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Herting JR, König JH, Hadova K, Heinick A, Müller FU, Pauls P, Seidl MD, Soppa C, Kirchhefer U. Hypercontractile cardiac phenotype in mice overexpressing the regulatory subunit PR72 of protein phosphatase 2A. Front Cardiovasc Med 2023; 10:1239555. [PMID: 37868783 PMCID: PMC10590119 DOI: 10.3389/fcvm.2023.1239555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Accepted: 09/22/2023] [Indexed: 10/24/2023] Open
Abstract
Background The activity, localization, and substrate specificity of the protein phosphatase 2A (PP2A) heterotrimer are controlled by various regulatory B subunits. PR72 belongs to the B'' gene family and has been shown to be upregulated in human heart failure. However, little is known about the functions of PR72 in the myocardium. Methods To address this issue, we generated a transgenic mouse model with heart-specific overexpression of PP2A-PR72. Biochemical and physiological methods were used to determine contractility, Ca2+ cycling parameters, and protein phosphorylation. Results A 2.5-fold increase in PR72 expression resulted in moderate cardiac hypertrophy. Maximal ventricular pressure was increased in catheterized transgenic mice (TG) compared to wild-type (WT) littermates. This was accompanied by an increased shortening of sarcomere length and faster relaxation at the single-cell level in TG. In parallel with these findings, the peak amplitude of Ca2+ transients was increased, and the decay in intracellular Ca2+ levels was shortened in TG compared to WT. The changes in Ca2+ cycling in TG were also evident from an increase in the full duration and width at half maximum of Ca2+ sparks. Consistent with the contractile data, phosphorylation of phospholamban at threonine-17 was higher in TG hearts. The lower expression of the Na+/Ca2+ exchanger may also contribute to the hypercontractile state in transgenic myocardium. Conclusion Our results suggest that PP2A-PR72 plays an important role in regulating cardiac contractile function and Ca2+ cycling, indicating that the upregulation of PR72 in heart failure is an attempt to compensate functionally.
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Affiliation(s)
- Julius R. Herting
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
| | - Jule H. König
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
| | - Katarina Hadova
- Department of Pharmacology and Toxicology, Faculty of Pharmacy, Comenius University in Bratislava, Bratislava, Slovakia
| | - Alexander Heinick
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
| | - Frank U. Müller
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
| | - Paul Pauls
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
| | - Matthias D. Seidl
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
| | - Carolina Soppa
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
| | - Uwe Kirchhefer
- Institut für Pharmakologie und Toxikologie, Universitätsklinikum Münster, Universität Münster, Münster, Germany
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Structure-Based Function and Regulation of NCX Variants: Updates and Challenges. Int J Mol Sci 2022; 24:ijms24010061. [PMID: 36613523 PMCID: PMC9820601 DOI: 10.3390/ijms24010061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2022] [Revised: 12/14/2022] [Accepted: 12/15/2022] [Indexed: 12/24/2022] Open
Abstract
The plasma-membrane homeostasis Na+/Ca2+ exchangers (NCXs) mediate Ca2+ extrusion/entry to dynamically shape Ca2+ signaling/in biological systems ranging from bacteria to humans. The NCX gene orthologs, isoforms, and their splice variants are expressed in a tissue-specific manner and exhibit nearly 104-fold differences in the transport rates and regulatory specificities to match the cell-specific requirements. Selective pharmacological targeting of NCX variants could benefit many clinical applications, although this intervention remains challenging, mainly because a full-size structure of eukaryotic NCX is unavailable. The crystal structure of the archaeal NCX_Mj, in conjunction with biophysical, computational, and functional analyses, provided a breakthrough in resolving the ion transport mechanisms. However, NCX_Mj (whose size is nearly three times smaller than that of mammalian NCXs) cannot serve as a structure-dynamic model for imitating high transport rates and regulatory modules possessed by eukaryotic NCXs. The crystal structures of isolated regulatory domains (obtained from eukaryotic NCXs) and their biophysical analyses by SAXS, NMR, FRET, and HDX-MS approaches revealed structure-based variances of regulatory modules. Despite these achievements, it remains unclear how multi-domain interactions can decode and integrate diverse allosteric signals, thereby yielding distinct regulatory outcomes in a given ortholog/isoform/splice variant. This article summarizes the relevant issues from the perspective of future developments.
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Jost N, Christ T, Magyar J. New Strategies for the Treatment of Atrial Fibrillation. Pharmaceuticals (Basel) 2021; 14:ph14090926. [PMID: 34577626 PMCID: PMC8466466 DOI: 10.3390/ph14090926] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Revised: 09/07/2021] [Accepted: 09/08/2021] [Indexed: 12/19/2022] Open
Abstract
Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia in the clinical practice. It significantly contributes to the morbidity and mortality of the elderly population. Over the past 25-30 years intense effort in basic research has advanced the understanding of the relationship between the pathophysiology of AF and atrial remodelling. Nowadays it is clear that the various forms of atrial remodelling (electrical, contractile and structural) play crucial role in initiating and maintaining the persistent and permanent types of AF. Unlike in ventricular fibrillation, in AF rapid ectopic firing originating from pulmonary veins and re-entry mechanism may induce and maintain (due to atrial remodelling) this complex cardiac arrhythmia. The present review presents and discusses in detail the latest knowledge on the role of remodelling in AF. Special attention is paid to novel concepts and pharmacological targets presumably relevant to the drug treatment of atrial fibrillation.
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Affiliation(s)
- Norbert Jost
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, 6725 Szeged, Hungary
- Department of Pharmacology and Pharmacotherapy, Interdisciplinary Excellence Centre, University of Szeged, 6725 Szeged, Hungary
- ELKH-SZTE Research Group for Cardiovascular Pharmacology, Eötvös Loránd Research Network, 6725 Szeged, Hungary
- Correspondence:
| | - Torsten Christ
- Institute of Experimental Pharmacology and Toxicology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany;
- DZHK (German Center for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, 20246 Hamburg, Germany
| | - János Magyar
- Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary;
- Department of Sport Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary
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4
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Lariccia V, Macrì ML, Matteucci A, Maiolino M, Amoroso S, Magi S. Effects of ticagrelor on the sodium/calcium exchanger 1 (NCX1) in cardiac derived H9c2 cells. Eur J Pharmacol 2019; 850:158-166. [PMID: 30721704 DOI: 10.1016/j.ejphar.2019.01.067] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2018] [Revised: 01/08/2019] [Accepted: 01/17/2019] [Indexed: 12/15/2022]
Abstract
Ticagrelor is a direct acting and reversibly binding P2Y12 antagonist approved for the prevention of thromboembolic events. Clinical effects of ticagrelor cannot be simply accounted for by pure platelet inhibition, and off-target mechanisms can potentially play a role. In particular, recent evidence suggests that ticagrelor may also influence heart function and improve the evolution of myocardial ischemic injury by more direct effects on myocytes. The cardiac sodium/calcium exchanger 1 (NCX1) is a critical player in the generation and control of calcium (Ca2+) signals, which orchestrate multiple myocyte activities in health and disease. Altered expression and/or activity of NCX1 can have profound consequences for the function and fate of myocytes. Whether ticagrelor affects cardiac NCX1 has not been investigated yet. To explore this hypothesis, we analyzed the expression, localization and activity of NCX1 in the heart derived H9c2-NCX1 cells following ticagrelor exposure. We found that ticagrelor concentration- and time-dependently reduced the activity of the cardiac NCX1 in H9c2 cells. In particular, the inhibitory effect of ticagrelor on the Ca2+-influx mode of NCX1 was evident within 1 h and further developed after 24 h, when NCX1 activity was suppressed by about 55% in cells treated with 1 μM ticagrelor. Ticagrelor-induced inhibition of exchanger activity was reached at clinically relevant concentrations, without affecting the expression levels and subcellular distribution of NCX1. Collectively, these findings suggest that cardiac NCX1 is a new downstream target of ticagrelor, which may contribute to the therapeutic profile of ticagrelor in clinical practice.
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Affiliation(s)
- Vincenzo Lariccia
- Department of Biomedical Sciences and Public Health, School of Medicine, University "Politecnica delle Marche", Via Tronto 10/A, 60126 Ancona, Italy.
| | - Maria Loredana Macrì
- Department of Biomedical Sciences and Public Health, School of Medicine, University "Politecnica delle Marche", Via Tronto 10/A, 60126 Ancona, Italy
| | - Alessandra Matteucci
- Department of Biomedical Sciences and Public Health, School of Medicine, University "Politecnica delle Marche", Via Tronto 10/A, 60126 Ancona, Italy
| | - Marta Maiolino
- Department of Biomedical Sciences and Public Health, School of Medicine, University "Politecnica delle Marche", Via Tronto 10/A, 60126 Ancona, Italy
| | - Salvatore Amoroso
- Department of Biomedical Sciences and Public Health, School of Medicine, University "Politecnica delle Marche", Via Tronto 10/A, 60126 Ancona, Italy
| | - Simona Magi
- Department of Biomedical Sciences and Public Health, School of Medicine, University "Politecnica delle Marche", Via Tronto 10/A, 60126 Ancona, Italy
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5
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Lubelwana Hafver T, Wanichawan P, Manfra O, de Souza GA, Lunde M, Martinsen M, Louch WE, Sejersted OM, Carlson CR. Mapping the in vitro interactome of cardiac sodium (Na + )-calcium (Ca 2+ ) exchanger 1 (NCX1). Proteomics 2017; 17. [PMID: 28755400 DOI: 10.1002/pmic.201600417] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Revised: 07/03/2017] [Accepted: 07/26/2017] [Indexed: 11/07/2022]
Abstract
The sodium (Na+ )-calcium (Ca2+ ) exchanger 1 (NCX1) is an antiporter membrane protein encoded by the SLC8A1 gene. In the heart, it maintains cytosolic Ca2+ homeostasis, serving as the primary mechanism for Ca2+ extrusion during relaxation. Dysregulation of NCX1 is observed in end-stage human heart failure. In this study, we used affinity purification coupled with MS in rat left ventricle lysates to identify novel NCX1 interacting proteins in the heart. Two screens were conducted using: (1) anti-NCX1 against endogenous NCX1 and (2) anti-His (where His is histidine) with His-trigger factor-NCX1cyt recombinant protein as bait. The respective methods identified 112 and 350 protein partners, of which several were known NCX1 partners from the literature, and 29 occurred in both screens. Ten novel protein partners (DYRK1A, PPP2R2A, SNTB1, DMD, RABGGTA, DNAJB4, BAG3, PDE3A, POPDC2, STK39) were validated for binding to NCX1, and two partners (DYRK1A, SNTB1) increased NCX1 activity when expressed in HEK293 cells. A cardiac NCX1 protein-protein interaction map was constructed. The map was highly connected, containing distinct clusters of proteins with different biological functions, where "cell communication" and "signal transduction" formed the largest clusters. The NCX1 interactome was also significantly enriched with proteins/genes involved in "cardiovascular disease" which can be explored as novel drug targets in future research.
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Affiliation(s)
- Tandekile Lubelwana Hafver
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Pimthanya Wanichawan
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Ornella Manfra
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Gustavo Antonio de Souza
- Department of Immunology and Centre for Immune Regulation, Oslo University Hospital HF Rikshospitalet, University of Oslo, Oslo, Norway.,The Brain Institute, Universidade Federal do Rio Grande do Norte, Natal, RN, Brazil.,Bioinformatics Multidisciplinary Environment, Instituto Metrópole Digital, UFRN, Natal, RN, Brazil
| | - Marianne Lunde
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Marita Martinsen
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - William Edward Louch
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Ole Mathias Sejersted
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Cathrine Rein Carlson
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
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6
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Gong H, Li Y, Wang L, Lv Q, Wang X. Short-term effects of β2-AR blocker ICI 118,551 on sarcoplasmic reticulum SERCA2a and cardiac function of rats with heart failure. Exp Ther Med 2016; 12:1355-1362. [PMID: 27602067 PMCID: PMC4998176 DOI: 10.3892/etm.2016.3450] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Accepted: 06/13/2016] [Indexed: 01/15/2023] Open
Abstract
The study was conducted to examine the effects of ICI 118,551 on the systolic function of cardiac muscle cells of rats in heart failure and determine the molecular mechanism of selective β2-adrenergic receptor (β2-AR) antagonist on these cells. The chronic heart failure model for rats was prepared through abdominal aortic constriction and separate cardiac muscle cells using the collagenase digestion method. The rats were then divided into Sham, HF and HF+ICI 50 nM goups and cultivated for 48 h. β2-AR, Gi/Gs and sarcoplasmic reticulum Ca2+-ATPase (SERCA2a) protein expression levels in the cardiac muscle cells were evaluated by western blotting and changes in the systolic function of cardiac muscle cells based on the boundary detection system of contraction dynamics for individual cells was measured. The results showed that compared with the Sham group, the survival rate, percentage of basic contraction and maximum contraction amplitude percentage of cardiac muscle cells with heart failure decreased, Gi protein expression increased while Gs and SERCA2a protein expression decreased. Compared with the HF group, the maximum contraction amplitude percentage of cardiac muscle cells in group HF+ICI 50 nM decreased, the Gi protein expression level increased while the SERCA2a protein expression level decreased. Following the stimulation of Ca2+ and ISO, the maximum contraction amplitude percentage of cardiac muscle cells in the HF+ICI 50 nM group was lower than that in group HF. This indicated that ICI 118,551 has negative inotropic effects on cardiac muscle cells with heart failure, which may be related to Gi protein. Systolic function of cardiac muscle cells with heart failure can therefore be reduced by increasing Gi protein expression and lowering SERCA2a protein expression.
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Affiliation(s)
- Haibin Gong
- Department of Cardiology, Xuzhou Central Hospital, Xuzhou Cardiovascular Disease Institute, Xuzhou, Jiangsu 221009, P.R. China
| | - Yanfei Li
- Department of Cardiology, Xuzhou Central Hospital, Xuzhou Cardiovascular Disease Institute, Xuzhou, Jiangsu 221009, P.R. China
| | - Lei Wang
- Department of Cardiology, Xuzhou Central Hospital, Xuzhou Cardiovascular Disease Institute, Xuzhou, Jiangsu 221009, P.R. China
| | - Qian Lv
- Department of Cardiology, Xuzhou Central Hospital, Xuzhou Cardiovascular Disease Institute, Xuzhou, Jiangsu 221009, P.R. China
| | - Xiuli Wang
- Department of Cardiology, Xuzhou Central Hospital, Xuzhou Cardiovascular Disease Institute, Xuzhou, Jiangsu 221009, P.R. China
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7
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Geramipour A, Kohajda Z, Corici C, Prorok J, Szakonyi Z, Oravecz K, Márton Z, Nagy N, Tóth A, Acsai K, Virág L, Varró A, Jost N. The investigation of the cellular electrophysiological and antiarrhythmic effects of a novel selective sodium-calcium exchanger inhibitor, GYKB-6635, in canine and guinea-pig hearts. Can J Physiol Pharmacol 2016; 94:1090-1101. [PMID: 27508313 DOI: 10.1139/cjpp-2015-0566] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The sodium-calcium exchanger (NCX) is considered as the major transmembrane transport mechanism that controls Ca2+ homeostasis. Its contribution to the cardiac repolarization has not yet been directly studied due to lack of specific inhibitors, so that an urgent need for more selective compounds. In this study, the electrophysiological effects of GYKB-6635, a novel NCX inhibitor, on the NCX, L-type calcium, and main repolarizing potassium currents as well as action potential (AP) parameters were investigated. Ion currents and AP recordings were investigated by applying the whole-cell patch clamp and standard microelectrode techniques in canine heart at 37 °C. Effects of GYKB-6635 were studied in ouabain-induced arrhythmias in isolated guinea-pig hearts. At a concentration of 1 μmol/L, GYKB significantly reduced both the inward and outward NCX currents (57% and 58%, respectively). Even at a high concentration (10 μmol/L), GYKB-6635 did not change the ICaL, the maximum rate of depolarization (dV/dtmax), the main repolarizing K+ currents, and the main AP parameters. GYKB-6635 pre-treatment significantly delayed the time to the development of ventricular fibrillation (by about 18%). It is concluded that GYKB-6635 is a potent and highly selective inhibitor of the cardiac NCX and, in addition, it is suggested to also contribute to the prevention of DAD-based arrhythmias.
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Affiliation(s)
- Amir Geramipour
- a Department of Pharmacology & Pharmacotherapy, Faculty of Medicine, University of Szeged, H-6720 Szeged, Hungary
| | - Zsófia Kohajda
- b MTA-SZTE Research Group of Cardiovascular Pharmacology, Szeged, Hungary
| | - Claudia Corici
- a Department of Pharmacology & Pharmacotherapy, Faculty of Medicine, University of Szeged, H-6720 Szeged, Hungary
| | - János Prorok
- a Department of Pharmacology & Pharmacotherapy, Faculty of Medicine, University of Szeged, H-6720 Szeged, Hungary
| | - Zsolt Szakonyi
- c Institute of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Szeged, H-6720 Szeged, Hungary
| | - Kinga Oravecz
- a Department of Pharmacology & Pharmacotherapy, Faculty of Medicine, University of Szeged, H-6720 Szeged, Hungary
| | - Zoltán Márton
- a Department of Pharmacology & Pharmacotherapy, Faculty of Medicine, University of Szeged, H-6720 Szeged, Hungary
| | - Norbert Nagy
- b MTA-SZTE Research Group of Cardiovascular Pharmacology, Szeged, Hungary
| | - András Tóth
- a Department of Pharmacology & Pharmacotherapy, Faculty of Medicine, University of Szeged, H-6720 Szeged, Hungary.,b MTA-SZTE Research Group of Cardiovascular Pharmacology, Szeged, Hungary
| | - Károly Acsai
- b MTA-SZTE Research Group of Cardiovascular Pharmacology, Szeged, Hungary
| | - László Virág
- a Department of Pharmacology & Pharmacotherapy, Faculty of Medicine, University of Szeged, H-6720 Szeged, Hungary.,b MTA-SZTE Research Group of Cardiovascular Pharmacology, Szeged, Hungary
| | - András Varró
- a Department of Pharmacology & Pharmacotherapy, Faculty of Medicine, University of Szeged, H-6720 Szeged, Hungary.,b MTA-SZTE Research Group of Cardiovascular Pharmacology, Szeged, Hungary
| | - Norbert Jost
- b MTA-SZTE Research Group of Cardiovascular Pharmacology, Szeged, Hungary.,d "Victor Babes" University of Medicine and Pharmacy, Timisoara, Romania
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8
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Inhibition of the cardiac ATP-dependent potassium current by KB-R7943. Comp Biochem Physiol A Mol Integr Physiol 2014; 175:38-45. [PMID: 24845199 DOI: 10.1016/j.cbpa.2014.05.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Revised: 05/12/2014] [Accepted: 05/13/2014] [Indexed: 11/23/2022]
Abstract
KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea) was developed as a specific inhibitor of the sarcolemmal sodium-calcium exchanger (NCX) with potential experimental and therapeutic use. However, in cardiomyocytes KB-R7943 also effectively blocks several K(+) currents including the delayed rectifier, IKr, and background inward rectifier, IK1. In the present study we analyze the effects of KB-R7943 on the ATP-dependent potassium current (IKATP) recorded by whole-cell patch-clamp in ventricular cardiomyocytes from a mammal (mouse) and a fish (crucian carp). IKATP was induced by external application of a mitochondrial uncoupler CCCP (3×10(-7) M) and internal perfusion of the cell with ATP-free pipette solution. A weakly inwardly rectifying current with a large outward component, recorded in the presence of CCCP, was blocked with 10(-5) M glibenclamide by 56.1±4.6% and 56.9±3.6% in crucian carp and mouse ventricular myocytes, respectively. In fish cardiomyocytes IKATP was blocked by KB-R7943 with an IC50 value of 3.14×10(-7) M, while in mammalian cells IC50 was 2.8×10(-6) M (P<0.05). 10(-5) M KB-R7943 inhibited CCCP-induced IKATP by 99.9±0.13% and 97.5±1.2% in crucian carp and mouse ventricular myocytes, respectively. In crucian carp the IKATP is about an order of magnitude more sensitive to KB-R7943 than the background IK1, but in mammals IKATP and IK1 are almost equally sensitive to KB-R7943. Therefore, the ability of KB-R7943 to block IKATP should be taken into account together with INCX inhibition when investigating possible cardioprotective effects of this compound.
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Khananshvili D. Sodium-calcium exchangers (NCX): molecular hallmarks underlying the tissue-specific and systemic functions. Pflugers Arch 2013; 466:43-60. [PMID: 24281864 DOI: 10.1007/s00424-013-1405-y] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2013] [Revised: 11/06/2013] [Accepted: 11/09/2013] [Indexed: 12/19/2022]
Abstract
NCX proteins explore the electrochemical gradient of Na(+) to mediate Ca(2+)-fluxes in exchange with Na(+) either in the Ca(2+)-efflux (forward) or Ca(2+)-influx (reverse) mode, whereas the directionality depends on ionic concentrations and membrane potential. Mammalian NCX variants (NCX1-3) and their splice variants are expressed in a tissue-specific manner to modulate the heartbeat rate and contractile force, the brain's long-term potentiation and learning, blood pressure, renal Ca(2+) reabsorption, the immune response, neurotransmitter and insulin secretion, apoptosis and proliferation, mitochondrial bioenergetics, etc. Although the forward mode of NCX represents a major physiological module, a transient reversal of NCX may contribute to EC-coupling, vascular constriction, and synaptic transmission. Notably, the reverse mode of NCX becomes predominant in pathological settings. Since the expression levels of NCX variants are disease-related, the selective pharmacological targeting of tissue-specific NCX variants could be beneficial, thereby representing a challenge. Recent structural and biophysical studies revealed a common module for decoding the Ca(2+)-induced allosteric signal in eukaryotic NCX variants, although the phenotype variances in response to regulatory Ca(2+) remain unclear. The breakthrough discovery of the archaebacterial NCX structure may serve as a template for eukaryotic NCX, although the turnover rates of the transport cycle may differ ~10(3)-fold among NCX variants to fulfill the physiological demands for the Ca(2+) flux rates. Further elucidation of ion-transport and regulatory mechanisms may lead to selective pharmacological targeting of NCX variants under disease conditions.
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Affiliation(s)
- Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, 69978, Israel,
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10
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Sensitivity of rabbit ventricular action potential and Ca²⁺ dynamics to small variations in membrane currents and ion diffusion coefficients. BIOMED RESEARCH INTERNATIONAL 2013; 2013:565431. [PMID: 24222910 PMCID: PMC3814049 DOI: 10.1155/2013/565431] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/28/2013] [Accepted: 08/19/2013] [Indexed: 12/19/2022]
Abstract
Little is known about how small variations in ionic currents and Ca²⁺ and Na⁺ diffusion coefficients impact action potential and Ca²⁺ dynamics in rabbit ventricular myocytes. We applied sensitivity analysis to quantify the sensitivity of Shannon et al. model (Biophys. J., 2004) to 5%-10% changes in currents conductance, channels distribution, and ion diffusion in rabbit ventricular cells. We found that action potential duration and Ca²⁺ peaks are highly sensitive to 10% increase in L-type Ca²⁺ current; moderately influenced by 10% increase in Na⁺-Ca²⁺ exchanger, Na⁺-K⁺ pump, rapid delayed and slow transient outward K⁺ currents, and Cl⁻ background current; insensitive to 10% increases in all other ionic currents and sarcoplasmic reticulum Ca²⁺ fluxes. Cell electrical activity is strongly affected by 5% shift of L-type Ca²⁺ channels and Na⁺-Ca²⁺ exchanger in between junctional and submembrane spaces while Ca²⁺-activated Cl⁻-channel redistribution has the modest effect. Small changes in submembrane and cytosolic diffusion coefficients for Ca²⁺, but not in Na⁺ transfer, may alter notably myocyte contraction. Our studies highlight the need for more precise measurements and further extending and testing of the Shannon et al. model. Our results demonstrate usefulness of sensitivity analysis to identify specific knowledge gaps and controversies related to ventricular cell electrophysiology and Ca²⁺ signaling.
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11
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Jost N, Virág L, Comtois P, Ordög B, Szuts V, Seprényi G, Bitay M, Kohajda Z, Koncz I, Nagy N, Szél T, Magyar J, Kovács M, Puskás LG, Lengyel C, Wettwer E, Ravens U, Nánási PP, Papp JG, Varró A, Nattel S. Ionic mechanisms limiting cardiac repolarization reserve in humans compared to dogs. J Physiol 2013; 591:4189-206. [PMID: 23878377 DOI: 10.1113/jphysiol.2013.261198] [Citation(s) in RCA: 106] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The species-specific determinants of repolarization are poorly understood. This study compared the contribution of various currents to cardiac repolarization in canine and human ventricle. Conventional microelectrode, whole-cell patch-clamp, molecular biological and mathematical modelling techniques were used. Selective IKr block (50-100 nmol l(-1) dofetilide) lengthened AP duration at 90% of repolarization (APD90) >3-fold more in human than dog, suggesting smaller repolarization reserve in humans. Selective IK1 block (10 μmol l(-1) BaCl2) and IKs block (1 μmol l(-1) HMR-1556) increased APD90 more in canine than human right ventricular papillary muscle. Ion current measurements in isolated cardiomyocytes showed that IK1 and IKs densities were 3- and 4.5-fold larger in dogs than humans, respectively. IKr density and kinetics were similar in human versus dog. ICa and Ito were respectively ~30% larger and ~29% smaller in human, and Na(+)-Ca(2+) exchange current was comparable. Cardiac mRNA levels for the main IK1 ion channel subunit Kir2.1 and the IKs accessory subunit minK were significantly lower, but mRNA expression of ERG and KvLQT1 (IKr and IKs α-subunits) were not significantly different, in human versus dog. Immunostaining suggested lower Kir2.1 and minK, and higher KvLQT1 protein expression in human versus canine cardiomyocytes. IK1 and IKs inhibition increased the APD-prolonging effect of IKr block more in dog (by 56% and 49%, respectively) than human (34 and 16%), indicating that both currents contribute to increased repolarization reserve in the dog. A mathematical model incorporating observed human-canine ion current differences confirmed the role of IK1 and IKs in repolarization reserve differences. Thus, humans show greater repolarization-delaying effects of IKr block than dogs, because of lower repolarization reserve contributions from IK1 and IKs, emphasizing species-specific determinants of repolarization and the limitations of animal models for human disease.
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Affiliation(s)
- Norbert Jost
- A. Varró: Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, H-6720 Szeged, Dóm tér 12, PO Box 427, Hungary.
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Cheng H, Zhang Y, Du C, Dempsey CE, Hancox JC. High potency inhibition of hERG potassium channels by the sodium-calcium exchange inhibitor KB-R7943. Br J Pharmacol 2012; 165:2260-73. [PMID: 21950687 DOI: 10.1111/j.1476-5381.2011.01688.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE KB-R7943 is an isothiourea derivative that is used widely as a pharmacological inhibitor of sodium-calcium exchange (NCX) in experiments on cardiac and other tissue types. This study investigated KB-R7943 inhibition of hERG (human ether-à-go-go-related gene) K(+) channels that underpin the cardiac rapid delayed rectifier potassium current, I(Kr) . EXPERIMENTAL APPROACH Whole-cell patch-clamp measurements were made of hERG current (I(hERG) ) carried by wild-type or mutant hERG channels and of native rabbit ventricular I(Kr) . Docking simulations utilized a hERG homology model built on a MthK-based template. KEY RESULTS KB-R7943 inhibited both I(hERG) and native I(Kr) rapidly on membrane depolarization with IC(50) values of ∼89 and ∼120 nM, respectively, for current tails at -40 mV following depolarizing voltage commands to +20 mV. Marked I(hERG) inhibition also occurred under ventricular action potential voltage clamp. I(hERG) inhibition by KB-R7943 exhibited both time- and voltage-dependence but showed no preference for inactivated over activated channels. Results of alanine mutagenesis and docking simulations indicate that KB-R7943 can bind to a pocket formed of the side chains of aromatic residues Y652 and F656, with the compound's nitrobenzyl group orientated towards the cytoplasmic side of the channel pore. The structurally related NCX inhibitor SN-6 also inhibited I(hERG) , but with a markedly reduced potency. CONCLUSIONS AND IMPLICATIONS KB-R7943 inhibits I(hERG) /I(Kr) with a potency that exceeds that reported previously for acute cardiac NCX inhibition. Our results also support the feasibility of benzyloxyphenyl-containing NCX inhibitors with reduced potential, in comparison with KB-R7943, to inhibit hERG.
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de la Cruz GG, Groschner K, Oliver Kappe C, Glasnov TN. High-speed microwave assisted synthesis of SEA0400—a selective inhibitor of the Na+/Ca2+ exchanger. Tetrahedron Lett 2012. [DOI: 10.1016/j.tetlet.2012.04.120] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Frommeyer G, Eckardt L, Milberg P. Calcium handling and ventricular tachyarrhythmias. Wien Med Wochenschr 2012; 162:283-6. [PMID: 22673935 DOI: 10.1007/s10354-012-0104-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2012] [Accepted: 05/30/2012] [Indexed: 10/28/2022]
Abstract
Pharmacologic modification of cellular calcium handling recently moved into focus as an alternative for prevention and treatment of ventricular tachyarrhythmias. Calcium overload and spontaneous calcium release from the sarcoplasmatic reticulum are regarded as possible initiations of early and delayed afterdepolarization thereby triggering ventricular arrhythmias. In chronic heart failure, calcium overload is more likely to occur compared with healthy hearts, which is one explantation for the increased vulnerability in this condition. L-type calcium channel, sodium-calcium-exchanger (NCX), and ryanodine receptor are crucial for calcium homeostasis and therefore represent potential targets for antiarrhythmic drug therapy. Experimental studies have proven beneficial effects for all these three mechanisms in prevention and suppression of tachyarrhythmias. However, clinical data is mainly available for the L-type calcium channel inhibitor verapamil. Therefore, it is still a long way to clinical employment of drugs modifying cellular calcium handling for antiarrhythmic therapy.
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Affiliation(s)
- Gerrit Frommeyer
- Division of Clinical and Experimental Electrophysiology, Department of Cardiology and Angiology, University of Münster, Albert-Schweitzer Campus 1, 48149 Münster, Germany.
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Romero L, Carbonell B, Trenor B, Rodríguez B, Saiz J, Ferrero JM. Systematic characterization of the ionic basis of rabbit cellular electrophysiology using two ventricular models. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 107:60-73. [PMID: 21749896 DOI: 10.1016/j.pbiomolbio.2011.06.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Accepted: 06/27/2011] [Indexed: 01/08/2023]
Abstract
Several mathematical models of rabbit ventricular action potential (AP) have been proposed to investigate mechanisms of arrhythmias and excitation-contraction coupling. Our study aims at systematically characterizing how ionic current properties modulate the main cellular biomarkers of arrhythmic risk using two widely-used rabbit ventricular models, and comparing simulation results using the two models with experimental data available for rabbit. A sensitivity analysis of AP properties, Ca²⁺ and Na⁺ dynamics, and their rate dependence to variations (±15% and ±30%) in the main transmembrane current conductances and kinetics was performed using the Shannon et al. (2004) and the Mahajan et al. (2008a,b) AP rabbit models. The effects of severe transmembrane current blocks (up to 100%) on steady-state AP and calcium transients, and AP duration (APD) restitution curves were also simulated using both models. Our simulations show that, in both virtual rabbit cardiomyocytes, APD is significantly modified by most repolarization currents, AP triangulation is regulated mostly by the inward rectifier K⁺ current (I(K1)) whereas APD rate adaptation as well as [Na⁺](i) rate dependence is influenced by the Na⁺/K⁺ pump current (I(NaK)). In addition, steady-state [Ca²⁺](i) levels, APD restitution properties and [Ca²⁺](i) rate dependence are strongly dependent on I(NaK), the L-Type Ca²⁺ current (I(CaL)) and the Na⁺/Ca²⁺ exchanger current (I(NaCa)), although the relative role of these currents is markedly model dependent. Furthermore, our results show that simulations using both models agree with many experimentally-reported electrophysiological characteristics. However, our study shows that the Shannon et al. model mimics rabbit electrophysiology more accurately at normal pacing rates, whereas Mahajan et al. model behaves more appropriately at faster rates. Our results reinforce the usefulness of sensitivity analysis for further understanding of cellular electrophysiology and validation of cardiac AP models.
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Affiliation(s)
- Lucía Romero
- Instituto de Investigación Interuniversitario en Bioingeniería y Tecnología Orientada al Ser Humano (I3BH), Universitat Politècnica de València (UPV), Camino de Vera s/n, 46022 Valencia, Spain.
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Haizlip KM, Janssen PML. In vitro studies of early cardiac remodeling: impact on contraction and calcium handling. Front Biosci (Schol Ed) 2011; 3:1047-57. [PMID: 21622254 DOI: 10.2741/209] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Cardiac remodeling, hypertrophy, and alterations in calcium signaling are changes of the heart that often lead to failure. After a hypertrophic stimulus, the heart progresses through a state of compensated hypertrophy which over time leads to decompensated hypertrophy or failure. It is at this point that a cardiac transplant is required for survival making early detection imperative. Current experimental systems used to study the remodeling of the heart include in vivo systems (the whole body), isolated organ and sub-organ tissue, and the individual cardiac muscle cells and organelles.. During pathological remodeling there is a derangement in the intracellular calcium handling processes. These derangements are thought to lead to a dysregulation of contractile output. Hence, understanding the mechanism between remodeling and dysregulation is of great interest in the cardiac field and will ultimately help in the development of future treatment and early detection. This review will center on changes in contraction and calcium handling in early cardiac remodeling, with a specific focus on findings in two different in vitro model systems: multicellular and individual cell preparations.
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Affiliation(s)
- Kaylan M Haizlip
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH 43210-1218, USA
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Chen L, Zhang J, Hu X, Philipson KD, Scharf SM. The Na+/Ca2+ exchanger-1 mediates left ventricular dysfunction in mice with chronic intermittent hypoxia. J Appl Physiol (1985) 2010; 109:1675-85. [PMID: 20947716 DOI: 10.1152/japplphysiol.01372.2009] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Chronic intermittent hypoxia (CIH) and cardiovascular dysfunction occur in patients with obstructive sleep apnea. We hypothesized that the Na(+)/Ca(2+) exchanger-1 (NCX1) mediates, at least partially, left ventricular (LV) dysfunction in CIH. Four groups of mice (N = 15-17 per group), either cardiac-specific NCX1 knockouts (KO) or wild types (WT), were exposed to either CIH or normoxia [i.e., handled controls (HC)] 10 h/day for 8 wk. As expected, myocardial expression of NCX1 was greater in WT than in KO animals, both in HC and CIH-exposed groups. In both CIH groups (WT or KO), but not the HC groups, blood pressure increased by 10% at week 1 over their baseline and remained elevated for all 8 wk, with no differences between WT and KO. LV dilation (increased diastolic and systolic dimension) and hypertrophy (increased left heart weight), along with LV dysfunction (greater end-diastolic pressure and lower ejection fraction), were observed in the WT animals compared with the KO following CIH exposure. Compared with HC, CIH exposure was associated with apoptosis (terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling and caspase-3) in WT, but not KO, mice. We conclude that myocardial NCX1 does not mediate changes in blood pressure, but is one of the mediators for LV global dysfunction and cardiomyocyte injury in CIH.
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Affiliation(s)
- Ling Chen
- Department of Medicine, University of Maryland, Baltimore, Maryland, USA.
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