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Tarifa C, Vallmitjana A, Jiménez-Sábado V, Marchena M, Llach A, Herraiz-Martínez A, Godoy-Marín H, Nolla-Colomer C, Ginel A, Viñolas X, Montiel J, Ciruela F, Echebarria B, Benítez R, Cinca J, Hove-Madsen L. Spatial Distribution of Calcium Sparks Determines Their Ability to Induce Afterdepolarizations in Human Atrial Myocytes. JACC. BASIC TO TRANSLATIONAL SCIENCE 2022; 8:1-15. [PMID: 36777175 PMCID: PMC9911326 DOI: 10.1016/j.jacbts.2022.07.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Revised: 07/18/2022] [Accepted: 07/18/2022] [Indexed: 11/25/2022]
Abstract
Analysis of the spatio-temporal distribution of calcium sparks showed a preferential increase in sparks near the sarcolemma in atrial myocytes from patients with atrial fibrillation (AF), linked to higher ryanodine receptor (RyR2) phosphorylation at s2808 and lower calsequestrin-2 levels. Mathematical modeling, incorporating modulation of RyR2 gating, showed that only the observed combinations of RyR2 phosphorylation and calsequestrin-2 levels can account for the spatio-temporal distribution of sparks in patients with and without AF. Furthermore, we demonstrate that preferential calcium release near the sarcolemma is key to a higher incidence and amplitude of afterdepolarizations in atrial myocytes from patients with AF.
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Affiliation(s)
- Carmen Tarifa
- Instituto de Investigaciones Biomédicas de Barcelona, IIBB-CSIC, Barcelona, Spain,IIB Sant Pau, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
| | - Alexander Vallmitjana
- Department d’Enginyeria de Sistemes, Automàtica i Informàtica Industrial, Universitat Politècnica de Catalunya, Spain
| | - Verónica Jiménez-Sábado
- Instituto de Investigaciones Biomédicas de Barcelona, IIBB-CSIC, Barcelona, Spain,IIB Sant Pau, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain,Centro de Investigación Biomédica en Red Enfermedades Cardiovaculares, Madrid, Spain
| | - Miquel Marchena
- Department Physics, Universitat Politècnica de Catalunya, Barcelona, Spain
| | - Anna Llach
- IIB Sant Pau, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
| | - Adela Herraiz-Martínez
- Instituto de Investigaciones Biomédicas de Barcelona, IIBB-CSIC, Barcelona, Spain,IIB Sant Pau, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
| | - Héctor Godoy-Marín
- Department Pathology and Experimental Therapeutics, IDIBELL, University of Barcelona, Barcelona, Spain,Neuroscience Institute, University of Barcelona, Barcelona, Spain
| | - Carme Nolla-Colomer
- Department d’Enginyeria de Sistemes, Automàtica i Informàtica Industrial, Universitat Politècnica de Catalunya, Spain
| | - Antonino Ginel
- Servicio de Cirugía Cardiaca, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
| | - Xavier Viñolas
- Servicio de Cardiología, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
| | - José Montiel
- Servicio de Cirugía Cardiaca, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
| | - Francisco Ciruela
- Department Pathology and Experimental Therapeutics, IDIBELL, University of Barcelona, Barcelona, Spain,Neuroscience Institute, University of Barcelona, Barcelona, Spain
| | - Blas Echebarria
- Department Physics, Universitat Politècnica de Catalunya, Barcelona, Spain
| | - Raúl Benítez
- Department d’Enginyeria de Sistemes, Automàtica i Informàtica Industrial, Universitat Politècnica de Catalunya, Spain
| | - Juan Cinca
- IIB Sant Pau, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain,Centro de Investigación Biomédica en Red Enfermedades Cardiovaculares, Madrid, Spain,Servicio de Cardiología, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
| | - Leif Hove-Madsen
- Instituto de Investigaciones Biomédicas de Barcelona, IIBB-CSIC, Barcelona, Spain,IIB Sant Pau, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain,Centro de Investigación Biomédica en Red Enfermedades Cardiovaculares, Madrid, Spain,Address for correspondence: Dr Leif Hove-Madsen, Cardiac Rhythm and Contraction Group, Biomedical Research Institute Barcelona, Hospital de la Santa Creu i Sant Pau, St Antoni Ma Claret 167, 08025 Barcelona, Spain.
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2
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Qu Z, Yan D, Song Z. Modeling Calcium Cycling in the Heart: Progress, Pitfalls, and Challenges. Biomolecules 2022; 12:1686. [PMID: 36421700 PMCID: PMC9687412 DOI: 10.3390/biom12111686] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Revised: 11/08/2022] [Accepted: 11/11/2022] [Indexed: 11/16/2022] Open
Abstract
Intracellular calcium (Ca) cycling in the heart plays key roles in excitation-contraction coupling and arrhythmogenesis. In cardiac myocytes, the Ca release channels, i.e., the ryanodine receptors (RyRs), are clustered in the sarcoplasmic reticulum membrane, forming Ca release units (CRUs). The RyRs in a CRU act collectively to give rise to discrete Ca release events, called Ca sparks. A cell contains hundreds to thousands of CRUs, diffusively coupled via Ca to form a CRU network. A rich spectrum of spatiotemporal Ca dynamics is observed in cardiac myocytes, including Ca sparks, spark clusters, mini-waves, persistent whole-cell waves, and oscillations. Models of different temporal and spatial scales have been developed to investigate these dynamics. Due to the complexities of the CRU network and the spatiotemporal Ca dynamics, it is challenging to model the Ca cycling dynamics in the cardiac system, particularly at the tissue sales. In this article, we review the progress of modeling of Ca cycling in cardiac systems from single RyRs to the tissue scale, the pros and cons of the current models and different modeling approaches, and the challenges to be tackled in the future.
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Affiliation(s)
- Zhilin Qu
- Department of Medicine, David Geffen School of Medicine, University of California, A2-237 CHS, 650 Charles E. Young Drive South, Los Angeles, CA 90095, USA
- Department of Computational Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Dasen Yan
- Peng Cheng Laboratory, Shenzhen 518066, China
| | - Zhen Song
- Peng Cheng Laboratory, Shenzhen 518066, China
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3
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Zhang X, Ni H, Morotti S, Smith CER, Sato D, Louch WE, Edwards AG, Grandi E. Mechanisms of spontaneous Ca 2+ release-mediated arrhythmia in a novel 3D human atrial myocyte model: I. Transverse-axial tubule variation. J Physiol 2022. [PMID: 36094888 PMCID: PMC10008525 DOI: 10.1113/jp283363] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Accepted: 09/02/2022] [Indexed: 11/08/2022] Open
Abstract
Intracellular calcium (Ca2+ ) cycling is tightly regulated in the healthy heart ensuring effective contraction. This is achieved by transverse (t)-tubule membrane invaginations that facilitate close coupling of key Ca2+ -handling proteins such as the L-type Ca2+ channel and Na+ -Ca2+ exchanger (NCX) on the cell surface with ryanodine receptors (RyRs) on the intracellular Ca2+ store. Although less abundant and regular than in the ventricle, t-tubules also exist in atrial myocytes as a network of transverse invaginations with axial extensions known as the transverse-axial tubule system (TATS). In heart failure and atrial fibrillation, there is TATS remodelling that is associated with aberrant Ca2+ -handling and Ca2+ -induced arrhythmic activity; however, the mechanism underlying this is not fully understood. To address this, we developed a novel 3D human atrial myocyte model that couples electrophysiology and Ca2+ -handling with variable TATS organization and density. We extensively parameterized and validated our model against experimental data to build a robust tool examining TATS regulation of subcellular Ca2+ release. We found that varying TATS density and thus the localization of key Ca2+ -handling proteins has profound effects on Ca2+ handling. Following TATS loss, there is reduced NCX that results in increased cleft Ca2+ concentration through decreased Ca2+ extrusion. This elevated Ca2+ increases RyR open probability causing spontaneous Ca2+ releases and the promotion of arrhythmogenic waves (especially in the cell interior) leading to voltage instabilities through delayed afterdepolarizations. In summary, the present study demonstrates a mechanistic link between TATS remodelling and Ca2+ -driven proarrhythmic behaviour that probably reflects the arrhythmogenic state observed in disease. KEY POINTS: Transverse-axial tubule systems (TATS) modulate Ca2+ handling and excitation-contraction coupling in atrial myocytes, with TATS remodelling in heart failure and atrial fibrillation being associated with altered Ca2+ cycling and subsequent arrhythmogenesis. To investigate the poorly understood mechanisms linking TATS variation and spontaneous Ca2+ release, we built, parameterized and validated a 3D human atrial myocyte model coupling electrophysiology and spatially-detailed subcellular Ca2+ handling governed by the TATS. Simulated TATS loss causes diastolic Ca2+ and voltage instabilities through reduced Na+ -Ca2+ exchanger-mediated Ca2+ removal, cleft Ca2+ accumulation and increased ryanodine receptor open probability, resulting in spontaneous Ca2+ release and promotion of arrhythmogenic waves and delayed afterdepolarizations. At fast electrical rates typical of atrial tachycardia/fibrillation, spontaneous Ca2+ releases are larger and more frequent in the cell interior than at the periphery. Our work provides mechanistic insight into how atrial TATS remodelling can lead to Ca2+ -driven instabilities that may ultimately contribute to the arrhythmogenic state in disease.
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Affiliation(s)
- Xianwei Zhang
- Department of Pharmacology, University of California Davis, Davis, CA, USA
| | - Haibo Ni
- Department of Pharmacology, University of California Davis, Davis, CA, USA
| | - Stefano Morotti
- Department of Pharmacology, University of California Davis, Davis, CA, USA
| | | | - Daisuke Sato
- Department of Pharmacology, University of California Davis, Davis, CA, USA
| | - William E Louch
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,K.G. Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| | - Andrew G Edwards
- Department of Pharmacology, University of California Davis, Davis, CA, USA.,Simula Research Laboratory, Lysaker, Norway
| | - Eleonora Grandi
- Department of Pharmacology, University of California Davis, Davis, CA, USA
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4
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Novaes GM, Alvarez-Lacalle E, Muñoz SA, dos Santos RW. An ensemble of parameters from a robust Markov-based model reproduces L-type calcium currents from different human cardiac myocytes. PLoS One 2022; 17:e0266233. [PMID: 35381041 PMCID: PMC8982880 DOI: 10.1371/journal.pone.0266233] [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: 08/13/2021] [Accepted: 03/16/2022] [Indexed: 11/18/2022] Open
Abstract
The development of modeling structures at the channel level that can integrate subcellular and cell models and properly reproduce different experimental data is of utmost importance in cardiac electrophysiology. In contrast to gate-based models, Markov Chain models are well suited to promote the integration of the subcellular level of the cardiomyocyte to the whole cell. In this paper, we develop Markov Chain models for the L-type Calcium current that can reproduce the electrophysiology of two established human models for the ventricular and Purkinje cells. In addition, instead of presenting a single set of parameters, we present a collection of set of parameters employing Differential Evolution algorithms that can properly reproduce very different protocol data. We show the importance of using an ensemble of a set of parameter values to obtain proper results when considering a second protocol that suppresses calcium inactivation and mimics a pathological condition. We discuss how model discrepancy, data availability, and parameter identifiability can influence the choice of the size of the collection. In summary, we have modified two cardiac models by proposing new Markov Chain models for the L-type Calcium. We keep the original whole-cell dynamics by reproducing the same characteristic action potential and calcium dynamics, whereas the Markov chain-based description of the L-type Calcium channels allows novel small spatial scale simulations of subcellular processes. Finally, the use of collections of parameters was crucial for addressing model discrepancy, identifiability issues, and avoiding fitting parameters overly precisely, i.e., overfitting.
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Affiliation(s)
- Gustavo Montes Novaes
- Graduate Program in Computational Modeling, Federal University of Juiz de Fora, Juiz de Fora, MG, Brazil
- Department of Physics, Universitat Politècnica de Catalunya-BarcelonaTech, Barcelona, Spain
- Department of Computation and Mechanics, Federal Center of Technological Education of Minas Gerais, Leopoldina, MG, Brazil
- * E-mail:
| | | | - Sergio Alonso Muñoz
- Department of Physics, Universitat Politècnica de Catalunya-BarcelonaTech, Barcelona, Spain
| | - Rodrigo Weber dos Santos
- Graduate Program in Computational Modeling, Federal University of Juiz de Fora, Juiz de Fora, MG, Brazil
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5
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Colman MA, Alvarez-Lacalle E, Echebarria B, Sato D, Sutanto H, Heijman J. Multi-Scale Computational Modeling of Spatial Calcium Handling From Nanodomain to Whole-Heart: Overview and Perspectives. Front Physiol 2022; 13:836622. [PMID: 35370783 PMCID: PMC8964409 DOI: 10.3389/fphys.2022.836622] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Accepted: 01/31/2022] [Indexed: 11/13/2022] Open
Abstract
Regulation of intracellular calcium is a critical component of cardiac electrophysiology and excitation-contraction coupling. The calcium spark, the fundamental element of the intracellular calcium transient, is initiated in specialized nanodomains which co-locate the ryanodine receptors and L-type calcium channels. However, calcium homeostasis is ultimately regulated at the cellular scale, by the interaction of spatially separated but diffusively coupled nanodomains with other sub-cellular and surface-membrane calcium transport channels with strong non-linear interactions; and cardiac electrophysiology and arrhythmia mechanisms are ultimately tissue-scale phenomena, regulated by the interaction of a heterogeneous population of coupled myocytes. Recent advances in imaging modalities and image-analysis are enabling the super-resolution reconstruction of the structures responsible for regulating calcium homeostasis, including the internal structure of nanodomains themselves. Extrapolating functional and imaging data from the nanodomain to the whole-heart is non-trivial, yet essential for translational insight into disease mechanisms. Computational modeling has important roles to play in relating structural and functional data at the sub-cellular scale and translating data across the scales. This review covers recent methodological advances that enable image-based modeling of the single nanodomain and whole cardiomyocyte, as well as the development of multi-scale simulation approaches to integrate data from nanometer to whole-heart. Firstly, methods to overcome the computational challenges of simulating spatial calcium dynamics in the nanodomain are discussed, including image-based modeling at this scale. Then, recent whole-cell models, capable of capturing a range of different structures (such as the T-system and mitochondria) and cellular heterogeneity/variability are discussed at two different levels of discretization. Novel methods to integrate the models and data across the scales and simulate stochastic dynamics in tissue-scale models are then discussed, enabling elucidation of the mechanisms by which nanodomain remodeling underlies arrhythmia and contractile dysfunction. Perspectives on model differences and future directions are provided throughout.
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Affiliation(s)
- Michael A. Colman
- School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom
- *Correspondence: Michael A. Colman,
| | | | - Blas Echebarria
- Departament de Fisica, Universitat Politècnica de Catalunya-BarcelonaTech, Barcelona, Spain
| | - Daisuke Sato
- Department of Pharmacology, School of Medicine, University of California, Davis, Davis, CA, United States
| | - Henry Sutanto
- Department of Physiology and Pharmacology, State University of New York Downstate Health Sciences University, Brooklyn, NY, United States
- Department of Cardiology, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, Netherlands
| | - Jordi Heijman
- Department of Cardiology, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, Netherlands
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6
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Basnayake K, Mazaud D, Kushnireva L, Bemelmans A, Rouach N, Korkotian E, Holcman D. Nanoscale molecular architecture controls calcium diffusion and ER replenishment in dendritic spines. SCIENCE ADVANCES 2021; 7:eabh1376. [PMID: 34524854 PMCID: PMC8443180 DOI: 10.1126/sciadv.abh1376] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Accepted: 07/19/2021] [Indexed: 06/13/2023]
Abstract
Dendritic spines are critical components of neuronal synapses as they receive and transform synaptic inputs into a succession of calcium-regulated biochemical events. The spine apparatus (SA), an extension of smooth endoplasmic reticulum, regulates slow and fast calcium dynamics in spines. Calcium release events deplete SA calcium ion reservoir rapidly, yet the next cycle of signaling requires its replenishment. How spines achieve this replenishment without triggering calcium release remains unclear. Using computational modeling, calcium and STED superresolution imaging, we show that the SA replenishment involves the store-operated calcium entry pathway during spontaneous calcium transients. We identified two main conditions for SA replenishment without depletion: a small amplitude and a slow timescale for calcium influx, and a close proximity between SA and plasma membranes. Thereby, spine’s nanoscale organization separates SA replenishment from depletion. We further conclude that spine’s receptor organization also determines the calcium dynamics during the induction of long-term synaptic changes.
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Affiliation(s)
- Kanishka Basnayake
- Computational Biology and Applied Mathematics, Institut de Biologie de l’École Normale Supérieure-PSL, Paris, France
| | - David Mazaud
- Neuroglial Interactions in Cerebral Physiology, Center for Interdisciplinary Research in Biology, Collège de France, CNRS UMR 7241, INSERM U1050, Labex Memolife, PSL Research University, Paris, France
| | | | - Alexis Bemelmans
- Commissariat à l’Energie Atomique et aux Energies Alternatives, Département de la Recherche Fondamentale, Institut de biologie François Jacob, Molecular Imaging Research Center and Centre National de la Recherche Scientifique UMR9199, Université Paris-Sud, Neurodegenerative Diseases Laboratory, Fontenay-aux-Roses, France
| | - Nathalie Rouach
- Neuroglial Interactions in Cerebral Physiology, Center for Interdisciplinary Research in Biology, Collège de France, CNRS UMR 7241, INSERM U1050, Labex Memolife, PSL Research University, Paris, France
| | - Eduard Korkotian
- Faculty of Biology, Perm State University, Perm, Russia
- Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel
| | - David Holcman
- Computational Biology and Applied Mathematics, Institut de Biologie de l’École Normale Supérieure-PSL, Paris, France
- Churchill College and the Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, UK
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7
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Vagos MR, Arevalo H, Heijman J, Schotten U, Sundnes J. A Novel Computational Model of the Rabbit Atrial Cardiomyocyte With Spatial Calcium Dynamics. Front Physiol 2020; 11:556156. [PMID: 33162894 PMCID: PMC7583320 DOI: 10.3389/fphys.2020.556156] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Accepted: 08/28/2020] [Indexed: 12/21/2022] Open
Abstract
Models of cardiac electrophysiology are widely used to supplement experimental results and to provide insight into mechanisms of cardiac function and pathology. The rabbit has been a particularly important animal model for studying mechanisms of atrial pathophysiology and atrial fibrillation, which has motivated the development of models for the rabbit atrial cardiomyocyte electrophysiology. Previously developed models include detailed representations of membrane currents and intracellular ionic concentrations, but these so-called “common-pool” models lack a spatially distributed description of the calcium handling system, which reflects the detailed ultrastructure likely found in cells in vivo. Because of the less well-developed T-tubular system in atrial compared to ventricular cardiomyocytes, spatial gradients in intracellular calcium concentrations may play a more significant role in atrial cardiomyocyte pathophysiology, rendering common-pool models less suitable for investigating underlying electrophysiological mechanisms. In this study, we developed a novel computational model of the rabbit atrial cardiomyocyte incorporating detailed compartmentalization of intracellular calcium dynamics, in addition to a description of membrane currents and intracellular processes. The spatial representation of calcium was based on dividing the intracellular space into eighteen different compartments in the transversal direction, each with separate systems for internal calcium storage and release, and tracking ionic fluxes between compartments in addition to the dynamics driven by membrane currents and calcium release. The model was parameterized employing a population-of-models approach using experimental data from different sources. The parameterization of this novel model resulted in a reduced population of models with inherent variability in calcium dynamics and electrophysiological properties, all of which fall within the range of observed experimental values. As such, the population of models may represent natural variability in cardiomyocyte electrophysiology or inherent uncertainty in the underlying experimental data. The ionic model population was also able to reproduce the U-shaped waveform observed in line-scans of triggered calcium waves in atrial cardiomyocytes, characteristic of the absence of T-tubules, resulting in a centripetal calcium wave due to subcellular calcium diffusion. This novel spatial model of the rabbit atrial cardiomyocyte can be used to integrate experimental findings, offering the potential to enhance our understanding of the pathophysiological role of calcium-handling abnormalities under diseased conditions, such as atrial fibrillation.
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Affiliation(s)
- Márcia R Vagos
- Simula Research Laboratory, Computational Physiology Department, Lysaker, Norway.,Department of Informatics, University of Oslo, Oslo, Norway
| | - Hermenegild Arevalo
- Simula Research Laboratory, Computational Physiology Department, Lysaker, Norway.,Center for Cardiological Innovation, Rikshospitalet, Oslo, Norway
| | - Jordi Heijman
- Faculty of Health, Medicine and Life Sciences, CARIM School for Cardiovascular Diseases, Maastricht University, Maastricht, Netherlands
| | - Ulrich Schotten
- Faculty of Health, Medicine and Life Sciences, CARIM School for Cardiovascular Diseases, Maastricht University, Maastricht, Netherlands
| | - Joakim Sundnes
- Simula Research Laboratory, Computational Physiology Department, Lysaker, Norway.,Department of Informatics, University of Oslo, Oslo, Norway.,Center for Cardiological Innovation, Rikshospitalet, Oslo, Norway
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8
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Marchena M, Echebarria B, Shiferaw Y, Alvarez-Lacalle E. Buffering and total calcium levels determine the presence of oscillatory regimes in cardiac cells. PLoS Comput Biol 2020; 16:e1007728. [PMID: 32970668 PMCID: PMC7537911 DOI: 10.1371/journal.pcbi.1007728] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Revised: 10/06/2020] [Accepted: 07/07/2020] [Indexed: 12/16/2022] Open
Abstract
Calcium oscillations and waves induce depolarization in cardiac cells which are believed to cause life-threathening arrhythimas. In this work, we study the conditions for the appearance of calcium oscillations in both a detailed subcellular model of calcium dynamics and a minimal model that takes into account just the minimal ingredients of the calcium toolkit. To avoid the effects of homeostatic changes and the interaction with the action potential we consider the somewhat artificial condition of a cell without pacing and with no calcium exchange with the extracellular medium. Both the full subcellular model and the minimal model present the same scenarios depending on the calcium load: two stationary states, one with closed ryanodine receptors (RyR) and most calcium in the cell stored in the sarcoplasmic reticulum (SR), and another, with open RyRs and a depleted SR. In between, calcium oscillations may appear. The robustness of these oscillations is determined by the amount of calsequestrin (CSQ). The lack of this buffer in the SR enhances the appearance of oscillations. The minimal model allows us to relate the stability of the oscillating state to the nullcline structure of the system, and find that its range of existence is bounded by a homoclinic and a Hopf bifurcation, resulting in a sudden transition to the oscillatory regime as the cell calcium load is increased. Adding a small amount of noise to the RyR behavior increases the parameter region where oscillations appear and provides a gradual transition from the resting state to the oscillatory regime, as observed in the subcellular model and experimentally. In cardiac cells, calcium plays a very important role. An increase in calcium levels is the trigger used by the cell to initiate contraction. Besides, calcium modulates several transmembrane currents, affecting the cell transmembrane potential. Thus, dysregulations in calcium handling have been associated with the appearance of arrhythmias. Often, this dysregulation results in the appearance of periodic calcium waves or global oscillations, providing a pro-arrhythmic substrate. In this paper, we study the onset of calcium oscillations in cardiac cells using both a detailed subcellular model of calcium dynamics and a minimal model that takes into account the essential ingredients of the calcium toolkit. Both reproduce the main experimental results and link this behavior with the presence of different steady-state solutions and bifurcations that depend on the total amount of calcium in the cell and in the level of buffering present. We expect that this work will help to clarify the conditions under which calcium oscillations appear in cardiac myocytes and, therefore, will represent a step further in the understanding of the origin of cardiac arrhythmias.
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Affiliation(s)
- Miquel Marchena
- Departament de Física, Universitat Politècnica de Catalunya-BarcelonaTech, Barcelona, Spain
| | - Blas Echebarria
- Departament de Física, Universitat Politècnica de Catalunya-BarcelonaTech, Barcelona, Spain
| | - Yohannes Shiferaw
- Physics Department, California State University, Northridge, California 91330, USA
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9
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Lo ACY, Bai J, Gladding PA, Fedorov VV, Zhao J. Afterdepolarizations and abnormal calcium handling in atrial myocytes with modulated SERCA uptake: a sensitivity analysis of calcium handling channels. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20190557. [PMID: 32448059 PMCID: PMC7287332 DOI: 10.1098/rsta.2019.0557] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 04/23/2020] [Indexed: 05/21/2023]
Abstract
Delayed afterdepolarizations (DADs) and spontaneous depolarizations (SDs) are typically triggered by spontaneous diastolic Ca2+ release from the sarcoplasmic reticulum (SR) which is caused by an elevated SR Ca2+-ATPase (SERCA) uptake and dysfunctional ryanodine receptors. However, recent studies on the T-box transcription factor gene (TBX5) demonstrated that abnormal depolarizations could occur despite a reduced SERCA uptake. Similar findings have also been reported in experimental or clinical studies of diabetes and heart failure. To investigate the sensitivity of SERCA in the genesis of DADs/SDs as well as its dependence on other Ca2+ handling channels, we performed systematic analyses using the Maleckar et al. model. Results showed that the modulation of SERCA alone cannot trigger abnormal depolarizations, but can instead affect the interdependency of other Ca2+ handling channels in triggering DADs/SDs. Furthermore, we discovered the existence of a threshold value for the intracellular concentration of Ca2+ ([Ca2+]i) for abnormal depolarizations, which is modulated by the maximum SERCA uptake and the concentration of Ca2+ in the uptake and release compartments in the SR ([Ca2+]up and [Ca2+]rel). For the first time, our modelling study reconciles different mechanisms of abnormal depolarizations in the setting of 'lone' AF, reduced TBX5, diabetes and heart failure, and may lead to more targeted treatment for these patients. This article is part of the theme issue 'Uncertainty quantification in cardiac and cardiovascular modelling and simulation'.
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Affiliation(s)
- Andy C. Y. Lo
- Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
| | - Jieyun Bai
- Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
- Department of Electronic Engineering, College of Information Science and Technology, Jinan University, Guangzhou, People's Republic of China
| | - Patrick A. Gladding
- Department of Cardiology, Waitemata District Health Board, Auckland, New Zealand
| | - Vadim V. Fedorov
- Department of Physiology and Cell Biology and Bob and Corrine Frick Center for Heart Failure and Arrhythmia, The Ohio State University Wexner Medical Center, Columbus, OH, USA
| | - Jichao Zhao
- Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
- e-mail:
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10
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Marchena M, Echebarria B. Influence of the tubular network on the characteristics of calcium transients in cardiac myocytes. PLoS One 2020; 15:e0231056. [PMID: 32302318 PMCID: PMC7164608 DOI: 10.1371/journal.pone.0231056] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Accepted: 03/14/2020] [Indexed: 01/09/2023] Open
Abstract
Transverse and axial tubules (TATS) are an essential ingredient of the excitation-contraction machinery that allow the effective coupling of L-type Calcium Channels (LCC) and ryanodine receptors (RyR2). They form a regular network in ventricular cells, while their presence in atrial myocytes is variable regionally and among animal species We have studied the effect of variations in the TAT network using a bidomain computational model of an atrial myocyte with variable density of tubules. At each z-line the t-tubule length is obtained from an exponential distribution, with a given mean penetration length. This gives rise to a distribution of t-tubules in the cell that is characterized by the fractional area (F.A.) occupied by the t-tubules. To obtain consistent results, we average over different realizations of the same mean penetration length. To this, in some simulations we add the effect of a network of axial tubules. Then we study global properties of calcium signaling, as well as regional heterogeneities and local properties of sparks and RyR2 openings. In agreement with recent experiments in detubulated ventricular and atrial cells, we find that detubulation reduces the calcium transient and synchronization in release. However, it does not affect sarcoplasmic reticulum (SR) load, so the decrease in SR calcium release is due to regional differences in Ca2+ release, that is restricted to the cell periphery in detubulated cells. Despite the decrease in release, the release gain is larger in detubulated cells, due to recruitment of orphaned RyR2s, i.e, those that are not confronting a cluster of LCCs. This probably provides a safeguard mechanism, allowing physiological values to be maintained upon small changes in the t-tubule density. Finally, we do not find any relevant change in spark properties between tubulated and detubulated cells, suggesting that the differences found in experiments could be due to differential properties of the RyR2s in the membrane and in the t-tubules, not incorporated in the present model. This work will help understand the effect of detubulation, that has been shown to occur in disease conditions such as heart failure (HF) in ventricular cells, or atrial fibrillation (AF) in atrial cells.
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Affiliation(s)
- Miquel Marchena
- Departament de Física, Universitat Politècnica de Catalunya, Barcelona, Spain
| | - Blas Echebarria
- Departament de Física, Universitat Politècnica de Catalunya, Barcelona, Spain
- * E-mail:
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Cardiomyocyte calcium handling in health and disease: Insights from in vitro and in silico studies. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2020; 157:54-75. [PMID: 32188566 DOI: 10.1016/j.pbiomolbio.2020.02.008] [Citation(s) in RCA: 63] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 12/31/2019] [Accepted: 02/29/2020] [Indexed: 02/07/2023]
Abstract
Calcium (Ca2+) plays a central role in cardiomyocyte excitation-contraction coupling. To ensure an optimal electrical impulse propagation and cardiac contraction, Ca2+ levels are regulated by a variety of Ca2+-handling proteins. In turn, Ca2+ modulates numerous electrophysiological processes. Accordingly, Ca2+-handling abnormalities can promote cardiac arrhythmias via various mechanisms, including the promotion of afterdepolarizations, ion-channel modulation and structural remodeling. In the last 30 years, significant improvements have been made in the computational modeling of cardiomyocyte Ca2+ handling under physiological and pathological conditions. However, numerous questions involving the Ca2+-dependent regulation of different macromolecular complexes, cross-talk between Ca2+-dependent regulatory pathways operating over a wide range of time scales, and bidirectional interactions between electrophysiology and mechanics remain to be addressed by in vitro and in silico studies. A better understanding of disease-specific Ca2+-dependent proarrhythmic mechanisms may facilitate the development of improved therapeutic strategies. In this review, we describe the fundamental mechanisms of cardiomyocyte Ca2+ handling in health and disease, and provide an overview of currently available computational models for cardiomyocyte Ca2+ handling. Finally, we discuss important uncertainties and open questions about cardiomyocyte Ca2+ handling and highlight how synergy between in vitro and in silico studies may help to answer several of these issues.
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