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Bovo E, Nikolaienko R, Kahn D, Cho E, Robia SL, Zima AV. Presenilin 1 is a direct regulator of the cardiac sarco/endoplasmic reticulum calcium pump. Cell Calcium 2021; 99:102468. [PMID: 34517214 PMCID: PMC8541915 DOI: 10.1016/j.ceca.2021.102468] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Revised: 08/30/2021] [Accepted: 09/01/2021] [Indexed: 10/20/2022]
Abstract
The gamma secretase catalytic subunit presenilin 1 (PS1) is expressed in the endoplasmic reticulum (ER) of neurons, where it regulates Ca2+ signaling. PS1 is also expressed in heart, but its role in regulation of cardiac Ca2+ transport remains unknown. Since the type 2 sarco/endoplasmic reticulum Ca2+ ATPase (SERCA2a) plays a central role in cardiac Ca2+ homeostasis, we studied whether PS1 regulates the cardiac SERCA2a function. The experiments were conducted in an inducible human SERCA2a stable T-Rex-293 cell line transfected with fluorescently labeled PS1 and the ER Ca2+ sensor R-CEPIA1er. Confocal imaging showed that that PS1 is localized predominantly in the ER membrane. Fluorescent resonance energy transfer (FRET) experiments in HEK293 cells transfected with fluorescently labeled SERCA2a and PS1 revealed that the two proteins directly interact with a 1:1 stoichiometry. The functional significance of this interaction was investigated in a heterologous cellular environment using a novel approach to directly measure ER Ca2+ dynamics. Measurements of SERCA2a-mediated Ca2+ transport showed that PS1 enhanced Ca2+ uptake at low ER Ca2+ loads (<0.15 mM) and reduced uptake at high loads (>0.35 mM). The results of this study revealed that PS1 could act as an important regulator of the cardiac Ca2+ pump function with a complex stimulatory/inhibitory profile.
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Affiliation(s)
- Elisa Bovo
- Department of Cell and Molecular Physiology, Loyola University Chicago, IL, USA.
| | - Roman Nikolaienko
- Department of Cell and Molecular Physiology, Loyola University Chicago, IL, USA
| | - Daniel Kahn
- Department of Cell and Molecular Physiology, Loyola University Chicago, IL, USA
| | - Ellen Cho
- Department of Cell and Molecular Physiology, Loyola University Chicago, IL, USA
| | - Seth L Robia
- Department of Cell and Molecular Physiology, Loyola University Chicago, IL, USA
| | - Aleksey V Zima
- Department of Cell and Molecular Physiology, Loyola University Chicago, IL, USA
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2
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Ventricular arrhythmias in mouse models of diabetic kidney disease. Sci Rep 2021; 11:20570. [PMID: 34663875 PMCID: PMC8523538 DOI: 10.1038/s41598-021-99891-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Accepted: 09/27/2021] [Indexed: 12/05/2022] Open
Abstract
Chronic kidney disease (CKD) affects more than 20 million people in the US, and it is associated with a significantly increased risk of sudden cardiac death (SCD). Despite the significance, the mechanistic relationship between SCD and CKD is not clear and there are few effective therapies. Using optical mapping techniques, we tested the hypothesis that mouse models of progressive diabetic kidney disease (DKD) exhibit enhanced ventricular arrhythmia incidence and underlying arrhythmia substrates. Compared to wild-type mice, both Leprdb/db eNOS−/− (2KO) and high fat diet plus low dose streptozotocin (HFD + STZ) mouse models of DKD experienced sudden death and greater arrhythmia inducibility, which was more common with isoproterenol than programmed electrical stimulation. 2KO mice demonstrated slowed conduction velocity, prolonged action potential duration (APD), and myocardial fibrosis; both 2KO and HFD + STZ mice exhibited arrhythmias and calcium dysregulation with isoproterenol challenge. Finally, circulating concentrations of the uremic toxin asymmetric dimethylarginine (ADMA) were elevated in 2KO mice. Incubation of human cardiac myocytes with ADMA prolonged APD, as also observed in 2KO mice hearts ex vivo. The present study elucidates an arrhythmia-associated mechanism of sudden death associated with DKD, which may lead to more effective treatments in the vulnerable DKD patient population.
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Multisite phosphorylation of the cardiac ryanodine receptor: a random or coordinated event? Pflugers Arch 2020; 472:1793-1807. [PMID: 33078311 DOI: 10.1007/s00424-020-02473-3] [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: 07/09/2020] [Revised: 09/03/2020] [Accepted: 10/02/2020] [Indexed: 10/23/2022]
Abstract
Many proteins are phosphorylated at more than one phosphorylation site to achieve precise tuning of protein function and/or integrate a multitude of signals into the activity of one protein. Increasing the number of phosphorylation sites significantly broadens the complexity of molecular mechanisms involved in processing multiple phosphorylation sites by one or more distinct kinases. The cardiac ryanodine receptor (RYR2) is a well-established multiple phospho-target of kinases activated in response to β-adrenergic stimulation because this Ca2+ channel is a critical component of Ca2+ handling machinery which is responsible for β-adrenergic enhancement of cardiac contractility. Our review presents a selective overview of the extensive, often conflicting, literature which focuses on identifying reliable lines of evidence to establish if multiple RYR2 phosphorylation is achieved randomly or in a specific sequence, and whether phosphorylation at individual sites is functionally specific and additive or similar and can therefore be substituted.
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Marchena M, Echebarria B, Shiferaw Y, Alvarez-Lacalle E. Buffering and total calcium levels determine the presence of oscillatory regimes in cardiac cells. PLoS Comput Biol 2020; 16:e1007728. [PMID: 32970668 PMCID: PMC7537911 DOI: 10.1371/journal.pcbi.1007728] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Revised: 10/06/2020] [Accepted: 07/07/2020] [Indexed: 12/16/2022] Open
Abstract
Calcium oscillations and waves induce depolarization in cardiac cells which are believed to cause life-threathening arrhythimas. In this work, we study the conditions for the appearance of calcium oscillations in both a detailed subcellular model of calcium dynamics and a minimal model that takes into account just the minimal ingredients of the calcium toolkit. To avoid the effects of homeostatic changes and the interaction with the action potential we consider the somewhat artificial condition of a cell without pacing and with no calcium exchange with the extracellular medium. Both the full subcellular model and the minimal model present the same scenarios depending on the calcium load: two stationary states, one with closed ryanodine receptors (RyR) and most calcium in the cell stored in the sarcoplasmic reticulum (SR), and another, with open RyRs and a depleted SR. In between, calcium oscillations may appear. The robustness of these oscillations is determined by the amount of calsequestrin (CSQ). The lack of this buffer in the SR enhances the appearance of oscillations. The minimal model allows us to relate the stability of the oscillating state to the nullcline structure of the system, and find that its range of existence is bounded by a homoclinic and a Hopf bifurcation, resulting in a sudden transition to the oscillatory regime as the cell calcium load is increased. Adding a small amount of noise to the RyR behavior increases the parameter region where oscillations appear and provides a gradual transition from the resting state to the oscillatory regime, as observed in the subcellular model and experimentally. In cardiac cells, calcium plays a very important role. An increase in calcium levels is the trigger used by the cell to initiate contraction. Besides, calcium modulates several transmembrane currents, affecting the cell transmembrane potential. Thus, dysregulations in calcium handling have been associated with the appearance of arrhythmias. Often, this dysregulation results in the appearance of periodic calcium waves or global oscillations, providing a pro-arrhythmic substrate. In this paper, we study the onset of calcium oscillations in cardiac cells using both a detailed subcellular model of calcium dynamics and a minimal model that takes into account the essential ingredients of the calcium toolkit. Both reproduce the main experimental results and link this behavior with the presence of different steady-state solutions and bifurcations that depend on the total amount of calcium in the cell and in the level of buffering present. We expect that this work will help to clarify the conditions under which calcium oscillations appear in cardiac myocytes and, therefore, will represent a step further in the understanding of the origin of cardiac arrhythmias.
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Affiliation(s)
- Miquel Marchena
- Departament de Física, Universitat Politècnica de Catalunya-BarcelonaTech, Barcelona, Spain
| | - Blas Echebarria
- Departament de Física, Universitat Politècnica de Catalunya-BarcelonaTech, Barcelona, Spain
| | - Yohannes Shiferaw
- Physics Department, California State University, Northridge, California 91330, USA
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Dharmawan T, Nakajima T, Ohno S, Iizuka T, Tamura S, Kaneko Y, Horie M, Kurabayashi M. Identification of a novel exon3 deletion of RYR2 in a family with catecholaminergic polymorphic ventricular tachycardia. Ann Noninvasive Electrocardiol 2019; 24:e12623. [PMID: 30615235 PMCID: PMC6850420 DOI: 10.1111/anec.12623] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/14/2018] [Revised: 11/01/2018] [Accepted: 11/13/2018] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND RYR2, encoding cardiac ryanodine receptor, is the major responsible gene for catecholaminergic polymorphic ventricular tachycardia (CPVT). Meanwhile, KCNJ2, encoding inward-rectifier potassium channel (IK1 ), can be the responsible gene for atypical CPVT. We recently encountered a family with CPVT and sought to identify a responsible gene variant. METHODS A targeted panel sequencing (TPS) was employed in the proband. Copy number variation (CNV) in RYR2 was identified by focusing on read numbers in the TPS and long-range PCR. Cascade screening was conducted by a Sanger method and long-range PCR. KCNJ2 wild-type (WT) or an identified variant was expressed in COS-1 cells, and whole-cell currents (IK1 ) were recorded using patch-clamp techniques. RESULTS A 40-year-old female experienced cardiopulmonary arrest while cycling. Her ECG showed sinus bradycardia with prominent U-waves (≥0.2 mV). She had left ventricular hypertrabeculation at apex. Exercise induced frequent polymorphic ventricular arrhythmias. Her sister died suddenly at age 35 while bouldering. Her father and paternal aunt, with prominent U-waves, received permanent pacemaker due to sinus node dysfunction. The initial TPS and cascade screening identified a KCNJ2 E118D variant in all three symptomatic patients. However, after focusing on read numbers, we identified a novel exon3 deletion of RYR2 (RYR2-exon3 deletion) in all of them. Functional analysis revealed that KCNJ2 E118D generated IK1 indistinguishable from KCNJ2 WT, even in the presence of catecholaminergic stimulation. CONCLUSIONS Focusing on the read numbers in the TPS enabled us to identify a novel CNV, RYR2-exon3 deletion, which was associated with phenotypic features of this family.
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Affiliation(s)
- Tommy Dharmawan
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Tadashi Nakajima
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Seiko Ohno
- Department of Bioscience and Genetics, National Cerebral and Cardiovascular Center, Suita, Japan.,Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
| | - Takashi Iizuka
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Shuntaro Tamura
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Yoshiaki Kaneko
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Minoru Horie
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan.,Center for Epidemiologic Research in Asia, Shiga University of Medical Science, Otsu, Japan
| | - Masahiko Kurabayashi
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Japan
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Bovo E, Mazurek SR, de Tombe PP, Zima AV. Increased Energy Demand during Adrenergic Receptor Stimulation Contributes to Ca(2+) Wave Generation. Biophys J 2016; 109:1583-91. [PMID: 26488649 DOI: 10.1016/j.bpj.2015.09.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 08/21/2015] [Accepted: 09/01/2015] [Indexed: 02/07/2023] Open
Abstract
While β-adrenergic receptor (β-AR) stimulation ensures adequate cardiac output during stress, it can also trigger life-threatening cardiac arrhythmias. We have previously shown that proarrhythmic Ca(2+) waves during β-AR stimulation temporally coincide with augmentation of reactive oxygen species (ROS) production. In this study, we tested the hypothesis that increased energy demand during β-AR stimulation plays an important role in mitochondrial ROS production and Ca(2+)-wave generation in rabbit ventricular myocytes. We found that β-AR stimulation with isoproterenol (0.1 μM) decreased the mitochondrial redox potential and the ratio of reduced to oxidated glutathione. As a result, β-AR stimulation increased mitochondrial ROS production. These metabolic changes induced by isoproterenol were associated with increased sarcoplasmic reticulum (SR) Ca(2+) leak and frequent diastolic Ca(2+) waves. Inhibition of cell contraction with the myosin ATPase inhibitor blebbistatin attenuated oxidative stress as well as spontaneous SR Ca(2+) release events during β-AR stimulation. Furthermore, we found that oxidative stress induced by β-AR stimulation caused the formation of disulfide bonds between two ryanodine receptor (RyR) subunits, referred to as intersubunit cross-linking. Preventing RyR cross-linking with N-ethylmaleimide decreased the propensity of Ca(2+) waves induced by β-AR stimulation. These data suggest that increased energy demand during sustained β-AR stimulation weakens mitochondrial antioxidant defense, causing ROS release into the cytosol. By inducing RyR intersubunit cross-linking, ROS can increase SR Ca(2+) leak to the critical level that can trigger proarrhythmic Ca(2+) waves.
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Affiliation(s)
- Elisa Bovo
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine, Maywood, Illinois
| | - Stefan R Mazurek
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine, Maywood, Illinois
| | - Pieter P de Tombe
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine, Maywood, Illinois
| | - Aleksey V Zima
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine, Maywood, Illinois.
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7
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Lassaletta AD, Elmadhun NY, Zanetti AVD, Feng J, Anduaga J, Gohh RY, Sellke FW, Bianchi C. Rapamycin treatment of healthy pigs subjected to acute myocardial ischemia-reperfusion injury attenuates cardiac functions and increases myocardial necrosis. Ann Thorac Surg 2013; 97:901-7. [PMID: 24266948 DOI: 10.1016/j.athoracsur.2013.09.059] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2012] [Revised: 09/18/2013] [Accepted: 09/23/2013] [Indexed: 01/22/2023]
Abstract
BACKGROUND The mammalian target of rapamycin (mTOR) pathway is a major regulator of cell immunity and metabolism. mTOR is a well-known suppressor of tissue rejection in organ transplantation. However, it has other nonimmune functions: in the cardiovascular system, it is a regulator of heart hypertrophy and locally, in coated vascular stents, it inhibits vascular wall cell growth and hence neointimal formation/restenosis. Because the mTOR pathway plays major roles in normal cell growth, metabolism, and survival, we hypothesized that inhibiting it with rapamycin before an acute myocardial ischemia-reperfusion injury (IRI) would confer cardioprotection by virtue of slowing down cardiac function and metabolism. METHODS Yorkshire pigs received either placebo or 4 mg/d rapamycin orally for 7 days before the IRI. All animals underwent median sternotomy, and the mid-left anterior descending coronary artery was occluded for 60 minutes followed by 120 minutes of reperfusion. Left ventricular pressure-volume data were collected throughout the operation. The ischemic and infarcted areas were determined by monastral blue and triphenyltetrazolium chloride staining, respectively, and plasma cardiac troponin I concentration. mTOR kinase activities were monitored in remote cardiac tissue by Western blotting with specific antibodies against mTOR substrates phosphorylating sites. RESULTS Rapamycin before treatment impaired endothelial-dependent vasorelaxation, attenuated cardiac function during IRI, and increased myocardial necrosis. Western blotting confirmed effective inhibition of myocardial mTOR kinase activities. CONCLUSIONS Acute myocardial IRI, in healthy pigs treated with rapamycin, is associated with decreased cardiac function and higher myocardial necrosis.
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Affiliation(s)
- Antonio D Lassaletta
- Rhode Island Hospital Division of Cardiothoracic Surgery, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Nassrene Y Elmadhun
- Rhode Island Hospital Division of Cardiothoracic Surgery, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Arthus V D Zanetti
- Rhode Island Hospital Division of Cardiothoracic Surgery, Warren Alpert Medical School of Brown University, Providence, Rhode Island; Faculdade de Ciencias Medicas da Santa Casa de Sao Paulo, Sao Paulo, Brazil
| | - Jun Feng
- Rhode Island Hospital Division of Cardiothoracic Surgery, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Javier Anduaga
- Rhode Island Hospital Division of Cardiothoracic Surgery, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Reginald Y Gohh
- Organ Transplantation, and Cardiovascular Research Center, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Frank W Sellke
- Rhode Island Hospital Division of Cardiothoracic Surgery, Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Cesario Bianchi
- Rhode Island Hospital Division of Cardiothoracic Surgery, Warren Alpert Medical School of Brown University, Providence, Rhode Island.
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Di Diego JM, Sicouri S, Myles RC, Burton FL, Smith GL, Antzelevitch C. Optical and electrical recordings from isolated coronary-perfused ventricular wedge preparations. J Mol Cell Cardiol 2012; 54:53-64. [PMID: 23142540 DOI: 10.1016/j.yjmcc.2012.10.017] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2012] [Revised: 10/22/2012] [Accepted: 10/29/2012] [Indexed: 01/06/2023]
Abstract
The electrophysiological heterogeneity that exists across the ventricular wall in the mammalian heart has long been recognized, but remains an area that is incompletely understood. Experimental studies of the mechanisms of arrhythmogenesis in the whole heart often examine the epicardial surface in isolation and thereby disregard transmural electrophysiology. Significant heterogeneity exists in the electrophysiological properties of cardiomyocytes isolated from different layers of the ventricular wall, and given that regional heterogeneities of membrane repolarization properties can influence the electrophysiological substrate for re-entry, the diversity of cell types and characteristics spanning the ventricular wall is important in the study of arrhythmogenesis. For these reasons, coronary-perfused left ventricular wedge preparations have been developed to permit the study of transmural electrophysiology in the intact ventricle. Since the first report by Yan and Antzelevitch in 1996, electrical recordings from the transmural surface of canine wedge preparations have provided a wealth of data regarding the cellular basis for the electrocardiogram, the role of transmural heterogeneity in arrhythmogenesis, and differences in the response of the different ventricular layers to drugs and neurohormones. Use of the wedge preparation has since been expanded to other species and more recently it has also been widely used in optical mapping studies. The isolated perfused wedge preparation has become an important tool in cardiac electrophysiology. In this review, we detail the methodology involved in recording both electrical and optical signals from the coronary-perfused wedge preparation and review the advances in cardiac electrophysiology achieved through study of the wedge.
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Affiliation(s)
- José M Di Diego
- Masonic Medical Research Laboratory, 2150 Bleecker St., Utica, NY 13501, USA
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9
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Bovo E, Lipsius SL, Zima AV. Reactive oxygen species contribute to the development of arrhythmogenic Ca²⁺ waves during β-adrenergic receptor stimulation in rabbit cardiomyocytes. J Physiol 2012; 590:3291-304. [PMID: 22586224 DOI: 10.1113/jphysiol.2012.230748] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
While β-adrenergic receptor (β-AR) stimulation leads to positive inotropic effects, it can also induce arrhythmogenic Ca2+ waves. β-AR stimulation increases mitochondrial oxygen consumption and, thereby, the production of reactive oxygen species (ROS). We therefore investigated the role of ROS in the generation of Ca2+ waves during β-AR stimulation in rabbit ventricular myocytes. Isoproterenol (ISO) increased Ca2+ transient amplitude during systole, sarcoplasmic reticulum (SR) Ca2+ load and the occurrence of Ca2+ waves during diastole. These effects, however, developed at different time points during ISO application.While SR Ca2+ release and load reached a maximum level after 3 min, Ca2+ waves occurred at the highest frequency only after 6 min of ISO application.Measurement of intra-SR-free Ca2+ concentration ([Ca2+]SR) showed an initial increase of SR Ca2+ load followed by a gradual decline over time during ISO application. This decline of [Ca2+]SR was not due to decreased SR Ca2+ uptake, but instead was the result of increased SRCa2+ leak mainly in the form of Ca2+ waves. ISO application led to significant RyR phosphorylation at the protein kinase A (PKA)-specific site, which remained relatively stable throughout β-AR activation.Moreover, β-AR stimulation significantly increased ROS production after 4–6 min of ISO application. The ROS scavenger Tiron and the superoxide dismutase mimetic MnTBPA abolished the ISO-mediated ROS production. The mitochondria-specific antioxidant Mito-Tempo and an inhibitor of the electron transport chain, rotenone, also effectively prevented the ISO-mediated ROS production. Scavenging ROS during ISO application decreased the occurrence of Ca2+ waves and partially prevented augmentation of SRCa2+ leak, but did not affect the increase of Ca2+ transient amplitude. Treatment of myocytes with ISO for 15 min significantly reduced the free thiol content in RyRs. These data suggest that increased mitochondrial ROS production during β-AR stimulation causes RyR oxidation. Together with RyR phosphorylation, oxidation of RyRs increases diastolic SR Ca2+ leak to a critical level leading to the generation of arrhythmogenic Ca2+ waves.
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Affiliation(s)
- Elisa Bovo
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Avenue, Maywood, IL 60153, USA
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Steriotis AK, Nava A, Rampazzo A, Basso C, Thiene G, Daliento L, Folino AF, Rigato I, Mazzotti E, Beffagna G, Carturan E, Corrado D, Bauce B. Follow-up with exercise test of effort-induced ventricular arrhythmias linked to ryanodine receptor type 2 gene mutations. Am J Cardiol 2012; 109:1015-9. [PMID: 22221940 PMCID: PMC3318118 DOI: 10.1016/j.amjcard.2011.11.033] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Revised: 11/23/2011] [Accepted: 11/23/2011] [Indexed: 02/04/2023]
Abstract
The aim of this study was to assess exercise test results and efficacy of therapy with a β blocker (acebutolol) in ryanodine receptor type 2 (RyR2) mutation carriers with documented ventricular arrhythmias (VAs) and long-term follow-up. Twenty RyR2 mutation carriers belonging to 8 families and regularly followed at our center were analyzed using a study protocol involving electrocardiography, exercise tests off and on β-blocker therapy, 2-dimensional echocardiography, and signal-averaged electrocardiography. Off-therapy exercise testing triggered the onset of VAs at different heart rates (mean 132 ± 13 beats/min) with various patterns that worsened while exercising and disappeared immediately after stopping. The most severe VAs detected were nonsustained ventricular tachycardia in 35% and ventricular couplets in 35%. In the remaining subjects single ventricular premature beats were recorded. In 15% of patients single monomorphic ventricular premature beats were detected and identified to be linked to RyR2 mutations owing to the presence of sudden deaths of their family members and subsequent family screening. Acebutolol made the VAs disappear completely in 20% of subjects and decreased their complexity in 50%, whereas it did not change VAs appreciably in 30% of patients with less complex VAs. After 11 ± 8 years of follow-up 2 patients developed syncope. In conclusion, exercise testing was a fundamental tool for assessing the clinical phenotype and efficacy of therapy in RyR2 mutation carriers and therapy with acebutolol led in most subjects to a decreased complexity of the arrhythmic pattern or to complete suppression.
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11
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Ke J, Xiao X, Chen F, He L, Dai MS, Wang XP, Chen B, Chen M, Zhang CT. Function of the CaMKII-ryanodine receptor signaling pathway in rabbits with left ventricular hypertrophy and triggered ventricular arrhythmia. World J Emerg Med 2012; 3:65-70. [PMID: 25215041 DOI: 10.5847/wjem.j.issn.1920-8642.2012.01.012] [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: 08/27/2011] [Accepted: 12/19/2011] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Calcium calmodulin-dependent kinase II (CaMKII) can be more active in patients with left ventricular hypertrophy (LVH), which in turn causes phosphorylation of ryanodine receptors, resulting in inactivation and the instability of intracellular calcium homeostasis. The present study aimed to determine the effect of CaMKII-ryanodine receptor pathway signaling in rabbits with left ventricular hypertrophy and triggered ventricular arrhythmia. METHODS Forty New Zealand rabbits were randomized into four groups (10 per group): sham group, LVH group, KN-93 group (LVH+KN-93), and ryanodine group (LVH+ryanodine). Rabbits in the LVH, KN-93, and ryanodine groups were used to establish a left ventricular hypertrophy model by the coarctation of the abdominal aorta, while those in the sham group did not undergo the coarctation. After eight weeks, action potentials (APs) were recorded simultaneously in the endocardium and epicardium, and a transmural electrocardiogram (ECG) was also recorded in the rabbit left ventricular wedge model. Drugs were administered to the animals in the KN-93 and ryanodine groups, and the frequency of triggered APs and ventricular tachycardia was recorded after the rabbits were given isoprenaline (1 μmol/L) and high-frequency stimulation. RESULTS The frequency (animals/group) of triggered APs was 0/10 in the sham group, 10/10 in the LVH group, 4/10 in the KN-93 group, and 1/10 in the ryanodine group. The frequencies of ventricular tachycardia were 0/10, 9/10, 3/10, and 1/10, respectively. The frequencies of polymorphic ventricular tachycardia or ventricular fibrillation were 0/10, 7/10, 2/10, and 1/10, respectively. The frequencies of triggered ventricular arrhythmias in the KN-93 and ryanodine groups were much lower than those in the LVH group (P<0.05). CONCLUSIONS KN-93 and ryanodine can effectively reduce the occurrence of triggered ventricular arrhythmia in rabbits with LVH. The CaMKII-ryanodine signaling pathway can be used as a new means of treating ventricular arrhythmia.
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Affiliation(s)
- Jun Ke
- Department of Emergency Internal Medicine, Fujian Provincial Hospital, Provincial Clinical Medical College of Fujian Medical University, Fuzhou 350001, China
| | - Xing Xiao
- Integrated Department, Tongji Hospital Affiliated to Tongji Medical College of Huazhong Science Technology University, Wuhan 430030, China
| | - Feng Chen
- Department of Emergency Internal Medicine, Fujian Provincial Hospital, Provincial Clinical Medical College of Fujian Medical University, Fuzhou 350001, China
| | - Li He
- Department of Cardiology, Tongji Hospital Affiliated to Tongji Medical College of Huazhong Science Technology University, Wuhan 430030, China
| | - Mu-Sen Dai
- Department of Emergency Internal Medicine, Fujian Provincial Hospital, Provincial Clinical Medical College of Fujian Medical University, Fuzhou 350001, China
| | - Xiao-Ping Wang
- Department of Emergency Internal Medicine, Fujian Provincial Hospital, Provincial Clinical Medical College of Fujian Medical University, Fuzhou 350001, China
| | - Bing Chen
- Department of Emergency Internal Medicine, Fujian Provincial Hospital, Provincial Clinical Medical College of Fujian Medical University, Fuzhou 350001, China
| | - Min Chen
- Department of Emergency Internal Medicine, Fujian Provincial Hospital, Provincial Clinical Medical College of Fujian Medical University, Fuzhou 350001, China
| | - Cun-Tai Zhang
- Integrated Department, Tongji Hospital Affiliated to Tongji Medical College of Huazhong Science Technology University, Wuhan 430030, China
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Plummer BN, Cutler MJ, Wan X, Laurita KR. Spontaneous calcium oscillations during diastole in the whole heart: the influence of ryanodine reception function and gap junction coupling. Am J Physiol Heart Circ Physiol 2011; 300:H1822-8. [PMID: 21378143 DOI: 10.1152/ajpheart.00766.2010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Triggered arrhythmias due to spontaneous cytoplasmic calcium oscillations occur in a variety of disease conditions; however, their cellular mechanisms in tissue are not clear. We hypothesize that spontaneous calcium oscillations in the whole heart are due to calcium release from the sarcoplasmic reticulum and are facilitated by calcium diffusion through gap junctions. Optical mapping of cytoplasmic calcium from Langendorff perfused guinea pig hearts (n = 10) was performed using oxygenated Tyrode's solution (in mM): 140 NaCl, 0.7 MgCl, 4.5 KCl, 5.5 dextrose, 5 HEPES, and 5.5 CaCl₂ (pH 7.45, 34°C). Rapid pacing was used to induce diastolic calcium oscillations. In all preparations, pacing-induced multicellular diastolic calcium oscillations (m-SCR) occurred across most of the mapping field, at all pacing rates tested. Ryanodine (1 μM) eliminated all m-SCR activity. Low-dose caffeine (1 mM) increased m-SCR amplitude (+10.4 ± 4.4%, P < 0.05) and decreased m-SCR time-to-peak (-17.4 ± 6.7%, P < 0.05) and its temporal synchronization (i.e., range) across the mapping field (-26.9 ± 17.1%, P < 0.05). Surprisingly, carbenoxolone increased the amplitude of m-SCR activity (+14.8 ± 4.1%, P < 0.05) and decreased m-SCR time-to-peak (-11.3 ± 9.6%, P < 0.01) and its synchronization (-37.0 ± 19.1%, P < 0.05), similar to caffeine. In isolated myocytes, carbenoxolone (50 μM) had no effect on the frequency of aftercontractions, suggesting the effect of cell-to-cell uncoupling on m-SCR activity is tissue specific. Therefore, in the whole heart, overt m-SCR activity caused by calcium release from the SR can be induced over a broad range of pacing rates. Enhanced ryanodine receptor open probability and, surprisingly, decreased cell-to-cell coupling increased the amplitude and temporal synchronization of spontaneous calcium release in tissue.
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Affiliation(s)
- Bradley N Plummer
- Heart and Vascular Research Center, Department of Medicine, MetroHealth Campus, Case Western Reserve Univ, Cleveland, OH 44109-1997, USA
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Posnack NG, Lee NH, Brown R, Sarvazyan N. Gene expression profiling of DEHP-treated cardiomyocytes reveals potential causes of phthalate arrhythmogenicity. Toxicology 2010; 279:54-64. [PMID: 20920545 DOI: 10.1016/j.tox.2010.09.007] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Revised: 09/14/2010] [Accepted: 09/15/2010] [Indexed: 01/12/2023]
Abstract
BACKGROUND Di-(2-ethylhexyl)-phthalate (DEHP) is a widely used plasticizer that imparts flexibility to polyvinyl chloride. We have recently reported that clinically relevant concentrations of DEHP can affect electrical coupling between cardiac myocytes causing significant rhythm disturbances. The underlying causes for this effect are currently unknown. OBJECTIVES To use data on global mRNA expression as a tool to reveal possible pathways leading to arrhythmogenic effects of DEHP. METHODS Rat neonatal cardiomyocytes were treated with 50 μg/mL DEHP for 72 h. Extracted RNA samples were hybridized onto Affymetrix Rat Gene 1.0 ST arrays. The mRNA expression of a subset of genes was validated by qRT-PCR. In a second set of experiments, cells were treated in a concentration dependent manner to identify genes affected by low DEHP concentrations. RESULTS DEHP exposure is associated with global changes in mRNA expression, with differentially expressed genes overrepresented in 47 Gene Ontology categories. Modified expression was detected for genes associated with cell electrical activity, calcium handling, adhesion and microtubular transport. For a number of key proteins, including kinesin, TGFβ2, α-tubulin, and α1 & β1 integrins, changes in mRNA levels were confirmed on the level of the protein expression. A number of genes associated with cell adhesion and electrical activity were identified as early DEHP targets as they were affected by concentrations as low as 1 μg/mL. CONCLUSIONS Exposure of neonatal rat cardiomyocytes to clinically relevant DEHP concentrations leads to global changes in mRNA expression. These changes help to explain the arrhythmogenic effects of phthalates on these cells.
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Affiliation(s)
- Nikki Gillum Posnack
- The Pharmacology & Physiology Department, The George Washington University, 2300 Eye Street, Washington, DC 20037, USA
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14
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Bondarenko VE, Rasmusson RL. Transmural heterogeneity of repolarization and Ca2+ handling in a model of mouse ventricular tissue. Am J Physiol Heart Circ Physiol 2010; 299:H454-69. [PMID: 20525874 DOI: 10.1152/ajpheart.00907.2009] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mouse hearts have a diversity of action potentials (APs) generated by the cardiac myocytes from different regions. Recent evidence shows that cells from the epicardial and endocardial regions of the mouse ventricle have a diversity in Ca(2+) handling properties as well as K(+) current expression. To examine the mechanisms of AP generation, propagation, and stability in transmurally heterogeneous tissue, we developed a comprehensive model of the mouse cardiac cells from the epicardial and endocardial regions of the heart. Our computer model simulates the following differences between epicardial and endocardial myocytes: 1) AP duration is longer in endocardial and shorter in epicardial myocytes, 2) diastolic and systolic intracellular Ca(2+) concentration and intracellular Ca(2+) concentration transients are higher in paced endocardial and lower in epicardial myocytes, 3) Ca(2+) release rate is about two times larger in endocardial than in epicardial myocytes, and 4) Na(+)/Ca(2+) exchanger rate is greater in epicardial than in endocardial myocytes. Isolated epicardial cells showed a higher threshold for stability of AP generation but more complex patterns of AP duration at fast pacing rates. AP propagation velocities in the model of two-dimensional tissue are close to those measured experimentally. Simulations show that heterogeneity of repolarization and Ca(2+) handling are sustained across the mouse ventricular wall. Stability analysis of AP propagation in the two-dimensional model showed the generation of Ca(2+) alternans and more complex transmurally heterogeneous irregular structures of repolarization and intracellular Ca(2+) transients at fast pacing rates.
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Affiliation(s)
- Vladimir E Bondarenko
- Department of Mathematics and Statistics, Georgia State University, Atlanta, GA, USA
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15
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Hoeker GS, Katra RP, Wilson LD, Plummer BN, Laurita KR. Spontaneous calcium release in tissue from the failing canine heart. Am J Physiol Heart Circ Physiol 2009; 297:H1235-42. [PMID: 19648256 DOI: 10.1152/ajpheart.01320.2008] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Abnormalities in calcium handling have been implicated as a significant source of electrical instability in heart failure (HF). While these abnormalities have been investigated extensively in isolated myocytes, how they manifest at the tissue level and trigger arrhythmias is not clear. We hypothesize that in HF, triggered activity (TA) is due to spontaneous calcium release from the sarcoplasmic reticulum that occurs in an aggregate of myocardial cells (an SRC) and that peak SCR amplitude is what determines whether TA will occur. Calcium and voltage optical mapping was performed in ventricular wedge preparations from canines with and without tachycardia-induced HF. In HF, steady-state calcium transients have reduced amplitude [135 vs. 170 ratiometric units (RU), P < 0.05] and increased duration (252 vs. 229 s, P < 0.05) compared with those of normal. Under control conditions and during beta-adrenergic stimulation, TA was more frequent in HF (53% and 93%, respectively) compared with normal (0% and 55%, respectively, P < 0.025). The mechanism of arrhythmias was SCRs, leading to delayed afterdepolarization-mediated triggered beats. Interestingly, the rate of SCR rise was greater for events that triggered a beat (0.41 RU/ms) compared with those that did not (0.18 RU/ms, P < 0.001). In contrast, there was no difference in SCR amplitude between the two groups. In conclusion, TA in HF tissue is associated with abnormal calcium regulation and mediated by the spontaneous release of calcium from the sarcoplasmic reticulum in aggregates of myocardial cells (i.e., an SCR), but importantly, it is the rate of SCR rise rather than amplitude that was associated with TA.
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Affiliation(s)
- Gregory S Hoeker
- Department of Biomedical Engineering, CaseWestern Reserve University, The Heart and Vascular Research Center, Cleveland, Ohio 44109-1998, USA
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16
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Wilson LD, Jeyaraj D, Wan X, Hoeker GS, Said TH, Gittinger M, Laurita KR, Rosenbaum DS. Heart failure enhances susceptibility to arrhythmogenic cardiac alternans. Heart Rhythm 2008; 6:251-9. [PMID: 19187920 DOI: 10.1016/j.hrthm.2008.11.008] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/08/2008] [Accepted: 11/05/2008] [Indexed: 10/21/2022]
Abstract
BACKGROUND Although heart failure (HF) is closely associated with susceptibility to sudden cardiac death (SCD), the mechanisms linking contractile dysfunction to cardiac electrical instability are poorly understood. Cardiac alternans has also been closely associated with SCD, and has been linked to a mechanism for amplifying electrical heterogeneities in the heart. However, previous studies have focused on alternans in normal rather than failing myocardium. OBJECTIVE This study sought to investigate the hypothesis that HF enhances susceptibility to arrhythmogenic cardiac alternans. METHODS High-resolution transmural optical mapping was performed in canine wedge preparations from normal (n = 8) and HF (n = 8) hearts produced by rapid ventricular pacing. RESULTS HF significantly (P < .004) lowered the heart rate (HR) threshold for action potential duration alternans (APD-ALT) from 236 +/- 25 beats/min to 185 +/- 25 beats/min. In dual optical mapping of action potentials and intracellular Ca experiments (n = 16), HF lowered the HR threshold for Ca-ALT (beat-to-beat alternations of cellular Ca cycling) from 238 +/- 35 to 177 +/- 26 beats/min (P < .005). Importantly: (1) Ca-ALT always either developed at slower HR or simultaneously with APD-ALT in the same cells, and (2) the magnitude of Ca-ALT and APD-ALT were closely correlated (P < .05). HF similarly lowered the HR threshold for Ca-ALT in isolated myocytes under nonalternating action potential clamp, indicating that HF enhances susceptibility to cellular alternans independent of HF-associated changes in repolarization. Importantly, HF significantly (P < .02) lowered the HR threshold for spatially discordant arrhythmogenic alternans (different regions of cells alternating in opposite phase, DIS-ALT). Ventricular fibrillation (VF) was induced in 88% of HF preparations, but only 12% of normal preparations (P < .003) and was uniformly preceded by development of DIS-ALT. CONCLUSION Heart failure increases the susceptibility to arrhythmogenic cardiac alternans, which arises from HF-induced impairment in calcium cycling.
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Affiliation(s)
- Lance D Wilson
- Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio 44109-1998, USA
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17
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18
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He H, Shi M, Zeng X, Yang X, Yang J, Wu L, Li L. Decreased FKBP12.6 expression and enhanced endothelin receptor signaling associated with arrhymogenesis in myocardial infarction rats. Phytother Res 2008; 22:1115-24. [PMID: 18570278 DOI: 10.1002/ptr.2470] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
An increased propensity towards cardiac arrhythmias and aggravated heart function is observed in myocardial infarction (MI), the development of which is associated with the calcium handling system in the myocardium. It was hypothesized that the abnormal changes in the MI model may be a consequence of the abnormal expression and function of the RyR2-FKBP12.6 channel complex and that these abnormalities may be related to an over-activated endothelin (ET) system. Salvianolic acid B is expected to suppress life-threatening arrhythmias and to restore the abnormality of the RyR2-FKBP12.6 complex in rats. MI was produced by ligating the coronary artery for 4 weeks. Salvianolic acid B (100 mg/kg/day, p.o. for 4 weeks) was administered to rats 0.5 h before surgery. Measurements of cardiac arrhythmias, cardiac function, calcium transient, cardiac calcium release channel handling proteins and the endothelin system were conducted. The aggravated arrhythmia and compromised cardiac function in MI rats was accompanied by elevated diastolic Ca(2+) levels in the cytosol and a significant down-regulation of expression of RyR2-FKBP12.6. These were closely linked with an over-activated ET pathway in the myocardium. After a 4-week treatment with salvianolic acid B, all abnormalities were reversed significantly. Salvianolic acid B was capable of normalizing FKBP12.6 expression levels and decreasing the propensity towards arrhythmias by attenuating the up-regulated ET pathway.
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Affiliation(s)
- Haibo He
- Institute of Chinese Herb Medicine, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, Zhejiang, 310058, PRC
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Said M, Becerra R, Palomeque J, Rinaldi G, Kaetzel MA, Diaz-Sylvester PL, Copello JA, Dedman JR, Mundiña-Weilenmann C, Vittone L, Mattiazzi A. Increased intracellular Ca2+ and SR Ca2+ load contribute to arrhythmias after acidosis in rat heart. Role of Ca2+/calmodulin-dependent protein kinase II. Am J Physiol Heart Circ Physiol 2008; 295:H1669-83. [PMID: 18723772 DOI: 10.1152/ajpheart.00010.2008] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Returning to normal pH after acidosis, similar to reperfusion after ischemia, is prone to arrhythmias. The type and mechanisms of these arrhythmias have never been explored and were the aim of the present work. Langendorff-perfused rat/mice hearts and rat-isolated myocytes were subjected to respiratory acidosis and then returned to normal pH. Monophasic action potentials and left ventricular developed pressure were recorded. The removal of acidosis provoked ectopic beats that were blunted by 1 muM of the CaMKII inhibitor KN-93, 1 muM thapsigargin, to inhibit sarcoplasmic reticulum (SR) Ca(2+) uptake, and 30 nM ryanodine or 45 muM dantrolene, to inhibit SR Ca(2+) release and were not observed in a transgenic mouse model with inhibition of CaMKII targeted to the SR. Acidosis increased the phosphorylation of Thr(17) site of phospholamban (PT-PLN) and SR Ca(2+) load. Both effects were precluded by KN-93. The return to normal pH was associated with an increase in SR Ca(2+) leak, when compared with that of control or with acidosis at the same SR Ca(2+) content. Ca(2+) leak occurred without changes in the phosphorylation of ryanodine receptors type 2 (RyR2) and was blunted by KN-93. Experiments in planar lipid bilayers confirmed the reversible inhibitory effect of acidosis on RyR2. Ectopic activity was triggered by membrane depolarizations (delayed afterdepolarizations), primarily occurring in epicardium and were prevented by KN-93. The results reveal that arrhythmias after acidosis are dependent on CaMKII activation and are associated with an increase in SR Ca(2+) load, which appears to be mainly due to the increase in PT-PLN.
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Affiliation(s)
- M Said
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina.
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Peltonen LM, Mänttäri S. Is there life in the horny layer? Dihydropyridine and ryanodine receptors in the skin of female and male chickens (Gallus domesticus). J Exp Biol 2008; 211:1394-401. [PMID: 18424673 DOI: 10.1242/jeb.014282] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Previous findings in pigeons and chickens show that Ca(2+) may be accumulated inside the cornified skin cells and that Ca(2+) microenvironments with a lower- or higher-than-blood concentration may exist in the skin. It has been suggested that the skin may function as a secretory pathway or a reservoir for Ca(2+) recycling. To test this hypothesis, we studied the dermis and epidermis of female and male chickens in vivo to find out whether cellular mechanisms exist for the accumulation, recycling or secretion of Ca(2+). For calcium influx and intracellular Ca(2+) release, respectively, the density of dihydropyridine receptors (DHPRs) and ryanodine receptors (RyRs) was examined, using high-affinity (-)-enantiomers of dihydropyridine and ryanodine labelled with fluorophores. To investigate Ca(2+) utilization in the skin, the systemic and local activity of the enzyme alkaline phosphatase (ALP) and the concentration of ionic Ca(2+) were measured in plasma and in cutaneous extracellular fluid, collected by suction blister technique. We found that both DHPRs and RyRs were present in all skin layers from dermis to horny layer. However, receptor densities were highest in the surface layers. With a basic calcium-rich diet, receptor densities were higher in males, particularly in the dermis and mid-epidermis. After a reduction in the nutritional Ca(2+) input, receptor densities in males decreased to the same level as in females, in which the receptor densities were not affected by the amount of Ca(2+) in the diet or that resulting from coming out of lay. The extracellular concentration of ionic Ca(2+) per se was not found to affect the density of DHPRs and RyRs in the skin. Spatially, RyRs seem to be located in the periphery of the sebokeratinocyte. ALP activity was shown to be lower in the extracellular fluid than in the plasma in both sexes. However, activity in both extracellular domains increased significantly in females that had come out of lay. This was probably connected with the increased osteoblast activity related to the reformation of structural bone. In conclusion, voltage-sensitive L-type Ca(2+) channels for ion influx and RyRs for Ca(2+) release are present in the cells of the skin of female and male chickens. Higher densities in the males receiving excessive Ca(2+) imply an increased capacity for Ca(2+) influx and intracellular processing. Even though the functional interactions between DHPRs and RyRs in the sebokeratinocytes could not be demonstrated, peripheral colocation and high receptor densities at the level of exocytosis of the lamellar bodies point to their role as part of a signalling pathway for secretion. The finding that DHPRs and RyRs are present in the horny layer implies that the function of the outermost skin might be more active than had been previously thought and that this function might be both secretory and sensory.
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Affiliation(s)
- Liisa M Peltonen
- Department of Biomedicine/Physiology, Biomedicum Helsinki, PO Box 63, 00014 University of Helsinki, Finland
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Laurita KR, Rosenbaum DS. Cellular mechanisms of arrhythmogenic cardiac alternans. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 97:332-47. [PMID: 18395246 DOI: 10.1016/j.pbiomolbio.2008.02.014] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Despite the strong association between mechanical dysfunction of the heart and sudden death due to arrhythmias, the causal relationship is not well understood. Cardiac alternans has been linked to arrhythmogenesis and can be mediated by intracellular calcium handling. Given the integral role intracellular calcium plays in contractile function, calcium-mediated alternans may represent an important mechanistic link between mechanical dysfunction and electrical instability. This relationship, however, is not well understood due to complex feedback between membrane currents, intracellular calcium, and contraction. This manuscript describes the cellular mechanisms of cardiac alternans. Through several pathways, calcium transient alternans is coupled to repolarization alternans that can form a substrate for reentrant excitation. Abnormal intracellular calcium cycling, either impaired release or impaired reuptake of sarcoplasmic reticulum calcium, is a cellular mechanism of calcium transient alternans. Thus, cardiac alternans is an important mechanistic link between mechanical dysfunction and sudden cardiac death.
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Affiliation(s)
- Kenneth R Laurita
- The Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, Cleveland, OH, USA.
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Laurita KR, Rosenbaum DS. Mechanisms and potential therapeutic targets for ventricular arrhythmias associated with impaired cardiac calcium cycling. J Mol Cell Cardiol 2007; 44:31-43. [PMID: 18061204 DOI: 10.1016/j.yjmcc.2007.10.012] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2007] [Revised: 10/11/2007] [Accepted: 10/16/2007] [Indexed: 11/30/2022]
Abstract
The close relationship between life-threatening ventricular arrhythmias and contractile dysfunction in the heart implicates intracellular calcium cycling as an important underlying mechanism of arrhythmogenesis. Despite this close association, however, the mechanisms of arrhythmogenesis attributable to impaired calcium cycling are not fully appreciated or understood. In this report we review some of the current thinking regarding arrhythmia mechanisms associated with either abnormal impulse initiation (i.e. arrhythmia triggers) or impulse propagation (i.e. arrhythmia substrates). In all cases, the mechanisms are primarily related to dysfunction of calcium regulatory proteins associated with the sarcomere. These findings highlight the broad scope of arrhythmias associated with abnormal calcium cycling, and provide a basis for a causal relationship between cardiac electrical instability and contractile dysfunction. Moreover, calcium cycling proteins may provide much needed targets for novel antiarrhythmic therapies.
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Affiliation(s)
- Kenneth R Laurita
- The Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio 44109-1998, USA
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