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Pásek M, Bébarová M, Šimurdová M, Šimurda J. Functional consequences of changes in the distribution of Ca 2+ extrusion pathways between t-tubular and surface membranes in a model of human ventricular cardiomyocyte. J Mol Cell Cardiol 2024; 193:113-124. [PMID: 38960316 DOI: 10.1016/j.yjmcc.2024.06.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Revised: 06/10/2024] [Accepted: 06/29/2024] [Indexed: 07/05/2024]
Abstract
The sarcolemmal Ca2+ efflux pathways, Na+-Ca2+-exchanger (NCX) and Ca2+-ATPase (PMCA), play a crucial role in the regulation of intracellular Ca2+ load and Ca2+ transient in cardiomyocytes. The distribution of these pathways between the t-tubular and surface membrane of ventricular cardiomyocytes varies between species and is not clear in human. Moreover, several studies suggest that this distribution changes during the development and heart diseases. However, the consequences of NCX and PMCA redistribution in human ventricular cardiomyocytes have not yet been elucidated. In this study, we aimed to address this point by using a mathematical model of the human ventricular myocyte incorporating t-tubules, dyadic spaces, and subsarcolemmal spaces. Effects of various combinations of t-tubular fractions of NCX and PMCA were explored, using values between 0.2 and 1 as reported in animal experiments under normal and pathological conditions. Small variations in the action potential duration (≤ 2%), but significant changes in the peak value of cytosolic Ca2+ transient (up to 17%) were observed at stimulation frequencies corresponding to the human heart rate at rest and during activity. The analysis of model results revealed that the changes in Ca2+ transient induced by redistribution of NCX and PMCA were mainly caused by alterations in Ca2+ concentrations in the subsarcolemmal spaces and cytosol during the diastolic phase of the stimulation cycle. The results suggest that redistribution of both transporters between the t-tubular and surface membranes contributes to changes in contractility in human ventricular cardiomyocytes during their development and heart disease and may promote arrhythmogenesis.
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Affiliation(s)
- Michal Pásek
- Institute of Thermomechanics, Czech Academy of Sciences, Prague, Czech Republic; Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic.
| | - Markéta Bébarová
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic; Department of Internal Medicine and Cardiology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Milena Šimurdová
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Jiří Šimurda
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
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2
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Brandalise F, Ramieri M, Pastorelli E, Priori EC, Ratto D, Venuti MT, Roda E, Talpo F, Rossi P. Role of Na +/Ca 2+ Exchanger (NCX) in Glioblastoma Cell Migration (In Vitro). Int J Mol Sci 2023; 24:12673. [PMID: 37628853 PMCID: PMC10454658 DOI: 10.3390/ijms241612673] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Revised: 08/07/2023] [Accepted: 08/08/2023] [Indexed: 08/27/2023] Open
Abstract
Glioblastoma (GBM) is the most malignant form of primary brain tumor. It is characterized by the presence of highly invasive cancer cells infiltrating the brain by hijacking neuronal mechanisms and interacting with non-neuronal cell types, such as astrocytes and endothelial cells. To enter the interstitial space of the brain parenchyma, GBM cells significantly shrink their volume and extend the invadopodia and lamellipodia by modulating their membrane conductance repertoire. However, the changes in the compartment-specific ionic dynamics involved in this process are still not fully understood. Here, using noninvasive perforated patch-clamp and live imaging approaches on various GBM cell lines during a wound-healing assay, we demonstrate that the sodium-calcium exchanger (NCX) is highly expressed in the lamellipodia compartment, is functionally active during GBM cell migration, and correlates with the overexpression of large conductance K+ channel (BK) potassium channels. Furthermore, a NCX blockade impairs lamellipodia formation and maintenance, as well as GBM cell migration. In conclusion, the functional expression of the NCX in the lamellipodia of GBM cells at the migrating front is a conditio sine qua non for the invasion strategy of these malignant cells and thus represents a potential target for brain tumor treatment.
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Affiliation(s)
| | - Martino Ramieri
- Department of Biology and Biotechnology “L. Spallanzani”, University of Pavia, 27100 Pavia, Italy; (M.R.); (E.P.); (E.C.P.); (D.R.); (M.T.V.)
| | - Emanuela Pastorelli
- Department of Biology and Biotechnology “L. Spallanzani”, University of Pavia, 27100 Pavia, Italy; (M.R.); (E.P.); (E.C.P.); (D.R.); (M.T.V.)
| | - Erica Cecilia Priori
- Department of Biology and Biotechnology “L. Spallanzani”, University of Pavia, 27100 Pavia, Italy; (M.R.); (E.P.); (E.C.P.); (D.R.); (M.T.V.)
| | - Daniela Ratto
- Department of Biology and Biotechnology “L. Spallanzani”, University of Pavia, 27100 Pavia, Italy; (M.R.); (E.P.); (E.C.P.); (D.R.); (M.T.V.)
| | - Maria Teresa Venuti
- Department of Biology and Biotechnology “L. Spallanzani”, University of Pavia, 27100 Pavia, Italy; (M.R.); (E.P.); (E.C.P.); (D.R.); (M.T.V.)
| | - Elisa Roda
- Laboratory of Clinical & Experimental Toxicology, Pavia Poison Centre, National Toxicology Information Centre, Toxicology Unit, Istituti Clinici Scientifici Maugeri IRCCS Pavia, 27100 Pavia, Italy;
| | - Francesca Talpo
- Department of Biology and Biotechnology “L. Spallanzani”, University of Pavia, 27100 Pavia, Italy; (M.R.); (E.P.); (E.C.P.); (D.R.); (M.T.V.)
| | - Paola Rossi
- Department of Biology and Biotechnology “L. Spallanzani”, University of Pavia, 27100 Pavia, Italy; (M.R.); (E.P.); (E.C.P.); (D.R.); (M.T.V.)
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3
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Birkedal R, Laasmaa M, Branovets J, Vendelin M. Ontogeny of cardiomyocytes: ultrastructure optimization to meet the demand for tight communication in excitation-contraction coupling and energy transfer. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210321. [PMID: 36189816 PMCID: PMC9527910 DOI: 10.1098/rstb.2021.0321] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The ontogeny of the heart describes its development from the fetal to the adult stage. In newborn mammals, blood pressure and thus cardiac performance are relatively low. The cardiomyocytes are thin, and with a central core of mitochondria surrounded by a ring of myofilaments, while the sarcoplasmic reticulum (SR) is sparse. During development, as blood pressure and performance increase, the cardiomyocytes become more packed with structures involved in excitation–contraction (e-c) coupling (SR and myofilaments) and the generation of ATP (mitochondria) to fuel the contraction. In parallel, the e-c coupling relies increasingly on calcium fluxes through the SR, while metabolism relies increasingly on fatty acid oxidation. The development of transverse tubules and SR brings channels and transporters interacting via calcium closer to each other and is crucial for e-c coupling. However, for energy transfer, it may seem counterintuitive that the increased structural density restricts the overall ATP/ADP diffusion. In this review, we discuss how this is because of the organization of all these structures forming modules. Although the overall diffusion across modules is more restricted, the energy transfer within modules is fast. A few studies suggest that in failing hearts this modular design is disrupted, and this may compromise intracellular energy transfer. This article is part of the theme issue ‘The cardiomyocyte: new revelations on the interplay between architecture and function in growth, health, and disease’.
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Affiliation(s)
- Rikke Birkedal
- Laboratory of Systems Biology, Department of Cybernetics, Tallinn University of Technology, Akadeemia 15, room SCI-218, 12618 Tallinn, Estonia
| | - Martin Laasmaa
- Laboratory of Systems Biology, Department of Cybernetics, Tallinn University of Technology, Akadeemia 15, room SCI-218, 12618 Tallinn, Estonia
| | - Jelena Branovets
- Laboratory of Systems Biology, Department of Cybernetics, Tallinn University of Technology, Akadeemia 15, room SCI-218, 12618 Tallinn, Estonia
| | - Marko Vendelin
- Laboratory of Systems Biology, Department of Cybernetics, Tallinn University of Technology, Akadeemia 15, room SCI-218, 12618 Tallinn, Estonia
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4
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Ottolia M, John S, Hazan A, Goldhaber JI. The Cardiac Na + -Ca 2+ Exchanger: From Structure to Function. Compr Physiol 2021; 12:2681-2717. [PMID: 34964124 DOI: 10.1002/cphy.c200031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Ca2+ homeostasis is essential for cell function and survival. As such, the cytosolic Ca2+ concentration is tightly controlled by a wide number of specialized Ca2+ handling proteins. One among them is the Na+ -Ca2+ exchanger (NCX), a ubiquitous plasma membrane transporter that exploits the electrochemical gradient of Na+ to drive Ca2+ out of the cell, against its concentration gradient. In this critical role, this secondary transporter guides vital physiological processes such as Ca2+ homeostasis, muscle contraction, bone formation, and memory to name a few. Herein, we review the progress made in recent years about the structure of the mammalian NCX and how it relates to function. Particular emphasis will be given to the mammalian cardiac isoform, NCX1.1, due to the extensive studies conducted on this protein. Given the degree of conservation among the eukaryotic exchangers, the information highlighted herein will provide a foundation for our understanding of this transporter family. We will discuss gene structure, alternative splicing, topology, regulatory mechanisms, and NCX's functional role on cardiac physiology. Throughout this article, we will attempt to highlight important milestones in the field and controversial topics where future studies are required. © 2021 American Physiological Society. Compr Physiol 12:1-37, 2021.
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Affiliation(s)
- Michela Ottolia
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA
| | - Scott John
- Department of Medicine (Cardiology), UCLA, Los Angeles, California, USA
| | - Adina Hazan
- Smidt Heart Institute, Cedars Sinai Medical Center, Los Angeles, California, USA
| | - Joshua I Goldhaber
- Smidt Heart Institute, Cedars Sinai Medical Center, Los Angeles, California, USA
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5
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Alghamdi AM, Testrow CP, Whittaker DG, Boyett MR, Hancox JC, Zhang H. Mechanistic Insights Into the Reduced Pacemaking Rate of the Rabbit Sinoatrial Node During Postnatal Development: A Simulation Study. Front Physiol 2020; 11:547577. [PMID: 33329016 PMCID: PMC7715043 DOI: 10.3389/fphys.2020.547577] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 10/29/2020] [Indexed: 12/19/2022] Open
Abstract
Marked age- and development- related differences have been observed in morphology and characteristics of action potentials (AP) of neonatal and adult sinoatrial node (SAN) cells. These may be attributable to a different set of ion channel interactions between the different ages. However, the underlying mechanism(s) have yet to be elucidated. The objective of this study was to determine the mechanisms underlying different spontaneous APs and heart rate between neonatal and adult SAN cells of the rabbit heart by biophysical modeling approaches. A mathematical model of neonatal rabbit SAN cells was developed by modifying the current densities and/or kinetics of ion channels and transporters in an adult cell model based on available experimental data obtained from neonatal SAN cells. The single cell models were then incorporated into a multi-cellular, two-dimensional model of the intact SAN-atrium to investigate the functional impact of altered ion channels during maturation on pacemaking electrical activities and their conduction at the tissue level. Effects of the neurotransmitter acetylcholine on the pacemaking activities in neonatal cells were also investigated and compared to those in the adult. Our results showed: (1) the differences in ion channel properties between neonatal and adult SAN cells are able to account for differences in their APs and the heart rate, providing mechanistic insight into understanding the reduced pacemaking rate of the rabbit sinoatrial node during postnatal development; (2) in the 2D model of the intact SAN-atria, it was shown that cellular changes during postnatal development impaired pacemaking activity through increasing the activation time and reducing the conduction velocity across the SAN; (3) the neonatal SAN model, with its faster beating rates, showed a greater sensitivity to parasympathetic modulation in response to acetylcholine than did the adult model. These results provide novel insights into the understanding of the cellular mechanisms underlying the differences in the cardiac pacemaking activities of the neonatal and adult SAN.
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Affiliation(s)
- Azzah M Alghamdi
- Biological Physics Group, School of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom.,Department of Physics, Faculty of Science, University of Jeddah, Jeddah, Saudi Arabia
| | - Craig P Testrow
- Biological Physics Group, School of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom
| | - Dominic G Whittaker
- Department of Mathematics, University of Nottingham, Nottingham, United Kingdom
| | - Mark R Boyett
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jules C Hancox
- Biological Physics Group, School of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom.,School of Physiology, Pharmacology and Neuroscience, and Cardiovascular Research Laboratories, School of Medical Sciences, University of Bristol, Bristol, United Kingdom
| | - Henggui Zhang
- Biological Physics Group, School of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom.,Peng Cheng Laboratory, Shenzhen, China.,Key Laboratory of Medical Electrophysiology of Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, China
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6
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Sghari S, Davies WIL, Gunhaga L. Elucidation of Cellular Mechanisms That Regulate the Sustained Contraction and Relaxation of the Mammalian Iris. Invest Ophthalmol Vis Sci 2020; 61:5. [PMID: 32882011 PMCID: PMC7476664 DOI: 10.1167/iovs.61.11.5] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Purpose In mammals, pupil constriction and dilation form the pupillary light reflex (PLR), which is mediated by both brain-regulated (parasympathetic) and local iris-driven reflexes. To better understand the cellular mechanisms that regulate pupil physiological dynamics via central and local photoreception, we have examined the regulation of the PLR via parasympathetic and local activation, respectively. Methods In this study, the PLR was examined in mouse enucleated eyes ex vivo in real-time under different ionic conditions in response to acetylcholine and/or blue light (480 nm). The use of pupillometry recordings captured the relaxation, contraction, and pupil escape (redilation) processes for 10 minutes up to 1 hour. Results Among others, our results show that ryanodine receptor channels are the main driver for iridal stimulation–contraction coupling, in which extracellular influx of Ca2+ is required for amplification of pupil constriction. Both local and parasympathetic iridal activations are necessary, but not sufficient for sustained pupil constriction. Moreover, the degree of membrane potential repolarization in the dark is correlated with the latency and velocity of iridal constriction. Furthermore, pupil escape is driven by membrane potential hyperpolarization where voltage-gated potassium channels play a crucial role. Conclusions Together, this study presents new mechanisms regulating synchronized pupil dilation and contraction, sustained pupil constriction, iridal stimulation-contraction coupling, and pupil escape.
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Affiliation(s)
- Soufien Sghari
- Umeå Centre for Molecular Medicine (UCMM), Umeå University, Umeå, Sweden
| | - Wayne I L Davies
- Umeå Centre for Molecular Medicine (UCMM), Umeå University, Umeå, Sweden
| | - Lena Gunhaga
- Umeå Centre for Molecular Medicine (UCMM), Umeå University, Umeå, Sweden
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7
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Ladd D, Tilūnaitė A, Roderick HL, Soeller C, Crampin EJ, Rajagopal V. Assessing Cardiomyocyte Excitation-Contraction Coupling Site Detection From Live Cell Imaging Using a Structurally-Realistic Computational Model of Calcium Release. Front Physiol 2019; 10:1263. [PMID: 31632297 PMCID: PMC6783691 DOI: 10.3389/fphys.2019.01263] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Accepted: 09/17/2019] [Indexed: 01/11/2023] Open
Abstract
Calcium signaling plays a pivotal role in cardiomyocytes, coupling electrical excitation to mechanical contraction of the heart. Determining locations of active calcium release sites, and how their recruitment changes in response to stimuli and in disease states is therefore of central interest in cardiac physiology. Current algorithms for detecting release sites from live cell imaging data are however not easily validated against a known “ground truth,” which makes interpretation of the output of such algorithms, in particular the degree of confidence in site detection, a challenging task. Computational models are capable of integrating findings from multiple sources into a consistent, predictive framework. In cellular physiology, such models have the potential to reveal structure and function beyond the temporal and spatial resolution limitations of individual experimental measurements. Here, we create a spatially detailed computational model of calcium release in an eight sarcomere section of a ventricular cardiomyocyte, using electron tomography reconstruction of cardiac ultrastructure and confocal imaging of protein localization. This provides a high-resolution model of calcium diffusion from intracellular stores, which can be used as a platform to simulate confocal fluorescence imaging in the context of known ground truth structures from the higher resolution model. We use this capability to evaluate the performance of a recently proposed method for detecting the functional response of calcium release sites in live cells. Model permutations reveal how calcium release site density and mitochondria acting as diffusion barriers impact the detection performance of the algorithm. We demonstrate that site density has the greatest impact on detection precision and recall, in particular affecting the effective detectable depth of sites in confocal data. Our findings provide guidance on how such detection algorithms may best be applied to experimental data and give insights into limitations when using two-dimensional microscopy images to analyse three-dimensional cellular structures.
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Affiliation(s)
- David Ladd
- Systems Biology Lab, Department of Biomedical Engineering, School of Mathematics and Statistics, University of Melbourne, Melbourne, VIC, Australia.,ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, School of Chemical and Biomedical Engineering, University of Melbourne, Melbourne, VIC, Australia.,Cell Structure and Mechanobiology Group, Department of Biomedical Engineering, University of Melbourne, Melbourne, VIC, Australia
| | - Agnė Tilūnaitė
- Systems Biology Lab, Department of Biomedical Engineering, School of Mathematics and Statistics, University of Melbourne, Melbourne, VIC, Australia
| | - H Llewelyn Roderick
- Laboratory of Experimental Cardiology, Department of Cardiovascular Sciences, KU Leuven, Leuven, Belgium
| | - Christian Soeller
- Living Systems Institute, University of Exeter, Exeter, United Kingdom
| | - Edmund J Crampin
- Systems Biology Lab, Department of Biomedical Engineering, School of Mathematics and Statistics, University of Melbourne, Melbourne, VIC, Australia.,ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, School of Chemical and Biomedical Engineering, University of Melbourne, Melbourne, VIC, Australia
| | - Vijay Rajagopal
- Cell Structure and Mechanobiology Group, Department of Biomedical Engineering, University of Melbourne, Melbourne, VIC, Australia
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8
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Hiess F, Detampel P, Nolla-Colomer C, Vallmitjana A, Ganguly A, Amrein M, Ter Keurs HEDJ, Benítez R, Hove-Madsen L, Chen SRW. Dynamic and Irregular Distribution of RyR2 Clusters in the Periphery of Live Ventricular Myocytes. Biophys J 2019; 114:343-354. [PMID: 29401432 DOI: 10.1016/j.bpj.2017.11.026] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 10/01/2017] [Accepted: 11/03/2017] [Indexed: 10/18/2022] Open
Abstract
Cardiac ryanodine receptors (RyR2s) are Ca2+ release channels clustering in the sarcoplasmic reticulum membrane. These clusters are believed to be the elementary units of Ca2+ release. The distribution of these Ca2+ release units plays a critical role in determining the spatio-temporal profile and stability of sarcoplasmic reticulum Ca2+ release. RyR2 clusters located in the interior of cardiomyocytes are arranged in highly ordered arrays. However, little is known about the distribution and function of RyR2 clusters in the periphery of cardiomyocytes. Here, we used a knock-in mouse model expressing a green fluorescence protein (GFP)-tagged RyR2 to localize RyR2 clusters in live ventricular myocytes by virtue of their GFP fluorescence. Confocal imaging and total internal reflection fluorescence microscopy was employed to determine and compare the distribution of GFP-RyR2 in the interior and periphery of isolated live ventricular myocytes and in intact hearts. We found tightly ordered arrays of GFP-RyR2 clusters in the interior, as previously described. In contrast, irregular distribution of GFP-RyR2 clusters was observed in the periphery. Time-lapse total internal reflection fluorescence imaging revealed dynamic movements of GFP-RyR2 clusters in the periphery, which were affected by external Ca2+ and RyR2 activator (caffeine) and inhibitor (tetracaine), but little detectable movement of GFP-RyR2 clusters in the interior. Furthermore, simultaneous Ca2+- and GFP-imaging demonstrated that peripheral RyR2 clusters with an irregular distribution pattern are functional with a Ca2+ release profile similar to that in the interior. These results indicate that the distribution of RyR2 clusters in the periphery of live ventricular myocytes is irregular and dynamic, which is different from that of RyR2 clusters in the interior.
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Affiliation(s)
- Florian Hiess
- Libin Cardiovascular Institute of Alberta, Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada
| | - Pascal Detampel
- Department of Pharmaceutical Sciences, University of Basel, Basel, Switzerland
| | - Carme Nolla-Colomer
- Automatic Control Department, Universitat Politècnica de Catalunya-Barcelona Tech, Barcelona, Spain
| | - Alex Vallmitjana
- Automatic Control Department, Universitat Politècnica de Catalunya-Barcelona Tech, Barcelona, Spain
| | - Anutosh Ganguly
- Department of Microbiology, Immunology and Infectious Diseases, University of Calgary, Calgary, Alberta, Canada
| | - Matthias Amrein
- Department of Biology and Anatomy, University of Calgary, Calgary, Alberta, Canada
| | - Henk E D J Ter Keurs
- Libin Cardiovascular Institute of Alberta, Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada
| | - Raul Benítez
- Automatic Control Department, Universitat Politècnica de Catalunya-Barcelona Tech, Barcelona, Spain
| | - Leif Hove-Madsen
- Biomedical Research Institute Barcelona CSIC-IIBB, Sant Pau, Hospital de Sant Pau, Barcelona, Spain
| | - S R Wayne Chen
- Libin Cardiovascular Institute of Alberta, Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada.
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9
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Chu L, Greenstein JL, Winslow RL. Na + microdomains and sparks: Role in cardiac excitation-contraction coupling and arrhythmias in ankyrin-B deficiency. J Mol Cell Cardiol 2019; 128:145-157. [PMID: 30731085 DOI: 10.1016/j.yjmcc.2019.02.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 02/01/2019] [Accepted: 02/02/2019] [Indexed: 01/25/2023]
Abstract
Cardiac sodium (Na+) potassium ATPase (NaK) pumps, neuronal sodium channels (INa), and sodium calcium (Ca2+) exchangers (NCX1) may co-localize to form a Na+ microdomain. It remains controversial as to whether neuronal INa contributes to local Na+ accumulation, resulting in reversal of nearby NCX1 and influx of Ca2+ into the cell. Therefore, there has been great interest in the possible roles of a Na+ microdomain in cardiac Ca2+-induced Ca2+ release (CICR). In addition, the important role of co-localization of NaK and NCX1 in regulating localized Na+ and Ca2+ levels and CICR in ankyrin-B deficient (ankyrin-B+/-) cardiomyocytes has been examined in many recent studies. Altered Na+ dynamics may contribute to the appearance of arrhythmias, but the mechanisms underlying this relationship remain unclear. In order to investigate this, we present a mechanistic canine cardiomyocyte model which reproduces independent local dyadic junctional SR (JSR) Ca2+ release events underlying cell-wide excitation-contraction coupling, as well as a three-dimensional super-resolution model of the Ca2+ spark that describes local Na+ dynamics as governed by NaK pumps, neuronal INa, and NCX1. The model predicts the existence of Na+ sparks, which are generated by NCX1 and exhibit significantly slower dynamics as compared to Ca2+ sparks. Moreover, whole-cell simulations indicate that neuronal INa in the cardiac dyad plays a key role during the systolic phase. Rapid inward neuronal INa can elevate dyadic [Na+] to 35-40 mM, which drives reverse-mode NCX1 transport, and therefore promotes Ca2+ entry into the dyad, enhancing the trigger for JSR Ca2+ release. The specific role of decreased co-localization of NaK and NCX1 in ankyrin-B+/- cardiomyocytes was examined. Model results demonstrate that a reduction in the local NCX1- and NaK-mediated regulation of dyadic [Ca2+] and [Na+] results in an increase in Ca2+ spark activity during isoproterenol stimulation, which in turn stochastically activates NCX1 in the dyad. This alteration in NCX1/NaK co-localization interrupts the balance between NCX1 and NaK currents in a way that leads to enhanced depolarizing inward current during the action potential plateau, which ultimately leads to a higher probability of L-type Ca2+ channel reopening and arrhythmogenic early-afterdepolarizations.
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Affiliation(s)
- Lulu Chu
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD 21218, USA.
| | - Joseph L Greenstein
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD 21218, USA.
| | - Raimond L Winslow
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD 21218, USA.
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10
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van Opbergen CJ, van der Voorn SM, Vos MA, de Boer TP, van Veen TA. Cardiac Ca2+ signalling in zebrafish: Translation of findings to man. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2018; 138:45-58. [DOI: 10.1016/j.pbiomolbio.2018.05.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 04/09/2018] [Accepted: 05/04/2018] [Indexed: 02/07/2023]
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11
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Sutanto H, van Sloun B, Schönleitner P, van Zandvoort MAMJ, Antoons G, Heijman J. The Subcellular Distribution of Ryanodine Receptors and L-Type Ca 2+ Channels Modulates Ca 2+-Transient Properties and Spontaneous Ca 2+-Release Events in Atrial Cardiomyocytes. Front Physiol 2018; 9:1108. [PMID: 30166973 PMCID: PMC6107030 DOI: 10.3389/fphys.2018.01108] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Accepted: 07/23/2018] [Indexed: 11/13/2022] Open
Abstract
Spontaneous Ca2+-release events (SCaEs) from the sarcoplasmic reticulum play crucial roles in the initiation of cardiac arrhythmias by promoting triggered activity. However, the subcellular determinants of these SCaEs remain incompletely understood. Structural differences between atrial and ventricular cardiomyocytes, e.g., regarding the density of T-tubular membrane invaginations, may influence cardiomyocyte Ca2+-handling and the distribution of cardiac ryanodine receptors (RyR2) has recently been shown to undergo remodeling in atrial fibrillation. These data suggest that the subcellular distribution of Ca2+-handling proteins influences proarrhythmic Ca2+-handling abnormalities. Here, we employ computational modeling to provide an in-depth analysis of the impact of variations in subcellular RyR2 and L-type Ca2+-channel distributions on Ca2+-transient properties and SCaEs in a human atrial cardiomyocyte model. We incorporate experimentally observed RyR2 expression patterns and various configurations of axial tubules in a previously published model of the human atrial cardiomyocyte. We identify an increased SCaE incidence for larger heterogeneity in RyR2 expression, in which SCaEs preferentially arise from regions of high local RyR2 expression. Furthermore, we show that the propagation of Ca2+ waves is modulated by the distance between RyR2 bands, as well as the presence of experimentally observed RyR2 clusters between bands near the lateral membranes. We also show that incorporation of axial tubules in various amounts and locations reduces Ca2+-transient time to peak. Furthermore, selective hyperphosphorylation of RyR2 around axial tubules increases the number of spontaneous waves. Finally, we present a novel model of the human atrial cardiomyocyte with physiological RyR2 and L-type Ca2+-channel distributions that reproduces experimentally observed Ca2+-handling properties. Taken together, these results significantly enhance our understanding of the structure-function relationship in cardiomyocytes, identifying that RyR2 and L-type Ca2+-channel distributions have a major impact on systolic Ca2+ transients and SCaEs.
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Affiliation(s)
- Henry Sutanto
- Department of Cardiology, CARIM School for Cardiovascular Diseases, Maastricht University, Maastricht, Netherlands
| | - Bart van Sloun
- Department of Cardiology, CARIM School for Cardiovascular Diseases, Maastricht University, Maastricht, Netherlands
| | - Patrick Schönleitner
- Department of Physiology, CARIM School for Cardiovascular Diseases, Maastricht University, Maastricht, Netherlands
| | | | - Gudrun Antoons
- Department of Physiology, CARIM School for Cardiovascular Diseases, Maastricht University, Maastricht, Netherlands
| | - Jordi Heijman
- Department of Cardiology, CARIM School for Cardiovascular Diseases, Maastricht University, Maastricht, Netherlands
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12
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Different Densities of Na-Ca Exchange Current in T-Tubular and Surface Membranes and Their Impact on Cellular Activity in a Model of Rat Ventricular Cardiomyocyte. BIOMED RESEARCH INTERNATIONAL 2017; 2017:6343821. [PMID: 28321411 PMCID: PMC5340987 DOI: 10.1155/2017/6343821] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Revised: 12/18/2016] [Accepted: 01/04/2017] [Indexed: 01/13/2023]
Abstract
The ratio of densities of Na-Ca exchanger current (INaCa) in the t-tubular and surface membranes (INaCa-ratio) computed from the values of INaCa and membrane capacitances (Cm) measured in adult rat ventricular cardiomyocytes before and after detubulation ranges between 1.7 and 25 (potentially even 40). Variations of action potential waveform and of calcium turnover within this span of the INaCa-ratio were simulated employing previously developed model of rat ventricular cell incorporating separate description of ion transport systems in the t-tubular and surface membranes. The increase of INaCa-ratio from 1.7 to 25 caused a prolongation of APD (duration of action potential at 90% repolarisation) by 12, 9, and 6% and an increase of peak intracellular Ca2+ transient by 45, 19, and 6% at 0.1, 1, and 5 Hz, respectively. The prolonged APD resulted from the increase of INaCa due to the exposure of a larger fraction of Na-Ca exchangers to higher Ca2+ transients under the t-tubular membrane. The accompanying rise of Ca2+ transient was a consequence of a higher Ca2+ load in sarcoplasmic reticulum induced by the increased Ca2+ cycling between the surface and t-tubular membranes. However, the reason for large differences in the INaCa-ratio assessed from measurements in adult rat cardiomyocytes remains to be explained.
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13
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Revealing calcium fluxes by analyzing inhibition dynamics in action potential clamp. J Mol Cell Cardiol 2016; 100:93-108. [DOI: 10.1016/j.yjmcc.2016.08.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Revised: 07/19/2016] [Accepted: 08/22/2016] [Indexed: 11/29/2022]
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14
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Chu L, Greenstein JL, Winslow RL. Modeling Na +-Ca 2+ exchange in the heart: Allosteric activation, spatial localization, sparks and excitation-contraction coupling. J Mol Cell Cardiol 2016; 99:174-187. [PMID: 27377851 DOI: 10.1016/j.yjmcc.2016.06.068] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Revised: 06/14/2016] [Accepted: 06/30/2016] [Indexed: 01/19/2023]
Abstract
The cardiac sodium (Na+)/calcium (Ca2+) exchanger (NCX1) is an electrogenic membrane transporter that regulates Ca2+ homeostasis in cardiomyocytes, serving mainly to extrude Ca2+ during diastole. The direction of Ca2+ transport reverses at membrane potentials near that of the action potential plateau, generating an influx of Ca2+ into the cell. Therefore, there has been great interest in the possible roles of NCX1 in cardiac Ca2+-induced Ca2+ release (CICR). Interest has been reinvigorated by a recent super-resolution optical imaging study suggesting that ~18% of NCX1 co-localize with ryanodine receptor (RyR2) clusters, and ~30% of additional NCX1 are localized to within ~120nm of the nearest RyR2. NCX1 may therefore occupy a privileged position in which to modulate CICR. To examine this question, we have developed a mechanistic biophysically-detailed model of NCX1 that describes both NCX1 transport kinetics and Ca2+-dependent allosteric regulation. This NCX1 model was incorporated into a previously developed super-resolution model of the Ca2+ spark as well as a computational model of the cardiac ventricular myocyte that includes a detailed description of CICR with stochastic gating of L-type Ca2+ channels and RyR2s, and that accounts for local Ca2+ gradients near the dyad via inclusion of a peri-dyadic (PD) compartment. Both models predict that increasing the fraction of NCX1 in the dyad and PD decreases spark frequency, fidelity, and diastolic Ca2+ levels. Spark amplitude and duration are less sensitive to NCX1 spatial redistribution. On the other hand, NCX1 plays an important role in promoting Ca2+ entry into the dyad, and hence contributing to the trigger for RyR2 release at depolarized membrane potentials and in the presence of elevated local Na+ concentration. Whole-cell simulation of NCX1 tail currents are consistent with the finding that a relatively high fraction of NCX1 (~45%) resides in the dyadic and PD spaces, with a dyad-to-PD ratio of roughly 1:2. Allosteric Ca2+ activation of NCX1 helps to "functionally localize" exchanger activity to the dyad and PD by reducing exchanger activity in the cytosol thereby protecting the cell from excessive loss of Ca2+ during diastole.
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Affiliation(s)
- Lulu Chu
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD, 21218, USA.
| | - Joseph L Greenstein
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD, 21218, USA.
| | - Raimond L Winslow
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD, 21218, USA.
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15
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Spontaneous inward currents reflecting oscillatory activation of Na+/Ca2+ exchangers in human embryonic stem cell-derived cardiomyocytes. Pflugers Arch 2015; 468:609-22. [DOI: 10.1007/s00424-015-1769-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2015] [Revised: 11/30/2015] [Accepted: 12/03/2015] [Indexed: 11/25/2022]
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16
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Hiess F, Vallmitjana A, Wang R, Cheng H, ter Keurs HEDJ, Chen J, Hove-Madsen L, Benitez R, Chen SRW. Distribution and Function of Cardiac Ryanodine Receptor Clusters in Live Ventricular Myocytes. J Biol Chem 2015; 290:20477-87. [PMID: 26109063 DOI: 10.1074/jbc.m115.650531] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2015] [Indexed: 11/06/2022] Open
Abstract
The cardiac Ca(2+) release channel (ryanodine receptor, RyR2) plays an essential role in excitation-contraction coupling in cardiac muscle cells. Effective and stable excitation-contraction coupling critically depends not only on the expression of RyR2, but also on its distribution. Despite its importance, little is known about the distribution and organization of RyR2 in living cells. To study the distribution of RyR2 in living cardiomyocytes, we generated a knock-in mouse model expressing a GFP-tagged RyR2 (GFP-RyR2). Confocal imaging of live ventricular myocytes isolated from the GFP-RyR2 mouse heart revealed clusters of GFP-RyR2 organized in rows with a striated pattern. Similar organization of GFP-RyR2 clusters was observed in fixed ventricular myocytes. Immunofluorescence staining with the anti-α-actinin antibody (a z-line marker) showed that nearly all GFP-RyR2 clusters were localized in the z-line zone. There were small regions with dislocated GFP-RyR2 clusters. Interestingly, these same regions also displayed dislocated z-lines. Staining with di-8-ANEPPS revealed that nearly all GFP-RyR2 clusters were co-localized with transverse but not longitudinal tubules, whereas staining with MitoTracker Red showed that GFP-RyR2 clusters were not co-localized with mitochondria in live ventricular myocytes. We also found GFP-RyR2 clusters interspersed between z-lines only at the periphery of live ventricular myocytes. Simultaneous detection of GFP-RyR2 clusters and Ca(2+) sparks showed that Ca(2+) sparks originated exclusively from RyR2 clusters. Ca(2+) sparks from RyR2 clusters induced no detectable changes in mitochondrial Ca(2+) level. These results reveal, for the first time, the distribution of RyR2 clusters and its functional correlation in living ventricular myocytes.
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Affiliation(s)
- Florian Hiess
- From the Libin Cardiovascular Institute of Alberta, Department of Physiology and Pharmacology and
| | - Alexander Vallmitjana
- the Department of Automatic Control, Universitat Politècnica de Catalunya, 08034 Barcelona, Spain
| | - Ruiwu Wang
- From the Libin Cardiovascular Institute of Alberta, Department of Physiology and Pharmacology and
| | - Hongqiang Cheng
- the Department of Medicine, University of California at San Diego, La Jolla, California 92161, and
| | - Henk E D J ter Keurs
- the Libin Cardiovascular Institute of Alberta, Department of Cardiac Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada
| | - Ju Chen
- the Department of Medicine, University of California at San Diego, La Jolla, California 92161, and
| | - Leif Hove-Madsen
- the Cardiovascular Research Centre CSIC-ICCC, Hospital de Sant Pau, 08025 Barcelona, Spain
| | - Raul Benitez
- the Department of Automatic Control, Universitat Politècnica de Catalunya, 08034 Barcelona, Spain
| | - S R Wayne Chen
- From the Libin Cardiovascular Institute of Alberta, Department of Physiology and Pharmacology and
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17
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Birkedal R, Laasmaa M, Vendelin M. The location of energetic compartments affects energetic communication in cardiomyocytes. Front Physiol 2014; 5:376. [PMID: 25324784 PMCID: PMC4178378 DOI: 10.3389/fphys.2014.00376] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Accepted: 09/10/2014] [Indexed: 01/08/2023] Open
Abstract
The heart relies on accurate regulation of mitochondrial energy supply to match energy demand. The main regulators are Ca2+ and feedback of ADP and Pi. Regulation via feedback has intrigued for decades. First, the heart exhibits a remarkable metabolic stability. Second, diffusion of ADP and other molecules is restricted specifically in heart and red muscle, where a fast feedback is needed the most. To explain the regulation by feedback, compartmentalization must be taken into account. Experiments and theoretical approaches suggest that cardiomyocyte energetic compartmentalization is elaborate with barriers obstructing diffusion in the cytosol and at the level of the mitochondrial outer membrane (MOM). A recent study suggests the barriers are organized in a lattice with dimensions in agreement with those of intracellular structures. Here, we discuss the possible location of these barriers. The more plausible scenario includes a barrier at the level of MOM. Much research has focused on how the permeability of MOM itself is regulated, and the importance of the creatine kinase system to facilitate energetic communication. We hypothesize that at least part of the diffusion restriction at the MOM level is not by MOM itself, but due to the close physical association between the sarcoplasmic reticulum (SR) and mitochondria. This will explain why animals with a disabled creatine kinase system exhibit rather mild phenotype modifications. Mitochondria are hubs of energetics, but also ROS production and signaling. The close association between SR and mitochondria may form a diffusion barrier to ADP added outside a permeabilized cardiomyocyte. But in vivo, it is the structural basis for the mitochondrial-SR coupling that is crucial for the regulation of mitochondrial Ca2+-transients to regulate energetics, and for avoiding Ca2+-overload and irreversible opening of the mitochondrial permeability transition pore.
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Affiliation(s)
- Rikke Birkedal
- Laboratory of Systems Biology, Institute of Cybernetics, Tallinn University of Technology Tallinn, Estonia
| | - Martin Laasmaa
- Laboratory of Systems Biology, Institute of Cybernetics, Tallinn University of Technology Tallinn, Estonia
| | - Marko Vendelin
- Laboratory of Systems Biology, Institute of Cybernetics, Tallinn University of Technology Tallinn, Estonia
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18
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Aronsen JM, Swift F, Sejersted OM. Cardiac sodium transport and excitation-contraction coupling. J Mol Cell Cardiol 2013; 61:11-9. [PMID: 23774049 DOI: 10.1016/j.yjmcc.2013.06.003] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Revised: 05/17/2013] [Accepted: 06/05/2013] [Indexed: 01/12/2023]
Abstract
The excitation-contraction coupling (EC-coupling) links membrane depolarization with contraction in cardiomyocytes. Ca(2+) induced opening of ryanodine receptors (RyRs) leads to Ca(2+) induced Ca(2+) release (CICR) from the sarcoplasmic reticulum (SR) into the dyadic cleft between the t-tubules and SR. Ca(2+) is removed from the cytosol by the SR Ca(2+) ATPase (SERCA2) and the Na,Ca-exchanger (NCX). The NCX connects cardiac Ca(2+) and Na(+)-transport, leading to Na(+)-dependent regulation of EC-coupling by several mechanisms of which some still lack firm experimental evidence. Firstly, NCX might contribute to CICR during an action potential (AP) as Na(+)-accumulation at the intracellular site together with depolarization will trigger reverse mode exchange bringing Ca(2+) into the dyadic cleft. The controversial issue is the nature of the compartment in which Na(+) accumulates. It seems not to be the bulk cytosol, but is it part of a widespread subsarcolemmal space, a localized microdomain ("fuzzy space"), or as we propose, a more localized "spot" to which only a few membrane proteins have shared access (nanodomains)? Also, there seems to be spots where the Na,K-pump (NKA) will cause local Na(+) depletion. Secondly, Na(+) determines the rate of cytosolic Ca(2+) removal and SR Ca(2+) load by regulating the SERCA2/NCX-balance during the decay of the Ca(2+) transient. The aim of this review is to describe available data and current concepts of Na(+)-mediated regulation of cardiac EC-coupling, with special focus on subcellular microdomains and the potential roles of Na(+) transport proteins in regulating CICR and Ca(2+) extrusion in cardiomyocytes. We propose that voltage gated Na(+) channels, NCX and the NKA α2-isoform all regulate cardiac EC-coupling through control of the "Na(+) concentration in specific subcellular nanodomains in cardiomyocytes. This article is part of a Special Issue entitled "Na(+) Regulation in Cardiac Myocytes."
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Affiliation(s)
- J M Aronsen
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo, Oslo, Norway
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19
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Ottolia M, Torres N, Bridge JHB, Philipson KD, Goldhaber JI. Na/Ca exchange and contraction of the heart. J Mol Cell Cardiol 2013; 61:28-33. [PMID: 23770352 DOI: 10.1016/j.yjmcc.2013.06.001] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2013] [Revised: 05/30/2013] [Accepted: 06/04/2013] [Indexed: 12/19/2022]
Abstract
Sodium-calcium exchange (NCX) is the major calcium (Ca) efflux mechanism of ventricular cardiomyocytes. Consequently the exchanger plays a critical role in the regulation of cellular Ca content and hence contractility. Reductions in Ca efflux by the exchanger, such as those produced by elevated intracellular sodium (Na) in response to cardiac glycosides, raise sarcoplasmic reticulum (SR) Ca stores. The result is an increased Ca transient and cardiac contractility. Enhanced Ca efflux activity by the exchanger, for example during heart failure, may reduce diadic cleft Ca and excitation-contraction (EC) coupling gain. This aggravates the impaired contractility associated with SR Ca ATPase dysfunction and reduced SR Ca load in failing heart muscle. Recent data from our laboratories indicate that NCX can also impact the efficiency of EC coupling and contractility independent of SR Ca load through diadic cleft priming with Ca during the upstroke of the action potential. This article is part of a Special Issue entitled "Na(+) Regulation in Cardiac Myocytes".
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Affiliation(s)
- Michela Ottolia
- Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA
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20
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Abstract
Ca(2+) waves were probably first observed in the early 1940s. Since then Ca(2+) waves have captured the attention of an eclectic mixture of mathematicians, neuroscientists, muscle physiologists, developmental biologists, and clinical cardiologists. This review discusses the current state of mathematical models of Ca(2+) waves, the normal physiological functions Ca(2+) waves might serve in cardiac cells, as well as how the spatial arrangement of Ca(2+) release channels shape Ca(2+) waves, and we introduce the idea of Ca(2+) phase waves that might provide a useful framework for understanding triggered arrhythmias.
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Affiliation(s)
- Leighton T Izu
- Department of Pharmacology, University of California, Davis, USA.
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21
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Ca2+ channel and Na+/Ca2+ exchange localization in cardiac myocytes. J Mol Cell Cardiol 2013; 58:22-31. [DOI: 10.1016/j.yjmcc.2012.11.022] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2012] [Revised: 11/20/2012] [Accepted: 11/28/2012] [Indexed: 01/01/2023]
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22
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Ginsburg KS, Weber CR, Bers DM. Cardiac Na+-Ca2+ exchanger: dynamics of Ca2+-dependent activation and deactivation in intact myocytes. J Physiol 2013; 591:2067-86. [PMID: 23401616 PMCID: PMC3634520 DOI: 10.1113/jphysiol.2013.252080] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Accepted: 02/10/2013] [Indexed: 01/05/2023] Open
Abstract
Cardiac Na(+)-Ca(2+) exchange (NCX) activity is regulated by [Ca(2+)]i. The physiological role and dynamics of this process in intact cardiomyocytes are largely unknown. We examined NCX Ca(2+) activation in intact rabbit and mouse cardiomyocytes at 37°C. Sarcoplasmic reticulum (SR) function was blocked, and cells were bathed in 2 mm Ca(2+). We probed Ca(2+) activation without voltage clamp by applying Na(+)-free (0 Na(+)) solution for 5 s bouts, repeated each 10 s, which should evoke [Ca(2+)]i transients due to Ca(2+) influx via NCX. In rested rabbit myocytes, Ca(2+) influx was undetectable even after 0 Na(+) applications were repeated for 2-5 min or more, suggesting that NCX was inactive. After external electric field stimulation pulses were applied, to admit Ca(2+) via L-type Ca(2+) channels, 0 Na(+) bouts activated Ca(2+) influx efficaciously, indicating that NCX had become active. Calcium activation increased with more field pulses, reaching a maximum typically after 15-20 pulses (1 Hz). At rest, NCX deactivated with a time constant typically of 20-40 s. An increase in [Na(+)]i, either in rabbit cardiomyocytes as a result of inhibition of Na(+)-K(+) pumping, or in mouse cardiomyocytes where normal [Na(+)]i is higher vs. rabbit, sensitized NCX to self-activation by 0 Na(+) bouts. In experiments with the SR functional but initially empty, the activation time course was slowed. It is possible that the SR initially accumulated Ca(2+) that would otherwise cause activation. We modelled Ca(2+) activation as a fourth-order highly co-operative process ([Ca]i required for half-activation K0.5act = 375 nm), with dynamics severalfold slower than the cardiac cycle. We incorporated this NCX model into an established ventricular myocyte model, which allowed us to predict responses to twitch stimulation in physiological conditions with the SR intact. Model NCX fractional activation increased from 0.1 to 1.0 as the frequency was increased from 0.2 to 2 Hz. By adjusting Ca(2+) activation on a multibeat time scale, NCX might better maintain a stable long-term Ca(2+) balance while contributing to the ability of myocytes to produce Ca(2+) transients over a wide range of intensity.
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Affiliation(s)
- Kenneth S Ginsburg
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
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23
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24
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Kekenes-Huskey PM, Cheng Y, Hake JE, Sachse FB, Bridge JH, Holst MJ, McCammon JA, McCulloch AD, Michailova AP. Modeling effects of L-type ca(2+) current and na(+)-ca(2+) exchanger on ca(2+) trigger flux in rabbit myocytes with realistic T-tubule geometries. Front Physiol 2012; 3:351. [PMID: 23060801 PMCID: PMC3463892 DOI: 10.3389/fphys.2012.00351] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Accepted: 08/16/2012] [Indexed: 12/26/2022] Open
Abstract
The transverse tubular system of rabbit ventricular myocytes consists of cell membrane invaginations (t-tubules) that are essential for efficient cardiac excitation-contraction coupling. In this study, we investigate how t-tubule micro-anatomy, L-type Ca2+ channel (LCC) clustering, and allosteric activation of Na+/Ca2+ exchanger by L-type Ca2+ current affects intracellular Ca2+ dynamics. Our model includes a realistic 3D geometry of a single t-tubule and its surrounding half-sarcomeres for rabbit ventricular myocytes. The effects of spatially distributed membrane ion-transporters (LCC, Na+/Ca2+ exchanger, sarcolemmal Ca2+ pump, and sarcolemmal Ca2+ leak), and stationary and mobile Ca2+ buffers (troponin C, ATP, calmodulin, and Fluo-3) are also considered. We used a coupled reaction-diffusion system to describe the spatio-temporal concentration profiles of free and buffered intracellular Ca2+. We obtained parameters from voltage-clamp protocols of L-type Ca2+ current and line-scan recordings of Ca2+ concentration profiles in rabbit cells, in which the sarcoplasmic reticulum is disabled. Our model results agree with experimental measurements of global Ca2+ transient in myocytes loaded with 50 μM Fluo-3. We found that local Ca2+ concentrations within the cytosol and sub-sarcolemma, as well as the local trigger fluxes of Ca2+ crossing the cell membrane, are sensitive to details of t-tubule micro-structure and membrane Ca2+ flux distribution. The model additionally predicts that local Ca2+ trigger fluxes are at least threefold to eightfold higher than the whole-cell Ca2+ trigger flux. We found also that the activation of allosteric Ca2+-binding sites on the Na+/Ca2+ exchanger could provide a mechanism for regulating global and local Ca2+ trigger fluxes in vivo. Our studies indicate that improved structural and functional models could improve our understanding of the contributions of L-type and Na+/Ca2+ exchanger fluxes to intracellular Ca2+ dynamics.
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25
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Abd Allah ES, Aslanidi OV, Tellez JO, Yanni J, Billeter R, Zhang H, Dobrzynski H, Boyett MR. Postnatal development of transmural gradients in expression of ion channels and Ca2+-handling proteins in the ventricle. J Mol Cell Cardiol 2012; 53:145-55. [DOI: 10.1016/j.yjmcc.2012.04.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2011] [Revised: 03/06/2012] [Accepted: 04/06/2012] [Indexed: 01/30/2023]
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26
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Schulson MN, Scriven DRL, Fletcher P, Moore EDW. Couplons in rat atria form distinct subgroups defined by their molecular partners. J Cell Sci 2011; 124:1167-74. [PMID: 21385843 DOI: 10.1242/jcs.080929] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Standard local control theory, which describes Ca(2+) release during excitation-contraction coupling (ECC), assumes that all ryanodine receptor 2 (RyR2) complexes are equivalent. Findings from our laboratory have called this assumption into question. Specifically, we have shown that the RyR2 complexes in ventricular myocytes are different, depending on their location within the cell. This has led us to hypothesize that similar differences occur within the rat atrial cell. To test this hypothesis, we have triple-labelled enzymatically isolated fixed myocytes to examine the distribution and colocalization of RyR2, calsequestrin (Casq), voltage-gated Ca(2+) channels (Ca(v)1.2), the sodium-calcium exchanger (Ncx) and caveolin-3 (Cav3). A number of different surface RyR2 populations were identified, and one of these groups, in which RyR2, Ca(v)1.2 and Ncx colocalized, might provide the structural basis for 'eager' sites of Ca(2+) release in atria. A small percentage of the dyads containing RyR2 and Ca(v)1.2 were colocalized with Cav3, and therefore could be influenced by the signalling molecules it anchors. The majority of the RyR2 clusters were tightly linked to Ca(v)1.2, and, whereas some were coupled to both Ca 1.2 and Ncx, none were with Ncx alone. This suggests that Ca(v)1.2-mediated Ca(2+) -induced Ca(2+) release is the primary method of ECC. The two molecules studied that were found in the interior of atrial cells, RyR2 and Casq, showed significantly less colocalization and a reduced nearest-neighbour distance in the interior, compared with the surface of the cell. These differences might result in a higher excitability for RyR2 in the interior of the cells, facilitating the spread of excitation from the periphery to the centre. We also present morphometric data for all of the molecules studied, as well as for those colocalizations found to be significant.
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Affiliation(s)
- Meredith N Schulson
- Department of Cellular and Physiological Sciences, University of British Columbia, Life Sciences Institute, 2350 Health Sciences Mall, Vancouver, BC V6T 1Z3, Canada
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27
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Allah EA, Tellez JO, Yanni J, Nelson T, Monfredi O, Boyett MR, Dobrzynski H. Changes in the expression of ion channels, connexins and Ca2+-handling proteins in the sino-atrial node during postnatal development. Exp Physiol 2011; 96:426-38. [DOI: 10.1113/expphysiol.2010.055780] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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28
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Gershome C, Lin E, Kashihara H, Hove-Madsen L, Tibbits GF. Colocalization of voltage-gated Na+ channels with the Na+/Ca2+ exchanger in rabbit cardiomyocytes during development. Am J Physiol Heart Circ Physiol 2011; 300:H300-11. [DOI: 10.1152/ajpheart.00798.2010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Reverse-mode activity of the Na+/Ca2+ exchanger (NCX) has been previously shown to play a prominent role in excitation-contraction coupling in the neonatal rabbit heart, where we have proposed that a restricted subsarcolemmal domain allows a Na+ current to cause an elevation in the Na+ concentration sufficiently large to bring Ca2+ into the myocyte through reverse-mode NCX. In the present study, we tested the hypothesis that there is an overlapping expression and distribution of voltage-gated Na+ (Nav) channel isoforms and the NCX in the neonatal heart. For this purpose, Western blot analysis, immunocytochemistry, confocal microscopy, and image analyses were used. Here, we report the robust expression of skeletal Nav1.4 and cardiac Nav1.5 in neonatal myocytes. Both isoforms colocalized with the NCX, and Nav1.5-NCX colocalization was not statistically different from Nav1.4-NCX colocalization in the neonatal group. Western blot analysis also showed that Nav1.4 expression decreased by sixfold in the adult ( P < 0.01) and Nav1.1 expression decreased by ninefold ( P < 0.01), whereas Nav1.5 expression did not change. Although Nav1.4 underwent large changes in expression levels, the Nav1.4-NCX colocalization relationship did not change with age. In contrast, Nav1.5-NCX colocalization decreased ∼50% with development. Distance analysis indicated that the decrease in Nav1.5-NCX colocalization occurs due to a statistically significant increase in separation distances between Nav1.5 and NCX objects. Taken together, the robust expression of both Nav1.4 and Nav1.5 isoforms and their colocalization with the NCX in the neonatal heart provides structural support for Na+ current-induced Ca2+ entry through reverse-mode NCX. In contrast, this mechanism is likely less efficient in the adult heart because the expression of Nav1.4 and NCX is lower and the separation distance between Nav1.5 and NCX is larger.
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Affiliation(s)
- Cynthia Gershome
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby
- Child and Family Research Institute, Vancouver, British Columbia, Canada; and
| | - Eric Lin
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby
- Child and Family Research Institute, Vancouver, British Columbia, Canada; and
| | - Haruyo Kashihara
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby
- Child and Family Research Institute, Vancouver, British Columbia, Canada; and
| | - Leif Hove-Madsen
- Centro de Investigación Cardiovascular CSIC-ICCC, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
| | - Glen F. Tibbits
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby
- Child and Family Research Institute, Vancouver, British Columbia, Canada; and
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Fu JD, Jiang P, Rushing S, Liu J, Chiamvimonvat N, Li RA. Na+/Ca2+ exchanger is a determinant of excitation-contraction coupling in human embryonic stem cell-derived ventricular cardiomyocytes. Stem Cells Dev 2010; 19:773-82. [PMID: 19719399 DOI: 10.1089/scd.2009.0184] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In adult cardiomyocytes (CMs), the Na(+)/Ca(2+) exchanger (NCX) is a well-defined determinant of Ca(2+) homeostasis. Developmentally, global NCX knockout in mice leads to abnormal myofibrillar organization, electrical defects, and early embryonic death. Little is known about the expression and function of NCX in human heart development. Self-renewable, pluripotent human embryonic stem cells (hESCs) can serve as an excellent experimental model. However, hESC-derived CMs are highly heterogeneous. A stably lentivirus-transduced hESC line (MLC2v-dsRed) was generated to express dsRed under the transcriptional control of the ventricular-restricted myosin light chain-2v (MLC2v) promoter. Electrophysiologically, dsRed+ cells differentiated from MLC2vdsRed hESCs displayed ventricular action potentials (AP), exclusively. Neither atrial nor pacemaker APs were observed. While I(Ca-L), I(f), and I(Kr) were robustly expressed, I(Ks) and I(K1) were absent in dsRed+ ventricular hESCCMs. Upon differentiation (7+40 to +90 days), the basal [Ca(2+)](i), Ca(2+) transient amplitude, maximum upstroke, and decay velocities significantly increased (P < 0.05). The I(Ca-L) antagonizer nifedipine (1 microM) decreased the Ca(2+) transient amplitude (to approximately 30%) and slowed the kinetics (by approximately 2-fold), but Ca(2+) transients could still be elicited even after complete ICa-L blockade, suggesting the presence of additional Ca(2+) influx(es). Indeed, Ni(2+)-sensitive INCX could be recorded in 7+40- and +90-day dsRed+ hESC-CMs, and its densities increased from -1.2 +/- 0.6 pA/pF at -120 mV and 3.6 +/- 1.0 pA/pF at 60 mV by 6- and 2-folds, respectively. With higher [Ca(2+)](i), 7+90-day ventricular hESC-CMs spontaneously but irregularly fired transients upon a single stimulus under an external Na(+)-free condition; however, without extracellular Na(+), nifedipine could completely inhibit Ca(2+) transients. We conclude that I(NCX) is functionally expressed in developing ventricular hESC-CMs and contributes to their excitation-contraction coupling.
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Affiliation(s)
- Ji-Dong Fu
- Human Embryonic Stem Cell Consortium, University of California, Davis, California, USA
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Zahradníková A, Valent I, Zahradník I. Frequency and release flux of calcium sparks in rat cardiac myocytes: a relation to RYR gating. ACTA ACUST UNITED AC 2010; 136:101-16. [PMID: 20548054 PMCID: PMC2894546 DOI: 10.1085/jgp.200910380] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cytosolic calcium concentration in resting cardiac myocytes locally fluctuates as a result of spontaneous microscopic Ca2+ releases or abruptly rises as a result of an external trigger. These processes, observed as calcium sparks, are fundamental for proper function of cardiac muscle. In this study, we analyze how the characteristics of spontaneous and triggered calcium sparks are related to cardiac ryanodine receptor (RYR) gating. We show that the frequency of spontaneous sparks and the probability distribution of calcium release flux quanta of triggered sparks correspond quantitatively to predictions of an allosteric homotetrameric model of RYR gating. This model includes competitive binding of Ca2+ and Mg2+ ions to the RYR activation sites and allosteric interaction between divalent ion binding and channel opening. It turns out that at rest, RYRs are almost fully occupied by Mg2+. Therefore, spontaneous sparks are most frequently evoked by random openings of the highly populated but rarely opening Mg4RYR and CaMg3RYR forms, whereas triggered sparks are most frequently evoked by random openings of the less populated but much more readily opening Ca2Mg2RYR and Ca3MgRYR forms. In both the spontaneous and the triggered sparks, only a small fraction of RYRs in the calcium release unit manages to open during the spark because of the limited rate of Mg2+ unbinding. This mechanism clarifies the unexpectedly low calcium release flux during elementary release events and unifies the theory of calcium signaling in resting and contracting cardiac myocytes.
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Affiliation(s)
- Alexandra Zahradníková
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic.
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31
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Sokolova N, Vendelin M, Birkedal R. Intracellular diffusion restrictions in isolated cardiomyocytes from rainbow trout. BMC Cell Biol 2009; 10:90. [PMID: 20017912 PMCID: PMC2806299 DOI: 10.1186/1471-2121-10-90] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2009] [Accepted: 12/17/2009] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Restriction of intracellular diffusion of adenine nucleotides has been studied intensively on adult rat cardiomyocytes. However, their cause and role in vivo is still uncertain. Intracellular membrane structures have been suggested to play a role. We therefore chose to study cardiomyocytes from rainbow trout (Oncorhynchus mykiss), which are thinner and have fewer intracellular membrane structures than adult rat cardiomyocytes. Previous studies suggest that trout permeabilized cardiac fibers also have diffusion restrictions. However, results from fibers may be affected by incomplete separation of the cells. This is avoided when studying permeabilized, isolated cardiomyocytes. The aim of this study was to verify the existence of diffusion restrictions in trout cardiomyocytes by comparing ADP-kinetics of mitochondrial respiration in permeabilized fibers, permeabilized cardiomyocytes and isolated mitochondria from rainbow trout heart. Experiments were performed at 10, 15 and 20 degrees C in the absence and presence of creatine. RESULTS Trout cardiomyocytes hypercontracted in the solutions used for mammalian cardiomyocytes. We developed a new solution in which they retained their shape and showed stable steady state respiration rates throughout an experiment. The apparent ADP-affinity of permeabilized cardiomyocytes was different from that of fibers. It was higher, independent of temperature and not increased by creatine. However, it was still about ten times lower than in isolated mitochondria. CONCLUSIONS The differences between fibers and cardiomyocytes suggest that results from trout heart fibers were affected by incomplete separation of the cells. However, the lower ADP-affinity of cardiomyocytes compared to isolated mitochondria indicate that intracellular diffusion restrictions are still present in trout cardiomyocytes despite their lower density of intracellular membrane structures. The lack of a creatine effect indicates that trout heart lacks mitochondrial creatine kinase tightly coupled to respiration. This argues against diffusion restriction by the outer mitochondrial membrane. These results from rainbow trout cardiomyocytes resemble those from other low-performance hearts such as neonatal rat and rabbit hearts. Thus, it seems that metabolic regulation is related to cardiac performance, and it is likely that rainbow trout can be used as a model animal for further studies of the localization and role of diffusion restrictions in low-performance hearts.
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Affiliation(s)
- Niina Sokolova
- Laboratory of Systems Biology, Institute of Cybernetics, Tallinn University of Technology, Akadeemia 21, 12618 Tallinn, Estonia.
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32
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Birkedal R, Christopher J, Thistlethwaite A, Shiels HA. Temperature acclimation has no effect on ryanodine receptor expression or subcellular localization in rainbow trout heart. J Comp Physiol B 2009; 179:961-9. [DOI: 10.1007/s00360-009-0377-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2009] [Revised: 05/29/2009] [Accepted: 06/02/2009] [Indexed: 11/30/2022]
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Homer and the ryanodine receptor. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:91-102. [PMID: 19513708 DOI: 10.1007/s00249-009-0494-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2009] [Revised: 05/15/2009] [Accepted: 05/18/2009] [Indexed: 10/20/2022]
Abstract
Homer proteins have recently been identified as novel high-affinity ligands that modulate ryanodine receptor (RyR) Ca(2+) release channels in heart and skeletal muscle, through an EVH1 domain which binds to proline-rich regions in target proteins. Many Homer proteins can also self-associate through a coiled-coil domain that allows their multimerisation. In other tissues, especially neurons, Homer anchors proteins embedded in the surface membrane to the Ca(2+) release channel in the endoplasmic reticulum and can anchor membrane or cytosolic proteins to the cytoskeleton. Although this anchoring aspect of Homer function has not been extensively investigated in muscle, there are consensus sequences for Homer binding in the RyR and on many of the proteins that it interacts with in the massive RyR ion channel complex. In this review we explore the potential of Homer to contribute to a variety of cell processes in muscle and neurons that also involve RyR channels.
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Wiegerinck RF, Cojoc A, Zeidenweber CM, Ding G, Shen M, Joyner RW, Fernandez JD, Kanter KR, Kirshbom PM, Kogon BE, Wagner MB. Force frequency relationship of the human ventricle increases during early postnatal development. Pediatr Res 2009; 65:414-9. [PMID: 19127223 PMCID: PMC2788428 DOI: 10.1203/pdr.0b013e318199093c] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Understanding developmental changes in contractility is critical to improving therapies for young cardiac patients. Isometric developed force was measured in human ventricular muscle strips from two age groups: newborns (<2 wk) and infants (3-14 mo) undergoing repair for congenital heart defects. Muscle strips were paced at several cycle lengths (CLs) to determine the force frequency response (FFR). Changes in Na/Ca exchanger (NCX), sarcoplasmic reticulum Ca-ATPase (SERCA), and phospholamban (PLB) were characterized. At CL 2000 ms, developed force was similar in the two groups. Decreasing CL increased developed force in the infant group to 131 +/- 8% (CL 1000 ms) and 157 +/- 18% (CL 500 ms) demonstrating a positive FFR. The FFR in the newborn group was flat. NCX mRNA and protein levels were significantly larger in the newborn than infant group whereas SERCA levels were unchanged. PLB mRNA levels and PLB/SERCA ratio increased with age. Immunostaining for NCX in isolated newborn cells showed peripheral staining. In infant cells, NCX was also found in T-tubules. SERCA staining was regular and striated in both groups. This study shows for the first time that the newborn human ventricle has a flat FFR, which increases with age and may be caused by developmental changes in calcium handling.
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Affiliation(s)
- Rob F Wiegerinck
- Department of Pediatrics, Emory University, Atlanta, Georgia 30322, USA
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35
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Lin E, Hung VHY, Kashihara H, Dan P, Tibbits GF. Distribution patterns of the Na+-Ca2+ exchanger and caveolin-3 in developing rabbit cardiomyocytes. Cell Calcium 2009; 45:369-83. [PMID: 19250668 DOI: 10.1016/j.ceca.2009.01.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2008] [Revised: 11/21/2008] [Accepted: 01/08/2009] [Indexed: 11/26/2022]
Abstract
In adult cardiac cells the established mechanism of excitation-contraction coupling is by calcium-induced calcium release (CICR) mediated by L-type Ca(2+) channels. However, in neonate cardiomyocytes, a CICR modality involving reverse mode Na(+)-Ca(2+) exchanger (NCX) activity predominates. This has been hypothesized to be due, in part, to the high expression levels of NCX in the neonate heart which drop several fold during ontogeny. Very little is known about the nature of NCX distribution within the cardiomyocyte and how this might change with development given the significant differences in gene expression. We investigated the spatial arrangements of NCX in developing rabbit ventricular myocytes with traditional as well as novel image processing and analysis techniques. Using image segmentation, colocalization analysis was conducted at the whole cell, compartmental (cell periphery and cell interior) and object levels. Because NCX has been suggested to colocalize with caveolin-3 (cav-3) and perhaps form a signaling unit within caveolae, the spatial relationship of NCX relative to cav-3 was also examined in detail. NCX and cav-3 objects were found to be isolated islands of lit voxels that are present after thresholding. These objects were categorized into non-colocalized (0%), lowly colocalized (<50%) and highly colocalized (>50%) subpopulations in both the interior and peripheral compartments. Our results show that NCX and cav-3 are distributed on the peripheral membrane as discrete objects and are not highly colocalized throughout development. 3D distance analysis revealed that NCX and cav-3 objects are organized with a longitudinal and lateral periodicity of about 1mum and that NCX and cav-3 cluster appear to be mutually exclusive on the cell periphery. We conclude that despite the very significant decrease in NCX expression with maturation, qualitatively there were no differences in NCX surface distribution or in the spatial relationship to caveolin 3.
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Affiliation(s)
- Eric Lin
- Molecular Cardiac Physiology Group, Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
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36
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Wang LJ, Sobie EA. Mathematical model of the neonatal mouse ventricular action potential. Am J Physiol Heart Circ Physiol 2008; 294:H2565-75. [PMID: 18408122 DOI: 10.1152/ajpheart.01376.2007] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Therapies for heart disease are based largely on our understanding of the adult myocardium. The dramatic differences in action potential (AP) shape between neonatal and adult cardiac myocytes, however, indicate that a different set of molecular interactions in neonatal myocytes necessitates different treatment for newborns. Computational modeling is useful for synthesizing data to determine how interactions between components lead to systems-level behavior, but this technique has not been used extensively to study neonatal heart cell function. We created a mathematical model of the neonatal (day 1) mouse myocyte by modifying, on the basis of experimental data, the densities and/or formulations of ion transport mechanisms in an adult cell model. The new model reproduces the characteristic AP shape of neonatal cells, with a brief plateau phase and longer duration than the adult (action potential duration at 80% repolarization = 60.1 vs. 12.6 ms). The simulation results are consistent with experimental data, including 1) decreased density and altered inactivation of transient outward K+ currents, 2) increased delayed rectifier K+ currents, 3) Ca2+ entry through T-type as well as L-type Ca2+ channels, 4) increased Ca2+ influx through Na+/Ca2+ exchange, and 5) Ca2+ transients resulting from transmembrane Ca2+ entry rather than release from the sarcoplasmic reticulum (SR). Simulations performed with the model generated novel predictions, including increased SR Ca2+ leak and elevated intracellular Na+ concentration in neonatal compared with adult myocytes. This new model can therefore be used for testing hypotheses and obtaining a better quantitative understanding of differences between neonatal and adult physiology.
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Affiliation(s)
- Linda J Wang
- Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, New York, USA
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37
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Scriven DRL, Lynch RM, Moore EDW. Image acquisition for colocalization using optical microscopy. Am J Physiol Cell Physiol 2008; 294:C1119-22. [PMID: 18353895 DOI: 10.1152/ajpcell.00133.2008] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Colocalization, in which images of two or more fluorescent markers are overlaid, and coincidence between the probes is measured or displayed, is a common analytical tool in cell biology. Interpreting the images and the meaning of this identified coincidence is difficult in the absence of basic information about the acquisition parameters. In this commentary, we highlight important factors in the acquisition of images used to demonstrate colocalization, and we discuss the minimum information that authors should include in a manuscript so that a reader can interpret both the fluorescent images and any observed colocalization.
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Affiliation(s)
- David R L Scriven
- Department of Cellular and Physiological Sciences, University of British Columbia, Life Sciences Institute, Vancouver, British Columbia, Canada
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38
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Huang J, Hove-Madsen L, Tibbits GF. Ontogeny of Ca2+-induced Ca2+ release in rabbit ventricular myocytes. Am J Physiol Cell Physiol 2007; 294:C516-25. [PMID: 18094144 DOI: 10.1152/ajpcell.00417.2007] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It is commonly accepted that L-type Ca(2+) channel-mediated Ca(2+)-induced Ca(2+) release (CICR) is the dominant mode of excitation-contraction (E-C) coupling in the adult mammalian heart and that there is no appreciable CICR in neonates. However, we have observed that cell contraction in the neonatal heart was significantly decreased after sarcoplasmic reticulum (SR) Ca(2+) depletion with caffeine. Therefore, the present study investigated the developmental changes of CICR in rabbit ventricular myocytes at 3, 10, 20, and 56 days of age. We found that the inhibitory effect of the L-type Ca(2+) current (I(Ca)) inhibitor nifedipine (Nif; 15 microM) caused an increasingly larger reduction of Ca(2+) transients on depolarization in older age groups [from approximately 15% in 3-day-old (3d) myocytes to approximately 90% in 56-day-old (56d) myocytes]. The remaining Ca(2+) transient in the presence of Nif in younger age groups was eliminated by the inhibition of Na(+)/Ca(2+) exchanger (NCX) with the subsequent addition of 10 microM KB-R7943 (KB-R). Furthermore, Ca(2+) transients were significantly reduced in magnitude after the depletion of SR Ca(2+) with caffeine in all age groups, although the effect was significantly greater in the older age groups (from approximately 40% in 3d myocytes up to approximately 70% in 56d myocytes). This SR Ca(2+)-sensitive Ca(2+) transient in the earliest developmental stage was insensitive to Nif but was sensitive to the subsequent addition of KB-R, indicating the presence of NCX-mediated CICR that decreased significantly with age (from approximately 37% in 3d myocytes to approximately 0.5% in 56d myocytes). In contrast, the I(Ca)-mediated CICR increased significantly with age (from approximately 10% in 3d myocytes to approximately 70% in 56d myocytes). The CICR gain as estimated by the integral of the CICR Ca(2+) transient divided by the integral of its Ca(2+) transient trigger was smaller when mediated by NCX ( approximately 1.0 for 3d myocytes) than when mediated by I(Ca) ( approximately 3.0 for 56d myocytes). We conclude that the lower-efficiency NCX-mediated CICR is a predominant mode of CICR in the earliest developmental stages that gradually decreases as the more efficient L-type Ca(2+) channel-mediated CICR increases in prominence with ontogeny.
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Affiliation(s)
- Jingbo Huang
- Cardiac Membrane Research Laboratory, Simon Fraser University, Burnaby, BC, Canada
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