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Williams ZJ, Payne LB, Wu X, Gourdie RG. New focus on cardiac voltage-gated sodium channel β1 and β1B: Novel targets for treating and understanding arrhythmias? Heart Rhythm 2024:S1547-5271(24)02742-5. [PMID: 38908461 DOI: 10.1016/j.hrthm.2024.06.029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Revised: 06/09/2024] [Accepted: 06/17/2024] [Indexed: 06/24/2024]
Abstract
Voltage-gated sodium channels (VGSCs) are transmembrane protein complexes that are vital to the generation and propagation of action potentials in nerve and muscle fibers. The canonical VGSC is generally conceived as a heterotrimeric complex formed by two classes of membrane-spanning subunit-an α-subunit (pore forming) and two β-subunits (non-pore forming). NaV1.5 is the main sodium channel α-subunit of mammalian ventricle, with lower amounts of other α-subunits, including NaV1.6, being present. There are four β-subunits, β1-β4, encoded by four genes, SCN1B-SCN4B, each of which are expressed in cardiac tissues. Recent studies suggest that in addition to assignments in channel gating and trafficking, products of Scn1b may have novel roles in conduction of action potential in the heart and intracellular signaling. This includes evidence that the β-subunit extracellular Amino-terminal domain facilitates adhesive interactions in intercalated discs and that its Carboxyl-terminal region is a substrate for a regulated intramembrane proteolysis (RIP) signaling pathway-with a Carboxyl-terminal peptide generated by β1 RIP trafficked to the nucleus and altering transcription of various genes, including NaV1.5. In addition to β1, the Scn1b gene encodes for an alternative splice variant, β1B, which contains an identical extracellular adhesion domain to β1, but has a unique Carboxyl-terminus. Whilst β1B is generally understood to be a secreted variant, evidence indicates that when co-expressed with NaV1.5, it is maintained at the cell membrane, suggesting potential unique roles for this understudied protein. In this review, we focus on what is known on the two β-subunit variants encoded by Scn1b in heart, with particular focus on recent findings and the questions raised by this new information. We also explore data that indicate β1 and β1B may be attractive targets for novel anti-arrhythmic therapeutics.
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Affiliation(s)
- Zachary J Williams
- Fralin Biomedical Research Institute, Virginia Polytechnic University, Roanoke, VA, United States
| | - Laura Beth Payne
- Fralin Biomedical Research Institute, Virginia Polytechnic University, Roanoke, VA, United States
| | - Xiaobo Wu
- Fralin Biomedical Research Institute, Virginia Polytechnic University, Roanoke, VA, United States
| | - Robert G Gourdie
- Fralin Biomedical Research Institute, Virginia Polytechnic University, Roanoke, VA, United States; School of Medicine, Virgina Polytechnic University, Roanoke, VA, United States; Department of Biomedical Engineering and Mechanics, Virginia Polytechnic University, Blacksburg, VA, United States.
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2
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Struckman HL, Moise N, King DR, Soltisz A, Buxton A, Dunlap I, Chen Z, Radwański PB, Weinberg SH, Veeraraghavan R. Unraveling Impacts of Chamber-Specific Differences in Intercalated Disc Ultrastructure and Molecular Organization on Cardiac Conduction. JACC Clin Electrophysiol 2023; 9:2425-2443. [PMID: 37498248 PMCID: PMC11102000 DOI: 10.1016/j.jacep.2023.05.042] [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: 04/12/2023] [Revised: 05/26/2023] [Accepted: 05/30/2023] [Indexed: 07/28/2023]
Abstract
BACKGROUND Propagation of action potentials through the heart coordinates the heartbeat. Thus, intercalated discs, specialized cell-cell contact sites that provide electrical and mechanical coupling between cardiomyocytes, are an important target for study. Impaired propagation leads to arrhythmias in many pathologies, where intercalated disc remodeling is a common finding, hence the importance and urgency of understanding propagation dependence on intercalated disc structure. Conventional modeling approaches cannot predict changes in propagation elicited by perturbations that alter intercalated disc ultrastructure or molecular organization, because of lack of quantitative structural data at subcellular through nano scales. OBJECTIVES This study sought to quantify intercalated disc structure at these spatial scales in the healthy adult mouse heart and relate them to chamber-specific properties of propagation as a precursor to understanding the effects of pathological intercalated disc remodeling. METHODS Using super-resolution light microscopy, electron microscopy, and computational image analysis, we provide here the first ever systematic, multiscale quantification of intercalated disc ultrastructure and molecular organization. RESULTS By incorporating these data into a rule-based model of cardiac tissue with realistic intercalated disc structure, and comparing model predictions of electrical propagation with experimental measures of conduction velocity, we reveal that atrial intercalated discs can support faster conduction than their ventricular counterparts, which is normally masked by interchamber differences in myocyte geometry. Further, we identify key ultrastructural and molecular organization features underpinning the ability of atrial intercalated discs to support faster conduction. CONCLUSIONS These data provide the first stepping stone to elucidating chamber-specific effects of pathological intercalated disc remodeling, as occurs in many arrhythmic diseases.
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Affiliation(s)
- Heather L Struckman
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, Columbus, Ohio, USA; The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA
| | - Nicolae Moise
- The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA
| | - D Ryan King
- The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA
| | - Andrew Soltisz
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, Columbus, Ohio, USA; The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA
| | - Andrew Buxton
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, Columbus, Ohio, USA
| | - Izabella Dunlap
- The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA
| | - Zhenhui Chen
- Krannert Cardiovascular Research Center, Department of Medicine, Indiana University, Indianapolis, Indiana, USA
| | - Przemysław B Radwański
- The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA; Division of Outcomes and Translational Sciences, College of Pharmacy, The Ohio State University, Columbus, Ohio, USA
| | - Seth H Weinberg
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, Columbus, Ohio, USA; The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA
| | - Rengasayee Veeraraghavan
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, Columbus, Ohio, USA; The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA.
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3
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Mezache L, Soltisz AM, Johnstone SR, Isakson BE, Veeraraghavan R. Vascular Endothelial Barrier Protection Prevents Atrial Fibrillation by Preserving Cardiac Nanostructure. JACC Clin Electrophysiol 2023; 9:2444-2458. [PMID: 38032579 PMCID: PMC11134328 DOI: 10.1016/j.jacep.2023.10.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 10/20/2023] [Accepted: 10/21/2023] [Indexed: 12/01/2023]
Abstract
BACKGROUND Atrial fibrillation (AF), the most common cardiac arrhythmia, is widely associated with inflammation, vascular dysfunction, and elevated levels of the vascular leak-inducing cytokine, vascular endothelial growth factor (VEGF). Mechanisms underlying AF are poorly understood and current treatments only manage this progressive disease, rather than arresting the underlying pathology. The authors previously identified edema-induced disruption of sodium channel (NaV1.5)-rich intercalated disk nanodomains as a novel mechanism for AF initiation secondary to acute inflammation. Therefore, we hypothesized that protecting the vascular barrier can prevent vascular leak-induced atrial arrhythmias. OBJECTIVES In this study the authors tested the hypothesis that protecting the vascular barrier can prevent vascular leak-induced atrial arrhythmias. They identified 2 molecular targets for vascular barrier protection, connexin43 (Cx43) hemichannels and pannexin-1 (Panx1) channels, which have been implicated in cytokine-induced vascular leak. METHODS The authors undertook in vivo electrocardiography, electron microscopy, and super-resolution light microscopy studies in mice acutely treated with a clinically relevant level of VEGF. RESULTS AF incidence was increased in untreated mice exposed to VEGF relative to vehicle control subjects. VEGF also increased the average number of AF episodes. VEGF shifted NaV1.5 signal to longer distances from Cx43 gap junctions, measured by a distance transformation-based spatial analysis of 3-dimensional confocal images of intercalated disks. Similar effects were observed with NaV1.5 localized near mechanical junctions composed of neural cadherin. Blocking connexin43 hemichannels (αCT11 peptide) or Panx1 channels (PxIL2P peptide) significantly reduced the duration of AF episodes compared with VEGF alone with no treatment. Concurrently, both peptide therapies preserved NaV1.5 distance from gap junctions to control levels and reduced mechanical junction-adjacent intermembrane distance in these hearts. Notably, similar antiarrhythmic efficacy was also achieved with clinically-relevant small-molecule inhibitors of Cx43 and Panx1. CONCLUSIONS These results highlight vascular barrier protection as an antiarrhythmic strategy following inflammation-induced vascular leak.
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Affiliation(s)
- Louisa Mezache
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, Columbus, Ohio, USA
| | - Andrew M Soltisz
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, Columbus, Ohio, USA
| | - Scott R Johnstone
- Fralin Biomedical Research Institute at VTC, Centre for Vascular and Heart Research, Virginia Tech, Roanoke, Virginia, USA; Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, USA; Virginia Tech Carilion School of Medicine, Department of Surgery, Roanoke, Virginia, USA
| | - Brant E Isakson
- Department of Molecular Physiology and Biological Physics, School of Medicine, University of Virginia, Charlottesville, Virginia, USA; Robert M. Berne Cardiovascular Research Center, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| | - Rengasayee Veeraraghavan
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, Columbus, Ohio, USA; The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA; Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, Ohio, USA.
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Adams WP, Raisch TB, Zhao Y, Davalos R, Barrett S, King DR, Bain CB, Colucci-Chang K, Blair GA, Hanlon A, Lozano A, Veeraraghavan R, Wan X, Deschenes I, Smyth JW, Hoeker GS, Gourdie RG, Poelzing S. Extracellular Perinexal Separation Is a Principal Determinant of Cardiac Conduction. Circ Res 2023; 133:658-673. [PMID: 37681314 PMCID: PMC10561697 DOI: 10.1161/circresaha.123.322567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Accepted: 08/29/2023] [Indexed: 09/09/2023]
Abstract
BACKGROUND Cardiac conduction is understood to occur through gap junctions. Recent evidence supports ephaptic coupling as another mechanism of electrical communication in the heart. Conduction via gap junctions predicts a direct relationship between conduction velocity (CV) and bulk extracellular resistance. By contrast, ephaptic theory is premised on the existence of a biphasic relationship between CV and the volume of specialized extracellular clefts within intercalated discs such as the perinexus. Our objective was to determine the relationship between ventricular CV and structural changes to micro- and nanoscale extracellular spaces. METHODS Conduction and Cx43 (connexin43) protein expression were quantified from optically mapped guinea pig whole-heart preparations perfused with the osmotic agents albumin, mannitol, dextran 70 kDa, or dextran 2 MDa. Peak sodium current was quantified in isolated guinea pig ventricular myocytes. Extracellular resistance was quantified by impedance spectroscopy. Intercellular communication was assessed in a heterologous expression system with fluorescence recovery after photobleaching. Perinexal width was quantified from transmission electron micrographs. RESULTS CV primarily in the transverse direction of propagation was significantly reduced by mannitol and increased by albumin and both dextrans. The combination of albumin and dextran 70 kDa decreased CV relative to albumin alone. Extracellular resistance was reduced by mannitol, unchanged by albumin, and increased by both dextrans. Cx43 expression and conductance and peak sodium currents were not significantly altered by the osmotic agents. In response to osmotic agents, perinexal width, in order of narrowest to widest, was albumin with dextran 70 kDa; albumin or dextran 2 MDa; dextran 70 kDa or no osmotic agent, and mannitol. When compared in the same order, CV was biphasically related to perinexal width. CONCLUSIONS Cardiac conduction does not correlate with extracellular resistance but is biphasically related to perinexal separation, providing evidence that the relationship between CV and extracellular volume is determined by ephaptic mechanisms under conditions of normal gap junctional coupling.
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Affiliation(s)
- William P. Adams
- Center for Vascular and Heart Research at Fralin Biomedical Research Institute at VTC
- Translational Biology, Medicine and Health Program at Virginia Tech
| | - Tristan B. Raisch
- Center for Vascular and Heart Research at Fralin Biomedical Research Institute at VTC
- Translational Biology, Medicine and Health Program at Virginia Tech
| | - Yajun Zhao
- School of Biomedical Engineering and Sciences, Virginia Tech
| | - Rafael Davalos
- School of Biomedical Engineering and Sciences, Virginia Tech
| | | | - D. Ryan King
- Center for Vascular and Heart Research at Fralin Biomedical Research Institute at VTC
- Translational Biology, Medicine and Health Program at Virginia Tech
| | - Chandra B. Bain
- Center for Vascular and Heart Research at Fralin Biomedical Research Institute at VTC
| | - Katrina Colucci-Chang
- Center for Vascular and Heart Research at Fralin Biomedical Research Institute at VTC
- School of Biomedical Engineering and Sciences, Virginia Tech
| | - Grace A. Blair
- Center for Vascular and Heart Research at Fralin Biomedical Research Institute at VTC
- Translational Biology, Medicine and Health Program at Virginia Tech
| | - Alexandra Hanlon
- Virginia Tech Center for Biostatistics and Health Data Science, Roanoke, Virginia
| | - Alicia Lozano
- Virginia Tech Center for Biostatistics and Health Data Science, Roanoke, Virginia
| | - Rengasayee Veeraraghavan
- Department of Biomedical Engineering, College of Engineering, The Ohio State University
- The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center
| | - Xiaoping Wan
- The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center
| | - Isabelle Deschenes
- The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center
| | - James W. Smyth
- Center for Vascular and Heart Research at Fralin Biomedical Research Institute at VTC
- Department of Biological Sciences, College of Science, Virginia Tech
- Department of Basic Science Education, Virginia Tech Carilion School of Medicine, Roanoke, Virginia
| | - Gregory S. Hoeker
- Center for Vascular and Heart Research at Fralin Biomedical Research Institute at VTC
| | - Robert G. Gourdie
- Center for Vascular and Heart Research at Fralin Biomedical Research Institute at VTC
- School of Biomedical Engineering and Sciences, Virginia Tech
- Department of Basic Science Education, Virginia Tech Carilion School of Medicine, Roanoke, Virginia
| | - Steven Poelzing
- Center for Vascular and Heart Research at Fralin Biomedical Research Institute at VTC
- Translational Biology, Medicine and Health Program at Virginia Tech
- School of Biomedical Engineering and Sciences, Virginia Tech
- Department of Basic Science Education, Virginia Tech Carilion School of Medicine, Roanoke, Virginia
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5
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Struckman HL, Moise N, King DR, Soltisz A, Buxton A, Dunlap I, Chen Z, Radwański PB, Weinberg SH, Veeraraghavan R. Unraveling Chamber-specific Differences in Intercalated Disc Ultrastructure and Molecular Organization and Their Impact on Cardiac Conduction. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.13.528369. [PMID: 36824727 PMCID: PMC9949041 DOI: 10.1101/2023.02.13.528369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
During each heartbeat, the propagation of action potentials through the heart coordinates the contraction of billions of individual cardiomyocytes and is thus, a critical life process. Unsurprisingly, intercalated discs, which are cell-cell contact sites specialized to provide electrical and mechanical coupling between adjacent cardiomyocytes, have been the focus of much investigation. Slowed or disrupted propagation leads to potentially life-threatening arrhythmias in a wide range of pathologies, where intercalated disc remodeling is a common finding. Hence, the importance and urgency of understanding intercalated disc structure and its influence on action potential propagation. Surprisingly, however, conventional modeling approaches cannot predict changes in propagation elicited by perturbations that alter intercalated disc ultrastructure or molecular organization, owing to lack of quantitative structural data at subcellular through nano scales. In order to address this critical gap in knowledge, we sought to quantify intercalated disc structure at these finer spatial scales in the healthy adult mouse heart and relate them to function in a chamber-specific manner as a precursor to understanding the impacts of pathological intercalated disc remodeling. Using super-resolution light microscopy, electron microscopy, and computational image analysis, we provide here the first ever systematic, multiscale quantification of intercalated disc ultrastructure and molecular organization. By incorporating these data into a rule-based model of cardiac tissue with realistic intercalated disc structure, and comparing model predictions of electrical propagation with experimental measures of conduction velocity, we reveal that atrial intercalated discs can support faster conduction than their ventricular counterparts, which is normally masked by inter-chamber differences in myocyte geometry. Further, we identify key ultrastructural and molecular organization features underpinning the ability of atrial intercalated discs to support faster conduction. These data provide the first stepping stone to elucidating chamber-specific impacts of pathological intercalated disc remodeling, as occurs in many arrhythmic diseases.
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Patel KHK, Hwang T, Se Liebers C, Ng FS. Epicardial adipose tissue as a mediator of cardiac arrhythmias. Am J Physiol Heart Circ Physiol 2022; 322:H129-H144. [PMID: 34890279 PMCID: PMC8742735 DOI: 10.1152/ajpheart.00565.2021] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Obesity is associated with higher risks of cardiac arrhythmias. Although this may be partly explained by concurrent cardiometabolic ill-health, growing evidence suggests that increasing adiposity independently confers risk for arrhythmias. Among fat depots, epicardial adipose tissue (EAT) exhibits a proinflammatory secretome and, given the lack of fascial separation, has been implicated as a transducer of inflammation to the underlying myocardium. The present review explores the mechanisms underpinning adverse electrophysiological remodeling as a consequence of EAT accumulation and the consequent inflammation. We first describe the physiological and pathophysiological function of EAT and its unique secretome and subsequently discuss the evidence for ionic channel and connexin expression modulation as well as fibrotic remodeling induced by cytokines and free fatty acids that are secreted by EAT. Finally, we highlight how weight reduction and regression of EAT volume may cause reverse remodeling to ameliorate arrhythmic risk.
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Affiliation(s)
| | - Taesoon Hwang
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Curtis Se Liebers
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Fu Siong Ng
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
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7
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Computational modeling of aberrant electrical activity following remuscularization with intramyocardially injected pluripotent stem cell-derived cardiomyocytes. J Mol Cell Cardiol 2022; 162:97-109. [PMID: 34487753 PMCID: PMC8766907 DOI: 10.1016/j.yjmcc.2021.08.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Revised: 08/16/2021] [Accepted: 08/31/2021] [Indexed: 01/03/2023]
Abstract
Acute engraftment arrhythmias (EAs) remain a serious complication of remuscularization therapy. Preliminary evidence suggests that a focal source underlies these EAs stemming from the automaticity of immature pluripotent stem cell-derived cardiomyocytes (PSC-CMs) in nascent myocardial grafts. How these EAs arise though during early engraftment remains unclear. In a series of in silico experiments, we probed the origin of EAs-exploring aspects of altered impulse formation and altered impulse propagation within nascent PSC-CM grafts and at the host-graft interface. To account for poor gap junctional coupling during early PSC-CM engraftment, the voltage dependence of gap junctions and the possibility of ephaptic coupling were incorporated. Inspired by cardiac development, we also studied the contributions of another feature of immature PSC-CMs, circumferential sodium channel (NaCh) distribution in PSC-CMs. Ectopic propagations emerged from nascent grafts of immature PSC-CMs at a rate of <96 bpm. Source-sink effects dictated this rate and contributed to intermittent capture between host and graft. Moreover, ectopic beats emerged from dynamically changing sites along the host-graft interface. The latter arose in part because circumferential NaCh distribution in PSC-CMs contributed to preferential conduction slowing and block of electrical impulses from host to graft myocardium. We conclude that additional mechanisms, in addition to focal ones, contribute to EAs and recognize that their relative contributions are dynamic across the engraftment process.
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8
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Wu X, Hoeker GS, Blair GA, King DR, Gourdie RG, Weinberg SH, Poelzing S. Hypernatremia and intercalated disc edema synergistically exacerbate long-QT syndrome type 3 phenotype. Am J Physiol Heart Circ Physiol 2021; 321:H1042-H1055. [PMID: 34623182 DOI: 10.1152/ajpheart.00366.2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Cardiac voltage-gated sodium channel gain-of-function prolongs repolarization in the long-QT syndrome type 3 (LQT3). Previous studies suggest that narrowing the perinexus within the intercalated disc, leading to rapid sodium depletion, attenuates LQT3-associated action potential duration (APD) prolongation. However, it remains unknown whether extracellular sodium concentration modulates APD prolongation during sodium channel gain-of-function. We hypothesized that elevated extracellular sodium concentration and widened perinexus synergistically prolong APD in LQT3. LQT3 was induced with sea anemone toxin (ATXII) in Langendorff-perfused guinea pig hearts (n = 34). Sodium concentration was increased from 145 to 160 mM. Perinexal expansion was induced with mannitol or the sodium channel β1-subunit adhesion domain antagonist (βadp1). Epicardial ventricular action potentials were optically mapped. Individual and combined effects of varying clefts and sodium concentrations were simulated in a computational model. With ATXII, both mannitol and βadp1 significantly widened the perinexus and prolonged APD, respectively. The elevated sodium concentration alone significantly prolonged APD as well. Importantly, the combination of elevated sodium concentration and perinexal widening synergistically prolonged APD. Computational modeling results were consistent with animal experiments. Concurrently elevating extracellular sodium and increasing intercalated disc edema prolongs repolarization more than the individual interventions alone in LQT3. This synergistic effect suggests an important clinical implication that hypernatremia in the presence of cardiac edema can markedly increase LQT3-associated APD prolongation. Therefore, to our knowledge, this is the first study to provide evidence of a tractable and effective strategy to mitigate LQT3 phenotype by means of managing sodium levels and preventing cardiac edema in patients.NEW & NOTEWORTHY This is the first study to demonstrate that the long-QT syndrome type 3 (LQT3) phenotype can be exacerbated or concealed by regulating extracellular sodium concentrations and/or the intercalated disc separation. The animal experiments and computational modeling in the current study reveal a critically important clinical implication: sodium dysregulation in the presence of edema within the intercalated disc can markedly increase the risk of arrhythmia in LQT3. These findings strongly suggest that maintaining extracellular sodium within normal physiological limits may be an effective and inexpensive therapeutic option for patients with congenital or acquired sodium channel gain-of-function diseases.
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Affiliation(s)
- Xiaobo Wu
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia.,Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
| | - Gregory S Hoeker
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
| | - Grace A Blair
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia.,Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
| | - D Ryan King
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia.,Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
| | - Robert G Gourdie
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
| | - Seth H Weinberg
- Department of Biomedical Engineering, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio
| | - Steven Poelzing
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia.,Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
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9
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Poelzing S, Weinberg SH, Keener JP. Initiation and entrainment of multicellular automaticity via diffusion limited extracellular domains. Biophys J 2021; 120:5279-5294. [PMID: 34757078 DOI: 10.1016/j.bpj.2021.10.034] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Revised: 09/12/2021] [Accepted: 10/26/2021] [Indexed: 01/07/2023] Open
Abstract
Electrically excitable cells often spontaneously and synchronously depolarize in vitro and in vivo preparations. It remains unclear how cells entrain and autorhythmically activate above the intrinsic mean activation frequency of isolated cells with or without pacemaking mechanisms. Recent studies suggest that cyclic ion accumulation and depletion in diffusion-limited extracellular volumes modulate electrophysiology by ephaptic mechanisms (nongap junction or synaptic coupling). This report explores how potassium accumulation and depletion in a restricted extracellular domain induces spontaneous action potentials in two different computational models of excitable cells without gap junctional coupling: Hodgkin-Huxley and Luo-Rudy. Importantly, neither model will spontaneously activate on its own without external stimuli. Simulations demonstrate that cells sharing a diffusion-limited extracellular compartment can become autorhythmic and entrained despite intercellular electrical heterogeneity. Autorhythmic frequency is modulated by the cleft volume and potassium fluxes through the cleft. Additionally, inexcitable cells can suppress or induce autorhythmic activity in an excitable cell via a shared cleft. Diffusion-limited shared clefts can also entrain repolarization. Critically, this model predicts a mechanism by which diffusion-limited shared clefts can initiate, entrain, and modulate multicellular automaticity in the absence of gap junctions.
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Affiliation(s)
- Steven Poelzing
- Fralin Biomedical Research Institute at Virginia Tech Carilion, Center for Heart and Reparative Medicine, and the Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Roanoke, Virginia.
| | - Seth H Weinberg
- Department of Biomedical Engineering, Davis Heart and Lung Research Institute, and the Wexner Medical Center, The Ohio State University, Columbus, Ohio
| | - James P Keener
- Department of Mathematics, University of Utah, Salt Lake City, Utah
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10
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Veeraraghavan R, Moise N, Weinberg SH. Sodium channels and the intercalated disk - it is all about location, location, location. J Physiol 2021; 599:4735-4736. [PMID: 34555182 DOI: 10.1113/jp282350] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
| | - Nicolae Moise
- Department of Biomedical Engineering, Ohio State University, Columbus, OH, USA
| | - Seth H Weinberg
- Department of Biomedical Engineering, Ohio State University, Columbus, OH, USA
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11
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Ivanovic E, Kucera JP. Localization of Na + channel clusters in narrowed perinexi of gap junctions enhances cardiac impulse transmission via ephaptic coupling: a model study. J Physiol 2021; 599:4779-4811. [PMID: 34533834 PMCID: PMC9293295 DOI: 10.1113/jp282105] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Accepted: 09/06/2021] [Indexed: 01/06/2023] Open
Abstract
Abstract It has been proposed that when gap junctional coupling is reduced in cardiac tissue, action potential propagation can be supported via ephaptic coupling, a mechanism mediated by negative electric potentials occurring in narrow intercellular clefts of intercalated discs (IDs). Recent studies showed that sodium (Na+) channels form clusters near gap junction plaques in nanodomains called perinexi, where the ID cleft is even narrower. To examine the electrophysiological relevance of Na+ channel clusters being located in perinexi, we developed a 3D finite element model of two longitudinally abutting cardiomyocytes, with a central Na+ channel cluster on the ID membranes. When this cluster was located in the perinexus of a closely positioned gap junction plaque, varying perinexal width greatly modulated impulse transmission from one cell to the other, with narrow perinexi potentiating ephaptic coupling. This modulation occurred via the interplay of Na+ currents, extracellular potentials in the cleft and patterns of current flow within the cleft. In contrast, when the Na+ channel cluster was located remotely from the gap junction plaque, this modulation by perinexus width largely disappeared. Interestingly, the Na+ current in the ID membrane of the pre‐junctional cell switched from inward to outward during excitation, thus contributing ions to the activating channels on the post‐junctional ID membrane. In conclusion, these results indicate that the localization of Na+ channel clusters in the perinexi of gap junction plaques is crucial for ephaptic coupling, which is furthermore greatly modulated by perinexal width. These findings are relevant for a comprehensive understanding of cardiac excitation. Key points Ephaptic coupling is a cardiac conduction mechanism involving nanoscale‐level interactions between the sodium (Na+) current and the extracellular potential in narrow intercalated disc clefts. When gap junctional coupling is reduced, ephaptic coupling acts in conjunction with the classical cardiac conduction mechanism based on gap junctional current flow. In intercalated discs, Na+ channels form clusters that are preferentially located in the periphery of gap junction plaques, in nanodomains known as perinexi, but the electrophysiological role of these perinexi has never been examined. In our new 3D finite element model of two cardiac cells abutting each other with their intercalated discs, a Na+ channel cluster located inside a narrowed perinexus facilitated impulse transmission via ephaptic coupling. Our simulations demonstrate the role of narrowed perinexi as privileged sites for ephaptic coupling in pathological situations when gap junctional coupling is decreased.
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Affiliation(s)
- Ena Ivanovic
- Department of Physiology, University of Bern, Bern, Switzerland
| | - Jan P Kucera
- Department of Physiology, University of Bern, Bern, Switzerland
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12
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Moise N, Struckman HL, Dagher C, Veeraraghavan R, Weinberg SH. Intercalated disk nanoscale structure regulates cardiac conduction. J Gen Physiol 2021; 153:212474. [PMID: 34264306 PMCID: PMC8287520 DOI: 10.1085/jgp.202112897] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 04/13/2021] [Accepted: 06/07/2021] [Indexed: 12/31/2022] Open
Abstract
The intercalated disk (ID) is a specialized subcellular region that provides electrical and mechanical connections between myocytes in the heart. The ID has a clearly defined passive role in cardiac tissue, transmitting mechanical forces and electrical currents between cells. Recent studies have shown that Na+ channels, the primary current responsible for cardiac excitation, are preferentially localized at the ID, particularly within nanodomains such as the gap junction-adjacent perinexus and mechanical junction-associated adhesion-excitability nodes, and that perturbations of ID structure alter cardiac conduction. This suggests that the ID may play an important, active role in regulating conduction. However, the structures of the ID and intercellular cleft are not well characterized and, to date, no models have incorporated the influence of ID structure on conduction in cardiac tissue. In this study, we developed an approach to generate realistic finite element model (FEM) meshes replicating nanoscale of the ID structure, based on experimental measurements from transmission electron microscopy images. We then integrated measurements of the intercellular cleft electrical conductivity, derived from the FEM meshes, into a novel cardiac tissue model formulation. FEM-based calculations predict that the distribution of cleft conductances is sensitive to regional changes in ID structure, specifically the intermembrane separation and gap junction distribution. Tissue-scale simulations predict that ID structural heterogeneity leads to significant spatial variation in electrical polarization within the intercellular cleft. Importantly, we found that this heterogeneous cleft polarization regulates conduction by desynchronizing the activation of postjunctional Na+ currents. Additionally, these heterogeneities lead to a weaker dependence of conduction velocity on gap junctional coupling, compared with prior modeling formulations that neglect or simplify ID structure. Further, we found that disruption of local ID nanodomains can either slow or enhance conduction, depending on gap junctional coupling strength. Our study therefore suggests that ID nanoscale structure can play a significant role in regulating cardiac conduction.
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Affiliation(s)
| | | | | | - Rengasayee Veeraraghavan
- The Ohio State University, Columbus, OH.,Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, OH
| | - Seth H Weinberg
- The Ohio State University, Columbus, OH.,Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, OH
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13
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Nowak MB, Poelzing S, Weinberg SH. Mechanisms underlying age-associated manifestation of cardiac sodium channel gain-of-function. J Mol Cell Cardiol 2021; 153:60-71. [PMID: 33373643 PMCID: PMC8026540 DOI: 10.1016/j.yjmcc.2020.12.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Revised: 12/04/2020] [Accepted: 12/06/2020] [Indexed: 10/22/2022]
Abstract
Cardiac action potentials are initiated by sodium ion (Na+) influx through voltage-gated Na+ channels. Na+ channel gain-of-function (GOF) can arise in inherited conditions due to mutations in the gene encoding the cardiac Na+ channel, such as Long QT syndrome type 3 (LQT3). LQT3 can be a "concealed" disease, as patients with LQT3-associated mutations can remain asymptomatic until later in life; however, arrhythmias can also arise early in life in LQT3 patients, demonstrating a complex age-associated manifestation. We and others recently demonstrated that cardiac Na+ channels preferentially localize at the intercalated disc (ID) in adult cardiac tissue, which facilitates ephaptic coupling and formation of intercellular Na+ nanodomains that regulate pro-arrhythmic early afterdepolarization (EAD) formation in tissue with Na+ channel GOF. Several properties related to ephaptic coupling vary with age, such as cell size and Na+ channel and gap junction (GJ) expression and distribution: neonatal cells have immature IDs, with Na+ channels and GJs primarily diffusively distributed, while adult myocytes have mature IDs with preferentially localized Na+ channels and GJs. Here, we perform an in silico study varying critical age-dependent parameters to investigate mechanisms underlying age-associated manifestation of Na+ channel GOF in a model of guinea pig cardiac tissue. Simulations predict that total Na+ current conductance is a critical factor in action potential duration (APD) prolongation. We find a complex cell size/ Na+ channel expression relationship: increases in cell size (without concurrent increases in Na+ channel expression) suppress EAD formation, while increases in Na+ channel expression (without concurrent increases in cell size) promotes EAD formation. Finally, simulations with neonatal and early age-associated parameters predict normal APD with minimal dependence on intercellular cleft width; however, variability in cellular properties can lead to EADs presenting in early developmental stages. In contrast, for adult-associated parameters, EAD formation is highly dependent on cleft width, consistent with a mechanism underlying the age-associated manifestation of the Na+ channel GOF.
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Affiliation(s)
- Madison B Nowak
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States of America
| | - Steven Poelzing
- Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States of America; Fralin Biomedical Research Institute at Virginia Tech Carilion, Virginia Polytechnic Institute and State University, Roanoke, VA, United States of America
| | - Seth H Weinberg
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States of America; Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, OH, United States of America.
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14
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King DR, Entz M, Blair GA, Crandell I, Hanlon AL, Lin J, Hoeker GS, Poelzing S. The conduction velocity-potassium relationship in the heart is modulated by sodium and calcium. Pflugers Arch 2021; 473:557-571. [PMID: 33660028 PMCID: PMC7940307 DOI: 10.1007/s00424-021-02537-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 01/28/2021] [Accepted: 02/04/2021] [Indexed: 01/27/2023]
Abstract
The relationship between cardiac conduction velocity (CV) and extracellular potassium (K+) is biphasic, with modest hyperkalemia increasing CV and severe hyperkalemia slowing CV. Recent studies from our group suggest that elevating extracellular sodium (Na+) and calcium (Ca2+) can enhance CV by an extracellular pathway parallel to gap junctional coupling (GJC) called ephaptic coupling that can occur in the gap junction adjacent perinexus. However, it remains unknown whether these same interventions modulate CV as a function of K+. We hypothesize that Na+, Ca2+, and GJC can attenuate conduction slowing consequent to severe hyperkalemia. Elevating Ca2+ from 1.25 to 2.00 mM significantly narrowed perinexal width measured by transmission electron microscopy. Optically mapped, Langendorff-perfused guinea pig hearts perfused with increasing K+ revealed the expected biphasic CV-K+ relationship during perfusion with different Na+ and Ca2+ concentrations. Neither elevating Na+ nor Ca2+ alone consistently modulated the positive slope of CV-K+ or conduction slowing at 10-mM K+; however, combined Na+ and Ca2+ elevation significantly mitigated conduction slowing at 10-mM K+. Pharmacologic GJC inhibition with 30-μM carbenoxolone slowed CV without changing the shape of CV-K+ curves. A computational model of CV predicted that elevating Na+ and narrowing clefts between myocytes, as occur with perinexal narrowing, reduces the positive and negative slopes of the CV-K+ relationship but do not support a primary role of GJC or sodium channel conductance. These data demonstrate that combinatorial effects of Na+ and Ca2+ differentially modulate conduction during hyperkalemia, and enhancing determinants of ephaptic coupling may attenuate conduction changes in a variety of physiologic conditions.
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Affiliation(s)
- D Ryan King
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, USA
| | - Michael Entz
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, USA
- Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
| | - Grace A Blair
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, USA
| | - Ian Crandell
- Center for Biostatistics and Health Data Science, Virginia Polytechnic Institute and State University, Roanoke, VA, USA
| | - Alexandra L Hanlon
- Center for Biostatistics and Health Data Science, Virginia Polytechnic Institute and State University, Roanoke, VA, USA
| | - Joyce Lin
- Department of Mathematics, California Polytechnic State University, San Luis Obispo, CA, USA
| | - Gregory S Hoeker
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, USA
| | - Steven Poelzing
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, USA.
- Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.
- School of Medicine, Virginia Tech Carilion, Roanoke, VA, USA.
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15
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Mezache L, Struckman HL, Greer-Short A, Baine S, Györke S, Radwański PB, Hund TJ, Veeraraghavan R. Vascular endothelial growth factor promotes atrial arrhythmias by inducing acute intercalated disk remodeling. Sci Rep 2020; 10:20463. [PMID: 33235263 PMCID: PMC7687901 DOI: 10.1038/s41598-020-77562-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 11/09/2020] [Indexed: 12/30/2022] Open
Abstract
Atrial fibrillation (AF) is the most common arrhythmia and is associated with inflammation. AF patients have elevated levels of inflammatory cytokines known to promote vascular leak, such as vascular endothelial growth factor A (VEGF). However, the contribution of vascular leak and consequent cardiac edema to the genesis of atrial arrhythmias remains unknown. Previous work suggests that interstitial edema in the heart can acutely promote ventricular arrhythmias by disrupting ventricular myocyte intercalated disk (ID) nanodomains rich in cardiac sodium channels (NaV1.5) and slowing cardiac conduction. Interestingly, similar disruption of ID nanodomains has been identified in atrial samples from AF patients. Therefore, we tested the hypothesis that VEGF-induced vascular leak can acutely increase atrial arrhythmia susceptibility by disrupting ID nanodomains and slowing atrial conduction. Treatment of murine hearts with VEGF (30–60 min, at clinically relevant levels) prolonged the electrocardiographic P wave and increased susceptibility to burst pacing-induced atrial arrhythmias. Optical voltage mapping revealed slower atrial conduction following VEGF treatment (10 ± 0.4 cm/s vs. 21 ± 1 cm/s at baseline, p < 0.05). Transmission electron microscopy revealed increased intermembrane spacing at ID sites adjacent to gap junctions (GJs; 64 ± 9 nm versus 17 ± 1 nm in controls, p < 0.05), as well as sites next to mechanical junctions (MJs; 63 ± 4 nm versus 27 ± 2 nm in controls, p < 0.05) in VEGF–treated hearts relative to controls. Importantly, super-resolution microscopy and quantitative image analysis revealed reorganization of NaV1.5 away from dense clusters localized near GJs and MJs to a more diffuse distribution throughout the ID. Taken together, these data suggest that VEGF can acutely predispose otherwise normal hearts to atrial arrhythmias by dynamically disrupting NaV1.5-rich ID nanodomains and slowing atrial conduction. These data highlight inflammation-induced vascular leak as a potential factor in the development and progression of AF.
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Affiliation(s)
- Louisa Mezache
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, 460 Medical Center Dr., Rm 415A, IBMR, Columbus, OH, 43210, USA
| | - Heather L Struckman
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, 460 Medical Center Dr., Rm 415A, IBMR, Columbus, OH, 43210, USA
| | - Amara Greer-Short
- The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, USA
| | - Stephen Baine
- The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, USA.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, USA
| | - Sándor Györke
- The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, USA.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, USA
| | - Przemysław B Radwański
- The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, USA.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, USA.,Division of Pharmacy Practice and Sciences, College of Pharmacy, The Ohio State University, Columbus, OH, USA
| | - Thomas J Hund
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, 460 Medical Center Dr., Rm 415A, IBMR, Columbus, OH, 43210, USA.,The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, USA
| | - Rengasayee Veeraraghavan
- Department of Biomedical Engineering, College of Engineering, The Ohio State University, 460 Medical Center Dr., Rm 415A, IBMR, Columbus, OH, 43210, USA. .,The Frick Center for Heart Failure and Arrhythmia, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, USA. .,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, USA.
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16
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Hoeker GS, James CC, Tegge AN, Gourdie RG, Smyth JW, Poelzing S. Attenuating loss of cardiac conduction during no-flow ischemia through changes in perfusate sodium and calcium. Am J Physiol Heart Circ Physiol 2020; 319:H396-H409. [PMID: 32678707 DOI: 10.1152/ajpheart.00112.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Myocardial ischemia leads to conduction slowing, cell-to-cell uncoupling, and arrhythmias. We previously demonstrated that varying perfusate sodium (Na+) and calcium (Ca2+) attenuates conduction slowing and arrhythmias during simulated ischemia with continuous perfusion. Cardioprotection was selectively associated with widening of the perinexus, a gap junction adjacent nanodomain important to ephaptic coupling. It is unknown whether perfusate composition affects the perinexus or ischemic conduction during nonsimulated ischemia, when coronary flow is reduced or halted. We hypothesized that altering preischemic perfusate composition could facilitate perinexal expansion and attenuate conduction slowing during global ischemia. To test this hypothesis, ex vivo guinea pig hearts (n = 49) were Langendorff perfused with 145 or 153 mM Na+ and 1.25 or 2.0 mM Ca2+ and optically mapped during 30 min of no-flow ischemia. Altering Na+ and Ca2+ did not substantially affect baseline conduction. Increasing Na+ and decreasing Ca2+ both lowered pacing thresholds, whereas increasing Ca2+ narrowed perinexal width (Wp). A least squares mean estimate revealed that reduced perfusate Na+ and Ca2+ resulted in the most severe conduction slowing during ischemia. Increasing Na+ alone modestly attenuated conduction slowing, yet significantly delayed the median time to conduction block (10 to 16 min). Increasing both Na+ and Ca2+ selectively widened Wp during ischemia (22.7 vs. 15.7 nm) and attenuated conduction slowing to the greatest extent. Neither repolarization nor levels of total or phosphorylated connexin43 correlated with conduction slowing or block. Thus, perfusate-dependent widening of the perinexus preserved ischemic conduction and may be an adaptive response to ischemic stress.NEW & NOTEWORTHY Conduction slowing during acute ischemia creates an arrhythmogenic substrate. We have shown that extracellular ionic concentrations can alter conduction by modulating ephaptic coupling. Here, we demonstrate increased extracellular sodium and calcium significantly attenuate conduction slowing during no-flow ischemia. This effect was associated with selective widening of the perinexus, an intercalated disc nanodomain and putative cardiac ephapse. These findings suggest that acute changes in ephaptic coupling may serve as an adaptive response to ischemic stress.
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Affiliation(s)
- Gregory S Hoeker
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
| | - Carissa C James
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia
| | - Allison N Tegge
- Virginia Tech Carilion School of Medicine, Roanoke, Virginia.,Department of Statistics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
| | - Robert G Gourdie
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Virginia Tech Carilion School of Medicine, Roanoke, Virginia.,Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
| | - James W Smyth
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Virginia Tech Carilion School of Medicine, Roanoke, Virginia.,Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
| | - Steven Poelzing
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia.,Virginia Tech Carilion School of Medicine, Roanoke, Virginia.,Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
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17
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Salvage SC, Huang CLH, Jackson AP. Cell-Adhesion Properties of β-Subunits in the Regulation of Cardiomyocyte Sodium Channels. Biomolecules 2020; 10:biom10070989. [PMID: 32630316 PMCID: PMC7407995 DOI: 10.3390/biom10070989] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2020] [Revised: 06/25/2020] [Accepted: 06/27/2020] [Indexed: 12/17/2022] Open
Abstract
Voltage-gated sodium (Nav) channels drive the rising phase of the action potential, essential for electrical signalling in nerves and muscles. The Nav channel α-subunit contains the ion-selective pore. In the cardiomyocyte, Nav1.5 is the main Nav channel α-subunit isoform, with a smaller expression of neuronal Nav channels. Four distinct regulatory β-subunits (β1–4) bind to the Nav channel α-subunits. Previous work has emphasised the β-subunits as direct Nav channel gating modulators. However, there is now increasing appreciation of additional roles played by these subunits. In this review, we focus on β-subunits as homophilic and heterophilic cell-adhesion molecules and the implications for cardiomyocyte function. Based on recent cryogenic electron microscopy (cryo-EM) data, we suggest that the β-subunits interact with Nav1.5 in a different way from their binding to other Nav channel isoforms. We believe this feature may facilitate trans-cell-adhesion between β1-associated Nav1.5 subunits on the intercalated disc and promote ephaptic conduction between cardiomyocytes.
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Affiliation(s)
- Samantha C. Salvage
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK;
- Correspondence: (S.C.S.); (A.P.J.); Tel.: +44-1223-765950 (S.C.S.); +44-1223-765951 (A.P.J.)
| | - Christopher L.-H. Huang
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK;
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3EG, UK
| | - Antony P. Jackson
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK;
- Correspondence: (S.C.S.); (A.P.J.); Tel.: +44-1223-765950 (S.C.S.); +44-1223-765951 (A.P.J.)
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18
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Real-Time In Vivo Imaging of Mouse Left Ventricle Reveals Fluctuating Movements of the Intercalated Discs. NANOMATERIALS 2020; 10:nano10030532. [PMID: 32188039 PMCID: PMC7153594 DOI: 10.3390/nano10030532] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Revised: 03/10/2020] [Accepted: 03/11/2020] [Indexed: 12/24/2022]
Abstract
Myocardial contraction is initiated by action potential propagation through the conduction system of the heart. It has been thought that connexin 43 in the gap junctions (GJ) within the intercalated disc (ID) provides direct electric connectivity between cardiomyocytes (electronic conduction). However, recent studies challenge this view by providing evidence that the mechanosensitive cardiac sodium channels Nav1.5 localized in perinexii at the GJ edge play an important role in spreading action potentials between neighboring cells (ephaptic conduction). In the present study, we performed real-time confocal imaging of the CellMask-stained ID in the living mouse heart in vivo. We found that the ID structure was not rigid. Instead, we observed marked flexing of the ID during propagation of contraction from cell to cell. The variation in ID length was between ~30 and ~42 μm (i.e., magnitude of change, ~30%). In contrast, tracking of α-actinin-AcGFP revealed a comparatively small change in the lateral dimension of the transitional junction near the ID (i.e., magnitude of change, ~20%). The present findings suggest that, when the heart is at work, mechanostress across the perinexii may activate Nav1.5 by promoting ephaptic conduction in coordination with electronic conduction, and, thereby, efficiently transmitting excitation-contraction coupling between cardiomyocytes.
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19
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Gourdie RG. The Cardiac Gap Junction has Discrete Functions in Electrotonic and Ephaptic Coupling. Anat Rec (Hoboken) 2018; 302:93-100. [PMID: 30565418 DOI: 10.1002/ar.24036] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Revised: 07/10/2018] [Accepted: 07/17/2018] [Indexed: 12/31/2022]
Abstract
Connexin43-formed gap junctions have long been thought to contribute to cardiac conduction in the mammalian ventricle by providing direct electrotonic connectivity between the cytoplasms of neighboring cardiomyocytes. However, accumulating data from studies of non-mammalian hearts, Connexin 43 (Cx43) knockout mice and human Cx43 mutations have raised questions as to whether gap junctions are the sole means by which electrical coupling between cardiomyocytes is accomplished. Computational and experimental work over the last decade have indicated that intercellular propagation of action potentials in the heart may involve both electrotonic and ephaptic contributions-in what has been dubbed "mixed-mode" conduction. Interestingly, the Cx43 gap junction may provide a common structural platform in mammals that facilitates the operation of these two mechanisms. In addition to gap junction channels functioning in an electrotonic role, the perinexus region at the edge of gap junctions may be provide a niche for voltage-gated sodium channels from neighboring cells to be in sufficiently close proximity to enable ephaptic transmission of action potential. A novel role has recently been identified in this potential ephaptic mechanism for inter-membrane adhesion mediated by the beta subunit (beta1/Scn1b) of the sodium channel. The new perspective of the operational redundancy that is built into cardiac electrical connectivity could provide new understanding of arrhythmia mechanisms and holds the promise for new approach to anti-arrhythmic therapy. Anat Rec, 302:93-100, 2019. © 2018 Wiley Periodicals, Inc.
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Affiliation(s)
- Robert G Gourdie
- Center for Heart and Regenerative Medicine, Virginia Tech Carilion Research Institute, Virginia Tech, Roanoke, Virginia, 24016.,Department of Emergency Medicine, Virginia Tech Carilion School of Medicine, Virginia Tech, Roanoke, Virginia, 24016.,Department of Biomedical Engineering and Mechanics, Virginia Tech, Blacksburg, Virginia, 24061
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20
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Abstract
The connexin family of channel-forming proteins is present in every tissue type in the human anatomy. Connexins are best known for forming clustered intercellular channels, structurally known as gap junctions, where they serve to exchange members of the metabolome between adjacent cells. In their single-membrane hemichannel form, connexins can act as conduits for the passage of small molecules in autocrine and paracrine signalling. Here, we review the roles of connexins in health and disease, focusing on the potential of connexins as therapeutic targets in acquired and inherited diseases as well as wound repair, while highlighting the associated clinical challenges.
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21
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Abstract
A recently-described extracellular nanodomain, termed the perinexus, has been implicated in ephaptic coupling, which is an alternative mechanism for electrical conduction between cardiomyocytes. The current method for quantifying this space by manual segmentation is slow and has low spatial resolution.We developed an algorithm that uses serial image dilations of a binary outline to count the number of pixels between two opposing 2 dimensional edges.This algorithm requires fewer man hours and has a higher spatial resolution than the manual method while preserving the reproducibility of the manual process.In fact, experienced and novice investigators were able to recapitulate the results of a previous study with this new algorithm.The algorithm is limited by the human input needed to manually outline the perinexus and computational power mainly encumbered by a pre-existing pathfinding algorithm.However, the algorithm's high-throughput capabilities, high spatial resolution and reproducibility make it a versatile and robust measurement tool for use across a variety of applications requiring the measurement of the distance between any 2-dimensional (2D) edges.
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Affiliation(s)
- Tristan Raisch
- Virginia Tech Carilion Research Institute, Virginia Tech; Translational Biology, Medicine and Health, Virginia Tech
| | - Momina Khan
- Virginia Tech Carilion Research Institute, Virginia Tech
| | - Steven Poelzing
- Virginia Tech Carilion Research Institute, Virginia Tech; Translational Biology, Medicine and Health, Virginia Tech;
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22
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The role of the gap junction perinexus in cardiac conduction: Potential as a novel anti-arrhythmic drug target. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2018; 144:41-50. [PMID: 30241906 DOI: 10.1016/j.pbiomolbio.2018.08.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Revised: 07/09/2018] [Accepted: 08/10/2018] [Indexed: 12/16/2022]
Abstract
Cardiovascular disease remains the single largest cause of natural death in the United States, with a significant cause of mortality associated with cardiac arrhythmias. Presently, options for treating and preventing myocardial electrical dysfunction, including sudden cardiac death, are limited. Recent studies have indicated that conduction of electrical activation in the heart may have an ephaptic component, wherein intercellular coupling occurs via electrochemical signaling across narrow extracellular clefts between cardiomyocytes. The perinexus is a 100-200 nm-wide stretch of closely apposed membrane directly adjacent to connexin 43 gap junctions. Electron and super-resolution microscopy studies, as well as biochemical analyses, have provided evidence that perinexal nanodomains may be candidate structures for facilitating ephaptic coupling. This work has included characterization of the perinexus as a region of close inter-membrane contact between cardiomyocytes (<30 nm) containing dense clusters of voltage-gated sodium channels. Here, we review what is known about perinexal structure and function and the potential that the perinexus may have novel and pivotal roles in disorders of cardiac conduction. Of particular interest is the prospect that cell adhesion mediated by the cardiac sodium channel β subunit (Scn1b) may be a novel anti-arrhythmic target.
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Radwański PB, Johnson CN, Györke S, Veeraraghavan R. Cardiac Arrhythmias as Manifestations of Nanopathies: An Emerging View. Front Physiol 2018; 9:1228. [PMID: 30233404 PMCID: PMC6131669 DOI: 10.3389/fphys.2018.01228] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Accepted: 08/14/2018] [Indexed: 12/21/2022] Open
Abstract
A nanodomain is a collection of proteins localized within a specialized, nanoscale structural environment, which can serve as the functional unit of macroscopic physiologic processes. We are beginning to recognize the key roles of cardiomyocyte nanodomains in essential processes of cardiac physiology such as electrical impulse propagation and excitation–contraction coupling (ECC). There is growing appreciation of nanodomain dysfunction, i.e., nanopathy, as a mechanistic driver of life-threatening arrhythmias in a variety of pathologies. Here, we offer an overview of current research on the role of nanodomains in cardiac physiology with particular emphasis on: (1) sodium channel-rich nanodomains within the intercalated disk that participate in cell-to-cell electrical coupling and (2) dyadic nanodomains located along transverse tubules that participate in ECC. The beat to beat function of cardiomyocytes involves three phases: the action potential, the calcium transient, and mechanical contraction/relaxation. In all these phases, cell-wide function results from the aggregation of the stochastic function of individual proteins. While it has long been known that proteins that exist in close proximity influence each other’s function, it is increasingly appreciated that there exist nanoscale structures that act as functional units of cardiac biophysical phenomena. Termed nanodomains, these structures are collections of proteins, localized within specialized nanoscale structural environments. The nano-environments enable the generation of localized electrical and/or chemical gradients, thereby conferring unique functional properties to these units. Thus, the function of a nanodomain is determined by its protein constituents as well as their local structural environment, adding an additional layer of complexity to cardiac biology and biophysics. However, with the emergence of experimental techniques that allow direct investigation of structure and function at the nanoscale, our understanding of cardiac physiology and pathophysiology at these scales is rapidly advancing. Here, we will discuss the structure and functions of multiple cardiomyocyte nanodomains, and novel strategies that target them for the treatment of cardiac arrhythmias.
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Affiliation(s)
- Przemysław B Radwański
- Bob and Corinne Frick Center for Heart Failure and Arrhythmia, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, United States.,Division of Pharmacy Practice and Science, College of Pharmacy, The Ohio State University, Columbus, OH, United States
| | - Christopher N Johnson
- Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Vanderbilt Center for Arrhythmia Research and Therapeutics, Nashville, TN, United States
| | - Sándor Györke
- Bob and Corinne Frick Center for Heart Failure and Arrhythmia, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, United States
| | - Rengasayee Veeraraghavan
- Bob and Corinne Frick Center for Heart Failure and Arrhythmia, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, United States.,Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States
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Veeraraghavan R, Hoeker GS, Alvarez-Laviada A, Hoagland D, Wan X, King DR, Sanchez-Alonso J, Chen C, Jourdan J, Isom LL, Deschenes I, Smyth JW, Gorelik J, Poelzing S, Gourdie RG. The adhesion function of the sodium channel beta subunit (β1) contributes to cardiac action potential propagation. eLife 2018; 7:37610. [PMID: 30106376 PMCID: PMC6122953 DOI: 10.7554/elife.37610] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Accepted: 08/06/2018] [Indexed: 12/22/2022] Open
Abstract
Computational modeling indicates that cardiac conduction may involve ephaptic coupling – intercellular communication involving electrochemical signaling across narrow extracellular clefts between cardiomyocytes. We hypothesized that β1(SCN1B) –mediated adhesion scaffolds trans-activating NaV1.5 (SCN5A) channels within narrow (<30 nm) perinexal clefts adjacent to gap junctions (GJs), facilitating ephaptic coupling. Super-resolution imaging indicated preferential β1 localization at the perinexus, where it co-locates with NaV1.5. Smart patch clamp (SPC) indicated greater sodium current density (INa) at perinexi, relative to non-junctional sites. A novel, rationally designed peptide, βadp1, potently and selectively inhibited β1-mediated adhesion, in electric cell-substrate impedance sensing studies. βadp1 significantly widened perinexi in guinea pig ventricles, and selectively reduced perinexal INa, but not whole cell INa, in myocyte monolayers. In optical mapping studies, βadp1 precipitated arrhythmogenic conduction slowing. In summary, β1-mediated adhesion at the perinexus facilitates action potential propagation between cardiomyocytes, and may represent a novel target for anti-arrhythmic therapies.
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Affiliation(s)
- Rengasayee Veeraraghavan
- Virginia Tech Carilion Research Institute, Virginia Polytechnic University, Roanoke, United States.,School of Medicine, Virginia Polytechnic University, Roanoke, United States
| | - Gregory S Hoeker
- Virginia Tech Carilion Research Institute, Virginia Polytechnic University, Roanoke, United States.,School of Medicine, Virginia Polytechnic University, Roanoke, United States
| | | | - Daniel Hoagland
- Virginia Tech Carilion Research Institute, Virginia Polytechnic University, Roanoke, United States.,School of Medicine, Virginia Polytechnic University, Roanoke, United States
| | - Xiaoping Wan
- Heart and Vascular Research Center, MetroHealth Medical Center, Department of Medicine, Case Western Reserve University, Cleveland, United States
| | - D Ryan King
- Virginia Tech Carilion Research Institute, Virginia Polytechnic University, Roanoke, United States.,School of Medicine, Virginia Polytechnic University, Roanoke, United States.,Graduate Program in Translational Biology, Medicine and Health, Virginia Tech, Virginia, United States
| | - Jose Sanchez-Alonso
- Department of Myocardial Function, Imperial College London, London, United Kingdom
| | - Chunling Chen
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, United States
| | - Jane Jourdan
- Virginia Tech Carilion Research Institute, Virginia Polytechnic University, Roanoke, United States.,School of Medicine, Virginia Polytechnic University, Roanoke, United States
| | - Lori L Isom
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, United States
| | - Isabelle Deschenes
- Heart and Vascular Research Center, MetroHealth Medical Center, Department of Medicine, Case Western Reserve University, Cleveland, United States.,Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Unites States
| | - James W Smyth
- Virginia Tech Carilion Research Institute, Virginia Polytechnic University, Roanoke, United States.,School of Medicine, Virginia Polytechnic University, Roanoke, United States.,Department of Biological Sciences, College of Science, Blacksburg, United States
| | - Julia Gorelik
- Department of Myocardial Function, Imperial College London, London, United Kingdom
| | - Steven Poelzing
- Virginia Tech Carilion Research Institute, Virginia Polytechnic University, Roanoke, United States.,School of Medicine, Virginia Polytechnic University, Roanoke, United States.,Department of Biomedical Engineering and Mechanics, Virginia Polytechnic University, Blacksburg, United States
| | - Robert G Gourdie
- Virginia Tech Carilion Research Institute, Virginia Polytechnic University, Roanoke, United States.,School of Medicine, Virginia Polytechnic University, Roanoke, United States.,Department of Biomedical Engineering and Mechanics, Virginia Polytechnic University, Blacksburg, United States
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