1
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Nayak AR, Rangubpit W, Will AH, Hu Y, Castro-Hartmann P, Lobo JJ, Dryden K, Lamb GD, Sompornpisut P, Samsó M. Interplay between Mg 2+ and Ca 2+ at multiple sites of the ryanodine receptor. Nat Commun 2024; 15:4115. [PMID: 38750013 PMCID: PMC11096358 DOI: 10.1038/s41467-024-48292-3] [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: 12/31/2023] [Accepted: 04/26/2024] [Indexed: 05/18/2024] Open
Abstract
RyR1 is an intracellular Ca2+ channel important in excitable cells such as neurons and muscle fibers. Ca2+ activates it at low concentrations and inhibits it at high concentrations. Mg2+ is the main physiological RyR1 inhibitor, an effect that is overridden upon activation. Despite the significance of Mg2+-mediated inhibition, the molecular-level mechanisms remain unclear. In this work we determined two cryo-EM structures of RyR1 with Mg2+ up to 2.8 Å resolution, identifying multiple Mg2+ binding sites. Mg2+ inhibits at the known Ca2+ activating site and we propose that the EF hand domain is an inhibitory divalent cation sensor. Both divalent cations bind to ATP within a crevice, contributing to the precise transmission of allosteric changes within the enormous channel protein. Notably, Mg2+ inhibits RyR1 by interacting with the gating helices as validated by molecular dynamics. This structural insight enhances our understanding of how Mg2+ inhibition is overcome during excitation.
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Affiliation(s)
- Ashok R Nayak
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, USA
| | - Warin Rangubpit
- Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand
| | - Alex H Will
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, USA
| | - Yifan Hu
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, USA
| | - Pablo Castro-Hartmann
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, USA
- ThermoFisher Scientific, Cambridge, UK
| | - Joshua J Lobo
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, USA
| | - Kelly Dryden
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
- Department of Chemistry and Biochemistry, UC Santa Barbara, Santa Barbara, CA, USA
| | - Graham D Lamb
- Department of Microbiology, Anatomy, Physiology and Pharmacology, La Trobe University, Melbourne, VIC, Australia
| | - Pornthep Sompornpisut
- Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand.
| | - Montserrat Samsó
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, VA, USA.
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2
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Magyar ZÉ, Bauer J, Bauerová-Hlinková V, Jóna I, Gaburjakova J, Gaburjakova M, Almássy J. Eu 3+ detects two functionally distinct luminal Ca 2+ binding sites in ryanodine receptors. Biophys J 2023; 122:3516-3531. [PMID: 37533257 PMCID: PMC10502479 DOI: 10.1016/j.bpj.2023.07.029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2023] [Revised: 06/26/2023] [Accepted: 07/31/2023] [Indexed: 08/04/2023] Open
Abstract
Ryanodine receptors (RyRs) are Ca2+ release channels, gated by Ca2+ in the cytosol and the sarcoplasmic reticulum lumen. Their regulation is impaired in certain cardiac and muscle diseases. Although a lot of data is available on the luminal Ca2+ regulation of RyR, its interpretation is complicated by the possibility that the divalent ions used to probe the luminal binding sites may contaminate the cytoplasmic sites by crossing the channel pore. In this study, we used Eu3+, an impermeable agonist of Ca2+ binding sites, as a probe to avoid this complication and to gain more specific information about the function of the luminal Ca2+ sensor. Single-channel currents were measured from skeletal muscle and cardiac RyRs (RyR1 and RyR2) using the lipid bilayer technique. We show that RyR2 is activated by the luminal addition of Ca2+, whereas RyR1 is inhibited. These results were qualitatively reproducible using Eu3+. The luminal regulation of RyR1 carrying a mutation associated with malignant hyperthermia was not different from that of the wild-type. RyR1 inhibition by Eu3+ was extremely voltage dependent, whereas RyR2 activation did not depend on the membrane potential. These results suggest that the RyR1 inhibition site is in the membrane's electric field (channel pore), whereas the RyR2 activation site is outside. Using in silico analysis and previous results, we predicted putative Ca2+ binding site sequences. We propose that RyR2 bears an activation site, which is missing in RyR1, but both isoforms share the same inhibitory Ca2+ binding site near the channel gate.
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Affiliation(s)
- Zsuzsanna É Magyar
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Jacob Bauer
- Institute of Molecular Biology, Slovak Academy of Sciences, Bratislava, Slovakia
| | | | - István Jóna
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Jana Gaburjakova
- Institute of Molecular Physiology and Genetics, Centre of Biosciences, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Marta Gaburjakova
- Institute of Molecular Physiology and Genetics, Centre of Biosciences, Slovak Academy of Sciences, Bratislava, Slovakia
| | - János Almássy
- Department of Physiology, Semmelweis University, Budapest, Hungary.
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3
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Hadiatullah H, He Z, Yuchi Z. Structural Insight Into Ryanodine Receptor Channelopathies. Front Pharmacol 2022; 13:897494. [PMID: 35677449 PMCID: PMC9168041 DOI: 10.3389/fphar.2022.897494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Accepted: 05/09/2022] [Indexed: 11/28/2022] Open
Abstract
The ryanodine receptors (RyRs) are large cation-selective ligand-gated channels that are expressed in the sarcoplasmic reticulum (SR) membrane. They mediate the controlled release of Ca2+ from SR and play an important role in many cellular processes. The mutations in RyRs are associated with several skeletal muscle and cardiac conditions, including malignant hyperthermia (MH), central core disease (CCD), catecholaminergic polymorphic ventricular tachycardia (CPVT), and arrhythmogenic right ventricular dysplasia (ARVD). Recent breakthroughs in structural biology including cryo-electron microscopy (EM) and X-ray crystallography allowed the determination of a number of near-atomic structures of RyRs, including wildtype and mutant structures as well as the structures in complex with different modulating molecules. This allows us to comprehend the physiological gating and regulatory mechanisms of RyRs and the underlying pathological mechanisms of the disease-causing mutations. In this review, based on the insights gained from the available high-resolution structures of RyRs, we address several questions: 1) what are the gating mechanisms of different RyR isoforms; 2) how RyRs are regulated by multiple channel modulators, including ions, small molecules, and regulatory proteins; 3) how do disease-causing mutations affect the structure and function of RyRs; 4) how can these structural information aid in the diagnosis of the related diseases and the development of pharmacological therapies.
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Affiliation(s)
- Hadiatullah Hadiatullah
- Tianjin Key Laboratory for Modern Drug Delivery and High-Efficiency, Collaborative Innovation Center of Chemical Science and Engineering, School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, China
- Department of Molecular Pharmacology, National Clinical Research Center for Cancer, Key Laboratory of Cancer Prevention and Therapy, Tianjin’s Clinical Research Center for Cancer, Tianjin Medical University Cancer Institute and Hospital, Tianjin, China
| | - Zhao He
- Tianjin Key Laboratory for Modern Drug Delivery and High-Efficiency, Collaborative Innovation Center of Chemical Science and Engineering, School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, China
- Department of Molecular Pharmacology, National Clinical Research Center for Cancer, Key Laboratory of Cancer Prevention and Therapy, Tianjin’s Clinical Research Center for Cancer, Tianjin Medical University Cancer Institute and Hospital, Tianjin, China
| | - Zhiguang Yuchi
- Tianjin Key Laboratory for Modern Drug Delivery and High-Efficiency, Collaborative Innovation Center of Chemical Science and Engineering, School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, China
- Department of Molecular Pharmacology, National Clinical Research Center for Cancer, Key Laboratory of Cancer Prevention and Therapy, Tianjin’s Clinical Research Center for Cancer, Tianjin Medical University Cancer Institute and Hospital, Tianjin, China
- *Correspondence: Zhiguang Yuchi,
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4
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Kobayashi T, Kurebayashi N, Murayama T. The Ryanodine Receptor as a Sensor for Intracellular Environments in Muscles. Int J Mol Sci 2021; 22:ijms221910795. [PMID: 34639137 PMCID: PMC8509754 DOI: 10.3390/ijms221910795] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Revised: 10/02/2021] [Accepted: 10/04/2021] [Indexed: 01/12/2023] Open
Abstract
The ryanodine receptor (RyR) is a Ca2+ release channel in the sarcoplasmic reticulum of skeletal and cardiac muscles and plays a key role in excitation-contraction coupling. The activity of the RyR is regulated by the changes in the level of many intracellular factors, such as divalent cations (Ca2+ and Mg2+), nucleotides, associated proteins, and reactive oxygen species. Since these intracellular factors change depending on the condition of the muscle, e.g., exercise, fatigue, or disease states, the RyR channel activity will be altered accordingly. In this review, we describe how the RyR channel is regulated under various conditions and discuss the possibility that the RyR acts as a sensor for changes in the intracellular environments in muscles.
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Woll KA, Van Petegem F. Calcium Release Channels: Structure and Function of IP3 Receptors and Ryanodine Receptors. Physiol Rev 2021; 102:209-268. [PMID: 34280054 DOI: 10.1152/physrev.00033.2020] [Citation(s) in RCA: 87] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Ca2+-release channels are giant membrane proteins that control the release of Ca2+ from the endoplasmic and sarcoplasmic reticulum. The two members, ryanodine receptors (RyRs) and inositol-1,4,5-trisphosphate Receptors (IP3Rs), are evolutionarily related and are both activated by cytosolic Ca2+. They share a common architecture, but RyRs have evolved additional modules in the cytosolic region. Their massive size allows for the regulation by tens of proteins and small molecules, which can affect the opening and closing of the channels. In addition to Ca2+, other major triggers include IP3 for the IP3Rs, and depolarization of the plasma membrane for a particular RyR subtype. Their size has made them popular targets for study via electron microscopic methods, with current structures culminating near 3Å. The available structures have provided many new mechanistic insights int the binding of auxiliary proteins and small molecules, how these can regulate channel opening, and the mechanisms of disease-associated mutations. They also help scrutinize previously proposed binding sites, as some of these are now incompatible with the structures. Many questions remain around the structural effects of post-translational modifications, additional binding partners, and the higher-order complexes these channels can make in situ. This review summarizes our current knowledge about the structures of Ca2+-release channels and how this informs on their function.
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Affiliation(s)
- Kellie A Woll
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada
| | - Filip Van Petegem
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada
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6
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Iaparov BI, Zahradnik I, Moskvin AS, Zahradníková A. In silico simulations reveal that RYR distribution affects the dynamics of calcium release in cardiac myocytes. J Gen Physiol 2021; 153:211900. [PMID: 33735373 PMCID: PMC7980188 DOI: 10.1085/jgp.202012685] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2020] [Accepted: 02/08/2021] [Indexed: 11/20/2022] Open
Abstract
The dyads of cardiac myocytes contain ryanodine receptors (RYRs) that generate calcium sparks upon activation. To test how geometric factors of RYR distribution contribute to the formation of calcium sparks, which cannot be addressed experimentally, we performed in silico simulations on a large set of models of calcium release sites (CRSs). Our models covered the observed range of RYR number, density, and spatial arrangement. The calcium release function of CRSs was modeled by RYR openings, with an open probability dependent on concentrations of free Ca2+ and Mg2+ ions, in a rapidly buffered system, with a constant open RYR calcium current. We found that simulations of spontaneous sparks by repeatedly opening one of the RYRs in a CRS produced three different types of calcium release events (CREs) in any of the models. Transformation of simulated CREs into fluorescence signals yielded calcium sparks with characteristics close to the observed ones. CRE occurrence varied broadly with the spatial distribution of RYRs in the CRS but did not consistently correlate with RYR number, surface density, or calcium current. However, it correlated with RYR coupling strength, defined as the weighted product of RYR vicinity and calcium current, so that CRE characteristics of all models followed the same state-response function. This finding revealed the synergy between structure and function of CRSs in shaping dyad function. Lastly, rearrangements of RYRs simulating hypothetical experiments on splitting and compaction of a dyad revealed an increased propensity to generate spontaneous sparks and an overall increase in calcium release in smaller and more compact dyads, thus underlying the importance and physiological role of RYR arrangement in cardiac myocytes.
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Affiliation(s)
- Bogdan I Iaparov
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, Slovak Academy of Sciences, Bratislava, Slovakia.,Research Institute of Physics and Applied Mathematics, and Department of Theoretical and Mathematical Physics, Ural Federal University, Ekaterinburg, Russia
| | - Ivan Zahradnik
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Alexander S Moskvin
- Research Institute of Physics and Applied Mathematics, and Department of Theoretical and Mathematical Physics, Ural Federal University, Ekaterinburg, Russia
| | - Alexandra Zahradníková
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, Slovak Academy of Sciences, Bratislava, Slovakia
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7
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Fill M, Gillespie D. Simulating cardiac Ca 2+ release units: effects of RyR cluster size and Ca 2+ buffers on diastolic Ca 2+ leak. Pflugers Arch 2021; 473:435-446. [PMID: 33608799 DOI: 10.1007/s00424-021-02539-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Revised: 01/27/2021] [Accepted: 02/05/2021] [Indexed: 10/22/2022]
Abstract
Leak of Ca2+ out of the cardiac sarcoplasmic reticulum (SR) via ryanodine receptors (RyRs) during diastole is vital to regulate SR Ca2+ levels. This leak can become deleterious when large spontaneous RyR-mediated Ca2+ release events evoke proarrhythmic Ca2+ waves that can lead to delayed after-depolarizations. Here, we model diastolic SR Ca2+ leak at individual SR Ca2+ release sites using computer simulations of RyR arrays like those in the dyadic cleft. The results show that RyR arrays size has a significant effect on SR Ca2+ leak, with bigger arrays producing larger and more frequent Ca2+ release events. Moreover, big RyR arrays are more susceptible to small changes in the levels of dyadic Ca2+ buffers. Such changes in buffering shift Ca2+ leak from small Ca2+ release events (involving few open RyRs) to larger events (with many open RyRs). Moreover, by analyzing a large parameter space of possible buffering and SR Ca2+ loads, we find further evidence for the hypothesis that SR Ca2+ leak by RyR arrays can undergo a sudden phase transition.
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Affiliation(s)
- Michael Fill
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA
| | - Dirk Gillespie
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA.
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8
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Chami M, Checler F. Alterations of the Endoplasmic Reticulum (ER) Calcium Signaling Molecular Components in Alzheimer's Disease. Cells 2020; 9:cells9122577. [PMID: 33271984 PMCID: PMC7760721 DOI: 10.3390/cells9122577] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 11/18/2020] [Accepted: 11/30/2020] [Indexed: 02/07/2023] Open
Abstract
Sustained imbalance in intracellular calcium (Ca2+) entry and clearance alters cellular integrity, ultimately leading to cellular homeostasis disequilibrium and cell death. Alzheimer’s disease (AD) is the most common cause of dementia. Beside the major pathological features associated with AD-linked toxic amyloid beta (Aβ) and hyperphosphorylated tau (p-tau), several studies suggested the contribution of altered Ca2+ handling in AD development. These studies documented physical or functional interactions of Aβ with several Ca2+ handling proteins located either at the plasma membrane or in intracellular organelles including the endoplasmic reticulum (ER), considered the major intracellular Ca2+ pool. In this review, we describe the cellular components of ER Ca2+ dysregulations likely responsible for AD. These include alterations of the inositol 1,4,5-trisphosphate receptors’ (IP3Rs) and ryanodine receptors’ (RyRs) expression and function, dysfunction of the sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) activity and upregulation of its truncated isoform (S1T), as well as presenilin (PS1, PS2)-mediated ER Ca2+ leak/ER Ca2+ release potentiation. Finally, we highlight the functional consequences of alterations of these ER Ca2+ components in AD pathology and unravel the potential benefit of targeting ER Ca2+ homeostasis as a tool to alleviate AD pathogenesis.
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Affiliation(s)
- Mounia Chami
- Correspondence: ; Tel.: +33-4939-53457; Fax: +33-4939-53408
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9
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Liu M, Dudley SC. Magnesium, Oxidative Stress, Inflammation, and Cardiovascular Disease. Antioxidants (Basel) 2020; 9:E907. [PMID: 32977544 PMCID: PMC7598282 DOI: 10.3390/antiox9100907] [Citation(s) in RCA: 53] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 09/17/2020] [Accepted: 09/18/2020] [Indexed: 12/15/2022] Open
Abstract
Hypomagnesemia is commonly observed in heart failure, diabetes mellitus, hypertension, and cardiovascular diseases. Low serum magnesium (Mg) is a predictor for cardiovascular and all-cause mortality and treating Mg deficiency may help prevent cardiovascular disease. In this review, we discuss the possible mechanisms by which Mg deficiency plays detrimental roles in cardiovascular diseases and review the results of clinical trials of Mg supplementation for heart failure, arrhythmias and other cardiovascular diseases.
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Affiliation(s)
- Man Liu
- Division of Cardiology, Department of Medicine, the Lillehei Heart Institute, University of Minnesota at Twin Cities, Minneapolis, MN 55455, USA
| | - Samuel C. Dudley
- Division of Cardiology, Department of Medicine, the Lillehei Heart Institute, University of Minnesota at Twin Cities, Minneapolis, MN 55455, USA
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10
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Guo W, Sun B, Estillore JP, Wang R, Chen SRW. The central domain of cardiac ryanodine receptor governs channel activation, regulation, and stability. J Biol Chem 2020; 295:15622-15635. [PMID: 32878990 DOI: 10.1074/jbc.ra120.013512] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Revised: 08/25/2020] [Indexed: 11/06/2022] Open
Abstract
Structural analyses identified the central domain of ryanodine receptor (RyR) as a transducer converting conformational changes in the cytoplasmic platform to the RyR gate. The central domain is also a regulatory hub encompassing the Ca2+-, ATP-, and caffeine-binding sites. However, the role of the central domain in RyR activation and regulation has yet to be defined. Here, we mutated five residues that form the Ca2+ activation site and 10 residues with negatively charged or oxygen-containing side chains near the Ca2+ activation site. We also generated eight disease-associated mutations within the central domain of RyR2. We determined the effect of these mutations on Ca2+, ATP, and caffeine activation and Mg2+ inhibition of RyR2. Mutating the Ca2+ activation site markedly reduced the sensitivity of RyR2 to Ca2+ and caffeine activation. Unexpectedly, Ca2+ activation site mutation E3848A substantially enhanced the Ca2+-independent basal activity of RyR2, suggesting that E3848A may also affect the stability of the closed state of RyR2. Mutations in the Ca2+ activation site also abolished the effect of ATP/caffeine on the Ca2+-independent basal activity, suggesting that the Ca2+ activation site is also a critical determinant of ATP/caffeine action. Mutating residues with negatively charged or oxygen-containing side chains near the Ca2+ activation site significantly altered Ca2+ and caffeine activation and reduced Mg2+ inhibition. Furthermore, disease-associated RyR2 mutations within the central domain significantly enhanced Ca2+ and caffeine activation and reduced Mg2+ inhibition. Our data demonstrate that the central domain plays an important role in channel activation, channel regulation, and closed state stability.
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Affiliation(s)
- Wenting Guo
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada; Department of Biochemistry and Molecular Biology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada
| | - Bo Sun
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada; Department of Biochemistry and Molecular Biology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada; Medical School, Kunming University of Science and Technology, Kunming, China
| | - John Paul Estillore
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada; Department of Biochemistry and Molecular Biology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada
| | - Ruiwu Wang
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada; Department of Biochemistry and Molecular Biology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada
| | - S R Wayne Chen
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada; Department of Biochemistry and Molecular Biology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada.
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11
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Geng X, Yu J, Xu J, Jin S, Shao W, Wang Y, Guo M, Cao X, Zou J, Xu X, Ding X. Role of magnesium in the risk of intradialytic hypotension among maintenance hemodialysis patients. Hemodial Int 2020; 24:351-358. [PMID: 32395903 DOI: 10.1111/hdi.12833] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 02/20/2020] [Accepted: 04/02/2020] [Indexed: 01/09/2023]
Affiliation(s)
- Xuemei Geng
- Department of Nephrology, Zhongshan Hospital Fudan University, Shanghai Institute of Kidney and Dialysis, Shanghai Key Laboratory of Kidney and Blood Purification, Shanghai Medical Center of Kidney Disease Shanghai China
| | - Jinbo Yu
- Department of Nephrology, Zhongshan Hospital Fudan University, Shanghai Institute of Kidney and Dialysis, Shanghai Key Laboratory of Kidney and Blood Purification, Shanghai Medical Center of Kidney Disease Shanghai China
| | - Jiarui Xu
- Department of Nephrology, Zhongshan Hospital Fudan University, Shanghai Institute of Kidney and Dialysis, Shanghai Key Laboratory of Kidney and Blood Purification, Shanghai Medical Center of Kidney Disease Shanghai China
| | - Shi Jin
- Department of Nephrology, Zhongshan Hospital Fudan University, Shanghai Institute of Kidney and Dialysis, Shanghai Key Laboratory of Kidney and Blood Purification, Shanghai Medical Center of Kidney Disease Shanghai China
| | - Wenqi Shao
- Department of Laboratory Medicine Zhongshan Hospital, Fudan University Shanghai China
| | - Yimei Wang
- Department of Nephrology, Zhongshan Hospital Fudan University, Shanghai Institute of Kidney and Dialysis, Shanghai Key Laboratory of Kidney and Blood Purification, Shanghai Medical Center of Kidney Disease Shanghai China
| | - Man Guo
- Department of Nephrology, Zhongshan Hospital Fudan University, Shanghai Institute of Kidney and Dialysis, Shanghai Key Laboratory of Kidney and Blood Purification, Shanghai Medical Center of Kidney Disease Shanghai China
| | - Xuesen Cao
- Department of Nephrology, Zhongshan Hospital Fudan University, Shanghai Institute of Kidney and Dialysis, Shanghai Key Laboratory of Kidney and Blood Purification, Shanghai Medical Center of Kidney Disease Shanghai China
| | - Jianzhou Zou
- Department of Nephrology, Zhongshan Hospital Fudan University, Shanghai Institute of Kidney and Dialysis, Shanghai Key Laboratory of Kidney and Blood Purification, Shanghai Medical Center of Kidney Disease Shanghai China
| | - Xialian Xu
- Department of Nephrology, Zhongshan Hospital Fudan University, Shanghai Institute of Kidney and Dialysis, Shanghai Key Laboratory of Kidney and Blood Purification, Shanghai Medical Center of Kidney Disease Shanghai China
| | - Xiaoqiang Ding
- Department of Nephrology, Zhongshan Hospital Fudan University, Shanghai Institute of Kidney and Dialysis, Shanghai Key Laboratory of Kidney and Blood Purification, Shanghai Medical Center of Kidney Disease Shanghai China
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12
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Sarcoplasmic reticulum and calcium signaling in muscle cells: Homeostasis and disease. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2020; 350:197-264. [PMID: 32138900 DOI: 10.1016/bs.ircmb.2019.12.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The sarco/endoplasmic reticulum is an extensive, dynamic and heterogeneous membranous network that fulfills multiple homeostatic functions. Among them, it compartmentalizes, stores and releases calcium within the intracellular space. In the case of muscle cells, calcium released from the sarco/endoplasmic reticulum in the vicinity of the contractile machinery induces cell contraction. Furthermore, sarco/endoplasmic reticulum-derived calcium also regulates gene transcription in the nucleus, energy metabolism in mitochondria and cytosolic signaling pathways. These diverse and overlapping processes require a highly complex fine-tuning that the sarco/endoplasmic reticulum provides by means of its numerous tubules and cisternae, specialized domains and contacts with other organelles. The sarco/endoplasmic reticulum also possesses a rich calcium-handling machinery, functionally coupled to both contraction-inducing stimuli and the contractile apparatus. Such is the importance of the sarco/endoplasmic reticulum for muscle cell physiology, that alterations in its structure, function or its calcium-handling machinery are intimately associated with the development of cardiometabolic diseases. Cardiac hypertrophy, insulin resistance and arterial hypertension are age-related pathologies with a common mechanism at the muscle cell level: the accumulation of damaged proteins at the sarco/endoplasmic reticulum induces a stress response condition termed endoplasmic reticulum stress, which impairs proper organelle function, ultimately leading to pathogenesis.
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13
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Gaburjakova J, Almassy J, Gaburjakova M. Luminal addition of non-permeant Eu 3+ interferes with luminal Ca 2+ regulation of the cardiac ryanodine receptor. Bioelectrochemistry 2020; 132:107449. [PMID: 31918058 DOI: 10.1016/j.bioelechem.2019.107449] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 12/17/2019] [Accepted: 12/17/2019] [Indexed: 10/25/2022]
Abstract
Dysregulation of the cardiac ryanodine receptor (RYR2) by luminal Ca2+ has been implicated in a life-threatening, stress-induced arrhythmogenic disease. The mechanism of luminal Ca2+-mediated RYR2 regulation is under debate, and it has been attributed to Ca2+ binding on the cytosolic face (the Ca2+ feedthrough mechanism) and/or the luminal face of the RYR2 channel (the true luminal mechanism). The molecular nature and location of the luminal Ca2+ site is unclear. At the single-channel level, we directly probed the RYR2 luminal face by Eu3+, considering the non-permeant nature of trivalent cations and their high binding affinities for Ca2+ sites. Without affecting essential determinants of the Ca2+ feedthrough mechanism, we found that luminal Eu3+ competitively antagonized the activation effect of luminal Ca2+ on RYR2 responsiveness to cytosolic caffeine, and no appreciable effect was observed for luminal Ba2+ (mimicking the absence of luminal Ca2+). Importantly, luminal Eu3+ caused no changes in RYR2 gating. Our results indicate that two distinct Ca2+ sites (available for luminal Ca2+ even when the channel is closed) are likely involved in the true luminal mechanism. One site facing the lumen regulates channel responsiveness to caffeine, while the other site, presumably positioned in the channel pore, governs the gating behavior.
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Affiliation(s)
- Jana Gaburjakova
- Institute of Molecular Physiology and Genetics, Centre of Biosciences, Slovak Academy of Sciences, Dubravska Cesta 9, 840 05 Bratislava, Slovak Republic.
| | - Janos Almassy
- Department of Physiology, Faculty of Medicine, University of Debrecen, PO Box 400, Debrecen 4002, Hungary.
| | - Marta Gaburjakova
- Institute of Molecular Physiology and Genetics, Centre of Biosciences, Slovak Academy of Sciences, Dubravska Cesta 9, 840 05 Bratislava, Slovak Republic.
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Gillespie D. Recruiting RyRs to Open in a Ca 2+ Release Unit: Single-RyR Gating Properties Make RyR Group Dynamics. Biophys J 2019; 118:232-242. [PMID: 31839264 DOI: 10.1016/j.bpj.2019.11.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 11/01/2019] [Accepted: 11/19/2019] [Indexed: 01/01/2023] Open
Abstract
In cardiac myocytes, clusters of type-2 ryanodine receptors (RyR2s) release Ca2+ from the sarcoplasmic reticulum (SR) via a positive feedback mechanism in which fluxed Ca2+ activates nearby RyRs. Although the general principles of this are understood, less is known about how single-RyR gating properties define the RyR group dynamics in an array of many channels. Here, we examine this using simulations with three models of RyR gating that have identical open probabilities: the commonly used two-state Markov gating model, one that utilizes multiple exponentials to fit single-channel open time (OT) and closed time (CT) distributions, and an extension of this multiexponential model that also includes experimentally measured correlations between single-channel OTs and CTs. The simulations of RyR clusters that utilize the multiexponential gating model produce infrequent Ca2+ release events with relatively few open RyRs. Ca2+ release events become even smaller when OT/CT correlations are included. This occurs because the correlations produce a small but consistent bias against recruiting more RyRs to open during the middle of a Ca2+ release event, between the initiation and termination phases (which are unaltered compared to the uncorrelated simulations). In comparison, the two-state model produces frequent, large, and long Ca2+ release events because it had a recruitment bias in favor of opening more RyRs. This difference stems from the two-state model's single-RyR OT and CT distributions being qualitatively different from the experimental ones. Thus, the details of single-RyR gating can profoundly affect SR Ca2+ release even if open probability and mean OTs and CTs are identical. We also show that Ca2+ release events can terminate spontaneously without any reduction in SR [Ca2+], luminal regulation, Ca2+-dependent inactivation, or physical coupling between RyRs when Ca2+ flux is below a threshold value. This supports and extends the pernicious attrition/induction decay hypothesis that SR Ca2+ release events terminate below a threshold Ca2+ flux.
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Affiliation(s)
- Dirk Gillespie
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois.
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15
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Magnesium: A Magic Bullet for Cardiovascular Disease in Chronic Kidney Disease? Nutrients 2019; 11:nu11020455. [PMID: 30813254 PMCID: PMC6412491 DOI: 10.3390/nu11020455] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Revised: 02/17/2019] [Accepted: 02/19/2019] [Indexed: 12/19/2022] Open
Abstract
Magnesium is essential for many physiological functions in the human body. Its homeostasis involves dietary intake, absorption, uptake and release from bone, swifts between the intra- and extracellular compartment, and renal excretion. Renal excretion is mainly responsible for regulation of magnesium balance. In chronic kidney disease (CKD), for a long time the general policy has been limiting magnesium intake. However, this may not be appropriate for many patients. The reference ranges for magnesium are not necessarily optimal concentrations, and risks for insufficient magnesium intake exist in patients with CKD. In recent years, many observational studies have shown that higher (in the high range of “normal” or slightly above) magnesium concentrations are associated with better survival in CKD cohorts. This review gives an overview of epidemiological associations between magnesium and overall and cardiovascular survival in patients with CKD. In addition, potential mechanisms explaining the protective role of magnesium in clinical cardiovascular outcomes are described by reviewing evidence from in vitro studies, animal studies, and human intervention studies with non-clinical endpoints. This includes the role of magnesium in cardiac arrhythmia, heart failure, arterial calcification, and endothelial dysfunction. Possible future implications will be addressed, which will need prospective clinical trials with relevant clinical endpoints before these can be adopted in clinical practice.
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16
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Xie Y, Yang Y, Galice S, Bers DM, Sato D. Size Matters: Ryanodine Receptor Cluster Size Heterogeneity Potentiates Calcium Waves. Biophys J 2019; 116:530-539. [PMID: 30686487 PMCID: PMC6369574 DOI: 10.1016/j.bpj.2018.12.017] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Revised: 11/11/2018] [Accepted: 12/12/2018] [Indexed: 12/21/2022] Open
Abstract
Ryanodine receptors (RyRs) mediate calcium (Ca)-induced Ca release and intracellular Ca homeostasis. In a cardiac myocyte, RyRs group into clusters of variable size from a few to several hundred RyRs, creating a spatially nonuniform intracellular distribution. It is unclear how heterogeneity of RyR cluster size alters spontaneous sarcoplasmic reticulum (SR) Ca releases (Ca sparks) and arrhythmogenic Ca waves. Here, we tested the impact of heterogeneous RyR cluster size on the initiation of Ca waves. Experimentally, we measured RyR cluster sizes at Ca spark sites in rat ventricular myocytes and further tested functional impacts using a physiologically detailed computational model with spatial and stochastic intracellular Ca dynamics. We found that the spark frequency and amplitude increase nonlinearly with the size of RyR clusters. Larger RyR clusters have lower SR Ca release threshold for local Ca spark initiation and exhibit steeper SR Ca release versus SR Ca load relationship. However, larger RyR clusters tend to lower SR Ca load because of the higher Ca leak rate. Conversely, smaller clusters have a higher threshold and a lower leak, which tends to increase SR Ca load. At the myocyte level, homogeneously large or small RyR clusters limit Ca waves (because of low load for large clusters but low excitability for small clusters). Mixtures of large and small RyR clusters potentiates Ca waves because the enhanced SR Ca load driven by smaller clusters enables Ca wave initiation and propagation from larger RyR clusters. Our study suggests that a spatially heterogeneous distribution of RyR cluster size under pathological conditions may potentiate Ca waves and thus afterdepolarizations and triggered arrhythmias.
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Affiliation(s)
- Yuanfang Xie
- Department of Pharmacology, University of California Davis, Davis, California
| | - Yi Yang
- Department of Pharmacology, University of California Davis, Davis, California
| | - Samuel Galice
- Department of Pharmacology, University of California Davis, Davis, California
| | - Donald M Bers
- Department of Pharmacology, University of California Davis, Davis, California
| | - Daisuke Sato
- Department of Pharmacology, University of California Davis, Davis, California.
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17
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Fill M, Gillespie D. Ryanodine Receptor Open Times Are Determined in the Closed State. Biophys J 2018; 115:1160-1165. [PMID: 30220413 DOI: 10.1016/j.bpj.2018.08.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 08/16/2018] [Accepted: 08/23/2018] [Indexed: 01/08/2023] Open
Abstract
The ryanodine receptor (RyR) ion channel releases Ca2+ from intracellular stores by conducting Ca2+ but also by recruiting neighboring RyRs to open, as RyRs are activated by micromolar levels of cytosolic Ca2+. Using long single-RyR recordings of the cardiac isoform (RyR2), we conclude that Ca2+ binding to the cytosolic face of RyR while the channel is closed determines the distribution of open times. This mechanism explains previous findings that RyR is not activated by its own fluxed Ca2+. Our measurements also bolster previous findings that luminal [Ca2+] can affect both the cytosolic activation and inactivation sites and that RyR has different gating modes for the same ionic conditions.
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Affiliation(s)
- Michael Fill
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois
| | - Dirk Gillespie
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois.
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18
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Laver DR. Regulation of the RyR channel gating by Ca 2+ and Mg 2. Biophys Rev 2018; 10:1087-1095. [PMID: 29926426 PMCID: PMC6082316 DOI: 10.1007/s12551-018-0433-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Accepted: 06/06/2018] [Indexed: 12/21/2022] Open
Abstract
Ryanodine receptors (RyRs) are the Ca2+ release channels in the sarcoplasmic reticulum in striated muscle which play an important role in excitation-contraction coupling and cardiac pacemaking. Single channel recordings have revealed a wealth of information about ligand regulation of RyRs from mammalian skeletal and cardiac muscle (RyR1 and RyR2, respectively). RyR subunit has a Ca2+ activation site located in the luminal and cytoplasmic domains of the RyR. These sites synergistically feed into a common gating mechanism for channel activation by luminal and cytoplasmic Ca2+. RyRs also possess two inhibitory sites in their cytoplasmic domains with Ca2+ affinities of the order of 1 μM and 1 mM. Magnesium competes with Ca2+ at these sites to inhibit RyRs and this plays an important role in modulating their Ca2+-dependent activity in muscle. This review focuses on how these sites lead to RyR modulation by Ca2+ and Mg2+ and how these mechanisms control Ca2+ release in excitation-contraction coupling and cardiac pacemaking.
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Affiliation(s)
- Derek R Laver
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, NSW, 2308, Australia.
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19
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Meissner G. The structural basis of ryanodine receptor ion channel function. J Gen Physiol 2017; 149:1065-1089. [PMID: 29122978 PMCID: PMC5715910 DOI: 10.1085/jgp.201711878] [Citation(s) in RCA: 147] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2017] [Accepted: 10/12/2017] [Indexed: 01/25/2023] Open
Abstract
Large-conductance Ca2+ release channels known as ryanodine receptors (RyRs) mediate the release of Ca2+ from an intracellular membrane compartment, the endo/sarcoplasmic reticulum. There are three mammalian RyR isoforms: RyR1 is present in skeletal muscle; RyR2 is in heart muscle; and RyR3 is expressed at low levels in many tissues including brain, smooth muscle, and slow-twitch skeletal muscle. RyRs form large protein complexes comprising four 560-kD RyR subunits, four ∼12-kD FK506-binding proteins, and various accessory proteins including calmodulin, protein kinases, and protein phosphatases. RyRs share ∼70% sequence identity, with the greatest sequence similarity in the C-terminal region that forms the transmembrane, ion-conducting domain comprising ∼500 amino acids. The remaining ∼4,500 amino acids form the large regulatory cytoplasmic "foot" structure. Experimental evidence for Ca2+, ATP, phosphorylation, and redox-sensitive sites in the cytoplasmic structure have been described. Exogenous effectors include the two Ca2+ releasing agents caffeine and ryanodine. Recent work describing the near atomic structures of mammalian skeletal and cardiac muscle RyRs provides a structural basis for the regulation of the RyRs by their multiple effectors.
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Affiliation(s)
- Gerhard Meissner
- Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, NC
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20
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Asp ML, Sjaastad FV, Siddiqui JK, Davis JP, Metzger JM. Effects of Modified Parvalbumin EF-Hand Motifs on Cardiac Myocyte Contractile Function. Biophys J 2017; 110:2094-105. [PMID: 27166817 DOI: 10.1016/j.bpj.2016.03.037] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Revised: 03/28/2016] [Accepted: 03/31/2016] [Indexed: 10/21/2022] Open
Abstract
Cardiac gene delivery of parvalbumin (Parv), an EF-hand Ca(2+) buffer, has been studied as a therapeutic strategy for diastolic heart failure, in which slow Ca(2+) reuptake is an important contributor. A limitation of wild-type (WT) Parv is the significant trade-off between faster relaxation and blunted contraction amplitude, occurring because WT-Parv sequesters Ca(2+) too early in the cardiac cycle and prematurely truncates sarcomere shortening in the facilitation of rapid relaxation. We recently demonstrated that an E → Q substitution (ParvE101Q) at amino acid 12 of the EF-hand Ca(2+)/Mg(2+) binding loop disrupts bidentate Ca(2+) binding, reducing Ca(2+) affinity by 99-fold and increasing Mg(2+) affinity twofold. ParvE101Q caused faster relaxation and not only preserved contractility, but unexpectedly increased it above untreated myocytes. To gain mechanistic insight into the increased contractility, we focused here on amino acid 12 of the EF-hand motif. We introduced an E → D substitution (ParvE101D) at this site, which converts bidentate Ca(2+) coordination to monodentate coordination. ParvE101D decreased Ca(2+) affinity by 114-fold and increased Mg(2+) affinity 28-fold compared to WT-Parv. ParvE101D increased contraction amplitude compared to both untreated myocytes and myocytes with ParvE101Q, with limited improvement in relaxation. Additionally, ParvE101D increased spontaneous contractions after pacing stress. ParvE101D also increased Ca(2+) transient peak height and was diffusely localized around the Z-line of the sarcomere, suggesting a Ca(2+)-dependent mechanism of enhanced contractility. Sarcoplasmic reticulum Ca(2+) load was not changed with ParvE101D, but postpacing Ca(2+) waves were increased. Together, these data show that inverted Ca(2+)/Mg(2+) binding affinities of ParvE101D increase myocyte contractility through a Ca(2+)-dependent mechanism without altering sarcoplasmic reticulum Ca(2+) load and by increasing unstimulated contractions and Ca(2+) waves. ParvE101D provides mechanistic insight into how changes in the Ca(2+)/Mg(2+) binding affinities of parvalbumin's EF-hand motif alter function of cardiac myocytes. These data are informative in developing new Ca(2+) buffering strategies for the failing heart.
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Affiliation(s)
- Michelle L Asp
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota
| | - Frances V Sjaastad
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota
| | - Jalal K Siddiqui
- Department of Physiology and Cell Biology, The Ohio State University College of Medicine, Columbus, Ohio
| | - Jonathan P Davis
- Department of Physiology and Cell Biology, The Ohio State University College of Medicine, Columbus, Ohio
| | - Joseph M Metzger
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota.
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21
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Cardiac Calcium Release Channel (Ryanodine Receptor 2) Regulation by Halogenated Anesthetics. Anesthesiology 2017; 126:495-506. [DOI: 10.1097/aln.0000000000001519] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Abstract
Background
Halogenated anesthetics activate cardiac ryanodine receptor 2–mediated sarcoplasmic reticulum Ca2+ release, leading to sarcoplasmic reticulum Ca2+ depletion, reduced cardiac function, and providing cell protection against ischemia-reperfusion injury. Anesthetic activation of ryanodine receptor 2 is poorly defined, leaving aspects of the protective mechanism uncertain.
Methods
Ryanodine receptor 2 from the sheep heart was incorporated into artificial lipid bilayers, and their gating properties were measured in response to five halogenated anesthetics.
Results
Each anesthetic rapidly and reversibly activated ryanodine receptor 2, but only from the cytoplasmic side. Relative activation levels were as follows: halothane (approximately 4-fold; n = 8), desflurane and enflurane (approximately 3-fold,n = 9), and isoflurane and sevoflurane (approximately 1.5-fold, n = 7, 10). Half-activating concentrations (Ka) were in the range 1.3 to 2.1 mM (1.4 to 2.6 minimum alveolar concentration [MAC]) with the exception of isoflurane (5.3 mM, 6.6 minimum alveolar concentration). Dantrolene (10 μM with 100 nM calmodulin) inhibited ryanodine receptor 2 by 40% but did not alter the Ka for halothane activation. Halothane potentiated luminal and cytoplasmic Ca2+ activation of ryanodine receptor 2 but had no effect on Mg2+ inhibition. Halothane activated ryanodine receptor 2 in the absence and presence (2 mM) of adenosine triphosphate (ATP). Adenosine, a competitive antagonist to ATP activation of ryanodine receptor 2, did not antagonize halothane activation in the absence of ATP.
Conclusions
At clinical concentrations (1 MAC), halothane desflurane and enflurane activated ryanodine receptor 2, whereas isoflurane and sevoflurane were ineffective. Dantrolene inhibition of ryanodine receptor 2 substantially negated the activating effects of anesthetics. Halothane acted independently of the adenine nucleotide–binding site on ryanodine receptor 2. The previously observed adenosine antagonism of halothane activation of sarcoplasmic reticulum Ca2+ release was due to competition between adenosine and ATP, rather than between halothane and ATP.
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22
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Walweel K, Molenaar P, Imtiaz MS, Denniss A, Dos Remedios C, van Helden DF, Dulhunty AF, Laver DR, Beard NA. Ryanodine receptor modification and regulation by intracellular Ca 2+ and Mg 2+ in healthy and failing human hearts. J Mol Cell Cardiol 2017; 104:53-62. [PMID: 28131631 DOI: 10.1016/j.yjmcc.2017.01.016] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Revised: 01/01/2017] [Accepted: 01/24/2017] [Indexed: 11/30/2022]
Abstract
RATIONALE Heart failure is a multimodal disorder, of which disrupted Ca2+ homeostasis is a hallmark. Central to Ca2+ homeostasis is the major cardiac Ca2+ release channel - the ryanodine receptor (RyR2) - whose activity is influenced by associated proteins, covalent modification and by Ca2+ and Mg2+. That RyR2 is remodelled and its function disturbed in heart failure is well recognized, but poorly understood. OBJECTIVE To assess Ca2+ and Mg2+ regulation of RyR2 from left ventricles of healthy, cystic fibrosis and failing hearts, and to correlate these functional changes with RyR2 modifications and remodelling. METHODS AND RESULTS The function of RyR2 from left ventricular samples was assessed using lipid bilayer single-channel measurements, whilst RyR2 modification and protein:protein interactions were determined using Western Blots and co-immunoprecipitation. In all failing hearts there was an increase in RyR2 activity at end-diastolic cytoplasmic Ca2+ (100nM), a decreased cytoplasmic [Ca2+] required for half maximal activation (Ka) and a decrease in inhibition by cytoplasmic Mg2+. This was accompanied by significant hyperphosphorylation of RyR2 S2808 and S2814, reduced free thiol content and a reduced interaction with FKBP12.0 and FKBP12.6. Either dephosphorylation of RyR2 using PP1 or thiol reduction using DTT eliminated any significant difference in the activity of RyR2 from healthy and failing hearts. We also report a subgroup of RyR2 in failing hearts that were not responsive to regulation by intracellular Ca2+ or Mg2+. CONCLUSION Despite different aetiologies, disrupted RyR2 Ca2+ sensitivity and biochemical modification of the channel are common constituents of failing heart RyR2 and may underlie the pathological disturbances in intracellular Ca2+ signalling.
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Affiliation(s)
- K Walweel
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, NSW 2308, Australia
| | - P Molenaar
- Biomedical Sciences, Queensland University of Technology, Brisbane, QLD, 4000, Northside Clinical School, School of Clinical Medicine, University of Queensland and Critical Care Research Group, The Prince Charles Hospital, Chermside, QLD, 4032, Australia
| | - M S Imtiaz
- Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales 2010, Australia
| | - A Denniss
- Health Research Institute, Faculty of Education Science and Mathematics, University of Canberra, Bruce, ACT 2617, Australia
| | - C Dos Remedios
- Bosch Institute, Discipline of Anatomy, University of Sydney, Sydney, New South Wales 2006, Australia
| | - D F van Helden
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, NSW 2308, Australia
| | - A F Dulhunty
- John Curtin School of Medical Research, Australian National University, Canberra, ACT, 0200, Australia
| | - D R Laver
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, NSW 2308, Australia
| | - N A Beard
- Health Research Institute, Faculty of Education Science and Mathematics, University of Canberra, Bruce, ACT 2617, Australia; John Curtin School of Medical Research, Australian National University, Canberra, ACT, 0200, Australia.
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23
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Dulhunty AF, Board PG, Beard NA, Casarotto MG. Physiology and Pharmacology of Ryanodine Receptor Calcium Release Channels. ADVANCES IN PHARMACOLOGY 2017; 79:287-324. [DOI: 10.1016/bs.apha.2016.12.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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24
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Walker MA, Williams GSB, Kohl T, Lehnart SE, Jafri MS, Greenstein JL, Lederer WJ, Winslow RL. Superresolution modeling of calcium release in the heart. Biophys J 2016; 107:3018-3029. [PMID: 25517166 PMCID: PMC4269784 DOI: 10.1016/j.bpj.2014.11.003] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Revised: 10/20/2014] [Accepted: 11/04/2014] [Indexed: 12/29/2022] Open
Abstract
Stable calcium-induced calcium release (CICR) is critical for maintaining normal cellular contraction during cardiac excitation-contraction coupling. The fundamental element of CICR in the heart is the calcium (Ca2+) spark, which arises from a cluster of ryanodine receptors (RyR). Opening of these RyR clusters is triggered to produce a local, regenerative release of Ca2+ from the sarcoplasmic reticulum (SR). The Ca2+ leak out of the SR is an important process for cellular Ca2+ management, and it is critically influenced by spark fidelity, i.e., the probability that a spontaneous RyR opening triggers a Ca2+ spark. Here, we present a detailed, three-dimensional model of a cardiac Ca2+ release unit that incorporates diffusion, intracellular buffering systems, and stochastically gated ion channels. The model exhibits realistic Ca2+ sparks and robust Ca2+ spark termination across a wide range of geometries and conditions. Furthermore, the model captures the details of Ca2+ spark and nonspark-based SR Ca2+ leak, and it produces normal excitation-contraction coupling gain. We show that SR luminal Ca2+-dependent regulation of the RyR is not critical for spark termination, but it can explain the exponential rise in the SR Ca2+ leak-load relationship demonstrated in previous experimental work. Perturbations to subspace dimensions, which have been observed in experimental models of disease, strongly alter Ca2+ spark dynamics. In addition, we find that the structure of RyR clusters also influences Ca2+ release properties due to variations in inter-RyR coupling via local subspace Ca2+ concentration ([Ca2+]ss). These results are illustrated for RyR clusters based on super-resolution stimulated emission depletion microscopy. Finally, we present a believed-novel approach by which the spark fidelity of a RyR cluster can be predicted from structural information of the cluster using the maximum eigenvalue of its adjacency matrix. These results provide critical insights into CICR dynamics in heart, under normal and pathological conditions.
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Affiliation(s)
- Mark A Walker
- Institute for Computational Medicine, Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland
| | - George S B Williams
- Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland
| | - Tobias Kohl
- Heart Research Center Goettingen, Clinic of Cardiology and Pulmonology, University Medical Center Goettingen, Goettingen, Germany
| | - Stephan E Lehnart
- Heart Research Center Goettingen, Clinic of Cardiology and Pulmonology, University Medical Center Goettingen, Goettingen, Germany
| | - M Saleet Jafri
- Department of Molecular Neuroscience, Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia
| | - Joseph L Greenstein
- Institute for Computational Medicine, Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland
| | - W J Lederer
- Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland
| | - Raimond L Winslow
- Institute for Computational Medicine, Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland.
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25
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Petrovič P, Valent I, Cocherová E, Pavelková J, Zahradníková A. Ryanodine receptor gating controls generation of diastolic calcium waves in cardiac myocytes. ACTA ACUST UNITED AC 2016; 145:489-511. [PMID: 26009544 PMCID: PMC4442793 DOI: 10.1085/jgp.201411281] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Calcium waves can form and propagate at low frequencies of spontaneous calcium sparks if the calcium dependence of spark frequency is sufficiently steep, or the number of open RyRs is sufficiently large. The role of cardiac ryanodine receptor (RyR) gating in the initiation and propagation of calcium waves was investigated using a mathematical model comprising a stochastic description of RyR gating and a deterministic description of calcium diffusion and sequestration. We used a one-dimensional array of equidistantly spaced RyR clusters, representing the confocal scanning line, to simulate the formation of calcium sparks. Our model provided an excellent description of the calcium dependence of the frequency of diastolic calcium sparks and of the increased tendency for the production of calcium waves after a decrease in cytosolic calcium buffering. We developed a hypothesis relating changes in the propensity to form calcium waves to changes of RyR gating and tested it by simulation. With a realistic RyR gating model, increased ability of RyR to be activated by Ca2+ strongly increased the propensity for generation of calcium waves at low (0.05–0.1-µM) calcium concentrations but only slightly at high (0.2–0.4-µM) calcium concentrations. Changes in RyR gating altered calcium wave formation by changing the calcium sensitivity of spontaneous calcium spark activation and/or the average number of open RyRs in spontaneous calcium sparks. Gating changes that did not affect RyR activation by Ca2+ had only a weak effect on the propensity to form calcium waves, even if they strongly increased calcium spark frequency. Calcium waves induced by modulating the properties of the RyR activation site could be suppressed by inhibiting the spontaneous opening of the RyR. These data can explain the increased tendency for production of calcium waves under conditions when RyR gating is altered in cardiac diseases.
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Affiliation(s)
- Pavol Petrovič
- Department of Physical and Theoretical Chemistry, Faculty of Natural Sciences, Comenius University, 842 15 Bratislava, Slovak Republic
| | - Ivan Valent
- Department of Physical and Theoretical Chemistry, Faculty of Natural Sciences, Comenius University, 842 15 Bratislava, Slovak Republic Department of Muscle Cell Research, Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic
| | - Elena Cocherová
- Department of Muscle Cell Research, Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic Institute of Electronics and Photonics, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology, 812 19 Bratislava, Slovak Republic
| | - Jana Pavelková
- Department of Muscle Cell Research, Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic
| | - Alexandra Zahradníková
- Department of Muscle Cell Research, Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic
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26
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Gaburjakova J, Gaburjakova M. Cardiac ryanodine receptor: Selectivity for alkaline earth metal cations points to the EF-hand nature of luminal binding sites. Bioelectrochemistry 2016; 109:49-56. [PMID: 26849106 DOI: 10.1016/j.bioelechem.2016.01.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Revised: 01/21/2016] [Accepted: 01/24/2016] [Indexed: 11/18/2022]
Abstract
A growing body of evidence suggests that the regulation of cardiac ryanodine receptor (RYR2) by luminal Ca(2+) is mediated by luminal binding sites located on the RYR2 channel itself and/or its auxiliary protein, calsequestrin. The localization and structure of RYR2-resident binding sites are not known because of the lack of a high-resolution structure of RYR2 luminal regions. To obtain the first structural insight, we probed the RYR2 luminal face stripped of calsequestrin by alkaline earth metal divalents (M(2+): Mg(2+), Ca(2+), Sr(2+) or Ba(2+)). We show that the RYR2 response to caffeine at the single-channel level is significantly modified by the nature of luminal M(2+). Moreover, we performed competition experiments by varying the concentration of luminal M(2+) (Mg(2+), Sr(2+) or Ba(2+)) from 8 mM to 53 mM and investigated its ability to compete with 1mM luminal Ca(2+). We demonstrate that all tested M(2+) bind to exactly the same RYR2 luminal binding sites. Their affinities decrease in the order: Ca(2+)>Sr(2+)>Mg(2+)~Ba(2+), showing a strong correlation with the M(2+) affinity of the EF-hand motif. This indicates that the RYR2 luminal binding regions and the EF-hand motif likely share some structural similarities because the structure ties directly to the function.
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Affiliation(s)
- Jana Gaburjakova
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Health Sciences Pavilion, 840 05, Bratislava, Slovak Republic.
| | - Marta Gaburjakova
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Health Sciences Pavilion, 840 05, Bratislava, Slovak Republic.
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Yamanaka R, Shindo Y, Karube T, Hotta K, Suzuki K, Oka K. Neural depolarization triggers Mg2+ influx in rat hippocampal neurons. Neuroscience 2015; 310:731-41. [DOI: 10.1016/j.neuroscience.2015.10.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Revised: 09/26/2015] [Accepted: 10/02/2015] [Indexed: 12/14/2022]
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Rajagopal V, Bass G, Walker CG, Crossman DJ, Petzer A, Hickey A, Siekmann I, Hoshijima M, Ellisman MH, Crampin EJ, Soeller C. Examination of the Effects of Heterogeneous Organization of RyR Clusters, Myofibrils and Mitochondria on Ca2+ Release Patterns in Cardiomyocytes. PLoS Comput Biol 2015; 11:e1004417. [PMID: 26335304 PMCID: PMC4559435 DOI: 10.1371/journal.pcbi.1004417] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2014] [Accepted: 06/26/2015] [Indexed: 11/18/2022] Open
Abstract
Spatio-temporal dynamics of intracellular calcium, [Ca2+]i, regulate the contractile function of cardiac muscle cells. Measuring [Ca2+]i flux is central to the study of mechanisms that underlie both normal cardiac function and calcium-dependent etiologies in heart disease. However, current imaging techniques are limited in the spatial resolution to which changes in [Ca2+]i can be detected. Using spatial point process statistics techniques we developed a novel method to simulate the spatial distribution of RyR clusters, which act as the major mediators of contractile Ca2+ release, upon a physiologically-realistic cellular landscape composed of tightly-packed mitochondria and myofibrils. We applied this method to computationally combine confocal-scale (~ 200 nm) data of RyR clusters with 3D electron microscopy data (~ 30 nm) of myofibrils and mitochondria, both collected from adult rat left ventricular myocytes. Using this hybrid-scale spatial model, we simulated reaction-diffusion of [Ca2+]i during the rising phase of the transient (first 30 ms after initiation). At 30 ms, the average peak of the simulated [Ca2+]i transient and of the simulated fluorescence intensity signal, F/F0, reached values similar to that found in the literature ([Ca2+]i ≈1 μM; F/F0≈5.5). However, our model predicted the variation in [Ca2+]i to be between 0.3 and 12.7 μM (~3 to 100 fold from resting value of 0.1 μM) and the corresponding F/F0 signal ranging from 3 to 9.5. We demonstrate in this study that: (i) heterogeneities in the [Ca2+]i transient are due not only to heterogeneous distribution and clustering of mitochondria; (ii) but also to heterogeneous local densities of RyR clusters. Further, we show that: (iii) these structure-induced heterogeneities in [Ca2+]i can appear in line scan data. Finally, using our unique method for generating RyR cluster distributions, we demonstrate the robustness in the [Ca2+]i transient to differences in RyR cluster distributions measured between rat and human cardiomyocytes. Calcium (Ca2+) acts as a signal for many functions in the heart cell, from its primary role in triggering contractions during the heartbeat to acting as a signal for cell growth. Cellular function is tightly coupled to its ultra-structural organization. Spatially-realistic and biophysics-based computational models can provide quantitative insights into structure-function relationships in Ca2+ signaling. We developed a novel computational model of a rat ventricular myocyte that integrates structural information from confocal and electron microscopy datasets that were independently acquired and includes: myofibrils (protein complexes that contract during the heartbeat), mitochondria (organelles that provide energy for contraction), and ryanodine receptors (RyR, ion channels that release the Ca2+ required to trigger myofibril contraction from intracellular stores). Using this model, we examined [Ca2+]i dynamics throughout the cell cross-section at a much higher resolution than previously possible. We estimated the size of structural maladaptation that would cause disease-related alterations in [Ca2+]i dynamics. Using our methods for data integration, we also tested whether reducing the density of RyRs in human cardiomyocytes (~40% relative to rat) would have a significant effect on [Ca2+]i. We found that Ca2+ release patterns between the two species are similar, suggesting Ca2+ dynamics are robust to variations in cell ultrastructure.
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Affiliation(s)
- Vijay Rajagopal
- Department of Mechanical Engineering, University of Melbourne, Melbourne, Australia
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
- Systems Biology Laboratory, Melbourne School of Engineering, University of Melbourne, Melbourne, Australia
- * E-mail:
| | - Gregory Bass
- Systems Biology Laboratory, Melbourne School of Engineering, University of Melbourne, Melbourne, Australia
| | - Cameron G. Walker
- Department of Engineering Science, University of Auckland, Auckland, New Zealand
| | - David J. Crossman
- Department of Physiology, University of Auckland, Auckland, New Zealand
| | - Amorita Petzer
- School of Biological Sciences, University of Auckland, Auckland. New Zealand
| | - Anthony Hickey
- School of Biological Sciences, University of Auckland, Auckland. New Zealand
| | - Ivo Siekmann
- Department of Mechanical Engineering, University of Melbourne, Melbourne, Australia
| | - Masahiko Hoshijima
- Department of Medicine, University of California San Diego, San Diego, United States of America
- National Center for Microscopy and Imaging Research, University of California San Diego, San Diego, United States of America
| | - Mark H. Ellisman
- National Center for Microscopy and Imaging Research, University of California San Diego, San Diego, United States of America
| | - Edmund J. Crampin
- Systems Biology Laboratory, Melbourne School of Engineering, University of Melbourne, Melbourne, Australia
- School of Mathematics and Statistics, Faculty of Science, University of Melbourne, Melbourne, Australia
- School of Medicine, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Melbourne, Australia
- ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, University of Melbourne, Melbourne, Australia
| | - Christian Soeller
- Department of Physiology, University of Auckland, Auckland, New Zealand
- Biomedical Physics, University of Exeter, Exeter, United Kingdom
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Cheungpasitporn W, Thongprayoon C, Qian Q. Dysmagnesemia in Hospitalized Patients: Prevalence and Prognostic Importance. Mayo Clin Proc 2015; 90:1001-10. [PMID: 26250725 DOI: 10.1016/j.mayocp.2015.04.023] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Revised: 04/12/2015] [Accepted: 04/29/2015] [Indexed: 10/23/2022]
Abstract
OBJECTIVE To examine the prevalence of serum magnesium (Mg) alterations and outcomes in hospitalized patients. PATIENTS AND METHODS All admissions to Mayo Clinic in Rochester, Minnesota, from January 1, 2009, through December 31, 2013 (288,120 patients), were screened. Admission Mg from each unique patient and relevant clinical data were extracted from the institutional electronic database. RESULTS After excluding patients aged less than 18 years, those without Mg measurement, and readmission episodes, a total of 65,974 patients were studied. Magnesium levels of 2.1 mg/dL or higher were found in 20,777 patients (31.5%), and levels less than 1.7 mg/dL were noted in 13,320 (20.2%). Hypomagnesemia was common in patients with hematologic/oncological disorders, and hypermagnesemia was common in those with cardiovascular disease. The lowest hospital mortality, assessed by restricted cubic spline and percentage death, occurred in patients with Mg levels between 1.7 and 1.89 mg/dL. An Mg level of less than 1.7 mg/dL was independently associated with an increased risk of hospital mortality after adjusting for all variables except the admission diagnosis; risk for longer hospital stay and being discharged to a care facility were increased in the fully adjusted model. An elevated Mg level of 2.3 mg/dL or higher was a predictor for all adverse outcomes. The magnitude of Mg elevations in patients with levels of 2.3 mg/dL or higher (N=7908) was associated with worse hospital mortality in a dose-response manner. In patients with cardiovascular diseases, Mg levels of 1.5 to 1.69 mg/dL and 2.3 mg/dL or higher both independently predicted poor outcomes including hospital mortality. CONCLUSION Dysmagnesemia in hospitalized patients is common, with hypermagnesemia being most prevalent. Compared with hypomagnesemia, hypermagnesemia is a stronger predictor for poor outcomes. Magnesium supplementation for patients without Mg deficiency should be avoided in the absence of randomized controlled trials documenting a benefit.
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Affiliation(s)
| | - Charat Thongprayoon
- Division of Nephrology and Hypertension, Mayo Clinic, Rochester, MN; Department of Anesthesiology, Mayo Clinic, Rochester, MN
| | - Qi Qian
- Division of Nephrology and Hypertension, Mayo Clinic, Rochester, MN.
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Walweel K, Li J, Molenaar P, Imtiaz MS, Quail A, dos Remedios CG, Beard NA, Dulhunty AF, van Helden DF, Laver DR. Differences in the regulation of RyR2 from human, sheep, and rat by Ca²⁺ and Mg²⁺ in the cytoplasm and in the lumen of the sarcoplasmic reticulum. ACTA ACUST UNITED AC 2015; 144:263-71. [PMID: 25156119 PMCID: PMC4144672 DOI: 10.1085/jgp.201311157] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Cardiac ryanodine receptors (RyR2) from humans, rats, and sheep show differential sensitivity to calcium and magnesium, with regulation of human RyR2 resembling that of sheep more than that of rat. Regulation of the cardiac ryanodine receptor (RyR2) by intracellular Ca2+ and Mg2+ plays a key role in determining cardiac contraction and rhythmicity, but their role in regulating the human RyR2 remains poorly defined. The Ca2+- and Mg2+-dependent regulation of human RyR2 was recorded in artificial lipid bilayers in the presence of 2 mM ATP and compared with that in two commonly used animal models for RyR2 function (rat and sheep). Human RyR2 displayed cytoplasmic Ca2+ activation (Ka = 4 µM) and inhibition by cytoplasmic Mg2+ (Ki = 10 µM at 100 nM Ca2+) that was similar to RyR2 from rat and sheep obtained under the same experimental conditions. However, in the presence of 0.1 mM Ca2+, RyR2s from human were 3.5-fold less sensitive to cytoplasmic Mg2+ inhibition than those from sheep and rat. The Ka values for luminal Ca2+ activation were similar in the three species (35 µM for human, 12 µM for sheep, and 10 µM for rat). From the relationship between open probability and luminal [Ca2+], the peak open probability for the human RyR2 was approximately the same as that for sheep, and both were ∼10-fold greater than that for rat RyR2. Human RyR2 also showed the same sensitivity to luminal Mg2+ as that from sheep, whereas rat RyR2 was 10-fold more sensitive. In all species, modulation of RyR2 gating by luminal Ca2+ and Mg2+ only occurred when cytoplasmic [Ca2+] was <3 µM. The activation response of RyR2 to luminal and cytoplasmic Ca2+ was strongly dependent on the Mg2+ concentration. Addition of physiological levels (1 mM) of Mg2+ raised the Ka for cytoplasmic Ca2+ to 30 µM (human and sheep) or 90 µM (rat) and raised the Ka for luminal Ca2+ to ∼1 mM in all species. This is the first report of the regulation by Ca2+ and Mg2+ of native RyR2 receptor activity from healthy human hearts.
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Affiliation(s)
- Kafa Walweel
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales 2308, Australia
| | - Jiao Li
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales 2308, Australia
| | - Peter Molenaar
- Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland 4001, Australia School of Medicine, University of Queensland, Brisbane, Queensland 4006, Australia Critical Care Research Group, The Prince Charles Hospital Foundation, Chermside, Queensland 4032, Australia
| | - Mohammad S Imtiaz
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales 2308, Australia
| | - Anthony Quail
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales 2308, Australia
| | - Cris G dos Remedios
- Bosch Institute, Discipline of Anatomy, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Nicole A Beard
- Faculty of Education, Science, Technology, and Mathematics, University of Canberra, Canberra, Australian Capital Territory 2601, Australia
| | - Angela F Dulhunty
- The John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory 2600, Australia
| | - Dirk F van Helden
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales 2308, Australia
| | - Derek R Laver
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales 2308, Australia
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Romani AMP. Effect of acute and prolonged alcohol administration on Mg(2+) homeostasis in cardiac cells. Alcohol 2015; 49:265-73. [PMID: 25800156 DOI: 10.1016/j.alcohol.2015.02.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 01/27/2015] [Accepted: 02/10/2015] [Indexed: 11/15/2022]
Abstract
Alcoholic cardiomyopathy represents a major clinical complication in chronic alcoholics. Previous studies from our laboratory indicate that acute and chronic exposure of liver cells to ethanol results in a major loss of cellular Mg(2+) as a result of alcohol oxidation. We investigated whether exposure to ethanol induces a similar Mg(2+) loss in cardiac cells. The results indicate that chronic exposure to a 6% ethanol-containing diet depleted cardiac myocytes of >25% of their cellular Mg(2+) content. Acute ethanol exposure, instead, induced a time- and dose-dependent manner of Mg(2+) extrusion from perfused hearts and collagenase-dispersed cardiac ventricular myocytes. Pretreatment with chlormethiazole prevented ethanol-induced Mg(2+) loss to a large extent, suggesting a role of ethanol oxidation via cyP4502E1 in the process. Magnesium extrusion across the sarcolemma occurred via the amiloride-inhibited Na(+)/Mg(2+) exchanger. Taken together, our data indicate that Mg(2+) extrusion also occurs in cardiac cells exposed to ethanol as a result of alcohol metabolism by cyP4502E1. The extrusion, which is mediated by the Na(+)/Mg(2+) exchanger, only occurs at doses of ethanol ≥0.1%, and depends on ethanol-induced decline in cellular ATP. The significance of Mg(2+) extrusion for the onset of alcoholic cardiomyopathy remains to be elucidated.
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Affiliation(s)
- Andrea M P Romani
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA.
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Walweel K, Laver DR. Mechanisms of SR calcium release in healthy and failing human hearts. Biophys Rev 2015; 7:33-41. [PMID: 28509976 PMCID: PMC5425750 DOI: 10.1007/s12551-014-0152-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Accepted: 11/25/2014] [Indexed: 01/08/2023] Open
Abstract
Normal heart contraction and rhythm relies on the proper flow of calcium ions (Ca2+) into cardiac cells and between their intracellular organelles, and any disruption can lead to arrhythmia and sudden cardiac death. Electrical excitation of the surface membrane activates voltage-dependent L-type Ca2+ channels to open and allow Ca2+ to enter the cytoplasm. The subsequent increase in cytoplasmic Ca2+ concentration activates calcium release channels (RyR2) located at specialised Ca2+ release sites in the sarcoplasmic reticulum (SR), which serves as an intracellular Ca2+ store. Animal models have provided valuable insights into how intracellular Ca2+ transport mechanisms are altered in human heart failure. The aim of this review is to examine how Ca2+ release sites are remodelled in heart failure and how this affects intracellular Ca2+ transport with an emphasis on Ca2+ release mechanisms in the SR. Current knowledge on how heart failure alters the regulation of RyR2 by Ca2+ and Mg2+ and how these mechanisms control the activity of RyR2 in the confines of the Ca2+ release sites is reviewed.
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Affiliation(s)
- K Walweel
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, NSW, 2308, Australia
| | - D R Laver
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, NSW, 2308, Australia.
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33
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Zhang JZ, Waddell HMM, Jones PP. Regulation of RYR2 by sarcoplasmic reticulum Ca(2+). Clin Exp Pharmacol Physiol 2015; 42:720-6. [PMID: 25603835 DOI: 10.1111/1440-1681.12364] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2014] [Revised: 09/17/2014] [Accepted: 10/09/2014] [Indexed: 11/28/2022]
Abstract
Ca(2+) is arguably the most important ion involved in the contraction of the heart. The cardiac ryanodine receptor (RyR2), the major Ca(2+) release channel located in the sarcoplasmic reticulum (SR) membrane, is responsible for releasing the bulk of Ca(2+) required for contraction. Moreover, RyR2 is also crucial for maintaining SR Ca(2+) homeostasis by releasing Ca(2+) from the SR when it becomes overloaded with Ca(2+) . During normal contraction, RyR2 is activated by cytosolic Ca(2+) , whereas during store overload conditions, the opening of RyR2 is governed by SR Ca(2+) . Although the process of the cytosolic control of RyR2 is well established, the molecular mechanism by which SR luminal Ca(2+) regulates RyR2 has only recently been elucidated and remains controversial. In addition to the activation of RyR2, SR luminal Ca(2+) also determines when the RyR2 channel closes. RyR2-mediated Ca(2+) release from the SR does not continue until the SR is completely depleted. Rather, it ceases when SR luminal Ca(2+) falls below a certain level. Given the importance of SR Ca(2+) , it is not surprising that the SR luminal Ca(2+) level is tightly controlled by SR Ca(2+) -buffering proteins. Consequently, the opening and closing of RyR2 is heavily influenced by the presence of such proteins, particularly those associated with RyR2, such as calsequestrin and the histidine-rich Ca(2+) -binding protein. These proteins appear to indirectly alter RyR2 activity by modifying the microdomain SR Ca(2+) level surrounding RyR2.
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Affiliation(s)
- Joe Z Zhang
- Department of Physiology and HeartOtago, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand
| | - Helen M M Waddell
- Department of Physiology and HeartOtago, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand
| | - Peter P Jones
- Department of Physiology and HeartOtago, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand
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Cannell MB, Kong CHT, Imtiaz MS, Laver DR. Control of sarcoplasmic reticulum Ca2+ release by stochastic RyR gating within a 3D model of the cardiac dyad and importance of induction decay for CICR termination. Biophys J 2013; 104:2149-59. [PMID: 23708355 DOI: 10.1016/j.bpj.2013.03.058] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 03/18/2013] [Accepted: 03/25/2013] [Indexed: 10/26/2022] Open
Abstract
The factors responsible for the regulation of regenerative calcium-induced calcium release (CICR) during Ca(2+) spark evolution remain unclear. Cardiac ryanodine receptor (RyR) gating in rats and sheep was recorded at physiological Ca(2+), Mg(2+), and ATP levels and incorporated into a 3D model of the cardiac dyad, which reproduced the time course of Ca(2+) sparks, Ca(2+) blinks, and Ca(2+) spark restitution. The termination of CICR by induction decay in the model principally arose from the steep Ca(2+) dependence of RyR closed time, with the measured sarcoplasmic reticulum (SR) lumen Ca(2+) dependence of RyR gating making almost no contribution. The start of CICR termination was strongly dependent on the extent of local depletion of junctional SR Ca(2+), as well as the time course of local Ca(2+) gradients within the junctional space. Reducing the dimensions of the dyad junction reduced Ca(2+) spark amplitude by reducing the strength of regenerative feedback within CICR. A refractory period for Ca(2+) spark initiation and subsequent Ca(2+) spark amplitude restitution arose from 1), the extent to which the regenerative phase of CICR can be supported by the partially depleted junctional SR, and 2), the availability of releasable Ca(2+) in the junctional SR. The physical organization of RyRs within the junctional space had minimal effects on Ca(2+) spark amplitude when more than nine RyRs were present. Spark amplitude had a nonlinear dependence on RyR single-channel Ca(2+) flux, and was approximately halved by reducing the flux from 0.6 to 0.2 pA. Although rat and sheep RyRs had quite different Ca(2+) sensitivities, Ca(2+) spark amplitude was hardly affected. This suggests that moderate changes in RyR gating by second-messenger systems will principally alter the spatiotemporal properties of SR release, with smaller effects on the amount released.
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Affiliation(s)
- M B Cannell
- Department of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.
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Romani AMP. Modulation of cellular Mg2+ content in cardiac cells by α1-adrenoceptor stimulation and anti-arrhythmic agents. Recent Pat Biotechnol 2013; 6:212-22. [PMID: 23092432 PMCID: PMC3613808 DOI: 10.2174/1872208311206030212] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 07/30/2012] [Accepted: 08/04/2012] [Indexed: 11/22/2022]
Abstract
Magnesium (Mg2+) is used pharmacologically to sedate specific forms of arrhythmias. Administration of pharmacological doses of catecholamine or adrenergic receptor agonists often results in arrhythmias onset. Results from the present study indicate that stimulation of cardiac adrenergic receptors elicits an extrusion of cellular Mg2+ into the extracellular space. This effect occurs in both perfused hearts and isolated cells within 5-6 min following either β- or α1-adrenergic receptor stimulation, and is prevented by specific adrenergic receptors antagonists. Sequential stimulation of the two classes of adrenergic receptor results in a larger mobilization of cellular Mg2+ provided that the two agonists are administered together or within 1-2 min from each other. A longer delay in administering the second stimulus results in the abolishment of Mg2+ extrusion. Hence, these data suggest that the stimulation of β- and α1-adrenergic receptors mobilizes Mg2+ from two distinct cellular pools, and that Mg2+ loss from either pool triggers a Mg2+ redistribution within the cardiac myocyte. At the sarcolemmal level, Mg2+ extrusion occurs through a Na+/Mg2+ exchange mechanism phosphorylated by cAMP. Administration of quinidine, a patent anti-arrhythmic agent, blocks Na+ transport in a non-specific manner and prevents Mg2+ extrusion. Taken together, these data indicate that catecholamine administration induces dynamic changes in total and compartmentalized Mg2+ pools within the cardiac myocytes, and suggest that prevention of Mg2+ extrusion and redistribution may be an integral component of the effectiveness of quinidine and possibly other cardiac anti-arrhythmic agents. Confirmation of this possibility by future experimental and clinical studies might result in new patents of these compounds as Mg2+ preserving agents.
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Affiliation(s)
- Andrea M P Romani
- Dept. Physiology and Biophysics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4970, USA.
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36
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Gaburjakova M, Bal NC, Gaburjakova J, Periasamy M. Functional interaction between calsequestrin and ryanodine receptor in the heart. Cell Mol Life Sci 2013; 70:2935-45. [PMID: 23109100 PMCID: PMC11113811 DOI: 10.1007/s00018-012-1199-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Revised: 10/02/2012] [Accepted: 10/15/2012] [Indexed: 11/25/2022]
Abstract
Evidence obtained in the last two decades indicates that calsequestrin (CSQ2), as the major Ca(2+)-binding protein in the sarcoplasmic reticulum of cardiac myocytes, communicates changes in the luminal Ca(2+) concentration to the cardiac ryanodine receptor (RYR2) channel. This review summarizes the major aspects in the interaction between CSQ2 and the RYR2 channel. The single channel properties of RYR2 channels, discussed here in the context of structural changes in CSQ2 after Ca(2+) binding, are particularly important. We focus on five important questions concerning: (1) the method for reliable detection of CSQ2 on the reconstituted RYR2 channel complex; (2) the power of the procedure to strip CSQ2 from the RYR2 channel complex; (3) structural changes in CSQ2 upon binding of Ca(2+) which cause CSQ2 dissociation; (4) the potential role of CSQ2-independent regulation of the RYR2 activity by luminal Ca(2+); and (5) the vizualization of CSQ2 dissociation from the RYR2 channel complex on the single channel level. We discuss the potential sources of the conflicting experimental results which may aid detailed understanding of the CSQ2 regulatory role. Although we mainly focus on the cardiac isoform of the proteins, some aspects of more extensive work carried out on the skeletal isoform are also discussed.
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Affiliation(s)
- Marta Gaburjakova
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlarska 5, Bratislava, Slovak Republic.
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Li J, Imtiaz MS, Beard NA, Dulhunty AF, Thorne R, vanHelden DF, Laver DR. ß-Adrenergic stimulation increases RyR2 activity via intracellular Ca2+ and Mg2+ regulation. PLoS One 2013; 8:e58334. [PMID: 23533585 PMCID: PMC3606165 DOI: 10.1371/journal.pone.0058334] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Accepted: 02/02/2013] [Indexed: 01/19/2023] Open
Abstract
Here we investigate how ß-adrenergic stimulation of the heart alters regulation of ryanodine receptors (RyRs) by intracellular Ca2+ and Mg2+ and the role of these changes in SR Ca2+ release. RyRs were isolated from rat hearts, perfused in a Langendorff apparatus for 5 min and subject to 1 min perfusion with 1 µM isoproterenol or without (control) and snap frozen in liquid N2 to capture their phosphorylation state. Western Blots show that RyR2 phosphorylation was increased by isoproterenol, confirming that RyR2 were subject to normal ß-adrenergic signaling. Under basal conditions, S2808 and S2814 had phosphorylation levels of 69% and 15%, respectively. These levels were increased to 83% and 60%, respectively, after 60 s of ß-adrenergic stimulation consistent with other reports that ß-adrenergic stimulation of the heart can phosphorylate RyRs at specific residues including S2808 and S2814 causing an increase in RyR activity. At cytoplasmic [Ca2+] <1 µM, ß-adrenergic stimulation increased luminal Ca2+ activation of single RyR channels, decreased luminal Mg2+ inhibition and decreased inhibition of RyRs by mM cytoplasmic Mg2+. At cytoplasmic [Ca2+] >1 µM, ß-adrenergic stimulation only decreased cytoplasmic Mg2+ and Ca2+ inhibition of RyRs. The Ka and maximum levels of cytoplasmic Ca2+ activation site were not affected by ß-adrenergic stimulation. Our RyR2 gating model was fitted to the single channel data. It predicted that in diastole, ß-adrenergic stimulation is mediated by 1) increasing the activating potency of Ca2+ binding to the luminal Ca2+ site and decreasing its affinity for luminal Mg2+ and 2) decreasing affinity of the low-affinity Ca2+/Mg2+ cytoplasmic inhibition site. However in systole, ß-adrenergic stimulation is mediated mainly by the latter.
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Affiliation(s)
- Jiao Li
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales, Australia
| | - Mohammad S. Imtiaz
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales, Australia
| | - Nicole A. Beard
- John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Angela F. Dulhunty
- John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Rick Thorne
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales, Australia
| | - Dirk F. vanHelden
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales, Australia
| | - Derek R. Laver
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, New South Wales, Australia
- * E-mail:
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Dulhunty AF, Wium E, Li L, Hanna AD, Mirza S, Talukder S, Ghazali NA, Beard NA. Proteins within the intracellular calcium store determine cardiac RyR channel activity and cardiac output. Clin Exp Pharmacol Physiol 2013; 39:477-84. [PMID: 22524859 DOI: 10.1111/j.1440-1681.2012.05704.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
SUMMARY The contractile function of the heart requires the release of Ca(2+) from intracellular Ca(2+) stores in the sarcoplasmic reticulum (SR) of cardiac muscle cells. The efficacy of Ca(2+) release depends on the amount of Ca(2+) loaded into the Ca(2+) store and the way in which this 'Ca(2+) load' influences the activity of the cardiac ryanodine receptor Ca(2+) release channel (RyR2). The effects of the Ca(2+) load on Ca(2+) release through RyR2 are facilitated by: (i) the sensitivity of RyR2 itself to luminal Ca(2+) concentrations; and (ii) interactions between the cardiac Ca(2+) -binding protein calsequestrin (CSQ) 2 and RyR2, transmitted through the 'anchoring' proteins junctin and/or triadin. Mutations in RyR2 are linked to catecholaminergic polymorphic ventricular tachycardia (CPVT) and sudden cardiac death. The tachycardia is associated with changes in the sensitivity of RyR2 to luminal Ca(2+) . Triadin-, junctin- or CSQ-null animals survive, but their longevity and ability to tolerate stress is compromised. These studies reveal the importance of the proteins in normal muscle function, but do not reveal the molecular nature of their functional interactions, which must be defined before changes in the proteins leading to CPVT and heart disease can be understood. Herein, we discuss known interactions between the RyR, triadin, junctin and CSQ with emphasis on the cardiac isoforms of the proteins. Where there is little known about the cardiac isoforms, we discuss evidence from skeletal isoforms.
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Affiliation(s)
- Angela F Dulhunty
- Department of Translational Biosciences, John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory, Australia.
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Tencerová B, Zahradníková A, Gaburjáková J, Gaburjáková M. Luminal Ca2+ controls activation of the cardiac ryanodine receptor by ATP. ACTA ACUST UNITED AC 2012; 140:93-108. [PMID: 22851674 PMCID: PMC3409101 DOI: 10.1085/jgp.201110708] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The synergic effect of luminal Ca2+, cytosolic Ca2+, and cytosolic adenosine triphosphate (ATP) on activation of cardiac ryanodine receptor (RYR2) channels was examined in planar lipid bilayers. The dose–response of RYR2 gating activity to ATP was characterized at a diastolic cytosolic Ca2+ concentration of 100 nM over a range of luminal Ca2+ concentrations and, vice versa, at a diastolic luminal Ca2+ concentration of 1 mM over a range of cytosolic Ca2+ concentrations. Low level of luminal Ca2+ (1 mM) significantly increased the affinity of the RYR2 channel for ATP but without substantial activation of the channel. Higher levels of luminal Ca2+ (8–53 mM) markedly amplified the effects of ATP on the RYR2 activity by selectively increasing the maximal RYR2 activation by ATP, without affecting the affinity of the channel to ATP. Near-diastolic cytosolic Ca2+ levels (<500 nM) greatly amplified the effects of luminal Ca2+. Fractional inhibition by cytosolic Mg2+ was not affected by luminal Ca2+. In models, the effects of luminal and cytosolic Ca2+ could be explained by modulation of the allosteric effect of ATP on the RYR2 channel. Our results suggest that luminal Ca2+ ions potentiate the RYR2 gating activity in the presence of ATP predominantly by binding to a luminal site with an apparent affinity in the millimolar range, over which local luminal Ca2+ likely varies in cardiac myocytes.
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Affiliation(s)
- Barbora Tencerová
- Institute of Molecular Physiology and Genetics, Centre of Excellence for Cardiovascular Research, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic
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Abstract
RATIONALE In cardiac muscle, Ca(2+)-induced Ca(2+) release (CICR) from the sarcoplasmic reticulum (SR) is mediated by ryanodine receptor (RyR) Ca(2+) release channels. The inherent positive feedback of CICR is normally well-controlled. Understanding this control mechanism is a priority because its malfunction has life-threatening consequences. OBJECTIVE We show that CICR local control is governed by SR Ca(2+) load, largely because load determines the single RyR current amplitude that drives inter-RyR CICR. METHODS AND RESULTS We differentially manipulated single RyR Ca(2+) flux amplitude and SR Ca(2+) load in permeabilized ventricular myocytes as an endogenous cell biology model of the heart. Large RyR-permeable organic cations were used to interfere with Ca(2+) conductance through the open RyR pore. Single-channel studies show this attenuates current amplitude without altering other aspects of RyR function. In cells, the same experimental maneuver increased resting SR Ca(2+) load. Despite the increased load, Ca(2+) spark (inter-RyR CICR events) frequency decreased and sparks terminated earlier. CONCLUSIONS Spark local control follows single RyR current amplitude, not simply SR Ca(2+) load. Spark frequency increases with load because spontaneous RyR openings at high loads produce larger currents (ie, a larger CICR trigger signal). Sparks terminate when load falls to the point at which single RyR current amplitude is no longer sufficient to sustain inter-RyR CICR. Thus, RyRs that spontaneously close no longer reopen and local Ca(2+) release ends.
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Affiliation(s)
- Tao Guo
- Department of Molecular Biophysics and Physiology, Section of Cellular Signaling, Rush University Medical Center, Chicago, IL 60112, USA
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Asghari P, Scriven DRL, Hoskins J, Fameli N, van Breemen C, Moore EDW. The structure and functioning of the couplon in the mammalian cardiomyocyte. PROTOPLASMA 2012; 249 Suppl 1:S31-S38. [PMID: 22057630 DOI: 10.1007/s00709-011-0347-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2011] [Accepted: 10/18/2011] [Indexed: 05/31/2023]
Abstract
The couplons of the cardiomyocyte form nanospaces within the cell that place the L-type calcium channel (Ca(v)1.2), situated on the plasmalemma, in opposition to the type 2 ryanodine receptor (RyR2), situated on the sarcoplasmic reticulum. These two molecules, which form the basis of excitation-contraction coupling, are separated by a very limited space, which allows a few Ca(2+) ions passing through Ca(v)1.2 to activate the RyR2 at concentration levels that would be deleterious to the whole cell. The limited space also allows Ca(2+) inactivation of Ca(v)1.2. We have found that not all couplons are the same and that their properties are likely determined by their molecular partners which, in turn, determine their excitability. In particular, there are a class of couplons that lie outside the RyR2-Ca(v)1.2 dyad; in this case, the RyR2 is close to caveolin-3 rather than Ca(v)1.2. These extra-dyadic couplons are probably controlled by the multitude of molecules associated with caveolin-3 and may modulate contractile force under situations such as stress. It has long been assumed that like the skeletal muscle, the RyR2 in the couplon are arranged in a structured array with the RyR2 interacting with each other via domain 6 of the RyR2 molecule. This arrangement was thought to provide local control of RyR2 excitability. Using 3D electron tomography of the couplon, we show that the RyR2 in the couplon do not form an ordered pattern, but are scattered throughout it. Relatively few are in a checkerboard pattern--many RyR2 sit edge-to-edge, a configuration which might preclude their controlling each other's excitability. The discovery of this structure makes many models of cardiac couplon function moot and is a current avenue of further research.
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Affiliation(s)
- Parisa Asghari
- Department of Cellular and Physiological Sciences, University of British Columbia, Life Sciences Institute, 2350 Health Sciences Mall, Vancouver, BC, Canada
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Diaz-Sylvester PL, Porta M, Copello JA. Modulation of cardiac ryanodine receptor channels by alkaline earth cations. PLoS One 2011; 6:e26693. [PMID: 22039534 PMCID: PMC3198824 DOI: 10.1371/journal.pone.0026693] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Accepted: 10/02/2011] [Indexed: 01/20/2023] Open
Abstract
Cardiac ryanodine receptor (RyR2) function is modulated by Ca(2+) and Mg(2+). To better characterize Ca(2+) and Mg(2+) binding sites involved in RyR2 regulation, the effects of cytosolic and luminal earth alkaline divalent cations (M(2+): Mg(2+), Ca(2+), Sr(2+), Ba(2+)) were studied on RyR2 from pig ventricle reconstituted in bilayers. RyR2 were activated by M(2+) binding to high affinity activating sites at the cytosolic channel surface, specific for Ca(2+) or Sr(2+). This activation was interfered by Mg(2+) and Ba(2+) acting at low affinity M(2+)-unspecific binding sites. When testing the effects of luminal M(2+) as current carriers, all M(2+) increased maximal RyR2 open probability (compared to Cs(+)), suggesting the existence of low affinity activating M(2+)-unspecific sites at the luminal surface. Responses to M(2+) vary from channel to channel (heterogeneity). However, with luminal Ba(2+)or Mg(2+), RyR2 were less sensitive to cytosolic Ca(2+) and caffeine-mediated activation, openings were shorter and voltage-dependence was more marked (compared to RyR2 with luminal Ca(2+)or Sr(2+)). Kinetics of RyR2 with mixtures of luminal Ba(2+)/Ca(2+) and additive action of luminal plus cytosolic Ba(2+) or Mg(2+) suggest luminal M(2+) differentially act on luminal sites rather than accessing cytosolic sites through the pore. This suggests the presence of additional luminal activating Ca(2+)/Sr(2+)-specific sites, which stabilize high P(o) mode (less voltage-dependent) and increase RyR2 sensitivity to cytosolic Ca(2+) activation. In summary, RyR2 luminal and cytosolic surfaces have at least two sets of M(2+) binding sites (specific for Ca(2+) and unspecific for Ca(2+)/Mg(2+)) that dynamically modulate channel activity and gating status, depending on SR voltage.
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Affiliation(s)
- Paula L. Diaz-Sylvester
- Department of Pharmacology, Southern Illinois School of Medicine, Springfield, Illinois, United States of America
| | - Maura Porta
- Department of Physiology, Midwestern University, Downers Grove, Illinois, United States of America
| | - Julio A. Copello
- Department of Pharmacology, Southern Illinois School of Medicine, Springfield, Illinois, United States of America
- * E-mail:
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Huang CLH, Pedersen TH, Fraser JA. Reciprocal dihydropyridine and ryanodine receptor interactions in skeletal muscle activation. J Muscle Res Cell Motil 2011; 32:171-202. [PMID: 21993921 DOI: 10.1007/s10974-011-9262-9] [Citation(s) in RCA: 110] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2011] [Accepted: 09/12/2011] [Indexed: 11/25/2022]
Abstract
Dihydropyridine (DHPR) and ryanodine receptors (RyRs) are central to transduction of transverse (T) tubular membrane depolarisation initiated by surface action potentials into release of sarcoplasmic reticular (SR) Ca2+ in skeletal muscle excitation-contraction coupling. Electronmicroscopic methods demonstrate an orderly positioning of such tubular DHPRs relative to RyRs in the SR at triad junctions where their membranes come into close proximity. Biochemical and genetic studies associated expression of specific, DHPR and RyR, isoforms with the particular excitation-contraction coupling processes and related elementary Ca2+ release events found respectively in skeletal and cardiac muscle. Physiological studies of intramembrane charge movements potentially related to voltage triggering of Ca2+ release demonstrated a particular qγ charging species identifiable with DHPRs through its T-tubular localization, pharmacological properties, and steep voltage-dependence paralleling Ca2+ release. Its nonlinear kinetics implicated highly co-operative conformational events in its transitions in response to voltage change. The effects of DHPR and RyR agonists and antagonists upon this intramembrane charge in turn implicated reciprocal rather than merely unidirectional DHPR-RyR interactions in these complex reactions. Thus, following membrane potential depolarization, an orthograde qγ-DHPR-RyR signaling likely initiates conformational alterations in the RyR with which it makes contact. The latter changes could then retrogradely promote further qγ-DHPR transitions through reciprocal co-operative allosteric interactions between receptors. These would relieve the resting constraints on both further, delayed, nonlinear qγ-DHPR charge transfers and on RyR-mediated Ca2+ release. They would also explain the more rapid charging and recovery qγ transients following larger depolarizations and membrane potential repolarization to the resting level.
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Affiliation(s)
- Christopher L-H Huang
- Physiological Laboratory, Department of Biochemistry, University of Cambridge, Cambridge, CB2 3EG, UK.
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Schendel T, Thul R, Sneyd J, Falcke M. How does the ryanodine receptor in the ventricular myocyte wake up: by a single or by multiple open L-type Ca2+ channels? EUROPEAN BIOPHYSICS JOURNAL: EBJ 2011; 41:27-39. [DOI: 10.1007/s00249-011-0755-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Revised: 08/23/2011] [Accepted: 09/14/2011] [Indexed: 02/07/2023]
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Abstract
CASQ (calsequestrin) is a Ca2+-buffering protein localized in the muscle SR (sarcoplasmic reticulum); however, it is unknown whether Ca2+ binding to CASQ2 is due to its location inside the SR rich in Ca2+ or due to its preference for Ca2+ over other ions. Therefore a major aim of the present study was to determine how CASQ2 selects Ca2+ over other metal ions by studying monomer folding and subsequent aggregation upon exposure to alkali (monovalent), alkaline earth (divalent) and transition (polyvalent) metals. We additionally investigated how CPVT (catecholaminergic polymorphic ventricular tachycardia) mutations affect CASQ2 structure and its molecular behaviour when exposed to different metal ions. Our results show that alkali and alkaline earth metals can initiate similar molecular compaction (folding), but only Ca2+ can promote CASQ2 to aggregate, suggesting that CASQ2 has a preferential binding to Ca2+ over all other metals. We additionally found that transition metals (having higher co-ordinated bonding ability than Ca2+) can also initiate folding and promote aggregation of CASQ2. These studies led us to suggest that folding and formation of higher-order structures depends on cationic properties such as co-ordinate bonding ability and ionic radius. Among the CPVT mutants studied, the L167H mutation disrupts the Ca2+-dependent folding and, when folding is achieved by Mn2+, L167H can undergo aggregation in a Ca2+-dependent manner. Interestingly, domain III mutants (D307H and P308L) lost their selectivity to Ca2+ and could be aggregated in the presence of Mg2+. In conclusion, these studies suggest that CPVT mutations modify CASQ2 behaviour, including folding, aggregation/polymerization and selectivity towards Ca2+.
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Romani AMP. Cellular magnesium homeostasis. Arch Biochem Biophys 2011; 512:1-23. [PMID: 21640700 PMCID: PMC3133480 DOI: 10.1016/j.abb.2011.05.010] [Citation(s) in RCA: 354] [Impact Index Per Article: 27.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 05/16/2011] [Accepted: 05/17/2011] [Indexed: 12/12/2022]
Abstract
Magnesium, the second most abundant cellular cation after potassium, is essential to regulate numerous cellular functions and enzymes, including ion channels, metabolic cycles, and signaling pathways, as attested by more than 1000 entries in the literature. Despite significant recent progress, however, our understanding of how cells regulate Mg(2+) homeostasis and transport still remains incomplete. For example, the occurrence of major fluxes of Mg(2+) in either direction across the plasma membrane of mammalian cells following metabolic or hormonal stimuli has been extensively documented. Yet, the mechanisms ultimately responsible for magnesium extrusion across the cell membrane have not been cloned. Even less is known about the regulation in cellular organelles. The present review is aimed at providing the reader with a comprehensive and up-to-date understanding of the mechanisms enacted by eukaryotic cells to regulate cellular Mg(2+) homeostasis and how these mechanisms are altered under specific pathological conditions.
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Affiliation(s)
- Andrea M P Romani
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4970, USA.
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Cannell MB, Kong CHT. Local control in cardiac E-C coupling. J Mol Cell Cardiol 2011; 52:298-303. [PMID: 21586292 DOI: 10.1016/j.yjmcc.2011.04.014] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2011] [Revised: 04/12/2011] [Accepted: 04/29/2011] [Indexed: 10/18/2022]
Abstract
The development of local control theories in cardiac excitation-contraction coupling solved a major problem in the calcium-induced calcium release (CICR) hypothesis. Local control explained how regeneration, inherent in the CICR mechanism, might be limited spatially to enable graded Ca release (and force production). The key lies in the stochastic recruitment of individual calcium release units (couplons or CRUs) where adjacent CRUs are partially uncoupled by the distance between them. In the CRU, individual groups of sarcoplasmic reticulum calcium release channels (RyRs) are very close to the surface membrane where calcium influx, controlled by membrane depolarization, leads to high local Ca levels that enable a high speed response from RyRs that have a very low probability to opening at resting Ca levels. However, calcium diffusion from an activated CRU results in adjacent CRUs being exposed to much lower levels of Ca and probability of activation. This effectively uncouples the CRUs and limits overall regenerative gain to enable stability without compromising sensitivity. Nevertheless, it is still unclear how the CRU terminates its release of calcium on the physiological timescale, and possible mechanisms (and problems) are briefly reviewed. We suggest that modulation in RyR gating may serve to control average SR Ca levels to regulate other metabolic functions of the sarco(endo)plasmic reticulum beyond regulating contractility. This article is part of a special issue entitled "Local Signaling in Myocytes."
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Affiliation(s)
- M B Cannell
- School of Physiology & Pharmacology, University of Bristol, Medical Sciences Building, University Walk, Bristol, BS8 1TD, UK.
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Zahradníková A, Gaburjáková M, Bridge JH, Zahradník I. Challenging quantal calcium signaling in cardiac myocytes. ACTA ACUST UNITED AC 2010; 136:581-3. [PMID: 20974774 PMCID: PMC2964521 DOI: 10.1085/jgp.201010542] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Alexandra Zahradníková
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 83334 Bratislava, Slovak Republic
| | - Marta Gaburjáková
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 83334 Bratislava, Slovak Republic
| | - John H.B. Bridge
- Division of Cardiology, University of Utah Health Sciences Center, Nora Eccles Harrison Cardiovascular Research and Training Institute, Salt Lake City, UT 84112
| | - Ivan Zahradník
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 83334 Bratislava, Slovak Republic
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Blayney LM, Jones JL, Griffiths J, Lai FA. A mechanism of ryanodine receptor modulation by FKBP12/12.6, protein kinase A, and K201. Cardiovasc Res 2010; 85:68-78. [PMID: 19661110 DOI: 10.1093/cvr/cvp273] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
AIMS Our objective was to explore the functional interdependence of protein kinase A (PKA) phosphorylation with binding of modulatory FK506 binding proteins (FKBP12/12.6) to the ryanodine receptor (RyR). RyR type 1 or type 2 was prepared from rabbit skeletal muscle or pig cardiac muscle, respectively. In heart failure, RyR2 dysfunction is implicated in fatal arrhythmia and RyR1 dysfunction is associated with muscle fatigue. A controversial underlying mechanism of RyR1/2 dysfunction is proposed to be hyperphosphorylation of RyR1/2 by PKA, causing loss of FKBP12/12.6 binding that is reversible by the experimental inhibitory drug K201 (JTV519). Phosphorylation is also a trigger for fatal arrhythmia in catecholaminergic polymorphic ventricular tachycardia associated with point mutations in RyR2. METHODS AND RESULTS Equilibrium binding kinetics of RyR1/2 to FKBP12/12.6 were measured using surface plasmon resonance (Biacore). Free Ca(2+) concentration was used to modulate the open/closed conformation of RyR1/2 channels measured using [(3)H]ryanodine binding assays. The affinity constant-K(A), for RyR1/2 binding to FKBP12/12.6, was significantly greater for the closed compared with the open conformation. The effect of phosphorylation or K201 was to reduce the K(A) of the closed conformation by increasing the rate of dissociation k(d). K201 reduced [(3)H]ryanodine binding to RyR1/2 at all free Ca(2+) concentrations including PKA phosphorylated preparations. CONCLUSION The results are explained through a model proposing that phosphorylation and K201 acted similarly to change the conformation of RyR1/2 and regulate FKBP12/12.6 binding. K201 stabilized the conformation, whereas phosphorylation facilitated a subsequent molecular event that might increase the rate of an open/closed conformational transition.
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Affiliation(s)
- Lynda M Blayney
- Department of Medicine - Cardiology, Wales Heart Research Institute, Cardiff University, Heath Park, Cardiff CF14 4XN, UK.
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Abstract
The versatility of Ca(2+) as an intracellular messenger derives largely from the spatial organization of cytosolic Ca(2+) signals, most of which are generated by regulated openings of Ca(2+)-permeable channels. Most Ca(2+) channels are expressed in the plasma membrane (PM). Others, including the almost ubiquitous inositol 1,4,5-trisphosphate receptors (IP(3)R) and their relatives, the ryanodine receptors (RyR), are predominantly expressed in membranes of the sarcoplasmic or endoplasmic reticulum (ER). Targeting of these channels to appropriate destinations underpins their ability to generate spatially organized Ca(2+) signals. All Ca(2+) channels begin life in the cytosol, and the vast majority are then functionally assembled in the ER, where they may either remain or be dispatched to other membranes. Here, by means of selective examples, we review two issues related to this trafficking of Ca(2+) channels via the ER. How do cells avoid wayward activity of Ca(2+) channels in transit as they pass from the ER via other membranes to their final destination? How and why do some cells express small numbers of the archetypal intracellular Ca(2+) channels, IP(3)R and RyR, in the PM?
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Affiliation(s)
- Colin W Taylor
- Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, UK.
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