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Xia Y, Zhang XH, Yamaguchi N, Morad M. Point mutations in RyR2 Ca2+-binding residues of human cardiomyocytes cause cellular remodelling of cardiac excitation contraction-coupling. Cardiovasc Res 2024; 120:44-55. [PMID: 37890099 PMCID: PMC10898933 DOI: 10.1093/cvr/cvad163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Revised: 07/17/2023] [Accepted: 09/26/2023] [Indexed: 10/29/2023] Open
Abstract
AIMS CRISPR/Cas9 gene edits of cardiac ryanodine receptor (RyR2) in human-induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) provide a novel platform for introducing mutations in RyR2 Ca2+-binding residues and examining the resulting excitation contraction (EC)-coupling remodelling consequences. METHODS AND RESULTS Ca2+-signalling phenotypes of mutations in RyR2 Ca2+-binding site residues associated with cardiac arrhythmia (RyR2-Q3925E) or not proven to cause cardiac pathology (RyR2-E3848A) were determined using ICa- and caffeine-triggered Ca2+ releases in voltage-clamped and total internal reflection fluorescence-imaged wild type and mutant cardiomyocytes infected with sarcoplasmic reticulum (SR)-targeted ER-GCaMP6 probe. (i) ICa- and caffeine-triggered Fura-2 or ER-GCaMP6 signals were suppressed, even when ICa was significantly enhanced in Q3925E and E3848A mutant cardiomyocytes; (ii) spontaneous beating (Fura-2 Ca2+ transients) persisted in mutant cells without the SR-release signals; (iii) while 5-20 mM caffeine failed to trigger Ca2+-release in voltage-clamped mutant cells, only ∼20% to ∼70% of intact myocytes responded respectively to caffeine; (iv) and 20 mM caffeine transients, however, activated slowly, were delayed, and variably suppressed by 2-APB, FCCP, or ruthenium red. CONCLUSION Mutating RyR2 Ca2+-binding residues, irrespective of their reported pathogenesis, suppressed both ICa- and caffeine-triggered Ca2+ releases, suggesting interaction between Ca2+- and caffeine-binding sites. Enhanced transmembrane calcium influx and remodelling of EC-coupling pathways may underlie the persistence of spontaneous beating in Ca2+-induced Ca2+ release-suppressed mutant myocytes.
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Affiliation(s)
- Yanli Xia
- Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina and Clemson University, 68 President Street, Bioengineering building Rm 306, Charleston, SC 29425, USA
| | - Xiao-hua Zhang
- Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina and Clemson University, 68 President Street, Bioengineering building Rm 306, Charleston, SC 29425, USA
| | - Naohiro Yamaguchi
- Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina and Clemson University, 68 President Street, Bioengineering building Rm 306, Charleston, SC 29425, USA
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, 68 President Street, Bioengineering building Rm 306, Charleston, SC 29425, USA
| | - Martin Morad
- Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina and Clemson University, 68 President Street, Bioengineering building Rm 306, Charleston, SC 29425, USA
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, 68 President Street, Bioengineering building Rm 306, Charleston, SC 29425, USA
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Oropeza-Almazán Y, Blatter LA. Mitochondrial calcium uniporter complex activation protects against calcium alternans in atrial myocytes. Am J Physiol Heart Circ Physiol 2020; 319:H873-H881. [PMID: 32857593 DOI: 10.1152/ajpheart.00375.2020] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Cardiac alternans, defined as beat-to-beat alternations in action potential duration, cytosolic Ca transient (CaT) amplitude, and cardiac contraction is associated with atrial fibrillation (AF) and sudden cardiac death. At the cellular level, cardiac alternans is linked to abnormal intracellular calcium handling during excitation-contraction coupling. We investigated how pharmacological activation or inhibition of cytosolic Ca sequestration via mitochondrial Ca uptake and mitochondrial Ca retention affects the occurrence of pacing-induced CaT alternans in isolated rabbit atrial myocytes. Cytosolic CaTs were recorded using Fluo-4 fluorescence microscopy. Alternans was quantified as the alternans ratio (AR = 1 - CaTsmall/CaTlarge, where CaTsmall and CaTlarge are the amplitudes of the small and large CaTs of a pair of alternating CaTs). Inhibition of mitochondrial Ca sequestration via mitochondrial Ca uniporter complex (MCUC) with Ru360 enhanced the severity of CaT alternans (AR increase) and lowered the pacing frequency threshold for alternans. In contrast, stimulation of MCUC mediated mitochondrial Ca uptake with spermine-rescued alternans (AR decrease) and increased the alternans pacing threshold. Direct measurement of mitochondrial [Ca] in membrane permeabilized myocytes with Fluo-4 loaded mitochondria revealed that spermine enhanced and accelerated mitochondrial Ca uptake. Stimulation of mitochondrial Ca retention by preventing mitochondrial Ca efflux through the mitochondrial permeability transition pore with cyclosporin A also protected from alternans and increased the alternans pacing threshold. Pharmacological manipulation of MCUC activity did not affect sarcoplasmic reticulum Ca load. Our results suggest that activation of Ca sequestration by mitochondria protects from CaT alternans and could be a potential therapeutic target for cardiac alternans and AF prevention.NEW & NOTEWORTHY This study provides conclusive evidence that mitochondrial Ca uptake and retention protects from Ca alternans, whereas uptake inhibition enhances Ca alternans. The data suggest pharmacological mitochondrial Ca cycling modulation as a potential therapeutic strategy for alternans-related cardiac arrhythmia prevention.
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Affiliation(s)
| | - Lothar A Blatter
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois
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3
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Werley CA, Boccardo S, Rigamonti A, Hansson EM, Cohen AE. Multiplexed Optical Sensors in Arrayed Islands of Cells for multimodal recordings of cellular physiology. Nat Commun 2020; 11:3881. [PMID: 32753572 PMCID: PMC7403318 DOI: 10.1038/s41467-020-17607-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2019] [Accepted: 07/07/2020] [Indexed: 11/29/2022] Open
Abstract
Cells typically respond to chemical or physical perturbations via complex signaling cascades which can simultaneously affect multiple physiological parameters, such as membrane voltage, calcium, pH, and redox potential. Protein-based fluorescent sensors can report many of these parameters, but spectral overlap prevents more than ~4 modalities from being recorded in parallel. Here we introduce the technique, MOSAIC, Multiplexed Optical Sensors in Arrayed Islands of Cells, where patterning of fluorescent sensor-encoding lentiviral vectors with a microarray printer enables parallel recording of multiple modalities. We demonstrate simultaneous recordings from 20 sensors in parallel in human embryonic kidney (HEK293) cells and in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), and we describe responses to metabolic and pharmacological perturbations. Together, these results show that MOSAIC can provide rich multi-modal data on complex physiological responses in multiple cell types.
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Affiliation(s)
- Christopher A Werley
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, 02138, USA
- Q-State Biosciences, Cambridge, MA, 02139, USA
| | - Stefano Boccardo
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, 02138, USA
- Nobel Biocare AG, Kloten, Switzerland
| | - Alessandra Rigamonti
- Integrated Cardio Metabolic Centre, Department of Medicine Huddinge, Karolinska Institute, Huddinge, Sweden
| | - Emil M Hansson
- Integrated Cardio Metabolic Centre, Department of Medicine Huddinge, Karolinska Institute, Huddinge, Sweden
- Department of Stem Cell and Regenerative Biology, Harvard University, Cambridge, MA, 02138, USA
| | - Adam E Cohen
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, 02138, USA.
- Howard Hughes Medical Institute, Chevy Chase, MD, 20815, USA.
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4
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Cao JL, Adaniya SM, Cypress MW, Suzuki Y, Kusakari Y, Jhun BS, O-Uchi J. Role of mitochondrial Ca 2+ homeostasis in cardiac muscles. Arch Biochem Biophys 2019; 663:276-287. [PMID: 30684463 PMCID: PMC6469710 DOI: 10.1016/j.abb.2019.01.027] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 01/10/2019] [Accepted: 01/22/2019] [Indexed: 12/22/2022]
Abstract
Recent discoveries of the molecular identity of mitochondrial Ca2+ influx/efflux mechanisms have placed mitochondrial Ca2+ transport at center stage in views of cellular regulation in various cell-types/tissues. Indeed, mitochondria in cardiac muscles also possess the molecular components for efficient uptake and extraction of Ca2+. Over the last several years, multiple groups have taken advantage of newly available molecular information about these proteins and applied genetic tools to delineate the precise mechanisms for mitochondrial Ca2+ handling in cardiomyocytes and its contribution to excitation-contraction/metabolism coupling in the heart. Though mitochondrial Ca2+ has been proposed as one of the most crucial secondary messengers in controlling a cardiomyocyte's life and death, the detailed mechanisms of how mitochondrial Ca2+ regulates physiological mitochondrial and cellular functions in cardiac muscles, and how disorders of this mechanism lead to cardiac diseases remain unclear. In this review, we summarize the current controversies and discrepancies regarding cardiac mitochondrial Ca2+ signaling that remain in the field to provide a platform for future discussions and experiments to help close this gap.
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Affiliation(s)
- Jessica L Cao
- Cardiovascular Research Center, Rhode Island Hospital, Providence, RI, USA; Department of Medicine, Division of Cardiology, The Warren Alpert Medical School of Brown University, Providence, RI, USA
| | - Stephanie M Adaniya
- Cardiovascular Research Center, Rhode Island Hospital, Providence, RI, USA; Department of Medicine, Division of Cardiology, The Warren Alpert Medical School of Brown University, Providence, RI, USA; Lillehei Heart Institute, Department of Medicine, Cardiovascular Division, University of Minnesota, Minneapolis, MN, USA
| | - Michael W Cypress
- Lillehei Heart Institute, Department of Medicine, Cardiovascular Division, University of Minnesota, Minneapolis, MN, USA
| | - Yuta Suzuki
- Lillehei Heart Institute, Department of Medicine, Cardiovascular Division, University of Minnesota, Minneapolis, MN, USA
| | - Yoichiro Kusakari
- Department of Cell Physiology, The Jikei University School of Medicine, Minato-ku, Tokyo, Japan
| | - Bong Sook Jhun
- Lillehei Heart Institute, Department of Medicine, Cardiovascular Division, University of Minnesota, Minneapolis, MN, USA
| | - Jin O-Uchi
- Lillehei Heart Institute, Department of Medicine, Cardiovascular Division, University of Minnesota, Minneapolis, MN, USA.
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5
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Fernández-Morales JC, Morad M. Regulation of Ca 2+ signaling by acute hypoxia and acidosis in rat neonatal cardiomyocytes. J Mol Cell Cardiol 2017; 114:58-71. [PMID: 29032102 DOI: 10.1016/j.yjmcc.2017.10.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Revised: 09/20/2017] [Accepted: 10/08/2017] [Indexed: 11/25/2022]
Abstract
Ischemic heart disease is an arrhythmogenic condition, accompanied by hypoxia, acidosis, and impaired Ca2+ signaling. Here we report on effects of acute hypoxia and acidification in rat neonatal cardiomyocytes cultures. RESULTS Two populations of neonatal cardiomyocyte were identified based on inactivation kinetics of L-type ICa: rapidly-inactivating ICa (τ~20ms) myocytes (prevalent in 3-4-day cultures), and slow-inactivating ICa (τ≥40ms) myocytes (dominant in 7-day cultures). Acute hypoxia (pO2<5mmHg for 50-100s) suppressed ICa reversibly in both cell-types to different extent and with different kinetics. This disparity disappeared when Ba2+ was the channel charge carrier, or when the intracellular Ca2+ buffering capacity was increased by dialysis of high concentrations of EGTA and BAPTA, suggesting critical role for calcium-dependent inactivation. Suppressive effect of acute acidosis on ICa (~40%, pH6.7), on the other hand, was not cell-type dependent. Isoproterenol enhanced ICa in both cell-types, but protected only against suppressive effects of acidosis and not hypoxia. Hypoxia and acidosis suppressed global Ca2+ transients by ~20%, but suppression was larger, ~35%, at the RyR2 microdomains, using GCaMP6-FKBP targeted probe. Hypoxia and acidosis also suppressed mitochondrial Ca2+ uptake by 40% and 10%, respectively, using mitochondrial targeted Ca2+ biosensor (mito-GCaMP6). CONCLUSION Our studies suggest that acute hypoxia suppresses ICa in rapidly inactivating cell population by a mechanism involving Ca2+-dependent inactivation, while compromised mitochondrial Ca2+ uptake seems also to contribute to ICa suppression in slowly inactivating cell population. Proximity of cellular Ca2+ pools to sarcolemmal Ca2+ channels may contribute to the variability of inactivation kinetics of ICa in the two cell populations, while acidosis suppression of ICa appears mediated by proton-induced block of the calcium channel.
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Affiliation(s)
| | - Martin Morad
- Cardiac Signaling Center of MUSC, USC and Clemson, Charleston, SC, USA; Department of Pharmacology, Georgetown University Medical Center, Washington, DC, USA.
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6
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Morad M, Zhang XH. Mechanisms of spontaneous pacing: sinoatrial nodal cells, neonatal cardiomyocytes, and human stem cell derived cardiomyocytes. Can J Physiol Pharmacol 2017; 95:1100-1107. [DOI: 10.1139/cjpp-2016-0743] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The sinoatrial (SA) node is the primary site from which the mammalian heart is paced, but the mechanisms underlying the pacemaking still remain clouded. It is generally believed that the hyperpolarization-activated current If, encoded by hyperpolarization-activated cyclic nucleotide–gated (HCN) genes, contributes significantly to pacing, which in tandem with inward current generated by efflux of Ca2+ via the Na+–Ca2+ exchanger (NCX), resulting from the released Ca2+, mediates the diastolic depolarization. Here, we review the data that implicate If as the “pacemaker current” and conclude that there is not only a significant discrepancy between the range of diastolic depolarization potential (–60 to –40 mV) and the activation potential of If (negative to –70 mV), but that also the kinetics of If and its pharmacology are incompatible with the frequency of a heartbeat in rodents and humans. We propose that If serves as a functional insulator, which protects the SA-nodal cells against the large negative electrical sink of atrial tissue connected to it with connexins. We also evaluate the role of If and calcium signaling in mediating the diastolic depolarization in rat neonatal cardiomyocytes (rN-CM), and human induced pluripotent stem-cell derived cardiomyocytes (hiPSC-CM), and provide evidence for a possible involvement of mitochondrial Ca2+ in initiating the oscillatory events required for the spontaneous pacing.
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Affiliation(s)
- Martin Morad
- Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina and Clemson University, Charleston, SC 29425, USA
- Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina and Clemson University, Charleston, SC 29425, USA
| | - Xiao-hua Zhang
- Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina and Clemson University, Charleston, SC 29425, USA
- Cardiac Signaling Center of University of South Carolina, Medical University of South Carolina and Clemson University, Charleston, SC 29425, USA
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Yang Z, Kirton HM, Al-Owais M, Thireau J, Richard S, Peers C, Steele DS. Epac2-Rap1 Signaling Regulates Reactive Oxygen Species Production and Susceptibility to Cardiac Arrhythmias. Antioxid Redox Signal 2017; 27:117-132. [PMID: 27649969 PMCID: PMC5510674 DOI: 10.1089/ars.2015.6485] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Revised: 09/19/2016] [Accepted: 09/19/2016] [Indexed: 12/19/2022]
Abstract
AIMS In the heart, β1-adrenergic signaling involves cyclic adenosine monophosphate (cAMP) acting via both protein kinase-A (PKA) and exchange protein directly activated by cAMP (Epac): a guanine nucleotide exchange factor for the small GTPase Rap1. Inhibition of Epac-Rap1 signaling has been proposed as a therapeutic strategy for both cancer and cardiovascular disease. However, previous work suggests that impaired Rap1 signaling may have detrimental effects on cardiac function. The aim of the present study was to investigate the influence of Epac2-Rap1 signaling on the heart using both in vivo and in vitro approaches. RESULTS Inhibition of Epac2 signaling induced early afterdepolarization arrhythmias in ventricular myocytes. The underlying mechanism involved an increase in mitochondrial reactive oxygen species (ROS) and activation of the late sodium current (INalate). Arrhythmias were blocked by inhibition of INalate or the mitochondria-targeted antioxidant, mitoTEMPO. In vivo, inhibition of Epac2 caused ventricular tachycardia, torsades de pointes, and sudden death. The in vitro and in vivo effects of Epac2 inhibition were mimicked by inhibition of geranylgeranyltransferase-1, which blocks interaction of Rap1 with downstream targets. INNOVATION Our findings show for the first time that Rap1 acts as a negative regulator of mitochondrial ROS production in the heart and that impaired Epac2-Rap1 signaling causes arrhythmias due to ROS-dependent activation of INalate. This has implications for the use of chemotherapeutics that target Epac2-Rap1 signaling. However, selective inhibition of INalate provides a promising strategy to prevent arrhythmias caused by impaired Epac2-Rap1 signaling. CONCLUSION Epac2-Rap1 signaling attenuates mitochondrial ROS production and reduces myocardial arrhythmia susceptibility. Antioxid. Redox Signal. 27, 117-132.
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Affiliation(s)
- Zhaokang Yang
- Faculty of Biological Sciences, School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom
| | - Hannah M. Kirton
- Faculty of Biological Sciences, School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom
| | - Moza Al-Owais
- Division of Cardiovascular Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, United Kingdom
| | - Jérôme Thireau
- PHYMEDEXP, Physiologie et Médecine Expérimentale, Cœur et Muscles, INSERM U1046, CNRS UMR 9214, Université de Montpellier, Montpellier, France
| | - Sylvain Richard
- PHYMEDEXP, Physiologie et Médecine Expérimentale, Cœur et Muscles, INSERM U1046, CNRS UMR 9214, Université de Montpellier, Montpellier, France
| | - Chris Peers
- Division of Cardiovascular Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, United Kingdom
| | - Derek S. Steele
- Faculty of Biological Sciences, School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom
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8
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Pahlavan S, Morad M. Total internal reflectance fluorescence imaging of genetically engineered ryanodine receptor-targeted Ca 2+ probes in rat ventricular myocytes. Cell Calcium 2017; 66:98-110. [PMID: 28807154 DOI: 10.1016/j.ceca.2017.07.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Revised: 07/13/2017] [Accepted: 07/14/2017] [Indexed: 12/11/2022]
Abstract
The details of cardiac Ca2+ signaling within the dyadic junction remain unclear because of limitations in rapid spatial imaging techniques, and availability of Ca2+ probes localized to dyadic junctions. To critically monitor ryanodine receptors' (RyR2) Ca2+ nano-domains, we combined the use of genetically engineered RyR2-targeted pericam probes, (FKBP-YCaMP, Kd=150nM, or FKBP-GCaMP6, Kd=240nM) with rapid total internal reflectance fluorescence (TIRF) microscopy (resolution, ∼80nm). The punctate z-line patterns of FKBP,2-targeted probes overlapped those of RyR2 antibodies and sharply contrasted to the images of probes targeted to sarcoplasmic reticulum (SERCA2a/PLB), or cytosolic Fluo-4 images. FKBP-YCaMP signals were too small (∼20%) and too slow (2-3s) to detect Ca2+ sparks, but the probe was effective in marking where Fluo-4 Ca2+ sparks developed. FKBP-GCaMP6, on the other hand, produced rapidly decaying Ca2+ signals that: a) had faster kinetics and activated synchronous with ICa3 but were of variable size at different z-lines and b) were accompanied by spatially confined spontaneous Ca2+ sparks, originating from a subset of eager sites. The frequency of spontaneously occurring sparks was lower in FKBP-GCaMP6 infected myocytes as compared to Fluo-4 dialyzed myocytes, but isoproterenol enhanced their frequency more effectively than in Fluo-4 dialyzed cells. Nevertheless, isoproterenol failed to dissociate FKBP-GCaMP6 from the z-lines. The data suggests that FKBP-GCaMP6 binds predominantly to junctional RyR2s and has sufficient on-rate efficiency as to monitor the released Ca2+ in individual dyadic clefts, and supports the idea that β-adrenergic agonists may modulate the stabilizing effects of native FKBP on RyR2.
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Affiliation(s)
- Sara Pahlavan
- Cardiac Signaling Center of University of South Carolina, Clemson University and Medical University of South Carolina, Charleston, SC 29425, USA.
| | - Marin Morad
- Cardiac Signaling Center of University of South Carolina, Clemson University and Medical University of South Carolina, Charleston, SC 29425, USA.
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9
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Wüst RCI, Helmes M, Martin JL, van der Wardt TJT, Musters RJP, van der Velden J, Stienen GJM. Rapid frequency-dependent changes in free mitochondrial calcium concentration in rat cardiac myocytes. J Physiol 2017; 595:2001-2019. [PMID: 28028811 DOI: 10.1113/jp273589] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Accepted: 12/16/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Calcium ions regulate mitochondrial ATP production and contractile activity and thus play a pivotal role in matching energy supply and demand in cardiac muscle. The magnitude and kinetics of the changes in free mitochondrial calcium concentration in cardiac myocytes are largely unknown. Rapid stimulation frequency-dependent increases but relatively slow decreases in free mitochondrial calcium concentration were observed in rat cardiac myocytes. This asymmetry caused a rise in the mitochondrial calcium concentration with stimulation frequency. These results provide insight into the mechanisms of mitochondrial calcium uptake and release that are important in healthy and diseased myocardium. ABSTRACT Calcium ions regulate mitochondrial ATP production and contractile activity and thus play a pivotal role in matching energy supply and demand in cardiac muscle. Little is known about the magnitude and kinetics of the changes in free mitochondrial calcium concentration in cardiomyocytes. Using adenoviral infection, a ratiometric mitochondrially targeted Förster resonance energy transfer (FRET)-based calcium indicator (4mtD3cpv, MitoCam) was expressed in cultured adult rat cardiomyocytes and the free mitochondrial calcium concentration ([Ca2+ ]m ) was measured at different stimulation frequencies (0.1-4 Hz) and external calcium concentrations (1.8-3.6 mm) at 37°C. Cytosolic calcium concentrations were assessed under the same experimental conditions in separate experiments using Fura-4AM. The increases in [Ca2+ ]m during electrical stimulation at 0.1 Hz were rapid (rise time = 49 ± 2 ms), while the decreases in [Ca2+ ]m occurred more slowly (decay half time = 1.17 ± 0.07 s). Model calculations confirmed that this asymmetry caused the rise in [Ca2+ ]m during diastole observed at elevated stimulation frequencies. Inhibition of the mitochondrial sodium-calcium exchanger (mNCE) resulted in a rise in [Ca2+ ]m at baseline and, paradoxically, in an acceleration of Ca2+ release. IN CONCLUSION rapid increases in [Ca2+ ]m allow for fast adjustment of mitochondrial ATP production to increases in myocardial demand on a beat-to-beat basis and mitochondrial calcium release depends on mNCE activity and mitochondrial calcium buffering.
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Affiliation(s)
- Rob C I Wüst
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, the Netherlands
| | - Michiel Helmes
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, the Netherlands.,IonOptix LLC, Milton, MA, USA
| | - Jody L Martin
- Cell and Molecular Physiology, Loyola University, Chicago, IL, USA
| | - Thomas J T van der Wardt
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, the Netherlands
| | - René J P Musters
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, the Netherlands
| | - Jolanda van der Velden
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, the Netherlands
| | - Ger J M Stienen
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, the Netherlands.,Faculty of Science, Department of Physics and Astronomy, VU University, Amsterdam, the Netherlands
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10
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Suzuki J, Kanemaru K, Iino M. Genetically Encoded Fluorescent Indicators for Organellar Calcium Imaging. Biophys J 2016; 111:1119-1131. [PMID: 27477268 DOI: 10.1016/j.bpj.2016.04.054] [Citation(s) in RCA: 89] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Revised: 03/30/2016] [Accepted: 04/01/2016] [Indexed: 12/14/2022] Open
Abstract
Optical Ca(2+) indicators are powerful tools for investigating intracellular Ca(2+) signals in living cells. Although a variety of Ca(2+) indicators have been developed, deciphering the physiological functions and spatiotemporal dynamics of Ca(2+) in intracellular organelles remains challenging. Genetically encoded Ca(2+) indicators (GECIs) using fluorescent proteins are promising tools for organellar Ca(2+) imaging, and much effort has been devoted to their development. In this review, we first discuss the key points of organellar Ca(2+) imaging and summarize the requirements for optimal organellar Ca(2+) indicators. Then, we highlight some of the recent advances in the engineering of fluorescent GECIs targeted to specific organelles. Finally, we discuss the limitations of currently available GECIs and the requirements for advancing the research on intraorganellar Ca(2+) signaling.
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Affiliation(s)
- Junji Suzuki
- Department of Pharmacology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; Department of Physiology, University of California San Francisco, San Francisco, California
| | - Kazunori Kanemaru
- Department of Pharmacology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Masamitsu Iino
- Department of Pharmacology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; Department of Cellular and Molecular Pharmacology, Nihon University School of Medicine, Tokyo, Japan.
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11
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Zhang XH, Morad M. Calcium signaling in human stem cell-derived cardiomyocytes: Evidence from normal subjects and CPVT afflicted patients. Cell Calcium 2015; 59:98-107. [PMID: 26725479 DOI: 10.1016/j.ceca.2015.12.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Revised: 12/10/2015] [Accepted: 12/11/2015] [Indexed: 10/22/2022]
Abstract
Derivation of cardiomyocyte cell lines from human fibroblasts (induced pluripotent stem cells, iPSCs) has made it possible not only to investigate the electrophysiological and Ca(2+) signaling properties of these cells, but also to determine the altered electrophysiological and Ca(2+)-signaling profiles of such cells lines derived from patients expressing mutation-inducing pathologies. This approach has the potential of generating in vitro human models of cardiovascular diseases where cellular pathology can be investigated in detail and possibly specific pharmacotherapy developed. Although this approach has been applied to a number of mutations in channel proteins that cause arrhythmias, there are only few detailed reports addressing Ca(2+) signaling pathologies beyond measurements of Ca(2+) transients in intact non-voltage clamped cells. Unfortunately, full understanding of Ca(2+) signaling pathologies remains elusive, not only because of the plethora of Ca(2+) signaling proteins defects that cause arrhythmias and cardiomyopathies, but also because detailed functional properties of Ca(2+) signaling proteins are difficult to obtain. Catecholaminergic polymorphic ventricular tachycardia (CPVT1) is a malignant inherited arrhythmogenic disorder predominantly caused by mutations in the cardiac ryanodine receptor (RyR2). Thus far over 150 mutations in RyR2 have been identified that appear to cause this arrhythmia, a number of which have been expressed and studied in transgenic mice or cell-line models. The development of human iPSC-technology makes it possible to create human heart cell-lines carrying these mutations, making detailed identification of Ca(2+) signaling defects and its specific pharmacotherapy possible. In this review we shall first briefly summarize the essential characteristics of the mammalian cardiac Ca(2+) signaling, then compare them to Ca(2+) signaling phenotypes of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) and to those of rat neonatal cardiomyocytes, and categorize the possible variance in Ca(2+) signaling defects caused by different CPVT-inducing mutations as expressed in hiPSC-CMs.
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Affiliation(s)
- Xiao-Hua Zhang
- Cardiac Signaling Center of USC, MUSC, & Clemson University, Charleston, SC 29425, USA
| | - Martin Morad
- Cardiac Signaling Center of USC, MUSC, & Clemson University, Charleston, SC 29425, USA.
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12
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Zhang XH, Wei H, Šarić T, Hescheler J, Cleemann L, Morad M. Regionally diverse mitochondrial calcium signaling regulates spontaneous pacing in developing cardiomyocytes. Cell Calcium 2015; 57:321-36. [PMID: 25746147 DOI: 10.1016/j.ceca.2015.02.003] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Revised: 01/28/2015] [Accepted: 02/10/2015] [Indexed: 12/16/2022]
Abstract
The quintessential property of developing cardiomyocytes is their ability to beat spontaneously. The mechanisms underlying spontaneous beating in developing cardiomyocytes are thought to resemble those of adult heart, but have not been directly tested. Contributions of sarcoplasmic and mitochondrial Ca(2+)-signaling vs. If-channel in initiating spontaneous beating were tested in human induced Pluripotent Stem cell-derived cardiomyocytes (hiPS-CM) and rat Neonatal cardiomyocytes (rN-CM). Whole-cell and perforated-patch voltage-clamping and 2-D confocal imaging showed: (1) both cell types beat spontaneously (60-140/min, at 24°C); (2) holding potentials between -70 and 0mV had no significant effects on spontaneous pacing, but suppressed action potential formation; (3) spontaneous pacing at -50mV activated cytosolic Ca(2+)-transients, accompanied by in-phase inward current oscillations that were suppressed by Na(+)-Ca(2+)-exchanger (NCX)- and ryanodine receptor (RyR2)-blockers, but not by Ca(2+)- and If-channels blockers; (4) spreading fluorescence images of cytosolic Ca(2+)-transients emanated repeatedly from preferred central cellular locations during spontaneous beating; (5) mitochondrial un-coupler, FCCP at non-depolarizing concentrations (∼50nM), reversibly suppressed spontaneous pacing; (6) genetically encoded mitochondrial Ca(2+)-biosensor (mitycam-E31Q) detected regionally diverse, and FCCP-sensitive mitochondrial Ca(2+)-uptake and release signals activating during INCX oscillations; (7) If-channel was absent in rN-CM, but activated only negative to -80mV in hiPS-CM; nevertheless blockers of If-channel failed to alter spontaneous pacing.
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Affiliation(s)
- Xiao-Hua Zhang
- Cardiac Signaling Center of USC, MUSC, & Clemson University, Charleston, SC, USA
| | - Hua Wei
- Cardiac Signaling Center of USC, MUSC, & Clemson University, Charleston, SC, USA
| | - Tomo Šarić
- Institute for Neurophysiology, Medical Faculty, University of Cologne, Cologne, Germany
| | - Jürgen Hescheler
- Institute for Neurophysiology, Medical Faculty, University of Cologne, Cologne, Germany
| | - Lars Cleemann
- Cardiac Signaling Center of USC, MUSC, & Clemson University, Charleston, SC, USA
| | - Martin Morad
- Cardiac Signaling Center of USC, MUSC, & Clemson University, Charleston, SC, USA.
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