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Fazlollahi F, Santini Gonzalez JJ, Repas SJ, Canan BD, Billman GE, Janssen PML. Contraction-relaxation coupling is unaltered by exercise training and infarction in isolated canine myocardium. J Gen Physiol 2021; 153:211978. [PMID: 33847735 PMCID: PMC8047736 DOI: 10.1085/jgp.202012829] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 02/20/2021] [Accepted: 03/18/2021] [Indexed: 12/28/2022] Open
Abstract
The two main phases of the mammalian cardiac cycle are contraction and relaxation; however, whether there is a connection between them in humans is not well understood. Routine exercise has been shown to improve cardiac function, morphology, and molecular signatures. Likewise, the acute and chronic changes that occur in the heart in response to injury, disease, and stress are well characterized, albeit not fully understood. In this study, we investigated how exercise and myocardial injury affect contraction–relaxation coupling. We retrospectively analyzed the correlation between the maximal speed of contraction and the maximal speed of relaxation of canine myocardium after receiving surgically induced myocardial infarction, followed by either sedentary recovery or exercise training for 10–12 wk. We used isolated right ventricular trabeculae, which were electrically paced at different lengths, frequencies, and with increasing β-adrenoceptor stimulation. In all conditions, contraction and relaxation were linearly correlated, irrespective of injury or training history. Based on these results and the available literature, we posit that contraction–relaxation coupling is a fundamental myocardial property that resides in the structural arrangement of proteins at the level of the sarcomere and that this may be regulated by the actions of cardiac myosin binding protein C (cMyBP-C) on actin and myosin.
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Affiliation(s)
- Farbod Fazlollahi
- Department of Physiology and Cell Biology, College of Medicine, Ohio State University, Columbus, OH
| | - Jorge J Santini Gonzalez
- Department of Physiology and Cell Biology, College of Medicine, Ohio State University, Columbus, OH
| | - Steven J Repas
- Department of Physiology and Cell Biology, College of Medicine, Ohio State University, Columbus, OH
| | - Benjamin D Canan
- Department of Physiology and Cell Biology, College of Medicine, Ohio State University, Columbus, OH
| | - George E Billman
- Department of Physiology and Cell Biology, College of Medicine, Ohio State University, Columbus, OH
| | - Paul M L Janssen
- Department of Physiology and Cell Biology, College of Medicine, Ohio State University, Columbus, OH
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2
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Medert R, Pironet A, Bacmeister L, Segin S, Londoño JEC, Vennekens R, Freichel M. Genetic background influences expression and function of the cation channel TRPM4 in the mouse heart. Basic Res Cardiol 2020; 115:70. [PMID: 33205255 PMCID: PMC7671982 DOI: 10.1007/s00395-020-00831-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Accepted: 11/02/2020] [Indexed: 01/21/2023]
Abstract
Transient receptor potential melastatin 4 (TRPM4) cation channels act in cardiomyocytes as a negative modulator of the L-type Ca2+ current. Ubiquitous Trpm4 deletion in mice leads to an increased β-adrenergic inotropy in healthy mice as well as after myocardial infarction. In this study, we set out to investigate cardiac inotropy in mice with cardiomyocyte-specific Trpm4 deletion. The results guided us to investigate the relevance of TRPM4 for catecholamine-evoked Ca2+ signaling in cardiomyocytes and inotropy in vivo in TRPM4-deficient mouse models of different genetic background. Cardiac hemodynamics were investigated using pressure-volume analysis. Surprisingly, an increased β-adrenergic inotropy was observed in global TRPM4-deficient mice on a 129SvJ genetic background, but the inotropic response was unaltered in mice with global and cardiomyocyte-specific TRPM4 deletion on the C57Bl/6N background. We found that the expression of TRPM4 proteins is about 78 ± 10% higher in wild-type mice on the 129SvJ versus C57Bl/6N background. In accordance with contractility measurements, our analysis of the intracellular Ca2+ transients revealed an increase in ISO-evoked Ca2+ rise in Trpm4-deficient cardiomyocytes of the 129SvJ strain, but not of the C57Bl/6N strain. No significant differences were observed between the two mouse strains in the expression of other regulators of cardiomyocyte Ca2+ homeostasis. We conclude that the relevance of TRPM4 for cardiac contractility depends on homeostatic TRPM4 expression levels or the genetic endowment in different mouse strains as well as on the health/disease status. Therefore, the concept of inhibiting TRPM4 channels to improve cardiac contractility needs to be carefully explored in specific strains and species and prospectively in different genetically diverse populations of patients.
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Affiliation(s)
- Rebekka Medert
- Institute of Pharmacology, Heidelberg University, im Neuenheimer Feld 366, 69120, Heidelberg, Germany
- DZHK (German Centre for Cardiovascular Research), Partner Site, Heidelberg/Mannheim, Germany
| | - Andy Pironet
- Laboratory of Ion Channel Research, TRP Research Platform Leuven, VIB Center for Brain and Disease Research, Department of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium
| | - Lucas Bacmeister
- Institute of Pharmacology, Heidelberg University, im Neuenheimer Feld 366, 69120, Heidelberg, Germany
- DZHK (German Centre for Cardiovascular Research), Partner Site, Heidelberg/Mannheim, Germany
| | - Sebastian Segin
- Institute of Pharmacology, Heidelberg University, im Neuenheimer Feld 366, 69120, Heidelberg, Germany
- DZHK (German Centre for Cardiovascular Research), Partner Site, Heidelberg/Mannheim, Germany
| | - Juan E Camacho Londoño
- Institute of Pharmacology, Heidelberg University, im Neuenheimer Feld 366, 69120, Heidelberg, Germany
- DZHK (German Centre for Cardiovascular Research), Partner Site, Heidelberg/Mannheim, Germany
| | - Rudi Vennekens
- Laboratory of Ion Channel Research, TRP Research Platform Leuven, VIB Center for Brain and Disease Research, Department of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium
| | - Marc Freichel
- Institute of Pharmacology, Heidelberg University, im Neuenheimer Feld 366, 69120, Heidelberg, Germany.
- DZHK (German Centre for Cardiovascular Research), Partner Site, Heidelberg/Mannheim, Germany.
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Steijns F, Renard M, Vanhomwegen M, Vermassen P, Desloovere J, Raedt R, Larsen LE, Tóth MI, De Backer J, Sips P. Spontaneous Right Ventricular Pseudoaneurysms and Increased Arrhythmogenicity in a Mouse Model of Marfan Syndrome. Int J Mol Sci 2020; 21:E7024. [PMID: 32987703 PMCID: PMC7582482 DOI: 10.3390/ijms21197024] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Revised: 09/22/2020] [Accepted: 09/22/2020] [Indexed: 02/08/2023] Open
Abstract
Patients with Marfan syndrome (MFS), a connective tissue disorder caused by pathogenic variants in the gene encoding the extracellular matrix protein fibrillin-1, have an increased prevalence of primary cardiomyopathy, arrhythmias, and sudden cardiac death. We have performed an in-depth in vivo and ex vivo study of the cardiac phenotype of Fbn1mgR/mgR mice, an established mouse model of MFS with a severely reduced expression of fibrillin-1. Using ultrasound measurements, we confirmed the presence of aortic dilatation and observed cardiac diastolic dysfunction in male Fbn1mgR/mgR mice. Upon post-mortem examination, we discovered that the mutant mice consistently presented myocardial lesions at the level of the right ventricular free wall, which we characterized as spontaneous pseudoaneurysms. Histological investigation demonstrated a decrease in myocardial compaction in the MFS mouse model. Furthermore, continuous 24 h electrocardiographic analysis showed a decreased heart rate variability and an increased prevalence of extrasystolic arrhythmic events in Fbn1mgR/mgR mice compared to wild-type littermates. Taken together, in this paper we document a previously unreported cardiac phenotype in the Fbn1mgR/mgR MFS mouse model and provide a detailed characterization of the cardiac dysfunction and rhythm disorders which are caused by fibrillin-1 deficiency. These findings highlight the wide spectrum of cardiac manifestations of MFS, which might have implications for patient care.
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Affiliation(s)
- Felke Steijns
- Center for Medical Genetics, Department of Biomolecular Medicine, Ghent University, 9000 Ghent, Belgium; (F.S.); (M.R.); (M.V.); (P.V.); (J.D.B.)
| | - Marjolijn Renard
- Center for Medical Genetics, Department of Biomolecular Medicine, Ghent University, 9000 Ghent, Belgium; (F.S.); (M.R.); (M.V.); (P.V.); (J.D.B.)
| | - Marine Vanhomwegen
- Center for Medical Genetics, Department of Biomolecular Medicine, Ghent University, 9000 Ghent, Belgium; (F.S.); (M.R.); (M.V.); (P.V.); (J.D.B.)
| | - Petra Vermassen
- Center for Medical Genetics, Department of Biomolecular Medicine, Ghent University, 9000 Ghent, Belgium; (F.S.); (M.R.); (M.V.); (P.V.); (J.D.B.)
| | - Jana Desloovere
- 4BRAIN, Department of Head and Skin, Ghent University, 9000 Ghent, Belgium; (J.D.); (R.R.); (L.E.L.)
| | - Robrecht Raedt
- 4BRAIN, Department of Head and Skin, Ghent University, 9000 Ghent, Belgium; (J.D.); (R.R.); (L.E.L.)
| | - Lars E. Larsen
- 4BRAIN, Department of Head and Skin, Ghent University, 9000 Ghent, Belgium; (J.D.); (R.R.); (L.E.L.)
- Institute Biomedical Technology, Ghent University, 9000 Ghent, Belgium;
| | - Máté I. Tóth
- Institute Biomedical Technology, Ghent University, 9000 Ghent, Belgium;
| | - Julie De Backer
- Center for Medical Genetics, Department of Biomolecular Medicine, Ghent University, 9000 Ghent, Belgium; (F.S.); (M.R.); (M.V.); (P.V.); (J.D.B.)
- Department of Cardiology, Ghent University Hospital, 9000 Ghent, Belgium
| | - Patrick Sips
- Center for Medical Genetics, Department of Biomolecular Medicine, Ghent University, 9000 Ghent, Belgium; (F.S.); (M.R.); (M.V.); (P.V.); (J.D.B.)
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Janssen PML, Elnakish MT. Modeling heart failure in animal models for novel drug discovery and development. Expert Opin Drug Discov 2019; 14:355-363. [PMID: 30861352 DOI: 10.1080/17460441.2019.1582636] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
INTRODUCTION When investigating drugs that treat heart diseases, it is critical when choosing an animal model for the said model to produce data that is translatable to the human patient population, while keeping in mind the principles of reduction, refinement, and replacement of the animal model in the research. Areas covered: In this review, the authors focus on mammalian models developed to study the impact of drug treatments on human heart failure. Furthermore, the authors address human patient variability and animal model invariability as well as the considerations that need to be made regarding choice of species. Finally, the authors discuss some of the most common models for the two most prominent human heart failure etiologies; increased load on the heart and myocardial ischemia. Expert opinion: In the authors' opinion, the data generated by drug studies is often heavily impacted by the choice of species and the physiologically relevant conditions under which the data are collected. Approaches that use multiple models and are not restricted to small rodents but involve some verification on larger mammals or on human myocardium, are needed to advance drug discovery for the very large patient population that suffers from heart failure.
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Affiliation(s)
- Paul M L Janssen
- a Department of Physiology and Cell Biology , The Ohio State University Wexner Medical Center , Columbus, OH, USA.,b Dorothy M. Davis Heart and Lung Research Institute , The Ohio State University Wexner Medical Center , Columbus, OH, USA.,c Department of Internal Medicine , The Ohio State University Wexner Medical Center , Columbus, OH, USA
| | - Mohammad T Elnakish
- a Department of Physiology and Cell Biology , The Ohio State University Wexner Medical Center , Columbus, OH, USA.,b Dorothy M. Davis Heart and Lung Research Institute , The Ohio State University Wexner Medical Center , Columbus, OH, USA
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Land S, Niederer SA. A Spatially Detailed Model of Isometric Contraction Based on Competitive Binding of Troponin I Explains Cooperative Interactions between Tropomyosin and Crossbridges. PLoS Comput Biol 2015; 11:e1004376. [PMID: 26262582 PMCID: PMC4532474 DOI: 10.1371/journal.pcbi.1004376] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Accepted: 06/03/2015] [Indexed: 01/20/2023] Open
Abstract
Biophysical models of cardiac tension development provide a succinct representation of our understanding of force generation in the heart. The link between protein kinetics and interactions that gives rise to high cooperativity is not yet fully explained from experiments or previous biophysical models. We propose a biophysical ODE-based representation of cross-bridge (XB), tropomyosin and troponin within a contractile regulatory unit (RU) to investigate the mechanisms behind cooperative activation, as well as the role of cooperativity in dynamic tension generation across different species. The model includes cooperative interactions between regulatory units (RU-RU), between crossbridges (XB-XB), as well more complex interactions between crossbridges and regulatory units (XB-RU interactions). For the steady-state force-calcium relationship, our framework predicts that: (1) XB-RU effects are key in shifting the half-activation value of the force-calcium relationship towards lower [Ca2+], but have only small effects on cooperativity. (2) XB-XB effects approximately double the duty ratio of myosin, but do not significantly affect cooperativity. (3) RU-RU effects derived from the long-range action of tropomyosin are a major factor in cooperative activation, with each additional unblocked RU increasing the rate of additional RU’s unblocking. (4) Myosin affinity for short (1–4 RU) unblocked stretches of actin of is very low, and the resulting suppression of force at low [Ca2+] is a major contributor in the biphasic force-calcium relationship. We also reproduce isometric tension development across mouse, rat and human at physiological temperature and pacing rate, and conclude that species differences require only changes in myosin affinity and troponin I/troponin C affinity. Furthermore, we show that the calcium dependence of the rate of tension redevelopment ktr is explained by transient blocking of RU’s by a temporary decrease in XB-RU effects. Force generation in cardiac muscle cells is driven by changes in calcium concentration. Relatively small changes in the calcium concentration over the course of a heart beat lead to the large changes in force required to fully contract and relax the heart. This is known as ‘cooperative activation’, and involves a complex interaction of several proteins involved in contraction. Current computer models which reproduce force generation often do not represent these processes explicitly, and stochastic approaches that do tend to require large amounts of computational power to solve, which limit the range of investigations in which they can be used. We have created an new computational model that captures the underlying physiological processes in more detail, and is more efficient than stochastic approaches, while still being able to run a large range of simulations. The model is able to explain the biological processes leading to the cooperative activation of muscle. In addition, the model reproduces how this cooperative activation translates to normal muscle function to generate force from changes in calcium across three different species.
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Affiliation(s)
- Sander Land
- Department of Biomedical Engineering, King’s College London, United Kingdom
- * E-mail:
| | - Steven A. Niederer
- Department of Biomedical Engineering, King’s College London, United Kingdom
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6
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Cowley PM, Wang G, Chang AN, Makwana O, Swigart PM, Lovett DH, Stull JT, Simpson PC, Baker AJ. The α1A-adrenergic receptor subtype mediates increased contraction of failing right ventricular myocardium. Am J Physiol Heart Circ Physiol 2015; 309:H888-96. [PMID: 26116709 DOI: 10.1152/ajpheart.00042.2015] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Accepted: 06/24/2015] [Indexed: 12/23/2022]
Abstract
Dysfunction of the right ventricle (RV) is closely related to prognosis for patients with RV failure. Therefore, strategies to improve failing RV function are significant. In a mouse RV failure model, we previously reported that α1-adrenergic receptor (α1-AR) inotropic responses are increased. The present study determined the roles of both predominant cardiac α1-AR subtypes (α1A and α1B) in upregulated inotropy in failing RV. We used the mouse model of bleomycin-induced pulmonary fibrosis, pulmonary hypertension, and RV failure. We assessed the myocardial contractile response in vitro to stimulation of the α1A-subtype (using α1A-subtype-selective agonist A61603) and α1B-subtype [using α1A-subtype knockout mice and nonsubtype selective α1-AR agonist phenylephrine (PE)]. In wild-type nonfailing RV, a negative inotropic effect of α1-AR stimulation with PE (force decreased ≈50%) was switched to a positive inotropic effect (PIE) with bleomycin-induced RV injury. Upregulated inotropy in failing RV occurred with α1A-subtype stimulation (force increased ≈200%), but not with α1B-subtype stimulation (force decreased ≈50%). Upregulated inotropy mediated by the α1A-subtype involved increased activator Ca(2+) transients and increased phosphorylation of myosin regulatory light chain (a mediator of increased myofilament Ca(2+) sensitivity). In failing RV, the PIE elicited by the α1A-subtype was appreciably less when the α1A-subtype was stimulated in combination with the α1B-subtype, suggesting functional antagonism between α1A- and α1B-subtypes. In conclusion, upregulation of α1-AR inotropy in failing RV myocardium requires the α1A-subtype and is opposed by the α1B-subtype. The α1A subtype might be a therapeutic target to improve the function of the failing RV.
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Affiliation(s)
- Patrick M Cowley
- Veterans Affairs Medical Center, San Francisco, and Department of Medicine, University California San Francisco, San Francisco, California; and
| | - Guanying Wang
- Veterans Affairs Medical Center, San Francisco, and Department of Medicine, University California San Francisco, San Francisco, California; and
| | - Audrey N Chang
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Om Makwana
- Veterans Affairs Medical Center, San Francisco, and Department of Medicine, University California San Francisco, San Francisco, California; and
| | - Philip M Swigart
- Veterans Affairs Medical Center, San Francisco, and Department of Medicine, University California San Francisco, San Francisco, California; and
| | - David H Lovett
- Veterans Affairs Medical Center, San Francisco, and Department of Medicine, University California San Francisco, San Francisco, California; and
| | - James T Stull
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Paul C Simpson
- Veterans Affairs Medical Center, San Francisco, and Department of Medicine, University California San Francisco, San Francisco, California; and
| | - Anthony J Baker
- Veterans Affairs Medical Center, San Francisco, and Department of Medicine, University California San Francisco, San Francisco, California; and
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7
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Trpm4 gene invalidation leads to cardiac hypertrophy and electrophysiological alterations. PLoS One 2014; 9:e115256. [PMID: 25531103 PMCID: PMC4274076 DOI: 10.1371/journal.pone.0115256] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Accepted: 11/20/2014] [Indexed: 12/14/2022] Open
Abstract
RATIONALE TRPM4 is a non-selective Ca2+-activated cation channel expressed in the heart, particularly in the atria or conduction tissue. Mutations in the Trpm4 gene were recently associated with several human conduction disorders such as Brugada syndrome. TRPM4 channel has also been implicated at the ventricular level, in inotropism or in arrhythmia genesis due to stresses such as ß-adrenergic stimulation, ischemia-reperfusion, and hypoxia re-oxygenation. However, the physiological role of the TRPM4 channel in the healthy heart remains unclear. OBJECTIVES We aimed to investigate the role of the TRPM4 channel on whole cardiac function with a Trpm4 gene knock-out mouse (Trpm4-/-) model. METHODS AND RESULTS Morpho-functional analysis revealed left ventricular (LV) eccentric hypertrophy in Trpm4-/- mice, with an increase in both wall thickness and chamber size in the adult mouse (aged 32 weeks) when compared to Trpm4+/+ littermate controls. Immunofluorescence on frozen heart cryosections and qPCR analysis showed no fibrosis or cellular hypertrophy. Instead, cardiomyocytes in Trpm4-/- mice were smaller than Trpm4+/+with a higher density. Immunofluorescent labeling for phospho-histone H3, a mitosis marker, showed that the number of mitotic myocytes was increased 3-fold in the Trpm4-/-neonatal stage, suggesting hyperplasia. Adult Trpm4-/- mice presented multilevel conduction blocks, as attested by PR and QRS lengthening in surface ECGs and confirmed by intracardiac exploration. Trpm4-/-mice also exhibited Luciani-Wenckebach atrioventricular blocks, which were reduced following atropine infusion, suggesting paroxysmal parasympathetic overdrive. In addition, Trpm4-/- mice exhibited shorter action potentials in atrial cells. This shortening was unrelated to modifications of the voltage-gated Ca2+ or K+ currents involved in the repolarizing phase. CONCLUSIONS TRPM4 has pleiotropic roles in the heart, including the regulation of conduction and cellular electrical activity which impact heart development.
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8
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High-throughput phenotypic assessment of cardiac physiology in four commonly used inbred mouse strains. J Comp Physiol B 2014; 184:763-75. [PMID: 24788387 DOI: 10.1007/s00360-014-0830-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Revised: 03/25/2014] [Accepted: 04/01/2014] [Indexed: 01/19/2023]
Abstract
Mice with genetic alterations are used in heart research as model systems of human diseases. In the last decade there was a marked increase in the recognition of genetic diversity within inbred mouse strains. Increasing numbers of inbred mouse strains and substrains and analytical variation of cardiac phenotyping methods require reproducible, high-throughput methods to standardize murine cardiovascular physiology. We describe methods for non-invasive, reliable, easy and fast to perform echocardiography and electrocardiography on awake mice. This method can be used for primary screening of the murine cardiovascular system in large-scale analysis. We provide insights into the physiological divergence of C57BL/6N, C57BL/6J, C3HeB/FeJ and 129P2/OlaHsd mouse hearts and define the expected normal values. Our report highlights that compared to the other three strains tested C57BL/6N hearts reveal features of heart failure such as hypertrophy and reduced contractile function. We found several features of the mouse ECG to be under genetic control and obtained several strain-specific differences in cardiac structure and function.
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9
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Milani-Nejad N, Janssen PML. Small and large animal models in cardiac contraction research: advantages and disadvantages. Pharmacol Ther 2014; 141:235-49. [PMID: 24140081 PMCID: PMC3947198 DOI: 10.1016/j.pharmthera.2013.10.007] [Citation(s) in RCA: 305] [Impact Index Per Article: 30.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Accepted: 08/15/2013] [Indexed: 12/22/2022]
Abstract
The mammalian heart is responsible for not only pumping blood throughout the body but also adjusting this pumping activity quickly depending upon sudden changes in the metabolic demands of the body. For the most part, the human heart is capable of performing its duties without complications; however, throughout many decades of use, at some point this system encounters problems. Research into the heart's activities during healthy states and during adverse impacts that occur in disease states is necessary in order to strategize novel treatment options to ultimately prolong and improve patients' lives. Animal models are an important aspect of cardiac research where a variety of cardiac processes and therapeutic targets can be studied. However, there are differences between the heart of a human being and an animal and depending on the specific animal, these differences can become more pronounced and in certain cases limiting. There is no ideal animal model available for cardiac research, the use of each animal model is accompanied with its own set of advantages and disadvantages. In this review, we will discuss these advantages and disadvantages of commonly used laboratory animals including mouse, rat, rabbit, canine, swine, and sheep. Since the goal of cardiac research is to enhance our understanding of human health and disease and help improve clinical outcomes, we will also discuss the role of human cardiac tissue in cardiac research. This review will focus on the cardiac ventricular contractile and relaxation kinetics of humans and animal models in order to illustrate these differences.
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Affiliation(s)
- Nima Milani-Nejad
- Department of Physiology and Cell Biology and D. Davis Heart Lung Institute, College of Medicine, The Ohio State University, OH, USA
| | - Paul M L Janssen
- Department of Physiology and Cell Biology and D. Davis Heart Lung Institute, College of Medicine, The Ohio State University, OH, USA.
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10
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Vaillant F, Lauzier B, Poirier I, Gélinas R, Rivard ME, Robillard Frayne I, Thorin E, Des Rosiers C. Mouse strain differences in metabolic fluxes and function of ex vivo working hearts. Am J Physiol Heart Circ Physiol 2013; 306:H78-87. [PMID: 24186097 DOI: 10.1152/ajpheart.00465.2013] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In mice, genetic background is known to influence various parameters, including cardiac function. Its impact on cardiac energy substrate metabolism-a factor known to be closely related to function and contributes to disease development-is, however, unclear. This was examined in this study. In commonly used control mouse substrains SJL/JCrNTac, 129S6/SvEvTac, C57Bl/6J, and C57Bl/6NCrl, we assessed the functional and metabolic phenotypes of 3-mo-old working mouse hearts perfused ex vivo with physiological concentrations of (13)C-labeled carbohydrates (CHO) and a fatty acid (FA). Marked variations in various functional and metabolic flux parameters were observed among all mouse substrains, although the pattern observed differed for these parameters. For example, among all strains, C57Bl/6NCrl hearts had a greater cardiac output (+1.7-fold vs. SJL/JCrNTac and C57Bl/6J; P < 0.05), whereas at the metabolic level, 129S6/SvEvTac hearts stood out by displaying (vs. all 3 strains) a striking shift from exogenous FA (~-3.5-fold) to CHO oxidation as well as increased glycolysis (+1.7-fold) and FA incorporation into triglycerides (+2-fold). Correlation analyses revealed, however, specific linkages between 1) glycolysis, FA oxidation, and pyruvate metabolism and 2) cardiac work, oxygen consumption with heart rate, respectively. This implies that any genetically determined factors affecting a given metabolic flux parameter may impact on the associated functional parameters. Our results emphasize the importance of selecting the appropriate control strain for cardiac metabolic studies using transgenic mice, a factor that has often been neglected. Understanding the molecular mechanisms underlying the diversity of strain-specific cardiac metabolic and functional profiles, particularly the 129S6/SvEvTac, may ultimately disclose new specific metabolic targets for interventions in heart disease.
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Affiliation(s)
- Fanny Vaillant
- Departments of Nutrition, Montreal Heart Institute and Université de Montréal, Montreal, Quebec, Canada; and
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11
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Land S, Niederer SA, Aronsen JM, Espe EKS, Zhang L, Louch WE, Sjaastad I, Sejersted OM, Smith NP. An analysis of deformation-dependent electromechanical coupling in the mouse heart. J Physiol 2012; 590:4553-69. [PMID: 22615436 PMCID: PMC3477757 DOI: 10.1113/jphysiol.2012.231928] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Accepted: 05/17/2012] [Indexed: 01/20/2023] Open
Abstract
To investigate the effects of the coupling between excitation and contraction on whole-organ function, we have developed a novel biophysically based multiscale electromechanical model of the murine heart. Through comparison with a comprehensive in vivo experimental data set, we show good agreement with pressure and volume measurements at both physiological temperatures and physiological pacing frequencies. This whole-organ model was used to investigate the effects of material and haemodynamic properties introduced at the tissue level, as well as emergent function of our novel cell contraction model. Through a comprehensive sensitivity analysis at both the cellular and whole organ level, we demonstrate the sensitivity of the model's results to its parameters and the constraining effect of experimental data. These results demonstrate the fundamental importance of length- and velocity-dependent feedback to the cellular scale for whole-organ function, and we show that a strong velocity dependence of tension is essential for explaining the differences between measured single cell tension and whole-organ pressure transients.
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Affiliation(s)
- Sander Land
- Department of Computer Science, University of Oxford, Oxford, UK
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12
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Roof SR, Shannon TR, Janssen PML, Ziolo MT. Effects of increased systolic Ca²⁺ and phospholamban phosphorylation during β-adrenergic stimulation on Ca²⁺ transient kinetics in cardiac myocytes. Am J Physiol Heart Circ Physiol 2011; 301:H1570-8. [PMID: 21765055 DOI: 10.1152/ajpheart.00402.2011] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Previous studies demonstrated higher systolic intracellular Ca(2+) concentration ([Ca(2+)](i)) amplitudes result in faster [Ca(2+)](i) decline rates, as does β-adrenergic (β-AR) stimulation. The purpose of this study is to determine the major factor responsible for the faster [Ca(2+)](i) decline rate with β-AR stimulation, the increased systolic Ca(2+) concentration levels, or phosphorylation of phospholamban. Mouse myocytes were perfused under basal conditions [1 mM extracellular Ca(2+) concentration ([Ca(2+)](o))], followed by high extracellular Ca(2+) (3 mM [Ca(2+)](o)), washout with 1 mM [Ca(2+)](o), followed by 1 μM isoproterenol (ISO) with 1 mM [Ca(2+)](o). ISO increased Ser(16) phosphorylation compared with 3 mM [Ca(2+)](o), whereas Thr(17) phosphorylation was similar. Ca(2+) transient (CaT) (fluo 4) data were obtained from matched CaT amplitudes with 3 mM [Ca(2+)](o) and ISO. [Ca(2+)](i) decline was significantly faster with ISO compared with 3 mM [Ca(2+)](o). Interestingly, the faster decline with ISO was only seen during the first 50% of the decline. CaT time to peak was significantly faster with ISO compared with 3 mM [Ca(2+)](o). A Ca(2+)/calmodulin-dependent protein kinase (CAMKII) inhibitor (KN-93) did not affect the CaT decline rates with 3 mM [Ca(2+)](o) or ISO but normalized ISO's time to peak with 3 mM [Ca(2+)](o). Thus, during β-AR stimulation, the major factor for the faster CaT decline is due to Ser(16) phosphorylation, and faster time to peak is due to CAMKII activation.
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Affiliation(s)
- Steve R Roof
- Department of Physiology & Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio 43210, USA
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Rose RA, Sellan M, Simpson JA, Izaddoustdar F, Cifelli C, Panama BK, Davis M, Zhao D, Markhani M, Murphy GG, Striessnig J, Liu PP, Heximer SP, Backx PH. Iron overload decreases CaV1.3-dependent L-type Ca2+ currents leading to bradycardia, altered electrical conduction, and atrial fibrillation. Circ Arrhythm Electrophysiol 2011; 4:733-42. [PMID: 21747058 DOI: 10.1161/circep.110.960401] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
BACKGROUND Chronic iron overload (CIO) is associated with blood disorders such as thalassemias and hemochromatosis. A major prognostic indicator of survival in patients with CIO is iron-mediated cardiomyopathy characterized by contractile dysfunction and electrical disturbances, including slow heart rate (bradycardia) and heart block. METHODS AND RESULTS We used a mouse model of CIO to investigate the effects of iron on sinoatrial node (SAN) function. As in humans, CIO reduced heart rate (≈20%) in conscious mice as well as in anesthetized mice with autonomic nervous system blockade and in isolated Langendorff-perfused mouse hearts, suggesting that bradycardia originates from altered intrinsic SAN pacemaker function. Indeed, spontaneous action potential frequencies in SAN myocytes with CIO were reduced in association with decreased L-type Ca(2+) current (I(Ca,L)) densities and positive (rightward) voltage shifts in I(Ca,L) activation. Pacemaker current (I(f)) was not affected by CIO. Because I(Ca,L) in SAN myocytes (as well as in atrial and conducting system myocytes) activates at relatively negative potentials due to the presence of Ca(V)1.3 channels (in addition to Ca(V)1.2 channels), our data suggest that elevated iron preferentially suppresses Ca(V)1.3 channel function. Consistent with this suggestion, CIO reduced Ca(V)1.3 mRNA levels by ≈40% in atrial tissue (containing SAN) and did not lower heart rate in Ca(V)1.3 knockout mice. CIO also induced PR-interval prolongation, heart block, and atrial fibrillation, conditions also seen in Ca(V)1.3 knockout mice. CONCLUSIONS Our results demonstrate that CIO selectively reduces Ca(V)1.3-mediated I(Ca,L), leading to bradycardia, slowing of electrical conduction, and atrial fibrillation as seen in patients with iron overload.
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Affiliation(s)
- Robert A Rose
- Department of Physiology, University Health Network, University of Toronto, Toronto, Ontario, Canada
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14
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Xu Y, Delfín DA, Rafael-Fortney JA, Janssen PML. Lengthening-contractions in isolated myocardium impact force development and worsen cardiac contractile function in the mdx mouse model of muscular dystrophy. J Appl Physiol (1985) 2010; 110:512-9. [PMID: 21127205 DOI: 10.1152/japplphysiol.00253.2010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Lengthening-contractions exert eccentric stress on myofibers in normal myocardium. In congestive heart failure caused by a variety of diseases, the impact of lengthening-contractions of myocardium likely becomes more prevalent and severe. The present study introduces a method to investigate the role of stretching imposed by repetitive lengthening-contractions in myocardium under near-physiological conditions. By exerting various stretch-release ramps while the muscle is contracting, consecutive lengthening-contractions and their potential detrimental effect on cardiac function can be studied. We tested our model and hypothesis in age-matched (young and adult) mdx and wild-type mouse right ventricular trabeculae. These linear and ultrathin muscles possess all major cardiac cell types, and their contractile behavior very closely mimics that of the whole myocardium. In the first group of experiments, 10 lengthening-contractions at various magnitudes of stretch were performed in trabeculae from 10-wk-old mdx and wild-type mice. In the second group, 100 lengthening-contractions at various magnitudes were conducted in trabeculae from 10- and 20-wk-old mice. The peak isometric active developed tension (F(dev), in mN/mm(2)) and kinetic parameters time to peak tension (TTP, in ms) and time from peak tension to half-relaxation (RT50, in ms) were measured. Our results indicate lengthening-contractions significantly impact contractile behavior, and that dystrophin-deficient myocardium in mdx mice is significantly more susceptible to these damaging lengthening-contractions. The results indicate that lengthening-contractions in intact myocardium can be used in vitro to study this emerging contributor to cardiomyopathy.
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Affiliation(s)
- Ying Xu
- Dept. of Physiology and Cell Biology, The Ohio State Univ., 304 Hamilton Hall, 1645 Neil Ave., Columbus, OH 43210-1218, USA
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15
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Janssen PML. Kinetics of cardiac muscle contraction and relaxation are linked and determined by properties of the cardiac sarcomere. Am J Physiol Heart Circ Physiol 2010; 299:H1092-9. [PMID: 20656885 PMCID: PMC2957358 DOI: 10.1152/ajpheart.00417.2010] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/29/2010] [Accepted: 07/21/2010] [Indexed: 01/08/2023]
Abstract
The regulation of myocardial contraction and relaxation kinetics is currently incompletely understood. When the amplitude of contraction is increased via the Frank-Starling mechanism, the kinetics of the contraction slow down, but when the amplitude of contraction is increased with either an increase in heart rate or via β-adrenergic stimulation, the kinetics speed up. It is also unknown how physiological mechanisms affect the kinetics of contraction versus those of relaxation. We investigated contraction-relaxation coupling in isolated trabeculae from the mouse and rat and stimulated them to contract at various temperatures, frequencies, preloads, and in the absence and presence of β-adrenergic stimulation. In each muscle at least 16 different conditions were assessed, and the correlation coefficient of the speed of contraction and relaxation was very close (generally >0.98). Moreover, in all but one of the analyzed murine strains, the ratio of the minimum rate of the derivative of force development (dF/dt) over maximum dF/dt was not significantly different. Only in trabeculae isolated from myosin-binding protein-C mutant mice was this ratio significantly lower (0.61 ± 0.07 vs. 0.84 ± 0.02 in 11 other strains of mice). Within each strain, this ratio was unaffected by modulation of length, frequency, or β-adrenergic stimulation. Rat trabeculae showed identical results; the balance between kinetics of contraction and relaxation was generally constant (0.85 ± 0.04). Because of the great variety in underlying excitation-contraction coupling in the assessed strains, we concluded that contraction-relation coupling is a property residing in the cardiac sarcomere.
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Affiliation(s)
- Paul M L Janssen
- Department of Physiology and Cell Biology and D. Davis Heart Lung Institute, College of Medicine, The Ohio State University, Columbus, OH 43210-1218, USA.
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16
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Abstract
Since the pioneering work of Henry Pickering Bowditch in the late 1800s to early 1900s, cardiac muscle contraction has remained an intensely studied topic for several reasons. The heart is located centrally in our body, and its pumping motion demands the attention of the observer. The contraction of the heart encompasses a complex interplay of mechanical, chemical, and electrical properties, and its function can thus be studied from any of these viewpoints. In addition, diseases of the heart are currently killing more people in the Westernized world than any other disease. When combined with the increasing emphasis of research to be clinically relevant, this contributes to the heart remaining a topic of continued basic and clinical investigation. Yet, there are significant aspects of cardiac muscle contraction that are still not well understood. A big complication of the study of cardiac muscle contraction is that there exists no equilibrium among many of the important governing parameters, which include pre- and afterload, intracellular ion concentrations, membrane potential, and velocity and direction of movement. Thus the classic approach of perturbing an equilibrium or a steady state to learn about the role of the perturbing factor in the system cannot be unambiguously interpreted, since each of the parameters that govern contraction are constantly changing, as well as constantly changing their interaction with each other. In this review, presented as the 54th Bowditch Lecture at Experimental Biology meeting in Anaheim in April 2010, I will revisit several governing factors of cardiac muscle relaxation by applying newly developed tools and protocols to isolated cardiac muscle tissue in which the dynamic interactions between the governing factors of contraction and relaxation can be studied.
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Affiliation(s)
- Paul M L Janssen
- Department of Physiology and Cell Biology and D. Davis Heart Lung Institute, College of Medicine, The Ohio State University, Columbus, Ohio 43210-1218, USA.
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Barnabei MS, Palpant NJ, Metzger JM. Influence of genetic background on ex vivo and in vivo cardiac function in several commonly used inbred mouse strains. Physiol Genomics 2010; 42A:103-13. [PMID: 20627938 DOI: 10.1152/physiolgenomics.00071.2010] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Inbred mouse strains play a critical role in biomedical research. Genetic homogeneity within inbred strains and their general amenability to genetic manipulation have made them an ideal resource for dissecting the physiological function(s) of individual genes. However, the inbreeding that makes inbred mice so useful also results in genetic divergence between them. This genetic divergence is often unaccounted for but may be a confounding factor when comparing studies that have utilized distinct inbred strains. Here, we compared the cardiac function of C57BL/6J mice to seven other commonly used inbred mouse strains: FVB/NJ, DBA/2J, C3H/HeJ, BALB/cJ, 129X1/SvJ, C57BL/10SnJ, and 129S1/SvImJ. The assays used to compare cardiac function were the ex vivo isolated Langendorff heart preparation and in vivo real-time hemodynamic analysis using conductance micromanometry. We report significant strain-dependent differences in cardiac function between C57BL/6J and other commonly used inbred strains. C57BL/6J maintained better cardiac function than most inbred strains after ex vivo ischemia, particularly compared with 129S1/SvImJ, 129X1/SvJ, and C57BL/10SnJ strains. However, during in vivo acute hypoxia 129X1/SvJ and 129S1/SvImJ maintained relatively normal cardiac function, whereas C57BL/6J animals showed dramatic cardiac decompensation. Additionally, C3H/HeJ showed rapid and marked cardiac decompensation in response to esmolol infusion compared with effects of other strains. These findings demonstrate the complex effects of genetic divergence between inbred strains on cardiac function. These results may help inform analysis of gene ablation or transgenic studies and further demonstrate specific quantitative traits that could be useful in discovery of genetic modifiers relevant to cardiac health and disease.
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Affiliation(s)
- Matthew S Barnabei
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, MN 55455, USA
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Mille M, Koenig X, Zebedin E, Uhrin P, Cervenka R, Todt H, Hilber K. Sodium current properties of primary skeletal myocytes and cardiomyocytes derived from different mouse strains. Pflugers Arch 2008; 457:1023-33. [PMID: 18704489 DOI: 10.1007/s00424-008-0570-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2008] [Revised: 07/25/2008] [Accepted: 07/30/2008] [Indexed: 10/21/2022]
Abstract
The mouse has become the preferred animal for genetic manipulations. Because of the diverse genetic backgrounds of various mouse strains, these can manifest strikingly different characteristics. Here, we studied the functional properties of currents through voltage-gated sodium channels in primary cultures of skeletal myocytes and cardiomyocytes derived from the three commonly used mouse strains BL6, 129/Sv, and FVB, by using the whole-cell patch-clamp technique. We found strain-specific sodium current function in skeletal myocytes, which could partly be explained by differences in sodium channel isoform expression. In addition, we found significant effects of cell source (neonatal or adult animal-derived) and variation of the differentiation time period. In contrast to skeletal myocytes, sodium current function in cardiomyocytes was similar in all strains. Our findings are relevant for the design and proper interpretation of electrophysiological studies, which use excitable cells in primary culture as a model system.
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Affiliation(s)
- M Mille
- Institute of Pharmacology, Center for Biomolecular Medicine and Pharmacology, Medical University of Vienna, Austria
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Secretory phospholipase A2 is required to produce histologic changes associated with gastroduodenal reflux in a murine model. J Thorac Cardiovasc Surg 2008; 135:1220-7. [PMID: 18544357 DOI: 10.1016/j.jtcvs.2007.10.080] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/22/2007] [Revised: 09/14/2007] [Accepted: 10/04/2007] [Indexed: 11/22/2022]
Abstract
OBJECTIVE The earliest response of esophageal mucosa to gastric reflux is the development of oxidative damage and inflammation. These processes contribute to the development of metaplasia known as Barrett's esophagus, as well as the progression to malignancy. Secretory phospholipase A(2) is a mediator of inflammation with levels that are increased in Barrett's metaplasia and carcinoma when compared with levels in normal samples. Our goal is to determine the role of secretory phospholipase A(2) in the development of reflux-associated changes in the esophageal mucosa. METHODS Secretory phospholipase A(2)-deficient mice (C57BL/6, n = 5) and mice known to express high levels of secretory phospholipase A(2) (BALB/c, n = 5) underwent side-to-side surgical anastomosis of the first portion of the duodenum and gastroesophageal junction, allowing exposure of esophageal mucosa to duodenal and gastric contents duodeno-gastroesophageal anastomosis. Control animals (n = 5) of each strain underwent laparotomy with esophagotomy and repair. Tissue was frozen in embedding medium. Hematoxylin and eosin staining and Ki67 and secretory phospholipase A(2) immunohistochemistry were used to evaluate esophageal tissue and its response to duodeno-gastroesophageal anastomosis. RESULTS Immunofluorescent staining confirmed the absence of secretory phospholipase A(2) in C57BL/6 mice and its presence in BALB/c mice. Hematoxylin and eosin staining demonstrated significant thickening of the esophageal mucosa in response to gastroesophageal reflux in the presence of secretory phospholipase A(2). Mice known to express high levels of secretory phospholipase A(2) also demonstrated increased numbers of proliferating cells. Secretory phospholipase A(2)-deficient mice were immune to the early changes induced by mixed reflux. CONCLUSIONS The presence of secretory phospholipase A(2) appears necessary for early histologic changes produced by exposure of the esophagus to gastroduodenal contents. This enzyme is identified as a promising target for evaluation of mechanisms of carcinogenesis and chemoprevention of esophageal carcinoma.
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Pillekamp F, Halbach M, Reppel M, Rubenchyk O, Pfannkuche K, Xi JY, Bloch W, Sreeram N, Brockmeier K, Hescheler J. Neonatal Murine Heart Slices. A Robust Model to Study Ventricular Isometric Contractions. Cell Physiol Biochem 2007; 20:837-46. [DOI: 10.1159/000110443] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/20/2007] [Indexed: 11/19/2022] Open
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Hiranandani N, Raman S, Kalyanasundaram A, Periasamy M, Janssen PML. Frequency-dependent contractile strength in mice over- and underexpressing the sarco(endo)plasmic reticulum calcium-ATPase. Am J Physiol Regul Integr Comp Physiol 2007; 293:R30-6. [PMID: 17255213 DOI: 10.1152/ajpregu.00508.2006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
One of the prominent markers of end-stage heart failure at the molecular level is a decrease in function and/or expression of the sarcoplasmic reticulum ATPase protein [sarco(endo)plasmic reticulum calcium-ATPase, SERCA]. It has been often postulated that a decrease in SERCA pump activity can contribute in a major way to decreased cardiac function. To establish a functional relationship, we assessed how alterations in SERCA activity level affect basic contractile function in healthy myocardium devoid of other significant molecular changes. We investigated baseline contractile function, frequency-dependent activation, and beta-adrenergic response in ultrathin trabeculae isolated from hearts of mice overexpressing SERCA (transgenic, TG), underexpressing SERCA2a (heterozygous knockout, Het), and their respective wild-type (WT) littermates. At physiological temperature and frequency, compared with their respective WT littermates, SERCA1a mice displayed increased developed force at frequencies of 4-8 Hz ( approximately 90% increase at 4 Hz) and force equal to WT mice at 10-14 Hz. Force development at 4 Hz in presence of 1 muM isoproterenol was similar in TG and WT mice. In Het mice, developed force was nearly identical at the lower end of the frequency range (4-8 Hz) but slightly depressed at higher frequency (P < 0.05 at 14 Hz). In presence of 1 muM isoproterenol, developed force at 4 Hz was equal to that in WT mice. Compared with normal levels, increased SERCA activity enhanced force development only at subphysiological frequencies. A reduction in SERCA activity only showed a depression of force at the higher frequency range. Thus generalizations regarding the correlation between SERCA activity and contractility can be highly ambiguous, because this relationship is critically dependent on other factors including stimulation frequency.
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Affiliation(s)
- Nitisha Hiranandani
- Department of Physiology and Cell Biology, Ohio State University, 1645 Neil Avenue, Columbus, OH 43210-1218, USA
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