1
|
Adams WP, Hoeker GS, Poelzing S. Flecainide sensitizes conduction to hyponatremia through an ephaptic mechanism. Heart Rhythm 2025:S1547-5271(25)02396-3. [PMID: 40300738 DOI: 10.1016/j.hrthm.2025.04.048] [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: 09/19/2024] [Revised: 04/21/2025] [Accepted: 04/23/2025] [Indexed: 05/01/2025]
Abstract
BACKGROUND Studies suggest that voltage-gated sodium channel (SC) loss-of-function (LoF), often through the use of SC blockers, such as tricyclic anti-depressants, some recreational drugs, and importantly, class 1c anti-arrhythmics, sensitizes cardiac conduction to hyponatremia. However, the mechanism driving conduction velocity (CV) sensitivity to sodium ion (Na+) concentration ([Na+]) is unknown. We recently demonstrated CV-[Na+] sensitivity in haploinsufficient Scn5a+/- mouse and reduced CV-[Na+] sensitivity when ephaptic coupling (extracellular conduction by electric fields) is also reduced. OBJECTIVE We aimed to determine which mechanisms influence CV sensitivity to [Na+] during voltage-gated SC LoF induced by the class 1c anti-arrhythmic, flecainide. METHODS CV was measured by optical mapping of Langendorff-perfused guinea pig hearts with either 145 or 120 mM [Na+] under control conditions, with flecainide alone, and the combination of flecainide with ephaptic coupling uncouplers mannitol or LQLEED, Na+-calcium ion exchanger inhibitor SEA0400, Na+-potassium ion (K+) adenosine triphosphatase inhibitor ouabain, IKr blocker E4031, or IK1 inhibitor barium chloride. CV-[Na+] sensitivity was quantified as percent CV slowing in response to lowering Na+. RESULTS Reducing [Na+] under control conditions did not slow CV. Reducing [Na+] in the presence of flecainide significantly slowed conduction (ie, [Na+] sensitivity). Both ephaptic coupling uncouplers significantly attenuated CV-[Na+] sensitivity. Inhibiting the Na+-calcium ion exchanger did not significantly change CV-[Na+] sensitivity. However, inhibiting outward K+ currents attenuated CV-[Na+] sensitivity. CONCLUSION SC LoF sensitizes conduction to changes in Na+ through ephaptic coupling and outward K+ current-mediated mechanisms. This study has implications for the management of plasma Na+ levels in patients on SC-blocking drugs.
Collapse
Affiliation(s)
- William P Adams
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia; Fralin Biomedical Research Institute at Virginia Tech Carilion, Center for Heart and Reparative Medicine Research, Roanoke, Virginia
| | - Gregory S Hoeker
- Fralin Biomedical Research Institute at Virginia Tech Carilion, Center for Heart and Reparative Medicine Research, Roanoke, Virginia
| | - Steven Poelzing
- Fralin Biomedical Research Institute at Virginia Tech Carilion, Center for Heart and Reparative Medicine Research, Roanoke, Virginia; Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia.
| |
Collapse
|
2
|
Hasan P, Berezhnaya E, Rodríguez-Prados M, Weaver D, Bekeova C, Cartes-Saavedra B, Birch E, Beyer AM, Santos JH, Seifert EL, Elrod JW, Hajnóczky G. MICU1 and MICU2 control mitochondrial calcium signaling in the mammalian heart. Proc Natl Acad Sci U S A 2024; 121:e2402491121. [PMID: 39163336 PMCID: PMC11363308 DOI: 10.1073/pnas.2402491121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Accepted: 07/08/2024] [Indexed: 08/22/2024] Open
Abstract
Activating Ca2+-sensitive enzymes of oxidative metabolism while preventing calcium overload that leads to mitochondrial and cellular injury requires dynamic control of mitochondrial Ca2+ uptake. This is ensured by the mitochondrial calcium uptake (MICU)1/2 proteins that gate the pore of the mitochondrial calcium uniporter (mtCU). MICU1 is relatively sparse in the heart, and recent studies claimed the mammalian heart lacks MICU1 gating of mtCU. However, genetic models have not been tested. We find that MICU1 is present in a complex with MCU in nonfailing human hearts. Furthermore, using murine genetic models and pharmacology, we show that MICU1 and MICU2 control cardiac mitochondrial Ca2+ influx, and that MICU1 deletion alters cardiomyocyte mitochondrial calcium signaling and energy metabolism. MICU1 loss causes substantial compensatory changes in the mtCU composition and abundance, increased turnover of essential MCU regulator (EMRE) early on and, later, of MCU, that limit mitochondrial Ca2+ uptake and allow cell survival. Thus, both the primary consequences of MICU1 loss and the ensuing robust compensation highlight MICU1's relevance in the beating heart.
Collapse
Affiliation(s)
- Prottoy Hasan
- Department of Pathology and Genomic Medicine, MitoCare Center, Thomas Jefferson University, Philadelphia, PA19107
| | - Elena Berezhnaya
- Department of Pathology and Genomic Medicine, MitoCare Center, Thomas Jefferson University, Philadelphia, PA19107
| | - Macarena Rodríguez-Prados
- Department of Pathology and Genomic Medicine, MitoCare Center, Thomas Jefferson University, Philadelphia, PA19107
| | - David Weaver
- Department of Pathology and Genomic Medicine, MitoCare Center, Thomas Jefferson University, Philadelphia, PA19107
| | - Carmen Bekeova
- Department of Pathology and Genomic Medicine, MitoCare Center, Thomas Jefferson University, Philadelphia, PA19107
| | - Benjamin Cartes-Saavedra
- Department of Pathology and Genomic Medicine, MitoCare Center, Thomas Jefferson University, Philadelphia, PA19107
| | - Erin Birch
- Department of Medicine, Cardiovascular Center, Medical College of Wisconsin, Milwaukee, WI53226
| | - Andreas M. Beyer
- Department of Medicine, Cardiovascular Center, Medical College of Wisconsin, Milwaukee, WI53226
| | - Janine H. Santos
- Mechanistic Toxicology Branch, Division of Translational Toxicology, National Institute of Environmental Health Sciences/NIH, Research Triangle Park, NC27709
| | - Erin L. Seifert
- Department of Pathology and Genomic Medicine, MitoCare Center, Thomas Jefferson University, Philadelphia, PA19107
| | - John W. Elrod
- Department of Cardiovascular Sciences, Aging+Cardiovascular Discovery Center, Lewis Katz School of Medicine at Temple University, Philadelphia, PA19140
| | - György Hajnóczky
- Department of Pathology and Genomic Medicine, MitoCare Center, Thomas Jefferson University, Philadelphia, PA19107
| |
Collapse
|
3
|
Scranton K, John S, Angelini M, Steccanella F, Umar S, Zhang R, Goldhaber JI, Olcese R, Ottolia M. Cardiac function is regulated by the sodium-dependent inhibition of the sodium-calcium exchanger NCX1. Nat Commun 2024; 15:3831. [PMID: 38714663 PMCID: PMC11076594 DOI: 10.1038/s41467-024-47850-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 04/15/2024] [Indexed: 05/10/2024] Open
Abstract
The Na+-Ca2+ exchanger (NCX1) is the dominant Ca2+ extrusion mechanism in cardiac myocytes. NCX1 activity is inhibited by intracellular Na+ via a process known as Na+-dependent inactivation. A central question is whether this inactivation plays a physiological role in heart function. Using CRISPR/Cas9, we inserted the K229Q mutation in the gene (Slc8a1) encoding for NCX1. This mutation removes the Na+-dependent inactivation while preserving transport properties and other allosteric regulations. NCX1 mRNA levels, protein expression, and protein localization are unchanged in K229Q male mice. However, they exhibit reduced left ventricular ejection fraction and fractional shortening, while displaying a prolonged QT interval. K229Q ventricular myocytes show enhanced NCX1 activity, resulting in action potential prolongation, higher incidence of aberrant action potentials, a faster decline of Ca2+ transients, and depressed cell shortening. The results demonstrate that NCX1 Na+-dependent inactivation plays an essential role in heart function by affecting both cardiac excitability and contractility.
Collapse
Affiliation(s)
- Kyle Scranton
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Scott John
- Department of Medicine, Division of Cardiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Marina Angelini
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Federica Steccanella
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Soban Umar
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Rui Zhang
- Smidt Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA
| | - Joshua I Goldhaber
- Smidt Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA
| | - Riccardo Olcese
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Michela Ottolia
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA.
| |
Collapse
|
4
|
Lachaud Q, Aziz MHN, Burton FL, Macquaide N, Myles RC, Simitev RD, Smith GL. Electrophysiological heterogeneity in large populations of rabbit ventricular cardiomyocytes. Cardiovasc Res 2022; 118:3112-3125. [PMID: 35020837 PMCID: PMC9732512 DOI: 10.1093/cvr/cvab375] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Accepted: 01/07/2022] [Indexed: 01/01/2023] Open
Abstract
AIMS Cardiac electrophysiological heterogeneity includes: (i) regional differences in action potential (AP) waveform, (ii) AP waveform differences in cells isolated from a single region, (iii) variability of the contribution of individual ion currents in cells with similar AP durations (APDs). The aim of this study is to assess intra-regional AP waveform differences, to quantify the contribution of specific ion channels to the APD via drug responses and to generate a population of mathematical models to investigate the mechanisms underlying heterogeneity in rabbit ventricular cells. METHODS AND RESULTS APD in ∼50 isolated cells from subregions of the LV free wall of rabbit hearts were measured using a voltage-sensitive dye. When stimulated at 2 Hz, average APD90 value in cells from the basal epicardial region was 254 ± 25 ms (mean ± standard deviation) in 17 hearts with a mean interquartile range (IQR) of 53 ± 17 ms. Endo-epicardial and apical-basal APD90 differences accounted for ∼10% of the IQR value. Highly variable changes in APD occurred after IK(r) or ICa(L) block that included a sub-population of cells (HR) with an exaggerated (hyper) response to IK(r) inhibition. A set of 4471 AP models matching the experimental APD90 distribution was generated from a larger population of models created by random variation of the maximum conductances (Gmax) of 8 key ion channels/exchangers/pumps. This set reproduced the pattern of cell-specific responses to ICa(L) and IK(r) block, including the HR sub-population. The models exhibited a wide range of Gmax values with constrained relationships linking ICa(L) with IK(r), ICl, INCX, and INaK. CONCLUSION Modelling the measured range of inter-cell APDs required a larger range of key Gmax values indicating that ventricular tissue has considerable inter-cell variation in channel/pump/exchanger activity. AP morphology is retained by relationships linking specific ionic conductances. These interrelationships are necessary for stable repolarization despite large inter-cell variation of individual conductances and this explains the variable sensitivity to ion channel block.
Collapse
Affiliation(s)
- Quentin Lachaud
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK
| | - Muhamad Hifzhudin Noor Aziz
- School of Mathematics and Statistics, University of Glasgow, Glasgow, UK
- Institute of Mathematical Sciences, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia
| | - Francis L Burton
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK
| | - Niall Macquaide
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK
- School of Health and Life Sciences, Glasgow Caledonian University, Glasgow, UK
| | - Rachel C Myles
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK
| | - Radostin D Simitev
- School of Mathematics and Statistics, University of Glasgow, Glasgow, UK
| | - Godfrey L Smith
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK
| |
Collapse
|
5
|
Oprea L, Desjardins N, Jiang X, Sareen K, Zheng JQ, Khadra A. Characterizing spontaneous Ca 2+ local transients in OPCs using computational modeling. Biophys J 2022; 121:4419-4432. [PMID: 36352783 PMCID: PMC9748374 DOI: 10.1016/j.bpj.2022.11.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2022] [Revised: 10/03/2022] [Accepted: 11/03/2022] [Indexed: 11/09/2022] Open
Abstract
Spontaneous Ca2+ local transients (SCaLTs) in isolated oligodendrocyte precursor cells are largely regulated by the following fluxes: store-operated Ca2+ entry (SOCE), Na+/Ca2+ exchange, Ca2+ pumping through Ca2+-ATPases, and Ca2+-induced Ca2+-release through ryanodine receptors and inositol-trisphosphate receptors. However, the relative contributions of these fluxes in mediating fast spiking and the slow baseline oscillations seen in SCaLTs remain incompletely understood. Here, we developed a stochastic spatiotemporal computational model to simulate SCaLTs in a homogeneous medium with ionic flow between the extracellular, cytoplasmic, and endoplasmic-reticulum compartments. By simulating the model and plotting both the histograms of SCaLTs obtained experimentally and from the model as well as the standard deviation of inter-SCaLT intervals against inter-SCaLT interval averages of multiple model and experimental realizations, we revealed the following: (1) SCaLTs exhibit very similar characteristics between the two data sets, (2) they are mostly random, (3) they encode information in their frequency, and (4) their slow baseline oscillations could be due to the stochastic slow clustering of inositol-trisphosphate receptors (modeled as an Ornstein-Uhlenbeck noise process). Bifurcation analysis of a deterministic temporal version of the model showed that the contribution of fluxes to SCaLTs depends on the parameter regime and that the combination of excitability, stochasticity, and mixed-mode oscillations are responsible for irregular spiking and doublets in SCaLTs. Additionally, our results demonstrated that blocking each flux reduces SCaLTs' frequency and that the reverse (forward) mode of Na+/Ca2+ exchange decreases (increases) SCaLTs. Taken together, these results provide a quantitative framework for SCaLT formation in oligodendrocyte precursor cells.
Collapse
Affiliation(s)
- Lawrence Oprea
- Department of Physiology, McGill University, Montréal, Quebec, Canada
| | | | - Xiaoyu Jiang
- Department of Physiology, McGill University, Montréal, Quebec, Canada
| | - Kushagra Sareen
- Department of Physiology, McGill University, Montréal, Quebec, Canada
| | - James Q Zheng
- Department of Cell Biology, School of Medicine, Emory University, Atlanta, Georgia
| | - Anmar Khadra
- Department of Physiology, McGill University, Montréal, Quebec, Canada.
| |
Collapse
|
6
|
Morciano G, Rimessi A, Patergnani S, Vitto VAM, Danese A, Kahsay A, Palumbo L, Bonora M, Wieckowski MR, Giorgi C, Pinton P. Calcium dysregulation in heart diseases: Targeting calcium channels to achieve a correct calcium homeostasis. Pharmacol Res 2022; 177:106119. [PMID: 35131483 DOI: 10.1016/j.phrs.2022.106119] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Revised: 02/01/2022] [Accepted: 02/03/2022] [Indexed: 12/16/2022]
Abstract
Intracellular calcium signaling is a universal language source shared by the most part of biological entities inside cells that, all together, give rise to physiological and functional anatomical units, the organ. Although preferentially recognized as signaling between cell life and death processes, in the heart it assumes additional relevance considered the importance of calcium cycling coupled to ATP consumption in excitation-contraction coupling. The concerted action of a plethora of exchangers, channels and pumps inward and outward calcium fluxes where needed, to convert energy and electric impulses in muscle contraction. All this without realizing it, thousands of times, every day. An improper function of those proteins (i.e., variation in expression, mutations onset, dysregulated channeling, differential protein-protein interactions) being part of this signaling network triggers a short circuit with severe acute and chronic pathological consequences reported as arrhythmias, cardiac remodeling, heart failure, reperfusion injury and cardiomyopathies. By acting with chemical, peptide-based and pharmacological modulators of these players, a correction of calcium homeostasis can be achieved accompanied by an amelioration of clinical symptoms. This review will focus on all those defects in calcium homeostasis which occur in the most common cardiac diseases, including myocardial infarction, arrhythmia, hypertrophy, heart failure and cardiomyopathies. This part will be introduced by the state of the art on the proteins involved in calcium homeostasis in cardiomyocytes and followed by the therapeutic treatments that to date, are able to target them and to revert the pathological phenotype.
Collapse
Affiliation(s)
- Giampaolo Morciano
- Laboratory for Technologies of Advanced Therapies (LTTA), Section of Experimental Medicine, Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy; Maria Cecilia Hospital, GVM Care & Research, 48033 Cotignola, RA, Italy.
| | - Alessandro Rimessi
- Laboratory for Technologies of Advanced Therapies (LTTA), Section of Experimental Medicine, Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy
| | - Simone Patergnani
- Laboratory for Technologies of Advanced Therapies (LTTA), Section of Experimental Medicine, Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy
| | - Veronica A M Vitto
- Laboratory for Technologies of Advanced Therapies (LTTA), Section of Experimental Medicine, Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy
| | - Alberto Danese
- Laboratory for Technologies of Advanced Therapies (LTTA), Section of Experimental Medicine, Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy
| | - Asrat Kahsay
- Laboratory for Technologies of Advanced Therapies (LTTA), Section of Experimental Medicine, Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy
| | - Laura Palumbo
- Laboratory for Technologies of Advanced Therapies (LTTA), Section of Experimental Medicine, Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy
| | - Massimo Bonora
- Laboratory for Technologies of Advanced Therapies (LTTA), Section of Experimental Medicine, Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy
| | - Mariusz R Wieckowski
- Laboratory of Mitochondrial Biology and Metabolism. Nencki Institute of Experimental Biology, Polish Academy of Sciences, 02-093 Warsaw, Poland
| | - Carlotta Giorgi
- Laboratory for Technologies of Advanced Therapies (LTTA), Section of Experimental Medicine, Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy
| | - Paolo Pinton
- Laboratory for Technologies of Advanced Therapies (LTTA), Section of Experimental Medicine, Department of Medical Sciences, University of Ferrara, 44121 Ferrara, Italy; Maria Cecilia Hospital, GVM Care & Research, 48033 Cotignola, RA, Italy.
| |
Collapse
|
7
|
Fernández-Morales JC, Xia Y, Rienzo TJ, Zhang XH, Morad M. Mutation in RyR2-FKBP Binding site alters Ca 2+ signaling modestly but increases "arrhythmogenesis" in human stem cells derived cardiomyocytes. Cell Calcium 2022; 101:102500. [PMID: 34813985 PMCID: PMC8752506 DOI: 10.1016/j.ceca.2021.102500] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Revised: 11/02/2021] [Accepted: 11/04/2021] [Indexed: 01/03/2023]
Abstract
AIMS To gain insights into FKBP regulation of cardiac ryanodine receptor (RyR2) and Ca2+ signaling, we introduced the point mutation (N771D-RyR2) corresponding to skeletal muscle mutation (N760D-RyR1) associated with central core disease (CCD) via CRISPR/Cas9 gene-editing in the RyR2 FKBP binding site expressed in human induced pluripotent stem cell-derived cardiomyocytes (hiPSCCMs). Patients inflicted with CCD and other hereditary skeletal muscle diseases often show higher incidence of atrial or ventricular arrhythmias. METHODS AND RESULTS Ca2+ imaging of voltage-clamped N771D-RyR2 mutant compared to WT hiPSCCMs showed: (1) ∼30% suppressed ICa with no significant changes in the gating kinetics of ICa; (2) 29% lower SR Ca2+ content and 33% lower RyR2 Ca2+ leak; (3) higher CICR gain and 30-35% increased efficiency of ICa-triggered Ca2±release; (4) higher incidence of aberrant SR Ca2+ releases, DADs, and Ca2+ sparks; (5) no change in fractional Ca2+-release, action potential morphology, sensitivity to isoproterenol, and sarcomeric FKBP-binding pattern. CONCLUSIONS The more frequent spontaneous Ca2+ releases and longer Ca2+ sparks underlie the increased incidence of DADs and cellular arrhythmogenesis of N771D-RyR2 mutant. The smaller RyR2 Ca2±leak and SR content result from suppressed ICathat is compensated by higher CICR gain.
Collapse
Affiliation(s)
| | - Yanli Xia
- Cardiac Signaling Center of MUSC, USC and Clemson University, Charleston, SC, USA
| | - Taylor J. Rienzo
- Cardiac Signaling Center of MUSC, USC and Clemson University, Charleston, SC, USA
| | - Xiao-Hua Zhang
- Cardiac Signaling Center of MUSC, USC and Clemson University, Charleston, SC, USA
| | - Martin Morad
- Cardiac Signaling Center of MUSC, USC and Clemson University, Charleston, SC, USA.,Department of Pharmacology, Georgetown University Medical Center, Washington, DC, USA
| |
Collapse
|
8
|
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: 24] [Impact Index Per Article: 6.0] [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.
Collapse
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
| |
Collapse
|
9
|
Hamada M, Shigematsu Y, Ikeda S, Ohshima K, Ogimoto A. Impact of cibenzoline treatment on left ventricular remodelling and prognosis in hypertrophic obstructive cardiomyopathy. ESC Heart Fail 2021; 8:4832-4842. [PMID: 34713615 PMCID: PMC8712831 DOI: 10.1002/ehf2.13672] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 09/03/2021] [Accepted: 10/01/2021] [Indexed: 12/14/2022] Open
Abstract
Aims This study aimed to elucidate the long‐term effect of cibenzoline therapy on cardiovascular complications and prognosis in patients with hypertrophic obstructive cardiomyopathy (HOCM). Methods and results Eighty‐eight patients with HOCM were treated with cibenzoline (Group A), and 41 patients did not receive cibenzoline (Group B). The changes in left ventricular (LV) remodelling, incidences of cardiovascular complications and deaths, were examined. The mean follow‐up period was 15.8 ± 5.6 years in Group A and 17.8 ± 7.2 years in Group B. In Group A, the LV pressure gradient (LVPG) decreased immediately after treatment, and the reduction was maintained throughout the study. In Group B, the LVPG decreased gradually according to the deterioration of LV function. LV reverse remodelling was confirmed in Group A, and LV remodelling advanced in Group B. In Group A, the incidence of each cardiovascular complication was <10%. Only one patient experienced LV heart failure (LVHF). LVHF incidence and atrial fibrillation were higher in Group B than those in Group A (P < 0.0001). The incidence of death was 20.5% in Group A and 90.2% in Group B (P < 0.0001). The most frequent cause of death was sudden cardiac death (SCD) (38.9%) in Group A and LVHF (67.6%) in Group B. The incidence of SCD showed no significant difference between the two groups. The cumulative cardiac survival rate was higher in Group A than that in Group B (P < 0.0001). Conclusions Cibenzoline treatment significantly reduced all cardiovascular complications and death due to LVHF and may be a promising treatment in patients with HOCM.
Collapse
Affiliation(s)
- Mareomi Hamada
- Division of Cardiology, Uwajima City Hospital, 1-1, Goten-machi, Uwajima, 798-8510, Japan
| | - Yuji Shigematsu
- Fundamental and Clinical Nursing, Ehime University Graduate School of Medicine, Toon, Japan
| | - Shuntaro Ikeda
- Department of Community and Emergency Medicine, Ehime University Graduate School of Medicine, Toon, Japan
| | - Kiyotaka Ohshima
- Division of Cardiology, Uwajima City Hospital, 1-1, Goten-machi, Uwajima, 798-8510, Japan
| | - Akiyoshi Ogimoto
- Division of Cardiology, Uwajima City Hospital, 1-1, Goten-machi, Uwajima, 798-8510, Japan
| |
Collapse
|
10
|
Pan-phylum genome-wide identification of sodium calcium exchangers reveal heterogeneous expansions and possible roles in nematode parasitism. Gene 2021; 810:146052. [PMID: 34756961 DOI: 10.1016/j.gene.2021.146052] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2021] [Revised: 10/19/2021] [Accepted: 10/26/2021] [Indexed: 12/13/2022]
Abstract
Calcium signaling is ubiquitous in nematode development from fertilization to cell specification to apoptosis. Calcium also regulates dauer entry in Caenorhabditis elegans, which corresponds to the infective stage of parasitic nematodes. In diverse parasites such as Trypanosoma cruzi and Toxoplasma gondii calcium has been shown to regulate host cell entry and egress, and perturbing calcium signaling represents a possible route to inhibit infection and parasitism in these species. Sodium calcium exchangers are considered the most important mechanism of calcium efflux, and our lab has previously characterized the sodium calcium exchanger gene family in C. elegans and studied the diversity of this family across a subset of specific nematode species. Here we build upon these data and explore sodium calcium exchangers across 108 species of nematodes. Our data reveal substantial differences in sodium calcium exchanger counts across the Phylum and detail expansions and contractions of specific exchanger subtypes within certain nematode clades. Finally, we also provide evidence for a role of sodium calcium exchangers in parasite activation by examining differentially expressed genes in non-activated versus activated infective stage larvae. Taken together our findings paint a heterogeneous picture of sodium calcium exchanger evolution across the Phylum Nematoda that may reflect unique adaptations to free-living and parasitic lifestyles.
Collapse
|
11
|
A novel substrate for arrhythmias in Chagas disease. PLoS Negl Trop Dis 2021; 15:e0009421. [PMID: 34077437 PMCID: PMC8172059 DOI: 10.1371/journal.pntd.0009421] [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] [Received: 10/16/2020] [Accepted: 04/28/2021] [Indexed: 11/19/2022] Open
Abstract
Background Chagas disease (CD) is a neglected disease that induces heart failure and arrhythmias in approximately 30% of patients during the chronic phase of the disease. Despite major efforts to understand the cellular pathophysiology of CD there are still relevant open questions to be addressed. In the present investigation we aimed to evaluate the contribution of the Na+/Ca2+ exchanger (NCX) in the electrical remodeling of isolated cardiomyocytes from an experimental murine model of chronic CD. Methodology/Principal findings Male C57BL/6 mice were infected with Colombian strain of Trypanosoma cruzi. Experiments were conducted in isolated left ventricular cardiomyocytes from mice 180–200 days post-infection and with age-matched controls. Whole-cell patch-clamp technique was used to measure cellular excitability and Real-time PCR for parasite detection. In current-clamp experiments, we found that action potential (AP) repolarization was prolonged in cardiomyocytes from chagasic mice paced at 0.2 and 1 Hz. After-depolarizations, both subthreshold and with spontaneous APs events, were more evident in the chronic phase of experimental CD. In voltage-clamp experiments, pause-induced spontaneous activity with the presence of diastolic transient inward current was enhanced in chagasic cardiomyocytes. AP waveform disturbances and diastolic transient inward current were largely attenuated in chagasic cardiomyocytes exposed to Ni2+ or SEA0400. Conclusions/Significance The present study is the first to describe NCX as a cellular arrhythmogenic substrate in chagasic cardiomyocytes. Our data suggest that NCX could be relevant to further understanding of arrhythmogenesis in the chronic phase of experimental CD and blocking NCX may be a new therapeutic strategy to treat arrhythmias in this condition. Chagas disease (CD), caused by the parasite Trypanosoma cruzi, is a neglected disease that induces heart failure and arrhythmias in approximately 30% of patients during the chronic phase of the disease. There are several substrates for arrhythmias in the heart. Some of them involve changes in the electrical properties of cardiomyocytes, the working cells of the heart. In our study we evaluate the potential involvement of Na+/Ca2+ exchanger (NCX) in the arrhythmic phenotype of cardiomyocytes isolated from mice infected with Trypanosoma cruzi, between 180- and 200- days post-infection, which is considered the chronic phase of CD in this animal model. In our study we found several arrhythmogenic membrane potential oscillations during action potential measurements, in rest and using a protocol to simulate a pause after a tachycardia. Using pharmacological approach, we determine that NCX significantly contributed to the arrhythmogenic phenomena observed. Thus, in our study we demonstrate that NCX may be relevant to the cellular arrhythmogenic profile observed in cardiomyocytes during the chronic phase of experimental CD and blocking NCX may be a new therapeutic strategy to treat arrhythmias in this condition.
Collapse
|
12
|
Vagos MR, Arevalo H, Heijman J, Schotten U, Sundnes J. A Computational Study of the Effects of Tachycardia-Induced Remodeling on Calcium Wave Propagation in Rabbit Atrial Myocytes. Front Physiol 2021; 12:651428. [PMID: 33897459 PMCID: PMC8063103 DOI: 10.3389/fphys.2021.651428] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2021] [Accepted: 03/08/2021] [Indexed: 11/24/2022] Open
Abstract
In atrial cardiomyocytes without a well-developed T-tubule system, calcium diffuses from the periphery toward the center creating a centripetal wave pattern. During atrial fibrillation, rapid activation of atrial myocytes induces complex remodeling in diffusion properties that result in failure of calcium to propagate in a fully regenerative manner toward the center; a phenomenon termed “calcium silencing.” This has been observed in rabbit atrial myocytes after exposure to prolonged rapid pacing. Although experimental studies have pointed to possible mechanisms underlying calcium silencing, their individual effects and relative importance remain largely unknown. In this study we used computational modeling of the rabbit atrial cardiomyocyte to query the individual and combined effects of the proposed mechanisms leading to calcium silencing and abnormal calcium wave propagation. We employed a population of models obtained from a newly developed model of the rabbit atrial myocyte with spatial representation of intracellular calcium handling. We selected parameters in the model that represent experimentally observed cellular remodeling which have been implicated in calcium silencing, and scaled their values in the population to match experimental observations. In particular, we changed the maximum conductances of ICaL, INCX, and INaK, RyR open probability, RyR density, Serca2a density, and calcium buffering strength. We incorporated remodeling in a population of 16 models by independently varying parameters that reproduce experimentally observed cellular remodeling, and quantified the resulting alterations in calcium dynamics and wave propagation patterns. The results show a strong effect of ICaL in driving calcium silencing, with INCX, INaK, and RyR density also resulting in calcium silencing in some models. Calcium alternans was observed in some models where INCX and Serca2a density had been changed. Simultaneously incorporating changes in all remodeled parameters resulted in calcium silencing in all models, indicating the predominant role of decreasing ICaL in the population phenotype.
Collapse
Affiliation(s)
- Márcia R Vagos
- Simula Research Laboratory, Computational Physiology Department, Lysaker, Norway
| | - Hermenegild Arevalo
- Simula Research Laboratory, Computational Physiology Department, Lysaker, Norway
| | - Jordi Heijman
- Faculty of Health, Medicine and Life Sciences, School for Cardiovascular Diseases, Maastricht, Netherlands
| | - Ulrich Schotten
- Faculty of Health, Medicine and Life Sciences, School for Cardiovascular Diseases, Maastricht, Netherlands
| | - Joakim Sundnes
- Simula Research Laboratory, Computational Physiology Department, Lysaker, Norway.,Department of Informatics, University of Oslo, Oslo, Norway
| |
Collapse
|
13
|
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: 0.6] [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.
Collapse
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
| |
Collapse
|
14
|
Zhao N, Li Q, Zhang K, Wang K, He R, Yuan Y, Zhang H. Heart failure-induced atrial remodelling promotes electrical and conduction alternans. PLoS Comput Biol 2020; 16:e1008048. [PMID: 32658888 PMCID: PMC7402519 DOI: 10.1371/journal.pcbi.1008048] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Revised: 08/04/2020] [Accepted: 06/12/2020] [Indexed: 11/19/2022] Open
Abstract
Heart failure (HF) is associated with an increased propensity for atrial fibrillation (AF), causing higher mortality than AF or HF alone. It is hypothesized that HF-induced remodelling of atrial cellular and tissue properties promotes the genesis of atrial action potential (AP) alternans and conduction alternans that perpetuate AF. However, the mechanism underlying the increased susceptibility to atrial alternans in HF remains incompletely elucidated. In this study, we investigated the effects of how HF-induced atrial cellular electrophysiological (with prolonged AP duration) and tissue structural (reduced cell-to-cell coupling caused by atrial fibrosis) remodelling can have an effect on the generation of atrial AP alternans and their conduction at the cellular and one-dimensional (1D) tissue levels. Simulation results showed that HF-induced atrial electrical remodelling prolonged AP duration, which was accompanied by an increased sarcoplasmic reticulum (SR) Ca2+ content and Ca2+ transient amplitude. Further analysis demonstrated that HF-induced atrial electrical remodelling increased susceptibility to atrial alternans mainly due to the increased sarcoplasmic reticulum Ca2+-ATPase (SERCA) Ca2+ reuptake, modulated by increased phospholamban (PLB) phosphorylation, and the decreased transient outward K+ current (Ito). The underlying mechanism has been suggested that the increased SR Ca2+ content and prolonged AP did not fully recover to their previous levels at the end of diastole, resulting in a smaller SR Ca2+ release and AP in the next beat. These produced Ca2+ transient alternans and AP alternans, and further caused AP alternans and Ca2+ transient alternans through Ca2+→AP coupling and AP→Ca2+ coupling, respectively. Simulation of a 1D tissue model showed that the combined action of HF-induced ion channel remodelling and a decrease in cell-to-cell coupling due to fibrosis increased the heart tissue's susceptibility to the formation of spatially discordant alternans, resulting in an increased functional AP propagation dispersion, which is pro-arrhythmic. These findings provide insights into how HF promotes atrial arrhythmia in association with atrial alternans.
Collapse
Affiliation(s)
- Na Zhao
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
| | - Qince Li
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
- Peng Cheng Laboratory, Shenzhen, China
| | - Kevin Zhang
- School of Medicine, Imperial College of London, United Kingdom
| | - Kuanquan Wang
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
| | - Runnan He
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
| | - Yongfeng Yuan
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
| | - Henggui Zhang
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
- Peng Cheng Laboratory, Shenzhen, China
- School of Physics & Astronomy, The University of Manchester, Manchester, United Kingdom
- 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
| |
Collapse
|
15
|
O’Halloran DM. Simulation model of CA1 pyramidal neurons reveal opposing roles for the Na+/Ca2+ exchange current and Ca2+-activated K+ current during spike-timing dependent synaptic plasticity. PLoS One 2020; 15:e0230327. [PMID: 32150746 PMCID: PMC7062500 DOI: 10.1371/journal.pone.0230327] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Accepted: 02/27/2020] [Indexed: 11/18/2022] Open
Abstract
Sodium Calcium exchanger (NCX) proteins utilize the electrochemical gradient of Na+ to generate Ca2+ efflux (forward mode) or influx (reverse mode). In mammals, there are three unique NCX encoding genes—NCX1, NCX2, and NCX3, that comprise the SLC8A family, and mRNA from all three exchangers is expressed in hippocampal pyramidal cells. Furthermore, mutant ncx2-/- and ncx3-/- mice have each been shown to exhibit altered long-term potentiation (LTP) in the hippocampal CA1 region due to delayed Ca2+ clearance after depolarization that alters synaptic transmission. In addition to the role of NCX at the synapse of hippocampal subfields required for LTP, the three NCX isoforms have also been shown to localize to the dendrite of hippocampal pyramidal cells. In the case of NCX1, it has been shown to localize throughout the basal and apical dendrite of CA1 neurons where it helps compartmentalize Ca2+ between dendritic shafts and spines. Given the role for NCX and calcium in synaptic plasticity, the capacity of NCX splice-forms to influence backpropagating action potentials has clear consequences for the induction of spike-timing dependent synaptic plasticity (STDP). To explore this, we examined the effect of NCX localization, density, and allosteric activation on forward and back propagating signals and, next employed a STDP paradigm to monitor the effect of NCX on plasticity using back propagating action potentials paired with EPSPs. From our simulation studies we identified a role for the sodium calcium exchange current in normalizing STDP, and demonstrate that NCX is required at the postsynaptic site for this response. We also screened other mechanisms in our model and identified a role for the Ca2+ activated K+ current at the postsynapse in producing STDP responses. Together, our data reveal opposing roles for the Na+/Ca2+ exchanger current and the Ca2+ activated K+ current in setting STDP.
Collapse
Affiliation(s)
- Damien M. O’Halloran
- Department of Biological Sciences, The George Washington University, Washington DC, United States of America
- * E-mail:
| |
Collapse
|
16
|
Scranton K, John S, Escobar A, Goldhaber JI, Ottolia M. Modulation of the cardiac Na +-Ca 2+ exchanger by cytoplasmic protons: Molecular mechanisms and physiological implications. Cell Calcium 2019; 87:102140. [PMID: 32070924 DOI: 10.1016/j.ceca.2019.102140] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Revised: 12/06/2019] [Accepted: 12/07/2019] [Indexed: 01/31/2023]
Abstract
A precise temporal and spatial control of intracellular Ca2+ concentration is essential for a coordinated contraction of the heart. Following contraction, cardiac cells need to rapidly remove intracellular Ca2+ to allow for relaxation. This task is performed by two transporters: the plasma membrane Na+-Ca2+ exchanger (NCX) and the sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA). NCX extrudes Ca2+ from the cell, balancing the Ca2+entering the cytoplasm during systole through L-type Ca2+ channels. In parallel, following SR Ca2+ release, SERCA activity replenishes the SR, reuptaking Ca2+ from the cytoplasm. The activity of the mammalian exchanger is fine-tuned by numerous ionic allosteric regulatory mechanisms. Micromolar concentrations of cytoplasmic Ca2+ potentiate NCX activity, while an increase in intracellular Na+ levels inhibits NCX via a mechanism known as Na+-dependent inactivation. Protons are also powerful inhibitors of NCX activity. By regulating NCX activity, Ca2+, Na+ and H+ couple cell metabolism to Ca2+ homeostasis and therefore cardiac contractility. This review summarizes the recent progress towards the understanding of the molecular mechanisms underlying the ionic regulation of the cardiac NCX with special emphasis on pH modulation and its physiological impact on the heart.
Collapse
Affiliation(s)
- Kyle Scranton
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, UCLA, Los Angeles, CA 90095, USA
| | - Scott John
- Department of Medicine (Cardiology), UCLA, Los Angeles, CA 90095, USA; Cardiovascular Research Laboratory, UCLA, Los Angeles, CA 90095, USA
| | - Ariel Escobar
- Department of Bioengineering, School of Engineering, UC Merced, Merced, CA 95343, USA
| | - Joshua I Goldhaber
- Smidt Heart Institute, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA
| | - Michela Ottolia
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, UCLA, Los Angeles, CA 90095, USA; Cardiovascular Research Laboratory, UCLA, Los Angeles, CA 90095, USA.
| |
Collapse
|
17
|
Xie M, Yu L, Bruschweiler-Li L, Xiang X, Hansen AL, Brüschweiler R. Functional protein dynamics on uncharted time scales detected by nanoparticle-assisted NMR spin relaxation. SCIENCE ADVANCES 2019; 5:eaax5560. [PMID: 31453342 PMCID: PMC6693908 DOI: 10.1126/sciadv.aax5560] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Accepted: 07/09/2019] [Indexed: 05/03/2023]
Abstract
Protein function depends critically on intrinsic internal dynamics, which is manifested in distinct ways, such as loop motions that regulate protein recognition and catalysis. Under physiological conditions, dynamic processes occur on a wide range of time scales from subpicoseconds to seconds. Commonly used NMR spin relaxation in solution provides valuable information on very fast and slow motions but is insensitive to the intermediate nanosecond to microsecond range that exceeds the protein tumbling correlation time. Presently, very little is known about the nature and functional role of these motions. It is demonstrated here how transverse spin relaxation becomes exquisitely sensitive to these motions at atomic resolution when studying proteins in the presence of nanoparticles. Application of this novel cross-disciplinary approach reveals large-scale dynamics of loops involved in functionally critical protein-protein interactions and protein-calcium ion recognition that were previously unobservable.
Collapse
Affiliation(s)
- Mouzhe Xie
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
| | - Lei Yu
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
| | - Lei Bruschweiler-Li
- Campus Chemical Instrument Center, The Ohio State University, Columbus, OH 43210, USA
| | - Xinyao Xiang
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
| | - Alexandar L. Hansen
- Campus Chemical Instrument Center, The Ohio State University, Columbus, OH 43210, USA
| | - Rafael Brüschweiler
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
- Campus Chemical Instrument Center, The Ohio State University, Columbus, OH 43210, USA
- Department of Biological Chemistry and Pharmacology, The Ohio State University, Columbus, OH 43210, USA
| |
Collapse
|
18
|
Brazhe AR, Verisokin AY, Verveyko DV, Postnov DE. Sodium-Calcium Exchanger Can Account for Regenerative Ca 2+ Entry in Thin Astrocyte Processes. Front Cell Neurosci 2018; 12:250. [PMID: 30154700 PMCID: PMC6102320 DOI: 10.3389/fncel.2018.00250] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2018] [Accepted: 07/23/2018] [Indexed: 01/05/2023] Open
Abstract
Calcium transients in thin astrocytic processes can be important in synaptic plasticity, but their mechanism is not completely understood. Clearance of synaptic glutamate leads to increase in astrocytic sodium. This can electrochemically favor the reverse mode of the Na/Ca-exchanger (NCX) and allow calcium into the cell, accounting for activity-dependent calcium transients in perisynaptic astrocytic processes. However, cytosolic sodium and calcium are also allosteric regulators of the NCX, thus adding kinetic constraints on the NCX-mediated fluxes and providing for complexity of the system dynamics. Our modeling indicates that the calcium-dependent activation and also calcium-dependent escape from the sodium-mediated inactive state of the NCX in astrocytes can form a positive feedback loop and lead to regenerative calcium influx. This can result in sodium-dependent amplification of calcium transients from nearby locations or other membrane mechanisms. Prolonged conditions of elevated sodium, for example in ischemia, can also lead to bistability in cytosolic calcium levels, where a delayed transition to the high-calcium state can be triggered by a short calcium transient. These theoretical predictions call for a dedicated experimental estimation of the kinetic parameters of the astrocytic Na/Ca-exchanger.
Collapse
Affiliation(s)
- Alexey R. Brazhe
- Department of Biophysics, Biological Faculty, Lomonosov Moscow State University, Moscow, Russia
| | | | - Darya V. Verveyko
- Department of Theoretical Physics, Kursk State University, Kursk, Russia
| | | |
Collapse
|
19
|
Zhong M, Rees CM, Terentyev D, Choi BR, Koren G, Karma A. NCX-Mediated Subcellular Ca 2+ Dynamics Underlying Early Afterdepolarizations in LQT2 Cardiomyocytes. Biophys J 2018; 115:1019-1032. [PMID: 30173888 DOI: 10.1016/j.bpj.2018.08.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 07/18/2018] [Accepted: 08/02/2018] [Indexed: 12/12/2022] Open
Abstract
Long QT syndrome type 2 (LQT2) is a congenital disease characterized by loss of function mutations in hERG potassium channels (IKr). LQT2 is associated with fatal ventricular arrhythmias promoted by triggered activity in the form of early afterdepolarizations (EADs). We previously demonstrated that intracellular Ca2+ handling is remodeled in LQT2 myocytes. Remodeling leads to aberrant late RyR-mediated Ca2+ releases that drive forward-mode Na+-Ca2+ exchanger (NCX) current and slow repolarization to promote reopening of L-type calcium channels and EADs. Forward-mode NCX was found to be enhanced despite the fact that these late releases do not significantly alter the whole-cell cytosolic calcium concentration during a vulnerable period of phase 2 of the action potential corresponding to the onset of EADs. Here, we use a multiscale ventricular myocyte model to explain this finding. We show that because the local NCX current is a saturating nonlinear function of the local submembrane calcium concentration, a larger number of smaller-amplitude discrete Ca2+ release events can produce a large increase in whole-cell forward-mode NCX current without increasing significantly the whole-cell cytosolic calcium concentration. Furthermore, we develop novel insights, to our knowledge, into how alterations of stochastic RyR activity at the single-channel level cause late aberrant Ca2+ release events. Experimental measurements in transgenic LTQ2 rabbits confirm the critical arrhythmogenic role of NCX and identify this current as a potential target for antiarrhythmic therapies in LQT2.
Collapse
Affiliation(s)
- Mingwang Zhong
- Physics Department and Center for Interdisciplinary Research in Complex Systems, Northeastern University, Boston, Massachusetts
| | - Colin M Rees
- Physics Department and Center for Interdisciplinary Research in Complex Systems, Northeastern University, Boston, Massachusetts
| | - Dmitry Terentyev
- Cardiovascular Research Centre, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Bum-Rak Choi
- Cardiovascular Research Centre, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Gideon Koren
- Cardiovascular Research Centre, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Alain Karma
- Physics Department and Center for Interdisciplinary Research in Complex Systems, Northeastern University, Boston, Massachusetts.
| |
Collapse
|
20
|
Jennings ML. Carriers, exchangers, and cotransporters in the first 100 years of the Journal of General Physiology. J Gen Physiol 2018; 150:1063-1080. [PMID: 30030301 PMCID: PMC6080889 DOI: 10.1085/jgp.201812078] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Jennings reviews the many contributions of JGP articles to our current understanding of solute transporter mechanisms. Transporters, pumps, and channels are proteins that catalyze the movement of solutes across membranes. The single-solute carriers, coupled exchangers, and coupled cotransporters that are collectively known as transporters are distinct from conductive ion channels, water channels, and ATP-hydrolyzing pumps. The main conceptual framework for studying transporter mechanisms is the alternating access model, which comprises substrate binding and release events on each side of the permeability barrier and translocation events involving conformational changes between inward-facing and outward-facing conformational states. In 1948, the Journal of General Physiology began to publish work that focused on the erythrocyte glucose transporter—the first transporter to be characterized kinetically—followed by articles on the rates, stoichiometries, asymmetries, voltage dependences, and regulation of coupled exchangers and cotransporters beginning in the 1960s. After the dawn of cDNA cloning and sequencing in the 1980s, heterologous expression systems and site-directed mutagenesis allowed identification of the functional roles of specific amino acid residues. In the past two decades, structures of transport proteins have made it possible to propose specific models for transporter function at the molecular level. Here, we review the contribution of JGP articles to our current understanding of solute transporter mechanisms. Whether the topic has been kinetics, energetics, regulation, mutagenesis, or structure-based modeling, a common feature of these articles has been a quantitative, mechanistic approach, leading to lasting insights into the functions of transporters.
Collapse
Affiliation(s)
- Michael L Jennings
- Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR
| |
Collapse
|
21
|
Importance of Altered Levels of SERCA, IP 3R, and RyR in Vascular Smooth Muscle Cell. Biophys J 2017; 112:265-287. [PMID: 28122214 DOI: 10.1016/j.bpj.2016.11.3206] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Revised: 10/26/2016] [Accepted: 11/21/2016] [Indexed: 11/23/2022] Open
Abstract
Calcium cycling between the sarcoplasmic reticulum (SR) and the cytosol via the sarco-/endoplasmic reticulum Ca-ATPase (SERCA) pump, inositol-1,4,5-triphosphate receptor (IP3R), and Ryanodine receptor (RyR), plays a major role in agonist-induced intracellular calcium ([Ca2+]cyt) dynamics in vascular smooth muscle cells (VSMC). Levels of these calcium handling proteins in SR get altered under disease conditions. We have developed a mathematical model to understand the significance of altered levels of SERCA, IP3R, and RyR on the intracellular calcium dynamics of VSMC and to understand how variation in protein levels that arise due to diabetes contribute to different VSMC behavior and thus vascular disease. SR is modeled as a single continuous entity with homogeneous intra-SR calcium. Model results show that agonist-induced intracellular calcium dynamics can be modified by changing the levels of SERCA, IP3R, and/or RyR. Lowering SERCA level will enable intracellular calcium oscillations at low agonist concentrations whereas lowered levels of IP3R and RyR need higher agonist concentration for intracellular calcium oscillations. This research suggests that reduced SERCA level is the main factor responsible for the reduced intracellular calcium transients and contractility in VSMCs.
Collapse
|
22
|
Dhindwal S, Lobo J, Cabra V, Santiago DJ, Nayak AR, Dryden K, Samsó M. A cryo-EM–based model of phosphorylation- and FKBP12.6-mediated allosterism of the cardiac ryanodine receptor. Sci Signal 2017; 10:10/480/eaai8842. [DOI: 10.1126/scisignal.aai8842] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
|
23
|
Hamada M, Ikeda S, Ohshima K, Nakamura M, Kubota N, Ogimoto A, Shigematsu Y. Impact of chronic use of cibenzoline on left ventricular pressure gradient and left ventricular remodeling in patients with hypertrophic obstructive cardiomyopathy. J Cardiol 2016; 67:279-86. [PMID: 26116980 DOI: 10.1016/j.jjcc.2015.05.014] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Revised: 05/12/2015] [Accepted: 05/19/2015] [Indexed: 11/28/2022]
Abstract
BACKGROUND Cibenzoline, a class Ia antiarrhythmic drug, is useful for reducing the left ventricular pressure gradient (LVPG) in patients with hypertrophic obstructive cardiomyopathy (HOCM). However, chronic effects of cibenzoline on LVPG and left ventricular (LV) remodeling are unknown. METHODS Forty-one patients with HOCM participated in this study. Echocardiographic, electrocardiographic, and brain natriuretic peptide (BNP) data collected before and after cibenzoline treatment were compared. From the relation between LVPG and plasma concentration of cibenzoline, an efficacious plasma concentration of cibenzoline was estimated. RESULTS The mean follow-up period was 74.2±47.1 months. The LVPG decreased from 104.8±62.6mmHg to 27.6±30.5mmHg (p<0.0001). The LV end-diastolic dimension increased from 42.8±5.8mm to 46.2±5.4mm (p<0.0001), but neither LV end-systolic dimension nor LV fractional shortening changed significantly. The left atrial dimension decreased from 40.0±4.7mm to 36.2±5.1mm (p<0.0001). The E-wave velocity/A-wave velocity ratio increased, early diastolic annular velocity (Ea) increased, and E/Ea ratio decreased. The interventricular septal wall thickness, LV posterior wall thickness, the Sokolow-Lyon index, and the depth of negative T wave decreased. The heart rate-corrected QT interval was shortened. Plasma BNP level decreased from 418.8±423.7pg/ml to 213.7±154.1pg/ml (p<0.02). The safe and efficacious plasma concentration of cibenzoline was between 300ng/mL and 1500ng/mL. CONCLUSIONS Long-term treatment with cibenzoline attenuated LVPG, improved LV diastolic dysfunction, and induced LV hypertrophy regression in patients with HOCM without causing serious complications.
Collapse
Affiliation(s)
- Mareomi Hamada
- Division of Cardiology, Uwajima City Hospital, Uwajima, Ehime, Japan.
| | - Shuntaro Ikeda
- Division of Cardiology, Uwajima City Hospital, Uwajima, Ehime, Japan
| | - Kiyotaka Ohshima
- Division of Cardiology, Uwajima City Hospital, Uwajima, Ehime, Japan
| | - Masayuki Nakamura
- Division of Cardiology, Uwajima City Hospital, Uwajima, Ehime, Japan
| | - Norio Kubota
- Division of Physiological Laboratory, Uwajima City Hospital, Uwajima, Ehime, Japan
| | - Akiyoshi Ogimoto
- Division of Cardiology, Department of Integrated Medicine and Informatics, Ehime University Graduate School of Medicine, Toon-city, Ehime, Japan
| | - Yuji Shigematsu
- Clinical Nursing, Ehime University Graduate School of Medicine, Toon-city, Ehime, Japan
| |
Collapse
|
24
|
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: 1.9] [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.
Collapse
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.
| |
Collapse
|
25
|
Devenyi RA, Sobie EA. There and back again: Iterating between population-based modeling and experiments reveals surprising regulation of calcium transients in rat cardiac myocytes. J Mol Cell Cardiol 2016; 96:38-48. [PMID: 26235057 PMCID: PMC4733425 DOI: 10.1016/j.yjmcc.2015.07.016] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Revised: 07/08/2015] [Accepted: 07/22/2015] [Indexed: 01/17/2023]
Abstract
While many ion channels and transporters involved in cardiac cellular physiology have been identified and described, the relative importance of each in determining emergent cellular behaviors remains unclear. Here we address this issue with a novel approach that combines population-based mathematical modeling with experimental tests to systematically quantify the relative contributions of different ion channels and transporters to the amplitude of the cellular Ca(2+) transient. Sensitivity analysis of a mathematical model of the rat ventricular cardiomyocyte quantified the response of cell behaviors to changes in the level of each ion channel and transporter, and experimental tests of these predictions were performed to validate or invalidate the predictions. The model analysis found that partial inhibition of the transient outward current in rat ventricular epicardial myocytes was predicted to have a greater impact on Ca(2+) transient amplitude than either: (1) inhibition of the same current in endocardial myocytes, or (2) comparable inhibition of the sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA). Experimental tests confirmed the model predictions qualitatively but showed some quantitative disagreement. This guided us to recalibrate the model by adjusting the relative importance of several Ca(2+) fluxes, thereby improving the consistency with experimental data and producing a more predictive model. Analysis of human cardiomyocyte models suggests that the relative importance of outward currents to Ca(2+) transporters is generalizable to human atrial cardiomyocytes, but not ventricular cardiomyocytes. Overall, our novel approach of combining population-based mathematical modeling with experimental tests has yielded new insight into the relative importance of different determinants of cell behavior.
Collapse
Affiliation(s)
- Ryan A Devenyi
- Department of Pharmacology and Systems Therapeutics, Icahn School of Medicine at Mount Sinai, 1 Gustave L Levy Place, New York, NY, USA
| | - Eric A Sobie
- Department of Pharmacology and Systems Therapeutics, Icahn School of Medicine at Mount Sinai, 1 Gustave L Levy Place, New York, NY, USA.
| |
Collapse
|
26
|
Pohl A, Wachter A, Hatam N, Leonhardt S. A computational model of a human single sinoatrial node cell. Biomed Phys Eng Express 2016; 2:035006. [PMID: 37608504 DOI: 10.1088/2057-1976/2/3/035006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Accepted: 03/18/2016] [Indexed: 02/07/2023]
Abstract
For the investigation of the spontaneous rhythmical activity response in the application of cardiac neuromodulation, we formulated a human sinoatrial node (SAN) cell model. With the aim of decreasing elevated heart rate (HR), we want to establish a hardware-in-the-loop system including this model for the analysis of optimal stimulation patterns of the neurostimulation system. Base model structures are adopted from rabbit SAN cell models available in literature and conveyed with Hodgkin-Huxley-type model equations describing the complex time and voltage dependent activation and deactivation processes of individual ion channels. The resulting model consists of 15 currents which are currently known to be responsible for the generation of the membrane action potential (AP). The model reproduces AP frequencies equivalent to those measured in isolated human SAN cells with a resulting HR of 71.8 bpm. Model validation via simulation of the inhibitory effect of ivabradine showed accordance with experimental results obtained in human studies. Furthermore, we could validate the model in regard to its HR effects upon parasympathetic stimulation with results obtained in a human trial study.
Collapse
Affiliation(s)
- A Pohl
- Philips Chair for Medical Information Technology, RWTH Aachen University, Pauwelsstr. 20, D-52074 Aachen, Germany
- Department of Cardiovascular and Thoracic Surgery, RWTH Aachen University Hospital, Pauwelsstr. 30, D-52074 Aachen, Germany
| | - A Wachter
- Department of Medical Statistics, University Medical Center Göttingen, Humboldtallee 32, D-37073 Göttingen, Germany
| | - N Hatam
- Department of Cardiovascular and Thoracic Surgery, RWTH Aachen University Hospital, Pauwelsstr. 30, D-52074 Aachen, Germany
| | - S Leonhardt
- Philips Chair for Medical Information Technology, RWTH Aachen University, Pauwelsstr. 20, D-52074 Aachen, Germany
| |
Collapse
|
27
|
Karppinen S, Rapila R, Naumenko N, Tuomainen T, Koivumäki JT, Hänninen SL, Korhonen T, Tavi P. Ca(2+) -activated K(+) current is essential for maintaining excitability and gene transcription in early embryonic cardiomyocytes. Acta Physiol (Oxf) 2016; 216:101-11. [PMID: 26095188 DOI: 10.1111/apha.12540] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Revised: 11/11/2014] [Accepted: 06/03/2015] [Indexed: 01/06/2023]
Abstract
AIM Activity of early embryonic cardiomyocytes relies on spontaneous Ca(2+) oscillations that are induced by interplay between sarcoplasmic reticulum (SR) - Ca(2+) release and ion currents of the plasma membrane. In a variety of cell types, Ca(2+) -activated K(+) current (IK(Ca) ) serves as a link between Ca(2+) signals and membrane voltage. This study aimed to determine the role of IK (Ca) in developing cardiomyocytes. METHODS Ion currents and membrane voltage of embryonic (E9-11) mouse cardiomyocytes were measured by patch clamp; [Ca(2+) ]i signals by confocal microscopy. Transcription of specific genes was measured with RT-qPCR and Ca(2+) -dependent transcriptional activity using NFAT-luciferase assay. Myocyte structure was assessed with antibody labelling and confocal microscopy. RESULTS E9-11 cardiomyocytes express small conductance (SK) channel subunits SK2 and SK3 and have a functional apamin-sensitive K(+) current, which is also sensitive to changes in cytosolic [Ca(2+) ]i . In spontaneously active cardiomyocytes, inhibition of IK (Ca) changed action and resting potentials, reduced SR Ca(2+) load and suppressed the amplitude and the frequency of spontaneously evoked Ca(2+) oscillations. Apamin caused dose-dependent suppression of NFAT-luciferase reporter activity, induced downregulation of a pattern of genes vital for cardiomyocyte development and triggered changes in the myocyte morphology. CONCLUSION The results show that apamin-sensitive IK (Ca) is required for maintaining excitability and activity of the developing cardiomyocytes as well as having a fundamental role in promoting Ca(2+) - dependent gene expression.
Collapse
Affiliation(s)
- S. Karppinen
- Department of Biotechnology and Molecular Medicine; A.I. Virtanen Institute for Molecular Sciences; University of Eastern Finland; Kuopio Finland
| | - R. Rapila
- Department of Biotechnology and Molecular Medicine; A.I. Virtanen Institute for Molecular Sciences; University of Eastern Finland; Kuopio Finland
| | - N. Naumenko
- Department of Biotechnology and Molecular Medicine; A.I. Virtanen Institute for Molecular Sciences; University of Eastern Finland; Kuopio Finland
| | - T. Tuomainen
- Department of Biotechnology and Molecular Medicine; A.I. Virtanen Institute for Molecular Sciences; University of Eastern Finland; Kuopio Finland
| | - J. T. Koivumäki
- Department of Biotechnology and Molecular Medicine; A.I. Virtanen Institute for Molecular Sciences; University of Eastern Finland; Kuopio Finland
| | - S. L. Hänninen
- Department of Biotechnology and Molecular Medicine; A.I. Virtanen Institute for Molecular Sciences; University of Eastern Finland; Kuopio Finland
- Institute of Biomedicine; Department of Physiology and Biocenter Oulu; University of Oulu; Oulu Finland
| | - T. Korhonen
- Department of Biotechnology and Molecular Medicine; A.I. Virtanen Institute for Molecular Sciences; University of Eastern Finland; Kuopio Finland
| | - P. Tavi
- Department of Biotechnology and Molecular Medicine; A.I. Virtanen Institute for Molecular Sciences; University of Eastern Finland; Kuopio Finland
| |
Collapse
|
28
|
Burr AR, Molkentin JD. Genetic evidence in the mouse solidifies the calcium hypothesis of myofiber death in muscular dystrophy. Cell Death Differ 2015; 22:1402-12. [PMID: 26088163 PMCID: PMC4532779 DOI: 10.1038/cdd.2015.65] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Revised: 04/03/2015] [Accepted: 04/17/2015] [Indexed: 01/19/2023] Open
Abstract
Muscular dystrophy (MD) refers to a clinically and genetically heterogeneous group of degenerative muscle disorders characterized by progressive muscle wasting and often premature death. Although the primary defect underlying most forms of MD typically results from a loss of sarcolemmal integrity, the secondary molecular mechanisms leading to muscle degeneration and myofiber necrosis is debated. One hypothesis suggests that elevated or dysregulated cytosolic calcium is the common transducing event, resulting in myofiber necrosis in MD. Previous measurements of resting calcium levels in myofibers from dystrophic animal models or humans produced equivocal results. However, recent studies in genetically altered mouse models have largely solidified the calcium hypothesis of MD, such that models with artificially elevated calcium in skeletal muscle manifest fulminant dystrophic-like disease, whereas models with enhanced calcium clearance or inhibited calcium influx are resistant to myofiber death and MD. Here, we will review the field and the recent cadre of data from genetically altered mouse models, which we propose have collectively mostly proven the hypothesis that calcium is the primary effector of myofiber necrosis in MD. This new consensus on calcium should guide future selection of drugs to be evaluated in clinical trials as well as gene therapy-based approaches.
Collapse
Affiliation(s)
- A R Burr
- Department of Pediatrics, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, 240 Albert Sabin Way, Cincinnati, OH, USA
| | - J D Molkentin
- 1] Department of Pediatrics, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, 240 Albert Sabin Way, Cincinnati, OH, USA [2] Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Howard Hughes Medical Institute, Molecular Cardiovascular Biology, 240 Albert Sabin Way, Cincinnati, OH, USA
| |
Collapse
|
29
|
Sun Y, Ye L, Liu J, Hong H. Hypoxia-induced cytosolic calcium influx is mediated primarily by the reverse mode of Na+/Ca2+ exchanger in smooth muscle cells of fetal small pulmonary arteries. J Obstet Gynaecol Res 2015; 40:1578-83. [PMID: 24888919 DOI: 10.1111/jog.12391] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2013] [Accepted: 12/18/2013] [Indexed: 12/01/2022]
Abstract
AIM Constriction of small pulmonary arteries and high resistance of pulmonary circulation are important for maintaining fetal circulation before birth. In this study, we investigated how cytosolic free calcium concentration ([Ca(2+)]i) in fetal lamb small pulmonary artery smooth muscle cells (SPASMC) was affected by hypoxia and regulated by calcium pumps during this process. METHODS (Ca(2+))i in response to acute hypoxia was determined spectrofluorometrically with fluo-3AM in cultured fetal SPASMC. Chemicals or solutions, including ryanodine, 2-aminoethoxydiphenyl borate, Ca(2+)-free solution with 20 mmol ethyleneglycoltetraacetic (EGTA), nimodipine, Na(+)-free medium and KB-R7943, were administrated at the same time point when samples were exposed to acute hypoxia. RESULTS (Ca(2+))i in fetal lamb SPASMC increased under acute hypoxia. 2-Aminoethoxydiphenyl borate, an inhibitor of inositol triphosphate calcium store, partially attenuated the (Ca(2+))i increase after 6-min treatment. Ryanodine, an inhibitor of ryanodine-sensitive calcium stores, had no effect on the (Ca(2+))i increase. Ca(2+)-free solution with EGTA completely abolished this increase. Both nimodipine, that blocks the voltage-gated calcium channel, and KB-R7943, that inhibits the reverse mode of Na(+)/Ca(2+) exchanger, greatly diminished the hypoxia-induced (Ca(2+))i increase. The inhibitory effect of KB-R7943 was stronger than nimodipine, evidenced by the fact that (Ca(2+))i dropped near to the baseline level in the presence of KB-R7943 at a later time point. Low extracellular Na(+) concentration enhanced the hypoxia-induced increase of (Ca(2+))i. CONCLUSION These results suggest that hypoxia-induced Ca(2+) increase in fetal SPASMC results from cytosolic Ca(2+) influx mediated primarily by the reverse mode of Na(+)/Ca(2+) exchanger.
Collapse
Affiliation(s)
- Yanjuan Sun
- Department of Cardiac and Thoracic Surgery, Shanghai Children's Medical Center, Shanghai Jiaotong University School of Medicine and Shanghai Pediatric Congenital Heart Disease Institute, Shanghai, China
| | | | | | | |
Collapse
|
30
|
The role of cellular coupling in the spontaneous generation of electrical activity in uterine tissue. PLoS One 2015; 10:e0118443. [PMID: 25793276 PMCID: PMC4368634 DOI: 10.1371/journal.pone.0118443] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Accepted: 01/16/2015] [Indexed: 11/19/2022] Open
Abstract
The spontaneous emergence of contraction-inducing electrical activity in the uterus at the beginning of labor remains poorly understood, partly due to the seemingly contradictory observation that isolated uterine cells are not spontaneously active. It is known, however, that the expression of gap junctions increases dramatically in the approach to parturition, by more than one order of magnitude, which results in a significant increase in inter-cellular electrical coupling. In this paper, we build upon previous studies of the activity of electrically excitable smooth muscle cells (myocytes) and investigate the mechanism through which the coupling of these cells to electrically passive cells results in the generation of spontaneous activity in the uterus. Using a recently developed, realistic model of uterine muscle cell dynamics, we investigate a system consisting of a myocyte coupled to passive cells. We then extend our analysis to a simple two-dimensional lattice model of the tissue, with each myocyte being coupled to its neighbors, as well as to a random number of passive cells. We observe that different dynamical regimes can be observed over a range of gap junction conductances: at low coupling strength, corresponding to values measured long before delivery, the activity is confined to cell clusters, while the activity for high coupling, compatible with values measured shortly before delivery, may spread across the entire tissue. Additionally, we find that the system supports the spontaneous generation of spiral wave activity. Our results are both qualitatively and quantitatively consistent with observations from in vitro experiments. In particular, we demonstrate that the increase in inter-cellular electrical coupling observed experimentally strongly facilitates the appearance of spontaneous action potentials that may eventually lead to parturition.
Collapse
|
31
|
EAD and DAD mechanisms analyzed by developing a new human ventricular cell model. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2014; 116:11-24. [PMID: 25192800 DOI: 10.1016/j.pbiomolbio.2014.08.008] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Accepted: 08/09/2014] [Indexed: 12/31/2022]
Abstract
It has long been suggested that the Ca(2+)-mechanisms are largely involved in generating the early afterdepolarization (EAD) as well as the delayed afterdepolarization (DAD). This view was examined in a quantitative manner by applying the lead potential analysis to a new human ventricular cell model. In this ventricular cell model, the tight coupled LCC-RyR model (CaRU) based on local control theory (Hinch et al. 2004) and ion channel models mostly based on human electrophysiological data were included to reproduce realistic Ca(2+) dynamics as well as the membrane excitation. Simultaneously, the Ca(2+) accumulation near the Ca(2+) releasing site was incorporated as observed in real cardiac myocytes. The maximum rate of ventricular repolarization (-1.02 mV/ms) is due to IK1 (-0.55 mV/ms) and the rest is provided nearly equally by INCX (-0.20 mV/ms), INaL (-0.16 mV/ms) and INaT (-0.13 mV/ms). These INaL and INaT components are due to closure of the voltage gate, which remains partially open during the plateau potential. DADs could be evoked by applying high-frequency stimulations supplemented by a partial Na(+)/K(+) pump inhibition, or by a microinjection of Ca(2+). EADs was evoked by retarding the inactivation of INaL. The lead potential (VL) analysis revealed that IK1 and IKr played the primary role to reverse the AP repolarization to depolarizing limb of EAD. ICaL and INCX amplified EAD, while the remaining currents partially antagonized dVL/dt. The maximum rate of rise of EAD was attributable to the rapid activation of both ICaL (45.5%) and INCX (54.5%).
Collapse
|
32
|
Barr LA, Makarewich CA, Berretta RM, Gao H, Troupes CD, Woitek F, Recchia F, Kubo H, Force T, Houser SR. Imatinib activates pathological hypertrophy by altering myocyte calcium regulation. Clin Transl Sci 2014; 7:360-7. [PMID: 24931551 DOI: 10.1111/cts.12173] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND Imatinib mesylate is a selective tyrosine-kinase inhibitor used in the treatment of multiple cancers, most notably chronic myelogenous leukemia. There is evidence that imatinib can induce cardiotoxicity in cancer patients. Our hypothesis is that imatinib alters calcium regulatory mechanisms and can contribute to development of pathological cardiac hypertrophy. METHODS AND RESULTS Neonatal rat ventricular myocytes (NRVMs) were treated with clinical doses (low: 2 μM; high: 5 μM) of imatinib and assessed for molecular changes. Imatinib increased peak systolic Ca(2+) and Ca(2+) transient decay rates and Western analysis revealed significant increases in phosphorylation of phospholamban (Thr-17) and the ryanodine receptor (Ser-2814), signifying activation of calcium/calmodulin-dependent kinase II (CaMKII). Imatinib significantly increased NRVM volume as assessed by Coulter counter, myocyte surface area, and atrial natriuretic peptide abundance seen by Western. Imatinib induced cell death, but did not activate the classical apoptotic program as assessed by caspase-3 cleavage, indicating a necrotic mechanism of death in myocytes. We expressed AdNFATc3-green fluorescent protein in NRVMs and showed imatinib treatment significantly increased nuclear factor of activated T cells translocation that was inhibited by the calcineurin inhibitor FK506 or CaMKII inhibitors. CONCLUSION These data show that imatinib can activate pathological hypertrophic signaling pathways by altering intracellular Ca(2+) dynamics. This is likely a contributing mechanism for the adverse cardiac effects of imatinib.
Collapse
Affiliation(s)
- Larry A Barr
- Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
33
|
Na+ dysregulation coupled with Ca2+ entry through NCX1 promotes muscular dystrophy in mice. Mol Cell Biol 2014; 34:1991-2002. [PMID: 24662047 DOI: 10.1128/mcb.00339-14] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Unregulated Ca(2+) entry is thought to underlie muscular dystrophy. Here, we generated skeletal-muscle-specific transgenic (TG) mice expressing the Na(+)-Ca(2+) exchanger 1 (NCX1) to model its identified augmentation during muscular dystrophy. The NCX1 transgene induced dystrophy-like disease in all hind-limb musculature, as well as exacerbated the muscle disease phenotypes in δ-sarcoglycan (Sgcd(-/-)), Dysf(-/-), and mdx mouse models of muscular dystrophy. Antithetically, muscle-specific deletion of the Slc8a1 (NCX1) gene diminished hind-limb pathology in Sgcd(-/-) mice. Measured increases in baseline Na(+) and Ca(2+) in dystrophic muscle fibers of the hind-limb musculature predicts a net Ca(2+) influx state due to reverse-mode operation of NCX1, which mediates disease. However, the opposite effect is observed in the diaphragm, where NCX1 overexpression mildly protects from dystrophic disease through a predicted enhancement in forward-mode NCX1 operation that reduces Ca(2+) levels. Indeed, Atp1a2(+/-) (encoding Na(+)-K(+) ATPase α2) mice, which have reduced Na(+) clearance rates that would favor NCX1 reverse-mode operation, showed exacerbated disease in the hind limbs of NCX1 TG mice, similar to treatment with the Na(+)-K(+) ATPase inhibitor digoxin. Treatment of Sgcd(-/-) mice with ranolazine, a broadly acting Na(+) channel inhibitor that should increase NCX1 forward-mode operation, reduced muscular pathology.
Collapse
|
34
|
Khananshvili D. The SLC8 gene family of sodium-calcium exchangers (NCX) - structure, function, and regulation in health and disease. Mol Aspects Med 2013; 34:220-35. [PMID: 23506867 DOI: 10.1016/j.mam.2012.07.003] [Citation(s) in RCA: 153] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2011] [Accepted: 03/08/2012] [Indexed: 01/12/2023]
Abstract
The SLC8 gene family encoding Na(+)/Ca(2+) exchangers (NCX) belongs to the CaCA (Ca(2+)/Cation Antiporter) superfamily. Three mammalian genes (SLC8A1, SLC8A2, and SLC8A3) and their splice variants are expressed in a tissue-specific manner to mediate Ca(2+)-fluxes across the cell-membrane and thus, significantly contribute to regulation of Ca(2+)-dependent events in many cell types. A long-wanted mitochondrial Na(+)/Ca(2+) exchanger has been recently identified as NCLX protein, representing a gene product of SLC8B1. Distinct NCX isoform/splice variants contribute to excitation-contraction coupling, long-term potentiation of the brain and learning, blood pressure regulation, immune response, neurotransmitter and insulin secretion, mitochondrial bioenergetics, etc. Altered expression and regulation of NCX proteins contribute to distorted Ca(2+)-homeostasis in heart failure, arrhythmia, cerebral ischemia, hypertension, diabetes, renal Ca(2+) reabsorption, muscle dystrophy, etc. Recently, high-resolution X-ray structures of Ca(2+)-binding regulatory domains of eukaryotic NCX and of full-size prokaryotic NCX have become available and the dynamic properties have been analyzed by advanced biophysical approaches. Molecular silencing/overexpression of NCX in cellular systems and organ-specific KO mouse models provided useful information on the contribution of distinct NCX variants to cellular and systemic functions under various pathophysiological conditions. Selective inhibition or activation of predefined NCX variants in specific diseases might have clinical relevance, although this breakthrough has not yet been realized. A better understanding of the underlying molecular mechanisms as well as the development of in vitro procedures for high-throughput screening of "drug-like" compounds may lead to selective pharmacological targeting of NCX variants.
Collapse
Affiliation(s)
- Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978, Israel.
| |
Collapse
|
35
|
Abstract
Calcium (Ca(2+)) uptake into the mitochondrial matrix is critically important to cellular function. As a regulator of matrix Ca(2+) levels, this flux influences energy production and can initiate cell death. If large, this flux could potentially alter intracellular Ca(2+) ([Ca(2+)]i) signals. Despite years of study, fundamental disagreements on the extent and speed of mitochondrial Ca(2+) uptake still exist. Here, we review and quantitatively analyze mitochondrial Ca(2+) uptake fluxes from different tissues and interpret the results with respect to the recently proposed mitochondrial Ca(2+) uniporter (MCU) candidate. This quantitative analysis yields four clear results: (i) under physiological conditions, Ca(2+) influx into the mitochondria via the MCU is small relative to other cytosolic Ca(2+) extrusion pathways; (ii) single MCU conductance is ∼6-7 pS (105 mM [Ca(2+)]), and MCU flux appears to be modulated by [Ca(2+)]i, suggesting Ca(2+) regulation of MCU open probability (P(O)); (iii) in the heart, two features are clear: the number of MCU channels per mitochondrion can be calculated, and MCU probability is low under normal conditions; and (iv) in skeletal muscle and liver cells, uptake per mitochondrion varies in magnitude but total uptake per cell still appears to be modest. Based on our analysis of available quantitative data, we conclude that although Ca(2+) critically regulates mitochondrial function, the mitochondria do not act as a significant dynamic buffer of cytosolic Ca(2+) under physiological conditions. Nevertheless, with prolonged (superphysiological) elevations of [Ca(2+)]i, mitochondrial Ca(2+) uptake can increase 10- to 1,000-fold and begin to shape [Ca(2+)]i dynamics.
Collapse
|
36
|
Boyman L, Williams GSB, Khananshvili D, Sekler I, Lederer WJ. NCLX: the mitochondrial sodium calcium exchanger. J Mol Cell Cardiol 2013; 59:205-13. [PMID: 23538132 PMCID: PMC3951392 DOI: 10.1016/j.yjmcc.2013.03.012] [Citation(s) in RCA: 128] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Accepted: 03/15/2013] [Indexed: 11/18/2022]
Abstract
The free Ca(2+) concentration within the mitochondrial matrix ([Ca(2+)]m) regulates the rate of ATP production and other [Ca(2+)]m sensitive processes. It is set by the balance between total Ca(2+) influx (through the mitochondrial Ca(2+) uniporter (MCU) and any other influx pathways) and the total Ca(2+) efflux (by the mitochondrial Na(+)/Ca(2+) exchanger and any other efflux pathways). Here we review and analyze the experimental evidence reported over the past 40years which suggest that in the heart and many other mammalian tissues a putative Na(+)/Ca(2+) exchanger is the major pathway for Ca(2+) efflux from the mitochondrial matrix. We discuss those reports with respect to a recent discovery that the protein product of the human FLJ22233 gene mediates such Na(+)/Ca(2+) exchange across the mitochondrial inner membrane. Among its many functional similarities to other Na(+)/Ca(2+) exchanger proteins is a unique feature: it efficiently mediates Li(+)/Ca(2+) exchange (as well as Na(+)/Ca(2+) exchange) and was therefore named NCLX. The discovery of NCLX provides both the identity of a novel protein and new molecular means of studying various unresolved quantitative aspects of mitochondrial Ca(2+) movement out of the matrix. Quantitative and qualitative features of NCLX are discussed as is the controversy regarding the stoichiometry of the NCLX Na(+)/Ca(2+) exchange, the electrogenicity of NCLX, the [Na(+)]i dependency of NCLX and the magnitude of NCLX Ca(2+) efflux. Metabolic features attributable to NCLX and the physiological implication of the Ca(2+) efflux rate via NCLX during systole and diastole are also briefly discussed.
Collapse
Affiliation(s)
- Liron Boyman
- Center for Biomedical Engineering and Technology and Dept. Physiology, University of Maryland School of Medicine, Baltimore, MD 21201
| | - George S. B. Williams
- Center for Biomedical Engineering and Technology and Dept. Physiology, University of Maryland School of Medicine, Baltimore, MD 21201
- School of Systems Biology, College of Science, George Mason University, Manassas, VA 20110
| | - Daniel Khananshvili
- Sackler School of Medicine, Department of Physiology and Pharmacology, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Israel Sekler
- Goldman Medical School, Dept. Biology & Neurobiology, Ben Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105, Israel
| | - W. J. Lederer
- Center for Biomedical Engineering and Technology and Dept. Physiology, University of Maryland School of Medicine, Baltimore, MD 21201
| |
Collapse
|
37
|
Chu B, Postma M, Hardie R. Fractional Ca(2+) currents through TRP and TRPL channels in Drosophila photoreceptors. Biophys J 2013; 104:1905-16. [PMID: 23663833 PMCID: PMC3647204 DOI: 10.1016/j.bpj.2013.03.047] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Revised: 03/05/2013] [Accepted: 03/25/2013] [Indexed: 01/29/2023] Open
Abstract
Light responses in Drosophila photoreceptors are mediated by two Ca(2+) permeable cation channels, transient receptor potential (TRP) and TRP-like (TRPL). Although Ca(2+) influx via these channels is critical for amplification, inactivation, and light adaptation, the fractional contribution of Ca(2+) to the currents (Pf) has not been measured. We describe a slow (τ ∼ 350 ms) tail current in voltage-clamped light responses and show that it is mediated by electrogenic Na(+)/Ca(2+) exchange. Assuming a 3Na:1Ca stoichiometry, we derive empirical estimates of Pf by comparing the charge integrals of the exchanger and light-induced currents. For TRPL channels, Pf was ∼17% as predicted by Goldman-Hodgkin-Katz (GHK) theory. Pf for TRP (29%) and wild-type flies (26%) was higher, but lower than the GHK prediction (45% and 42%). As predicted by GHK theory, Pf for both channels increased with extracellular [Ca(2+)], and was largely independent of voltage between -100 and -30 mV. A model incorporating intra- and extracellular geometry, ion permeation, diffusion, extrusion, and buffering suggested that the deviation from GHK predictions was largely accounted for by extracellular ionic depletion during the light-induced currents, and the time course of the Na(+)/Ca(2+) exchange current could be used to obtain estimates of cellular Ca(2+) buffering capacities.
Collapse
Affiliation(s)
- Brian Chu
- Department of Physiology, Development and Neuroscience, Cambridge University, Cambridge, UK
| | - Marten Postma
- Section of Molecular Cytology, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands
| | - Roger C. Hardie
- Department of Physiology, Development and Neuroscience, Cambridge University, Cambridge, UK
| |
Collapse
|
38
|
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: 2.5] [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.
Collapse
Affiliation(s)
- Kenneth S Ginsburg
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
| | | | | |
Collapse
|
39
|
Giladi M, Khananshvili D. Molecular determinants of allosteric regulation in NCX proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 961:35-48. [PMID: 23224868 DOI: 10.1007/978-1-4614-4756-6_4] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Allosteric activation of NCX involves the binding of cytosolic Ca(2+) to regulatory domains CBD1 and CBD2. Previous studies with isolated CBD12 and full-size NCX identified synergistic interactions between the two CBD domains that modify the affinity and kinetic properties of Ca(2+) sensing, although it remains unclear how the Ca(2+)-binding signal is decoded and propagates to transmembrane domains. Biophysical analyses (X-ray, SAXS, and stopped-flow techniques) of isolated preparations of CBD1, CBD2, and CBD12 have shown that Ca(2+) binding to Ca3-Ca4 sites of CBD1 results in interdomain tethering of CBDs through specific amino acids on CBD1 (Asp499 and Asp500) and CBD2 (Arg532 and Asp565). Mutant analyses of isolated CBDs suggest that the two-domain interface governs Ca(2+)-driven conformational alignment of CBDs, resulting in slow dissociation of Ca(2+) from CBD12, and thus, it mediates Ca(2+)-induced conformational transitions associated with allosteric signal transmission. Specifically, occupation of Ca3-Ca4 sites by Ca(2+) induces disorder-to-order transition owing to charge neutralization and coordination, thereby constraining CBD conformational freedom, rigidifying the NCX1 f-loop, and triggering allosteric signal transmission to the membrane domain. The newly found interdomain switch is highly conserved among NCX isoform/splice variants, although some additional structural motifs may shape the regulatory specificity of NCX variants.
Collapse
Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, Israel
| | | |
Collapse
|
40
|
Roome CJ, Power EM, Empson RM. Transient reversal of the sodium/calcium exchanger boosts presynaptic calcium and synaptic transmission at a cerebellar synapse. J Neurophysiol 2012; 109:1669-80. [PMID: 23255722 DOI: 10.1152/jn.00854.2012] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The sodium/calcium exchanger (NCX) is a widespread transporter that exchanges sodium and calcium ions across excitable membranes. Normally, NCX mainly operates in its "forward" mode, harnessing the electrochemical gradient of sodium ions to expel calcium. During membrane depolarization or elevated internal sodium levels, NCX can instead switch the direction of net flux to expel sodium and allow calcium entry. Such "reverse"-mode NCX operation is frequently implicated during pathological or artificially extended periods of depolarization, not during normal activity. We have used fast calcium imaging, mathematical simulation, and whole cell electrophysiology to study the role of NCX at the parallel fiber-to-Purkinje neuron synapse in the mouse cerebellum. We show that nontraditional, reverse-mode NCX activity boosts the amplitude and duration of parallel fiber calcium transients during short bursts of high-frequency action potentials typical of their behavior in vivo. Simulations, supported by experimental manipulations, showed that accumulation of intracellular sodium drove NCX into reverse mode. This mechanism fueled additional calcium influx into the parallel fibers that promoted synaptic transmission to Purkinje neurons for up to 400 ms after the burst. Thus we provide the first functional demonstration of transient and fast NCX-mediated calcium entry at a major central synapse. This unexpected contribution from reverse-mode NCX appears critical for shaping presynaptic calcium dynamics and transiently boosting synaptic transmission, and is likely to optimize the accuracy of cerebellar information transfer.
Collapse
Affiliation(s)
- Chris J Roome
- Department of Physiology, Brain Health Research Centre, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand
| | | | | |
Collapse
|
41
|
Niederer SA, Land S, Omholt SW, Smith NP. Interpreting genetic effects through models of cardiac electromechanics. Am J Physiol Heart Circ Physiol 2012; 303:H1294-303. [PMID: 23042948 DOI: 10.1152/ajpheart.00121.2012] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Multiscale models of cardiac electromechanics are being increasingly focused on understanding how genetic variation and environment underpin multiple disease states. In this paper we review the current state of the art in both the development of specific models and the physiological insights they have produced. This growing research body includes the development of models for capturing the effects of changes in function in both single and multiple proteins in both specific expression systems and in vivo contexts. Finally, the potential for using this approach for ultimately predicting phenotypes from genetic sequence information is discussed.
Collapse
Affiliation(s)
- S A Niederer
- Department of Biomedical Engineering, King's College London, King's Health Partners, Saint Thomas' Hospital, London, UK
| | | | | | | |
Collapse
|
42
|
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: 1.8] [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.
Collapse
|
43
|
Gauthier LD, Greenstein JL, Winslow RL. Toward an integrative computational model of the Guinea pig cardiac myocyte. Front Physiol 2012; 3:244. [PMID: 22783206 PMCID: PMC3389778 DOI: 10.3389/fphys.2012.00244] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2012] [Accepted: 06/14/2012] [Indexed: 11/22/2022] Open
Abstract
The local control theory of excitation-contraction (EC) coupling asserts that regulation of calcium (Ca2+) release occurs at the nanodomain level, where openings of single L-type Ca2+ channels (LCCs) trigger openings of small clusters of ryanodine receptors (RyRs) co-localized within the dyad. A consequence of local control is that the whole-cell Ca2+ transient is a smooth continuous function of influx of Ca2+ through LCCs. While this so-called graded release property has been known for some time, its functional importance to the integrated behavior of the cardiac ventricular myocyte has not been fully appreciated. We previously formulated a biophysically based model, in which LCCs and RyRs interact via a coarse-grained representation of the dyadic space. The model captures key features of local control using a low-dimensional system of ordinary differential equations. Voltage-dependent gain and graded Ca2+ release are emergent properties of this model by virtue of the fact that model formulation is closely based on the sub-cellular basis of local control. In this current work, we have incorporated this graded release model into a prior model of guinea pig ventricular myocyte electrophysiology, metabolism, and isometric force production. The resulting integrative model predicts the experimentally observed causal relationship between action potential (AP) shape and timing of Ca2+ and force transients, a relationship that is not explained by models lacking the graded release property. Model results suggest that even relatively subtle changes in AP morphology that may result, for example, from remodeling of membrane transporter expression in disease or spatial variation in cell properties, may have major impact on the temporal waveform of Ca2+ transients, thus influencing tissue level electromechanical function.
Collapse
Affiliation(s)
- Laura Doyle Gauthier
- Department of Biomedical Engineering, Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering Baltimore, MD, USA
| | | | | |
Collapse
|
44
|
Nivala M, de Lange E, Rovetti R, Qu Z. Computational modeling and numerical methods for spatiotemporal calcium cycling in ventricular myocytes. Front Physiol 2012; 3:114. [PMID: 22586402 PMCID: PMC3346978 DOI: 10.3389/fphys.2012.00114] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Accepted: 04/06/2012] [Indexed: 11/13/2022] Open
Abstract
Intracellular calcium (Ca) cycling dynamics in cardiac myocytes is regulated by a complex network of spatially distributed organelles, such as sarcoplasmic reticulum (SR), mitochondria, and myofibrils. In this study, we present a mathematical model of intracellular Ca cycling and numerical and computational methods for computer simulations. The model consists of a coupled Ca release unit (CRU) network, which includes a SR domain and a myoplasm domain. Each CRU contains 10 L-type Ca channels and 100 ryanodine receptor channels, with individual channels simulated stochastically using a variant of Gillespie’s method, modified here to handle time-dependent transition rates. Both the SR domain and the myoplasm domain in each CRU are modeled by 5 × 5 × 5 voxels to maintain proper Ca diffusion. Advanced numerical algorithms implemented on graphical processing units were used for fast computational simulations. For a myocyte containing 100 × 20 × 10 CRUs, a 1-s heart time simulation takes about 10 min of machine time on a single NVIDIA Tesla C2050. Examples of simulated Ca cycling dynamics, such as Ca sparks, Ca waves, and Ca alternans, are shown.
Collapse
Affiliation(s)
- Michael Nivala
- Department of Medicine (Cardiology), David Geffen School of Medicine University of California Los Angeles, CA, USA
| | | | | | | |
Collapse
|
45
|
Livshitz L, Acsai K, Antoons G, Sipido K, Rudy Y. Data-based theoretical identification of subcellular calcium compartments and estimation of calcium dynamics in cardiac myocytes. J Physiol 2012; 590:4423-46. [PMID: 22547631 DOI: 10.1113/jphysiol.2012.228791] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
In cardiac cells, Ca(2+) release flux (J(rel)) via ryanodine receptors (RyRs) from the sarcoplasmic reticulum (SR) has a complex effect on the action potential (AP). Coupling between J(rel) and the AP occurs via L-type Ca(2+) channels (I(Ca)) and the Na(+)/Ca(2+) exchanger (I(NCX)). We used a combined experimental and modelling approach to study interactions between J(rel), I(Ca) and I(NCX) in porcine ventricular myocytes.We tested the hypothesis that during normal uniform J(rel), the interaction between these fluxes can be represented as occurring in two myoplasmic subcompartments for Ca(2+) distribution, one (T-space) associated with RyR and enclosed by the junctional portion of the SR membrane and corresponding T-tubular portion of the sarcolemma, the other (M-space) encompassing the rest of the myoplasm. I(Ca) and I(NCX) were partitioned into subpopulations in the T-space and M-space sarcolemma. We denoted free Ca(2+) concentrations in T-space and M-space Ca(t) and Ca(m), respectively. Experiments were designed to allow separate measurements of I(Ca) and I(NCX) as a function of J(rel). Inclusion of T-space in themodel allowed us to reproduce in silico the following important experimental results: (1) hysteresis of I(NCX) dependence on Ca(m); (2) delay between peak I(NCX) and peak Ca(m) during caffeine application protocol; (3) delay between I(NCX) and Ca(m) during Ca(2+)-induced-Ca(2+)-release; (4) rapid I(Ca) inactivation (within 2 ms) due to J(rel), with magnitude graded as a function of the SR Ca(2+) content; (5) time delay between I(Ca) inactivation due to J(rel) and Ca(m). Partition of 25% NCX in T-space and 75% in M-space provided the best fit to the experimental data. Measured Ca(m) and I(Ca) or I(NCX) were used as input to the model for estimating Ca(t). The actual model-computed Ca(t), obtained by simulating specific experimental protocols, was used as a gold standard for comparison. The model predicted peak Ca(t) in the range of 6–25 μM, with time to equilibrium of Ca(t) with Ca(m) of ~350 ms. These Ca(t) values are in the range of LCC and RyR sensitivity to Ca(2+). An increase of the SR Ca(2+) load increased the time to equilibrium. The I(Ca)-based estimation method was most accurate during the ascending phase of Ca(t). The I(NCX)-based method provided a good estimate for the descending phase of Ca(t). Thus, application of both methods in combination provides the best estimate of the entire Ca(t) time course.
Collapse
Affiliation(s)
- Leonid Livshitz
- Cardiac Bioelectricity and Arrhythmia Centre, Washington University in St Louis, St Louis, MO 63130-4899, USA
| | | | | | | | | |
Collapse
|
46
|
Zhang XQ, Wang J, Song J, Ji AM, Chan TO, Cheung JY. Residues 248-252 and 300-304 of the cardiac Na+/Ca2+ exchanger are involved in its regulation by phospholemman. Am J Physiol Cell Physiol 2011; 301:C833-40. [PMID: 21734189 PMCID: PMC3191572 DOI: 10.1152/ajpcell.00069.2011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2011] [Accepted: 07/05/2011] [Indexed: 11/22/2022]
Abstract
Using split cardiac Na(+)/Ca(2+) exchangers (NCX1), we previously demonstrated that phospholemman (PLM) regulates NCX1 by interacting with the proximal linker domain (residues 218-358) of the intracellular loop of NCX1. With the use of overlapping loop deletion mutants, interaction sites are localized to two regions spanning residues 238-270 and residues 300-328 of NCX1. In this study, we used alanine (Ala) linker scanning to pinpoint the residues in the proximal linker domain involved in regulation of NCX1 by PLM. Transfection of human embryonic kidney (HEK)293 cells with wild-type (WT) NCX1 or its Ala mutants but not empty vector resulted in NCX1 current (I(NaCa)). Coexpression of PLM with WT NCX1 inhibited I(NaCa). Mutating residues 248-252 (PASKT) or 300-304 (QKHPD) in WT NCX1 to Ala resulted in loss of inhibition of I(NaCa) by PLM. By contrast, inhibition of I(NaCa) by PLM was preserved when residues 238-242, 243-247, 253-257, 258-262, 263-267, 305-309, 310-314, 315-319, 320-324, or 325-329 were mutated to Ala. While mutating residue 301 to alanine completely abolished PLM inhibition, mutation of any single residue 250-252, 300, or 302-304 resulted in partial reduction in inhibition. Mutating residues 248-252 to Ala resulted in significantly weaker association with PLM. The NCX1-G503P mutant that lacks Ca(2+)-dependent activation retained its sensitivity to PLM. We conclude that residues 248-252 and 300-304 in the proximal linker domain of NCX1 were involved in its inhibition by PLM.
Collapse
Affiliation(s)
- Xue-Qian Zhang
- Division of Nephrology, Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania, USA
| | | | | | | | | | | |
Collapse
|
47
|
Boyman L, Hagen BM, Giladi M, Hiller R, Lederer WJ, Khananshvili D. Proton-sensing Ca2+ binding domains regulate the cardiac Na+/Ca2+ exchanger. J Biol Chem 2011; 286:28811-28820. [PMID: 21680748 DOI: 10.1074/jbc.m110.214106] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cardiac Na(+)/Ca(2+) exchanger (NCX) regulates cellular [Ca(2+)](i) and plays a central role in health and disease, but its molecular regulation is poorly understood. Here we report on how protons affect this electrogenic transporter by modulating two critically important NCX C(2) regulatory domains, Ca(2+) binding domain-1 (CBD1) and CBD2. The NCX transport rate in intact cardiac ventricular myocytes was measured as a membrane current, I(NCX), whereas [H(+)](i) was varied using an ammonium chloride "rebound" method at constant extracellular pH 7.4. At pH(i) = 7.2 and [Ca(2+)](i) < 120 nM, I(NCX) was less than 4% that of its maximally Ca(2+)-activated value. I(NCX) increases steeply at [Ca(2+)](i) between 130-150 nM with a Hill coefficient (n(H)) of 8.0 ± 0.7 and K(0.5) = 310 ± 5 nM. At pH(i) = 6.87, the threshold of Ca(2+)-dependent activation of I(NCX) was shifted to much higher [Ca(2+)](i) (600-700 nM), and the relationship was similarly steep (n(H) = 8.0±0.8) with K(0.5) = 1042 ± 15 nM. The V(max) of Ca(2+)-dependent activation of I(NCX) was not significantly altered by low pH(i). The Ca(2+) affinities for CBD1 (0.39 ± 0.06 μM) and CBD2 (K(d) = 18.4 ± 6 μM) were exquisitely sensitive to [H(+)], decreasing 1.3-2.3-fold as pH(i) decreased from 7.2 to 6.9. This work reveals for the first time that NCX can be switched off by physiologically relevant intracellular acidification and that this depends on the competitive binding of protons to its C(2) regulatory domains CBD1 and CBD2.
Collapse
Affiliation(s)
- Liron Boyman
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat-Aviv 69978, Israel and; Laboratory of Molecular Cardiology, Center for Biomedical Engineering and Technology, University of Maryland, Baltimore, Maryland 21201
| | - Brian M Hagen
- Laboratory of Molecular Cardiology, Center for Biomedical Engineering and Technology, University of Maryland, Baltimore, Maryland 21201
| | - Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat-Aviv 69978, Israel and
| | - Reuben Hiller
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat-Aviv 69978, Israel and
| | - W Jonathan Lederer
- Laboratory of Molecular Cardiology, Center for Biomedical Engineering and Technology, University of Maryland, Baltimore, Maryland 21201
| | - Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat-Aviv 69978, Israel and.
| |
Collapse
|
48
|
Tong WC, Choi CY, Karche S, Holden AV, Zhang H, Taggart MJ. A computational model of the ionic currents, Ca2+ dynamics and action potentials underlying contraction of isolated uterine smooth muscle. PLoS One 2011; 6:e18685. [PMID: 21559514 PMCID: PMC3084699 DOI: 10.1371/journal.pone.0018685] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2010] [Accepted: 03/15/2011] [Indexed: 11/18/2022] Open
Abstract
Uterine contractions during labor are discretely regulated by rhythmic action potentials (AP) of varying duration and form that serve to determine calcium-dependent force production. We have employed a computational biology approach to develop a fuller understanding of the complexity of excitation-contraction (E-C) coupling of uterine smooth muscle cells (USMC). Our overall aim is to establish a mathematical platform of sufficient biophysical detail to quantitatively describe known uterine E-C coupling parameters and thereby inform future empirical investigations of physiological and pathophysiological mechanisms governing normal and dysfunctional labors. From published and unpublished data we construct mathematical models for fourteen ionic currents of USMCs: Ca2+ currents (L- and T-type), Na+ current, an hyperpolarization-activated current, three voltage-gated K+ currents, two Ca2+-activated K+ current, Ca2+-activated Cl current, non-specific cation current, Na+-Ca2+ exchanger, Na+-K+ pump and background current. The magnitudes and kinetics of each current system in a spindle shaped single cell with a specified surface area:volume ratio is described by differential equations, in terms of maximal conductances, electrochemical gradient, voltage-dependent activation/inactivation gating variables and temporal changes in intracellular Ca2+ computed from known Ca2+ fluxes. These quantifications are validated by the reconstruction of the individual experimental ionic currents obtained under voltage-clamp. Phasic contraction is modeled in relation to the time constant of changing [Ca2+]i. This integrated model is validated by its reconstruction of the different USMC AP configurations (spikes, plateau and bursts of spikes), the change from bursting to plateau type AP produced by estradiol and of simultaneous experimental recordings of spontaneous AP, [Ca2+]i and phasic force. In summary, our advanced mathematical model provides a powerful tool to investigate the physiological ionic mechanisms underlying the genesis of uterine electrical E-C coupling of labor and parturition. This will furnish the evolution of descriptive and predictive quantitative models of myometrial electrogenesis at the whole cell and tissue levels.
Collapse
Affiliation(s)
- Wing-Chiu Tong
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
- Maternal and Fetal Health Research Centre, St. Mary's Hospital, University of Manchester, Manchester, United Kingdom
| | - Cecilia Y. Choi
- School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
| | - Sanjay Karche
- School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
| | - Arun V. Holden
- Institute of Membrane and System Biology, University of Leeds, Leeds, United Kingdom
| | - Henggui Zhang
- School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
| | - Michael J. Taggart
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
- Maternal and Fetal Health Research Centre, St. Mary's Hospital, University of Manchester, Manchester, United Kingdom
| |
Collapse
|
49
|
Acsai K, Antoons G, Livshitz L, Rudy Y, Sipido KR. Microdomain [Ca²⁺] near ryanodine receptors as reported by L-type Ca²⁺ and Na+/Ca²⁺ exchange currents. J Physiol 2011; 589:2569-83. [PMID: 21486798 DOI: 10.1113/jphysiol.2010.202663] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
During Ca²⁺ release from the sarcoplasmic reticulum triggered by Ca²⁺ influx through L-type Ca²⁺ channels (LTCCs), [Ca²⁺] near release sites ([Ca²⁺]nrs) temporarily exceeds global cytosolic [Ca²⁺]. [Ca²⁺]nrs can at present not be measured directly but the Na+/Ca2+ exchanger (NCX) near release sites and LTCCs also experience [Ca²⁺]nrs. We have tested the hypothesis that ICaL and INCX could be calibrated to report [Ca²⁺]nrs and would report different time course and values for local [Ca²⁺]. Experiments were performed in pig ventricular myocytes (whole-cell voltage-clamp, Fluo-3 to monitor global cytosolic [Ca²⁺], 37◦C). [Ca²⁺]nrs-dependent inactivation of ICaL during a step to +10 mV peaked around 10 ms. For INCX we computationally isolateda current fraction activated by [Ca²⁺]nrs; values were maximal at 10 ms into depolarization. The recovery of [Ca²⁺]nrs was comparable with both reporters (>90% within 50 ms). Calibration yielded maximal values for [Ca²⁺]nrs between 10 and 15 μmol l⁻¹ with both methods. When applied to a step to less positive potentials (-30 to -20 mV), the time course of [Ca²⁺]nrs was slower but peak values were not very different. In conclusion, both ICaL inactivation and INCX activation, using a subcomponent analysis, can be used to report dynamic changes of [Ca²⁺]nrs. Absolute values obtained by these different methods are within the same range, suggesting that they are reporting on a similar functional compartment near ryanodine receptors. Comparable [Ca²⁺]nrs at +10 mV and -20 mV suggests that, although the number of activated release sites differs at these potentials, local gradients at release sites can reach similar values.
Collapse
Affiliation(s)
- Karoly Acsai
- Lab of Experimental Cardiology, Catholic University of Leuven, Belgium
| | | | | | | | | |
Collapse
|
50
|
Krishna A, Sun L, Valderrábano M, Palade PT, Clark JW. Modeling CICR in rat ventricular myocytes: voltage clamp studies. Theor Biol Med Model 2010; 7:43. [PMID: 21062495 PMCID: PMC3245510 DOI: 10.1186/1742-4682-7-43] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2010] [Accepted: 11/10/2010] [Indexed: 01/08/2023] Open
Abstract
Background The past thirty-five years have seen an intense search for the molecular mechanisms underlying calcium-induced calcium-release (CICR) in cardiac myocytes, with voltage clamp (VC) studies being the leading tool employed. Several VC protocols including lowering of extracellular calcium to affect Ca2+ loading of the sarcoplasmic reticulum (SR), and administration of blockers caffeine and thapsigargin have been utilized to probe the phenomena surrounding SR Ca2+ release. Here, we develop a deterministic mathematical model of a rat ventricular myocyte under VC conditions, to better understand mechanisms underlying the response of an isolated cell to calcium perturbation. Motivation for the study was to pinpoint key control variables influencing CICR and examine the role of CICR in the context of a physiological control system regulating cytosolic Ca2+ concentration ([Ca2+]myo). Methods The cell model consists of an electrical-equivalent model for the cell membrane and a fluid-compartment model describing the flux of ionic species between the extracellular and several intracellular compartments (cell cytosol, SR and the dyadic coupling unit (DCU), in which resides the mechanistic basis of CICR). The DCU is described as a controller-actuator mechanism, internally stabilized by negative feedback control of the unit's two diametrically-opposed Ca2+ channels (trigger-channel and release-channel). It releases Ca2+ flux into the cyto-plasm and is in turn enclosed within a negative feedback loop involving the SERCA pump, regulating[Ca2+]myo. Results Our model reproduces measured VC data published by several laboratories, and generates graded Ca2+ release at high Ca2+ gain in a homeostatically-controlled environment where [Ca2+]myo is precisely regulated. We elucidate the importance of the DCU elements in this process, particularly the role of the ryanodine receptor in controlling SR Ca2+ release, its activation by trigger Ca2+, and its refractory characteristics mediated by the luminal SR Ca2+ sensor. Proper functioning of the DCU, sodium-calcium exchangers and SERCA pump are important in achieving negative feedback control and hence Ca2+ homeostasis. Conclusions We examine the role of the above Ca2+ regulating mechanisms in handling various types of induced disturbances in Ca2+ levels by quantifying cellular Ca2+ balance. Our model provides biophysically-based explanations of phenomena associated with CICR generating useful and testable hypotheses.
Collapse
Affiliation(s)
- Abhilash Krishna
- Department of Electrical and Computer Engineering, Rice University, Houston, TX 77005, USA.
| | | | | | | | | |
Collapse
|