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Atici A, Tatlisu MA, Baycan OF, Yılmaz Y, Caliskan M. A rare cause of idiopathic right outflow tract premature ventricular contraction: Type-4 renal tubular acidosis. Pacing Clin Electrophysiol 2022; 45:811-814. [PMID: 35067955 DOI: 10.1111/pace.14455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/10/2021] [Revised: 01/11/2022] [Accepted: 01/21/2022] [Indexed: 12/29/2022]
Abstract
The premature ventricular contractions (PVCs) have usually good prognosis in patients without structural heart disease. In case of left ventricular ejection fraction depression or symptoms, antiarrhythmic drugs or cardiac ablations could be an option for management. We present a case of a patient with high burden of PVC admitted for cardiac ablation. Preoperative assessment revealed hyperkalemia and metabolic acidosis which ended up with type-4 renal tubular acidosis (RTA). Its rare cause and management may draw attention to the possibility of type -4 RTA as the cause of the PVC, and hyperkalemia.
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Affiliation(s)
- Adem Atici
- Cardiology Department, Istanbul Medeniyet University Faculty of Medicine, Goztepe Training and Research Hospital, Istanbul, Turkey
| | - Mustafa Adem Tatlisu
- Cardiology Department, Istanbul Medeniyet University Faculty of Medicine, Goztepe Training and Research Hospital, Istanbul, Turkey
| | - Omer Faruk Baycan
- Cardiology Department, Istanbul Medeniyet University Faculty of Medicine, Goztepe Training and Research Hospital, Istanbul, Turkey
| | - Yusuf Yılmaz
- Cardiology Department, Istanbul Medeniyet University Faculty of Medicine, Goztepe Training and Research Hospital, Istanbul, Turkey
| | - Mustafa Caliskan
- Cardiology Department, Istanbul Medeniyet University Faculty of Medicine, Goztepe Training and Research Hospital, Istanbul, Turkey
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Pharmacological Modulation and (Patho)Physiological Roles of TRPM4 Channel-Part 2: TRPM4 in Health and Disease. Pharmaceuticals (Basel) 2021; 15:ph15010040. [PMID: 35056097 PMCID: PMC8779181 DOI: 10.3390/ph15010040] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 12/21/2021] [Accepted: 12/22/2021] [Indexed: 02/06/2023] Open
Abstract
Transient receptor potential melastatin 4 (TRPM4) is a unique member of the TRPM protein family and, similarly to TRPM5, is Ca2+ sensitive and permeable for monovalent but not divalent cations. It is widely expressed in many organs and is involved in several functions; it regulates membrane potential and Ca2+ homeostasis in both excitable and non-excitable cells. This part of the review discusses the currently available knowledge about the physiological and pathophysiological roles of TRPM4 in various tissues. These include the physiological functions of TRPM4 in the cells of the Langerhans islets of the pancreas, in various immune functions, in the regulation of vascular tone, in respiratory and other neuronal activities, in chemosensation, and in renal and cardiac physiology. TRPM4 contributes to pathological conditions such as overactive bladder, endothelial dysfunction, various types of malignant diseases and central nervous system conditions including stroke and injuries as well as in cardiac conditions such as arrhythmias, hypertrophy, and ischemia-reperfusion injuries. TRPM4 claims more and more attention and is likely to be the topic of research in the future.
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Düsener S, Flenner F, Maack C, Kohlhaas M, Bay J, Carrier L, Friedrich FW. Ouabain worsens diastolic sarcomere length in myocytes from a cardiomyopathy mouse model. Eur J Pharmacol 2021; 904:174170. [PMID: 33984298 DOI: 10.1016/j.ejphar.2021.174170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Revised: 04/28/2021] [Accepted: 05/06/2021] [Indexed: 12/01/2022]
Abstract
Diastolic dysfunction is a major feature of hypertrophic cardiomyopathy (HCM). Data from patient tissue and animal models associate increased Ca2+ sensitivity of myofilaments with altered Na+ and Ca2+ ion homeostasis in cardiomyocytes with diastolic dysfunction. In this study, we tested the acute effects of ouabain on ventricular myocytes of an HCM mouse model. The effects of ouabain on contractility and Ca2+ transients were tested in intact adult mouse ventricular myocytes (AMVMs) of Mybpc3-targeted knock-in (KI) and wild-type (WT) mice. Concentration-response assessment of contractile function revealed low sensitivity of AMVMs to ouabain (10 μM) compared to literature data on human cardiomyocytes (100 nM). Three hundred μM ouabain increased contraction amplitude (WT ~1.8-fold; KI ~1.5-fold) and diastolic intracellular Ca2+ in both WT and KI (+12-18%), but further decreased diastolic sarcomere length in KI cardiomyocytes (-5%). Western Blot analysis of whole heart protein extracts revealed 50% lower amounts of Na+/K+ ATPase (NKA) in KI than in WT. Ouabain worsened the diastolic phenotype of KI cardiomyocytes at concentrations which did not impair WT diastolic function. Ouabain led to an elevation of intracellular Ca2+, which was poorly tolerated in KI showing already high cytosolic Ca2+ at baseline due to increased myofilament Ca2+ sensitivity. Lower amounts of NKA in KI could amplify the need to exchange excessive intracellular Na+ for Ca2+ and thereby explain the general tendency to higher diastolic Ca2+ in KI.
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Affiliation(s)
- Silke Düsener
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Germany
| | - Frederik Flenner
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Germany
| | - Christoph Maack
- Department of Translational Research, Comprehensive Heart Failure Center (CHFC), University Clinic Würzburg, Würzburg, Germany
| | - Michael Kohlhaas
- Department of Translational Research, Comprehensive Heart Failure Center (CHFC), University Clinic Würzburg, Würzburg, Germany
| | - Johannes Bay
- Department of Pediatrics and Neonatology, Saarland University Hospital, Homburg, Saar, Germany
| | - Lucie Carrier
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Germany.
| | - Felix W Friedrich
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Germany.
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Bacharova L. Missing Link between Molecular Aspects of Ventricular Arrhythmias and QRS Complex Morphology in Left Ventricular Hypertrophy. Int J Mol Sci 2019; 21:E48. [PMID: 31861705 PMCID: PMC6982310 DOI: 10.3390/ijms21010048] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Revised: 12/17/2019] [Accepted: 12/17/2019] [Indexed: 12/27/2022] Open
Abstract
The aim of this opinion paper is to point out the knowledge gap between evidence on the molecular level and clinical diagnostic possibilities in left ventricular hypertrophy (LVH) regarding the prediction of ventricular arrhythmias and monitoring the effect of therapy. LVH is defined as an increase in left ventricular size and is associated with increased occurrence of ventricular arrhythmia. Hypertrophic rebuilding of myocardium comprises interrelated processes on molecular, subcellular, cellular, tissue, and organ levels affecting electrogenesis, creating a substrate for triggering and maintaining arrhythmias. The knowledge of these processes serves as a basis for developing targeted therapy to prevent and treat arrhythmias. In the clinical practice, the method for recording electrical phenomena of the heart is electrocardiography. The recognized clinical electrocardiogram (ECG) predictors of ventricular arrhythmias are related to alterations in electrical impulse propagation, such as QRS complex duration, QT interval, early repolarization, late potentials, and fragmented QRS, and they are not specific for LVH. However, the simulation studies have shown that the QRS complex patterns documented in patients with LVH are also conditioned remarkably by the alterations in impulse propagation. These QRS complex patterns in LVH could be potentially recognized for predicting ventricular arrhythmia and for monitoring the effect of therapy.
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Affiliation(s)
- Ljuba Bacharova
- International Laser Center, 841 04 Bratislava, Slovakia
- Institute of Pathophysiology, Medical School, Comenius University, 841 04 Bratislava, Slovakia
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5
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Amoni M, Kelly-Laubscher R, Petersen M, Gwanyanya A. Cardioprotective and Anti-arrhythmic Effects of Magnesium Pretreatment Against Ischaemia/Reperfusion Injury in Isoprenaline-Induced Hypertrophic Rat Heart. Cardiovasc Toxicol 2017; 17:49-57. [PMID: 26696240 DOI: 10.1007/s12012-015-9355-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The effects of magnesium (Mg2+) on ischaemic complications of pathological cardiac hypertrophy are unclear. In this study, we investigated effects of Mg2+ pretreatment on ischaemia/reperfusion (I/R) injury in isoprenaline (ISO)-induced hypertrophic hearts. Wistar rats were treated for 7 days with different combinations of ISO (1.25 mg/kg) subcutaneously, MgSO4 (270 mg/kg) intraperitoneally, or vehicle (saline). On the eighth day, hearts were either subjected to regional I/R during Langendorff perfusion or histologically stained with haematoxylin and eosin and Masson's trichrome. Haemodynamic and electrocardiographic parameters were recorded using the PowerLab data-acquisition system. Infarcts were identified by triphenyltetrazolium chloride staining. Plasma Mg2+ was measured using photometric assays. Mg2+ pretreatment significantly decreased I/R-induced infarct size (p = 0.001) and the overall arrhythmia score (p < 0.001) of I/R-induced ventricular ectopics, ventricular tachycardia, and ventricular fibrillation in hypertrophic hearts, but not non-hypertrophied hearts. Mg2+ also improved post-I/R left ventricular developed pressure in hypertrophic hearts. However, Mg2+ did not reverse the ISO-induced myocyte thickening and interstitial fibrosis or increases in heart weight. Plasma Mg2+ was not different among treatment groups. These results suggest that Mg2+ pretreatment may protect against I/R-induced injury and malignant arrhythmias in hypertrophic hearts, possibly via mechanisms unrelated to long-lasting changes in plasma Mg2+ or prevention of structural changes such as fibrosis.
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Affiliation(s)
- Matthew Amoni
- Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Observatory, Cape Town, 7925, South Africa
| | - Roisin Kelly-Laubscher
- Department of Biological Sciences, Faculty of Science, University of Cape Town, Rondebosch, Cape Town, 7700, South Africa.,Academic Development Programme, Centre for Higher Education Development, University of Cape Town, Cape Town, South Africa
| | - Morea Petersen
- Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Observatory, Cape Town, 7925, South Africa
| | - Asfree Gwanyanya
- Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Observatory, Cape Town, 7925, South Africa.
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Bai J, Yin R, Wang K, Zhang H. Mechanisms Underlying the Emergence of Post-acidosis Arrhythmia at the Tissue Level: A Theoretical Study. Front Physiol 2017; 8:195. [PMID: 28424631 PMCID: PMC5371659 DOI: 10.3389/fphys.2017.00195] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Accepted: 03/15/2017] [Indexed: 11/17/2022] Open
Abstract
Acidosis has complex electrophysiological effects, which are associated with a high recurrence of ventricular arrhythmias. Through multi-scale cardiac computer modeling, this study investigated the mechanisms underlying the emergence of post-acidosis arrhythmia at the tissue level. In simulations, ten Tusscher-Panfilov ventricular model was modified to incorporate various data on acidosis-induced alterations of cellular electrophysiology and intercellular electrical coupling. The single cell models were incorporated into multicellular one-dimensional (1D) fiber and 2D sheet tissue models. Electrophysiological effects were quantified as changes of action potential profile, sink-source interactions of fiber tissue, and the vulnerability of tissue to the genesis of unidirectional conduction that led to initiation of re-entry. It was shown that acidosis-induced sarcoplasmic reticulum (SR) calcium load contributed to delayed afterdepolarizations (DADs) in single cells. These DADs may be synchronized to overcome the source-sink mismatch arising from intercellular electrotonic coupling, and produce a premature ventricular complex (PVC) at the tissue level. The PVC conduction can be unidirectionally blocked in the transmural ventricular wall with altered electrical heterogeneity, resulting in the genesis of re-entry. In conclusion, altered source-sink interactions and electrical heterogeneity due to acidosis-induced cellular electrophysiological alterations may increase susceptibility to post-acidosis ventricular arrhythmias.
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Affiliation(s)
- Jieyun Bai
- School of Computer Science and Technology, Harbin Institute of TechnologyHarbin, China
| | - Renli Yin
- State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of TechnologyHarbin, China
| | - Kuanquan Wang
- School of Computer Science and Technology, Harbin Institute of TechnologyHarbin, China
| | - Henggui Zhang
- School of Computer Science and Technology, Harbin Institute of TechnologyHarbin, China.,Biological Physics Group, School of Physics and Astronomy, University of ManchesterManchester, UK.,Space Institute of Southern ChinaShenzhen, China
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Sommese L, Valverde CA, Blanco P, Castro MC, Rueda OV, Kaetzel M, Dedman J, Anderson ME, Mattiazzi A, Palomeque J. Ryanodine receptor phosphorylation by CaMKII promotes spontaneous Ca(2+) release events in a rodent model of early stage diabetes: The arrhythmogenic substrate. Int J Cardiol 2016; 202:394-406. [PMID: 26432489 PMCID: PMC4872299 DOI: 10.1016/j.ijcard.2015.09.022] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Revised: 08/31/2015] [Accepted: 09/19/2015] [Indexed: 12/13/2022]
Abstract
BACKGROUND Heart failure and arrhythmias occur more frequently in patients with type 2 diabetes (T2DM) than in the general population. T2DM is preceded by a prediabetic condition marked by elevated reactive oxygen species (ROS) and subclinical cardiovascular defects. Although multifunctional Ca2+ calmodulin-dependent protein kinase II (CaMKII) is ROS-activated and CaMKII hyperactivity promotes cardiac diseases, a link between prediabetes and CaMKII in the heart is unprecedented. OBJECTIVES To prove the hypothesis that increased ROS and CaMKII activity contribute to heart failure and arrhythmogenic mechanisms in early stage diabetes. METHODS-RESULTS Echocardiography, electrocardiography, biochemical and intracellular Ca2+ (Ca2+i) determinations were performed in fructose-rich diet-induced impaired glucose tolerance, a prediabetes model, in rodents. Fructose-rich diet rats showed decreased contractility and hypertrophy associated with increased CaMKII activity, ROS production, oxidized CaMKII and enhanced CaMKII-dependent ryanodine receptor (RyR2) phosphorylation compared to rats fed with control diet. Isolated cardiomyocytes from fructose-rich diet showed increased spontaneous Ca2+i release events associated with spontaneous contractions, which were prevented by KN-93, a CaMKII inhibitor, or addition of Tempol, a ROS scavenger, to the diet. Moreover, fructose-rich diet myocytes showed increased diastolic Ca2+ during the burst of spontaneous Ca2+i release events. Mice treated with Tempol or with sarcoplasmic reticulum-targeted CaMKII-inhibition by transgenic expression of the CaMKII inhibitory peptide AIP, were protected from fructose-rich diet-induced spontaneous Ca2+i release events, spontaneous contractions and arrhythmogenesis in vivo, despite ROS increases. CONCLUSIONS RyR2 phosphorylation by ROS-activated CaMKII, contributes to impaired glucose tolerance-induced arrhythmogenic mechanisms, suggesting that CaMKII inhibition could prevent prediabetic cardiovascular complications and/or evolution.
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Affiliation(s)
- Leandro Sommese
- Centro de Investigaciones Cardiovasculares, CONICET-La Plata 1900, Facultad de Medicina, UNLP, Argentina
| | - Carlos A Valverde
- Centro de Investigaciones Cardiovasculares, CONICET-La Plata 1900, Facultad de Medicina, UNLP, Argentina
| | - Paula Blanco
- Servicio de Ecocardiografía, Facultad de Veterinaria, UNLP, La Plata 1900, Argentina
| | - María Cecilia Castro
- CENEXA, Centro Experimental de Endocrinología y Aplicada (UNLP-CONICET La Plata), Facultad de Ciencias Médicas, UNLP, La Plata 1900, Argentina
| | - Omar Velez Rueda
- Centro de Investigaciones Cardiovasculares, CONICET-La Plata 1900, Facultad de Medicina, UNLP, Argentina
| | - Marcia Kaetzel
- Department of Genome Science, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0575, USA
| | - John Dedman
- Department of Genome Science, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0575, USA
| | - Mark E Anderson
- University of Iowa, 285 Newton Rd, CBRB 2256, Iowa City, IA 52242, USA
| | - Alicia Mattiazzi
- Centro de Investigaciones Cardiovasculares, CONICET-La Plata 1900, Facultad de Medicina, UNLP, Argentina
| | - Julieta Palomeque
- Centro de Investigaciones Cardiovasculares, CONICET-La Plata 1900, Facultad de Medicina, UNLP, Argentina.
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Bögeholz N, Pauls P, Bauer BK, Schulte JS, Dechering DG, Frommeyer G, Kirchhefer U, Goldhaber JI, Müller FU, Eckardt L, Pott C. Suppression of Early and Late Afterdepolarizations by Heterozygous Knockout of the Na+/Ca2+ Exchanger in a Murine Model. Circ Arrhythm Electrophysiol 2015; 8:1210-8. [PMID: 26338832 DOI: 10.1161/circep.115.002927] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/07/2015] [Accepted: 08/13/2015] [Indexed: 11/16/2022]
Abstract
BACKGROUND The Na(+)/Ca(2+) exchanger (NCX) has been implied to cause arrhythmias. To date, information on the role of NCX in arrhythmogenesis derived from models with increased NCX expression, hypertrophy, and heart failure. Furthermore, the exact mechanism by which NCX exerts its potentially proarrhythmic effect, ie, by promoting early afterdepolarization (EAD) or delayed afterdepolarization (DAD) or both, is unknown. METHODS AND RESULTS We investigated isolated cardiomyocytes from a murine model with heterozygous knockout of NCX (hetKO) using the patch clamp and Ca(2+) imaging techniques. Action potential duration was shorter in hetKO with IKtot not being increased. The rate of spontaneous Ca(2+) release events and the rate of DADs were unaltered; however, DADs had lower amplitude in hetKO. A DAD triggered a spontaneous action potential significantly less often in hetKO when compared with wild-type. The occurrence of EADs was also drastically reduced in hetKO. ICa activity was reduced in hetKO, an effect that was abolished in the presence of the Ca(2+) buffer BAPTA. CONCLUSIONS Genetic suppression of NCX reduces both EADs and DADs. The following molecular mechanisms apply: (1) Although the absolute number of DADs is unaffected, an impaired translation of DADs into spontaneous action potentials results from a reduced DAD amplitude. (2) EADs are reduced in absolute number of occurrence, which is presumably a consequence of shortened action potential duration because of reduced NCX activity but also reduced ICa the latter possibly being caused by a direct modulation of Ca(2+)-dependent ICa inhibition by reduced NCX activity. This is the first study to demonstrate that genetic inhibition of NCX protects against afterdepolarizations and to investigate the underlying mechanisms.
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Affiliation(s)
- Nils Bögeholz
- From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.).
| | - Paul Pauls
- From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.)
| | - B Klemens Bauer
- From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.)
| | - Jan S Schulte
- From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.)
| | - Dirk G Dechering
- From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.)
| | - Gerrit Frommeyer
- From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.)
| | - Uwe Kirchhefer
- From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.)
| | - Joshua I Goldhaber
- From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.)
| | - Frank U Müller
- From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.)
| | - Lars Eckardt
- From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.)
| | - Christian Pott
- From the Division of Electrophysiology, Department of Cardiovascular Medicine (N.B., P.P., B.K.B., D.G.D., G.F., L.E., C.P.) and Institute of Pharmacology and Toxicology (P.P., B.K.B., J.S.S., U.K., F.U.M.), University Hospital Münster, Münster, Germany; and Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (J.I.G.)
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Vitamin D attenuates pro-inflammatory TNF-α cytokine expression by inhibiting NF-кB/p65 signaling in hypertrophied rat hearts. J Physiol Biochem 2015; 71:289-99. [PMID: 25929726 DOI: 10.1007/s13105-015-0412-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Accepted: 04/09/2015] [Indexed: 01/22/2023]
Abstract
A growing body of evidence suggests that immune activation and inflammatory mediators may play a key role in the development and progression of left ventricle (LV) hypertrophy. The present study was designed to test the hypothesis that the cardioprotective effect of cholecalciferol (Vit-D3) is mediated via the regulation of messenger RNA (mRNA) expression of pro-inflammatory cytokines. Rats were randomly divided into four groups: control group received normal saline (0.9 % NaCl) i.p. for 14 days; Vit-D3 group received Vit-D3 at a dose of 12 μg/kg/day by gavage for 14 days; ISO group received saline for 7 days, and at day 7, ISO (5 mg/kg/day) was injected i.p. for 7 consecutive days to induce cardiac hypertrophy; and Vit-D3 + ISO group was treated with Vit-D3 for 14 days, and at day 7, ISO was administered for 7 consecutive days. Heart/body weight ratio, troponin-T, creatine kinase-MB, and tumor necrosis factor-α (TNF-α) levels of LV tissue were estimated. Levels of mRNA expression of NF-кB (NF-кB)/p65 and inhibitory kappa B (IкB)-α were determined by real-time PCR. Vit-D3 administration before and during induction of cardiac hypertrophy significantly reduced (P < 0.001) cardiac biomarkers. The histopathological examination further confirmed these results. In addition, Vit-D3 significantly decreased (P < 0.001) NF-кB-p65 mRNA expression and increased (P < 0.01) IкB-α mRNA expression in LV tissues compared to ISO group. Based on these findings, it was concluded that the administration of cholecalciferol markedly attenuated the development of ISO-induced cardiac hypertrophy likely through downregulation of TNF-α /NF-кb/p65 signaling pathways. However, it should be pointed out that other signaling pathways may contribute to the cardioprotective effect of Vit-D3 which requires further investigation.
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10
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Del Olmo-Turrubiarte A, Calzada-Torres A, Díaz-Rosas G, Palma-Lara I, Sánchez-Urbina R, Balderrábano-Saucedo NA, González-Márquez H, Garcia-Alonso P, Contreras-Ramos A. Mouse models for the study of postnatal cardiac hypertrophy. IJC HEART & VASCULATURE 2015; 7:131-140. [PMID: 28785661 PMCID: PMC5497247 DOI: 10.1016/j.ijcha.2015.02.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Revised: 01/19/2015] [Accepted: 02/01/2015] [Indexed: 12/16/2022]
Abstract
The main objective of this study was to create a postnatal model for cardiac hypertrophy (CH), in order to explain the mechanisms that are present in childhood cardiac hypertrophy. Five days after implantation, intraperitoneal (IP) isoproterenol (ISO) was injected for 7 days to pregnant female mice. The fetuses were obtained at 15, 17 and 19 dpc from both groups, also newborns (NB), neonates (7-15 days) and young adults (6 weeks of age). Histopathological exams were done on the hearts. Immunohistochemistry and western blot demonstrated GATA4 and PCNA protein expression, qPCR real time the mRNA of adrenergic receptors (α-AR and β-AR), alpha and beta myosins (α-MHC, β-MHC) and GATA4. After the administration of ISO, there was no change in the number of offsprings. We observed significant structural changes in the size of the offspring hearts. Morphometric analysis revealed an increase in the size of the left ventricular wall and interventricular septum (IVS). Histopathological analysis demonstrated loss of cellular compaction and presence of left ventricular small fibrous foci after birth. Adrenergic receptors might be responsible for changing a physiological into a pathological hypertrophy. However GATA4 seemed to be the determining factor in the pathology. A new animal model was established for the study of pathologic CH in early postnatal stages.
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Affiliation(s)
- A Del Olmo-Turrubiarte
- Laboratorio de Investigación de Biología del Desarrollo y Teratogénesis Experimental, Hospital Infantil de México Federico Gómez (HIMFG), Mexico.,Posgrado en Biología Experimental, Universidad Autónoma Metropolitana, Mexico
| | - A Calzada-Torres
- Laboratorio de Investigación de Biología del Desarrollo y Teratogénesis Experimental, Hospital Infantil de México Federico Gómez (HIMFG), Mexico
| | - G Díaz-Rosas
- Laboratorio de Investigación de Biología del Desarrollo y Teratogénesis Experimental, Hospital Infantil de México Federico Gómez (HIMFG), Mexico
| | | | - R Sánchez-Urbina
- Laboratorio de Investigación de Biología del Desarrollo y Teratogénesis Experimental, Hospital Infantil de México Federico Gómez (HIMFG), Mexico
| | | | - H González-Márquez
- Departamento de Ciencias de la Salud, Universidad Autónoma Metropolitana, Mexico
| | | | - A Contreras-Ramos
- Laboratorio de Investigación de Biología del Desarrollo y Teratogénesis Experimental, Hospital Infantil de México Federico Gómez (HIMFG), Mexico
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11
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Kessler EL, Boulaksil M, van Rijen HVM, Vos MA, van Veen TAB. Passive ventricular remodeling in cardiac disease: focus on heterogeneity. Front Physiol 2014; 5:482. [PMID: 25566084 PMCID: PMC4273631 DOI: 10.3389/fphys.2014.00482] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Accepted: 11/24/2014] [Indexed: 12/20/2022] Open
Abstract
Passive ventricular remodeling is defined by the process of molecular ventricular adaptation to different forms of cardiac pathophysiology. It includes changes in tissue architecture, such as hypertrophy, fiber disarray, alterations in cell size and fibrosis. Besides that, it also includes molecular remodeling of gap junctions, especially those composed by Connexin43 proteins (Cx43) in the ventricles that affect cell-to-cell propagation of the electrical impulse, and changes in the sodium channels that modify excitability. All those alterations appear mainly in a heterogeneous manner, creating irregular and inhomogeneous electrical and mechanical coupling throughout the heart. This can predispose to reentry arrhythmias and adds to a further deterioration into heart failure. In this review, passive ventricular remodeling is described in Hypertrophic Cardiomyopathy (HCM), Dilated Cardiomyopathy (DCM), Ischemic Cardiomyopathy (ICM), and Arrhythmogenic Cardiomyopathy (ACM), with a main focus on the heterogeneity of those alterations mentioned above.
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Affiliation(s)
- Elise L Kessler
- Division of Heart and Lungs, Department of Medical Physiology, University Medical Center Utrecht Utrecht, Netherlands
| | - Mohamed Boulaksil
- Division of Heart and Lungs, Department of Medical Physiology, University Medical Center Utrecht Utrecht, Netherlands ; Department of Cardiology, Radboud University Medical Center Nijmegen, Netherlands
| | - Harold V M van Rijen
- Division of Heart and Lungs, Department of Medical Physiology, University Medical Center Utrecht Utrecht, Netherlands
| | - Marc A Vos
- Division of Heart and Lungs, Department of Medical Physiology, University Medical Center Utrecht Utrecht, Netherlands
| | - Toon A B van Veen
- Division of Heart and Lungs, Department of Medical Physiology, University Medical Center Utrecht Utrecht, Netherlands
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12
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Electrocardiographic versus echocardiographic left ventricular hypertrophy and sudden cardiac arrest in the community. Heart Rhythm 2014; 11:1040-6. [PMID: 24657425 DOI: 10.1016/j.hrthm.2014.03.023] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Indexed: 12/22/2022]
Abstract
BACKGROUND Left ventricular hypertrophy (LVH) is associated with increased risk of sudden cardiac arrest (SCA). Whether LVH diagnosed by 12-lead ECG vs echocardiogram conveys identical or distinct risk information has not been previously evaluated. OBJECTIVE The purpose of this study was to compare the association between ECG vs echocardiographic LVH and SCA in the community. METHODS In a large, prospective population-based study (The Oregon Sudden Unexpected Death Study; population approximately 1 million), cases of SCA were compared to controls recruited from the same geographical area. The association between LVH and SCA was evaluated, specifically comparing LVH diagnosed by ECG vs echocardiogram. RESULTS Cases (n = 132, age 66.9 ± 13.5 years, 58.3% male) compared to controls (n = 211; age 66.2 ± 12 years, 59.2% male) were more likely to have both ECG LVH (12.1% vs 5.7%, P = .03) and echocardiographic LVH (35.0% vs 15.5%, P <.001). However, there was poor agreement between the tests (kappa statistic = 0.128). A large subgroup of patients with ECG LVH (57.1%) did not have echocardiographic LVH; conversely, 83.6% of patients with echocardiographic LVH did not have ECG LVH. In multivariate analysis, ECG LVH was significantly associated with SCA (odds ratio [OR] 2.5, 95% confidence interval [CI] 1.1-6.0, P = .04). When echocardiographic LVH was added to the model, this association was only mildly attenuated (OR 2.4, 95% CI 1.0-6.0, P= .05), and echocardiographic LVH was also independently associated with SCA (OR 2.7, 95% CI 1.5-4.9, P = .001). CONCLUSION ECG and echocardiographic LVH may convey distinct risk information in patients with SCA, reflecting electrical vs anatomic remodeling. These findings have potential implications for SCA mechanisms and risk stratification.
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13
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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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14
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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: 152] [Impact Index Per Article: 13.8] [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.
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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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15
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Elzwiei F, Bassien-Capsa V, St-Louis J, Chorvatova A. Regulation of the sodium pump during cardiomyocyte adaptation to pregnancy. Exp Physiol 2012; 98:183-92. [PMID: 22848078 DOI: 10.1113/expphysiol.2012.066282] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Regulation of the sodium pump during normal pregnancy and its effect on the function of cardiomyocytes is poorly understood. Our objective was to evaluate the possible implication of the Na(+)-K(+)-ATPase, the sodium pump which controls cellular ionic and metabolic homeostasis, in the adaptations of cardiomyocytes to normal pregnancy. We have used Western blots and patch-clamp measurements to identify changes in the sodium pump proteins. Confocal microscopy was applied to estimate intracellular sodium concentration. Time-resolved spectroscopy was employed to measure mitochondrial NAD(P)H fluorescence and estimate oxidative metabolic state. Optical microscopy was adopted to study the contractility responses of cardiomyocytes. Cells from non-pregnant and pregnant rats (1 day prior parturition) were studied. Our results showed lower protein expression of the α1 Na(+)-K(+)-ATPase isoform in cardiomyocytes in pregnant rats, decreased sodium pump membrane current and elevated steady-state sodium concentration. In addition, ouabain, the inhibitor of the sodium pump capable of increasing cardiomyocyte contractility in non-pregnant rats in a concentration-dependent manner, failed to affect cell contractions in pregnant rats. We also noted modified responsiveness of the mitochondrial metabolic state to ouabain in cardiac cells. The gathered data confirmed that in pregnant rats, the sodium pump protein content and transmembrane flux are decreased, while the sensitivity of cardiomyocyte contractility and the sensitivity of mitochondrial metabolic redox state to ouabain are modified, pointing to regulation of the Na(+)-K(+)-ATPase during cardiac cell adaptations to normal pregnancy.
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Affiliation(s)
- F Elzwiei
- CHU Sainte Justine, Research Centre, Montreal, Quebec, Canada H3T 1C5
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16
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Tamarappoo BK, John BT, Reinier K, Teodorescu C, Uy-Evanado A, Gunson K, Jui J, Chugh SS. Vulnerable myocardial interstitium in patients with isolated left ventricular hypertrophy and sudden cardiac death: a postmortem histological evaluation. J Am Heart Assoc 2012; 1:e001511. [PMID: 23130141 PMCID: PMC3487319 DOI: 10.1161/jaha.112.001511] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Accepted: 04/24/2012] [Indexed: 12/11/2022]
Abstract
BACKGROUND Concentric left ventricular hypertrophy (LVH) is independently associated with increased risk of sudden cardiac death (SCD). Some animal models of LVH display specific alterations of the myocardial interstitium that could increase myocardial vulnerability to ventricular arrhythmias, but these merit evaluation in humans with LVH and SCD. METHODS AND RESULTS Twelve consecutive patients with isolated LVH and SCD (LVH+SCD) in the absence of hypertrophic cardiomyopathy, coronary disease, or other cardiac structural abnormality were ascertained in the Oregon Sudden Unexpected Death Study. Detailed postmortem comparisons were conducted with 18 controls who had isolated LVH and unnatural deaths (Control Group A) and 6 controls who had structurally normal hearts and unnatural deaths (Control Group B). Postmortem left ventricular myocardial sections were obtained for measurement of collagen volume fraction, characterization of gap junctions, and quantification of collagen subtypes. Heart weight normalized to body weight was higher in LVH+SCD cases (6.9±1.2 g/kg) than in Control Group A (5.3±1.4 g/kg) and Control Group B (4.2±0.3 g/kg); P=0.001. Collagen volume fraction was also higher in LVH+SCD cases (3.1±0.4) than in Control Group A (2.3±0.4) and Control Group B (1.6±0.3); P=0.0002. The relative amount of collagen III was significantly higher in LVH+SCD cases (33.0±4.4%) than in Control Group A (20.9±4.3%) and Control Group B (13.4±3.5%); P=0.0001. There was an overall increase in the number of connexin 43-labeled gap junctions with increasing myocyte size. No subject was found to have high-risk hypertrophic cardiomyopathy mutations. CONCLUSIONS In addition to the expected increase in myocardial mass and overall collagen content, SCD with isolated LVH was associated with relative abundance of type III collagen, a novel finding that warrants further mechanistic evaluation. (J Am Heart Assoc. 2012;1:e001511 doi: 10.1161/JAHA.111.001511.).
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Affiliation(s)
- Balaji K. Tamarappoo
- Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (B.K.T., B.T.J., K.R., C.T.,
A.U.-E., S.S.C.)
- Cleveland Clinic Foundation, Cleveland OH (B.K.T.)
| | - Benjamin T. John
- Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (B.K.T., B.T.J., K.R., C.T.,
A.U.-E., S.S.C.)
- Vancouver Clinic, Vancouver, WA (B.T.J)
| | - Kyndaron Reinier
- Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (B.K.T., B.T.J., K.R., C.T.,
A.U.-E., S.S.C.)
| | - Carmen Teodorescu
- Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (B.K.T., B.T.J., K.R., C.T.,
A.U.-E., S.S.C.)
| | - Audrey Uy-Evanado
- Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (B.K.T., B.T.J., K.R., C.T.,
A.U.-E., S.S.C.)
| | - Karen Gunson
- Department of Pathology, Oregon Health and Science University, Portland, OR (K.G.)
| | - Jonathan Jui
- Department of Emergency Medicine, Oregon Health and Science University, Portland, OR (J.J.)
| | - Sumeet S. Chugh
- Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA (B.K.T., B.T.J., K.R., C.T.,
A.U.-E., S.S.C.)
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17
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Proarrhythmia in a non-failing murine model of cardiac-specific Na+/Ca 2+ exchanger overexpression: whole heart and cellular mechanisms. Basic Res Cardiol 2012; 107:247. [PMID: 22327339 DOI: 10.1007/s00395-012-0247-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2011] [Revised: 01/02/2012] [Accepted: 01/22/2012] [Indexed: 10/14/2022]
Abstract
The cardiac Na(+)/Ca(2+) exchanger (NCX) generates an inward electrical current during SR-Ca(2+) release, thus possibly promoting afterdepolarizations of the action potential (AP). We used transgenic mice 12.5 weeks or younger with cardiomyocyte-directed overexpression of NCX (NCX-Tg) to study the proarrhythmic potential and mechanisms of enhanced NCX activity. NCX-Tg exhibited normal echocardiographic left ventricular function and heart/body weight ratio, while the QT interval was prolonged in surface ECG recordings. Langendorff-perfused NCX-Tg, but not wild-type (WT) hearts, developed ventricular tachycardia. APs and ionic currents were measured in isolated cardiomyocytes. Cell capacitance was unaltered between groups. APs were prolonged in NCX-Tg versus WT myocytes along with voltage-activated K(+) currents (K(v)) not being reduced but even increased in amplitude. During abrupt changes in pacing cycle length, early afterdepolarizations (EADs) were frequently recorded in NCX-Tg but not in WT myocytes. Next to EADs, delayed afterdepolarizations (DAD) triggering spontaneous APs (sAPs) occurred in NCX-Tg but not in WT myocytes. To test whether sAPs were associated with spontaneous Ca(2+) release (sCR), Ca(2+) transients were recorded. Despite the absence of sAPs in WT, sCR was observed in myocytes of both genotypes suggesting a facilitated translation of sCR into DADs in NCX-Tg. Moreover, sCR was more frequent in NCX-Tg as compared to WT. Myocardial protein levels of Ca(2+)-handling proteins were not different between groups except the ryanodine receptor (RyR), which was increased in NCX-Tg versus WT. We conclude that NCX overexpression is proarrhythmic in a non-failing environment even in the absence of reduced K(V). The underlying mechanisms are: (1) occurrence of EADs due to delayed repolarization; (2) facilitated translation from sCR into DADs; (3) proneness to sCR possibly caused by altered Ca(2+) handling and/or increased RyR expression.
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18
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Pott C, Eckardt L, Goldhaber JI. Triple threat: the Na+/Ca2+ exchanger in the pathophysiology of cardiac arrhythmia, ischemia and heart failure. Curr Drug Targets 2011; 12:737-47. [PMID: 21291388 PMCID: PMC4406235 DOI: 10.2174/138945011795378559] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2010] [Accepted: 08/30/2010] [Indexed: 02/02/2023]
Abstract
The Na(+)/Ca(2+) exchanger (NCX) is the main Ca(2+) extrusion mechanism of the cardiac myocyte and thus is crucial for maintaining Ca(2+) homeostasis. It is involved in the regulation of several parameters of cardiac excitation contraction coupling, such as cytosolic Ca(2+) concentration, repolarization and contractility. Increased NCX activity has been identified as a mechanism promoting heart failure, cardiac ischemia and arrhythmia. Transgenic mice as well as pharmacological interventions have been used to support the idea of using NCX inhibition as a future pharmacological strategy to treat cardiovascular disease.
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Affiliation(s)
- Christian Pott
- University Hospital of Muenster, Department of Cardiology and Angiology, Albert-Schweitzer-Str. 33, 48149 Muenster, Germany.
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19
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Mikušová A, Kráľová E, Tylková L, Novotová M, Stankovičová T. Myocardial remodelling induced by repeated low doses of isoproterenol. Can J Physiol Pharmacol 2009; 87:641-51. [DOI: 10.1139/y09-053] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the present work, the effect of isoproterenol on the electrical properties of the rat heart and on the cytoarchitecture of the surviving cardiomyocytes was studied. Myocardial remodelling was induced by the daily administration of 5 mg/kg isoproterenol (Iso) for 7 days. Administration resulted in a significant increase (52%) in the ratio of left ventricular weight to body weight. ECG voltage criteria confirmed the presence of left ventricular hypertrophy. QT interval prolongation by 23% and 58% was found in Iso rats and in the corresponding isolated hearts, respectively. Spontaneously beating Iso hearts had a higher incidence of dysrhythmias. The surviving cardiomyocytes showed an irregular shape with cytoplasmic processes rich in ribosomes and rough endoplasmic reticulum. In these regions, myofibril disorganization and mitochondrial fission were observed. A greatly increased incidence of caveolae was seen in the plasma membrane and in the mouth of t-tubules. The membranes of t-tubules showed vesiculation, especially near the dyads. Repeated administration of isoproterenol led to hypertrophy, characterized by the existence of myocytes with simultaneous signs of both mature and postnatally developing cardiomyocytes. Structural microheterogeneities at the level of individual cells may represent one of the factors leading to electrical imbalance in the myocardial tissue remodelled by isoproterenol.
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Affiliation(s)
- Andrea Mikušová
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlárska 5, 833 34 Bratislava, Slovak Republic
- Comenius University, Faculty of Pharmacy, Department of Pharmacology and Toxicology, 8 Kalinčiakova, 832 32 Bratislava, Slovak Republic
| | - Eva Kráľová
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlárska 5, 833 34 Bratislava, Slovak Republic
- Comenius University, Faculty of Pharmacy, Department of Pharmacology and Toxicology, 8 Kalinčiakova, 832 32 Bratislava, Slovak Republic
| | - Lucia Tylková
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlárska 5, 833 34 Bratislava, Slovak Republic
- Comenius University, Faculty of Pharmacy, Department of Pharmacology and Toxicology, 8 Kalinčiakova, 832 32 Bratislava, Slovak Republic
| | - Marta Novotová
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlárska 5, 833 34 Bratislava, Slovak Republic
- Comenius University, Faculty of Pharmacy, Department of Pharmacology and Toxicology, 8 Kalinčiakova, 832 32 Bratislava, Slovak Republic
| | - Tatiana Stankovičová
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlárska 5, 833 34 Bratislava, Slovak Republic
- Comenius University, Faculty of Pharmacy, Department of Pharmacology and Toxicology, 8 Kalinčiakova, 832 32 Bratislava, Slovak Republic
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20
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Contribution of Na+/Ca2+ Exchange Current to the Formation of Delayed Afterdepolarizations in Intact Rat Ventricular Muscle. J Cardiovasc Pharmacol 2009; 53:517-22. [DOI: 10.1097/fjc.0b013e3181a913f4] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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21
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Abstract
The transmembrane sodium gradient is essential for both excitability of the cardiac cell and the regulation of the cytoplasmic concentrations of Ca and protons. In addition, movements of Na across the mitochondrial membrane affect matrix protons and calcium. In the first part of the review, we discuss the most important pathways responsible for sarcolemmal and mitochondrial sodium movements. The bulk of the review considers the changes of intracellular Na concentration ([Na(+)](i)) that occur in disease, specifically, ischemia, reperfusion, and heart failure. We review evidence implicating the increase of intracellular sodium to either increased influx of sodium (via either sodium channels or sodium/hydrogen exchange) or, alternatively, to decreased efflux on the Na/K pump. Although much has been learned about sodium regulation in the heart, there are still many unanswered questions, particularly concerning mitochondrial Na regulation.
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Affiliation(s)
- Elizabeth Murphy
- Translational Medicine Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, MD 20892, USA.
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22
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Boyman L, Hiller R, Lederer WJ, Khananshvili D. Direct Loading of the purified endogenous inhibitor into the cytoplasm of patched cardiomyocytes blocks the ion currents and calcium transport through the NCX1 protein. Biochemistry 2008; 47:6602-11. [PMID: 18507397 PMCID: PMC3522518 DOI: 10.1021/bi8004279] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Na(+)-Ca(2+) exchanger in mammalian heart muscle (NCX1) is the central transporter protein that regulates extrusion of Ca(2+) from the heart cell. However, the functional biochemistry and physiology of NCX1 have been severely hampered by the absence of any specific high-affinity inhibitor. Here we describe advanced procedures for purifying a candidate inhibitor, previously called endogenous inhibitor factor (NCX(IF)), and demonstrate its direct actions on NCX1 activities in the single-cell system. A combination of advanced HILIC (hydrophilic interaction liquid chromatography) procedures with analytical tests suggests that the properties of NCX(IF) resemble those of a small (disaccharide size) polar molecule lacking any aromatic rings, conjugated bonds, or a primary amino group. The effects of NCX(IF) on the NCX1-mediated ion currents (I(NCX)) and cytosolic Ca(2+) extrusion were detected by a combination of patch-clamp and confocal microscopy under conditions in which the purified NCX(IF) was directly loaded into the cytoplasm of patched cardiomyocytes. It was demonstrated that cytosolic NCX(IF) blocks the Ca(2+)-activated NCX1 inward current and the accompanying extrusion of Ca(2+) from the cell with high efficacy. A constant fraction of NCX1 inhibition was observed under conditions in which the cytosolic [Ca(2+)](i) was varied at fixed doses of NCX(IF), suggesting that the degree of inhibition is controlled by NCX(IF) dose and not by cytosolic Ca(2+) concentration. NCX(IF) blocks equally well both the Ca(2+) extrusion and Ca(2+) entry modes of NCX1, consistent with thermodynamic principles expected for the functioning of a bidirectional "carrier-type" transport system. We concluded that NCX(IF) interacts with a putative regulatory domain from the cytosolic side and, thus, may play an important regulatory role in controlling Ca(2+) signaling in the heart. This may represent a new potential tool for developing novel treatments for cardiac Ca(2+) signaling dysfunction.
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Affiliation(s)
- Liron Boyman
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Reuben Hiller
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - W. Jonathan Lederer
- Medical Biotechnology Center, University of Maryland Biotechnology Institute, Baltimore, Maryland 21201
| | - Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
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Bacharova L. Electrical and structural remodeling in left ventricular hypertrophy-a substrate for a decrease in QRS voltage? Ann Noninvasive Electrocardiol 2007; 12:260-73. [PMID: 17617072 PMCID: PMC6932385 DOI: 10.1111/j.1542-474x.2007.00170.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Electrical remodeling in advanced stages of cardiovascular diseases creates a substrate for triggering and maintenance of arrhythmias. The electrical remodeling is a continuous process initiated already in the early stages of cardiological pathology. The aim of this opinion article was to discuss the changes in electrical properties of myocardium in left ventricular hypertrophy (LVH), with special focus on its early stage, as well as their possible reflection in the QRS amplitude of the electrocardiogram. It critically appraises the classical hypothesis related to the QRS voltage changes in LVH. The hypothesis of the relative voltage deficit is discussed in the context of supporting evidence from clinical studies, animal experiments, and simulation studies. The underlying determinants of electrical impulse propagation which may explain discrepancies between "normal" ECG findings and increased left ventricular size/mass in LVH are reviewed.
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Affiliation(s)
- Ljuba Bacharova
- The International Laser Center, Bratislava, Slovak Republic.
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24
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Török TL. Electrogenic Na+/Ca2+-exchange of nerve and muscle cells. Prog Neurobiol 2007; 82:287-347. [PMID: 17673353 DOI: 10.1016/j.pneurobio.2007.06.003] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2006] [Revised: 04/12/2007] [Accepted: 06/12/2007] [Indexed: 12/19/2022]
Abstract
The plasma membrane Na(+)/Ca(2+)-exchanger is a bi-directional electrogenic (3Na(+):1Ca(2+)) and voltage-sensitive ion transport mechanism, which is mainly responsible for Ca(2+)-extrusion. The Na(+)-gradient, required for normal mode operation, is created by the Na(+)-pump, which is also electrogenic (3Na(+):2K(+)) and voltage-sensitive. The Na(+)/Ca(2+)-exchanger operational modes are very similar to those of the Na(+)-pump, except that the uncoupled flux (Na(+)-influx or -efflux?) is missing. The reversal potential of the exchanger is around -40 mV; therefore, during the upstroke of the AP it is probably transiently activated, leading to Ca(2+)-influx. The Na(+)/Ca(2+)-exchange is regulated by transported and non-transported external and internal cations, and shows ATP(i)-, pH- and temperature-dependence. The main problem in determining the role of Na(+)/Ca(2+)-exchange in excitation-secretion/contraction coupling is the lack of specific (mode-selective) blockers. During recent years, evidence has been accumulated for co-localisation of the Na(+)-pump, and the Na(+)/Ca(2+)-exchanger and their possible functional interaction in the "restricted" or "fuzzy space." In cardiac failure, the Na(+)-pump is down-regulated, while the exchanger is up-regulated. If the exchanger is working in normal mode (Ca(2+)-extrusion) during most of the cardiac cycle, upregulation of the exchanger may result in SR Ca(2+)-store depletion and further impairment in contractility. If so, a normal mode selective Na(+)/Ca(2+)-exchange inhibitor would be useful therapy for decompensation, and unlike CGs would not increase internal Na(+). In peripheral sympathetic nerves, pre-synaptic alpha(2)-receptors may regulate not only the VSCCs but possibly the reverse Na(+)/Ca(2+)-exchange as well.
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Affiliation(s)
- Tamás L Török
- Department of Pharmacodynamics, Semmelweis University, P.O. Box 370, VIII. Nagyvárad-tér 4, H-1445 Budapest, Hungary.
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25
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Abstract
Triggered activity in cardiac muscle and intracellular Ca2+ have been linked in the past. However, today not only are there a number of cellular proteins that show clear Ca2+ dependence but also there are a number of arrhythmias whose mechanism appears to be linked to Ca2+-dependent processes. Thus we present a systematic review of the mechanisms of Ca2+ transport (forward excitation-contraction coupling) in the ventricular cell as well as what is known for other cardiac cell types. Second, we review the molecular nature of the proteins that are involved in this process as well as the functional consequences of both normal and abnormal Ca2+ cycling (e.g., Ca2+ waves). Finally, we review what we understand to be the role of Ca2+ cycling in various forms of arrhythmias, that is, those associated with inherited mutations and those that are acquired and resulting from reentrant excitation and/or abnormal impulse generation (e.g., triggered activity). Further solving the nature of these intricate and dynamic interactions promises to be an important area of research for a better recognition and understanding of the nature of Ca2+ and arrhythmias. Our solutions will provide a more complete understanding of the molecular basis for the targeted control of cellular calcium in the treatment and prevention of such.
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Affiliation(s)
- Henk E D J Ter Keurs
- Department of Medicine, Physiology and Biophysics, University of Calgary, Alberta, Canada
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26
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Carvalho BMR, Bassani RA, Franchini KG, Bassani JWM. Enhanced calcium mobilization in rat ventricular myocytes during the onset of pressure overload-induced hypertrophy. Am J Physiol Heart Circ Physiol 2006; 291:H1803-13. [PMID: 16648178 DOI: 10.1152/ajpheart.01345.2005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Early cardiovascular changes evoked by pressure overload (PO) may reveal adaptive strategies that allow immediate survival to the increased hemodynamic load. In this study, systolic and diastolic Ca2+ cycling was analyzed in left ventricular rat myocytes before ( day 2, PO-2d group) and after ( day 7, PO-7d group) development of hypertrophy subsequent to aortic constriction, as well as in myocytes from time-matched sham-operated rats (sham group). Ca2+ transient amplitude was significantly augmented in the PO-2d group. In the PO-7d group, intracellular Ca2+ concentration ([Ca2+]i) was reduced during diastole, and mechanical twitch relaxation (but not [Ca2+]i decline) was slowed. In PO groups, fractional sarcoplasmic reticulum (SR) Ca2+ release at a twitch, SR Ca2+ content, SR Ca2+ loss during diastole, and SR-dependent integrated Ca2+ flux during twitch relaxation were significantly greater than in sham-operated groups, whereas the relaxation-associated Ca2+ flux carried by the Na+/Ca2+ exchanger was not significantly changed. In the PO-7d group, mRNA levels of cardiac isoforms of SR Ca2+-ATPase (SERCA2a), phospholamban, calsequestrin, ryanodine receptor, and NCX were not significantly altered, but the SERCA2a-to-phospholamban ratio was increased 2.5-fold. Moreover, greater sensitivity to the inotropic effects of the β-adrenoceptor agonist isoproterenol was observed in the PO-7d group. The results indicate enhanced Ca2+ cycling between SR and cytosol early after PO imposition, even before hypertrophy development. Increase in SR Ca2+ uptake may contribute to enhancement of excitation-contraction coupling (augmented SR Ca2+ content and release) and protection against arrhythmogenesis due to buildup of [Ca2+]i during diastole.
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Affiliation(s)
- Beatriz M R Carvalho
- Centro de Engenharia Biomédica, Universidade Estadual de Campinas, Caixa Postal 6040, 13084-971 Campinas, SP, Brazil
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27
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Narayan SM, Smith JM, Lindsay BD, Cain ME, Dávila-Román VG. Relation of T-wave alternans to regional left ventricular dysfunction and eccentric hypertrophy secondary to coronary heart disease. Am J Cardiol 2006; 97:775-80. [PMID: 16516574 DOI: 10.1016/j.amjcard.2005.09.127] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/02/2005] [Revised: 09/23/2005] [Accepted: 09/23/2005] [Indexed: 10/25/2022]
Abstract
Left ventricular (LV) hypertrophy and structural disease are associated with exaggerated repolarization dispersion and risk for cardiac arrest. We hypothesized that T-wave alternans (TWA) from the electrocardiogram, reflecting proarrhythmic repolarization dispersion, would increase with extent of eccentric LV hypertrophy and vary spatially with the distribution of myocardial scar. We studied 28 patients with coronary disease, systolic dysfunction, and nonsustained ventricular tachycardia. On echocardiography, 21 patients had wall motion abnormalities and 20 had LV hypertrophy (mass index > or =100 g/m(2)). TWA magnitude (voltage of alternation), which was computed spectrally during ventricular stimulation, varied linearly with LV mass index (p = 0.003). Spatially, positive TWA (magnitude > or =1.9 microV) in orthogonal electrocardiographic axes overlaid scar or wall motion abnormalities in corresponding echocardiographic segments (p <0.05 in x and y axes). After a follow-up of 35 +/- 13 months, positive TWA predicted the combined end point of death or sustained ventricular arrhythmias in all patients (p = 0.025), with a trend for those with echocardiographic LV hypertrophy (p = 0.058). In conclusion, in patients with systolic dysfunction due to coronary artery disease, TWA may indicate arrhythmic contributions from regional myocardial scar and eccentric LV hypertrophy.
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28
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Boyden PA, ter Keurs H. Would modulation of intracellular Ca2+ be antiarrhythmic? Pharmacol Ther 2005; 108:149-79. [PMID: 16038982 DOI: 10.1016/j.pharmthera.2005.03.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2005] [Accepted: 03/22/2005] [Indexed: 01/10/2023]
Abstract
Under several types of conditions, reversal of steps of excitation-contraction coupling (RECC) can give rise to nondriven electrical activity. In this review we explore those conditions for several cardiac cell types (SA, atrial, Purkinje, ventricular cells). We find that abnormal spontaneous Ca2+ release from intracellular Ca2+ stores, aberrant Ca2+ influx from sarcolemmal channels or abnormal Ca2+ surges in nonuniform muscle can be the initiators of the RECC. Often, with such increases in Ca2+, spontaneous Ca2+ waves occur and lead to membrane depolarizations. Because the change in membrane voltage is produced by Ca2+-dependent changes in ion channel function, we also review here what is known about the molecular interaction of Ca2+ and several Ca2+-dependent processes, including the intracellular Ca2+ release channels implicated in the genetic basis of some forms of human arrhythmias. Finally, we review what is known about the effectiveness of several agents in modifying such Ca2+-dependent arrhythmias.
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Affiliation(s)
- Penelope A Boyden
- Department of Pharmacology, Center for Molecular Therapeutics, Columbia University, NY 10032, USA.
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29
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Marumoto A, Hasegawa J, Zhang F, Moritani H, Harada T, Sano A, Miura N, Kishimoto Y, Ohgi S. Trapidil enhances the slowly activating delayed rectifier potassium current and suppresses the transient inward current induced by catecholamine in Guinea pig ventricular myocytes. J Cardiovasc Pharmacol 2005; 46:167-76. [PMID: 16044028 DOI: 10.1097/01.fjc.0000167011.75306.ca] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We examined the electrophysiological effects of trapidil on the ionic currents influencing the repolarization and on the transient inward current (ITi) that can cause triggered arrhythmia using the whole-cell patch-clamp technique in guinea pig ventricular myocytes. Trapidil shortened the action potential duration (APD) and increased the delayed rectifier potassium current (IK) in a concentration-dependent manner. The effect of trapidil on the rapidly and slowly activating components of IK (IKr and IKs, respectively) was studied by the envelope of tails test. Trapidil failed to affect IKr and selectively enhanced IKs. Trapidil increased the amplitude of the L-type Ca2+ current (ICa,L), with an acceleration of its inactivation, whereas isoproterenol, a beta-adrenoceptor agonist, increased the amplitude of the ICa,L in a different manner. Isoproterenol activated ITi; however, trapidil not only failed to facilitate ITi but also suppressed isoproterenol-induced ITi. The inhibitory effect of trapidil on isoproterenol-induced ITi is at least partly via a reduction of Ca2+ overload through an acceleration of ICa,L inactivation and/or a sarcoplasmic reticulum (SR) Ca channel modulation. These results suggest that trapidil does not prolong the QT interval and has an antiarrhythmic effect on arrhythmias elicited by triggered activity secondary to Ca2+ overload at much higher concentrations than clinical concentration.
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Affiliation(s)
- Akira Marumoto
- Division of Pharmacotherapeutics, Department of Pathophysiological and Therapeutic Science, Faculty of Medicine, Tottori University, Yonago, Japan
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30
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Ullrich ND, Voets T, Prenen J, Vennekens R, Talavera K, Droogmans G, Nilius B. Comparison of functional properties of the Ca2+-activated cation channels TRPM4 and TRPM5 from mice. Cell Calcium 2005; 37:267-78. [PMID: 15670874 DOI: 10.1016/j.ceca.2004.11.001] [Citation(s) in RCA: 174] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2004] [Revised: 10/29/2004] [Accepted: 11/03/2004] [Indexed: 11/26/2022]
Abstract
Non-selective cation (NSC) channels activated by intracellular Ca2+ ([Ca2+]i) play an important role in Ca2+ signaling and membrane excitability in many cell types. TRPM4 and TRPM5, two Ca2+-activated cation channels of the TRP superfamily, are potential molecular correlates of NSC channels. We compared the functional properties of mouse TRPM4 and TRPM5 heterologously expressed in HEK 293 cells. Dialyzing cells with different Ca2+ concentrations revealed a difference in Ca2+ sensitivity between TRPM4 and TRPM5, with EC50 values of 20.2+/-4.0 microM and 0.70+/-0.1 microM, respectively. Similarly, TRPM5 activated at lower Ca2+ concentration than TRPM4 when [Ca2+]i was raised by UV uncaging of the Ca2+-cage DMNP-EDTA. Current amplitudes of TRPM4 and TRPM5 were not correlated to the rate of changes in [Ca2+]i. The Ca2+ sensitivity of both channels was strongly reduced in inside-out patches, resulting in approximately 10-30 times higher EC50 values than under whole-cell conditions. Currents through TRPM4 and TRPM5 deactivated at negative and activated at positive potentials with similar kinetics. Both channels were equally sensitive to block by intracellular spermine. TRPM4 displayed a 10-fold higher affinity for block by flufenamic acid. Importantly, ATP4- blocked TRPM4 with high affinity (IC50 of 0.8+/-0.1 microM), whereas TRPM5 is insensitive to ATP4- at concentrations up to 1 mM.
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Affiliation(s)
- Nina D Ullrich
- Laboratorium voor Fysiologie, Department of Physiology, Campus Gasthuisberg, KU Leuven, Herestraat 49, B-3000 Leuven, Belgium
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31
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Abstract
The transient receptor potential (TRP) protein superfamily consists of a diverse group of cation channels that bear structural similarities to Drosophila TRP. TRP channels play important roles in nonexcitable cells; however, an emerging theme is that many TRP-related proteins are expressed predominantly in the nervous system and function in sensory physiology. The TRP superfamily is divided into seven subfamilies, the first of which is composed of the "classical" TRPs" (TRPC subfamily). Some TRPCs may be store-operated channels, whereas others appear to be activated by production of diacylglycerol or regulated through an exocytotic mechanism. Many members of a second subfamily (TRPV) function in sensory physiology and respond to heat, changes in osmolarity, odorants, and mechanical stimuli. Two members of the TRPM family function in sensory perception and three TRPM proteins are chanzymes, which contain C-terminal enzyme domains. The fourth and fifth subfamilies, TRPN and TRPA, include proteins with many ankyrin repeats. TRPN proteins function in mechanotransduction, whereas TRPA1 is activated by noxious cold and is also required for the auditory response. In addition to these five closely related TRP subfamilies, which comprise the Group 1 TRPs, members of the two Group 2 TRP subfamilies, TRPP and TRPML, are distantly related to the group 1 TRPs. Mutations in the founding members of these latter subfamilies are responsible for human diseases. Each of the TRP subfamilies are represented by members in worms and flies, providing the potential for using genetic approaches to characterize the normal functions and activation mechanisms of these channels.
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32
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Rossow CF, Minami E, Chase EG, Murry CE, Santana LF. NFATc3-Induced Reductions in Voltage-Gated K
+
Currents After Myocardial Infarction. Circ Res 2004; 94:1340-50. [PMID: 15087419 DOI: 10.1161/01.res.0000128406.08418.34] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Reductions in voltage-activated K
+
(Kv) currents may underlie arrhythmias after myocardial infarction (MI). We investigated the role of β-adrenergic signaling and the calcineurin/NFAT pathway in mediating the reductions in Kv currents observed after MI in mouse ventricular myocytes. Kv currents were produced by the summation of 3 distinct currents: I
to
, I
Kslow1
, and I
Kslow2
. At 48 hours after MI, we found a 4-fold increase in NFAT activity, which coincided with a decrease in the amplitudes of I
to
, I
Kslow1
, and I
Kslow2
. Consistent with this, mRNA and protein levels of Kv1.5, 2.1, 4.2, and 4.3, which underlie I
Kslow1
, I
Kslow2
, and I
to
, were decreased after MI. Administration of the β-blocker metoprolol prevented the activation of NFAT and the reductions in I
to
, I
Kslow1
, and I
Kslow2
after MI. Cyclosporine, an inhibitor of calcineurin, also prevented the reductions in these currents after MI. Importantly, Kv currents did not change after MI in ventricular myocytes from NFATc3 knockout mice. Conversely, chronic β-adrenergic stimulation or expression of an activated NFATc3 decreased Kv currents to a similar extent as MI. Taken together, these data indicate that NFATc3 plays an essential role in the signaling pathway leading to reduced I
to
, I
Kslow1
, and I
Kslow2
after MI. We propose that increased β-adrenergic signaling after MI activates calcineurin and NFATc3, which decreases I
to
, I
Kslow1
, and I
Kslow2
via a reduction in Kv1.5, Kv2.1, Kv4.2, and Kv4.3 expression.
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Affiliation(s)
- Charles F Rossow
- Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195, USA
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33
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Hofmann T, Chubanov V, Gudermann T, Montell C. TRPM5 is a voltage-modulated and Ca(2+)-activated monovalent selective cation channel. Curr Biol 2003; 13:1153-8. [PMID: 12842017 DOI: 10.1016/s0960-9822(03)00431-7] [Citation(s) in RCA: 281] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The TRPM subfamily of mammalian TRP channels displays unusually diverse activation mechanisms and selectivities. One member of this subfamily, TRPM5, functions in taste receptor cells and has been reported to be activated through G protein-coupled receptors linked to phospholipase C. However, the specific mechanisms regulating TRPM5 have not been described. Here, we demonstrate that TRPM5 is a monovalent-specific cation channel with a 23 pS unitary conductance. TRPM5 does not display constitutive activity. Rather, it is activated by stimulation of a receptor pathway coupled to phospholipase C and by IP(3)-mediated Ca(2+) release. Gating of TRPM5 was dependent on a rise in Ca(2+) because it was fully activated by Ca(2+). Unlike any previously described mammalian TRP channel, TRPM5 displayed voltage modulation and rapid activation and deactivation kinetics upon receptor stimulation. The most closely related protein, the Ca(2+)-activated monovalent-selective cation channel TRPM4b, also showed voltage modulation, although with slower relaxation kinetics than TRPM5. Taken together, the data demonstrate that TRPM5 and TRPM4b represent the first examples of voltage-modulated, Ca(2+)-activated, monovalent cation channels (VCAMs). The voltage modulation and rapid kinetics provide TRPM5 with an excellent set of properties for participating in signaling in taste receptors and other excitable cells.
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Affiliation(s)
- Thomas Hofmann
- Department of Biological Chemistry, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21215, USA
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34
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Ennis IL, Escudero EM, Console GM, Camihort G, Dumm CG, Seidler RW, Camilión de Hurtado MC, Cingolani HE. Regression of isoproterenol-induced cardiac hypertrophy by Na+/H+ exchanger inhibition. Hypertension 2003; 41:1324-9. [PMID: 12732584 DOI: 10.1161/01.hyp.0000071180.12012.6e] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Cardiac hypertrophy is often associated with an increased sympathetic drive, and both in vitro and in vivo studies have demonstrated the development of cardiomyocyte hypertrophy in response to either alpha- or beta-adrenergic stimulation. Because an association between the Na+/H+ exchanger and cellular growth has been proposed, this study aimed to analyze the possible role of the antiporter in isoproterenol-induced cardiac hypertrophy. Isoproterenol alone (5 mg/kg IP once daily) or combined with a selective inhibitor of the Na+/H+ exchanger activity (3 mg x kg(-1) x d(-1) BIIB723) was given to male Wistar rats for 30 days. Sex- and age-matched rats that received 0.9% saline IP daily served as controls. Echocardiographic follow-up showed a 33% increase in left ventricular mass in the isoproterenol-treated group, whereas it did not increase in the isoproterenol+BIIB723-treated group. Heart weight-to-body weight ratio at necropsy was 2.44+/-0.11 in controls and increased to 3.35+/-0.10 (P<0.05) with isoproterenol, an effect that was markedly attenuated by BIIB723 (2.82+/-0.07). Intense cardiomyocyte enlargement and severe subendocardial fibrosis were found in isoproterenol-treated rats, and both effects were attenuated by BIIB723. Myocardial Na+/H+ exchanger activity and protein expression significantly increased in isoproterenol-treated rats compared with the control group (1.45+/-0.11 vs 0.91+/-0.05 arbitrary units, P<0.05). This effect was significantly reduced by BIIB723 (1.17+/-0.02, P<0.05). In conclusion, our results show that Na+/H+ exchanger inhibition prevented the development of isoproterenol-induced hypertrophy and fibrosis, providing strong evidence in favor of a key role played by the antiporter in this model of cardiac hypertrophy.
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Affiliation(s)
- Irene L Ennis
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, UNLP 60 y 120 (1900), La Plata, Argentina.
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35
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Jiang D, Xiao B, Zhang L, Chen SRW. Enhanced basal activity of a cardiac Ca2+ release channel (ryanodine receptor) mutant associated with ventricular tachycardia and sudden death. Circ Res 2002; 91:218-25. [PMID: 12169647 DOI: 10.1161/01.res.0000028455.36940.5e] [Citation(s) in RCA: 150] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Mutations in the human cardiac Ca2+ release channel (ryanodine receptor, RyR2) gene have recently been shown to cause effort-induced ventricular arrhythmias. However, the consequences of these disease-causing mutations in RyR2 channel function are unknown. In the present study, we characterized the properties of mutation R4496C of mouse RyR2, which is equivalent to a disease-causing human RyR2 mutation R4497C, by heterologous expression of the mutant in HEK293 cells. [3H]ryanodine binding studies revealed that the R4496C mutation resulted in an increase in RyR2 channel activity in particular at low Ca2+ concentrations. This increased basal channel activity remained sensitive to modulation by caffeine, ATP, Mg2+, and ruthenium red. In addition, the R4496C mutation enhanced the sensitivity of RyR2 to activation by Ca2+ and by caffeine. Single-channel analysis showed that single R4496C mutant channels exhibited considerable channel openings at low Ca2+ concentrations. HEK293 cells transfected with mutant R4496C displayed spontaneous Ca2+ oscillations more frequently than cells transfected with wild-type RyR2. Substitution of a negatively charged glutamate for the positively charged R4496 (R4496E) further enhanced the basal channel activity, whereas replacement of R4496 by a positively charged lysine (R4496K) had no significant effect on the basal activity. These observations indicate that the charge and polarity at residue 4496 plays an essential role in RyR2 channel gating. Enhanced basal activity of RyR2 may underlie an arrhythmogenic mechanism for effort-induced ventricular tachycardia.
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Affiliation(s)
- Dawei Jiang
- Cardiovascular Research Group, Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada
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36
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Yang X, Salas PJI, Pham TV, Wasserlauf BJ, Smets MJD, Myerburg RJ, Gelband H, Hoffman BF, Bassett AL. Cytoskeletal actin microfilaments and the transient outward potassium current in hypertrophied rat ventriculocytes. J Physiol 2002; 541:411-21. [PMID: 12042348 PMCID: PMC2290334 DOI: 10.1113/jphysiol.2002.019562] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The durations of transmembrane action potentials recorded from single myocytes isolated from the endocardial surface of hypertrophied left ventricles of rats were increased, compared to the durations recorded from normal left ventricular cells at 36-37 degrees C. Exposure to phalloidin (1-20 microM, < 20 min), a specific stabilizer of the non-myofibrillar actin microfilament component of the cardiac cytoskeleton, had no effect on action potential duration of normal cells, but significantly shortened the prolonged action potentials of hypertrophied cells. Cytochalasin D (5-50 microM), a disrupter of the actin microfilaments, also had little effect on action potential duration of normal cells. However, cytochalasin D further increased the action potential duration of hypertrophied cells at 10 min exposure. The addition of phalloidin to solutions containing cytochalasin D, reduced the latter's increase of action potential duration in hypertrophied cells. Whole-cell transient outward K(+) current (I(to1)) density was significantly decreased in hypertrophied cells. At a test potential of +60 mV, the mean I(to1) density recorded from normal cells was 13.5 +/- 1.1 pA pF(-1) (n = 18) compared to 4.17 +/- 1.2 pA pF(-1) for LVH cells (n = 22; P < 0.05). Phalloidin (20 microM) increased and cytochalasin D (50 microM) decreased whole-cell I(to1) in hypertrophied cells but had no effect on I(to1), in normal cells. When equimolar concentrations were used, phalloidin, 10 microM, reversed the decrease in I(to1) brought about by cytochalasin D, 10 microM, in hypertrophied cells. The L-type calcium current density was reduced in LVH compared to normal cells. Phalloidin (20 microM) and cytochalasin D (50 microM) had no effect on I(Ca,L) in normal or LVH myocytes. The decrease in I(to1) in hypertrophied cells and the altered I(to1) responsiveness to phalloidin and cytochalasin D reflect modification of I(to1) channel function mediated, in part, through hypertrophy-altered cytoskeletal actin microfilament regulation of I(to1).
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Affiliation(s)
- Xiangjun Yang
- Department of Cardiology of the First Affiliated Hospital to Suzhou University, Suzhou Jiangsu 215006, People's Republic of China
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37
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Despa S, Islam MA, Weber CR, Pogwizd SM, Bers DM. Intracellular Na(+) concentration is elevated in heart failure but Na/K pump function is unchanged. Circulation 2002; 105:2543-8. [PMID: 12034663 DOI: 10.1161/01.cir.0000016701.85760.97] [Citation(s) in RCA: 245] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Intracellular sodium concentration ([Na(+)](i)) modulates cardiac contractile and electrical activity through Na/Ca exchange (NCX). Upregulation of NCX in heart failure (HF) may magnify the functional impact of altered [Na(+)](i). METHODS AND RESULTS We measured [Na(+)](i) by using sodium binding benzofuran isophthalate in control and HF rabbit ventricular myocytes (HF induced by aortic insufficiency and constriction). Resting [Na(+)](i) was 9.7+/-0.7 versus 6.6+/-0.5 mmol/L in HF versus control. In both cases, [Na(+)](i) increased by approximately 2 mmol/L when myocytes were stimulated (0.5 to 3 Hz). To identify the mechanisms responsible for [Na(+)](i) elevation in HF, we measured the [Na(+)](i) dependence of Na/K pump-mediated Na(+) extrusion. There was no difference in V(max) (8.3+/-0.7 versus 8.0+/-0.8 mmol/L/min) or K(m) (9.2+/-1.0 versus 9.9+/-0.8 mmol/L in HF and control, respectively). Therefore, at measured [Na(+)](i) levels, the Na/K pump rate is actually higher in HF. However, resting Na(+) influx was twice as high in HF versus control (2.3+/-0.3 versus 1.1+/-0.2 mmol/L/min), primarily the result of a tetrodotoxin-sensitive pathway. CONCLUSIONS Myocyte [Na(+)](i) is elevated in HF as a result of higher diastolic Na(+) influx (with unaltered Na/K-ATPase characteristics). In HF, the combined increased [Na(+)](i), decreased Ca(2+) transient, and prolonged action potential all profoundly affect cellular Ca(2+) regulation, promoting greater Ca(2+) influx through NCX during action potentials. Notably, the elevated [Na(+)](i) may be critical in limiting the contractile dysfunction observed in HF.
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Affiliation(s)
- Sanda Despa
- Department of Physiology, Loyola University Chicago, Maywood, IL 60153, USA
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