - B. Rodríguez
- Department of Computer Science, University of Oxford, Oxford, United Kingdom
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4
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Vijayvergiya V, Acharya S, Poulos J, Schmidt J. Single channel and ensemble hERG conductance measured in droplet bilayers. Biomed Microdevices 2015; 17:12. [PMID: 25653065 DOI: 10.1007/s10544-014-9919-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The human ether-a-go-go related gene (hERG) encodes the potassium channel Kv11.1, which plays a key role in the cardiac action potential and has been implicated in cardiac disorders as well as a number of off-target pharmaceutical interactions. The electrophysiology of this channel has been predominantly studied using patch clamp, but lipid bilayers have the potential to offer some advantages, including apparatus simplicity, ease of use, and the ability to control the membrane and solution compositions. We made membrane preparations from hERG-expressing cells and measured them using droplet bilayers, allowing measurement of channel ensemble currents and 13.5 pS single channel currents. These currents were ion selective and were blockable by E-4031 and dofetilide in a dose-dependent manner, allowing determination of IC50 values of 17 nM and 9.65 μM for E-4031 and dofetilide, respectively. We also observed time- and voltage- dependent currents following step changes in applied potential that were similar to previously reported patch clamp measurements.
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Affiliation(s)
- Viksita Vijayvergiya
- Department of Bioengineering, University of California Los Angeles, Los Angeles, CA, 90095, USA
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5
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Liu GX, Remme CA, Boukens BJ, Belardinelli L, Rajamani S. Overexpression of SCN5A in mouse heart mimics human syndrome of enhanced atrioventricular nodal conduction. Heart Rhythm 2015; 12:1036-45. [PMID: 25623181 DOI: 10.1016/j.hrthm.2015.01.029] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/09/2014] [Indexed: 11/19/2022]
Abstract
BACKGROUND In enhanced atrioventricular (A-V) nodal conduction (EAVNC) syndrome, patients have short A-V conduction times. Multiple mechanisms have been proposed to explain EAVNC; however, the electrophysiological or molecular substrate responsible for it remains unclear. OBJECTIVE The purpose of this study was to test the hypothesis that overexpression of SCN5A in the mouse heart may provide an animal model mimicking EAVNC. METHODS Electrocardiogram, atrial, His bundle, and ventricular electrograms were recorded from wild-type (WT) and transgenic (TG) mice overexpressing human SCN5A. The sodium current and NaV1.5 expression were measured using patch-clamp and immunohistochemistry techniques. RESULTS The P-R interval in TG mice (13.6 ± 1.2 ms) was much shorter than that in WT mice (40.2 ± 0.59 ms). In TG isolated hearts, the A-V conduction time (14.4 ± 0.81 ms) during right atrial pacing was also shorter than that in WT hearts (39.5 ± 0.62 ms). Records of His bundle electrograms revealed that atrial-to-His and His-to-ventricular intervals were shorter in TG than in WT hearts. In addition, TG hearts had a shorter Wenckebach cycle length and A-V effective refractory period. The sodium current was 2-fold greater in TG ventricular myocytes than in WT ventricular myocytes. Flecainide prolonged the A-V conduction time in TG hearts to a value close to that in WT hearts. Nifedipine prolonged the atrial-to-His interval in WT hearts but not in TG hearts. Immunohistochemistry studies revealed increased NaV1.5 labeling in TG atrial and ventricular tissues, and NaV1.5 expression in A-V junction and A-V ring regions in TG hearts. CONCLUSION Enhanced A-V conduction in mice overexpressing SCN5A in the heart mimics the human syndrome of EAVNC. Thus, variants in sodium channel expression in the A-V nodal region may be an electrophysiological substrate responsible for EAVNC.
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Affiliation(s)
- Gong Xin Liu
- Department of Biology, Gilead Sciences, Fremont, California
| | - Carol Ann Remme
- Department of Experimental Cardiology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands
| | - Bastiaan J Boukens
- Department of Biomedical Engineering, Washington University, St. Louis, Missouri
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6
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Oshima A, Hirano-Iwata A, Mozumi H, Ishinari Y, Kimura Y, Niwano M. Reconstitution of Human Ether-a-go-go-Related Gene Channels in Microfabricated Silicon Chips. Anal Chem 2013; 85:4363-9. [DOI: 10.1021/ac303484k] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Azusa Oshima
- Graduate School of Biomedical
Engineering, Tohoku University, 6-6 Aoba,
Aramaki, Aoba-ku, Sendai 980-8579, Japan
| | - Ayumi Hirano-Iwata
- Graduate School of Biomedical
Engineering, Tohoku University, 6-6 Aoba,
Aramaki, Aoba-ku, Sendai 980-8579, Japan
- PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi,
Saitama 332-0012, Japan
| | - Hideki Mozumi
- Graduate School of Biomedical
Engineering, Tohoku University, 6-6 Aoba,
Aramaki, Aoba-ku, Sendai 980-8579, Japan
| | - Yutaka Ishinari
- Graduate School of Biomedical
Engineering, Tohoku University, 6-6 Aoba,
Aramaki, Aoba-ku, Sendai 980-8579, Japan
| | - Yasuo Kimura
- Laboratory
for Nanoelectronics
and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai,
Miyagi 980-8577, Japan
| | - Michio Niwano
- Graduate School of Biomedical
Engineering, Tohoku University, 6-6 Aoba,
Aramaki, Aoba-ku, Sendai 980-8579, Japan
- Laboratory
for Nanoelectronics
and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai,
Miyagi 980-8577, Japan
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7
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Bilet A, Bauer CK. Effects of the small molecule HERG activator NS1643 on Kv11.3 channels. PLoS One 2012; 7:e50886. [PMID: 23226420 PMCID: PMC3511382 DOI: 10.1371/journal.pone.0050886] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2012] [Accepted: 10/26/2012] [Indexed: 01/15/2023] Open
Abstract
NS1643 is one of the small molecule HERG (Kv11.1) channel activators and has also been found to increase erg2 (Kv11.2) currents. We now investigated whether NS1643 is also able to act as an activator of Kv11.3 (erg3) channels expressed in CHO cells. Activation of rat Kv11.3 current occurred in a dose-dependent manner and maximal current increasing effects were obtained with 10 µM NS1643. At this concentration, steady-state outward current increased by about 80% and the current increase was associated with a significant shift in the voltage dependence of activation to more negative potentials by about 15 mV. In addition, activation kinetics were accelerated, whereas deactivation was slowed. There was no significant effect on the kinetics of inactivation and recovery from inactivation. The strong current-activating agonistic effect of NS1643 did not result from a shift in the voltage dependence of Kv11.3 channel inactivation and was independent from external Na+ or Ca2+. At the higher concentration of 20 µM, NS1643 induced clearly less current increase. The left shift in the voltage dependence of activation reversed and the voltage sensitivity of activation dramatically decreased along with a slowing of Kv11.3 channel activation. These data show that, in comparison to other Kv11 family members, NS1643 exerts distinct effects on Kv11.3 channels with especially pronounced partial antagonistic effects at higher concentration.
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Affiliation(s)
- Arne Bilet
- Institute of Cellular and Integrative Physiology, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany
| | - Christiane K. Bauer
- Institute of Cellular and Integrative Physiology, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany
- * E-mail:
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8
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Wu CT, Nattel S. Triggering of cardiac arrhythmic events in long QT syndrome: lessons from funny bunnies. J Physiol 2012; 590:1311-2. [PMID: 22422115 DOI: 10.1113/jphysiol.2012.229344] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Chia Tung Wu
- Department of Medicine and Research Centre, Montreal Heart Institute and Université de Montréal, Canada
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9
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HIRANO-IWATA A, OSHIMA A, MOZUMI H, KIMURA Y, NIWANO M. Stable Lipid Bilayers Based on Micro- and Nano-Fabrication as a Platform for Recording Ion-Channel Activities. ANAL SCI 2012; 28:1049-57. [DOI: 10.2116/analsci.28.1049] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Ayumi HIRANO-IWATA
- Graduate School of Biomedical Engineering, Tohoku University
- PRESTO, Japan Science and Technology Agency (JST)
| | - Azusa OSHIMA
- Graduate School of Biomedical Engineering, Tohoku University
| | - Hideki MOZUMI
- Graduate School of Biomedical Engineering, Tohoku University
| | - Yasuo KIMURA
- Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University
| | - Michio NIWANO
- Graduate School of Biomedical Engineering, Tohoku University
- Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University
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10
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Vaidyanathan R, Taffet SM, Vikstrom KL, Anumonwo JMB. Regulation of cardiac inward rectifier potassium current (I(K1)) by synapse-associated protein-97. J Biol Chem 2010; 285:28000-9. [PMID: 20530486 DOI: 10.1074/jbc.m110.110858] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Synapse-associated protein-97 (SAP97) is a membrane-associated guanylate kinase scaffolding protein expressed in cardiomyocytes. SAP97 has been shown to associate and modulate voltage-gated potassium (Kv) channel function. In contrast to Kv channels, little information is available on interactions involving SAP97 and inward rectifier potassium (Kir2.x) channels that underlie the classical inward rectifier current, I(K1). To investigate the functional effects of silencing SAP97 on I(K1) in adult rat ventricular myocytes, SAP97 was silenced using an adenoviral short hairpin RNA vector. Western blot analysis showed that SAP97 was silenced by approximately 85% on day 3 post-infection. Immunostaining showed that Kir2.1 and Kir2.2 co-localize with SAP97. Co-immunoprecipitation (co-IP) results demonstrated that Kir2.x channels associate with SAP97. Voltage clamp experiments showed that silencing SAP97 reduced I(K1) whole cell density by approximately 55%. I(K1) density at -100 mV was -1.45 +/- 0.15 pA/picofarads (n = 6) in SAP97-silenced cells as compared with -3.03 +/- 0.37 pA/picofarads (n = 5) in control cells. Unitary conductance properties of I(K1) were unaffected by SAP97 silencing. The major mechanism for the reduction of I(K1) density appears to be a decrease in Kir2.x channel abundance. Furthermore, SAP97 silencing impaired I(K1) regulation by beta(1)-adrenergic receptor (beta1-AR) stimulation. In control, isoproterenol reduced I(K1) amplitude by approximately 75%, an effect that was blunted following SAP97 silencing. Our co-IP data show that beta1-AR associates with SAP97 and Kir2.1 and also that Kir2.1 co-IPs with protein kinase A and beta1-AR. SAP97 immunolocalizes with protein kinase A and beta1-AR in the cardiac myocytes. Our results suggest that in cardiac myocytes SAP97 regulates surface expression of channels underlying I(K1), as well as assembles a signaling complex involved in beta1-AR regulation of I(K1).
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Affiliation(s)
- Ravi Vaidyanathan
- Department of Pharmacology, State University of New York Upstate Medical University, Syracuse, New York 13210, USA
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11
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Lin EC, Holzem KM, Anson BD, Moungey BM, Balijepalli SY, Tester DJ, Ackerman MJ, Delisle BP, Balijepalli RC, January CT. Properties of WT and mutant hERG K(+) channels expressed in neonatal mouse cardiomyocytes. Am J Physiol Heart Circ Physiol 2010; 298:H1842-9. [PMID: 20363883 DOI: 10.1152/ajpheart.01236.2009] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mutations in human ether-a-go-go-related gene 1 (hERG) are linked to long QT syndrome type 2 (LQT2). hERG encodes the pore-forming alpha-subunits that coassemble to form rapidly activating delayed rectifier K(+) current in the heart. LQT2-linked missense mutations have been extensively studied in noncardiac heterologous expression systems, where biogenic (protein trafficking) and biophysical (gating and permeation) abnormalities have been postulated to underlie the loss-of-function phenotype associated with LQT2 channels. Little is known about the properties of LQT2-linked hERG channel proteins in native cardiomyocyte systems. In this study, we expressed wild-type (WT) hERG and three LQT2-linked mutations in neonatal mouse cardiomyocytes and studied their electrophysiological and biochemical properties. Compared with WT hERG channels, the LQT2 missense mutations G601S and N470D hERG exhibited altered protein trafficking and underwent pharmacological correction, and N470D hERG channels gated at more negative voltages. The DeltaY475 hERG deletion mutation trafficked similar to WT hERG channels, gated at more negative voltages, and had rapid deactivation kinetics, and these properties were confirmed in both neonatal mouse cardiomyocyte and human embryonic kidney (HEK)-293 cell expression systems. Differences between the cardiomyocytes and HEK-293 cell expression systems were that hERG current densities were reduced 10-fold and deactivation kinetics were accelerated 1.5- to 2-fold in neonatal mouse cardiomyocytes. An important finding of this work is that pharmacological correction of trafficking-deficient LQT2 mutations, as a potential innovative approach to therapy, is possible in native cardiac tissue.
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Affiliation(s)
- Eric C Lin
- Section of Cardiovascular Medicine, Departments of Medicine and Physiology, University of Wisconsin, Madison, Wisconsin, USA
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12
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Arrhythmia phenotype in mouse models of human long QT. J Interv Card Electrophysiol 2009; 24:77-87. [PMID: 19148726 DOI: 10.1007/s10840-008-9339-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/04/2007] [Accepted: 10/27/2008] [Indexed: 10/21/2022]
Abstract
Enhanced dispersion of repolarization (DR) was proposed as a unifying mechanism, central to arrhythmia genesis in the long QT (LQT) syndrome. In mammalian hearts, K(+) channels are heterogeneously expressed across the ventricles resulting in 'intrinsic' DR that may worsen in long QT. DR was shown to be central to the arrhythmia phenotype of transgenic mice with LQT caused by loss of function of the dominant mouse K(+) currents. Here, we investigated the arrhythmia phenotype of mice with targeted deletions of KCNE1 and KCNH2 genes which encode for minK/IsK and Merg1 (mouse homolog of human ERG) proteins resulting in loss of function of I(Ks) and I(Kr), respectively. Both currents are important human K(+) currents associated with LQT5 and LQT2. Loss of minK, a protein subunit that interacts with KvLQT1, results in a marked reduction of I(Ks) giving rise to the Jervell and Lange-Nielsen syndrome and the reduced KCNH2 gene reduces MERG and I(Kr). Hearts were perfused, stained with di-4-ANEPPS and optically mapped to compare action potential durations (APDs) and arrhythmia phenotype in homozygous minK (minK(-/-)) and heterozygous Merg1 (Merg(+/-)) deletions and littermate control mice. MinK(-/-) mice has similar APDs and no arrhythmias (n = 4). Merg(+/-) mice had prolonged APDs (from 20 +/- 6 to 32 +/- 9 ms at the base, p < 0.01; from 18 +/- 5 to 25 +/- 9 ms at the apex, p < 0.01; n = 8), longer refractory periods (RP) (36 +/- 14 to 63 +/- 27 at the base, p < 0.01 and 34 +/- 5 to 53 +/- 21 ms at the apex, p < 0.03; n = 8), higher DR 10.4 +/- 4.1 vs. 14 +/- 2.3 ms, p < 0.02) and similar conduction velocities (n = 8). Programmed stimulation exposed a higher propensity to VT in Merg(+/-) mice (60% vs. 10%). A comparison of mouse models of LQT based on K(+) channel mutations important to human and mouse repolarization emphasizes DR as a major determinant of arrhythmia vulnerability.
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13
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Dispersions of repolarization and ventricular arrhythmogenesis: Lessons from animal models. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 98:219-29. [DOI: 10.1016/j.pbiomolbio.2008.10.008] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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14
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Abstract
Background—
Inhibition of individual K
+
currents causes functionally based compensatory increases in other K
+
currents that minimize changes in action potential duration, a phenomenon known as repolarization reserve. The possibility that sustained K
+
channel inhibition may induce remodeling of ion current expression has not been tested. Accordingly, we assessed the effects of sustained inhibition of one K
+
current on various other cardiac ionic currents.
Methods and Results—
Adult canine left ventricular cardiomyocytes were incubated in primary culture and paced at a physiological rate (1 Hz) for 24 hours in the presence or absence of the highly selective rapid delayed-rectifier K
+
current (I
Kr
) blocker dofetilide (5 nmol/L). Sustained dofetilide exposure led to shortened action potential duration and increased repolarization reserve (manifested as a reduced action potential duration–prolonging response to I
Kr
blockade). These repolarization changes were accompanied by increased slow delayed-rectifier (I
Ks
) density, whereas I
Kr
, transient-outward (I
to
), inward-rectifier (I
K1
), L-type Ca
2+
(I
CaL
), and late Na
+
current remained unchanged. The mRNA expression corresponding to KvLQT1 and minK (real-time polymerase chain reaction) was unchanged, but their protein expression (Western blot) was increased, suggesting posttranscriptional regulation. To analyze possible mechanisms, we quantified the muscle-specific microRNA subtypes
miR
-133a and
miR
-133b, which can posttranscriptionally regulate and repress KvLQT1 protein expression without affecting mRNA expression. The expression levels of
miR
-133a and
miR
-133b were significantly decreased in cells cultured in dofetilide compared with control, possibly accounting for KvLQT1 protein upregulation.
Conclusions—
Sustained reductions in I
Kr
may lead to compensatory upregulation of I
Ks
through posttranscriptional upregulation of underlying subunits, likely mediated (at least partly) by microRNA changes. These results suggest that feedback control of ion channel expression may influence repolarization reserve.
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Affiliation(s)
- Ling Xiao
- From the Department of Medicine, Montreal Heart Institute and Université de Montréal (L.X., J.X., X.L., H.L., Z.W., S.N.), and Department of Pharmacology and Therapeutics, McGill University (L.X., S.N.), Montreal, Quebec, Canada
| | - Jiening Xiao
- From the Department of Medicine, Montreal Heart Institute and Université de Montréal (L.X., J.X., X.L., H.L., Z.W., S.N.), and Department of Pharmacology and Therapeutics, McGill University (L.X., S.N.), Montreal, Quebec, Canada
| | - Xiaobin Luo
- From the Department of Medicine, Montreal Heart Institute and Université de Montréal (L.X., J.X., X.L., H.L., Z.W., S.N.), and Department of Pharmacology and Therapeutics, McGill University (L.X., S.N.), Montreal, Quebec, Canada
| | - Huixian Lin
- From the Department of Medicine, Montreal Heart Institute and Université de Montréal (L.X., J.X., X.L., H.L., Z.W., S.N.), and Department of Pharmacology and Therapeutics, McGill University (L.X., S.N.), Montreal, Quebec, Canada
| | - Zhiguo Wang
- From the Department of Medicine, Montreal Heart Institute and Université de Montréal (L.X., J.X., X.L., H.L., Z.W., S.N.), and Department of Pharmacology and Therapeutics, McGill University (L.X., S.N.), Montreal, Quebec, Canada
| | - Stanley Nattel
- From the Department of Medicine, Montreal Heart Institute and Université de Montréal (L.X., J.X., X.L., H.L., Z.W., S.N.), and Department of Pharmacology and Therapeutics, McGill University (L.X., S.N.), Montreal, Quebec, Canada
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15
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Killeen MJ, Thomas G, Olesen SP, Demnitz J, Stokoe KS, Grace AA, Huang CLH. Effects of potassium channel openers in the isolated perfused hypokalaemic murine heart. Acta Physiol (Oxf) 2008; 193:25-36. [PMID: 18005217 PMCID: PMC2343060 DOI: 10.1111/j.1748-1716.2007.01773.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Aim We explored the anti-arrhythmic efficacy of K+ channel activation in the hypokalaemic murine heart using NS1643 and nicorandil, compounds which augment IKr and IKATP respectively. Methods Left ventricular epicardial and endocardial monophasic action potentials were compared in normokalaemic and hypokalaemic preparations in the absence and presence of NS1643 (30 μm) and nicorandil (20 μm). Results Spontaneously beating hypokalaemic hearts (3 mm K+) all elicited early afterdepolarizations (EADs) and episodes of ventricular tachycardia (VT). Perfusion with NS1643 and nicorandil suppressed EADs and VT in 7 of 13 and five of six hypokalaemic hearts. Provoked arrhythmia studies using programmed electrical stimulation induced VT in all hypokalaemic hearts, but failed to do so in 7 of 13 and five of six hearts perfused with NS1643 and nicorandil respectively. These anti-arrhythmic effects were accompanied by reductions in action potential duration at 90% repolarization (APD90) and changes in the transmural gradient of repolarization, reflected in ΔAPD90. NS1643 and nicorandil reduced epicardial APD90 from 68.3 ± 1.1 to 56.5 ± 4.1 and 51.5 ± 1.5 ms, respectively, but preserved endocardial APD90 in hypokalaemic hearts. NS1643 and nicorandil thus restored ΔAPD90 from −9.6 ± 4.3 ms under baseline hypokalaemic conditions to 3.9 ± 4.1 and 9.9 ± 2.1 ms, respectively, close to normokalaemic values. Conclusion These findings demonstrate, for the first time, the anti-arrhythmic efficacy of K+ channel activation in the setting of hypokalaemia. NS1643 and nicorandil are anti-arrhythmic through the suppression of EADs, reductions in APD90 and restorations of ΔAPD90.
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Affiliation(s)
- M J Killeen
- Physiological Laboratory, University of Cambridge, Cambridge, UK.
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16
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Abstract
Sudden cardiac death stemming from ventricular arrhythmogenesis is one of the major causes of mortality in the developed world. Congenital and acquired forms of long QT syndrome (LQTS) are in turn associated with life threatening arrhythmias. Over the past decade our understanding of arrhythmogenic mechanisms in the setting of these diseases has increased greatly due to the creation of a number of animal models. Of these, the genetically amenable mouse has proved to be a particularly powerful tool. This review summarizes the congenital and acquired LQTS and describes the various mouse models that have been created to further probe arrhythmogenic mechanisms.
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Affiliation(s)
- M J Killeen
- Physiological Laboratory, University of Cambridge, Cambridge, UK.
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17
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Single-channel properties of I K,slow1 and I K,slow2 in mouse ventricular myocytes. Pflugers Arch 2008; 456:541-7. [PMID: 18197415 DOI: 10.1007/s00424-007-0436-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2007] [Accepted: 12/14/2007] [Indexed: 10/22/2022]
Abstract
I K,slow1 and I K,slow2 are two important voltage-gated potassium (K+) currents expressed in mouse ventricular myocytes. However, their properties at the single-channel level have not been characterized. In this paper, we report two new single K+ channels, mK1 and mK2, in myocytes isolated from mouse ventricles and their possible correlation with the macroscopic currents I K,slow1 and I K,slow2. The conductance of mK1 and mK2 was 24 and 17 pS, respectively. Ensemble-averaged current demonstrated an inactivation time constant of 400 to 500 ms for mK1 compared with 1,300 to 2,000 ms for mK2. The mK1 channel was more sensitive than the MK2 channel to the K channel blocker 4-AP. In myocytes isolated from Kv1DN mice with functional knock out of the Kv1.5 channel, mK1 was not detectable but mK2 was present. Our data suggest that the newly characterized K+ channels, mK1 and mK2, likely correspond to the macroscopic currents of I K,slow1 and I K,slow2, respectively.
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18
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Zhu M, Gach AA, Liu G, Xu X, Lim CC, Zhang JX, Mao L, Chuprun K, Koch WJ, Liao R, Koren G, Blaxall BC, Mende U. Enhanced calcium cycling and contractile function in transgenic hearts expressing constitutively active G alpha o* protein. Am J Physiol Heart Circ Physiol 2008; 294:H1335-47. [PMID: 18192223 DOI: 10.1152/ajpheart.00584.2007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In contrast to the other heterotrimeric GTP-binding proteins (G proteins) Gs and Gi, the functional role of G o is still poorly defined. To investigate the role of G alpha o in the heart, we generated transgenic mice with cardiac-specific expression of a constitutively active form of G alpha o1* (G alpha o*), the predominant G alpha o isoform in the heart. G alpha o expression was increased 3- to 15-fold in mice from 5 independent lines, all of which had a normal life span and no gross cardiac morphological abnormalities. We demonstrate enhanced contractile function in G alpha o* transgenic mice in vivo, along with increased L-type Ca2+ channel current density, calcium transients, and cell shortening in ventricular G alpha o*-expressing myocytes compared with wild-type controls. These changes were evident at baseline and maintained after isoproterenol stimulation. Expression levels of all major Ca2+ handling proteins were largely unchanged, except for a modest reduction in Na+/Ca2+ exchanger in transgenic ventricles. In contrast, phosphorylation of the ryanodine receptor and phospholamban at known PKA sites was increased 1.6- and 1.9-fold, respectively, in G alpha o* ventricles. Density and affinity of beta-adrenoceptors, cAMP levels, and PKA activity were comparable in G alpha o* and wild-type myocytes, but protein phosphatase 1 activity was reduced upon G alpha o* expression, particularly in the vicinity of the ryanodine receptor. We conclude that G alpha o* exerts a positive effect on Ca2+ cycling and contractile function. Alterations in protein phosphatase 1 activity rather than PKA-mediated phosphorylation might be involved in hyperphosphorylation of key Ca2+ handling proteins in hearts with constitutive G alpha o activation.
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Affiliation(s)
- Ming Zhu
- Division of Cardiology, Rhode Island Hospital and The Warren Alpert Medical School of Brown University, Providence, RI 02903, USA
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19
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Shibata H, Satoh TO, Ugawa T, Masuda N, Yanai-Inamura H, Abe A, Kondo Y, Kuramochi T, Akamatsu S, Uchida W. Characterization of the Pharmacology of YM-198313 on Volume-Regulated Anion Channels. Biol Pharm Bull 2005; 28:1187-91. [PMID: 15997095 DOI: 10.1248/bpb.28.1187] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Activation of the volume-regulated anion channels (VRAC) is considered to be involved in arrhythmia, but it has not yet been fully elucidated because of the lack of its high affinitive and selective compounds. A newly synthesized compound, YM-198313 (sodium 4-({[2-(methylthio)benzyl]amino}-5-[(1-phenylethyl)thio]isothiazol-3-olate), strongly inhibited VRAC in HeLa cells with an IC50 of 3.03+/-0.05 microM. However, YM-198313 weakly affected both the Ca2+-activated Cl- channels in HTC cells and the cAMP-activated Cl- channels in T84 cells, demonstrating that this compound is selective for VRAC among Cl- channels. At 10 microM, YM-198313 almost completely (100+/-7.8%) inhibited the VRAC current in guinea pig atrial myocytes. However, at the same concentration, YM-198313 showed little inhibitory effect on the cardiac cation currents in ventricular myocytes. We believe that YM-198313 is a potent and selective VRAC inhibitor, therefore, it should be use to clarify the role VRAC plays in arrhythmia.
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Affiliation(s)
- Hiroshi Shibata
- Institute for Drug Discovery Research, Yamanouchi Pharmaceutical Co., Ltd., Ibaraki, Japan.
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20
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Bondarenko VE, Szigeti GP, Bett GCL, Kim SJ, Rasmusson RL. Computer model of action potential of mouse ventricular myocytes. Am J Physiol Heart Circ Physiol 2004; 287:H1378-403. [PMID: 15142845 DOI: 10.1152/ajpheart.00185.2003] [Citation(s) in RCA: 187] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have developed a mathematical model of the mouse ventricular myocyte action potential (AP) from voltage-clamp data of the underlying currents and Ca2+ transients. Wherever possible, we used Markov models to represent the molecular structure and function of ion channels. The model includes detailed intracellular Ca2+ dynamics, with simulations of localized events such as sarcoplasmic Ca2+ release into a small intracellular volume bounded by the sarcolemma and sarcoplasmic reticulum. Transporter-mediated Ca2+ fluxes from the bulk cytosol are closely matched to the experimentally reported values and predict stimulation rate-dependent changes in Ca2+ transients. Our model reproduces the properties of cardiac myocytes from two different regions of the heart: the apex and the septum. The septum has a relatively prolonged AP, which reflects a relatively small contribution from the rapid transient outward K+ current in the septum. The attribution of putative molecular bases for several of the component currents enables our mouse model to be used to simulate the behavior of genetically modified transgenic mice.
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Affiliation(s)
- Vladimir E Bondarenko
- Department of Physiology and Biophysics, School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, Buffalo, New York 14214-3078, USA
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