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Rhana P, Matsumoto C, Fong Z, Costa AD, Del Villar SG, Dixon RE, Santana LF. Fueling the heartbeat: Dynamic regulation of intracellular ATP during excitation-contraction coupling in ventricular myocytes. Proc Natl Acad Sci U S A 2024; 121:e2318535121. [PMID: 38865270 PMCID: PMC11194497 DOI: 10.1073/pnas.2318535121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Accepted: 05/14/2024] [Indexed: 06/14/2024] Open
Abstract
The heart beats approximately 100,000 times per day in humans, imposing substantial energetic demands on cardiac muscle. Adenosine triphosphate (ATP) is an essential energy source for normal function of cardiac muscle during each beat, as it powers ion transport, intracellular Ca2+ handling, and actin-myosin cross-bridge cycling. Despite this, the impact of excitation-contraction coupling on the intracellular ATP concentration ([ATP]i) in myocytes is poorly understood. Here, we conducted real-time measurements of [ATP]i in ventricular myocytes using a genetically encoded ATP fluorescent reporter. Our data reveal rapid beat-to-beat variations in [ATP]i. Notably, diastolic [ATP]i was <1 mM, which is eightfold to 10-fold lower than previously estimated. Accordingly, ATP-sensitive K+ (KATP) channels were active at physiological [ATP]i. Cells exhibited two distinct types of ATP fluctuations during an action potential: net increases (Mode 1) or decreases (Mode 2) in [ATP]i. Mode 1 [ATP]i increases necessitated Ca2+ entry and release from the sarcoplasmic reticulum (SR) and were associated with increases in mitochondrial Ca2+. By contrast, decreases in mitochondrial Ca2+ accompanied Mode 2 [ATP]i decreases. Down-regulation of the protein mitofusin 2 reduced the magnitude of [ATP]i fluctuations, indicating that SR-mitochondrial coupling plays a crucial role in the dynamic control of ATP levels. Activation of β-adrenergic receptors decreased [ATP]i, underscoring the energetic impact of this signaling pathway. Finally, our work suggests that cross-bridge cycling is the largest consumer of ATP in a ventricular myocyte during an action potential. These findings provide insights into the energetic demands of EC coupling and highlight the dynamic nature of ATP concentrations in cardiac muscle.
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Affiliation(s)
- Paula Rhana
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA95616
| | - Collin Matsumoto
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA95616
| | - Zhihui Fong
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA95616
| | - Alexandre D. Costa
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA95616
| | - Silvia G. Del Villar
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA95616
| | - Rose E. Dixon
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA95616
| | - L. Fernando Santana
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA95616
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2
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Mazgaoker S, Yaniv Y. Computational insight into energy control balance by Ca 2+ and cAMP-PKA signaling in pacemaker cells. J Mol Cell Cardiol 2023; 185:77-87. [PMID: 37866739 DOI: 10.1016/j.yjmcc.2023.10.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Revised: 09/19/2023] [Accepted: 10/10/2023] [Indexed: 10/24/2023]
Abstract
Cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling controls sinoatrial node cell (SANC) function by affecting the degree of coupling between Ca2+ and membrane clocks. PKA is known to phosphorylate ionic channels, Ca2+ pump and release from the sarcoplasmic reticulum, and enzymes controlling ATP production in the mitochondria. While the PKA cytosolic targets in SANC have been extensively explored, its mitochondrial targets and its ability to maintain SANC energetic balance remain to be elucidated. To investigate the role of PKA in SANC energetics, we tested three hypotheses: (i) PKA is an important regulator of the ATP supply-to-demand balance, (ii) Ca2+ regulation of energetics is important for maintenance of NADH level and (iii) abrupt reduction in ATP demand first reduces the AP firing rate and, after dropping below a certain threshold, leads to a reduction in ATP. To gain mechanistic insights into the ATP supply-to-demand matching regulators, a modified model of mitochondrial energy metabolism was integrated into our coupled-clock model that describes ATP demand. Experimentally, increased ATP demand was accompanied by maintained ATP and NADH levels. Ca2+ regulation of energetics was found by the model to be important in the maintenance of NADH and PKA regulation was found to be important in the maintenance of intracellular ATP and the increase in oxygen consumption. PKA inhibition led to a biphasic reduction in AP firing rate, with the first phase being rapid and ATP-independent, while the second phase was slow and ATP-dependent. Thus, SANC energy balance is maintained by both Ca2+ and PKA signaling.
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Affiliation(s)
- Savyon Mazgaoker
- Laboratory of Bioelectric and Bioenergetic Systems, Faculty of Biomedical Engineering, Technion-IIT, Haifa, Israel
| | - Yael Yaniv
- Laboratory of Bioelectric and Bioenergetic Systems, Faculty of Biomedical Engineering, Technion-IIT, Haifa, Israel.
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3
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Keidar N, Peretz NK, Yaniv Y. Ca 2+ pushes and pulls energetics to maintain ATP balance in atrial cells: computational insights. Front Physiol 2023; 14:1231259. [PMID: 37528893 PMCID: PMC10387757 DOI: 10.3389/fphys.2023.1231259] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Accepted: 07/03/2023] [Indexed: 08/03/2023] Open
Abstract
To maintain atrial function, ATP supply-to-demand matching must be tightly controlled. Ca2+ can modulate both energy consumption and production. In light of evidence suggesting that Ca2+ affects energetics through "push" (activating metabolite flux and enzymes in the Krebs cycle to push the redox flux) and "pull" (acting directly on ATP synthase and driving the redox flux through the electron transport chain and increasing ATP production) pathways, we investigated whether both pathways are necessary to maintain atrial ATP supply-to-demand matching. Rabbit right atrial cells were electrically stimulated at different rates, and oxygen consumption and flavoprotein fluorescence were measured. To gain mechanistic insight into the regulators of ATP supply-to-demand matching in atrial cells, models of atrial electrophysiology, Ca2+ cycling and force were integrated with a model of mitochondrial Ca2+ and a modified model of mitochondrial energy metabolism. The experimental results showed that oxygen consumption increased in response to increases in the electrical stimulation rate. The model reproduced these findings and predicted that the increase in oxygen consumption is associated with metabolic homeostasis. The model predicted that Ca2+ must act both in "push" and "pull" pathways to increase oxygen consumption. In contrast to ventricular trabeculae, no rapid time-dependent changes in mitochondrial flavoprotein fluorescence were measured upon an abrupt change in workload. The model reproduced these findings and predicted that the maintenance of metabolic homeostasis is due to the effects of Ca2+ on ATP production. Taken together, this work provides evidence of Ca2+ "push" and "pull" activity to maintain metabolic homeostasis in atrial cells.
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Manoj P, Kim JA, Kim S, Li T, Sewani M, Chelu MG, Li N. Sinus node dysfunction: current understanding and future directions. Am J Physiol Heart Circ Physiol 2023; 324:H259-H278. [PMID: 36563014 PMCID: PMC9886352 DOI: 10.1152/ajpheart.00618.2022] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Revised: 12/20/2022] [Accepted: 12/21/2022] [Indexed: 12/24/2022]
Abstract
The sinoatrial node (SAN) is the primary pacemaker of the heart. Normal SAN function is crucial in maintaining proper cardiac rhythm and contraction. Sinus node dysfunction (SND) is due to abnormalities within the SAN, which can affect the heartbeat frequency, regularity, and the propagation of electrical pulses through the cardiac conduction system. As a result, SND often increases the risk of cardiac arrhythmias. SND is most commonly seen as a disease of the elderly given the role of degenerative fibrosis as well as other age-dependent changes in its pathogenesis. Despite the prevalence of SND, current treatment is limited to pacemaker implantation, which is associated with substantial medical costs and complications. Emerging evidence has identified various genetic abnormalities that can cause SND, shedding light on the molecular underpinnings of SND. Identification of these molecular mechanisms and pathways implicated in the pathogenesis of SND is hoped to identify novel therapeutic targets for the development of more effective therapies for this disease. In this review article, we examine the anatomy of the SAN and the pathophysiology and epidemiology of SND. We then discuss in detail the most common genetic mutations correlated with SND and provide our perspectives on future research and therapeutic opportunities in this field.
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Affiliation(s)
- Pavan Manoj
- School of Public Health, Texas A&M University, College Station, Texas
| | - Jitae A Kim
- Department of Medicine, Baylor College of Medicine, Houston, Texas
| | - Stephanie Kim
- Department of BioSciences, Rice University, Houston, Texas
| | - Tingting Li
- Section of Cardiovascular Research, Department of Medicine, Baylor College of Medicine, Houston, Texas
| | - Maham Sewani
- Department of BioSciences, Rice University, Houston, Texas
| | - Mihail G Chelu
- Division of Cardiology, Department of Medicine, Baylor College of Medicine, Houston, Texas
| | - Na Li
- Section of Cardiovascular Research, Department of Medicine, Baylor College of Medicine, Houston, Texas
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5
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Mitochondrial Dysfunction in Cardiac Arrhythmias. Cells 2023; 12:cells12050679. [PMID: 36899814 PMCID: PMC10001005 DOI: 10.3390/cells12050679] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2022] [Revised: 02/14/2023] [Accepted: 02/17/2023] [Indexed: 02/24/2023] Open
Abstract
Electrophysiological and structural disruptions in cardiac arrhythmias are closely related to mitochondrial dysfunction. Mitochondria are an organelle generating ATP, thereby satisfying the energy demand of the incessant electrical activity in the heart. In arrhythmias, the homeostatic supply-demand relationship is impaired, which is often accompanied by progressive mitochondrial dysfunction leading to reduced ATP production and elevated reactive oxidative species generation. Furthermore, ion homeostasis, membrane excitability, and cardiac structure can be disrupted through pathological changes in gap junctions and inflammatory signaling, which results in impaired cardiac electrical homeostasis. Herein, we review the electrical and molecular mechanisms of cardiac arrhythmias, with a particular focus on mitochondrial dysfunction in ionic regulation and gap junction action. We provide an update on inherited and acquired mitochondrial dysfunction to explore the pathophysiology of different types of arrhythmias. In addition, we highlight the role of mitochondria in bradyarrhythmia, including sinus node dysfunction and atrioventricular node dysfunction. Finally, we discuss how confounding factors, such as aging, gut microbiome, cardiac reperfusion injury, and electrical stimulation, modulate mitochondrial function and cause tachyarrhythmia.
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Ren L, Gopireddy RR, Perkins G, Zhang H, Timofeyev V, Lyu Y, Diloretto DA, Trinh P, Sirish P, Overton JL, Xu W, Grainger N, Xiang YK, Dedkova EN, Zhang XD, Yamoah EN, Navedo MF, Thai PN, Chiamvimonvat N. Disruption of mitochondria-sarcoplasmic reticulum microdomain connectomics contributes to sinus node dysfunction in heart failure. Proc Natl Acad Sci U S A 2022; 119:e2206708119. [PMID: 36044551 PMCID: PMC9456763 DOI: 10.1073/pnas.2206708119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Accepted: 08/01/2022] [Indexed: 11/18/2022] Open
Abstract
The sinoatrial node (SAN), the leading pacemaker region, generates electrical impulses that propagate throughout the heart. SAN dysfunction with bradyarrhythmia is well documented in heart failure (HF). However, the underlying mechanisms are not completely understood. Mitochondria are critical to cellular processes that determine the life or death of the cell. The release of Ca2+ from the ryanodine receptors 2 (RyR2) on the sarcoplasmic reticulum (SR) at mitochondria-SR microdomains serves as the critical communication to match energy production to meet metabolic demands. Therefore, we tested the hypothesis that alterations in the mitochondria-SR connectomics contribute to SAN dysfunction in HF. We took advantage of a mouse model of chronic pressure overload-induced HF by transverse aortic constriction (TAC) and a SAN-specific CRISPR-Cas9-mediated knockdown of mitofusin-2 (Mfn2), the mitochondria-SR tethering GTPase protein. TAC mice exhibited impaired cardiac function with HF, cardiac fibrosis, and profound SAN dysfunction. Ultrastructural imaging using electron microscope (EM) tomography revealed abnormal mitochondrial structure with increased mitochondria-SR distance. The expression of Mfn2 was significantly down-regulated and showed reduced colocalization with RyR2 in HF SAN cells. Indeed, SAN-specific Mfn2 knockdown led to alterations in the mitochondria-SR microdomains and SAN dysfunction. Finally, disruptions in the mitochondria-SR microdomains resulted in abnormal mitochondrial Ca2+ handling, alterations in localized protein kinase A (PKA) activity, and impaired mitochondrial function in HF SAN cells. The current study provides insights into the role of mitochondria-SR microdomains in SAN automaticity and possible therapeutic targets for SAN dysfunction in HF patients.
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Affiliation(s)
- Lu Ren
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
- Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | | | - Guy Perkins
- National Center for Microscopy and Imaging Research, University of California San Diego, La Jolla, CA 92093
| | - Hao Zhang
- Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Valeriy Timofeyev
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
| | - Yankun Lyu
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
| | - Daphne A. Diloretto
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
| | - Pauline Trinh
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
| | - Padmini Sirish
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
| | - James L. Overton
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
| | - Wilson Xu
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
| | - Nathan Grainger
- Department of Physiology and Membrane Biology, University of California, Davis, CA 95616
| | - Yang K. Xiang
- Department of Pharmacology, University of California, Davis, CA 95616
| | - Elena N. Dedkova
- Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA 95616
| | - Xiao-Dong Zhang
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
| | - Ebenezer N. Yamoah
- Department of Physiology and Cell Biology, University of Nevada, Reno, NV 89557
| | - Manuel F. Navedo
- Department of Pharmacology, University of California, Davis, CA 95616
| | - Phung N. Thai
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
- Department of Physiology and Cell Biology, University of Nevada, Reno, NV 89557
| | - Nipavan Chiamvimonvat
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, CA 95616
- Department of Pharmacology, University of California, Davis, CA 95616
- Department of Veterans Affairs, Northern California Health Care System, Mather, CA 95655
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7
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Chou PC, Liu CM, Weng CH, Yang KC, Cheng ML, Lin YC, Yang RB, Shyu BC, Shyue SK, Liu JD, Chen SP, Hsiao M, Hu YF. Fibroblasts Drive Metabolic Reprogramming in Pacemaker Cardiomyocytes. Circ Res 2022; 131:6-20. [PMID: 35611699 DOI: 10.1161/circresaha.121.320301] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND The sinoatrial node (SAN) is characterized by the microenvironment of pacemaker cardiomyocytes (PCs) encased with fibroblasts. An altered microenvironment leads to rhythm failure. Operable cell or tissue models are either generally lacking or difficult to handle. The biological process behind the milieu of SANs to evoke pacemaker rhythm is unknown. We explored how fibroblasts interact with PCs and regulate metabolic reprogramming and rhythmic activity in the SAN. METHODS Tbx18 (T-box transcription factor 18)-induced PCs and fibroblasts were used for cocultures and engineered tissues, which were used as the in vitro models to explore how fibroblasts regulate the functional integrity of SANs. RNA-sequencing, metabolomics, and cellular and molecular techniques were applied to characterize the molecular signals underlying metabolic reprogramming and identify its critical regulators. These pathways were further validated in vivo in rodents and induced human pluripotent stem cell-derived cardiomyocytes. RESULTS We observed that rhythmicity in Tbx18-induced PCs was regulated by aerobic glycolysis. Fibroblasts critically activated metabolic reprogramming and aerobic glycolysis within PCs, and, therefore, regulated pacemaker activity in PCs. The metabolic reprogramming was attributed to the exclusive induction of Aldoc (aldolase c) within PCs after fibroblast-PC integration. Fibroblasts activated the integrin-dependent mitogen-activated protein kinase-E2F1 signal through cell-cell contact and turned on Aldoc expression in PCs. Interruption of fibroblast-PC interaction or Aldoc knockdown nullified electrical activity. Engineered Tbx18-PC tissue sheets were generated to recapitulate the microenvironment within SANs. Aldoc-driven rhythmic machinery could be replicated within tissue sheets. Similar machinery was faithfully validated in de novo PCs of adult mice and rats, and in human PCs derived from induced pluripotent stem cells. CONCLUSIONS Fibroblasts drive Aldoc-mediated metabolic reprogramming and rhythmic regulation in SANs. This work details the cellular machinery behind the complex milieu of vertebrate SANs and opens a new direction for future therapy.
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Affiliation(s)
- Pei-Chun Chou
- Division of Cardiology, Department of Medicine, Heart Rhythm Center, Taipei Veterans General Hospital, Taiwan. (P.-C.C., C.-M.L., C.-H.W., J.-D.L., Y.-F.H.).,Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan (P.-C.C., C.-H.W., K.-C.Y., Y.-C.L., R.-B.Y., B.-C.S., S.-K.S., J.-D.L., Y.-F.H.)
| | - Chih-Min Liu
- Division of Cardiology, Department of Medicine, Heart Rhythm Center, Taipei Veterans General Hospital, Taiwan. (P.-C.C., C.-M.L., C.-H.W., J.-D.L., Y.-F.H.).,Faculty of Medicine, School of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan (C.-M.L., Y.-F.H.)
| | - Ching-Hui Weng
- Division of Cardiology, Department of Medicine, Heart Rhythm Center, Taipei Veterans General Hospital, Taiwan. (P.-C.C., C.-M.L., C.-H.W., J.-D.L., Y.-F.H.).,Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan (P.-C.C., C.-H.W., K.-C.Y., Y.-C.L., R.-B.Y., B.-C.S., S.-K.S., J.-D.L., Y.-F.H.)
| | - Kai-Chien Yang
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan (P.-C.C., C.-H.W., K.-C.Y., Y.-C.L., R.-B.Y., B.-C.S., S.-K.S., J.-D.L., Y.-F.H.).,Department and Graduate Institute of Pharmacology, National Taiwan University College of Medicine, Taipei (K.-C.Y.)
| | - Mei-Ling Cheng
- Metabolomics Core Laboratory, Healthy Aging Research Center, Chang Gung University, Taoyuan City, Taiwan (M.-L.C.)
| | - Yuh-Charn Lin
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan (P.-C.C., C.-H.W., K.-C.Y., Y.-C.L., R.-B.Y., B.-C.S., S.-K.S., J.-D.L., Y.-F.H.).,Department of Physiology, School of Medicine, College of Medicine, Taipei Medical University, Taiwan (Y.-C.L.)
| | - Ruey-Bing Yang
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan (P.-C.C., C.-H.W., K.-C.Y., Y.-C.L., R.-B.Y., B.-C.S., S.-K.S., J.-D.L., Y.-F.H.)
| | - Bai-Chuang Shyu
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan (P.-C.C., C.-H.W., K.-C.Y., Y.-C.L., R.-B.Y., B.-C.S., S.-K.S., J.-D.L., Y.-F.H.)
| | - Song-Kun Shyue
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan (P.-C.C., C.-H.W., K.-C.Y., Y.-C.L., R.-B.Y., B.-C.S., S.-K.S., J.-D.L., Y.-F.H.)
| | - Jin-Dian Liu
- Division of Cardiology, Department of Medicine, Heart Rhythm Center, Taipei Veterans General Hospital, Taiwan. (P.-C.C., C.-M.L., C.-H.W., J.-D.L., Y.-F.H.).,Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan (P.-C.C., C.-H.W., K.-C.Y., Y.-C.L., R.-B.Y., B.-C.S., S.-K.S., J.-D.L., Y.-F.H.)
| | - Shih-Pin Chen
- Department of Neurology, Neurological Institute, Taipei Veterans General Hospital, Taiwan. (S.-P.C.)
| | - Michael Hsiao
- The Genomics Research Center, Academia Sinica, Taipei, Taiwan (M.H.)
| | - Yu-Feng Hu
- Division of Cardiology, Department of Medicine, Heart Rhythm Center, Taipei Veterans General Hospital, Taiwan. (P.-C.C., C.-M.L., C.-H.W., J.-D.L., Y.-F.H.).,Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan (P.-C.C., C.-H.W., K.-C.Y., Y.-C.L., R.-B.Y., B.-C.S., S.-K.S., J.-D.L., Y.-F.H.).,Faculty of Medicine, School of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan (C.-M.L., Y.-F.H.)
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8
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Earley S, Lederer WJ. Metabolic Control of Cardiac Pacemaking. FUNCTION (OXFORD, ENGLAND) 2021; 2:zqab043. [PMID: 35330951 PMCID: PMC8788821 DOI: 10.1093/function/zqab043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 08/17/2021] [Revised: 08/10/2021] [Accepted: 08/19/2021] [Indexed: 01/07/2023]
Affiliation(s)
| | - W Jonathan Lederer
- Center for Biomedical Engineering and Technology and Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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9
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Kim MS, Monfredi O, Maltseva LA, Lakatta EG, Maltsev VA. β-Adrenergic Stimulation Synchronizes a Broad Spectrum of Action Potential Firing Rates of Cardiac Pacemaker Cells toward a Higher Population Average. Cells 2021; 10:2124. [PMID: 34440893 PMCID: PMC8391682 DOI: 10.3390/cells10082124] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 08/10/2021] [Accepted: 08/14/2021] [Indexed: 01/28/2023] Open
Abstract
The heartbeat is initiated by pacemaker cells residing in the sinoatrial node (SAN). SAN cells generate spontaneous action potentials (APs), i.e., normal automaticity. The sympathetic nervous system increases the heart rate commensurate with the cardiac output demand via stimulation of SAN β-adrenergic receptors (βAR). While SAN cells reportedly represent a highly heterogeneous cell population, the current dogma is that, in response to βAR stimulation, all cells increase their spontaneous AP firing rate in a similar fashion. The aim of the present study was to investigate the cell-to-cell variability in the responses of a large population of SAN cells. We measured the βAR responses among 166 single SAN cells isolated from 33 guinea pig hearts. In contrast to the current dogma, the SAN cell responses to βAR stimulation substantially varied. In each cell, changes in the AP cycle length were highly correlated (R2 = 0.97) with the AP cycle length before βAR stimulation. While, as expected, on average, the cells increased their pacemaker rate, greater responses were observed in cells with slower basal rates, and vice versa: cells with higher basal rates showed smaller responses, no responses, or even decreased their rate. Thus, βAR stimulation synchronized the operation of the SAN cell population toward a higher average rate, rather than uniformly shifting the rate in each cell, creating a new paradigm of βAR-driven fight-or-flight responses among individual pacemaker cells.
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Affiliation(s)
| | | | | | | | - Victor A. Maltsev
- Laboratory of Cardiovascular Science, National Institute on Aging, NIH, Baltimore, MD 21224, USA; (M.S.K.); (O.M.); (L.A.M.); (E.G.L.)
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10
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Grainger N, Guarina L, Cudmore RH, Santana LF. The Organization of the Sinoatrial Node Microvasculature Varies Regionally to Match Local Myocyte Excitability. FUNCTION (OXFORD, ENGLAND) 2021; 2:zqab031. [PMID: 34250490 PMCID: PMC8259512 DOI: 10.1093/function/zqab031] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Revised: 05/28/2021] [Accepted: 06/10/2021] [Indexed: 01/06/2023]
Abstract
The cardiac cycle starts when an action potential is produced by pacemaking cells in the sinoatrial node. This cycle is repeated approximately 100 000 times in humans and 1 million times in mice per day, imposing a monumental metabolic demand on the heart, requiring efficient blood supply via the coronary vasculature to maintain cardiac function. Although the ventricular coronary circulation has been extensively studied, the relationship between vascularization and cellular pacemaking modalities in the sinoatrial node is poorly understood. Here, we tested the hypothesis that the organization of the sinoatrial node microvasculature varies regionally, reflecting local myocyte firing properties. We show that vessel densities are higher in the superior versus inferior sinoatrial node. Accordingly, sinoatrial node myocytes are closer to vessels in the superior versus inferior regions. Superior and inferior sinoatrial node myocytes produce stochastic subthreshold voltage fluctuations and action potentials. However, the intrinsic action potential firing rate of sinoatrial node myocytes is higher in the superior versus inferior node. Our data support a model in which the microvascular densities vary regionally within the sinoatrial node to match the electrical and Ca2+ dynamics of nearby myocytes, effectively determining the dominant pacemaking site within the node. In this model, the high vascular density in the superior sinoatrial node places myocytes with metabolically demanding, high-frequency action potentials near vessels. The lower vascularization and electrical activity of inferior sinoatrial node myocytes could limit these cells to function to support sinoatrial node periodicity with sporadic voltage fluctuations via a stochastic resonance mechanism.
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11
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Tan Q, Hu J, Zhou Y, Wan Y, Zhang C, Liu X, Long X, Tan F, Zhao X. Inhibitory Effect of Lactococcus lactis subsp. lactis HFY14 on Diphenoxylate-Induced Constipation in Mice by Regulating the VIP-cAMP-PKA-AQP3 Signaling Pathway. DRUG DESIGN DEVELOPMENT AND THERAPY 2021; 15:1971-1980. [PMID: 34007157 PMCID: PMC8123977 DOI: 10.2147/dddt.s309675] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Accepted: 04/24/2021] [Indexed: 12/26/2022]
Abstract
Aim The naturally fermented yak yogurt of pastoralists in the Tibetan Plateau, China, because of its unique geographical environment and the unique lifestyle of Tibetan pastoralists, is very different from other kinds of sour milk, and the microorganisms it contains are special. Lactococcus lactis subsp. lactis HFY14 (LLSL-HFY14) is a new lactic acid bacterium isolated from naturally fermented yak yogurt. The purpose of this study was to study the inhibitory effect of the bacterium on constipation. Methods Constipation was induced in ICR mice with diphenoxylate, and the constipated mice were treated with LLSL-HFY14. The weight and feces of the mice were visually detected. Colonic tissues were observed on hematoxylin and eosin-stained sections. Serum indices were detected with kits. mRNA expression in the colon was determined by quantitative polymerase chain reaction assay. Results Constipation caused weight loss, the number of defecation granules, defecation weight, fecal water content decreased, and the first black stool excretion time increased. LLSL-HFY14 alleviated these symptoms, and the effects were similar to those of lactulose (drug). The pathological examination revealed that constipation caused pathological changes in the colon, and LLSL-HFY14 effectively alleviated the disease. LLSL-HFY14 increased serum levels of motilin, gastrin, endothelin, substance P, acetylcholinesterase, and vasoactive intestinal peptide (VIP) and decreased serum levels of somatostatin in constipated mice. In addition, LLSL-HFY14 upregulated VIP, cAMP, protein kinase A, and aquaporin 3 expression in colonic tissues of constipated mice in a dose-dependent manner. Conclusion LLSL-HFY14 inhibited constipation, similar to lactulose, and has the potential to become a biological agent.
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Affiliation(s)
- Qian Tan
- Chongqing Collaborative Innovation Center for Functional Food, Chongqing Engineering Research Center of Functional Food, Chongqing Engineering Laboratory for Research and Development of Functional Food, Chongqing University of Education, Chongqing, 400067, People's Republic of China.,College of Biological and Chemical Engineering, Chongqing University of Education, Chongqing, 400067, People's Republic of China
| | - Jing Hu
- Department of Pharmacy, Southwest Hospital, Army Medical University (Third Military Medical University), Chongqing, 400038, People's Republic of China
| | - Yujing Zhou
- Chongqing Collaborative Innovation Center for Functional Food, Chongqing Engineering Research Center of Functional Food, Chongqing Engineering Laboratory for Research and Development of Functional Food, Chongqing University of Education, Chongqing, 400067, People's Republic of China.,College of Biological and Chemical Engineering, Chongqing University of Education, Chongqing, 400067, People's Republic of China
| | - Yunxiao Wan
- Chongqing Collaborative Innovation Center for Functional Food, Chongqing Engineering Research Center of Functional Food, Chongqing Engineering Laboratory for Research and Development of Functional Food, Chongqing University of Education, Chongqing, 400067, People's Republic of China.,College of Biological and Chemical Engineering, Chongqing University of Education, Chongqing, 400067, People's Republic of China
| | - Chuanlan Zhang
- Chongqing Collaborative Innovation Center for Functional Food, Chongqing Engineering Research Center of Functional Food, Chongqing Engineering Laboratory for Research and Development of Functional Food, Chongqing University of Education, Chongqing, 400067, People's Republic of China.,College of Biological and Chemical Engineering, Chongqing University of Education, Chongqing, 400067, People's Republic of China
| | - Xin Liu
- Chongqing Collaborative Innovation Center for Functional Food, Chongqing Engineering Research Center of Functional Food, Chongqing Engineering Laboratory for Research and Development of Functional Food, Chongqing University of Education, Chongqing, 400067, People's Republic of China.,College of Biological and Chemical Engineering, Chongqing University of Education, Chongqing, 400067, People's Republic of China
| | - Xingyao Long
- Chongqing Collaborative Innovation Center for Functional Food, Chongqing Engineering Research Center of Functional Food, Chongqing Engineering Laboratory for Research and Development of Functional Food, Chongqing University of Education, Chongqing, 400067, People's Republic of China.,Department of Food Science and Biotechnology, Cha University, Seongnam, 13488, South Korea
| | - Fang Tan
- Department of Public Health, Our Lady of Fatima University, 838 Valenzuela, Philippines
| | - Xin Zhao
- Chongqing Collaborative Innovation Center for Functional Food, Chongqing Engineering Research Center of Functional Food, Chongqing Engineering Laboratory for Research and Development of Functional Food, Chongqing University of Education, Chongqing, 400067, People's Republic of China
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12
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Characterization and validation of a preventative therapy for hypertrophic cardiomyopathy in a murine model of the disease. Proc Natl Acad Sci U S A 2020; 117:23113-23124. [PMID: 32859761 PMCID: PMC7502707 DOI: 10.1073/pnas.2002976117] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Hypertrophic cardiomyopathy affects 1:500 of the general population. Current drug therapy is used to manage symptoms in patients. There is an unmet need for treatments that can prevent the cardiomyopathy. Here we identify biomarkers of hypertrophic cardiomyopathy resulting from causing cardiac troponin I mutation Gly203Ser, and present a safe, nontoxic, preventative approach for the treatment of associated cardiomyopathy. Currently there is an unmet need for treatments that can prevent hypertrophic cardiomyopathy (HCM). Using a murine model we previously identified that HCM causing cardiac troponin I mutation Gly203Ser (cTnI-G203S) is associated with increased mitochondrial metabolic activity, consistent with the human condition. These alterations precede development of the cardiomyopathy. Here we examine the efficacy of in vivo treatment of cTnI-G203S mice with a peptide derived against the α-interaction domain of the cardiac L-type calcium channel (AID-TAT) on restoring mitochondrial metabolic activity, and preventing HCM. cTnI-G203S or age-matched wt mice were treated with active or inactive AID-TAT. Following treatment, targeted metabolomics was utilized to evaluate myocardial substrate metabolism. Cardiac myocyte mitochondrial metabolic activity was assessed as alterations in mitochondrial membrane potential and flavoprotein oxidation. Cardiac morphology and function were examined using echocardiography. Cardiac uptake was assessed using an in vivo multispectral imaging system. We identified alterations in six biochemical intermediates in cTnI-G203S hearts consistent with increased anaplerosis. We also reveal that AID-TAT treatment of precardiomyopathic cTnI-G203S mice, but not mice with established cardiomyopathy, restored cardiac myocyte mitochondrial membrane potential and flavoprotein oxidation, and prevented myocardial hypertrophy. Importantly, AID-TAT was rapidly targeted to the heart, and not retained by the liver or kidneys. Overall, we identify biomarkers of HCM resulting from the cTnI mutation Gly203Ser, and present a safe, preventative therapy for associated cardiomyopathy. Utilizing AID-TAT to modulate cardiac metabolic activity may be beneficial in preventing HCM in “at risk” patients with identified Gly203Ser gene mutations.
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13
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Kirschner Peretz N, Segal S, Yaniv Y. May the Force Not Be With You During Culture: Eliminating Mechano-Associated Feedback During Culture Preserves Cultured Atrial and Pacemaker Cell Functions. Front Physiol 2020; 11:163. [PMID: 32265724 PMCID: PMC7100534 DOI: 10.3389/fphys.2020.00163] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Accepted: 02/12/2020] [Indexed: 01/24/2023] Open
Abstract
Cultured cardiomyocytes have been shown to possess significant potential as a model for characterization of mechano-Ca2+, mechano-electric, and mechano-metabolic feedbacks in the heart. However, the majority of cultured cardiomyocytes exhibit impaired electrical, mechanical, biochemical, and metabolic functions. More specifically, the cells do not beat spontaneously (pacemaker cells) or beat at a rate far lower than their physiological counterparts and self-oscillate (atrial and ventricular cells) in culture. Thus, efforts are being invested in ensuring that cultured cardiomyocytes maintain the shape and function of freshly isolated cells. Elimination of contraction during culture has been shown to preserve the mechano-Ca2+, mechano-electric, and mechano-metabolic feedback loops of cultured cells. This review focuses on pacemaker cells, which reside in the sinoatrial node (SAN) and generate regular heartbeat through the initiation of the heart’s electrical, metabolic, and biochemical activities. In parallel, it places emphasis on atrial cells, which are responsible for bridging the electrical conductance from the SAN to the ventricle. The review provides a summary of the main mechanisms responsible for mechano-electrical, Ca2+, and metabolic feedback in pacemaker and atrial cells and of culture methods existing for both cell types. The work concludes with an explanation of how the elimination of mechano-electrical, mechano-Ca2+, and mechano-metabolic feedbacks during culture results in sustained cultured cell function.
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Affiliation(s)
- Noa Kirschner Peretz
- Biomedical Engineering Faculty, Technion Israel Institute of Technology, Haifa, Israel
| | - Sofia Segal
- Biomedical Engineering Faculty, Technion Israel Institute of Technology, Haifa, Israel
| | - Yael Yaniv
- Biomedical Engineering Faculty, Technion Israel Institute of Technology, Haifa, Israel
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14
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Yang B, Huang Y, Zhang H, Huang Y, Zhou HJ, Young L, Xiao H, Min W. Mitochondrial thioredoxin-2 maintains HCN4 expression and prevents oxidative stress-mediated sick sinus syndrome. J Mol Cell Cardiol 2020; 138:291-303. [DOI: 10.1016/j.yjmcc.2019.10.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Revised: 10/10/2019] [Accepted: 10/30/2019] [Indexed: 12/17/2022]
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15
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Hu HL, Kang Y, Zeng Y, Zhang M, Liao Q, Rong MQ, Zhang Q, Lai R. Region-resolved proteomics profiling of monkey heart. J Cell Physiol 2019; 234:13720-13734. [PMID: 30644093 PMCID: PMC7166496 DOI: 10.1002/jcp.28052] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Accepted: 12/06/2018] [Indexed: 02/05/2023]
Abstract
Nonhuman primates (NHPs) play an indispensable role in biomedical research because of their similarities in genetics, physiological, and neurological function to humans. Proteomics profiling of monkey heart could reveal significant cardiac biomarkers and help us to gain a better understanding of the pathogenesis of heart disease. However, the proteomic study of monkey heart is relatively lacking. Here, we performed the proteomics profiling of the normal monkey heart by measuring three major anatomical regions (vessels, valves, and chambers) based on iTRAQ‐coupled LC‐MS/MS analysis. Over 3,200 proteins were identified and quantified from three heart tissue samples. Furthermore, multiple bioinformatics analyses such as gene ontology analysis, protein–protein interaction analysis, and gene‐diseases association were used to investigate biological network of those proteins from each area. More than 60 genes in three heart regions are implicated with heart diseases such as hypertrophic cardiomyopathy, heart failure, and myocardial infarction. These genes associated with heart disease are mainly enriched in citrate cycle, amino acid degradation, and glycolysis pathway. At the anatomical level, the revelation of molecular characteristics of the healthy monkey heart would be an important starting point to investigate heart disease. As a unique resource, this study can serve as a reference map for future in‐depth research on cardiac disease‐related NHP model and novel biomarkers of cardiac injury.
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Affiliation(s)
- Hao-Liang Hu
- The National & Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
| | - Yu Kang
- Division of Cardiology, West China Hospital, Sichuan University, Chengdu, Sichuan, China
| | - Yong Zeng
- The National & Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
| | - Ming Zhang
- Key Laboratory of Animal Models and Human Disease Mechanisms of Chinese Academy of Sciences &Yunnan Province, Kunming Institute of Zoology, Chinese Academy of Sciences (CAS), Kunming, Yunnan, China
| | - Qiong Liao
- The National & Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
| | - Ming-Qiang Rong
- The National & Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
| | - Qin Zhang
- Division of Cardiology, West China Hospital, Sichuan University, Chengdu, Sichuan, China
| | - Ren Lai
- Key Laboratory of Animal Models and Human Disease Mechanisms of Chinese Academy of Sciences &Yunnan Province, Kunming Institute of Zoology, Chinese Academy of Sciences (CAS), Kunming, Yunnan, China
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16
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Segal S, Kirschner Peretz N, Arbel-Ganon L, Liang J, Li L, Marbach D, Yang D, Wang SQ, Yaniv Y. Eliminating contraction during culture maintains global and local Ca 2+ dynamics in cultured rabbit pacemaker cells. Cell Calcium 2018; 78:35-47. [PMID: 30594820 DOI: 10.1016/j.ceca.2018.12.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Revised: 12/17/2018] [Accepted: 12/17/2018] [Indexed: 12/12/2022]
Abstract
Pacemaker cells residing in the sinoatrial node generate the regular heartbeat. Ca2+ signaling controls the heartbeat rate-directly, through the effect on membrane molecules (NCX exchange, K+ channel), and indirectly, through activation of calmodulin-AC-cAMP-PKA signaling. Thus, the physiological role of signaling in pacemaker cells can only be assessed if the Ca2+ dynamics are in the physiological range. Cultured cells that can be genetically manipulated and/or virally infected with probes are required for this purpose. Because rabbit pacemaker cells in culture experience a decrease in their spontaneous action potential (AP) firing rate below the physiological range, Ca2+ dynamics are expected to be affected. However, Ca2+ dynamics in cultured pacemaker cells have not been reported before. We aim to a develop a modified culture method that sustains the global and local Ca2+ kinetics along with the AP firing rate of rabbit pacemaker cells. We used experimental and computational tools to test the viability of rabbit pacemaker cells in culture under various conditions. We tested the effect of culture dish coating, pH, phosphorylation, and energy balance on cultured rabbit pacemaker cells function. The cells were maintained in culture for 48 h in two types of culture media: one without the addition of a contraction uncoupler and one enriched with either 10 mM BDM (2,3-Butanedione 2-monoxime) or 25 μM blebbistatin. The uncoupler was washed out from the medium prior to the experiments. Cells were successfully infected with a GFP adenovirus cultured with either BDM or blebbistatin. Using either uncoupler during culture led to the cell surface area being maintained at the same level as fresh cells. Moreover, the phospholamban and ryanodine receptor densities and their phosphorylation level remained intact in culture when either blebbistatin or BDM were present. Spontaneous AP firing rate, spontaneous Ca2+ kinetics, and spontaneous local Ca2+ release parameters were similar in the cultured cells with blebbistatin as in fresh cells. However, BDM affects these parameters. Using experimental and a computational model, we showed that by eliminating contraction, phosphorylation activity is preserved and energy is reduced. However, the side-effects of BDM render it less effective than blebbistatin.
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Affiliation(s)
- Sofia Segal
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | | | | | - Jinghui Liang
- College of Life Sciences, Peking University, Beijing, China
| | - Linlin Li
- College of Life Sciences, Peking University, Beijing, China
| | - Daphna Marbach
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | - Dongmei Yang
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, Baltimore, MD, USA
| | - Shi-Qiang Wang
- College of Life Sciences, Peking University, Beijing, China
| | - Yael Yaniv
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel.
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17
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Yaniv Y, Lakatta EG. The end effector of circadian heart rate variation: the sinoatrial node pacemaker cell. BMB Rep 2016; 48:677-84. [PMID: 25999176 PMCID: PMC4791323 DOI: 10.5483/bmbrep.2015.48.12.061] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Indexed: 12/16/2022] Open
Abstract
Cardiovascular function is regulated by the rhythmicity of circadian, infradian and ultradian clocks. Specific time scales of different cell types drive their functions: circadian gene regulation at hours scale, activation-inactivation cycles of ion channels at millisecond scales, the heart's beating rate at hundreds of millisecond scales, and low frequency autonomic signaling at cycles of tens of seconds. Heart rate and rhythm are modulated by a hierarchical clock system: autonomic signaling from the brain releases neurotransmitters from the vagus and sympathetic nerves to the heart’s pacemaker cells and activate receptors on the cell. These receptors activating ultradian clock functions embedded within pacemaker cells include sarcoplasmic reticulum rhythmic spontaneous Ca2+ cycling, rhythmic ion channel current activation and inactivation, and rhythmic oscillatory mitochondria ATP production. Here we summarize the evidence that intrinsic pacemaker cell mechanisms are the end effector of the hierarchical brain-heart circadian clock system. [BMB Reports 2015; 48(12): 677-684]
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Affiliation(s)
- Yael Yaniv
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel
| | - Edward G Lakatta
- Laboratory of Cardiovascular Science, Biomedical Research Center, Intramural Research Program, National Institute on Aging, NIH, Baltimore, Maryland, USA
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18
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Behar J, Ganesan A, Zhang J, Yaniv Y. The Autonomic Nervous System Regulates the Heart Rate through cAMP-PKA Dependent and Independent Coupled-Clock Pacemaker Cell Mechanisms. Front Physiol 2016; 7:419. [PMID: 27729868 PMCID: PMC5037226 DOI: 10.3389/fphys.2016.00419] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Accepted: 09/05/2016] [Indexed: 12/19/2022] Open
Abstract
Sinoatrial nodal cells (SANCs) generate spontaneous action potentials (APs) that control the cardiac rate. The brain modulates SANC automaticity, via the autonomic nervous system, by stimulating membrane receptors that activate (adrenergic) or inactivate (cholinergic) adenylyl cyclase (AC). However, these opposing afferents are not simply additive. We showed that activation of adrenergic signaling increases AC-cAMP/PKA signaling, which mediates the increase in the SANC AP firing rate (i.e., positive chronotropic modulation). However, there is a limited understanding of the underlying internal pacemaker mechanisms involved in the crosstalk between cholinergic receptors and the decrease in the SANC AP firing rate (i.e., negative chronotropic modulation). We hypothesize that changes in AC-cAMP/PKA activity are crucial for mediating either decrease or increase in the AP firing rate and that the change in rate is due to both internal and membrane mechanisms. In cultured adult rabbit pacemaker cells infected with an adenovirus expressing the FRET sensor AKAR3, PKA activity and AP firing rate were tightly linked in response to either adrenergic receptor stimulation (by isoproterenol, ISO) or cholinergic stimulation (by carbachol, CCh). To identify the main molecular targets that mediate between PKA signaling and pacemaker function, we developed a mechanistic computational model. The model includes a description of autonomic-nervous receptors, post- translation signaling cascades, membrane molecules, and internal pacemaker mechanisms. Yielding results similar to those of the experiments, the model simulations faithfully reproduce the changes in AP firing rate in response to CCh or ISO or a combination of both (i.e., accentuated antagonism). Eliminating AC-cAMP-PKA signaling abolished the core effect of autonomic receptor stimulation on the AP firing rate. Specifically, disabling the phospholamban modulation of the SERCA activity resulted in a significantly reduced effect of CCh and a failure to increase the AP firing rate under ISO stimulation. Directly activating internal pacemaker mechanisms led to a similar extent of changes in the AP firing rate with respect to brain receptor stimulation. Thus, Ca2+ and cAMP/PKA-dependent phosphorylation limits the rate and magnitude of chronotropic changes in the spontaneous AP firing rate.
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Affiliation(s)
- Joachim Behar
- Laboratory of Bioenergetic and Bioelectric Systems, Biomedical Engineering Faculty, Technion-IIT Haifa, Israel
| | - Ambhighainath Ganesan
- Department of Biomedical Engineering, The Johns Hopkins University of Medicine Baltimore, MD, USA
| | - Jin Zhang
- Department of Pharmacology, University of California San Diego San Diego, CA, USA
| | - Yael Yaniv
- Laboratory of Bioenergetic and Bioelectric Systems, Biomedical Engineering Faculty, Technion-IIT Haifa, Israel
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García-Bermúdez J, Cuezva JM. The ATPase Inhibitory Factor 1 (IF1): A master regulator of energy metabolism and of cell survival. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1857:1167-1182. [PMID: 26876430 DOI: 10.1016/j.bbabio.2016.02.004] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Revised: 01/28/2016] [Accepted: 02/07/2016] [Indexed: 12/19/2022]
Abstract
In this contribution we summarize most of the findings reported for the molecular and cellular biology of the physiological inhibitor of the mitochondrial H(+)-ATP synthase, the engine of oxidative phosphorylation (OXPHOS) and gate of cell death. We first describe the structure and major mechanisms and molecules that regulate the activity of the ATP synthase placing the ATPase Inhibitory Factor 1 (IF1) as a major determinant in the regulation of the activity of the ATP synthase and hence of OXPHOS. Next, we summarize the post-transcriptional mechanisms that regulate the expression of IF1 and emphasize, in addition to the regulation afforded by the protonation state of histidine residues, that the activity of IF1 as an inhibitor of the ATP synthase is also regulated by phosphorylation of a serine residue. Phosphorylation of S39 in IF1 by the action of a mitochondrial cAMP-dependent protein kinase A hampers its interaction with the ATP synthase, i.e., only dephosphorylated IF1 interacts with the enzyme. Upon IF1 interaction with the ATP synthase both the synthetic and hydrolytic activities of the engine of OXPHOS are inhibited. These findings are further placed into the physiological context to stress the emerging roles played by IF1 in metabolic reprogramming in cancer, in hypoxia and in cellular differentiation. We review also the implication of IF1 in other cellular situations that involve the malfunctioning of mitochondria. Special emphasis is given to the role of IF1 as driver of the generation of a reactive oxygen species signal that, emanating from mitochondria, is able to reprogram the nucleus of the cell to confer by various signaling pathways a cell-death resistant phenotype against oxidative stress. Overall, our intention is to highlight the urgent need of further investigations in the molecular and cellular biology of IF1 and of its target, the ATP synthase, to unveil new therapeutic strategies in human pathology. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi.
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Affiliation(s)
- Javier García-Bermúdez
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid (CSIC-UAM), Centro de Investigación Biomédica en Red de Enfermedades Raras CIBERER-ISCIII, Instituto de Investigación Hospital 12 de Octubre, Universidad Autónoma de Madrid, 28049, Madrid, Spain
| | - José M Cuezva
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid (CSIC-UAM), Centro de Investigación Biomédica en Red de Enfermedades Raras CIBERER-ISCIII, Instituto de Investigación Hospital 12 de Octubre, Universidad Autónoma de Madrid, 28049, Madrid, Spain.
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20
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Viola H, Johnstone V, Cserne Szappanos H, Richman T, Tsoutsman T, Filipovska A, Semsarian C, Hool L. The L-type Ca(2+) channel facilitates abnormal metabolic activity in the cTnI-G203S mouse model of hypertrophic cardiomyopathy. J Physiol 2016; 594:4051-70. [PMID: 27062056 DOI: 10.1113/jp271681] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Accepted: 04/01/2016] [Indexed: 12/31/2022] Open
Abstract
KEY POINTS Genetic mutations in cardiac troponin I (cTnI) are associated with development of hypertrophic cardiomyopathy characterized by myocyte remodelling, disorganization of cytoskeletal proteins and altered energy metabolism. The L-type Ca(2+) channel is the main route for calcium influx and is crucial to cardiac excitation and contraction. The channel also regulates mitochondrial function in the heart by a functional communication between the channel and mitochondria via the cytoskeletal network. We find that L-type Ca(2+) channel kinetics are altered in cTnI-G203S cardiac myocytes and that activation of the channel causes a significantly greater increase in mitochondrial membrane potential and metabolic activity in cTnI-G203S cardiac myocytes. These responses occur as a result of impaired communication between the L-type Ca(2+) channel and cytoskeletal protein F-actin, involving decreased movement of actin-myosin and block of the mitochondrial voltage-dependent anion channel, resulting in a 'hypermetabolic' mitochondrial state. We propose that L-type Ca(2+) channel antagonists, such as diltiazem, might be effective in reducing the cardiomyopathy by normalizing mitochondrial metabolic activity. ABSTRACT Genetic mutations in cardiac troponin I (cTnI) account for 5% of families with hypertrophic cardiomyopathy. Hypertrophic cardiomyopathy is associated with disorganization of cytoskeletal proteins and altered energy metabolism. The L-type Ca(2+) channel (ICa-L ) plays an important role in regulating mitochondrial function. This involves a functional communication between the channel and mitochondria via the cytoskeletal network. We investigate the role of ICa-L in regulating mitochondrial function in 25- to 30-week-old cardiomyopathic mice expressing the human disease-causing mutation Gly203Ser in cTnI (cTnI-G203S). The inactivation rate of ICa-L is significantly faster in cTnI-G203S myocytes [cTnI-G203S: τ1 = 40.68 ± 3.22, n = 10 vs. wild-type (wt): τ1 = 59.05 ± 6.40, n = 6, P < 0.05]. Activation of ICa-L caused a greater increase in mitochondrial membrane potential (Ψm , 29.19 ± 1.85%, n = 15 vs. wt: 18.84 ± 2.01%, n = 10, P < 0.05) and metabolic activity (24.40 ± 6.46%, n = 8 vs. wt: 9.98 ± 1.57%, n = 9, P < 0.05). The responses occurred because of impaired communication between ICa-L and F-actin, involving lack of dynamic movement of actin-myosin and block of the mitochondrial voltage-dependent anion channel. Similar responses were observed in precardiomyopathic mice. ICa-L antagonists nisoldipine and diltiazem decreased Ψm to basal levels. We conclude that the Gly203Ser mutation leads to impaired functional communication between ICa-L and mitochondria, resulting in a 'hypermetabolic' state. This might contribute to development of cTnI-G203S cardiomyopathy because the response is present in young precardiomyopathic mice. ICa-L antagonists might be effective in reducing the cardiomyopathy by altering mitochondrial function.
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Affiliation(s)
- Helena Viola
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, WA, Australia
| | - Victoria Johnstone
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, WA, Australia
| | - Henrietta Cserne Szappanos
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, WA, Australia
| | - Tara Richman
- The Harry Perkins Institute for Medical Research, The University of Western Australia, Crawley, WA, Australia
| | - Tatiana Tsoutsman
- Agnes Ginges Centre for Molecular Cardiology, Centenary Institute, Sydney, NSW, Australia.,Sydney Medical School, University of Sydney, NSW, Australia
| | - Aleksandra Filipovska
- The Harry Perkins Institute for Medical Research, The University of Western Australia, Crawley, WA, Australia
| | - Christopher Semsarian
- Agnes Ginges Centre for Molecular Cardiology, Centenary Institute, Sydney, NSW, Australia.,Sydney Medical School, University of Sydney, NSW, Australia.,Department of Cardiology, Royal Prince Alfred Hospital, Sydney, NSW, Australia
| | - Livia Hool
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, WA, Australia.,Victor Chang Cardiac Research Institute, Sydney, NSW, Australia
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Vogt S, Rhiel A, Weber P, Ramzan R. Revisiting Kadenbach: Electron flux rate through cytochrome c-oxidase determines the ATP-inhibitory effect and subsequent production of ROS. Bioessays 2016; 38:556-67. [PMID: 27171124 PMCID: PMC5084804 DOI: 10.1002/bies.201600043] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Mitochondrial respiration is the predominant source of ATP. Excessive rates of electron transport cause a higher production of harmful reactive oxygen species (ROS). There are two regulatory mechanisms known. The first, according to Mitchel, is dependent on the mitochondrial membrane potential that drives ATP synthase for ATP production, and the second, the Kadenbach mechanism, is focussed on the binding of ATP to Cytochrome c Oxidase (CytOx) at high ATP/ADP ratios, which results in an allosteric conformational change to CytOx, causing inhibition. In times of stress, ATP-dependent inhibition is switched off and the activity of CytOx is exclusively determined by the membrane potential, leading to an increase in ROS production. The second mechanism for respiratory control depends on the quantity of electron transfer to the Heme aa3 of CytOx. When ATP is bound to CytOx the enzyme is inhibited, and ROS formation is decreased, although the mitochondrial membrane potential is increased.
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Affiliation(s)
- Sebastian Vogt
- Cardiovascular Research Lab, Biochemical Pharmacological Research CenterPhilipps‐University MarburgMarburgGermany
| | - Annika Rhiel
- Cardiovascular Research Lab, Biochemical Pharmacological Research CenterPhilipps‐University MarburgMarburgGermany
| | - Petra Weber
- Cardiovascular Research Lab, Biochemical Pharmacological Research CenterPhilipps‐University MarburgMarburgGermany
| | - Rabia Ramzan
- Cardiovascular Research Lab, Biochemical Pharmacological Research CenterPhilipps‐University MarburgMarburgGermany
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22
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Viola HM, Johnstone VPA, Cserne Szappanos H, Richman TR, Tsoutsman T, Filipovska A, Semsarian C, Seidman JG, Seidman CE, Hool LC. The Role of the L-Type Ca 2+ Channel in Altered Metabolic Activity in a Murine Model of Hypertrophic Cardiomyopathy. JACC Basic Transl Sci 2016; 1:61-72. [PMID: 30167506 PMCID: PMC6113168 DOI: 10.1016/j.jacbts.2015.12.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 12/31/2015] [Indexed: 01/08/2023]
Abstract
Heterozygous mice (αMHC403/+) expressing the human disease-causing mutation Arg403Gln exhibit cardinal features of hypertrophic cardiomyopathy (HCM) including hypertrophy, myocyte disarray, and increased myocardial fibrosis. Treatment of αMHC403/+mice with the L-type calcium channel (ICa-L) antagonist diltiazem has been shown to decrease left ventricular anterior wall thickness, cardiac myocyte hypertrophy, disarray, and fibrosis. However, the role of the ICa-L in the development of HCM is not known. In addition to maintaining cardiac excitation and contraction in myocytes, the ICa-L also regulates mitochondrial function through transmission of movement of ICa-L via cytoskeletal proteins to mitochondrial voltage-dependent anion channel. Here, the authors investigated the role of ICa-L in regulating mitochondrial function in αMHC403/+mice. Whole-cell patch clamp studies showed that ICa-L current inactivation kinetics were significantly increased in αMHC403/+cardiac myocytes, but that current density and channel expression were similar to wild-type cardiac myocytes. Activation of ICa-L caused a significantly greater increase in mitochondrial membrane potential and metabolic activity in αMHC403/+. These increases were attenuated with ICa-L antagonists and following F-actin or β-tubulin depolymerization. The authors observed increased levels of fibroblast growth factor-21 in αMHC403/+mice, and altered mitochondrial DNA copy number consistent with altered mitochondrial activity and the development of cardiomyopathy. These studies suggest that the Arg403Gln mutation leads to altered functional communication between ICa-L and mitochondria that is associated with increased metabolic activity, which may contribute to the development of cardiomyopathy. ICa-L antagonists may be effective in reducing the cardiomyopathy in HCM by altering metabolic activity. Heterozygous mice (αMHC403/+) expressing the human hypertrophic cardiomyopathy (HCM) disease causing mutation Arg403Gln exhibit cardinal features of HCM. This study investigated the role of L-type Ca2+ channel (ICa-L) in regulating mitochondrial function in Arg403Gln (αMHC403/+) mice. Activation of ICa-L in αMHC403/+mice caused a significantly greater increase in mitochondrial membrane potential and metabolic activity when compared to wild-type mice. Increases in mitochondrial membrane potential and metabolic activity were attenuated with ICa-L antagonists and when F-actin or β-tubulin were depolymerized. ICa-L antagonists may be effective in reducing the cardiomyopathy in HCM by altering metabolic activity.
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Affiliation(s)
- Helena M Viola
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, Australia
| | - Victoria P A Johnstone
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, Australia
| | - Henrietta Cserne Szappanos
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, Australia
| | - Tara R Richman
- The Harry Perkins Institute for Medical Research, The University of Western Australia, Crawley, Australia
| | - Tatiana Tsoutsman
- Agnes Ginges Centre for Molecular Cardiology, Centenary Institute, Sydney, Australia.,Sydney Medical School, University of Sydney, Australia
| | - Aleksandra Filipovska
- The Harry Perkins Institute for Medical Research, The University of Western Australia, Crawley, Australia
| | - Christopher Semsarian
- Agnes Ginges Centre for Molecular Cardiology, Centenary Institute, Sydney, Australia.,Sydney Medical School, University of Sydney, Australia.,Department of Cardiology, Royal Prince Alfred Hospital, Sydney, Australia
| | | | | | - Livia C Hool
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, Australia.,Victor Chang Cardiac Research Institute, Sydney, Australia
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23
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Yaniv Y, Ganesan A, Yang D, Ziman BD, Lyashkov AE, Levchenko A, Zhang J, Lakatta EG. Real-time relationship between PKA biochemical signal network dynamics and increased action potential firing rate in heart pacemaker cells: Kinetics of PKA activation in heart pacemaker cells. J Mol Cell Cardiol 2015; 86:168-78. [PMID: 26241846 PMCID: PMC4558217 DOI: 10.1016/j.yjmcc.2015.07.024] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Revised: 06/11/2015] [Accepted: 07/25/2015] [Indexed: 01/07/2023]
Abstract
cAMP-PKA protein kinase is a key nodal signaling pathway that regulates a wide range of heart pacemaker cell functions. These functions are predicted to be involved in regulation of spontaneous action potential (AP) generation of these cells. Here we investigate if the kinetics and stoichiometry of increase in PKA activity match the increase in AP firing rate in response to β-adrenergic receptor (β-AR) stimulation or phosphodiesterase (PDE) inhibition, that alters the AP firing rate of heart sinoatrial pacemaker cells. In cultured adult rabbit pacemaker cells infected with an adenovirus expressing the FRET sensor AKAR3, the EC50 in response to graded increases in the intensity of β-AR stimulation (by Isoproterenol) the magnitude of the increases in PKA activity and the spontaneous AP firing rate were similar (0.4±0.1nM vs. 0.6±0.15nM, respectively). Moreover, the kinetics (t1/2) of the increases in PKA activity and spontaneous AP firing rate in response to β-AR stimulation or PDE inhibition were tightly linked. We characterized the system rate-limiting biochemical reactions by integrating these experimentally derived data into a mechanistic-computational model. Model simulations predicted that phospholamban phosphorylation is a potent target of the increase in PKA activity that links to increase in spontaneous AP firing rate. In summary, the kinetics and stoichiometry of increases in PKA activity in response to a physiological (β-AR stimulation) or pharmacological (PDE inhibitor) stimuli match those of changes in the AP firing rate. Thus Ca(2+)-cAMP/PKA-dependent phosphorylation limits the rate and magnitude of increase in spontaneous AP firing rate.
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Affiliation(s)
- Yael Yaniv
- Biomedical Engineering Faculty, Technion-IIT, Haifa, Israel.
| | - Ambhighainath Ganesan
- Department of Biomedical Engineering, The Johns Hopkins University of Medicine, Baltimore, MD, USA
| | - Dongmei Yang
- Laboratory of Cardiovascular Science, Biomedical Research Center Intramural Research Program, National Institute on Aging, NIH, Baltimore, MD, USA
| | - Bruce D Ziman
- Laboratory of Cardiovascular Science, Biomedical Research Center Intramural Research Program, National Institute on Aging, NIH, Baltimore, MD, USA
| | - Alexey E Lyashkov
- Laboratory of Cardiovascular Science, Biomedical Research Center Intramural Research Program, National Institute on Aging, NIH, Baltimore, MD, USA
| | - Andre Levchenko
- System Biology Institute, Yale University, New Haven, CT, USA
| | - Jin Zhang
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD, USA; The Solomon H. Snyder Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD, USA; Department of Oncology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Edward G Lakatta
- Laboratory of Cardiovascular Science, Biomedical Research Center Intramural Research Program, National Institute on Aging, NIH, Baltimore, MD, USA.
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24
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Mizrahi R, Breitbart H. Mitochondrial PKA mediates sperm motility. Biochim Biophys Acta Gen Subj 2014; 1840:3404-12. [PMID: 25219457 DOI: 10.1016/j.bbagen.2014.09.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Revised: 08/03/2014] [Accepted: 09/03/2014] [Indexed: 11/26/2022]
Abstract
BACKGROUND Mitochondria are the major source of ATP to power sperm motility. Phosphorylation of mitochondrial proteins has been proposed as a major regulatory mechanism for mitochondrial bioenergetics. METHODS Sperm motility was measured by a computer-assisted analyzer, protein detection by western blotting, membrane potential by tetramethylrhodamine, cellular ATP by luciferase assay and localization of PKA by immuno-electron microscopy. RESULTS Bicarbonate is essential for the creation of mitochondrial electro-chemical gradient, ATP synthesis and sperm motility. Bicarbonate stimulates PKA-dependent phosphorylation of two 60kDa proteins identified as Tektin and glucose-6-phosphate isomerase. This phosphorylation was inhibited by respiration inhibition and phosphorylation could be restored by glucose in the presence of bicarbonate. However, this effect of glucose cannot be seen when the mitochondrial ATP/ADP exchanger was inhibited indicating that glycolytic-produced ATP is transported into the mitochondria and allows PKA-dependent protein phosphorylation inside the mitochondria. CONCLUSIONS Bicarbonate activates mitochondrial soluble adenylyl cyclase (sAC) which catalyzes cAMP production leading to the activation of mitochondrial PKA. Glucose can overcome the lack of ATP in the absence of bicarbonate but it cannot affect the mitochondrial sAC/PKA system, therefore the PKA-dependent phosphorylation of the 60kDa proteins does not occur in the absence of bicarbonate. GENERAL SIGNIFICANCE Production of CO2 in Krebs cycle, which is converted to bicarbonate is essential for sAC/PKA activation leading to mitochondrial membrane potential creation and ATP synthesis.
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Affiliation(s)
- Rashel Mizrahi
- The Mina & Everard Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 5290002, Israel
| | - Haim Breitbart
- The Mina & Everard Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 5290002, Israel.
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25
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Fernández-Sada E, Silva-Platas C, Villegas CA, Rivero SL, Willis BC, García N, Garza JR, Oropeza-Almazán Y, Valverde CA, Mazzocchi G, Zazueta C, Torre-Amione G, García-Rivas G. Cardiac responses to β-adrenoceptor stimulation is partly dependent on mitochondrial calcium uniporter activity. Br J Pharmacol 2014; 171:4207-21. [PMID: 24628066 DOI: 10.1111/bph.12684] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Revised: 02/06/2014] [Accepted: 03/01/2014] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND AND PURPOSE Despite the importance of mitochondrial Ca(2+) to metabolic regulation and cell physiology, little is known about the mechanisms that regulate Ca(2+) entry into the mitochondria. Accordingly, we established a system to determine the role of the mitochondrial Ca(2+) uniporter in an isolated heart model, at baseline and during increased workload following β-adrenoceptor stimulation. EXPERIMENTAL APPROACH Cardiac contractility, oxygen consumption and intracellular Ca(2+) transients were measured in ex vivo perfused murine hearts. Ru360 and spermine were used to modify mitochondrial Ca(2+) uniporter activity. Changes in mitochondrial Ca(2+) content and energetic phosphate metabolite levels were determined. KEY RESULTS The addition of Ru360 , a selective inhibitor of the mitochondrial Ca(2+) uniporter, induced progressively and sustained negative inotropic effects that were dose-dependent with an EC50 of 7 μM. Treatment with spermine, a uniporter agonist, showed a positive inotropic effect that was blocked by Ru360 . Inotropic stimulation with isoprenaline elevated oxygen consumption (2.7-fold), Ca(2+) -dependent activation of pyruvate dehydrogenase (5-fold) and mitochondrial Ca(2+) content (2.5-fold). However, in Ru360 -treated hearts, this parameter was attenuated. In addition, β-adrenoceptor stimulation in the presence of Ru360 did not affect intracellular Ca(2+) handling, PKA or Ca(2+) /calmodulin-dependent PK signalling. CONCLUSIONS AND IMPLICATIONS Inhibition of the mitochondrial Ca(2+) uniporter decreases β-adrenoceptor response, uncoupling between workload and production of energetic metabolites. Our results support the hypothesis that the coupling of workload and energy supply is partly dependent on mitochondrial Ca(2+) uniporter activity.
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Affiliation(s)
- E Fernández-Sada
- Cátedra de Cardiología y Medicina Vascular, Escuela de Medicina, Tecnológico de Monterrey, Monterrey, Nuevo León, México
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26
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Impaired functional communication between the L-type calcium channel and mitochondria contributes to metabolic inhibition in the mdx heart. Proc Natl Acad Sci U S A 2014; 111:E2905-14. [PMID: 24969422 DOI: 10.1073/pnas.1402544111] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Duchenne muscular dystrophy is a fatal X-linked disease characterized by the absence of dystrophin. Approximately 20% of boys will die of dilated cardiomyopathy that is associated with cytoskeletal protein disarray, contractile dysfunction, and reduced energy production. However, the mechanisms for altered energy metabolism are not yet fully clarified. Calcium influx through the L-type Ca(2+) channel is critical for maintaining cardiac excitation and contraction. The L-type Ca(2+) channel also regulates mitochondrial function and metabolic activity via transmission of movement of the auxiliary beta subunit through intermediate filament proteins. Here, we find that activation of the L-type Ca(2+) channel is unable to induce increases in mitochondrial membrane potential and metabolic activity in intact cardiac myocytes from the murine model of Duchenne muscular dystrophy (mdx) despite robust increases recorded in wt myocytes. Treatment of mdx mice with morpholino oligomers to induce exon skipping of dystrophin exon 23 (that results in functional dystrophin accumulation) or application of a peptide that resulted in block of voltage-dependent anion channel (VDAC) "rescued" mitochondrial membrane potential and metabolic activity in mdx myocytes. The mitochondrial VDAC coimmunoprecipitated with the L-type Ca(2+) channel. We conclude that the absence of dystrophin in the mdx ventricular myocyte leads to impaired functional communication between the L-type Ca(2+) channel and mitochondrial VDAC. This appears to contribute to metabolic inhibition. These findings provide new mechanistic and functional insight into cardiomyopathy associated with Duchenne muscular dystrophy.
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27
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Viola HM, Jordan MC, Roos KP, Hool LC. Decreased myocardial injury and improved contractility after administration of a peptide derived against the alpha-interacting domain of the L-type calcium channel. J Am Heart Assoc 2014; 3:e000961. [PMID: 24958783 PMCID: PMC4309103 DOI: 10.1161/jaha.114.000961] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Background Myocardial infarction remains the leading cause of morbidity and mortality associated with coronary artery disease. The L‐type calcium channel (ICa‐L) is critical to excitation and contraction. Activation of the channel also alters mitochondrial function. Here, we investigated whether application of a alpha‐interacting domain/transactivator of transcription (AID‐TAT) peptide, which immobilizes the auxiliary β2 subunit of the channel and decreases metabolic demand, could alter mitochondrial function and myocardial injury. Methods and Results Treatment with AID‐TAT peptide decreased ischemia‐reperfusion injury in guinea‐pig hearts ex vivo (n=11) and in rats in vivo (n=9) assessed with uptake of nitroblue tetrazolium, release of creatine kinase, and lactate dehydrogenase. Contractility (assessed with catheterization of the left ventricle) was improved after application of AID‐TAT peptide in hearts ex vivo (n=6) and in vivo (n=8) up to 12 weeks before sacrifice. In search of the mechanism for the effect, we found that intracellular calcium ([Ca2+]i, Fura‐2), superoxide production (dihydroethidium fluorescence), mitochondrial membrane potential (Ψm, JC‐1 fluorescence), reduced nicotinamide adenine dinucleotide production, and flavoprotein oxidation (autofluorescence) are decreased after application of AID‐TAT peptide. Conclusions Application of AID‐TAT peptide significantly decreased infarct size and supported contractility up to 12 weeks postcoronary artery occlusion as a result of a decrease in metabolic demand during reperfusion.
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Affiliation(s)
- Helena M Viola
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, WA, Australia (H.M.V., L.C.H.)
| | - Maria C Jordan
- Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA (M.C.J., K.P.R.)
| | - Kenneth P Roos
- Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA (M.C.J., K.P.R.)
| | - Livia C Hool
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, WA, Australia (H.M.V., L.C.H.)
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28
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Mechanisms of beat-to-beat regulation of cardiac pacemaker cell function by Ca²⁺ cycling dynamics. Biophys J 2014; 105:1551-61. [PMID: 24094396 DOI: 10.1016/j.bpj.2013.08.024] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2013] [Revised: 07/08/2013] [Accepted: 08/15/2013] [Indexed: 01/31/2023] Open
Abstract
Whether intracellular Ca(2+) cycling dynamics regulate cardiac pacemaker cell function on a beat-to-beat basis remains unknown. Here we show that under physiological conditions, application of low concentrations of caffeine (2-4 mM) to isolated single rabbit sinoatrial node cells acutely reduces their spontaneous action potential cycle length (CL) and increases Ca(2+) transient amplitude for several cycles. Numerical simulations, using a modified Maltsev-Lakatta coupled-clock model, faithfully reproduced these effects, and also the effects of CL prolongation and dysrhythmic spontaneous beating (produced by cytosolic Ca(2+) buffering) and an acute CL reduction (produced by flash-induced Ca(2+) release from a caged Ca(2+) buffer), which we had reported previously. Three contemporary numerical models (including the original Maltsev-Lakatta model) failed to reproduce the experimental results. In our proposed new model, Ca(2+) releases acutely change the CL via activation of the Na(+)/Ca(2+) exchanger current. Time-dependent CL reductions after flash-induced Ca(2+) releases (the memory effect) are linked to changes in Ca(2+) available for pumping into sarcoplasmic reticulum which, in turn, changes the sarcoplasmic reticulum Ca(2+) load, diastolic Ca(2+) releases, and Na(+)/Ca(2+) exchanger current. These results support the idea that Ca(2+) regulates CL in cardiac pacemaker cells on a beat-to-beat basis, and suggest a more realistic numerical mechanism of this regulation.
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29
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Maltsev VA, Yaniv Y, Maltsev AV, Stern MD, Lakatta EG. Modern perspectives on numerical modeling of cardiac pacemaker cell. J Pharmacol Sci 2014; 125:6-38. [PMID: 24748434 DOI: 10.1254/jphs.13r04cr] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Cardiac pacemaking is a complex phenomenon that is still not completely understood. Together with experimental studies, numerical modeling has been traditionally used to acquire mechanistic insights in this research area. This review summarizes the present state of numerical modeling of the cardiac pacemaker, including approaches to resolve present paradoxes and controversies. Specifically we discuss the requirement for realistic modeling to consider symmetrical importance of both intracellular and cell membrane processes (within a recent "coupled-clock" theory). Promising future developments of the complex pacemaker system models include the introduction of local calcium control, mitochondria function, and biochemical regulation of protein phosphorylation and cAMP production. Modern numerical and theoretical methods such as multi-parameter sensitivity analyses within extended populations of models and bifurcation analyses are also important for the definition of the most realistic parameters that describe a robust, yet simultaneously flexible operation of the coupled-clock pacemaker cell system. The systems approach to exploring cardiac pacemaker function will guide development of new therapies such as biological pacemakers for treating insufficient cardiac pacemaker function that becomes especially prevalent with advancing age.
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Affiliation(s)
- Victor A Maltsev
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, USA
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30
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Yaniv Y, Maltsev VA. Numerical Modeling Calcium and CaMKII Effects in the SA Node. Front Pharmacol 2014; 5:58. [PMID: 24744732 PMCID: PMC3978345 DOI: 10.3389/fphar.2014.00058] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2014] [Accepted: 03/16/2014] [Indexed: 11/13/2022] Open
Abstract
Sinoatrial node (SAN) is the primary heart pacemaker which initiates each heartbeat under normal conditions. Numerous experimental data have demonstrated that Ca(2+-) and CaMKII-dependent processes are crucially important for regulation of SAN cells. However, specific mechanisms of this regulation and their relative contribution to pacemaker function remain mainly unknown. Our review summarizes available data and existing numerical modeling approaches to understand Ca(2+) and CaMKII effects on the SAN. Data interpretation and future directions to address the problem are given within the coupled-clock theory, i.e., a modern view on the cardiac pacemaker cell function generated by a system of sarcolemmal and intracellular proteins.
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Affiliation(s)
- Yael Yaniv
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging - National Institutes of Health Baltimore, MD, USA ; Department of Biomedical Engineering, Technion - Israel Institute of Technology Haifa, Israel
| | - Victor A Maltsev
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging - National Institutes of Health Baltimore, MD, USA
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31
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Monfredi O, Maltsev VA, Lakatta EG. Modern concepts concerning the origin of the heartbeat. Physiology (Bethesda) 2014; 28:74-92. [PMID: 23455768 DOI: 10.1152/physiol.00054.2012] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Physiological processes governing the heart beat have been under investigation for several hundred years. Major advances have been made in the recent past. A review of the present paradigm is presented here, including a look back at important steps that led us to where we are today, alongside a glimpse into the exciting future of pacemaker research.
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Affiliation(s)
- Oliver Monfredi
- Institute of Cardiovascular Sciences, University of Manchester, Manchester, UK
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32
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Groenke S, Larson ED, Alber S, Zhang R, Lamp ST, Ren X, Nakano H, Jordan MC, Karagueuzian HS, Roos KP, Nakano A, Proenza C, Philipson KD, Goldhaber JI. Complete atrial-specific knockout of sodium-calcium exchange eliminates sinoatrial node pacemaker activity. PLoS One 2013; 8:e81633. [PMID: 24278453 PMCID: PMC3836769 DOI: 10.1371/journal.pone.0081633] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2013] [Accepted: 10/25/2013] [Indexed: 11/18/2022] Open
Abstract
The origin of sinoatrial node (SAN) pacemaker activity in the heart is controversial. The leading candidates are diastolic depolarization by "funny" current (If) through HCN4 channels (the "Membrane Clock" hypothesis), depolarization by cardiac Na-Ca exchange (NCX1) in response to intracellular Ca cycling (the "Calcium Clock" hypothesis), and a combination of the two ("Coupled Clock"). To address this controversy, we used Cre/loxP technology to generate atrial-specific NCX1 KO mice. NCX1 protein was undetectable in KO atrial tissue, including the SAN. Surface ECG and intracardiac electrograms showed no atrial depolarization and a slow junctional escape rhythm in KO that responded appropriately to β-adrenergic and muscarinic stimulation. Although KO atria were quiescent they could be stimulated by external pacing suggesting that electrical coupling between cells remained intact. Despite normal electrophysiological properties of If in isolated patch clamped KO SAN cells, pacemaker activity was absent. Recurring Ca sparks were present in all KO SAN cells, suggesting that Ca cycling persists but is uncoupled from the sarcolemma. We conclude that NCX1 is required for normal pacemaker activity in murine SAN.
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Affiliation(s)
- Sabine Groenke
- Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
| | - Eric D. Larson
- Department of Physiology & Biophysics, University of Colorado School of Medicine, Denver, Colorado, United States of America
| | - Sarah Alber
- Department of Physiology & Biophysics, University of Colorado School of Medicine, Denver, Colorado, United States of America
| | - Rui Zhang
- Heart Institute, Cedars-Sinai Medical Center, Los Angeles, California, United States of America
| | - Scott T. Lamp
- Heart Institute, Cedars-Sinai Medical Center, Los Angeles, California, United States of America
| | - Xiaoyan Ren
- Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
| | - Haruko Nakano
- Department of Molecular, Cell and Developmental Biology, Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research, University of California Los Angeles, Los Angeles, California, United States of America
| | - Maria C. Jordan
- Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
| | - Hrayr S. Karagueuzian
- Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
| | - Kenneth P. Roos
- Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
| | - Atsushi Nakano
- Department of Molecular, Cell and Developmental Biology, Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research, University of California Los Angeles, Los Angeles, California, United States of America
| | - Catherine Proenza
- Department of Physiology & Biophysics, University of Colorado School of Medicine, Denver, Colorado, United States of America
| | - Kenneth D. Philipson
- Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America
| | - Joshua I. Goldhaber
- Heart Institute, Cedars-Sinai Medical Center, Los Angeles, California, United States of America
- * E-mail:
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33
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Lakatta EG, Yaniv Y, Maltsev VA. Minding the gaps that link intrinsic circadian clock within the heart to its intrinsic ultradian pacemaker clocks. Focus on "The cardiomyocyte molecular clock, regulation of Scn5a, and arrhythmia susceptibility". Am J Physiol Cell Physiol 2013; 304:C941-4. [PMID: 23485714 PMCID: PMC3651642 DOI: 10.1152/ajpcell.00072.2013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Yaniv Y, Spurgeon HA, Ziman BD, Lyashkov AE, Lakatta EG. Mechanisms that match ATP supply to demand in cardiac pacemaker cells during high ATP demand. Am J Physiol Heart Circ Physiol 2013; 304:H1428-38. [PMID: 23604710 DOI: 10.1152/ajpheart.00969.2012] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The spontaneous action potential (AP) firing rate of sinoatrial node cells (SANCs) involves high-throughput signaling via Ca(2+)-calmodulin activated adenylyl cyclases (AC), cAMP-mediated protein kinase A (PKA), and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII)-dependent phosphorylation of SR Ca(2+) cycling and surface membrane ion channel proteins. When the throughput of this signaling increases, e.g., in response to β-adrenergic receptor activation, the resultant increase in spontaneous AP firing rate increases the demand for ATP. We hypothesized that an increase of ATP production to match the increased ATP demand is achieved via a direct effect of increased mitochondrial Ca(2+) (Ca(2+)m) and an indirect effect via enhanced Ca(2+)-cAMP/PKA-CaMKII signaling to mitochondria. To increase ATP demand, single isolated rabbit SANCs were superfused by physiological saline at 35 ± 0.5°C with isoproterenol, or by phosphodiesterase or protein phosphatase inhibition. We measured cytosolic and mitochondrial Ca(2+) and flavoprotein fluorescence in single SANC, and we measured cAMP, ATP, and O₂ consumption in SANC suspensions. Although the increase in spontaneous AP firing rate was accompanied by an increase in O₂ consumption, the ATP level and flavoprotein fluorescence remained constant, indicating that ATP production had increased. Both Ca(2+)m and cAMP increased concurrently with the increase in AP firing rate. When Ca(2+)m was reduced by Ru360, the increase in spontaneous AP firing rate in response to isoproterenol was reduced by 25%. Thus, both an increase in Ca(2+)m and an increase in Ca(2+) activated cAMP-PKA-CaMKII signaling regulate the increase in ATP supply to meet ATP demand above the basal level.
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Affiliation(s)
- Yael Yaniv
- Laboratory of Cardiovascular Science, Gerontology Research Center, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
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Maltsev VA, Lakatta EG. Numerical models based on a minimal set of sarcolemmal electrogenic proteins and an intracellular Ca(2+) clock generate robust, flexible, and energy-efficient cardiac pacemaking. J Mol Cell Cardiol 2013; 59:181-95. [PMID: 23507256 DOI: 10.1016/j.yjmcc.2013.03.004] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Revised: 02/26/2013] [Accepted: 03/02/2013] [Indexed: 10/27/2022]
Abstract
Recent evidence supports the idea that robust and, importantly, FLEXIBLE automaticity of cardiac pacemaker cells is conferred by a coupled system of membrane ion currents (an "M-clock") and a sarcoplasmic reticulum (SR)-based Ca(2+) oscillator ("Ca(2+)clock") that generates spontaneous diastolic Ca(2+) releases. This study identified numerical models of a human biological pacemaker that features robust and flexible automaticity generated by a minimal set of electrogenic proteins and a Ca(2+)clock. Following the Occam's razor principle (principle of parsimony), M-clock components of unknown molecular origin were excluded from Maltsev-Lakatta pacemaker cell model and thirteen different model types of only 4 or 5 components were derived and explored by a parametric sensitivity analysis. The extended ranges of SR Ca(2+) pumping (i.e. Ca(2+)clock performance) and conductance of ion currents were sampled, yielding a large variety of parameter combination, i.e. specific model sets. We tested each set's ability to simulate autonomic modulation of human heart rate (minimum rate of 50 to 70bpm; maximum rate of 140 to 210bpm) in response to stimulation of cholinergic and β-adrenergic receptors. We found that only those models that include a Ca(2+)clock (including the minimal 4-parameter model "ICaL+IKr+INCX+Ca(2+)clock") were able to reproduce the full range of autonomic modulation. Inclusion of If or ICaT decreased the flexibility, but increased the robustness of the models (a relatively larger number of sets did not fail during testing). The new models comprised of components with clear molecular identity (i.e. lacking IbNa & Ist) portray a more realistic pacemaking: A smaller Na(+) influx is expected to demand less energy for Na(+) extrusion. The new large database of the reduced coupled-clock numerical models may serve as a useful tool for the design of biological pacemakers. It will also provide a conceptual basis for a general theory of robust, flexible, and energy-efficient pacemaking based on realistic components.
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Affiliation(s)
- Victor A Maltsev
- Laboratory of Cardiovascular Science, NIA, NIH, 251 Bayview Blvd., Baltimore, MD 21224, USA.
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Yaniv Y, Spurgeon HA, Ziman BD, Lakatta EG. Ca²+/calmodulin-dependent protein kinase II (CaMKII) activity and sinoatrial nodal pacemaker cell energetics. PLoS One 2013; 8:e57079. [PMID: 23459256 PMCID: PMC3581576 DOI: 10.1371/journal.pone.0057079] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2012] [Accepted: 01/18/2013] [Indexed: 11/18/2022] Open
Abstract
UNLABELLED : Ca(2+)-activated basal adenylate cyclase (AC) in rabbit sinoatrial node cells (SANC) guarantees, via basal cAMP/PKA-calmodulin/CaMKII-dependent protein phosphorylation, the occurrence of rhythmic, sarcoplasmic-reticulum generated, sub-membrane Ca(2+) releases that prompt rhythmic, spontaneous action potentials (APs). This high-throughput signaling consumes ATP. AIMS We have previously demonstrated that basal AC-cAMP/PKA signaling directly, and Ca(2+) indirectly, regulate mitochondrial ATP production. While, clearly, Ca(2+)-calmodulin-CaMKII activity regulates ATP consumption, whether it has a role in the control of ATP production is unknown. METHODS AND RESULTS We superfused single, isolated rabbit SANC at 37°C with physiological saline containing CaMKII inhibitors, (KN-93 or autocamtide-2 Related Inhibitory Peptide (AIP)), or a calmodulin inhibitor (W-7) and measured cytosolic Ca(2+), flavoprotein fluorescence and spontaneous AP firing rate. We measured cAMP, ATP and O2 consumption in cell suspensions. Graded reductions in basal CaMKII activity by KN-93 (0.5-3 µmol/L) or AIP (2-10 µmol/L) markedly slow the kinetics of intracellular Ca(2+) cycling, decrease the spontaneous AP firing rate, decrease cAMP, and reduce O2 consumption and flavoprotein fluorescence. In this context of graded reductions in ATP demand, however, ATP also becomes depleted, indicating reduced ATP production. CONCLUSIONS CaMKII signaling, a crucial element of normal automaticity in rabbit SANC, is also involved in SANC bioenergetics.
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Affiliation(s)
- Yael Yaniv
- Laboratory of Cardiovascular Science, Gerontology Research Center, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Harold A. Spurgeon
- Laboratory of Cardiovascular Science, Gerontology Research Center, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Bruce D. Ziman
- Laboratory of Cardiovascular Science, Gerontology Research Center, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Edward G. Lakatta
- Laboratory of Cardiovascular Science, Gerontology Research Center, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
- * E-mail:
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Yaniv Y, Maltsev VA, Ziman BD, Spurgeon HA, Lakatta EG. The "funny" current (I(f)) inhibition by ivabradine at membrane potentials encompassing spontaneous depolarization in pacemaker cells. Molecules 2012; 17:8241-54. [PMID: 22777191 PMCID: PMC4523892 DOI: 10.3390/molecules17078241] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2012] [Revised: 07/03/2012] [Accepted: 07/04/2012] [Indexed: 11/16/2022] Open
Abstract
Recent clinical trials have shown that ivabradine (IVA), a drug that inhibits the funny current (I(f)) in isolated sinoatrial nodal cells (SANC), decreases heart rate and reduces morbidity and mortality in patients with cardiovascular diseases. While IVA inhibits I(f), this effect has been reported at essentially unphysiological voltages, i.e., those more negative than the spontaneous diastolic depolarization (DD) between action potentials (APs). We tested the relative potency of IVA to block I(f) over a wide range of membrane potentials, including those that encompass DD governing to the SANC spontaneous firing rate. A clinically relevant IVA concentration of 3 μM to single, isolated rabbit SANC slowed the spontaneous AP firing rate by 15%. During voltage clamp the maximal I(f) was 18 ± 3 pA/pF (at -120 mV) and the maximal I(f) reduction by IVA was 60 ± 8% observed at -92 ± 4 mV. At the maximal diastolic depolarization (~-60 mV) I(f) amplitude was only -2.9 ± 0.4 pA/pF, and was reduced by only 41 ± 6% by IVA. Thus, I(f) amplitude and its inhibition by IVA at physiologically relevant membrane potentials are substantially less than that at unphysiological (hyperpolarized) membrane potentials. This novel finding more accurately describes how IVA affects SANC function and is of direct relevance to numerical modeling of SANC automaticity.
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Affiliation(s)
| | | | | | | | - Edward G. Lakatta
- Author to whom correspondence should be addressed; ; Tel.: +1-410-558-8202; Fax: +1-410-558-8150
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Yaniv Y, Spurgeon HA, Lyashkov AE, Yang D, Ziman BD, Maltsev VA, Lakatta EG. Crosstalk between mitochondrial and sarcoplasmic reticulum Ca2+ cycling modulates cardiac pacemaker cell automaticity. PLoS One 2012; 7:e37582. [PMID: 22666369 PMCID: PMC3362629 DOI: 10.1371/journal.pone.0037582] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Accepted: 04/22/2012] [Indexed: 01/02/2023] Open
Abstract
Background Mitochondria dynamically buffer cytosolic Ca2+ in cardiac ventricular cells and this affects the Ca2+ load of the sarcoplasmic reticulum (SR). In sinoatrial-node cells (SANC) the SR generates periodic local, subsarcolemmal Ca2+ releases (LCRs) that depend upon the SR load and are involved in SANC automaticity: LCRs activate an inward Na+-Ca2+ exchange current to accelerate the diastolic depolarization, prompting the ensemble of surface membrane ion channels to generate the next action potential (AP). Objective To determine if mitochondrial Ca2+ (Ca2+m), cytosolic Ca2+ (Ca2+c)-SR-Ca2+ crosstalk occurs in single rabbit SANC, and how this may relate to SANC normal automaticity. Results Inhibition of mitochondrial Ca2+ influx into (Ru360) or Ca2+ efflux from (CGP-37157) decreased [Ca2+]m to 80±8% control or increased [Ca2+]m to 119±7% control, respectively. Concurrent with inhibition of mitochondrial Ca2+ influx or efflux, the SR Ca2+ load, and LCR size, duration, amplitude and period (imaged via confocal linescan) significantly increased or decreased, respectively. Changes in total ensemble LCR Ca2+ signal were highly correlated with the change in the SR Ca2+ load (r2 = 0.97). Changes in the spontaneous AP cycle length (Ru360, 111±1% control; CGP-37157, 89±2% control) in response to changes in [Ca2+]m were predicted by concurrent changes in LCR period (r2 = 0.84). Conclusion A change in SANC Ca2+m flux translates into a change in the AP firing rate by effecting changes in Ca2+c and SR Ca2+ loading, which affects the characteristics of spontaneous SR Ca2+ release.
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Affiliation(s)
- Yael Yaniv
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Harold A. Spurgeon
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Alexey E. Lyashkov
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Dongmei Yang
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Bruce D. Ziman
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Victor A. Maltsev
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
| | - Edward G. Lakatta
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, United States of America
- * E-mail:
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