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Meng Z, Capel RA, Bose SJ, Bosch E, de Jong S, Planque R, Galione A, Burton RAB, Bueno-Orovio A. Lysosomal calcium loading promotes spontaneous calcium release by potentiating ryanodine receptors. Biophys J 2023; 122:3044-3059. [PMID: 37329137 PMCID: PMC10432190 DOI: 10.1016/j.bpj.2023.06.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 05/03/2023] [Accepted: 06/12/2023] [Indexed: 06/18/2023] Open
Abstract
Spontaneous calcium release by ryanodine receptors (RyRs) due to intracellular calcium overload results in delayed afterdepolarizations, closely associated with life-threatening arrhythmias. In this regard, inhibiting lysosomal calcium release by two-pore channel 2 (TPC2) knockout has been shown to reduce the incidence of ventricular arrhythmias under β-adrenergic stimulation. However, mechanistic investigations into the role of lysosomal function on RyR spontaneous release remain missing. We investigate the calcium handling mechanisms by which lysosome function modulates RyR spontaneous release, and determine how lysosomes are able to mediate arrhythmias by its influence on calcium loading. Mechanistic studies were conducted using a population of biophysically detailed mouse ventricular models including for the first time modeling of lysosomal function, and calibrated by experimental calcium transients modulated by TPC2. We demonstrate that lysosomal calcium uptake and release can synergistically provide a pathway for fast calcium transport, by which lysosomal calcium release primarily modulates sarcoplasmic reticulum calcium reuptake and RyR release. Enhancement of this lysosomal transport pathway promoted RyR spontaneous release by elevating RyR open probability. In contrast, blocking either lysosomal calcium uptake or release revealed an antiarrhythmic impact. Under conditions of calcium overload, our results indicate that these responses are strongly modulated by intercellular variability in L-type calcium current, RyR release, and sarcoplasmic reticulum calcium-ATPase reuptake. Altogether, our investigations identify that lysosomal calcium handling directly influences RyR spontaneous release by regulating RyR open probability, suggesting antiarrhythmic strategies and identifying key modulators of lysosomal proarrhythmic action.
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Affiliation(s)
- Zhaozheng Meng
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Rebecca A Capel
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Samuel J Bose
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Erik Bosch
- Department of Mathematics, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
| | - Sophia de Jong
- Department of Mathematics, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
| | - Robert Planque
- Department of Mathematics, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
| | - Antony Galione
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Rebecca A B Burton
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom.
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2
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Chan XHS, Chotsiri P, Capel RA, Pike J, Hanboonkunupakarn B, Lee SJ, Hanafiah M, Win YN, Cremer MA, Kiechel J, Ogutu B, Taylor WRJ, Burton RB, Tarning J, White NJ. Cardiovascular concentration-effect relationships of amodiaquine and its metabolite desethylamodiaquine: Clinical and preclinical studies. Br J Clin Pharmacol 2023; 89:1176-1186. [PMID: 36256474 PMCID: PMC7614325 DOI: 10.1111/bcp.15569] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Revised: 09/18/2022] [Accepted: 10/10/2022] [Indexed: 11/02/2022] Open
Abstract
AIMS Amodiaquine is a 4-aminoquinoline used extensively for the treatment and prevention of malaria. Orally administered amodiaquine is largely converted to the active metabolite desethylamodiaquine. Amodiaquine can cause bradycardia, hypotension, and electrocardiograph QT interval prolongation, but the relationship of these changes to drug concentrations is not well characterized. METHODS We conducted a secondary analysis of a pharmacokinetic study of the cardiac safety of amodiaquine (10 mg base/kg/day over 3 days) in 54 Kenyan adults (≥18 years) with uncomplicated malaria. Nonlinear mixed effects modelling was used to assess amodiaquine and desethylamodiaquine concentration-effect relationships for vital sign (pulse rate, blood pressure) and electrocardiograph interval (QT, QRS, PR) outcomes. We also measured the spontaneous beating heart rate after cumulative dosing of amodiaquine and desethylamodiaquine in isolated mouse atrial preparations. RESULTS Amodiaquine and desethylamodiaquine caused concentration-dependent mean decreases in pulse rate (1.9 beats/min per 100 nmol/L; 95% confidence interval: 1.5-2.4), supine systolic blood pressure (1.7 mmHg per 100 nmol/L; 1.2-2.1), erect systolic blood pressure (1.5 mmHg per 100 nmol/L; 1.0-2.0) and erect diastolic blood pressure (1.4 mmHg per 100 nmol/L; 1.0-1.7). The mean QT interval prolongation was 1.4 ms per 100 nmol/L irrespective of correction factor after adjustment for residual heart rate dependency. There was no significant effect of drug concentration on postural change in blood pressure or PR and QRS intervals. In mouse atria, the spontaneous beating rate was significantly reduced by amodiaquine (n = 6) and desethylamodiaquine (n = 8) at 3 μmol/L (amodiaquine: 10 ± 2%; desethylamodiaquine: 12 ± 3%) and 10 μmol/L (amodiaquine: 50 ± 7%; desethylamodiaquine: 46 ± 6%) concentrations with no significant difference in potency between the 2 compounds. CONCLUSION Amodiaquine and desethylamodiaquine have concentration-dependent effects on heart rate, blood pressure, and ventricular repolarization.
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Affiliation(s)
- Xin Hui S. Chan
- Mahidol‐Oxford Tropical Medicine Research Unit, Faculty of Tropical MedicineMahidol UniversityBangkokThailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of MedicineUniversity of OxfordOxfordUK
| | - Palang Chotsiri
- Mahidol‐Oxford Tropical Medicine Research Unit, Faculty of Tropical MedicineMahidol UniversityBangkokThailand
| | | | - James Pike
- Mahidol‐Oxford Tropical Medicine Research Unit, Faculty of Tropical MedicineMahidol UniversityBangkokThailand
| | - Borimas Hanboonkunupakarn
- Mahidol‐Oxford Tropical Medicine Research Unit, Faculty of Tropical MedicineMahidol UniversityBangkokThailand
- Department of Clinical Tropical Medicine, Faculty of Tropical MedicineMahidol UniversityBangkokThailand
| | - Sue J. Lee
- Mahidol‐Oxford Tropical Medicine Research Unit, Faculty of Tropical MedicineMahidol UniversityBangkokThailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of MedicineUniversity of OxfordOxfordUK
| | - Maryam Hanafiah
- Mahidol‐Oxford Tropical Medicine Research Unit, Faculty of Tropical MedicineMahidol UniversityBangkokThailand
| | - Yan Naung Win
- Mahidol‐Oxford Tropical Medicine Research Unit, Faculty of Tropical MedicineMahidol UniversityBangkokThailand
- Department of Preventive and Social MedicineUniversity of MedicineTaunggyiMyanmar
| | | | | | | | - Walter R. J. Taylor
- Mahidol‐Oxford Tropical Medicine Research Unit, Faculty of Tropical MedicineMahidol UniversityBangkokThailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of MedicineUniversity of OxfordOxfordUK
| | | | - Joel Tarning
- Mahidol‐Oxford Tropical Medicine Research Unit, Faculty of Tropical MedicineMahidol UniversityBangkokThailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of MedicineUniversity of OxfordOxfordUK
- WorldWide Antimalarial Research Network, Centre for Tropical Medicine and Global Health, Nuffield Department of MedicineUniversity of OxfordOxfordUK
| | - Nicholas J. White
- Mahidol‐Oxford Tropical Medicine Research Unit, Faculty of Tropical MedicineMahidol UniversityBangkokThailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of MedicineUniversity of OxfordOxfordUK
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3
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Bose SJ, Read MJ, Akerman E, Capel RA, Ayagama T, Russell A, Terrar DA, Zaccolo M, Burton RAB. Inhibition of adenylyl cyclase 1 by ST034307 inhibits IP3-evoked changes in sino-atrial node beat rate. Front Pharmacol 2022; 13:951897. [PMID: 36105228 PMCID: PMC9465815 DOI: 10.3389/fphar.2022.951897] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Accepted: 08/01/2022] [Indexed: 11/13/2022] Open
Abstract
Atrial arrhythmias, such as atrial fibrillation (AF), are a major mortality risk and a leading cause of stroke. The IP3 signalling pathway has been proposed as an atrial-specific target for AF therapy, and atrial IP3 signalling has been linked to the activation of calcium sensitive adenylyl cyclases AC1 and AC8. We investigated the involvement of AC1 in the response of intact mouse atrial tissue and isolated guinea pig atrial and sino-atrial node (SAN) cells to the α-adrenoceptor agonist phenylephrine (PE) using the selective AC1 inhibitor ST034307. The maximum rate change of spontaneously beating mouse right atrial tissue exposed to PE was reduced from 14.5% to 8.2% (p = 0.005) in the presence of 1 μM ST034307, whereas the increase in tension generated in paced left atrial tissue in the presence of PE was not inhibited by ST034307 (Control = 14.2%, ST034307 = 16.3%; p > 0.05). Experiments were performed using isolated guinea pig atrial and SAN cells loaded with Fluo-5F-AM to record changes in calcium transients (CaT) generated by 10 μM PE in the presence and absence of 1 μM ST034307. ST034307 significantly reduced the beating rate of SAN cells (0.34-fold decrease; p = 0.003) but did not inhibit changes in CaT amplitude in response to PE in atrial cells. The results presented here demonstrate pharmacologically the involvement of AC1 in the downstream response of atrial pacemaker activity to α-adrenoreceptor stimulation and IP3R calcium release.
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Affiliation(s)
- Samuel J. Bose
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Matthew J. Read
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Emily Akerman
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Rebecca A. Capel
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Thamali Ayagama
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Angela Russell
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
- Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Oxford, United Kingdom
| | - Derek A. Terrar
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Manuela Zaccolo
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Rebecca A. B. Burton
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
- *Correspondence: Rebecca A. B. Burton,
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Ayagama T, Bose SJ, Capel RA, Priestman DA, Berridge G, Fischer R, Galione A, Platt FM, Kramer H, Burton RA. A modified density gradient proteomic-based method to analyze endolysosomal proteins in cardiac tissue. iScience 2021; 24:102949. [PMID: 34466782 PMCID: PMC8384914 DOI: 10.1016/j.isci.2021.102949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 03/04/2021] [Accepted: 08/02/2021] [Indexed: 11/22/2022] Open
Abstract
The importance of lysosomes in cardiac physiology and pathology is well established, and evidence for roles in calcium signaling is emerging. We describe a label-free proteomics method suitable for small cardiac tissue biopsies based on density-separated fractionation, which allows study of endolysosomal (EL) proteins. Density gradient fractions corresponding to tissue lysate; sarcoplasmic reticulum (SR), mitochondria (Mito) (1.3 g/mL); and EL with negligible contamination from SR or Mito (1.04 g/mL) were analyzed using Western blot, enzyme activity assay, and liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis (adapted discontinuous Percoll and sucrose differential density gradient). Kyoto Encyclopedia of Genes and Genomes, Reactome, Panther, and Gene Ontology pathway analysis showed good coverage of RAB proteins and lysosomal cathepsins (including cardiac-specific cathepsin D) in the purified EL fraction. Significant EL proteins recovered included catalytic activity proteins. We thus present a comprehensive protocol and data set of guinea pig atrial EL organelle proteomics using techniques also applicable for non-cardiac tissue.
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Affiliation(s)
- Thamali Ayagama
- University of Oxford, Department of Pharmacology, Oxford, OX1 3QT UK
| | - Samuel J. Bose
- University of Oxford, Department of Pharmacology, Oxford, OX1 3QT UK
| | - Rebecca A. Capel
- University of Oxford, Department of Pharmacology, Oxford, OX1 3QT UK
| | | | - Georgina Berridge
- Target Discovery Institute, University of Oxford, Oxford, OX3 7FZ UK
| | - Roman Fischer
- Target Discovery Institute, University of Oxford, Oxford, OX3 7FZ UK
| | - Antony Galione
- University of Oxford, Department of Pharmacology, Oxford, OX1 3QT UK
| | - Frances M. Platt
- University of Oxford, Department of Pharmacology, Oxford, OX1 3QT UK
| | - Holger Kramer
- Biological Mass Spectrometry and Proteomics Facility, MRC London Institute of Medical Sciences, Imperial College London, London, W12 0NN UK
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Whittaker DG, Capel RA, Hendrix M, Chan XHS, Herring N, White NJ, Mirams GR, Burton RAB. Cardiac TdP risk stratification modelling of anti-infective compounds including chloroquine and hydroxychloroquine. R Soc Open Sci 2021; 8:210235. [PMID: 33996135 PMCID: PMC8059594 DOI: 10.1098/rsos.210235] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Accepted: 03/30/2021] [Indexed: 05/06/2023]
Abstract
Hydroxychloroquine (HCQ), the hydroxyl derivative of chloroquine (CQ), is widely used in the treatment of rheumatological conditions (systemic lupus erythematosus, rheumatoid arthritis) and is being studied for the treatment and prevention of COVID-19. Here, we investigate through mathematical modelling the safety profile of HCQ, CQ and other QT-prolonging anti-infective agents to determine their risk categories for Torsade de Pointes (TdP) arrhythmia. We performed safety modelling with uncertainty quantification using a risk classifier based on the qNet torsade metric score, a measure of the net charge carried by major currents during the action potential under inhibition of multiple ion channels by a compound. Modelling results for HCQ at a maximum free therapeutic plasma concentration (free C max) of approximately 1.2 µM (malaria dosing) indicated it is most likely to be in the high-intermediate-risk category for TdP, whereas CQ at a free C max of approximately 0.7 µM was predicted to most likely lie in the intermediate-risk category. Combining HCQ with the antibacterial moxifloxacin or the anti-malarial halofantrine (HAL) increased the degree of human ventricular action potential duration prolongation at some or all concentrations investigated, and was predicted to increase risk compared to HCQ alone. The combination of HCQ/HAL was predicted to be the riskiest for the free C max values investigated, whereas azithromycin administered individually was predicted to pose the lowest risk. Our simulation approach highlights that the torsadogenic potentials of HCQ, CQ and other QT-prolonging anti-infectives used in COVID-19 prevention and treatment increase with concentration and in combination with other QT-prolonging drugs.
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Affiliation(s)
- Dominic G. Whittaker
- Centre for Mathematical Medicine and Biology, School of Mathematical Sciences, University of Nottingham, Nottingham, UK
| | | | - Maurice Hendrix
- Centre for Mathematical Medicine and Biology, School of Mathematical Sciences, University of Nottingham, Nottingham, UK
- Digital Research Service, University of Nottingham, Nottingham, UK
| | - Xin Hui S. Chan
- Mahidol-Oxford Tropical Medicine Research Unit, Mahidol University, Bangkok, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Neil Herring
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
| | - Nicholas J. White
- Mahidol-Oxford Tropical Medicine Research Unit, Mahidol University, Bangkok, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Gary R. Mirams
- Centre for Mathematical Medicine and Biology, School of Mathematical Sciences, University of Nottingham, Nottingham, UK
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6
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Capel RA, Bose SJ, Collins TP, Rajasundaram S, Ayagama T, Zaccolo M, Burton RAB, Terrar DA. IP 3-mediated Ca 2+ release regulates atrial Ca 2+ transients and pacemaker function by stimulation of adenylyl cyclases. Am J Physiol Heart Circ Physiol 2020; 320:H95-H107. [PMID: 33064562 PMCID: PMC7864251 DOI: 10.1152/ajpheart.00380.2020] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Inositol trisphosphate (IP3) is a Ca2+-mobilizing second messenger shown to modulate atrial muscle contraction and is thought to contribute to atrial fibrillation. Cellular pathways underlying IP3 actions in cardiac tissue remain poorly understood, and the work presented here addresses the question whether IP3-mediated Ca2+ release from the sarcoplasmic reticulum is linked to adenylyl cyclase activity including Ca2+-stimulated adenylyl cyclases (AC1 and AC8) that are selectively expressed in atria and sinoatrial node (SAN). Immunocytochemistry in guinea pig atrial myocytes identified colocalization of type 2 IP3 receptors with AC8, while AC1 was located in close vicinity. Intracellular photorelease of IP3 by UV light significantly enhanced the amplitude of the Ca2+ transient (CaT) evoked by electrical stimulation of atrial myocytes (31 ± 6% increase 60 s after photorelease, n = 16). The increase in CaT amplitude was abolished by inhibitors of adenylyl cyclases (MDL-12,330) or protein kinase A (H89), showing that cAMP signaling is required for this effect of photoreleased IP3. In mouse, spontaneously beating right atrial preparations, phenylephrine, an α-adrenoceptor agonist with effects that depend on IP3-mediated Ca2+ release, increased the maximum beating rate by 14.7 ± 0.5%, n = 10. This effect was substantially reduced by 2.5 µmol/L 2-aminoethyl diphenylborinate and abolished by a low dose of MDL-12,330, observations which are again consistent with a functional interaction between IP3 and cAMP signaling involving Ca2+ stimulation of adenylyl cyclases in the SAN pacemaker. Understanding the interaction between IP3 receptor pathways and Ca2+-stimulated adenylyl cyclases provides important insights concerning acute mechanisms for initiation of atrial arrhythmias. NEW & NOTEWORTHY This study provides evidence supporting the proposal that IP3 signaling in cardiac atria and sinoatrial node involves stimulation of Ca2+-activated adenylyl cyclases (AC1 and AC8) by IP3-evoked Ca2+ release from junctional sarcoplasmic reticulum. AC8 and IP3 receptors are shown to be located close together, while AC1 is nearby. Greater understanding of these novel aspects of the IP3 signal transduction mechanism is important for future study in atrial physiology and pathophysiology, particularly atrial fibrillation.
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Affiliation(s)
- Rebecca A Capel
- Department of Pharmacology, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Samuel J Bose
- Department of Pharmacology, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Thomas P Collins
- Department of Pharmacology, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Skanda Rajasundaram
- Department of Pharmacology, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Thamali Ayagama
- Department of Pharmacology, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Manuela Zaccolo
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Rebecca-Ann Beatrice Burton
- Department of Pharmacology, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Derek A Terrar
- Department of Pharmacology, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
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7
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Burton RAB, Tomek J, Ambrosi CM, Larsen HE, Sharkey AR, Capel RA, Corbett AD, Bilton S, Klimas A, Stephens G, Cremer M, Bose SJ, Li D, Gallone G, Herring N, Mann EO, Kumar A, Kramer H, Entcheva E, Paterson DJ, Bub G. Optical Interrogation of Sympathetic Neuronal Effects on Macroscopic Cardiomyocyte Network Dynamics. iScience 2020; 23:101334. [PMID: 32674058 PMCID: PMC7363704 DOI: 10.1016/j.isci.2020.101334] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 05/12/2020] [Accepted: 06/26/2020] [Indexed: 12/21/2022] Open
Abstract
Cardiac stimulation via sympathetic neurons can potentially trigger arrhythmias. We present approaches to study neuron-cardiomyocyte interactions involving optogenetic selective probing and all-optical electrophysiology to measure activity in an automated fashion. Here we demonstrate the utility of optical interrogation of sympathetic neurons and their effects on macroscopic cardiomyocyte network dynamics to address research targets such as the effects of adrenergic stimulation via the release of neurotransmitters, the effect of neuronal numbers on cardiac behavior, and the applicability of optogenetics in mechanistic in vitro studies. As arrhythmias are emergent behaviors that involve the coordinated activity of millions of cells, we image at macroscopic scales to capture complex dynamics. We show that neurons can both decrease and increase wave stability and re-entrant activity in culture depending on their induced activity-a finding that may help us understand the often conflicting results seen in experimental and clinical studies.
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Affiliation(s)
- Rebecca-Ann B Burton
- University of Oxford, Department of Pharmacology, Mansfield Road, Oxford OX1 3QT, UK; University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK.
| | - Jakub Tomek
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK
| | - Christina M Ambrosi
- The George Washington University, Department of Biomedical Engineering, Washington, DC 20052, USA
| | - Hege E Larsen
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK
| | - Amy R Sharkey
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK
| | - Rebecca A Capel
- University of Oxford, Department of Pharmacology, Mansfield Road, Oxford OX1 3QT, UK
| | | | - Samuel Bilton
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK
| | - Aleksandra Klimas
- The George Washington University, Department of Biomedical Engineering, Washington, DC 20052, USA
| | - Guy Stephens
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK
| | - Maegan Cremer
- University of Oxford, Department of Pharmacology, Mansfield Road, Oxford OX1 3QT, UK
| | - Samuel J Bose
- University of Oxford, Department of Pharmacology, Mansfield Road, Oxford OX1 3QT, UK
| | - Dan Li
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK
| | - Giuseppe Gallone
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK; Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Ihnestraße 63-73, 14195 Berlin, Germany
| | - Neil Herring
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK
| | - Edward O Mann
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK
| | - Abhinav Kumar
- University of Oxford, Department of Biochemistry, Glycobiology Institute, Oxford, UK
| | - Holger Kramer
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK
| | - Emilia Entcheva
- The George Washington University, Department of Biomedical Engineering, Washington, DC 20052, USA
| | - David J Paterson
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK
| | - Gil Bub
- University of Oxford, Department of Physiology, Anatomy and Genetics, British Heart Foundation Centre of Research Excellence, Parks Road, Oxford OX1 3PT, UK; McGill University, Department of Physiology, McIntyre Medical Sciences Building, Room 1128, 3655 Promenade Sir William Osler, Montréal, QC H3G 1Y6, Canada.
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8
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Wen Q, Gandhi K, Capel RA, Hao G, O'Shea C, Neagu G, Pearcey S, Pavlovic D, Terrar DA, Wu J, Faggian G, Camelliti P, Lei M. Transverse cardiac slicing and optical imaging for analysis of transmural gradients in membrane potential and Ca 2+ transients in murine heart. J Physiol 2018; 596:3951-3965. [PMID: 29928770 PMCID: PMC6117587 DOI: 10.1113/jp276239] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Accepted: 06/12/2018] [Indexed: 11/18/2022] Open
Abstract
Key points A robust cardiac slicing approach was developed for optical mapping of transmural gradients in transmembrane potential (Vm) and intracellular Ca2+ transient (CaT) of murine heart. Significant transmural gradients in Vm and CaT were observed in the left ventricle. Frequency‐dependent action potentials and CaT alternans were observed in all ventricular regions with rapid pacing, with significantly greater incidence in the endocardium than epicardium. The observations demonstrate the feasibility of our new approach to cardiac slicing for systematic analysis of intrinsic transmural and regional gradients in Vm and CaT.
Abstract Transmural and regional gradients in membrane potential and Ca2+ transient in the murine heart are largely unexplored. Here, we developed and validated a robust approach which combines transverse ultra‐thin cardiac slices and high resolution optical mapping to enable systematic analysis of transmural and regional gradients in transmembrane potential (Vm) and intracellular Ca2+ transient (CaT) across the entire murine ventricles. The voltage dye RH237 or Ca2+ dye Rhod‐2 AM were loaded through the coronary circulation using a Langendorff perfusion system. Short‐axis slices (300 μm thick) were prepared from the entire ventricles (from the apex to the base) by using a high‐precision vibratome. Action potentials (APs) and CaTs were recorded with optical mapping during steady‐state baseline and rapid pacing. Significant transmural gradients in Vm and CaT were observed in the left ventricle, with longer AP duration (APD50 and APD75) and CaT duration (CaTD50 and CaTD75) in the endocardium compared with that in the epicardium. No significant regional gradients were observed along the apico‐basal axis of the left ventricle. Interventricular gradients were detected with significantly shorter APD50, APD75 and CaTD50 in the right ventricle compared with left ventricle and ventricular septum. During rapid pacing, AP and CaT alternans were observed in most ventricular regions, with significantly greater incidence in the endocardium in comparison with epicardium. In conclusion, these observations demonstrate the feasibility of our new approach to cardiac slicing for systematic analysis of intrinsic transmural and regional gradients in Vm and CaT in murine ventricular tissue. A robust cardiac slicing approach was developed for optical mapping of transmural gradients in transmembrane potential (Vm) and intracellular Ca2+ transient (CaT) of murine heart. Significant transmural gradients in Vm and CaT were observed in the left ventricle. Frequency‐dependent action potentials and CaT alternans were observed in all ventricular regions with rapid pacing, with significantly greater incidence in the endocardium than epicardium. The observations demonstrate the feasibility of our new approach to cardiac slicing for systematic analysis of intrinsic transmural and regional gradients in Vm and CaT.
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Affiliation(s)
- Q Wen
- Institution of Cardiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - K Gandhi
- Medical School, University of Verona, Verona, Italy
| | - Rebecca A Capel
- Department of Pharmacology, University of Oxford, Oxford, UK
| | - G Hao
- Key Laboratory of Medical Electrophysiology of Ministry of Education, Collaborative Innovation Center for Prevention and Treatment of Cardiovascular Disease/Institute of Cardiovascular Research, Southwest Medical University, Luzhou, 6400, China
| | - C O'Shea
- Institute of Cardiovascular Sciences, University of Birmingham, Birmingham, UK
| | - G Neagu
- Department of Pharmacology, University of Oxford, Oxford, UK
| | - S Pearcey
- Department of Pharmacology, University of Oxford, Oxford, UK
| | - D Pavlovic
- Institute of Cardiovascular Sciences, University of Birmingham, Birmingham, UK
| | - Derek A Terrar
- Department of Pharmacology, University of Oxford, Oxford, UK
| | - J Wu
- Institution of Cardiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - G Faggian
- Medical School, University of Verona, Verona, Italy
| | | | - M Lei
- Department of Pharmacology, University of Oxford, Oxford, UK.,Key Laboratory of Medical Electrophysiology of Ministry of Education, Collaborative Innovation Center for Prevention and Treatment of Cardiovascular Disease/Institute of Cardiovascular Research, Southwest Medical University, Luzhou, 6400, China
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9
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Peyronnet R, Bollensdorff C, Capel RA, Rog-Zielinska EA, Woods CE, Charo DN, Lookin O, Fajardo G, Ho M, Quertermous T, Ashley EA, Kohl P. Load-dependent effects of apelin on murine cardiomyocytes. Prog Biophys Mol Biol 2017; 130:333-343. [PMID: 28935153 PMCID: PMC5726609 DOI: 10.1016/j.pbiomolbio.2017.09.013] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/13/2017] [Revised: 09/07/2017] [Accepted: 09/08/2017] [Indexed: 01/26/2023]
Abstract
The apelin peptide is described as one of the most potent inotropic agents, produced endogenously in a wide range of cells, including cardiomyocytes. Despite positive effects on cardiac contractility in multicellular preparations, as well as indications of cardio-protective actions in several diseases, its effects and mechanisms of action at the cellular level are incompletely understood. Here, we report apelin effects on dynamic mechanical characteristics of single ventricular cardiomyocytes, isolated from mouse models (control, apelin-deficient [Apelin-KO], apelin-receptor KO mouse [APJ-KO]), and rat. Dynamic changes in maximal velocity of cell shortening and relaxation were monitored. In addition, more traditional indicators of inotropic effects, such as maximum shortening (in mechanically unloaded cells) or peak force development (in auxotonic contracting cells, preloaded using the carbon fibre technique) were studied. The key finding is that, using Apelin-KO cardiomyocytes exposed to different preloads with the 2-carbon fibre technique, we observe a lowering of the slope of the end-diastolic stress-length relation in response to 10 nM apelin, an effect that is preload-dependent. This suggests a positive lusitropic effect of apelin, which could explain earlier counter-intuitive findings on an apelin-induced increase in contractility occurring without matching rise in oxygen consumption.
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Affiliation(s)
- Rémi Peyronnet
- Institute for Experimental Cardiovascular Medicine, University Heart Centre Freiburg · Bad Krozingen, Medical School of the University of Freiburg, Germany; Imperial College London, NHLI, Heart Science Centre, UK.
| | - Christian Bollensdorff
- Imperial College London, NHLI, Heart Science Centre, UK; Sidra Medical and Research Center, Qatar Foundation, Qatar
| | | | - Eva A Rog-Zielinska
- Institute for Experimental Cardiovascular Medicine, University Heart Centre Freiburg · Bad Krozingen, Medical School of the University of Freiburg, Germany; Imperial College London, NHLI, Heart Science Centre, UK
| | - Christopher E Woods
- Stanford University Division of Cardiovascular Medicine, Stanford, USA; Palo Alto Medical Foundation, Burlingame, CA, USA
| | - David N Charo
- Stanford University Division of Cardiovascular Medicine, Stanford, USA
| | - Oleg Lookin
- Ural Branch of the Russian Academy of Sciences, Ekaterinburg, Russian Federation
| | - Giovanni Fajardo
- Stanford University Division of Cardiovascular Medicine, Stanford, USA
| | - Michael Ho
- Stanford University Division of Cardiovascular Medicine, Stanford, USA
| | | | - Euan A Ashley
- Stanford University Division of Cardiovascular Medicine, Stanford, USA
| | - Peter Kohl
- Institute for Experimental Cardiovascular Medicine, University Heart Centre Freiburg · Bad Krozingen, Medical School of the University of Freiburg, Germany; Imperial College London, NHLI, Heart Science Centre, UK
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10
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Teh I, Burton RAB, McClymont D, Capel RA, Aston D, Kohl P, Schneider JE. Mapping cardiac microstructure of rabbit heart in different mechanical states by high resolution diffusion tensor imaging: A proof-of-principle study. Prog Biophys Mol Biol 2016; 121:85-96. [PMID: 27320383 PMCID: PMC4959513 DOI: 10.1016/j.pbiomolbio.2016.06.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Accepted: 06/13/2016] [Indexed: 01/27/2023]
Abstract
Myocardial microstructure and its macroscopic materialisation are fundamental to the function of the heart. Despite this importance, characterisation of cellular features at the organ level remains challenging, and a unifying description of the structure of the heart is still outstanding. Here, we optimised diffusion tensor imaging data to acquire high quality data in ex vivo rabbit hearts in slack and contractured states, approximating diastolic and systolic conditions. The data were analysed with a suite of methods that focused on different aspects of the myocardium. In the slack heart, we observed a similar transmural gradient in helix angle of the primary eigenvector of up to 23.6°/mm in the left ventricle and 24.2°/mm in the right ventricle. In the contractured heart, the same transmural gradient remained largely linear, but was offset by up to +49.9° in the left ventricle. In the right ventricle, there was an increase in the transmural gradient to 31.2°/mm and an offset of up to +39.0°. The application of tractography based on each eigenvector enabled visualisation of streamlines that depict cardiomyocyte and sheetlet organisation over large distances. We observed multiple V- and N-shaped sheetlet arrangements throughout the myocardium, and insertion of sheetlets at the intersection of the left and right ventricle. This study integrates several complementary techniques to visualise and quantify the heart's microstructure, projecting parameter representations across different length scales. This represents a step towards a more comprehensive characterisation of myocardial microstructure at the whole organ level.
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Affiliation(s)
- Irvin Teh
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom
| | - Rebecca A B Burton
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Darryl McClymont
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom
| | - Rebecca A Capel
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Daniel Aston
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Peter Kohl
- National Heart and Lung Institute, Imperial College London, London, United Kingdom; Institute for Experimental Cardiovascular Medicine, University Heart Centre Freiburg - Bad Krozingen, Medical School of the University of Freiburg, Germany
| | - Jürgen E Schneider
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom.
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11
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Capel RA, Mirams GR, Beattie KA, Paterson DJ, Terrar DA, Burton RAB. 6 Can you teach an old dog new tricks? The anti-malarial hydroxychloroquine shows promise in cardiac rate control through actions at the sino-atrial node. Heart 2015. [DOI: 10.1136/heartjnl-2015-308734.6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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12
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Capel RA, Bolton EL, Lin WK, Aston D, Wang Y, Liu W, Wang X, Burton RAB, Bloor-Young D, Shade KT, Ruas M, Parrington J, Churchill GC, Lei M, Galione A, Terrar DA. Two-pore Channels (TPC2s) and Nicotinic Acid Adenine Dinucleotide Phosphate (NAADP) at Lysosomal-Sarcoplasmic Reticular Junctions Contribute to Acute and Chronic β-Adrenoceptor Signaling in the Heart. J Biol Chem 2015; 290:30087-98. [PMID: 26438825 PMCID: PMC4705968 DOI: 10.1074/jbc.m115.684076] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Indexed: 12/12/2022] Open
Abstract
Ca2+-permeable type 2 two-pore channels (TPC2) are lysosomal proteins required for nicotinic acid adenine dinucleotide phosphate (NAADP)-evoked Ca2+ release in many diverse cell types. Here, we investigate the importance of TPC2 proteins for the physiology and pathophysiology of the heart. NAADP-AM failed to enhance Ca2+ responses in cardiac myocytes from Tpcn2−/− mice, unlike myocytes from wild-type (WT) mice. Ca2+/calmodulin-dependent protein kinase II inhibitors suppressed actions of NAADP in myocytes. Ca2+ transients and contractions accompanying action potentials were increased by isoproterenol in myocytes from WT mice, but these effects of β-adrenoreceptor stimulation were reduced in myocytes from Tpcn2−/− mice. Increases in amplitude of L-type Ca2+ currents evoked by isoproterenol remained unchanged in myocytes from Tpcn2−/− mice showing no loss of β-adrenoceptors or coupling mechanisms. Whole hearts from Tpcn2−/− mice also showed reduced inotropic effects of isoproterenol and a reduced tendency for arrhythmias following acute β-adrenoreceptor stimulation. Hearts from Tpcn2−/− mice chronically exposed to isoproterenol showed less cardiac hypertrophy and increased threshold for arrhythmogenesis compared with WT controls. Electron microscopy showed that lysosomes form close contacts with the sarcoplasmic reticulum (separation ∼25 nm). We propose that Ca2+-signaling nanodomains between lysosomes and sarcoplasmic reticulum dependent on NAADP and TPC2 comprise an important element in β-adrenoreceptor signal transduction in cardiac myocytes. In summary, our observations define a role for NAADP and TPC2 at lysosomal/sarcoplasmic reticulum junctions as unexpected but major contributors in the acute actions of β-adrenergic signaling in the heart and also in stress pathways linking chronic stimulation of β-adrenoceptors to hypertrophy and associated arrhythmias.
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Affiliation(s)
- Rebecca A Capel
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - Emma L Bolton
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - Wee K Lin
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - Daniel Aston
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - Yanwen Wang
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - Wei Liu
- the Faculty of Life Science, University of Manchester, Manchester M13 9NT, and
| | - Xin Wang
- the Faculty of Life Science, University of Manchester, Manchester M13 9NT, and
| | - Rebecca-Ann B Burton
- the Department of Physiology, Anatomy and Genetics, Sherrington Building, University of Oxford, Sherrington Road, Oxford OX1 3PT, United Kingdom
| | - Duncan Bloor-Young
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - Kai-Ting Shade
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - Margarida Ruas
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - John Parrington
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - Grant C Churchill
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - Ming Lei
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - Antony Galione
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT
| | - Derek A Terrar
- From the Department of Pharmacology, BHF Centre of Research Excellence, University of Oxford, Mansfield Road, Oxford OX1 3QT,
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13
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Capel RA, Herring N, Kalla M, Yavari A, Mirams GR, Douglas G, Bub G, Channon K, Paterson DJ, Terrar DA, Burton RAB. Hydroxychloroquine reduces heart rate by modulating the hyperpolarization-activated current If: Novel electrophysiological insights and therapeutic potential. Heart Rhythm 2015; 12:2186-94. [PMID: 26025323 PMCID: PMC4689153 DOI: 10.1016/j.hrthm.2015.05.027] [Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Indexed: 01/01/2023]
Abstract
BACKGROUND Bradycardic agents are of interest for the treatment of ischemic heart disease and heart failure, as heart rate is an important determinant of myocardial oxygen consumption. OBJECTIVES The purpose of this study was to investigate the propensity of hydroxychloroquine (HCQ) to cause bradycardia. METHODS We assessed the effects of HCQ on (1) cardiac beating rate in vitro (mice); (2) the "funny" current (If) in isolated guinea pig sinoatrial node (SAN) myocytes (1, 3, 10 µM); (3) heart rate and blood pressure in vivo by acute bolus injection (rat, dose range 1-30 mg/kg), (4) blood pressure and ventricular function during feeding (mouse, 100 mg/kg/d for 2 wk, tail cuff plethysmography, anesthetized echocardiography). RESULTS In mouse atria, spontaneous beating rate was significantly (P < .05) reduced (by 9% ± 3% and 15% ± 2% at 3 and 10 µM HCQ, n = 7). In guinea pig isolated SAN cells, HCQ conferred a significant reduction in spontaneous action potential firing rate (17% ± 6%, 1 μM dose) and a dose-dependent reduction in If (13% ± 3% at 1 µM; 19% ± 2% at 3 µM). Effects were also observed on L-type calcium ion current (ICaL) (12% ± 4% reduction) and rapid delayed rectifier potassium current (IKr) (35% ± 4%) at 3 µM. Intravenous HCQ decreased heart rate in anesthetized rats (14.3% ± 1.1% at 15mg/kg; n = 6) without significantly reducing mean arterial blood pressure. In vivo feeding studies in mice showed no significant change in systolic blood pressure nor left ventricular function. CONCLUSIONS We have shown that HCQ acts as a bradycardic agent in SAN cells, in atrial preparations, and in vivo. HCQ slows the rate of spontaneous action potential firing in the SAN through multichannel inhibition, including that of If.
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Affiliation(s)
- Rebecca A Capel
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Neil Herring
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Manish Kalla
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Arash Yavari
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Gary R Mirams
- Department of Computer Science, University of Oxford, Oxford, United Kingdom
| | - Gillian Douglas
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Gil Bub
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Keith Channon
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - David J Paterson
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Derek A Terrar
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Rebecca-Ann B Burton
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
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14
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Abstract
Mechanisms underlying pacemaker activity in the sinus node remain controversial, with some ascribing a dominant role to timing events in the surface membrane (“membrane clock”) and others to uptake and release of calcium from the sarcoplasmic reticulum (SR) (“calcium clock”). Here we discuss recent evidence on mechanisms underlying pacemaker activity with a particular emphasis on the many roles of calcium. There are particular areas of controversy concerning the contribution of calcium spark-like events and the importance of I(f) to spontaneous diastolic depolarisation, though it will be suggested that neither of these is essential for pacemaking. Sodium-calcium exchange (NCX) is most often considered in the context of mediating membrane depolarisation after spark-like events. We present evidence for a broader role of this electrogenic exchanger which need not always depend upon these spark-like events. Short (milliseconds or seconds) and long (minutes) term influences of calcium are discussed including direct regulation of ion channels and NCX, and control of the activity of calcium-dependent enzymes (including CaMKII, AC1, and AC8). The balance between the many contributory factors to pacemaker activity may well alter with experimental and clinical conditions, and potentially redundant mechanisms are desirable to ensure the regular spontaneous heart rate that is essential for life. This review presents evidence that calcium is central to the normal control of pacemaking across a range of temporal scales and seeks to broaden the accepted description of the “calcium clock” to cover these important influences.
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Affiliation(s)
- Rebecca A Capel
- British Heart Foundation Centre of Research Excellence, Department of Pharmacology, University of Oxford Oxford, UK
| | - Derek A Terrar
- British Heart Foundation Centre of Research Excellence, Department of Pharmacology, University of Oxford Oxford, UK
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15
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Capel RA, Terrar DA. Cytosolic calcium ions exert a major influence on the firing rate and maintenance of pacemaker activity in guinea-pig sinus node. Front Physiol 2015; 6:23. [PMID: 25713538 PMCID: PMC4322845 DOI: 10.3389/fphys.2015.00023] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Accepted: 01/14/2015] [Indexed: 01/01/2023] Open
Abstract
The sino-atrial node (SAN) provides the electrical stimulus to initiate every heart beat. Cellular processes underlying this activity have been debated extensively, especially with regards to the role of intracellular calcium. We have used whole-cell application of 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA), a rapid calcium chelator, to guinea pig isolated SAN myocytes to assess the effect of rapid reduction of intracellular calcium on SAN cell electrical activity. High-dose (10 mM) BAPTA induced rapid and complete cessation of rhythmic action potential (AP) firing (time to cessation 5.5 ± 1.7 s). Over a range of concentrations, BAPTA induced slowing of action potential firing and disruption of rhythmic activity, which was dose-dependent in its time of onset. Exposure to BAPTA was associated with stereotyped action potential changes similar to those previously reported in the presence of ryanodine, namely depolarization of the most negative diastolic potential, prolongation of action potentials and a reduction in action potential amplitude. These experiments are consistent with the view that cytosolic calcium is essential to the maintenance of rhythmic pacemaker activity.
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Affiliation(s)
| | - Derek A Terrar
- Department of Pharmacology, University of Oxford Oxford, UK
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