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Neeman-Egozi S, Livneh I, Dolgopyat I, Nussinovitch U, Milman H, Cohen N, Eisen B, Ciechanover A, Binah O. Stress-Induced Proteasome Sub-Cellular Translocation in Cardiomyocytes Causes Altered Intracellular Calcium Handling and Arrhythmias. Int J Mol Sci 2024; 25:4932. [PMID: 38732146 PMCID: PMC11084437 DOI: 10.3390/ijms25094932] [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: 03/10/2024] [Revised: 04/18/2024] [Accepted: 04/24/2024] [Indexed: 05/13/2024] Open
Abstract
The ubiquitin-proteasome system (UPS) is an essential mechanism responsible for the selective degradation of substrate proteins via their conjugation with ubiquitin. Since cardiomyocytes have very limited self-renewal capacity, as they are prone to protein damage due to constant mechanical and metabolic stress, the UPS has a key role in cardiac physiology and pathophysiology. While altered proteasomal activity contributes to a variety of cardiac pathologies, such as heart failure and ischemia/reperfusion injury (IRI), the environmental cues affecting its activity are still unknown, and they are the focus of this work. Following a recent study by Ciechanover's group showing that amino acid (AA) starvation in cultured cancer cell lines modulates proteasome intracellular localization and activity, we tested two hypotheses in human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs, CMs): (i) AA starvation causes proteasome translocation in CMs, similarly to the observation in cultured cancer cell lines; (ii) manipulation of subcellular proteasomal compartmentalization is associated with electrophysiological abnormalities in the form of arrhythmias, mediated via altered intracellular Ca2+ handling. The major findings are: (i) starving CMs to AAs results in proteasome translocation from the nucleus to the cytoplasm, while supplementation with the aromatic amino acids tyrosine (Y), tryptophan (W) and phenylalanine (F) (YWF) inhibits the proteasome recruitment; (ii) AA-deficient treatments cause arrhythmias; (iii) the arrhythmias observed upon nuclear proteasome sequestration(-AA+YWF) are blocked by KB-R7943, an inhibitor of the reverse mode of the sodium-calcium exchanger NCX; (iv) the retrograde perfusion of isolated rat hearts with AA starvation media is associated with arrhythmias. Collectively, our novel findings describe a newly identified mechanism linking the UPS to arrhythmia generation in CMs and whole hearts.
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Affiliation(s)
- Shunit Neeman-Egozi
- Department of Physiology, Biophysics and Systems Biology, Rappaport Faculty of Medicine, Technion—Israel Institute of Technology, Haifa 3190601, Israel; (S.N.-E.); (B.E.)
| | - Ido Livneh
- The Rappaport-Technion Integrated Cancer Center (R-TICC) and The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa 319060, Israel; (I.L.); (N.C.)
| | - Irit Dolgopyat
- Department of Physiology, Biophysics and Systems Biology, Rappaport Faculty of Medicine, Technion—Israel Institute of Technology, Haifa 3190601, Israel; (S.N.-E.); (B.E.)
| | - Udi Nussinovitch
- Department of Cardiology, Edith Wolfson Medical Center, Holon 5822012, Israel
- The Faculty of Medicine, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Helena Milman
- Department of Physiology, Biophysics and Systems Biology, Rappaport Faculty of Medicine, Technion—Israel Institute of Technology, Haifa 3190601, Israel; (S.N.-E.); (B.E.)
| | - Nadav Cohen
- The Rappaport-Technion Integrated Cancer Center (R-TICC) and The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa 319060, Israel; (I.L.); (N.C.)
| | - Binyamin Eisen
- Department of Physiology, Biophysics and Systems Biology, Rappaport Faculty of Medicine, Technion—Israel Institute of Technology, Haifa 3190601, Israel; (S.N.-E.); (B.E.)
| | - Aaron Ciechanover
- The Rappaport-Technion Integrated Cancer Center (R-TICC) and The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa 319060, Israel; (I.L.); (N.C.)
| | - Ofer Binah
- Department of Physiology, Biophysics and Systems Biology, Rappaport Faculty of Medicine, Technion—Israel Institute of Technology, Haifa 3190601, Israel; (S.N.-E.); (B.E.)
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Barton GP, de Lange WJ, Ralphe JC, Aiken J, Diffee G. Linking metabolic and contractile dysfunction in aged cardiac myocytes. Physiol Rep 2017; 5:5/20/e13485. [PMID: 29084842 PMCID: PMC5661240 DOI: 10.14814/phy2.13485] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 10/02/2017] [Accepted: 10/03/2017] [Indexed: 02/06/2023] Open
Abstract
Aging is associated with declining cardiac contractile function as well as changes in metabolism and mitochondrial function. The relationship between age‐related changes in cardiac metabolism and declining cardiac contractile function has not been determined. In order to define the role energetics play in changes in contractile function, we measured mitochondrial NADH, [NADH]m, during continuous contractions of isolated left ventricular myocytes from young (Y) and old (O) FBN rats. Second, we explored the role of metabolic disruption with rotenone and increased workload with isoproterenol (ISO) had on age‐related changes in myocytes shortening. Single, intact myocytes were stimulated for 10 min of continuous contraction at either 2 Hz or 4 Hz while being perfused with Ringer's solution. Properties of shortening (peak shortening and rate of shortening) were measured at the onset (T0) and after 10 min (T10) of continuous contraction, and the decline in shortening over time (T10/T0) was determined. Although young and old myocytes had similar contractile function under resting conditions, old myocytes demonstrated decrements in [NADH]m during continuous stimulation, while young myocytes maintained constant [NADH]m over this time. In addition, old myocytes exhibited impaired contractile function to a workload (ISO) and metabolic (rotenone) stress compared to young myocytes. Taken together, these results demonstrated that old myocytes are susceptible to stress‐induced contractile dysfunction which may be related to altered cellular energetics.
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Affiliation(s)
- Gregory P Barton
- Balke Biodynamics Laboratory, Department of Kinesiology, University of Wisconsin-Madison, Madison, Wisconsin
| | - Willem J de Lange
- Department of Pediatrics, University of Wisconsin-Madison, Madison, Wisconsin
| | - John C Ralphe
- Department of Pediatrics, University of Wisconsin-Madison, Madison, Wisconsin
| | - Judd Aiken
- Department of Agriculture, Food, and Nutritional Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Gary Diffee
- Balke Biodynamics Laboratory, Department of Kinesiology, University of Wisconsin-Madison, Madison, Wisconsin
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Alexander-Shani R, Mreisat A, Smeir E, Gerstenblith G, Stern MD, Horowitz M. Long-term HIF-1α transcriptional activation is essential for heat-acclimation-mediated cross tolerance: mitochondrial target genes. Am J Physiol Regul Integr Comp Physiol 2017; 312:R753-R762. [PMID: 28274939 DOI: 10.1152/ajpregu.00461.2016] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 03/01/2017] [Accepted: 03/03/2017] [Indexed: 11/22/2022]
Abstract
An important adaptive feature of heat acclimation (HA) is the induction of cross tolerance against novel stressors (HACT) Reprogramming of gene expression leading to enhanced innate cytoprotective features by attenuating damage and/or enhancing the response of "help" signals plays a pivotal role. Hypoxia-inducible factor-1α (HIF-1α), constitutively upregulated by HA (1 mo, 34°C), is a crucial transcription factor in this program, although its specific role is as yet unknown. By using a rat HA model, we studied the impact of disrupting HIF-1α transcriptional activation [HIF-1α:HIF-1β dimerization blockade by intraperitoneal acriflavine (4 mg/kg)] on its mitochondrial gene targets [phosphoinositide-dependent kinase-1 (PDK1), LON, and cyclooxygenase 4 (COX4) isoforms] in the HA rat heart. Physiological measures of cardiac HACT were infarct size after ischemia-reperfusion and time to rigor contracture during hypoxia in cardiomyocytes. We show that HACT requires transcriptional activation of HIF-1α throughout the course of HA and that this activation is accompanied by two metabolic switches: 1) profound upregulation of PDK1, which reduces pyruvate entry into the mitochondria, consequently increasing glycolytic lactate production; 2) remodeling of the COX4 isoform ratio, inducing hypoxic-tolerant COX4.2 dominance, and optimizing electron transfer and possibly ATP production during the ischemic and hypoxic insults. LON and COX4.2 transcript upregulation accompanied this shift. Loss of HACT despite elevated expression of the cytoprotective protein heat shock protein-72 concomitantly with disrupted HIF-1α dimerization suggests that HIF-1α is essential for HACT. The role of a PDK1 metabolic switch is well known in hypoxia acclimation but not in the HA model and its ischemic setting. Remodeling of COX4 isoforms by environmental acclimation is a novel finding.
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Affiliation(s)
- Rivka Alexander-Shani
- Laboratory of Environmental Physiology, Faculty of Dental Medicine, The Hebrew University, Jerusalem, Israel
| | - Ahmad Mreisat
- Laboratory of Environmental Physiology, Faculty of Dental Medicine, The Hebrew University, Jerusalem, Israel
| | - Elia Smeir
- Laboratory of Environmental Physiology, Faculty of Dental Medicine, The Hebrew University, Jerusalem, Israel
| | | | - Michael D Stern
- Gerontology Research Center, National Institute on Aging, Baltimore, Maryland
| | - Michal Horowitz
- Laboratory of Environmental Physiology, Faculty of Dental Medicine, The Hebrew University, Jerusalem, Israel;
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Ben-Ari M, Schick R, Barad L, Novak A, Ben-Ari E, Lorber A, Itskovitz-Eldor J, Rosen MR, Weissman A, Binah O. From beat rate variability in induced pluripotent stem cell-derived pacemaker cells to heart rate variability in human subjects. Heart Rhythm 2014; 11:1808-1818. [PMID: 25052725 PMCID: PMC4283811 DOI: 10.1016/j.hrthm.2014.05.037] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Indexed: 01/27/2023]
Abstract
BACKGROUND We previously reported that induced pluripotent stem cell-derived cardiomyocytes manifest beat rate variability (BRV) resembling heart rate variability (HRV) in the human sinoatrial node. We now hypothesized the BRV-HRV continuum originates in pacemaker cells. OBJECTIVE To investigate whether cellular BRV is a source of HRV dynamics, we hypothesized 3 levels of interaction among different cardiomyocyte entities: (1) single pacemaker cells, (2) networks of electrically coupled pacemaker cells, and (3) the in situ sinoatrial node. METHODS We measured BRV/HRV properties in single pacemaker cells, induced pluripotent stem cell-derived contracting embryoid bodies (EBs), and electrocardiograms from the same individual. RESULTS Pronounced BRV/HRV was present at all 3 levels. The coefficient of variance of interbeat intervals and Poincaré plot indices SD1 and SD2 for single cells were 20 times greater than those for EBs (P < .05) and the in situ heart (the latter two were similar; P > .05). We also compared BRV magnitude among single cells, small EBs (~5-10 cells), and larger EBs (>10 cells): BRV indices progressively increased with the decrease in the cell number (P < .05). Disrupting intracellular Ca(2+) handling markedly augmented BRV magnitude, revealing a unique bimodal firing pattern, suggesting that intracellular mechanisms contribute to BRV/HRV and the fractal behavior of heart rhythm. CONCLUSION The decreased BRV magnitude in transitioning from the single cell to the EB suggests that the HRV of in situ hearts originates from the summation and integration of multiple cell-based oscillators. Hence, complex interactions among multiple pacemaker cells and intracellular Ca(2+) handling determine HRV in humans and cardiomyocyte networks.
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Affiliation(s)
- Meital Ben-Ari
- The Sohnis Family Stem Cells Center, Technion, Haifa, Israel
- The Rappaport Institute, Technion, Haifa, Israel
- Ruth & Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel
| | - Revital Schick
- The Sohnis Family Stem Cells Center, Technion, Haifa, Israel
- The Rappaport Institute, Technion, Haifa, Israel
- Ruth & Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel
| | - Lili Barad
- The Sohnis Family Stem Cells Center, Technion, Haifa, Israel
- The Rappaport Institute, Technion, Haifa, Israel
- Ruth & Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel
| | - Atara Novak
- The Sohnis Family Stem Cells Center, Technion, Haifa, Israel
- The Rappaport Institute, Technion, Haifa, Israel
- Ruth & Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel
| | - Erez Ben-Ari
- Department of Electrical Engineering, Technion, Haifa, Israel
| | - Avraham Lorber
- Ruth & Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel
- Department of Pediatric Cardiology, Rambam Medical Center
| | - Joseph Itskovitz-Eldor
- The Sohnis Family Stem Cells Center, Technion, Haifa, Israel
- Ruth & Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel
- Department of Obstetrics and Gynecology, Rambam Medical Center, Haifa, Israel
| | - Michael R Rosen
- Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York, USA
| | - Amir Weissman
- Ruth & Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel
- Department of Obstetrics and Gynecology, Rambam Medical Center, Haifa, Israel
| | - Ofer Binah
- The Sohnis Family Stem Cells Center, Technion, Haifa, Israel
- The Rappaport Institute, Technion, Haifa, Israel
- Ruth & Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel
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5
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Chung CS, Campbell KS. Temperature and transmural region influence functional measurements in unloaded left ventricular cardiomyocytes. Physiol Rep 2013; 1:e00158. [PMID: 24400159 PMCID: PMC3871472 DOI: 10.1002/phy2.158] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2013] [Revised: 10/18/2013] [Accepted: 10/23/2013] [Indexed: 12/21/2022] Open
Abstract
Intact cardiomyocytes are increasingly being used to investigate the molecular mechanisms of contraction and to screen new therapeutic compounds. The function of the cardiomyocytes is often measured from the calcium transients and sarcomere length profiles. We studied the role of experimental temperature and transmural region on indices of function in freshly isolated, unloaded cardiomyocytes. Intact cardiomyocytes were isolated from the subendocardium, midmyocardium, and subepicardium of 3-month-old Sprague-Dawley rats. Myocytes from each region were studied at 25°C, 31°C, and 37°C. Cytosolic calcium transients were measured using Fura-2 fluorescence, whereas sarcomere length shortening and relengthening profiles were measured using high-speed video capture. For both the calcium transients and sarcomere length profiles, the time to peak and the time to half relaxation decreased significantly with increasing temperature. Increasing temperature also raised the minimum and maximum calcium levels of all cells. Of note, there was a reduced coefficient of variation (standard deviation divided by the mean) at higher temperatures for calcium fluorescence amplitudes, time to peak calcium, and rates of sarcomeric shortening and relengthening. The amplitudes and minimum of the calcium transients were significantly dependent on transmural region, and several sarcomere length parameters exhibited statistical interactions between temperature and transmural region. Together, these results show that biological variability can be reduced by performing experiments at 37°C rather than at room temperature, and by isolating cells from a specific transmural region. Adopting these procedures will improve the statistical power of subsequent analyses and increase the efficiency of future experiments.
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Affiliation(s)
- Charles S Chung
- Department of Physiology and Center for Muscle Biology, University of Kentucky Lexington, Kentucky
| | - Kenneth S Campbell
- Department of Physiology and Center for Muscle Biology, University of Kentucky Lexington, Kentucky
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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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Griffiths EJ. Mitochondria and heart disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 942:249-67. [PMID: 22399426 DOI: 10.1007/978-94-007-2869-1_11] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Mitochondria play a key role in the normal functioning of the heart, and in the pathogenesis and development of various types of heart disease. Physiologically, mitochondrial ATP supply needs to be matched to the often sudden changes in ATP demand of the heart, and this is mediated to a large extent by the mitochondrial Ca(2+) transport pathways allowing elevation of mitochondrial [Ca(2+)] ([Ca(2+)](m)). In turn this activates dehydrogenase enzymes to increase NADH and hence ATP supply. Pathologically, [Ca(2+)](m) is also important in generation of reactive oxygen species, and in opening of the mitochondrial permeability transition pore (MPTP); factors involved in both ischaemia-reperfusion injury and in heart failure. The MPTP has proved a promising target for protective strategies, with inhibitors widely used to show cardioprotection in experimental, and very recently human, studies. Similarly mitochondrially-targeted antioxidants have proved protective in various animal models of disease and await clinical trials. The mitochondrial Ca(2+) transport pathways, although in theory promising therapeutic targets, cannot yet be targeted in human studies due to non-specific effects of drugs used experimentally to inhibit them. Finally, specific mitochondrial cardiomyopathies due to mutations in mtDNA have been identified, usually in a gene for a tRNA, which, although rare, are almost always very severe once the mutation has exceeded its threshold.
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Dedkova EN, Blatter LA. Measuring mitochondrial function in intact cardiac myocytes. J Mol Cell Cardiol 2011; 52:48-61. [PMID: 21964191 DOI: 10.1016/j.yjmcc.2011.08.030] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2011] [Revised: 07/30/2011] [Accepted: 08/09/2011] [Indexed: 12/01/2022]
Abstract
Mitochondria are involved in cellular functions that go beyond the traditional role of these organelles as the power plants of the cell. Mitochondria have been implicated in several human diseases, including cardiac dysfunction, and play a role in the aging process. Many aspects of our knowledge of mitochondria stem from studies performed on the isolated organelle. Their relative inaccessibility imposes experimental difficulties to study mitochondria in their natural environment-the cytosol of intact cells-and has hampered a comprehensive understanding of the plethora of mitochondrial functions. Here we review currently available methods to study mitochondrial function in intact cardiomyocytes. These methods primarily use different flavors of fluorescent dyes and genetically encoded fluorescent proteins in conjunction with high-resolution imaging techniques. We review methods to study mitochondrial morphology, mitochondrial membrane potential, Ca(2+) and Na(+) signaling, mitochondrial pH regulation, redox state and ROS production, NO signaling, oxygen consumption, ATP generation and the activity of the mitochondrial permeability transition pore. Where appropriate we complement this review on intact myocytes with seminal studies that were performed on isolated mitochondria, permeabilized cells, and in whole hearts.
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Affiliation(s)
- Elena N Dedkova
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL 60612, USA
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Youm JB, Choi SW, Jang CH, Kim HK, Leem CH, Kim N, Han J. A computational model of cytosolic and mitochondrial [ca] in paced rat ventricular myocytes. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2011; 15:217-39. [PMID: 21994480 DOI: 10.4196/kjpp.2011.15.4.217] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Revised: 08/09/2011] [Accepted: 08/09/2011] [Indexed: 11/15/2022]
Abstract
We carried out a series of experiment demonstrating the role of mitochondria in the cytosolic and mitochondrial Ca(2+) transients and compared the results with those from computer simulation. In rat ventricular myocytes, increasing the rate of stimulation (1~3 Hz) made both the diastolic and systolic [Ca(2+)] bigger in mitochondria as well as in cytosol. As L-type Ca(2+) channel has key influence on the amplitude of Ca(2+)-induced Ca(2+) release, the relation between stimulus frequency and the amplitude of Ca(2+) transients was examined under the low density (1/10 of control) of L-type Ca(2+) channel in model simulation, where the relation was reversed. In experiment, block of Ca(2+) uniporter on mitochondrial inner membrane significantly reduced the amplitude of mitochondrial Ca(2+) transients, while it failed to affect the cytosolic Ca(2+) transients. In computer simulation, the amplitude of cytosolic Ca(2+) transients was not affected by removal of Ca(2+) uniporter. The application of carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP) known as a protonophore on mitochondrial membrane to rat ventricular myocytes gradually increased the diastolic [Ca(2+)] in cytosol and eventually abolished the Ca(2+) transients, which was similarly reproduced in computer simulation. The model study suggests that the relative contribution of L-type Ca(2+) channel to total transsarcolemmal Ca(2+) flux could determine whether the cytosolic Ca(2+) transients become bigger or smaller with higher stimulus frequency. The present study also suggests that cytosolic Ca(2+) affects mitochondrial Ca(2+) in a beat-to-beat manner, however, removal of Ca(2+) influx mechanism into mitochondria does not affect the amplitude of cytosolic Ca(2+) transients.
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Affiliation(s)
- Jae Boum Youm
- National Research Laboratory for Mitochondrial Signaling, Department of Physiology, College of Medicine, Cardiovascular and Metabolic Disease Center, Inje University, Busan 614-735, Korea
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10
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Neumann JT, Diaz-Sylvester PL, Fleischer S, Copello JA. CGP-37157 inhibits the sarcoplasmic reticulum Ca²+ ATPase and activates ryanodine receptor channels in striated muscle. Mol Pharmacol 2010; 79:141-7. [PMID: 20923851 DOI: 10.1124/mol.110.067165] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
7-Chloro-5-(2-chlorophenyl)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one [CGP-37157 (CGP)], a benzothiazepine derivative of clonazepam, is commonly used as a blocker of the mitochondrial Na+/Ca²+ exchanger. However, evidence suggests that CGP could also affect other targets, such as L-type Ca²+ channels and plasmalemma Na+/Ca²+ exchanger. Here, we tested the possibility of a direct modulation of ryanodine receptor channels (RyRs) and/or sarco/endoplasmic reticulum Ca²+-stimulated ATPase (SERCA) by CGP. In the presence of ruthenium red (inhibitor of RyRs), CGP decreased SERCA-mediated Ca²+ uptake of cardiac and skeletal sarcoplasmic reticulum (SR) microsomes (IC₅₀ values of 6.6 and 9.9 μM, respectively). The CGP effects on SERCA activity correlated with a decreased V(max) of ATPase activity of SERCA-enriched skeletal SR fractions. CGP (≥ 5 μM) also increased RyR-mediated Ca²+ leak from skeletal SR microsomes. Planar bilayer studies confirmed that both cardiac and skeletal RyRs are directly activated by CGP (EC(50) values of 9.4 and 12.0 μM, respectively). In summary, we found that CGP inhibits SERCA and activates RyR channels. Hence, the action of CGP on cellular Ca²+ homeostasis reported in the literature of cardiac, skeletal muscle, and other nonmuscle systems requires further analysis to take into account the contribution of all CGP-sensitive Ca²+ transporters.
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Affiliation(s)
- Jake T Neumann
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, USA
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12
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Koncz P, Szanda G, Fülöp L, Rajki A, Spät A. Mitochondrial Ca2+ uptake is inhibited by a concerted action of p38 MAPK and protein kinase D. Cell Calcium 2009; 46:122-9. [DOI: 10.1016/j.ceca.2009.06.004] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2009] [Revised: 06/05/2009] [Accepted: 06/20/2009] [Indexed: 10/20/2022]
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13
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Mitochondrial calcium transport in the heart: Physiological and pathological roles. J Mol Cell Cardiol 2009; 46:789-803. [DOI: 10.1016/j.yjmcc.2009.03.001] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2009] [Revised: 02/28/2009] [Accepted: 03/03/2009] [Indexed: 12/20/2022]
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Liu T, O’Rourke B. Regulation of mitochondrial Ca2+ and its effects on energetics and redox balance in normal and failing heart. J Bioenerg Biomembr 2009; 41:127-32. [PMID: 19390955 PMCID: PMC2946065 DOI: 10.1007/s10863-009-9216-8] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Ca(2+) has been well accepted as a signal that coordinates changes in cytosolic workload with mitochondrial energy metabolism in cardiomyocytes. During increased work, Ca(2+) is accumulated in mitochondria and stimulates ATP production to match energy supply and demand. The kinetics of mitochondrial Ca(2+) ([Ca(2+)](m)) uptake remains unclear, and we review the debate on this subject in this article. [Ca(2+)](m) has multiple targets in oxidative phosphorylation including the F1/FO ATPase, the adenine nucleotide translocase, and Ca(2+)-sensitive dehydrogenases (CaDH) of the tricarboxylic acid (TCA) cycle. The well established effect of [Ca(2+)](m) is to activate CaDHs of the TCA cycle to increase NADH production. Maintaining NADH level is not only critical to keep a high oxidative phosphorylation rate during increased cardiac work, but is also necessary for the reducing system of the cell to maintain its reactive oxygen species (ROS) -scavenging capacity. Further, we review recent data demonstrating the deleterious effects of elevated Na(+) in cardiac pathology by blunting [Ca(2+)](m) accumulation.
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Affiliation(s)
- Ting Liu
- Institute of Molecular Cardiobiology, Division of Cardiology, The Johns Hopkins University, Baltimore, MD, USA
| | - Brian O’Rourke
- Institute of Molecular Cardiobiology, The Johns Hopkins University, 720 Rutland Ave., 1060 Ross Bldg., Baltimore, MD 21205-2195, USA,
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15
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Griffiths EJ, Rutter GA. Mitochondrial calcium as a key regulator of mitochondrial ATP production in mammalian cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:1324-33. [PMID: 19366607 DOI: 10.1016/j.bbabio.2009.01.019] [Citation(s) in RCA: 267] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2008] [Revised: 01/23/2009] [Accepted: 01/27/2009] [Indexed: 12/30/2022]
Abstract
Mitochondrial Ca(2+) transport was initially considered important only in buffering of cytosolic Ca(2+) by acting as a "sink" under conditions of Ca(2+) overload. The main regulator of ATP production was considered to be the relative concentrations of high energy phosphates. However, work by Denton and McCormack in the 1970s and 1980s showed that free intramitochondrial Ca(2+) ([Ca(2+)](m)) activated dehydrogenase enzymes in mitochondria, leading to increased NADH and hence ATP production. This leads them to propose a scheme, subsequently termed a "parallel activation model" whereby increases in energy demand, such as hormonal stimulation or increased workload in muscle, produced an increase in cytosolic [Ca(2+)] that was relayed by the mitochondrial Ca(2+) transporters into the matrix to give an increase in [Ca(2+)](m). This then stimulated energy production to meet the increased energy demand. With the development of methods for measuring [Ca(2+)](m) in living cells that proved [Ca(2+)](m) changed over a dynamic physiological range rather than simply soaking up excess cytosolic [Ca(2+)], this model has now gained widespread acceptance. However, work by ourselves and others using targeted probes to measure changes in both [Ca(2+)] and [ATP] in different cell compartments has revealed variations in the interrelationships between these two in different tissues, suggesting that metabolic regulation by Ca(2+) is finely tuned to the demands and function of the individual organ.
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Affiliation(s)
- Elinor J Griffiths
- Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
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16
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Liu T, O'Rourke B. Enhancing mitochondrial Ca2+ uptake in myocytes from failing hearts restores energy supply and demand matching. Circ Res 2008; 103:279-88. [PMID: 18599868 DOI: 10.1161/circresaha.108.175919] [Citation(s) in RCA: 187] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Mitochondrial ATP production is continually adjusted to energy demand through coordinated increases in oxidative phosphorylation and NADH production mediated by mitochondrial Ca2+([Ca2+]m). Elevated cytosolic Na+ impairs [Ca2+]m accumulation during rapid pacing of myocytes, resulting in a decrease in NADH/NAD+ redox potential. Here, we determined 1) if accentuating [Ca2+]m accumulation prevents the impaired NADH response at high [Na+]i; 2) if [Ca2+]m handling and NADH/NAD+ balance during stimulation is impaired with heart failure (induced by aortic constriction); and 3) if inhibiting [Ca2+]m efflux improves NADH/NAD+ balance in heart failure. [Ca2+]m and NADH were recorded in cells at rest and during voltage clamp stimulation (4Hz) with either 5 or 15 mmol/L [Na+]i. Fast [Ca2+]m transients and a rise in diastolic [Ca2+]m were observed during electric stimulation. [Ca2+]m accumulation was [Na+]i-dependent; less [Ca2+]m accumulated in cells with 15 Na+ versus 5 mmol/L Na+ and NADH oxidation was evident at 15 mmol/L Na+, but not at 5 mmol/L Na+. Treatment with either the mitochondrial Na+/Ca2+ exchange inhibitor CGP-37157 (1 micromol/L) or raising cytosolic Pi (2 mmol/L) enhanced [Ca2+]m accumulation and prevented the NADH oxidation at 15 mmol/L [Na+]i. In heart failure myocytes, resting [Na+]i increased from 5.2+/-1.4 to 16.8+/-3.1mmol/L and net NADH oxidation was observed during pacing, whereas NADH was well matched in controls. Treatment with CGP-37157 or lowering [Na+]i prevented the impaired NADH response in heart failure. We conclude that high [Na+]i (at levels observed in heart failure) has detrimental effects on mitochondrial bioenergetics, and this impairment can be prevented by inhibiting the mitochondrial Na+/Ca2+ exchanger.
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Affiliation(s)
- Ting Liu
- Division of Cardiology, The Johns Hopkins University, Baltimore, MD, USA
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17
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Maack C, O'Rourke B. Excitation-contraction coupling and mitochondrial energetics. Basic Res Cardiol 2007; 102:369-92. [PMID: 17657400 PMCID: PMC2785083 DOI: 10.1007/s00395-007-0666-z] [Citation(s) in RCA: 188] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2007] [Revised: 06/12/2007] [Accepted: 06/13/2007] [Indexed: 12/20/2022]
Abstract
Cardiac excitation-contraction (EC) coupling consumes vast amounts of cellular energy, most of which is produced in mitochondria by oxidative phosphorylation. In order to adapt the constantly varying workload of the heart to energy supply, tight coupling mechanisms are essential to maintain cellular pools of ATP, phosphocreatine and NADH. To our current knowledge, the most important regulators of oxidative phosphorylation are ADP, Pi, and Ca2+. However, the kinetics of mitochondrial Ca2+-uptake during EC coupling are currently a matter of intense debate. Recent experimental findings suggest the existence of a mitochondrial Ca2+ microdomain in cardiac myocytes, justified by the close proximity of mitochondria to the sites of cellular Ca2+ release, i. e., the ryanodine receptors of the sarcoplasmic reticulum. Such a Ca2+ microdomain could explain seemingly controversial results on mitochondrial Ca2+ uptake kinetics in isolated mitochondria versus whole cardiac myocytes. Another important consideration is that rapid mitochondrial Ca2+ uptake facilitated by microdomains may shape cytosolic Ca2+ signals in cardiac myocytes and have an impact on energy supply and demand matching. Defects in EC coupling in chronic heart failure may adversely affect mitochondrial Ca2+ uptake and energetics, initiating a vicious cycle of contractile dysfunction and energy depletion. Future therapeutic approaches in the treatment of heart failure could be aimed at interrupting this vicious cycle.
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Affiliation(s)
- Christoph Maack
- Klinik für Innere Medizin III, Universitätsklinikum des Saarlandes, 66421, Homburg/Saar, Germany.
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18
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Kaddour-Djebbar I, Lakshmikanthan V, Shirley RB, Ma Y, Lewis RW, Kumar MV. Therapeutic advantage of combining calcium channel blockers and TRAIL in prostate cancer. Mol Cancer Ther 2006; 5:1958-66. [PMID: 16928816 DOI: 10.1158/1535-7163.mct-06-0011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Disruption of intracellular calcium initiates multiple cell-damaging processes, such as apoptosis. In normal cells, the levels of Ca(2+) are low in the mitochondria, whereas in apoptotic cells, Ca(2+) increases. Mitochondria uptake Ca(2+) via an inner membrane channel called the uniporter and extrude it into the cytoplasm through a Na(+)/Ca(2+) exchanger. Overload of Ca(2+) in the mitochondria in CGP-treated cells leads to its damage, thus affecting cellular function and survival. The goal of these experiments was to determine the importance of mitochondrial calcium ([Ca(2+)](m)) in apoptosis of prostate cancer cells. Furthermore, we have examined the advantages of increasing the [Ca(2+)](m) and treating the cells with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a potent apoptotic agent. Our results show that, under these treatment conditions, inhibiting the Na(+)/Ca(2+) exchanger using benzothiazepin CGP-37157 (CGP) did not induce apoptosis. However, combination of CGP and TRAIL increased the apoptotic response approximately 25-fold compared with control. Increase in apoptosis followed enhanced levels of [Ca(2+)](m) and was accompanied by pronounced mitochondrial changes characteristic of mitochondria-mediated apoptosis. Experiments with calcium ionophores showed that mere increase in cytosolic and/or mitochondrial Ca(2+) was not sufficient to induce apoptosis. These results have therapeutic implications as inhibitors of Na(+)/Ca(2+) exchanger are being used for treating some neurologic and cardiologic ailments, and TRAIL induces apoptosis preferentially in cancer cells. Furthermore, this system provides an excellent model to investigate the role of [Ca(2+)](m) in apoptosis.
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Affiliation(s)
- Ismail Kaddour-Djebbar
- Research Department, Veterans Affairs Medical Center, One Freedom Way, Augusta, GA 30904, USA
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19
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Bell CJ, Bright NA, Rutter GA, Griffiths EJ. ATP regulation in adult rat cardiomyocytes: time-resolved decoding of rapid mitochondrial calcium spiking imaged with targeted photoproteins. J Biol Chem 2006; 281:28058-67. [PMID: 16882672 DOI: 10.1074/jbc.m604540200] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mechanisms that enable the heart to rapidly increase ATP supply in line with increased demand have not been fully elucidated. Here we used an adenoviral system to express the photoproteins luciferase and aequorin, targeted to the mitochondria or cytosol of adult cardiomyocytes, to investigate the interrelationship between ATP and Ca(2+) in these compartments. In neither compartment were changes in free [ATP] observed upon increased workload (addition of isoproterenol) in myocytes that were already beating. However, when myocytes were stimulated to beat rapidly from rest, in the presence of isoproterenol, a significant but transient drop in mitochondrial [ATP] ([ATP](m)) occurred (on average to 10% of the initial signal). Corresponding changes in cytosolic [ATP] ([ATP](c)) were much smaller (<5%), indicating that [ATP](c) was effectively buffered in this compartment. Although mitochondrial [Ca(2+)] ([Ca(2+)](m)) is an important regulator of respiratory chain activity and ATP production in other cells, the kinetics of mitochondrial Ca(2+) transport are controversial. Parallel experiments in cells expressing mitochondrial aequorin showed that the drop in [ATP](m) occurred over the same time scale as average [Ca(2+)](m) was increasing. Conversely, in the absence or presence of isoproterenol, clear beat-to-beat peaks in [Ca(2+)](m) were observed at 0.9 or 1.3 mum, respectively, concentrations similar to those observed in the cytosol. These results suggest that mitochondrial Ca(2+) transients occur during the contractile cycle and are translated into a time-averaged increase in mitochondrial ATP production that keeps pace with increased cytosolic demand.
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Affiliation(s)
- Christopher J Bell
- Bristol Heart Institute, University of Bristol, Bristol BS8 1TD, United Kingdom
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20
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Jo H, Noma A, Matsuoka S. Calcium-mediated coupling between mitochondrial substrate dehydrogenation and cardiac workload in single guinea-pig ventricular myocytes. J Mol Cell Cardiol 2006; 40:394-404. [PMID: 16480740 DOI: 10.1016/j.yjmcc.2005.12.012] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/30/2005] [Revised: 11/23/2005] [Accepted: 12/19/2005] [Indexed: 11/29/2022]
Abstract
We measured mitochondrial NADH autofluorescence or Ca(2+) using Rhod-2, simultaneously with cell shortening in isolated guinea-pig ventricular myocytes. When both frequency and amplitude of twitch shortening (work intensity) were increased by raising stimulus frequency in incremental steps from 0.1 to 3.3 Hz, the steady level of NADH signal increased in a frequency-dependent manner. Mitochondrial Ca(2+) also increased with increasing work intensity. Applying Ru360, an inhibitor of mitochondrial Ca(2+) uniporter, largely attenuated the response of both NADH fluorescence and mitochondrial Ca(2+). The increase in mitochondrial Ca(2+) was slow with t(1/2)=~12 s and no obvious cyclic changes were observed in the NADH signal. When a step change from 0.1 to 3.3 Hz stimulation was applied, the NADH signal first decreased to 83% and then increased to 155% of the control level. Upon returning to 0.1 Hz, the NADH signal showed an overshoot before declining to the control level. The biphasic onset time course was well explained by the delayed Ca(2+) activation of the substrate dehydrogenation superimposed on the feedback control of the ATP synthesis, while the offset time course with a delayed deactivation of dehydrogenation. A computer simulation using an oxidative phosphorylation linked to the cardiac excitation contraction model well reconstructed the response of NADH. This model simulation predicts that the activation of substrate dehydrogenation provides ~23% of driving force of the ATP synthesis to meet the increased workload induced by the jump of stimulus from 0.1 to 3.3 Hz, and remaining ~77% is supplied by the feedback control.
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Affiliation(s)
- Hikari Jo
- Department of Physiology and Biophysics, Kyoto University Graduate School of Medicine, Yoshida-konoe, Sakyo-ku, Kyoto 606-8501, Japan
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21
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Hamahata K, Adachi S, Matsubara H, Okada M, Imai T, Watanabe KI, Toyokuni SY, Ueno M, Wakabayashi S, Katanosaka Y, Akiba S, Kubota M, Nakahata T. Mitochondrial dysfunction is related to necrosis-like programmed cell death induced by A23187 in CEM cells. Eur J Pharmacol 2005; 516:187-96. [PMID: 15963976 DOI: 10.1016/j.ejphar.2005.04.018] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2005] [Accepted: 04/11/2005] [Indexed: 11/25/2022]
Abstract
We have previously reported that calcium ionophore A23187 differentially induces necrosis in CEM cells, a T-lymphoblastic leukemia cell line, and apoptosis in HL60 cells, a promyelocytic leukemia cell line. Stimulation with VP16, however, induces typical apoptosis in both cell lines. Necrosis in CEM cells, characterized by cell shrinkage and clustering, began within 5 min of treatment. Swelling of the mitochondria, lumpy chromatin condensation and intact plasma membranes were evident by electron microscopy. These A23187-mediated changes in CEM cells were suppressed by clonazepam or CGP37157, inhibitors of the mitochondrial Na(+)/Ca(2+) exchanger. The changes, however, were not affected by cyclosporin A, an inhibitor of the mitochondrial permeability transition pore. In both CEM and HL60 cells, intra-cellular calcium increased with similar amplitude within 1 min of treatment with 2 microM A23187. Intra-mitochondrial calcium increased with clonazepam pre-treatment alone in both CEM and HL60 cells. However, intra-mitochondrial calcium did not change drastically in response to A23187 in CEM or HL60 cells, either untreated or pre-treated with clonazepam. A23187 induces necrosis in CEM cells concurrent with mitochondrial dysfunction, which is independent of the mitochondrial permeability transition, but affected by intra-mitochondrial calcium, while HL60 cells lack these early changes. Differences in the responses to A23187 between these two cell lines might derive from differences in the susceptibility of the mitochondrial membrane to rapid increases in intra-cellular calcium.
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Affiliation(s)
- Keigo Hamahata
- Department of Pediatrics, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan
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22
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Shirakawa H, Miyazaki S. Blind spectral decomposition of single-cell fluorescence by parallel factor analysis. Biophys J 2004; 86:1739-52. [PMID: 14990501 PMCID: PMC1304009 DOI: 10.1016/s0006-3495(04)74242-3] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Simultaneous measurement of multiple signaling molecules is essential to investigate their relations and interactions in living cells. Although a wide variety of fluorescent probes are currently available, the number of probes that can be applied simultaneously is often limited by the overlaps among their fluorescence spectra. We developed the experimental system to measure and analyze many overlapping fluorescent components in single cells. It is based on the recording of two-dimensional single-cell fluorescence spectra and on the blind spectral decomposition of fluorescence data by method of parallel factor analysis. Because this method does not require any preknowledge about the shapes of individual component spectra, it can be applied to the specimens that contain fluorescent components with unknown spectra. By examining the performance using the mixture solutions of fluorescent indicators, it was confirmed that >10 largely overlapping spectral components could be easily separated. The effectiveness in the physiological experiments was proven in the applications to the temporal analysis of intracellular Ca(2+) concentration and pH, as well as the intrinsic fluorescent components, in single mouse oocytes.
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Affiliation(s)
- Hideki Shirakawa
- Department of Physiology, Tokyo Women's Medical University School of Medicine, Shinjuku, Tokyo, 162-8666, Japan.
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23
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Brandes R, Bers DM. Simultaneous measurements of mitochondrial NADH and Ca(2+) during increased work in intact rat heart trabeculae. Biophys J 2002; 83:587-604. [PMID: 12124250 PMCID: PMC1302172 DOI: 10.1016/s0006-3495(02)75194-1] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The main goal of this study is to investigate the role of mitochondrial [Ca(2+)], [Ca(2+)](m), in the possible up-regulation of the NADH production rate during increased workload. Such up-regulation is necessary to support increased flux through the electron transport chain and increased ATP synthesis rates. Intact cardiac trabeculae were loaded with Rhod-2(AM), and [Ca(2+)](m) and mitochondrial [NADH] ([NADH](m)) were simultaneously measured during increased pacing frequency. It was found that 53% of Rhod-2 was localized in mitochondria. Increased pacing frequency caused a fast, followed by a slow rise of the Rhod-2 signal, which could be attributed to an abrupt increase in resting cytosolic [Ca(2+)], and a more gradual rise of [Ca(2+)](m), respectively. When the pacing frequency was increased from 0.25 to 2 Hz, the slow Rhod-2 component and the NADH signal increased by 18 and 11%, respectively. Based on a new calibration method, the 18% increase of the Rhod-2 signal was calculated to correspond to a 43% increase of [Ca(2+)](m). There was also a close temporal relationship between the rise (time constant approximately 25 s) and fall (time constant approximately 65 s) of [Ca(2+)](m) and [NADH](m) when the pacing frequency was increased and decreased, respectively, suggesting that increased workload and [Ca(2+)](c) cause increased [Ca(2+)](m) and consequently up-regulation of the NADH production rate.
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Affiliation(s)
- Rolf Brandes
- Novasite Pharmaceuticals, San Diego, California 92121, USA.
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24
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Buntinas L, Gunter KK, Sparagna GC, Gunter TE. The rapid mode of calcium uptake into heart mitochondria (RaM): comparison to RaM in liver mitochondria. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1504:248-61. [PMID: 11245789 DOI: 10.1016/s0005-2728(00)00254-1] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
A mechanism of Ca(2+) uptake, capable of sequestering significant amounts of Ca(2+) from cytosolic Ca(2+) pulses, has previously been identified in liver mitochondria. This mechanism, the Rapid Mode of Ca(2+) uptake (RaM), was shown to sequester Ca(2+) very rapidly at the beginning of each pulse in a sequence [Sparagna et al. (1995) J. Biol. Chem. 270, 27510-27515]. The existence and properties of RaM in heart mitochondria, however, are unknown and are the basis for this study. We show that RaM functions in heart mitochondria with some of the characteristics of RaM in liver, but its activation and inhibition are quite different. It is feasible that these differences represent different physiological adaptations in these two tissues. In both tissues, RaM is highly conductive at the beginning of a Ca(2+) pulse, but is inhibited by the rising [Ca(2+)] of the pulse itself. In heart mitochondria, the time required at low [Ca(2+)] to reestablish high Ca(2+) conductivity via RaM i.e. the 'resetting time' of RaM is much longer than in liver. RaM in liver mitochondria is strongly activated by spermine, activated by ATP or GTP and unaffected by ADP and AMP. In heart, RaM is activated much less strongly by spermine and unaffected by ATP or GTP. RaM in heart is strongly inhibited by AMP and has a biphasic response to ADP; it is activated at low concentrations and inhibited at high concentrations. Finally, an hypothesis consistent with the data and characteristics of liver and heart is presented to explain how RaM may function to control the rate of oxidative phosphorylation in each tissue. Under this hypothesis, RaM functions to create a brief, high free Ca(2+) concentration inside mitochondria which may activate intramitochondrial metabolic reactions with relatively small amounts of Ca(2+) uptake. This hypothesis is consistent with the view that intramitochondrial [Ca(2+)] may be used to control the rate of ADP phosphorylation in such a way as to minimize the probability of activating the Ca(2+)-induced mitochondrial membrane permeability transition (MPT).
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Affiliation(s)
- L Buntinas
- Department of Biochemistry and Biophysics, University of Rochester, School of Medicine and Dentistry, Rochester, NY 14642, USA.
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25
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Griffiths EJ. Use of ruthenium red as an inhibitor of mitochondrial Ca(2+) uptake in single rat cardiomyocytes. FEBS Lett 2000; 486:257-60. [PMID: 11119714 DOI: 10.1016/s0014-5793(00)02268-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
With the current resurgence of interest in the role of mitochondrial [Ca(2+)] in energy production and cellular Ca(2+) signalling, ruthenium red (RR) is being increasingly used as an inhibitor of mitochondrial Ca(2+) uptake. In the present study, the effects of RR on cell and mitochondrial [Ca(2+)], and on cell contractility were determined in isolated rat ventricular myocytes subjected to adrenergic and electrical stimulation. At low concentrations, 0-1 microM, RR inhibited mitochondrial Ca(2+) uptake but this was a secondary effect due to a reduced total intracellular [Ca(2+)], a conclusion supported by the ability of RR to inhibit cell shortening. 5 microM RR completely inhibited cell contraction, whereas higher concentrations, 10-25 microM, induced spontaneous Ca(2+) oscillations and contractile waves. These results indicate that great care must be taken when using RR in intact cells, and in interpreting any effects as resulting from a primary inhibition of mitochondrial Ca(2+) uptake.
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Affiliation(s)
- E J Griffiths
- Bristol Heart Institute, Department of Cardiac Surgery, Level 7, Bristol Royal Infirmary, University of Bristol, BS2 8HW, Bristol, UK.
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26
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Hajnóczky G, Csordás G, Madesh M, Pacher P. The machinery of local Ca2+ signalling between sarco-endoplasmic reticulum and mitochondria. J Physiol 2000; 529 Pt 1:69-81. [PMID: 11080252 PMCID: PMC2270182 DOI: 10.1111/j.1469-7793.2000.00069.x] [Citation(s) in RCA: 158] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Growing evidence suggests that propagation of cytosolic [Ca2+] ([Ca2+]c) spikes and oscillations to the mitochondria is important for the control of fundamental cellular functions. Delivery of [Ca2+]c spikes to the mitochondria may utilize activation of the mitochondrial Ca2+ uptake sites by the large local [Ca2+]c rise occurring in the vicinity of activated sarco-endoplasmic reticulum (SR/ER) Ca2+ release channels. Although direct measurement of the local [Ca2+]c sensed by the mitochondria has been difficult, recent studies shed some light onto the molecular mechanism of local Ca2+ communication between SR/ER and mitochondria. Subdomains of the SR/ER are in close contact with mitochondria and display a concentration of Ca2+ release sites, providing the conditions for an effective delivery of released Ca2+ to the mitochondrial targets. Furthermore, many functional properties of the signalling between SR/ER Ca2+ release sites and mitochondrial Ca2+ uptake sites, including transient microdomains of high [Ca2+], saturation of mitochondrial Ca2+ uptake sites by released Ca2+, connection of multiple release sites to each uptake site and quantal transmission, are analogous to the features of the coupling between neurotransmitter release sites and postsynaptic receptors in synaptic transmission. As such, Ca2+ signal transmission between SR/ER and mitochondria may utilize discrete communication sites and a closely related functional architecture to that used for synaptic signal propagation between cells.
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Affiliation(s)
- G Hajnóczky
- Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
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27
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Gunter TE, Buntinas L, Sparagna G, Eliseev R, Gunter K. Mitochondrial calcium transport: mechanisms and functions. Cell Calcium 2000; 28:285-96. [PMID: 11115368 DOI: 10.1054/ceca.2000.0168] [Citation(s) in RCA: 279] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Ca(2+)transport across the mitochondrial inner membrane is facilitated by transporters having four distinct sets of characteristics as well as through the Ca(2+)-induced mitochondrial permeability transition pore (PTP). There are two modes of inward transport, referred to as the Ca(2+)uniporter and the rapid mode or RaM. There are also two distinct mechanisms mediating outward transport, which are not associated with the PTP, referred to as the Na(+)-dependent and the Na(+)-independent Ca(2+)efflux mechanisms. Several important functions have been proposed for these mechanisms, including control of the metabolic rate for cellular energy (ATP) production, modulation of the amplitude and shape of cytosolic Ca(2+)transients, and induction of apoptosis through release of cytochrome c from the mitochondrial inter membrane space into the cytosolic space. The goals of this review are to survey the literature describing the characteristics of the mechanisms of mitochondrial Ca(2+)transport and their proposed physiological functions, emphasizing the more recent contributions, and to consider how the observed characteristics of the mitochondrial Ca(2+)transport mechanisms affect our understanding of their functions.
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Affiliation(s)
- T E Gunter
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
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28
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Scaduto RC, Grotyohann LW. 2,3-butanedione monoxime unmasks Ca(2+)-induced NADH formation and inhibits electron transport in rat hearts. Am J Physiol Heart Circ Physiol 2000; 279:H1839-48. [PMID: 11009471 DOI: 10.1152/ajpheart.2000.279.4.h1839] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We used 2,3-butanedione monoxime (BDM) to suppress work by the perfused rat heart and to investigate the effects of calcium on NADH production and tissue energetics. Hearts were perfused with buffer containing BDM and elevated perfusate calcium to maintain the rates of cardiac work and oxygen consumption at levels similar to those of control perfused hearts. BDM plus calcium hearts displayed higher levels of NADH surface fluorescence, indicating calcium activation of mitochondrial dehydrogenases. These hearts, however, displayed 20% lower phosphocreatine levels. BDM suppressed the rates of state 3 respiration of isolated mitochondria. Uncoupled respiration was suppressed to a lesser degree, and the state 4 respiration rates were not affected. Double-inhibitor experiments with liver mitochondria using BDM and carboxyatractyloside (CAT) were used to identify the site of inhibition. BDM at low levels (0-5 mM) suppressed respiration. In the presence of CAT at levels that inhibit respiration by 60%, low levels of BDM were without effect. Because these effects were not additive, BDM does not inhibit adenine nucleotide transport. This was supported by an assay of adenine nucleotide transport in liver mitochondria. BDM did not inhibit ATP hydrolysis by submitochondrial particles but strongly suppressed reversed electron transport from succinate to NAD(+). Oxidation of NADH by submitochondrial particles was inhibited by BDM but oxidation of succinate was not. We conclude that BDM inhibits electron transport at site 1.
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Affiliation(s)
- R C Scaduto
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Pennsylvania State University, Hershey, Pennsylvania 17033, USA.
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29
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Abstract
Mitochondrial dysfunction is implicated in bipolar disorder based on the following lines of evidence: 1) Abnormal brain energy metabolism measured by 31P-magnetic resonance spectroscopy, that is, decreased intracellular pH, decreased phosphocreatine (PCr), and enhanced response of PCr to photic stimulation. 2) Possible role of maternal inheritance in the transmission of bipolar disorder. 3) Increased levels of the 4977-bp deletion in mitochondrial DNA (mtDNA) in autopsied brains. 4) Comorbidity of affective disorders in certain types of mitochondrial disorders, such as autosomal inherited chronic progressive external ophthalmoplegia and mitochondrial diabetes mellitus with the 3243 mutation. Based on these findings, we searched for mtDNA mutations/ polymorphisms associated with bipolar disorder and found that 5178C and 10398A polymorphisms in mtDNA were risk factors for bipolar disorder. The 5178C genotype was associated with lower brain intracellular pH. mtDNA variations may play a part in the pathophysiology of bipolar disorder through alteration of intracellular calcium signaling systems. The mitochondrial dysfunction hypothesis, which comprehensively accounts for the pathophysiology of bipolar disorder, is proposed.
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Affiliation(s)
- T Kato
- Department of Neuropsychiatry, Faculty of Medicine, University of Tokyo, Japan.
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30
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Szalai G, Csordás G, Hantash BM, Thomas AP, Hajnóczky G. Calcium signal transmission between ryanodine receptors and mitochondria. J Biol Chem 2000; 275:15305-13. [PMID: 10809765 DOI: 10.1074/jbc.275.20.15305] [Citation(s) in RCA: 181] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Control of energy metabolism by increases of mitochondrial matrix [Ca(2+)] ([Ca(2+)](m)) may represent a fundamental mechanism to meet the ATP demand imposed by heart contractions, but the machinery underlying propagation of [Ca(2+)] signals from ryanodine receptor Ca(2+) release channels (RyR) to the mitochondria remains elusive. Using permeabilized cardiac (H9c2) cells we investigated the cytosolic [Ca(2+)] ([Ca(2+)](c)) and [Ca(2+)](m) signals elicited by activation of RyR. Caffeine, Ca(2+), and ryanodine evoked [Ca(2+)](c) spikes that often appeared as frequency-modulated [Ca(2+)](c) oscillations in these permeabilized cells. Rapid increases in [Ca(2+)](m) and activation of the Ca(2+)-sensitive mitochondrial dehydrogenases were synchronized to the rising phase of the [Ca(2+)](c) spikes. The RyR-mediated elevations of global [Ca(2+)](c) were in the submicromolar range, but the rate of [Ca(2+)](m) increases was as large as it was in the presence of 30 microm global [Ca(2+)](c). Furthermore, RyR-dependent increases of [Ca(2+)](m) were relatively insensitive to buffering of [Ca(2+)](c) by EGTA. Therefore, RyR-driven rises of [Ca(2+)](m) appear to result from large and rapid increases of perimitochondrial [Ca(2+)]. The falling phase of [Ca(2+)](c) spikes was followed by a rapid decay of [Ca(2+)](m). CGP37157 slowed down relaxation of [Ca(2+)](m) spikes, whereas cyclosporin A had no effect, suggesting that activation of the mitochondrial Ca(2+) exchangers accounts for rapid reversal of the [Ca(2+)](m) response with little contribution from the permeability transition pore. Thus, rapid activation of Ca(2+) uptake sites and Ca(2+) exchangers evoked by RyR-mediated local [Ca(2+)](c) signals allow mitochondria to respond rapidly to single [Ca(2+)](c) spikes in cardiac cells.
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Affiliation(s)
- G Szalai
- Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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31
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Griffiths EJ, Ocampo CJ, Savage JS, Stern MD, Silverman HS. Protective effects of low and high doses of cyclosporin A against reoxygenation injury in isolated rat cardiomyocytes are associated with differential effects on mitochondrial calcium levels. Cell Calcium 2000; 27:87-95. [PMID: 10756975 DOI: 10.1054/ceca.1999.0094] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In this study we aimed to determine the concentration range of cyclosporin A (CsA) which was effective in protecting against reoxygenation injury in isolated cardiomyocytes, and its effects on intramitochondrial free calcium levels ([Ca2+]m). We also determined whether a high [CsA] had any deleterious effect on normal myocyte function. Isolated adult rat ventricular myocytes were placed in a chamber on the stage of a fluorescence microscope for induction of hypoxia. [Ca2+]m was determined from indo-1/am loaded cells where the cytosolic fluorescence signal had been quenched by superfusion with Mn2+. Cell length was measured using an edge-tracking device. Upon induction of hypoxia, control cells underwent rigor-contracture in 37 +/- 1 min (n = 99) (T1); CsA had no effect on T1. The percentage of control cells which recovered upon reoxygenation depended on the time spent in rigor (T2). With a T2 of 21-30 min, only 36% of control cells recovered compared with 90% and 78% of cells treated with 0.2 microM and 1 microM CsA respectively. After 40 min in rigor, [Ca2+]m was 280 +/- 60 nM in control-recovered cells (50% of cells) and 543 +/- 172 nM and 153 +/- 26 nM in cells treated with 0.2 and 1 microM CsA, respectively (all CsA treated cells recovered). In normoxic studies, CsA had no effect on cell contractility or [Ca2+]m upon rapid pacing, even in presence of an elevated external [Ca2+]. In conclusion, both low and high [CsA] protected against reoxygenation injury to cardiomyocytes despite having opposing effects on [Ca2+]m, suggesting more than one mechanism of action. CsA had no effect on either cell contractility or [Ca2+]m in normoxic cells.
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Affiliation(s)
- E J Griffiths
- Division of Cardiology, Johns Hopkins University Hospital, Baltimore, MD, USA.
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32
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Abstract
To a certain extent, all cellular, physiological, and pathological phenomena that occur in cells are accompanied by ionic changes. The development of techniques allowing the measurement of such ion activities has contributed substantially to our understanding of normal and abnormal cellular function. Digital video microscopy, confocal laser scanning microscopy, and more recently multiphoton microscopy have allowed the precise spatial analysis of intracellular ion activity at the subcellular level in addition to measurement of its concentration. It is well known that Ca2+ regulates numerous physiological cellular phenomena as a second messenger as well as triggering pathological events such as cell injury and death. A number of methods have been developed to measure intracellular Ca2+. In this review, we summarize the advantages and pitfalls of a variety of Ca2+ indicators used in both optical and nonoptical techniques employed for measuring intracellular Ca2+ concentration.
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Affiliation(s)
- A Takahashi
- Department of Cellular and Structural Biology, Institute of Biotechnology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900, USA
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33
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Griffiths EJ. Species dependence of mitochondrial calcium transients during excitation-contraction coupling in isolated cardiomyocytes. Biochem Biophys Res Commun 1999; 263:554-9. [PMID: 10491330 DOI: 10.1006/bbrc.1999.1311] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Whether mitochondrial Ca(2+) transport is rapid enough to respond to changes in cytosolic [Ca(2+)] ([Ca(2+)](c)) which occur during excitation-contraction coupling in the heart is controversial; different results wereobtained with different techniques and different species. In this study mitochondrial [Ca(2+)] ([Ca(2+)](m)) was measured in indo-1/AM-loaded myocytes from rat and guinea-pig hearts where the cytosolic indo-1 had been removed by extended incubation of cells at 37 degrees C ("heat treatment"). The mitochondrial origin of the remaining fluorescence was confirmed by sensitivity of the indo-1 signal to ruthenium red. In resting rat myocytes, [Ca(2+)](m) was lower than [Ca(2+)](c), whereas in guinea-pig cells [Ca(2+)](m) was higher than [Ca(2+)](c). Upon electrical stimulation of cells, no change occurred in [Ca(2+)](m) in rat myocytes. However, in guinea-pig cells mitochondrial Ca(2+) transients were clearly visible with a mean indo-1 ratio amplitude of 0.153 +/- 0.2 (n = 20), compared with 0.306 +/- 0.02 (n = 25), p < 0.001, prior to heat treatment. These observations suggest significant differences in mitochondrial Ca(2+) transport in cardiomyocytes from different species.
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Affiliation(s)
- E J Griffiths
- Bristol Heart Institute, University of Bristol, United Kingdom
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34
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Griffiths EJ. Reversal of mitochondrial Na/Ca exchange during metabolic inhibition in rat cardiomyocytes. FEBS Lett 1999; 453:400-4. [PMID: 10405185 DOI: 10.1016/s0014-5793(99)00726-7] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
During hypoxia of isolated cardiomyocytes, Ca2+ entry into mitochondria may occur via the Na/Ca exchanger, the normal efflux pathway, and not the Ca-uniporter, the normal influx route. If this is the case, then depletion of myocyte Na+ should inhibit Ca2+ uptake, and collapse of the mitochondrial membrane potential (delta psi(m)) would inhibit the uniporter. To test these hypotheses, isolated rat myocytes were exposed to metabolic inhibition, to mimic hypoxia, and [Ca2+]m and [Ca2+]c determined by selective loading of indo-1 into these compartments. Delta psi(m) was determined using rhodamine 123. Following metabolic inhibition, [Ca2+]m was significantly lower in Na-depleted cells than controls (P<0.001), [Ca2+]c was approximately the same in both groups, and mitochondria depolarised completely. Thus Na-depletion inhibited mitochondrial Ca2+ uptake, suggesting that Ca2+ entry occurred via Na/Ca exchange, and the collapse of delta psi(m) during metabolic inhibition is consistent with inactivity of the Ca-uniporter.
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Affiliation(s)
- E J Griffiths
- Bristol Heart Institute, Bristol Royal Infirmary, University of Bristol, UK. elinor.
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35
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Takahashi E, Endoh H, Doi K. Intracellular gradients of O2 supply to mitochondria in actively respiring single cardiomyocyte of rats. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:H718-24. [PMID: 9950875 DOI: 10.1152/ajpheart.1999.276.2.h718] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We demonstrated in a previous study [Takahashi, E., K. Sato, H. Endoh, Z.-L. Xu, and K. Doi. Am. J. Physiol. 275 (Heart Circ. Physiol. 44): H225-H233, 1998] that significant radial gradients of intracellular PO2 may be produced in an uncoupled actively respiring, single isolated cardiomyocyte of the rat. The present study was designed to further determine whether such intracellular PO2 gradients can be a limiting factor of oxidative metabolism in uncoupled cardiomyocytes. The NAD(P)H fluorescence of a single cardiomyocyte was captured by a digital charge-coupled device camera and quantitated with a subcellular spatial resolution by a ratio-imaging technique. In the conditions that we demonstrated significant radial PO2 gradients (cells treated with 1 microM carbonyl cyanide m-chlorophenylhydrazone and superfused with 2.09% or 3.14% O2 gas at 27 degreesC), we demonstrated significant augmentation of NAD(P)H fluorescence near the core of an individual cell. The heterogeneous fluorescence pattern was not found in the control cell, whereas fluorescence intensity averaged over the cell was increased by hypoxia. These results suggest the possibility that oxidative phosphorylation near the core of actively respiring, uncoupled cardiomyocytes may be severely suppressed due to insufficient diffusional oxygen supply (hypoxic core) even if regions near the sarcolemma are adequately oxygenated.
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Affiliation(s)
- E Takahashi
- Department of Physiology, Yamagata University School of Medicine, Yamagata 990-9585, Japan
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36
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Ricken S, Leipziger J, Greger R, Nitschke R. Simultaneous measurements of cytosolic and mitochondrial Ca2+ transients in HT29 cells. J Biol Chem 1998; 273:34961-9. [PMID: 9857027 DOI: 10.1074/jbc.273.52.34961] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Loading of HT29 cells with the Ca2+ dye fura-2/AM resulted in an nonhomogeneous intracellular distribution of the dye. Cellular compartments with high fura-2 concentrations were identified by correlation with mitochondrial markers, cellular autofluorescence induced by UV, and dynamic measurement of autofluorescence after inhibition of oxidative phosphorylation. Stimulation with carbachol (10(-4) mol/liter) increased cytosolic, nuclear, and mitochondrial Ca2+ activity ([Ca2+]c, [Ca2+]n, and [Ca2+]m, respectively) measured by UV confocal and conventional imaging. Similar results were obtained with a prototype two-photon microscope (Zeiss, Jena, Germany) allowing for fura-2 excitation. The increase of [Ca2+]m lagged behind that of [Ca2+]c and [Ca2+]n by 10-20 s, and after removing the agonist, [Ca2+]m also decreased with a delay. A strong increase of [Ca2+]m occurred only when a certain threshold of [Ca2+]c (around 1 micromol/liter) was exceeded. In a very similar way, ATP, neurotensin, and thapsigargin increased [Ca2+]c and [Ca2+]m. Carbonyl cyanide p-trifluoromethoxyphenylhyrdrazone reversibly reduced the increase of [Ca2+]m. The source of the mitochondrial Ca2+ increase had intra- and extracellular components, as revealed by experiments in low extracellular Ca2+. We conclude that agonist-induced Ca2+ signals are transduced into mitochondria. 1) Mitochondria could serve as a Ca2+ sink, 2) mitochondria could allow the modulation of [Ca2+]c and [Ca2+]n signals, and 3) [Ca2+]m may serve as a stimulatory metabolic signal when a cell is highly stimulated.
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Affiliation(s)
- S Ricken
- Physiologisches Institut der Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany
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37
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Gunter TE, Buntinas L, Sparagna GC, Gunter KK. The Ca2+ transport mechanisms of mitochondria and Ca2+ uptake from physiological-type Ca2+ transients. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1366:5-15. [PMID: 9714709 DOI: 10.1016/s0005-2728(98)00117-0] [Citation(s) in RCA: 121] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Mitochondria contain a sophisticated system for transporting Ca2+. The existence of a uniporter and of both Na+-dependent and -independent efflux mechanisms has been known for years. Recently, a new mechanism, called the RaM, which seems adapted for sequestering Ca2+ from physiological transients or pulses has been discovered. The RaM shows a conductivity at the beginning of a Ca2+ pulse that is much higher than the conductivity of the uniporter. This conductivity decreases very rapidly following the increase in [Ca2+] outside the mitochondria. This decrease in the Ca2+ conductivity of the RaM is associated with binding of Ca2+ to an external regulatory site. When liver mitochondria are exposed to a sequence of pulses, uptake of labeled Ca2+ via the RaM appears additive between pulses. Ruthenium red inhibits the RaM in liver mitochondria but much larger amounts are required than for inhibition of the mitochondrial Ca2+ uniporter. Spermine, ATP and GTP increase Ca2+ uptake via the RaM. Maximum uptake via the RaM from a single Ca2+ pulse in the physiological range has been observed to be approximately 7 nmole/mg protein, suggesting that Ca2+ uptake via the RaM and uniporter from physiological pulses may be sufficient to activate the Ca2+-sensitive metabolic reactions in the mitochondrial matrix which increase the rate of ATP production. RaM-mediated Ca2+ uptake has also been observed in heart mitochondria. Evidence for Ca2+ uptake into the mitochondria in a variety of tissues described in the literature is reviewed for evidence of participation of the RaM in this uptake. Possible ways in which the differences in transport via the RaM and the uniporter may be used to differentiate between metabolic and apoptotic signaling are discussed.
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Affiliation(s)
- T E Gunter
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, 601 Elmwood Avenue, Rochester, NY 14642, USA.
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38
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Griffiths EJ, Lin H, Suleiman MS. NADH fluorescence in isolated guinea-pig and rat cardiomyocytes exposed to low or high stimulation rates and effect of metabolic inhibition with cyanide. Biochem Pharmacol 1998; 56:173-9. [PMID: 9698070 DOI: 10.1016/s0006-2952(98)00016-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
In this study we investigated whether NADH fluorescence levels changed in response to low or high rates of electrical stimulation in single ventricular myocytes isolated from rat and guinea-pig hearts, either during a single contraction or upon sustained electrical stimulation of cells. NADH levels were determined from cell autofluorescence and cell length monitored using an edge-tracking device. NADH/NAD+ was obtained by addition of cyanide, 100% NADH, and carbonylcyanide-p-trifluoromethoxy phenylhydrazone (FCCP), 100% NAD+. Rat myocytes exhibited slightly higher resting fluorescence levels than guinea-pig cells; however, NADH/NAD+ was higher in rat than guinea-pig cells (P < 0.05), 24.3+/-4.3 (N = 17) vs 14.6+/-1.6 (N = 17), respectively. There was no change in NADH fluorescence during a single contraction when cells were stimulated at either low (0.2 Hz) or high (3 Hz) rates in either species. Furthermore, NADH levels did not change upon sustained stimulation at 3 Hz in either species. Metabolic blockade with cyanide induced a dose dependent rise in NADH fluorescence which was similar for both rat and guinea-pig myocytes and reached a maximum at > or = 1 mM of cyanide. Although a full recovery of NADH fluorescence was seen in both types of cells after brief exposure to cyanide, the rate of recovery was significantly slower in rat myocytes; times to 90% recovery were 110+/-29 sec, N = 6, and 264+/-50 sec, N = 6, for guinea-pig and rat cells, respectively. This work demonstrates that although rat and guinea-pig myocytes have different resting NADH/NAD+, their response to electrical stimulation is the same, whereas in response to metabolic inhibition subtle differences are seen.
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Affiliation(s)
- E J Griffiths
- Bristol Heart Institute, Department of Cardiac Surgery, Bristol Royal Infirmary, UK
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39
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Brandes R, Maier LS, Bers DM. Regulation of mitochondrial [NADH] by cytosolic [Ca2+] and work in trabeculae from hypertrophic and normal rat hearts. Circ Res 1998; 82:1189-98. [PMID: 9633918 DOI: 10.1161/01.res.82.11.1189] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Pressure overload hypertrophy has previously been shown to reduce contractility but paradoxically to increase O2 consumption rates at a given force. Because O2 consumption rates are related to mitochondrial [NADH] ([NADH]m), we tested the hypothesis that with hypertrophy, control of [NADH]m may be altered. Left ventricular trabeculae were isolated from banded and control rat hearts, and fluorescence spectroscopy was used to monitor [NADH]m and cytosolic [Ca2+] ([Ca2+]c). The hearts from banded rats developed hypertrophy (heart-to-body weight ratio increased from 4.1+/-0.1 to 4.9+/-0.1 mg/g) and hypertension (systolic arterial pressure increased from 117+/-4 to 175+/-5 mm Hg). Muscle workload was increased by stepwise increases in pacing frequency (up to 2 Hz). After increased work, [NADH]m fell and then slowly recovered toward control levels. When work was decreased, [NADH]m overshot control values and then slowly returned. The Ca2+-independent initial fall was larger for trabeculae from rats with hypertrophied hearts than from control rats (eg, 17+/-2% versus 11+/-1% when work was increased by increasing the frequency from 0.25 to 1 Hz). At 1 Hz, average [Ca2+]c was approximately 280 nmol/L, and the Ca2+-dependent [NADH]m recovery was larger for trabeculae from rats with hypertrophied hearts (17+/-4% versus 10+/-2%) despite similar average [Ca2+]c. At steady state after Ca2+-dependent recovery, there was no difference in [NADH]m (fall of 1+/-2% versus 1+/-1%). Furthermore, the Ca2+-dependent overshoot was larger for trabeculae from hypertrophied than from control hearts (increase of 14+/-2% versus 9+/-2% when frequency was decreased from 1 to 0.25 Hz). We conclude that (1) there is initially a larger imbalance in NADH production versus consumption rate in hypertrophy (because NADH fell more) and (2) the Ca2+-dependent recovery mechanism is enhanced in hypertrophy (because NADH recovered and overshot more), thus compensating for the larger imbalance.
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Affiliation(s)
- R Brandes
- Department of Physiology, Loyola University-Chicago, School of Medicine, Maywood, Ill 60153, USA.
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40
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Abstract
Mitochondria, the metabolic powerhouses of the cell, can sequester and release large amounts of Ca2+. This import and export of Ca2+ helps to adjust energy production to cellular needs. Recent advances show that mitochondrial Ca2+ fluxes play a major role in normal Ca2+ signaling.
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Affiliation(s)
- D F Babcock
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195-7290, USA.
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41
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Abstract
The elemental composition of rat cardiac muscle was determined with electron probe x-ray microanalysis (EPMA) of rapidly frozen papillary muscles and trabeculae incubated with ryanodine (1 microM) in either 1.2 or 10 mM [Ca2+]o-containing solutions, paced at 0.6 Hz or tetanized at 10 Hz. Total mitochondrial calcium increased significantly, by 4.2 mmol/kg dry weight during a 7 s tetanus, only in muscles tetanized in the presence of 10 mM [Ca2+]o when cytoplasmic Ca2+ is 1-4 microM (Backx, P. H., W.-D. Gao, M. D. Azan-Backx, and E. Marban. 1995. The relationship between contractile force and intracellular [Ca2+] in intact rat trabeculae. J. Gen. Physiol. 105:1-19). Comparison of total mitochondrial with free mitochondrial Ca2+ reported in the literature indicates that the total/free ratio is approximately 6000 at physiological or near-physiological levels of total mitochondrial calcium. Increases in free mitochondrial [Ca2+] consistent with regulation of mitochondrial enzymes should be associated with increases in total mitochondrial calcium detectable with EPMA. However, such increases in mitochondrial calcium occur only as the result of prolonged, unphysiological elevations of cytosolic [Ca2+].
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Affiliation(s)
- Y Horikawa
- Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville 22906-0011, USA
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