1
|
Sánchez de la Nava AM, Gómez-Cid L, Domínguez-Sobrino A, Fernández-Avilés F, Berenfeld O, Atienza F. Artificial intelligence analysis of the impact of fibrosis in arrhythmogenesis and drug response. Front Physiol 2022; 13:1025430. [PMID: 36311248 PMCID: PMC9596790 DOI: 10.3389/fphys.2022.1025430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Accepted: 09/28/2022] [Indexed: 01/16/2023] Open
Abstract
Background: Cardiac fibrosis has been identified as a major factor in conduction alterations leading to atrial arrhythmias and modification of drug treatment response. Objective: To perform an in silico proof-of-concept study of Artificial Intelligence (AI) ability to identify susceptibility for conduction blocks in simulations on a population of models with diffused fibrotic atrial tissue and anti-arrhythmic drugs. Methods: Activity in 2D cardiac tissue planes were simulated on a population of variable electrophysiological and anatomical profiles using the Koivumaki model for the atrial cardiomyocytes and the Maleckar model for the diffused fibroblasts (0%, 5% and 10% fibrosis area). Tissue sheets were of 2 cm side and the effect of amiodarone, dofetilide and sotalol was simulated to assess the conduction of the electrical impulse across the planes. Four different AI algorithms (Quadratic Support Vector Machine, QSVM, Cubic Support Vector Machine, CSVM, decision trees, DT, and K-Nearest Neighbors, KNN) were evaluated in predicting conduction of a stimulated electrical impulse. Results: Overall, fibrosis implementation lowered conduction velocity (CV) for the conducting profiles (0% fibrosis: 67.52 ± 7.3 cm/s; 5%: 58.81 ± 14.04 cm/s; 10%: 57.56 ± 14.78 cm/s; p < 0.001) in combination with a reduced 90% action potential duration (0% fibrosis: 187.77 ± 37.62 ms; 5%: 93.29 ± 82.69 ms; 10%: 106.37 ± 85.15 ms; p < 0.001) and peak membrane potential (0% fibrosis: 89.16 ± 16.01 mV; 5%: 70.06 ± 17.08 mV; 10%: 82.21 ± 19.90 mV; p < 0.001). When the antiarrhythmic drugs were present, a total block was observed in most of the profiles. In those profiles in which electrical conduction was preserved, a decrease in CV was observed when simulations were performed in the 0% fibrosis tissue patch (Amiodarone ΔCV: -3.59 ± 1.52 cm/s; Dofetilide ΔCV: -13.43 ± 4.07 cm/s; Sotalol ΔCV: -0.023 ± 0.24 cm/s). This effect was preserved for amiodarone in the 5% fibrosis patch (Amiodarone ΔCV: -4.96 ± 2.15 cm/s; Dofetilide ΔCV: 0.14 ± 1.87 cm/s; Sotalol ΔCV: 0.30 ± 4.69 cm/s). 10% fibrosis simulations showed that part of the profiles increased CV while others showed a decrease in this variable (Amiodarone ΔCV: 0.62 ± 9.56 cm/s; Dofetilide ΔCV: 0.05 ± 1.16 cm/s; Sotalol ΔCV: 0.22 ± 1.39 cm/s). Finally, when the AI algorithms were tested for predicting conduction on input of variables from the population of modelled, Cubic SVM showed the best performance with AUC = 0.95. Conclusion: In silico proof-of-concept study demonstrates that fibrosis can alter the expected behavior of antiarrhythmic drugs in a minority of atrial population models and AI can assist in revealing the profiles that will respond differently.
Collapse
Affiliation(s)
- Ana María Sánchez de la Nava
- Department of Cardiology, Hospital General Universitario Gregorio Marañón, Instituto de Investigación Sanitaria Gregorio Marañón (IISGM), Madrid, Spain,Centro de Investigación Biomédica en Red de Enfermedades Cardiovasculares (CIBERCV), Madrid, Spain
| | - Lidia Gómez-Cid
- Department of Cardiology, Hospital General Universitario Gregorio Marañón, Instituto de Investigación Sanitaria Gregorio Marañón (IISGM), Madrid, Spain,Centro de Investigación Biomédica en Red de Enfermedades Cardiovasculares (CIBERCV), Madrid, Spain
| | - Alonso Domínguez-Sobrino
- Department of Cardiology, Hospital General Universitario Gregorio Marañón, Instituto de Investigación Sanitaria Gregorio Marañón (IISGM), Madrid, Spain
| | - Francisco Fernández-Avilés
- Department of Cardiology, Hospital General Universitario Gregorio Marañón, Instituto de Investigación Sanitaria Gregorio Marañón (IISGM), Madrid, Spain,Centro de Investigación Biomédica en Red de Enfermedades Cardiovasculares (CIBERCV), Madrid, Spain,Universidad Complutense de Madrid, Madrid, Spain
| | - Omer Berenfeld
- Center for Arrhythmia Research, University of Michigan, Ann Arbor, MI, United States
| | - Felipe Atienza
- Department of Cardiology, Hospital General Universitario Gregorio Marañón, Instituto de Investigación Sanitaria Gregorio Marañón (IISGM), Madrid, Spain,Centro de Investigación Biomédica en Red de Enfermedades Cardiovasculares (CIBERCV), Madrid, Spain,Universidad Complutense de Madrid, Madrid, Spain,*Correspondence: Felipe Atienza,
| |
Collapse
|
2
|
Saliani A, Biswas S, Jacquemet V. Simulation of atrial fibrillation in a non-ohmic propagation model with dynamic gap junctions. CHAOS (WOODBURY, N.Y.) 2022; 32:043113. [PMID: 35489863 DOI: 10.1063/5.0082763] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Accepted: 03/24/2022] [Indexed: 06/14/2023]
Abstract
Gap junctions exhibit nonlinear electrical properties that have been hypothesized to be relevant to arrhythmogenicity in a structurally remodeled tissue. Large-scale implementation of gap junction dynamics in 3D propagation models remains challenging. We aim to quantify the impact of nonlinear diffusion during episodes of arrhythmias simulated in a left atrial model. Homogenization of conduction properties in the presence of nonlinear gap junctions was performed by generalizing a previously developed mathematical framework. A monodomain model was solved in which conductivities were time-varying and depended on transjunctional potentials. Gap junction conductances were derived from a simplified Vogel-Weingart model with first-order gating and adjustable time constant. A bilayer interconnected cable model of the left atrium with 100 μm resolution was used. The diffusion matrix was recomputed at each time step according to the state of the gap junctions. Sinus rhythm and atrial fibrillation episodes were simulated in remodeled tissue substrates. Slow conduction was induced by reduced coupling and by diffuse or stringy fibrosis. Simulations starting from the same initial conditions were repeated with linear and nonlinear gap junctions. The discrepancy in activation times between the linear and nonlinear diffusion models was quantified. The results largely validated the linear approximation for conduction velocities >20 cm/s. In very slow conduction substrates, the discrepancy accumulated over time during atrial fibrillation, eventually leading to qualitative differences in propagation patterns, while keeping the descriptive statistics, such as cycle lengths, unchanged. The discrepancy growth rate was increased by impaired conduction, fibrosis, conduction heterogeneity, lateral uncoupling, fast gap junction time constant, and steeper action potential duration restitution.
Collapse
Affiliation(s)
- Ariane Saliani
- Institute of Biomedical Engineering, Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, C.P. 6128, succ. Centre-ville, Montreal, Quebec H3C 3J7, Canada
| | - Subhamoy Biswas
- Institute of Biomedical Engineering, Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, C.P. 6128, succ. Centre-ville, Montreal, Quebec H3C 3J7, Canada
| | - Vincent Jacquemet
- Institute of Biomedical Engineering, Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, C.P. 6128, succ. Centre-ville, Montreal, Quebec H3C 3J7, Canada
| |
Collapse
|
3
|
Ahmed MA, Venugopal S, Jung R. Engaging biological oscillators through second messenger pathways permits emergence of a robust gastric slow-wave during peristalsis. PLoS Comput Biol 2021; 17:e1009644. [PMID: 34871315 PMCID: PMC8675931 DOI: 10.1371/journal.pcbi.1009644] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2021] [Revised: 12/16/2021] [Accepted: 11/15/2021] [Indexed: 11/19/2022] Open
Abstract
Peristalsis, the coordinated contraction—relaxation of the muscles of the stomach is important for normal gastric motility and is impaired in motility disorders. Coordinated electrical depolarizations that originate and propagate within a network of interconnected layers of interstitial cells of Cajal (ICC) and smooth muscle (SM) cells of the stomach wall as a slow-wave, underly peristalsis. Normally, the gastric slow-wave oscillates with a single period and uniform rostrocaudal lag, exhibiting network entrainment. Understanding of the integrative role of neurotransmission and intercellular coupling in the propagation of an entrained gastric slow-wave, important for understanding motility disorders, however, remains incomplete. Using a computational framework constituted of a novel gastric motility network (GMN) model we address the hypothesis that engaging biological oscillators (i.e., ICCs) by constitutive gap junction coupling mechanisms and enteric neural innervation activated signals can confer a robust entrained gastric slow-wave. We demonstrate that while a decreasing enteric neural innervation gradient that modulates the intracellular IP3 concentration in the ICCs can guide the aboral slow-wave propagation essential for peristalsis, engaging ICCs by recruiting the exchange of second messengers (inositol trisphosphate (IP3) and Ca2+) ensures a robust entrained longitudinal slow-wave, even in the presence of biological variability in electrical coupling strengths. Our GMN with the distinct intercellular coupling in conjunction with the intracellular feedback pathways and a rostrocaudal enteric neural innervation gradient allows gastric slow waves to oscillate with a moderate range of frequencies and to propagate with a broad range of velocities, thus preventing decoupling observed in motility disorders. Overall, the findings provide a mechanistic explanation for the emergence of decoupled slow waves associated with motility impairments of the stomach, offer directions for future experiments and theoretical work, and can potentially aid in the design of new interventional pharmacological and neuromodulation device treatments for addressing gastric motility disorders. The coordinated contraction and relaxation of the muscles of the stomach, known as peristalsis is important for normal gastric motility and primarily governed by electrical depolarizations that originate and propagate within a network of interconnected layers of interstitial cells of Cajal (ICCs) and smooth muscle cells of the stomach wall as a slow-wave. Under normal conditions, a gastric slow-wave oscillates with a single period and uniform rostrocaudal lag, exhibiting network entrainment. However, the understanding of intrinsic and extrinsic mechanisms that ensure propagation of a robust entrained slow-wave remains incomplete. Here, using a computational framework, we show that in conjunction with an enteric neural innervation gradient along the rostrocaudal ICC chain, and intercellular electrical coupling, the intercellular exchange of inositol trisphosphate between ICCs prevents decoupling by extending the longitudinal entrainment range along the stomach wall, even when variability in intercellular coupling exists. The findings from our study indicate ways that ensure the rostrocaudal spread of a robust gastric slow-wave and provide a mechanistic explanation for the emergence of decoupled slow waves associated with motility impairments of the stomach.
Collapse
Affiliation(s)
- Md Ashfaq Ahmed
- Department of Biomedical Engineering, Florida International University, Miami, Florida, United States of America
| | - Sharmila Venugopal
- Integrative Biology and Physiology, University of California Los Angeles, Los Angeles, California, United States of America
- * E-mail: (SV); (RJ)
| | - Ranu Jung
- Department of Biomedical Engineering, Florida International University, Miami, Florida, United States of America
- * E-mail: (SV); (RJ)
| |
Collapse
|
4
|
Ai X, Yan J, Pogwizd SM. Serine-threonine protein phosphatase regulation of Cx43 dephosphorylation in arrhythmogenic disorders. Cell Signal 2021; 86:110070. [PMID: 34217833 PMCID: PMC8963383 DOI: 10.1016/j.cellsig.2021.110070] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 06/11/2021] [Accepted: 06/29/2021] [Indexed: 12/11/2022]
Abstract
Regulation of cell-to-cell communication in the heart by the gap junction protein Connexin43 (Cx43) involves modulation of Cx43 phosphorylation state by protein kinases, and dephosphorylation by protein phosphatases. Dephosphorylation of Cx43 has been associated with impaired intercellular coupling and enhanced arrhythmogenesis in various pathologic states. While there has been extensive study of the protein kinases acting on Cx43, there has been limited studies of the protein phosphatases that may underlie Cx43 dephosphorylation. The focus of this review is to introduce serine-threonine protein phosphatase regulation of Cx43 phosphorylation state and cell-to-cell communication, and its impact on arrhythmogenesis in the setting of chronic heart failure and myocardial ischemia, as well as on atrial fibrillation. We also discuss the therapeutic potential of modulating protein phosphatases to treat arrhythmias in these clinical settings.
Collapse
Affiliation(s)
- Xun Ai
- Department of Physiology & Biophysics, Rush University, Chicago, IL, United States of America
| | - Jiajie Yan
- Department of Physiology & Biophysics, Rush University, Chicago, IL, United States of America
| | - Steven M Pogwizd
- Department of Medicine, University of Alabama at Birmingham, Birmingham, AL, United States of America.
| |
Collapse
|
5
|
Fu YL, Tao L, Peng FH, Zheng NZ, Lin Q, Cai SY, Wang Q. GJA1-20k attenuates Ang II-induced pathological cardiac hypertrophy by regulating gap junction formation and mitochondrial function. Acta Pharmacol Sin 2021; 42:536-549. [PMID: 32620936 PMCID: PMC8115281 DOI: 10.1038/s41401-020-0459-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Accepted: 06/07/2020] [Indexed: 02/06/2023] Open
Abstract
Cardiac hypertrophy (CH) is characterized by an increase in cardiomyocyte size, and is the most common cause of cardiac-related sudden death. A decrease in gap junction (GJ) coupling and mitochondrial dysfunction are important features of CH, but the mechanisms of decreased coupling and energy impairment are poorly understood. It has been reported that GJA1-20k has a strong tropism for mitochondria and is required for the trafficking of connexin 43 (Cx43) to cell-cell borders. In this study, we investigated the effects of GJA1-20k on Cx43 GJ coupling and mitochondrial function in the pathogenesis of CH. We performed hematoxylin-eosin (HE) and Masson staining, and observed significant CH in 18-week-old male spontaneously hypertensive rats (SHRs) compared to age-matched normotensive Wistar-Kyoto (WKY) rats. In cardiomyocytes from SHRs, the levels of Cx43 at the intercalated disc (ID) and the expression of GJA1-20k were significantly reduced, whereas JAK-STAT signaling was activated. Furthermore, the SHR rats displayed suppressed mitochondrial GJA1-20k and mitochondrial biogenesis. Administration of valsartan (10 mg· [Formula: see text] d-1, i.g., for 8 weeks) prevented all of these changes. In neonatal rat cardiomyocytes (NRCMs), overexpression of GJA1-20k attenuated Ang II-induced cardiomyocyte hypertrophy and caused elevated levels of GJ coupling at the cell-cell borders. Pretreatment of NRCMs with the Jak2 inhibitor AG490 (10 µM) blocked Ang II-induced reduction in GJA1-20k expression and Cx43 gap junction formation; knockdown of Jak2 in NRCMs significantly lessened Ang II-induced cardiomyocyte hypertrophy and normalized GJA1-20k expression and Cx43 gap junction formation. Overexpression of GJA1-20k improved mitochondrial membrane potential and respiration and lowered ROS production in Ang II-induced cardiomyocyte hypertrophy. These results demonstrate the importance of GJA1-20k in regulating gap junction formation and mitochondrial function in Ang II-induced cardiomyocyte hypertrophy, thus providing a novel therapeutic strategy for patients with cardiomyocyte hypertrophy.
Collapse
Affiliation(s)
- Yi-le Fu
- Department of Pharmacology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, 510080, China
| | - Liang Tao
- Department of Pharmacology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, 510080, China
| | - Fu-Hua Peng
- Department of Pharmacology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, 510080, China
| | - Ning-Ze Zheng
- Department of Pharmacology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, 510080, China
| | - Qing Lin
- Department of Pharmacology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, 510080, China
| | - Shao-Yi Cai
- Department of Pharmacology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, 510080, China
| | - Qin Wang
- Department of Pharmacology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, 510080, China.
| |
Collapse
|
6
|
Calcium-calmodulin gating of a pH-insensitive isoform of connexin43 gap junctions. Biochem J 2019; 476:1137-1148. [PMID: 30910801 DOI: 10.1042/bcj20180912] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Revised: 03/20/2019] [Accepted: 03/22/2019] [Indexed: 12/13/2022]
Abstract
Intracellular protons and calcium ions are two major chemical factors that regulate connexin43 (Cx43) gap junction communication and the synergism or antagonism between pH and Ca2+ has been questioned for decades. To assess the ability of Ca2+ ions to modulate Cx43 junctional conductance (g j) in the absence of pH-sensitivity, patch clamp experiments were performed on Neuroblastoma-2a (N2a) cells or neonatal mouse ventricular myocytes (NMVMs) expressing either full-length Cx43 or the Cx43-M257 (Cx43K258stop) mutant protein, a carboxyl-terminus (CT) truncated version of Cx43 lacking pH-sensitivity. The addition of 1 μM ionomycin to normal calcium saline reduced Cx43 or Cx43-M257 g j to zero within 15 min of perfusion. This response was prevented by Ca2+-free saline or addition of 100 nM calmodulin (CaM) inhibitory peptide to the internal pipette solution. Internal addition of a connexin50 cytoplasmic loop calmodulin-binding domain (CaMBD) mimetic peptide (200 nM) prevented the Ca2+/ionomycin-induced decrease in Cx43 g j, while 100 μM Gap19 peptide had minimal effect. The investigation of the transjunctional voltage (V j) gating properties of NMVM Cx43-M257 gap junctions confirmed the loss of the fast inactivation of Cx43-M257 g j, but also noted the abolishment of the previously reported facilitated recovery of g j from inactivating potentials. We conclude that the distal CT domain of Cx43 contributes to the V j-dependent fast inactivation and facilitated recovery of Cx43 gap junctions, but the Ca2+/CaM-dependent gating mechanism remains intact in its absence. Sequence-specific connexin CaMBD mimetic peptides act by binding Ca2+/CaM non-specifically and the Cx43 mimetic Gap19 peptide has negligible effect on this chemical gating mechanism.
Collapse
|
7
|
Santos-Miranda A, Noureldin M, Bai D. Effects of temperature on transjunctional voltage-dependent gating kinetics in Cx45 and Cx40 gap junction channels. J Mol Cell Cardiol 2019; 127:185-193. [PMID: 30594539 DOI: 10.1016/j.yjmcc.2018.12.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Revised: 11/29/2018] [Accepted: 12/26/2018] [Indexed: 02/01/2023]
Abstract
Gap junctions (GJs) are intercellular channels directly linking neighbouring cells and are dodecamers of connexins. In the human heart, connexin40 (Cx40), Cx43, and Cx45 are expressed in different regions of the heart forming GJs ensuring rapid propagation of action potentials in the myocardium. Two of these connexins, Cx40 and Cx45, formed functional GJs with prominent transjunctional voltage-dependent gating (Vj-gating), which can be a mechanism to down regulate coupling conductance (Gj). It is not clear the effects of temperature on Vj-gating properties. We expressed Cx40 or Cx45 in N2A cells to study the Vj-gating extent, the kinetics of deactivation, and the recovery time course from deactivation at 22 °C, 28 °C, and 32 °C. Dynamic uncoupling between cell pairs were evaluated at different temperatures, junctional delays, and/or repeating frequencies. Cx40 or Cx45 GJs showed little changes in the extent of Vj-gating, but in both cases with a faster deactivation kinetics at high temperatures. The recovery from deactivation was faster at higher temperatures for Cx45 GJs, but not for Cx40 GJs. Cx45 GJs, but not Cx40 GJs, were dynamically uncoupled when sufficient junctional delays and/or repeating frequency in all tested temperatures. Gap junction specific dynamic uncoupling could play an important role in regulating action potential propagation speed in Cx45 enriched nodal cells in the heart.
Collapse
Affiliation(s)
- Artur Santos-Miranda
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Mahmoud Noureldin
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Donglin Bai
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada.
| |
Collapse
|
8
|
White J, Wang J, Fan Y, Dube DK, Sanger JW, Sanger JM. Myofibril Assembly in Cultured Mouse Neonatal Cardiomyocytes. Anat Rec (Hoboken) 2018; 301:2067-2079. [DOI: 10.1002/ar.23961] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Revised: 06/05/2018] [Accepted: 06/12/2018] [Indexed: 01/06/2023]
Affiliation(s)
- Jennifer White
- Department of Cell and Developmental BiologySUNY Upstate Medical University Syracuse New York
| | - Jushuo Wang
- Department of Cell and Developmental BiologySUNY Upstate Medical University Syracuse New York
| | - Yingli Fan
- Department of Cell and Developmental BiologySUNY Upstate Medical University Syracuse New York
| | - Dipak K. Dube
- Department of MedicineSUNY Upstate Medical University Syracuse New York
| | - Joseph W. Sanger
- Department of Cell and Developmental BiologySUNY Upstate Medical University Syracuse New York
| | - Jean M. Sanger
- Department of Cell and Developmental BiologySUNY Upstate Medical University Syracuse New York
| |
Collapse
|
9
|
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.
Collapse
|
10
|
Veenstra RD. Establishment of the Dual Whole Cell Recording Patch Clamp Configuration for the Measurement of Gap Junction Conductance. Methods Mol Biol 2016; 1437:213-231. [PMID: 27207298 DOI: 10.1007/978-1-4939-3664-9_16] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The development of the patch clamp technique has enabled investigators to directly measure gap junction conductance between isolated pairs of small cells with resolution to the single channel level. The dual patch clamp recording technique requires specialized equipment and the acquired skill to reliably establish gigaohm seals and the whole cell recording configuration with high efficiency. This chapter describes the equipment needed and methods required to achieve accurate measurement of macroscopic and single gap junction channel conductances. Inherent limitations with the dual whole cell recording technique and methods to correct for series access resistance errors are defined as well as basic procedures to determine the essential electrical parameters necessary to evaluate the accuracy of gap junction conductance measurements using this approach.
Collapse
Affiliation(s)
- Richard D Veenstra
- Department of Pharmacology, SUNY Upstate Medical University, 3162 Weiskotten Hall, 766 Irving Ave., Syracuse, NY, 13210, USA.
- Department Cell and Developmental Biology, SUNY Upstate Medical University, 3162 Weiskotten Hall, 766 Irving Ave., Syracuse, NY, 13210, USA.
| |
Collapse
|
11
|
Computational Approaches to Understanding the Role of Fibroblast-Myocyte Interactions in Cardiac Arrhythmogenesis. BIOMED RESEARCH INTERNATIONAL 2015; 2015:465714. [PMID: 26601107 PMCID: PMC4637154 DOI: 10.1155/2015/465714] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/31/2014] [Revised: 04/10/2015] [Accepted: 04/29/2015] [Indexed: 11/18/2022]
Abstract
The adult heart is composed of a dense network of cardiomyocytes surrounded by nonmyocytes, the most
abundant of which are cardiac fibroblasts. Several cardiac diseases, such as myocardial infarction or dilated
cardiomyopathy, are associated with an increased density of fibroblasts, that is, fibrosis. Fibroblasts play a
significant role in the development of electrical and mechanical dysfunction of the heart; however the underlying
mechanisms are only partially understood. One widely studied mechanism suggests that fibroblasts produce
excess extracellular matrix, resulting in collagenous septa. These collagenous septa slow propagation, cause
zig-zag conduction paths, and decouple cardiomyocytes resulting in a substrate for arrhythmia. Another
emerging mechanism suggests that fibroblasts promote arrhythmogenesis through direct electrical interactions
with cardiomyocytes via gap junctions. Due to the challenges of investigating fibroblast-myocyte coupling in
native cardiac tissue, computational modeling and in vitro experiments have facilitated the investigation into the
mechanisms underlying fibroblast-mediated changes in cardiomyocyte action potential morphology, conduction
velocity, spontaneous excitability, and vulnerability to reentry. In this paper, we summarize the major findings of
the existing computational studies investigating the implications of fibroblast-myocyte interactions in the normal
and diseased heart. We then present investigations from our group into the potential role of voltage-dependent
gap junctions in fibroblast-myocyte interactions.
Collapse
|
12
|
Lin X, Xu Q, Veenstra RD. Functional formation of heterotypic gap junction channels by connexins-40 and -43. Channels (Austin) 2015; 8:433-43. [PMID: 25483586 DOI: 10.4161/19336950.2014.949188] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Connexin40 (Cx40) and connexin43 (Cx43) are co-expressed in the cardiovascular system, yet their ability to form functional heterotypic Cx43/Cx40 gap junctions remains controversial. We paired Cx43 or Cx40 stably-transfected N2a cells to examine the formation and biophysical properties of heterotypic Cx43/Cx40 gap junction channels. Dual whole cell patch clamp recordings demonstrated that Cx43 and Cx40 form functional heterotypic gap junctions with asymmetric transjunctional voltage (Vj) dependent gating properties. The heterotypic Cx43/Cx40 gap junctions exhibited less Vj gating when the Cx40 cell was positive and pronounced gating when negative. Endogenous N2a cell connexin expression levels were 1,000-fold lower than exogenously expressed Cx40 and Cx43 levels, measured by real-time PCR and Western blotting methods, suggestive of heterotypic gap junction formation by exogenous Cx40 and Cx43. Imposing a [KCl] gradient across the heterotypic gap junction modestly diminished the asymmetry of the macroscopic normalized junctional conductance - voltage (Gj-Vj) curve when [KCl] was reduced by 50% on the Cx43 side and greatly exacerbated the Vj gating asymmetries when lowered on the Cx40 side. Pairing wild-type (wt) Cx43 with the Cx40 E9,13K mutant protein produced a nearly symmetrical heterotypic Gj-Vj curve. These studies conclusively demonstrate the ability of Cx40 and Cx43 to form rectifying heterotypic gap junctions, owing primarily to alternate amino-terminal (NT) domain acidic and basic amino acid differences that may play a significant role in the physiology and/or pathology of the cardiovascular tissues including cardiac conduction properties and myoendothelial intercellular communication.
Collapse
Key Words
- Connexin40
- Cx37, connexin37
- Cx40, connexin40; Cx43, connexin43
- Cx45, connexin45
- E1, first extracellular loop domain
- EDTA, Ethylenediaminetetraacetic acid
- FITC, fluorescein isothiocyante
- GAPDH, glyceraldehyde-3-phosphate dehydrogenase
- Gj, normalized junctional conductance
- Gj,max, maximum normalized gj
- Gj,min, mimimum normalized gj
- I1 and I2, whole cell currents for cell 1 and cell 2
- Ij, junctional current
- Kon, inactivation on-rate
- N2a, mouse Neuro2a
- NT, N-terminal domain
- Popen, open probability
- RT-PCR, real-time PCR
- Rel1 and Rel2, whole cell patch electrode resistance values for cell 1 and cell 2
- Rin, renal insulinoma
- TBS, Tris buffered saline
- TRITC, tetramethylrhodamine isothiocyanate
- V1 and V2, command voltage clamp potentials for cell 1 and cell 2
- V1/2, half-inactivation voltage
- Vj, transjunctional voltage
- connexin43
- gap junctions
- gj, junctional conductance
- heterotypic
- ij, single gap junction channel current
- mCx30.2/hCx31.9, mouse connexin30.2/human connexin31.9
- pS, picoSiemen
- spermine
- transjunctional voltage gating
- wt, wild-type
- ΔI2, change in I2 in response to an applied Vj gradient produced by changing V1
- γj, single gap junction channel conductance
- τdecay, exponential decay time constant
Collapse
Affiliation(s)
- Xianming Lin
- a Department of Pharmacology ; SUNY Upstate Medical University ; Syracuse , NY USA
| | | | | |
Collapse
|
13
|
Gao L, Cheng C, Sparatore A, Zhang H, Wang C. Hydrogen Sulfide Inhibits Human Platelet Aggregation In Vitro in Part by Interfering Gap Junction Channels: Effects of ACS14, a Hydrogen Sulfide-releasing Aspirin. Heart Lung Circ 2015; 24:77-85. [DOI: 10.1016/j.hlc.2014.05.019] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2014] [Revised: 05/24/2014] [Accepted: 05/27/2014] [Indexed: 01/22/2023]
|
14
|
Wang J, Fan Y, Dube DK, Sanger JM, Sanger JW. Jasplakinolide reduces actin and tropomyosin dynamics during myofibrillogenesis. Cytoskeleton (Hoboken) 2014; 71:513-29. [PMID: 25145272 DOI: 10.1002/cm.21189] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2014] [Accepted: 08/12/2014] [Indexed: 12/20/2022]
Abstract
The premyofibril model proposes a three-stage process for the de novo assembly of myofibrils in cardiac and skeletal muscles: premyofibrils to nascent myofibrils to mature myofibrils. FRAP experiments and jasplakinolide, a drug that stabilizes F-actin, permitted us to determine how decreasing the dynamics of actin filaments affected the dynamics of tropomyosin, troponin-T, troponin-C, and two Z-Band proteins (alpha-actinin, FATZ) in premyofibrils versus mature myofibrils. Jasplakinolide reduced markedly the dynamics of actin in premyofibrils and in mature myofibrils in skeletal muscles. Two isoforms of tropomyosin-1 (TPM1α, TPM1κ) are more dynamic in premyofibrils than in mature myofibrils in control skeletal muscles. Jasplakinolide reduced the exchange rates of tropomyosins in premyofibrils but not in mature myofibrils. The reduced tropomyosin recoveries did not match the YFP-actin recoveries in premyofibrils in jasplakinolide. There were no significant differences in the effects of jasplakinolide on the dynamics of troponins in the thin filaments or of two Z-band proteins in premyofibrils or skeletal mature myofibrils. Cardiac control mature myofibrils lack nebulin, and small decreases in actin (∼5%) and two tropomyosin isoforms (∼10-15%) dynamics are detected in premyofibril to mature myofibril transformations compared with skeletal muscle. In contrast to skeletal muscle, jasplakinolide lowered the dynamics of actin and tropomyosin isoforms in the cardiac mature myofibrils. These results suggest that the dynamics of tropomyosins in control muscle cells are related to actin exchange. These results also suggest a stabilizing role for nebulin, an actin and tropomyosin-binding protein, present in mature myofibrils but not in premyofibrils of skeletal muscles.
Collapse
Affiliation(s)
- Jushuo Wang
- Department of Cell and Developmental Biology, SUNY Upstate Medical University, Syracuse, New York
| | | | | | | | | |
Collapse
|
15
|
Ueda N, Yamamoto M, Honjo H, Kodama I, Kamiya K. The role of gap junctions in stretch-induced atrial fibrillation. Cardiovasc Res 2014; 104:364-70. [PMID: 25183791 PMCID: PMC4217686 DOI: 10.1093/cvr/cvu202] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
Aims The aim of this study was to investigate the role of gap junctions in atrial fibrillation (AF) by analysing the effects of a gap junction enhancer and blocker on AF vulnerability and electrophysiological properties of isolated hearts. Methods and results The acute atrial stretch model of AF in the isolated rabbit heart was used. Sustained AF (SAF) was induced by a burst of high-frequency stimulation of the Bachmann's bundle. The effective refractory period (ERP) was measured, and the total conduction time (TCT) and the pattern of conduction of the anterior surface of the left atrium were monitored by using an optical mapping system. The effect of enhancing gap junction function by 100–1000 nM rotigaptide (ZP123) and block by 30 μM carbenoxolone on these parameters was measured. SAF inducibility was increased with an elevation of intra-atrial pressure. Enhanced gap junction conductance induced by treatment with 100–1000 nM rotigaptide reduced SAF inducibility, and the gap junction blocker carbenoxolone increased SAF inducibility. In the absence of gap junction enhancer or blocker, normal conduction was observed at 0 cmH2O. When intra-atrial pressure was raised to 12 cmH2O, the conduction pattern was changed to a heterogeneous zig-zag pattern and TCT was prolonged. Conduction pattern was not affected by either agent. Rotigaptide shortened TCT, whereas carbenoxolone prolonged TCT. ERP was significantly shortened with an increase in intra-atrial pressure, but ERP was unaffected by either agent. Conclusion Gap junction modulators changed AF inducibility through their effects on atrial conduction, not by altering ERP.
Collapse
Affiliation(s)
- Norihiro Ueda
- Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
| | - Mitsuru Yamamoto
- Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
| | - Haruo Honjo
- Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
| | | | - Kaichiro Kamiya
- Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
| |
Collapse
|
16
|
Liu Y, Li H, Xia W, Yu S, Huang C, Huang H. Electrophysiological effect of rotigaptide in rabbits with heart failure. Arch Med Sci 2014; 10:374-80. [PMID: 24904675 PMCID: PMC4042033 DOI: 10.5114/aoms.2012.31385] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Revised: 01/31/2012] [Accepted: 03/11/2012] [Indexed: 11/18/2022] Open
Abstract
INTRODUCTION Rotigaptide is a new anti-arrhythmic peptide, which has recently been found to increase junctional conductance and prevent ischemia-induced ventricular tachycardia. In this study, we attempted to investigate the effects and mechanisms of rotigaptide on the vulnerability to ventricular arrhythmias in rabbits with heart failure (HF). MATERIAL AND METHODS Chronic volume-pressure overload was used to induce HF. After rotigaptide infusion, an electrophysiological study was performed to record monophasic action potential (MAP), determine the effective refractory period (ERP) and ventricular fibrillation threshold (VFT), and assess the susceptibility to ventricular arrhythmia. Finally, real-time PCR was used to detect the changes of connexin 43 (Cx43) mRNA expression. RESULTS HF rabbits exhibited significant down-regulation of Cx43 mRNA, increase of effective refractory period (ERP) and decrease of VFT (p < 0.05, respectively). These changes resulted in an increase of vulnerability to ventricular tachyarrhythmias (VT/VF). Rotigaptide administration shortened ERP (113.3 ±8.6 ms vs. 131.7 ±12.5 ms, p < 0.05), restored VFT (15.0 ±2.0 V vs. 6.3 ±1.4 V, p < 0.05), and decreased the vulnerability to VT/VF. However, short-term rotigaptide treatment had no significant effect on MAP duration (MAP duration at 90% repolarization: 169.3 ±6.0 ms vs. 172.7 ±6.2 ms, p > 0.05) or connexin 43 mRNA expression (p > 0.05). CONCLUSIONS Rotigaptide decreases the ERP, elevates VFT, and reduces the vulnerability to ventricular arrhythmias without changing Cx43 expression in rabbits with HF. It may be a promising antiarrhythmic drug for preventing ventricular arrhythmia in HF.
Collapse
Affiliation(s)
- Yu Liu
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Haitao Li
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Wenfang Xia
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Shengbo Yu
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Congxin Huang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - He Huang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| |
Collapse
|
17
|
Nielsen MS, Axelsen LN, Sorgen PL, Verma V, Delmar M, Holstein-Rathlou NH. Gap junctions. Compr Physiol 2013; 2:1981-2035. [PMID: 23723031 DOI: 10.1002/cphy.c110051] [Citation(s) in RCA: 298] [Impact Index Per Article: 27.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Gap junctions are essential to the function of multicellular animals, which require a high degree of coordination between cells. In vertebrates, gap junctions comprise connexins and currently 21 connexins are known in humans. The functions of gap junctions are highly diverse and include exchange of metabolites and electrical signals between cells, as well as functions, which are apparently unrelated to intercellular communication. Given the diversity of gap junction physiology, regulation of gap junction activity is complex. The structure of the various connexins is known to some extent; and structural rearrangements and intramolecular interactions are important for regulation of channel function. Intercellular coupling is further regulated by the number and activity of channels present in gap junctional plaques. The number of connexins in cell-cell channels is regulated by controlling transcription, translation, trafficking, and degradation; and all of these processes are under strict control. Once in the membrane, channel activity is determined by the conductive properties of the connexin involved, which can be regulated by voltage and chemical gating, as well as a large number of posttranslational modifications. The aim of the present article is to review our current knowledge on the structure, regulation, function, and pharmacology of gap junctions. This will be supported by examples of how different connexins and their regulation act in concert to achieve appropriate physiological control, and how disturbances of connexin function can lead to disease.
Collapse
Affiliation(s)
- Morten Schak Nielsen
- Department of Biomedical Sciences and The Danish National Research Foundation Centre for Cardiac Arrhythmia, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
| | | | | | | | | | | |
Collapse
|
18
|
Xu Q, Lin X, Andrews L, Patel D, Lampe PD, Veenstra RD. Histone deacetylase inhibition reduces cardiac connexin43 expression and gap junction communication. Front Pharmacol 2013; 4:44. [PMID: 23596417 PMCID: PMC3625725 DOI: 10.3389/fphar.2013.00044] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Accepted: 03/27/2013] [Indexed: 01/02/2023] Open
Abstract
Histone deacetylase inhibitors (HDACIs) are being investigated as novel therapies for cancer, inflammation, neurodegeneration, and heart failure. The effects of HDACIs on the functional expression of cardiac gap junctions (GJs) are essentially unknown. The purpose of this study was to determine the effects of trichostatin A (TSA) and vorinostat (VOR) on functional GJ expression in ventricular cardiomyocytes. The effects of HDAC inhibition on connexin43 (Cx43) expression and functional GJ assembly were examined in primary cultured neonatal mouse ventricular myocytes. TSA and VOR reduced Cx43 mRNA, protein expression, and immunolocalized Cx43 GJ plaque area within ventricular myocyte monolayer cultures in a dose-dependent manner. Chromatin immunoprecipitation experiments revealed altered protein interactions with the Cx43 promoter. VOR also altered the phosphorylation state of several key regulatory Cx43 phospho-serine sites. Patch clamp analysis revealed reduced electrical coupling between isolated ventricular myocyte pairs, altered transjunctional voltage-dependent inactivation kinetics, and steady state junctional conductance inactivation and recovery relationships. Single GJ channel conductance was reduced to 54 pS only by maximum inhibitory doses of TSA (≥ 100 nM). These two hydroxamate pan-HDACIs exert multiple levels of regulation on ventricular GJ communication by altering Cx43 expression, GJ area, post-translational modifications (e.g., phosphorylation, acetylation), gating, and channel conductance. Although a 50% downregulation of Cx43 GJ communication alone may not be sufficient to slow ventricular conduction or induce arrhythmias, the development of class-selective HDACIs may help avoid the potential negative cardiovascular effects of pan-HDACI.
Collapse
Affiliation(s)
- Qin Xu
- Department of Pharmacology, State University of New York Upstate Medical University Syracuse, NY, USA
| | | | | | | | | | | |
Collapse
|
19
|
Wang J, Dube DK, White J, Fan Y, Sanger JM, Sanger JW. Clock is not a component of Z-bands. Cytoskeleton (Hoboken) 2012; 69:1021-31. [PMID: 22907924 DOI: 10.1002/cm.21058] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Accepted: 07/23/2012] [Indexed: 01/16/2023]
Abstract
The process of Z-band assembly begins with the formation of small Z-bodies composed of a complex of proteins rich in alpha-actinin. As additional proteins are added to nascent myofibrils, Z-bodies are transformed into continuous bands that form coherent discs of interacting proteins at the boundaries of sarcomeres. The steps controlling the transition of Z-bodies to Z-bands are not known. The report that a circadian protein, Clock, was localized in the Z-bands of neonatal rat cardiomyocytes raised the question whether this transcription factor could be involved in Z-band assembly. We found that the anti-Clock antibody used in the reported study also stained the Z-bands and Z-bodies of mouse and avian cardiac and skeletal muscle cells. YFP constructs of Clock that were assembled, however, did not localize to the Z-bands of muscle cells. Controls of Clock's activity showed that cotransfection of muscle cells with pYFP-Clock and pCeFP-BMAL1 led to the expected nuclear localization of YFP-Clock with its binding partner CeFP-BMAL1. Neither CeFP-BMAL1 nor antibodies directed against BMAL1 localized to Z-bands. A bimolecular fluorescence complementation assay (VC-BMAL1 and VN-Clock) confirmed the absence of Clock and BMAL1 from Z-bands, and their nuclear colocalization. A second anti-Clock antibody stained nuclei, but not Z-bands, of cells cotransfected with Clock and BMAL1 plasmids. Western blots of reactions of muscle extracts and purified alpha-actinins with the two anti-Clock antibodies showed that the original antibody cross-reacted with alpha-actinin and the second did not. These results cannot confirm Clock as an active component of Z-bands. © 2012 Wiley Periodicals, Inc.
Collapse
Affiliation(s)
- Jushuo Wang
- Department of Cell and Developmental Biology, SUNY Upstate Medical University, Syracuse, NY 13210, USA
| | | | | | | | | | | |
Collapse
|
20
|
Olesen NE, Hofgaard JP, Holstein-Rathlou NH, Nielsen MS, Jacobsen JCB. Estimation of the effective intercellular diffusion coefficient in cell monolayers coupled by gap junctions. Eur J Pharm Sci 2012; 46:222-32. [DOI: 10.1016/j.ejps.2011.08.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Revised: 06/19/2011] [Accepted: 08/09/2011] [Indexed: 02/06/2023]
|
21
|
Xu Q, Kopp RF, Chen Y, Yang JJ, Roe MW, Veenstra RD. Gating of connexin 43 gap junctions by a cytoplasmic loop calmodulin binding domain. Am J Physiol Cell Physiol 2012; 302:C1548-56. [PMID: 22422398 PMCID: PMC3361999 DOI: 10.1152/ajpcell.00319.2011] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Accepted: 03/13/2012] [Indexed: 11/22/2022]
Abstract
Calmodulin (CaM) binding sites were recently identified on the cytoplasmic loop (CL) of at least three α-subfamily connexins (Cx43, Cx44, Cx50), while Cx40 does not have this putative CaM binding domain. The purpose of this study was to examine the functional relevance of the putative Cx43 CaM binding site on the Ca(2+)-dependent regulation of gap junction proteins formed by Cx43 and Cx40. Dual whole cell patch-clamp experiments were performed on stable murine Neuro-2a cells expressing Cx43 or Cx40. Addition of ionomycin to increase external Ca(2+) influx reduced Cx43 gap junction conductance (G(j)) by 95%, while increasing cytosolic Ca(2+) concentration threefold. By contrast, Cx40 G(j) declined by <20%. The Ca(2+)-induced decline in Cx43 G(j) was prevented by pretreatment with calmidazolium or reversed by the addition of 10 mM EGTA to Ca(2+)-free extracellular solution, if Ca(2+) chelation was commenced before complete uncoupling, after which g(j) was only 60% recoverable. The Cx43 CL(136-158) mimetic peptide, but not the scrambled control peptide, or Ca(2+)/CaM-dependent kinase II 290-309 inhibitory peptide also prevented the Ca(2+)/CaM-dependent decline of Cx43 G(j). Cx43 gap junction channel open probability decreased to zero without reductions in the current amplitudes during external Ca(2+)/ionomycin perfusion. We conclude that Cx43 gap junctions are gated closed by a Ca(2+)/CaM-dependent mechanism involving the carboxyl-terminal quarter of the connexin CL domain. This study provides the first evidence of intrinsic differences in the Ca(2+) regulatory properties of Cx43 and Cx40.
Collapse
Affiliation(s)
- Qin Xu
- Department of Pharmacology, SUNY Upstate Medical University, 750 East Adams St., Syracuse, NY 13210, USA
| | | | | | | | | | | |
Collapse
|
22
|
Note on a possible proarrhythmic property of antiarrhythmic drugs aimed at improving gap-junction coupling. Biophys J 2012; 102:231-7. [PMID: 22339859 DOI: 10.1016/j.bpj.2011.11.4015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2011] [Revised: 11/18/2011] [Accepted: 11/22/2011] [Indexed: 01/02/2023] Open
Abstract
Reduced conduction velocity (CV) in the myocardium is well known to increase the probability of arrhythmia and can be caused by structural changes, reduced excitability of individual myocytes, or decreased electrical coupling in the tissue. Recently, investigators have developed antiarrhythmic drugs that target the connections between individual myocytes with the goal of restoring tissue CV, specifically through increasing gap-junction coupling. In a simple but qualitatively relevant mathematical model, we show here that the introduction of a drug that improves intercellular conductance will indeed increase the CV. However, conditions that would require such a drug, such as fibrotic remodeling, may also increase the load of fibroblasts. Fibroblasts may couple to myocytes in much the same way as myocytes couple to each other, and therefore the use of such an agent may also improve coupling between myocytes and fibroblasts. We present numerical examples illustrating that when the load of coupled fibroblasts on myocytes is low or nonexistent, the drug works as expected, i.e., the drug increases CV. On the other hand, when the fibroblast load is high, changes in CV are nonmonotonic, i.e., the CV first increases and then decreases with an increase in dosage. The existence of coupled fibroblasts may therefore impair the effect of the drug, and under unfortunate conditions may be proarrhythmic.
Collapse
|
23
|
Macia E, Dolmatova E, Cabo C, Sosinsky AZ, Dun W, Coromilas J, Ciaccio EJ, Boyden PA, Wit AL, Duffy HS. Characterization of gap junction remodeling in epicardial border zone of healing canine infarcts and electrophysiological effects of partial reversal by rotigaptide. Circ Arrhythm Electrophysiol 2011; 4:344-51. [PMID: 21493965 DOI: 10.1161/circep.110.959312] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
BACKGROUND The border zone of healing myocardial infarcts is an arrhythmogenic substrate, partly the result of structural and functional remodeling of the ventricular gap junction protein, Connexin43 (Cx43). Cx43 in arrhythmogenic substrates is a potential target for antiarrhythmic therapy. METHODS AND RESULTS We characterized Cx43 remodeling in the epicardial border zone (EBZ) of healing canine infarcts 5 days after coronary occlusion and examined whether the gap junction-specific agent rotigaptide could reverse it. Cx43 remodeling in the EBZ was characterized by a decrease in Cx43 protein, lateralization, and increased Cx43 phosphorylation at serine (S) 368. Rotigaptide partially reversed the loss of Cx43 but did not affect the increase in S368 phosphorylation, nor did it reverse Cx43 lateralization. Rotigaptide did not prevent conduction slowing in the EBZ, nor did it decrease the induction of sustained ventricular tachycardia by programmed stimulation, although it did decrease the EBZ effective refractory period. CONCLUSIONS We conclude that partial reversal of Cx43 remodeling in healing infarct border zone may not be sufficient to restore normal conduction or prevent arrhythmias.
Collapse
Affiliation(s)
- Ester Macia
- Department of Pharmacology, Center for Molecular Therapeutics, Columbia University, New York, NY, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
24
|
Govindan M, Savelieva I, Catanchin A, Camm AJ. Atrial fibrillation-the final frontier. J Cardiovasc Pharmacol Ther 2010; 15:36S-50S. [PMID: 20940451 DOI: 10.1177/1074248410371947] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and represents a significant health care issue. The diagnosis and management of AF uses a significant proportion of the health care budget and is responsible for substantial morbidity and mortality. Restoration and maintenance of sinus rhythm is still an important treatment option for symptomatic AF. Anti-arrhythmic drugs (AADs) have had inconsistent results for the prevention of recurrent AF and have been hampered by significant adverse effects. Catheter ablation has rapidly evolved and is fast becoming an alternative for AF prevention. Although multiple treatment options exist, no single modality is effective for all patients. This review outlines best current practice for AF prevention and future perspectives, focusing on new and promising developments in antiarrhythmic drug therapy, strategies for ablation therapy, and forms of hybrid therapy that may offer improved outcomes in selected patients.
Collapse
Affiliation(s)
- Malini Govindan
- Division of Cardiac & Vascular Sciences, St George's University of London, London, UK
| | | | | | | |
Collapse
|
25
|
Kim JM, Bursac N, Henriquez CS. A computer model of engineered cardiac monolayers. Biophys J 2010; 98:1762-71. [PMID: 20441739 DOI: 10.1016/j.bpj.2010.01.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2009] [Revised: 12/17/2009] [Accepted: 01/05/2010] [Indexed: 11/24/2022] Open
Abstract
Engineered monolayers created using microabrasion and micropatterning methods have provided a simplified in vitro system to study the effects of anisotropy and fiber direction on electrical propagation. Interpreting the behavior in these culture systems has often been performed using classical computer models with continuous properties. However, such models do not account for the effects of random cell shapes, cell orientations, and cleft spaces inherent in these monolayers on the resulting wavefront conduction. This work presents a novel methodology for modeling a monolayer of cardiac tissue in which the factors governing cell shape, cell-to-cell coupling, and degree of cleft space are not constant but rather are treated as spatially random with assigned distributions. This modeling approach makes it possible to simulate wavefront propagation in a manner analogous to performing experiments on engineered monolayer tissues. Simulated results are compared to previously published measured data from monolayers used to investigate the role of cellular architecture on conduction velocities and anisotropy ratios. We also present an estimate for obtaining the electrical properties from these networks and demonstrate how variations in the discrete cellular architecture affect the macroscopic conductivities. The simulations support the common assumption that under normal ranges of coupling strength, tissues with relatively uniform distributions of cell shapes and connectivity can be represented using continuous models with conductivities derived from random discrete cellular architecture using either global or local estimates. The results also reveal that in the presence of abrupt changes in cell orientation, local estimates of tissue properties predict smoother changes in conductivity that may not adequately predict the discrete nature of propagation at the transition sites.
Collapse
Affiliation(s)
- Jong M Kim
- Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA.
| | | | | |
Collapse
|
26
|
Dhein S, Hagen A, Jozwiak J, Dietze A, Garbade J, Barten M, Kostelka M, Mohr FW. Improving cardiac gap junction communication as a new antiarrhythmic mechanism: the action of antiarrhythmic peptides. Naunyn Schmiedebergs Arch Pharmacol 2009; 381:221-34. [PMID: 19943035 DOI: 10.1007/s00210-009-0473-1] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2009] [Accepted: 11/08/2009] [Indexed: 12/22/2022]
Abstract
Co-ordinated electrical activation of the heart is maintained by intercellular coupling of cardiomyocytes via gap junctional channels located in the intercalated disks. These channels consist of two hexameric hemichannels, docked to each other, provided by either of the adjacent cells. Thus, a complete gap junction channel is made from 12 protein subunits, the connexins. While 21 isoforms of connexins are presently known, cardiomyocytes typically are coupled by Cx43 (most abundant), Cx40 or Cx45. Some years ago, antiarrhythmic peptides were discovered and synthesised, which were shown to increase macroscopic gap junction conductance (electrical coupling) and enhance dye transfer (metabolic coupling). The lead substance of these peptides is AAP10 (H-Gly-Ala-Gly-Hyp-Pro-Tyr-CONH(2)), a peptide with a horseshoe-like spatial structure as became evident from two-dimensional nuclear magnetic resonance studies. A stable D: -amino-acid derivative of AAP10, rotigaptide, as well as a non-peptide analogue, gap-134, has been developed in recent years. Antiarrhythmic peptides act on Cx43 and Cx45 gap junctions but not on Cx40 channels. AAP10 has been shown to enhance intercellular communication in rat, rabbit and human cardiomyocytes. Antiarrhythmic peptides are effective against ventricular tachyarrhythmias, such as late ischaemic (type IB) ventricular fibrillation, CaCl(2) or aconitine-induced arrhythmia. Interestingly, the effect of antiarrhythmic peptides is higher in partially uncoupled cells and was shown to be related to maintained Cx43 phosphorylation, while arrhythmogenic conditions like ischaemia result in Cx43 dephosphorylation and intercellular decoupling. It is still a matter of debate whether these drugs also act against atrial fibrillation. The present review outlines the development of this group of peptides and derivatives, their mode of action and molecular mechanisms, and discusses their possible therapeutic potential.
Collapse
Affiliation(s)
- Stefan Dhein
- Clinic for Cardiac Surgery, University of Leipzig, Struempellstr. 39, 04289, Leipzig, Germany.
| | | | | | | | | | | | | | | |
Collapse
|
27
|
Maass K, Chase SE, Lin X, Delmar M. Cx43 CT domain influences infarct size and susceptibility to ventricular tachyarrhythmias in acute myocardial infarction. Cardiovasc Res 2009; 84:361-7. [PMID: 19620131 DOI: 10.1093/cvr/cvp250] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AIMS Hearts of mice expressing K258stop in place of connexin43 (Cx43) protein were subjected to acute myocardial infarction in order to assess the importance of Cx43 regulation on infarct size and arrhythmia susceptibility. This mutation K258stop prevents chemical regulation of Cx43 channels, including by low intracellular pH. METHODS AND RESULTS Langendorff-perfused hearts of mice harbouring one Cx43 knockout (KO) allele and one K258stop or Cx43 allele (K258stop/KO; Cx43/KO as control) were subjected to 1 h of ischaemia and 4 h of reperfusion by reversibly occluding the left anterior descending (LAD) coronary artery. Inducibility of ventricular tachyarrhythmias (VTs) was tested by applying an endocardial burst-pacing protocol during LAD occlusion. Separately, time course and the extent of acidification-induced closure of gap junction channels were tested by dual-voltage clamp. Infarct volume (as per cent of area at risk) was significantly larger in K258stop/KO hearts compared with Cx43/KO controls (42.2 +/- 3 vs. 30.4 +/- 1.7%, P = 0.004, n = 8 each). During LAD occlusion, K258stop/KO hearts had a higher incidence of pacing-induced VT and a higher frequency of occurrence of spontaneous premature ventricular beats. The occurrence of ventricular arrhythmias was also significantly larger in the K258stop/KO hearts during reperfusion. In separate experiments, we demonstrated reduced sensitivity to acidification-induced uncoupling in cell pairs obtained from K258stop/KO hearts. CONCLUSION Loss of the regulatory domain of Cx43 leads to an increase in infarct size and increased susceptibility to arrhythmias following acute coronary occlusion.
Collapse
Affiliation(s)
- Karen Maass
- SUNY Upstate Medical University, Syracuse, NY, USA
| | | | | | | |
Collapse
|
28
|
Hagen A, Dietze A, Dhein S. Human cardiac gap-junction coupling: effects of antiarrhythmic peptide AAP10. Cardiovasc Res 2009; 83:405-15. [PMID: 19176598 DOI: 10.1093/cvr/cvp028] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
AIMS Ventricular arrhythmia is one of the most important causes of death in industrialized countries and often accompanies myocardial infarction and heart failure. In recent years modification of gap-junctional coupling has been proposed as a new antiarrhythmic principle. We wanted to examine whether the gap junction modulator (antiarrhythmic peptide) AAP10 exerts effects on human cardiac gap junctions, whether the effect might be enhanced in uncoupled cells, whether it affects electrical and metabolic coupling, and which of the cardiac connexin isoforms (Cx40, Cx43, Cx45) may be affected. METHODS AND RESULTS We determined the influence of 50 nM AAP10 (H(2)N-Gly-Ala-Gly-4Hyp-Pro-Tyr-CONH(2)) on macroscopic gap junction conductance by dual whole-cell voltage clamping in human and rat cardiomyocytes. Cells were partially uncoupled by CO(2)-mediated acidosis (pH 6.3) or kept at 'normal' conditions (pH 7.4, T 36 degrees C). Furthermore, we investigated effects of AAP10 in HeLa cells stably transfected with connexin 40, 43, or 45 and on metabolic coupling determined by dye transfer (Lucifer yellow). AAP10 (50 nM)-enhanced gap-junctional intercellular coupling in human and rat cardiomyocytes, completely prevented CO(2)-acidosis-induced uncoupling and improved metabolic coupling. The coupling effect of AAP10 was significantly enhanced in previously uncoupled cells. Regarding the connexin isoforms, AAP10-enhanced electrical and metabolic coupling in HeLa cells expressing Cx43 or Cx45, but not in HeLa cells expressing Cx40. CONCLUSION We conclude that the antiarrhythmic peptide AAP10, which improves gap-junctional intercellular coupling and prevents uncoupling by acidification in human cardiomyocytes, might be useful for antiarrhythmic strategies regarding arrhythmias caused by uncoupling of Cx43 and Cx45, but not Cx40.
Collapse
Affiliation(s)
- Anja Hagen
- Clinic for Cardiac Surgery, University of Leipzig, Heart Centre, Strümpellstr. 39, 04289 Leipzig, Germany.
| | | | | |
Collapse
|
29
|
Lin X, Gemel J, Glass A, Zemlin CW, Beyer EC, Veenstra RD. Connexin40 and connexin43 determine gating properties of atrial gap junction channels. J Mol Cell Cardiol 2009; 48:238-45. [PMID: 19486903 DOI: 10.1016/j.yjmcc.2009.05.014] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/26/2009] [Revised: 04/22/2009] [Accepted: 05/22/2009] [Indexed: 11/28/2022]
Abstract
While ventricular gap junctions contain only Cx43, atrial gap junctions contain both Cx40 and Cx43; yet the functional consequences of this co-expression remain poorly understood. We quantitated the expression of Cx40 and Cx43 and their contributions to atrial gap junctional conductance (g(j)). Neonatal murine atrial myocytes showed similar abundances of Cx40 and Cx43 proteins, while ventricular myocytes contained at least 20 times more Cx43 than Cx40. Since Cx40 gap junction channels are blocked by 2 mM spermine while Cx43 channels are unaffected, we used spermine block as a functional dual whole cell patch clamp assay to determine Cx40 contributions to cardiac g(j). Slightly more than half of atrial g(j) and <or=20% of ventricular g(j) were inhibited. In myocytes from Cx40 null mice, the inhibition of ventricular g(j) was completely abolished, and the block of atrial g(j) was reduced to <20%. Compared to ventricular gap junctions, the transjunctional voltage (V(j))-dependent inactivation of atrial g(j) was reduced and kinetically slowed, while the V(j)-dependence of fast and slow inactivation was unchanged. We conclude that Cx40 and Cx43 are equally abundant in atrium and make similar contributions to atrial g(j). Co-expression of Cx40 accounts for most, but not all, of the differences in the V(j)-dependent gating properties between atrium and ventricle that may play a role in the genesis of slow myocardial conduction and arrhythmias.
Collapse
Affiliation(s)
- Xianming Lin
- Department of Pharmacology, SUNY Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA
| | | | | | | | | | | |
Collapse
|