1
|
Sanders KM, Drumm BT, Cobine CA, Baker SA. Ca 2+ dynamics in interstitial cells: foundational mechanisms for the motor patterns in the gastrointestinal tract. Physiol Rev 2024; 104:329-398. [PMID: 37561138 PMCID: PMC11281822 DOI: 10.1152/physrev.00036.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Revised: 06/29/2023] [Accepted: 08/06/2023] [Indexed: 08/11/2023] Open
Abstract
The gastrointestinal (GI) tract displays multiple motor patterns that move nutrients and wastes through the body. Smooth muscle cells (SMCs) provide the forces necessary for GI motility, but interstitial cells, electrically coupled to SMCs, tune SMC excitability, transduce inputs from enteric motor neurons, and generate pacemaker activity that underlies major motor patterns, such as peristalsis and segmentation. The interstitial cells regulating SMCs are interstitial cells of Cajal (ICC) and PDGF receptor (PDGFR)α+ cells. Together these cells form the SIP syncytium. ICC and PDGFRα+ cells express signature Ca2+-dependent conductances: ICC express Ca2+-activated Cl- channels, encoded by Ano1, that generate inward current, and PDGFRα+ cells express Ca2+-activated K+ channels, encoded by Kcnn3, that generate outward current. The open probabilities of interstitial cell conductances are controlled by Ca2+ release from the endoplasmic reticulum. The resulting Ca2+ transients occur spontaneously in a stochastic manner. Ca2+ transients in ICC induce spontaneous transient inward currents and spontaneous transient depolarizations (STDs). Neurotransmission increases or decreases Ca2+ transients, and the resulting depolarizing or hyperpolarizing responses conduct to other cells in the SIP syncytium. In pacemaker ICC, STDs activate voltage-dependent Ca2+ influx, which initiates a cluster of Ca2+ transients and sustains activation of ANO1 channels and depolarization during slow waves. Regulation of GI motility has traditionally been described as neurogenic and myogenic. Recent advances in understanding Ca2+ handling mechanisms in interstitial cells and how these mechanisms influence motor patterns of the GI tract suggest that the term "myogenic" should be replaced by the term "SIPgenic," as this review discusses.
Collapse
Affiliation(s)
- Kenton M Sanders
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada-Reno, Reno, Nevada, United States
| | - Bernard T Drumm
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland
| | - Caroline A Cobine
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland
| | - Salah A Baker
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada-Reno, Reno, Nevada, United States
| |
Collapse
|
2
|
Smith HA, Thillaiappan NB, Rossi AM. IP 3 receptors: An "elementary" journey from structure to signals. Cell Calcium 2023; 113:102761. [PMID: 37271052 DOI: 10.1016/j.ceca.2023.102761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2023] [Revised: 05/15/2023] [Accepted: 05/18/2023] [Indexed: 06/06/2023]
Abstract
Inositol 1,4,5-trisphosphate receptors (IP3Rs) are large tetrameric channels which sit mostly in the membrane of the endoplasmic reticulum (ER) and mediate Ca2+ release from intracellular stores in response to extracellular stimuli in almost all cells. Dual regulation of IP3Rs by IP3 and Ca2+ itself, upstream "licensing", and the arrangement of IP3Rs into small clusters in the ER membrane, allow IP3Rs to generate spatially and temporally diverse Ca2+ signals. The characteristic biphasic regulation of IP3Rs by cytosolic Ca2+ concentration underpins regenerative Ca2+ signals by Ca2+-induced Ca2+-release, while also preventing uncontrolled explosive Ca2+ release. In this way, cells can harness a simple ion such as Ca2+ as a near-universal intracellular messenger to regulate diverse cellular functions, including those with conflicting outcomes such as cell survival and cell death. High-resolution structures of the IP3R bound to IP3 and Ca2+ in different combinations have together started to unravel the workings of this giant channel. Here we discuss, in the context of recently published structures, how the tight regulation of IP3Rs and their cellular geography lead to generation of "elementary" local Ca2+ signals known as Ca2+ "puffs", which form the fundamental bottleneck through which all IP3-mediated cytosolic Ca2+ signals must first pass.
Collapse
Affiliation(s)
- Holly A Smith
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
| | | | - Ana M Rossi
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom.
| |
Collapse
|
3
|
Wei J, Guo W, Wang R, Paul Estillore J, Belke D, Chen YX, Vallmitjana A, Benitez R, Hove-Madsen L, Chen SRW. RyR2 Serine-2030 PKA Site Governs Ca 2+ Release Termination and Ca 2+ Alternans. Circ Res 2023; 132:e59-e77. [PMID: 36583384 DOI: 10.1161/circresaha.122.321177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
BACKGROUND PKA (protein kinase A)-mediated phosphorylation of cardiac RyR2 (ryanodine receptor 2) has been extensively studied for decades, but the physiological significance of PKA phosphorylation of RyR2 remains poorly understood. Recent determination of high-resolution 3-dimensional structure of RyR2 in complex with CaM (calmodulin) reveals that the major PKA phosphorylation site in RyR2, serine-2030 (S2030), is located within a structural pathway of CaM-dependent inactivation of RyR2. This novel structural insight points to a possible role of PKA phosphorylation of RyR2 in CaM-dependent inactivation of RyR2, which underlies the termination of Ca2+ release and induction of cardiac Ca2+ alternans. METHODS We performed single-cell endoplasmic reticulum Ca2+ imaging to assess the impact of S2030 mutations on Ca2+ release termination in human embryonic kidney 293 cells. Here we determined the role of the PKA site RyR2-S2030 in a physiological setting, we generated a novel mouse model harboring the S2030L mutation and carried out confocal Ca2+ imaging. RESULTS We found that mutations, S2030D, S2030G, S2030L, S2030V, and S2030W reduced the endoplasmic reticulum luminal Ca2+ level at which Ca2+ release terminates (the termination threshold), whereas S2030P and S2030R increased the termination threshold. S2030A and S2030T had no significant impact on release termination. Furthermore, CaM-wild-type increased, whereas Ca2+ binding deficient CaM mutant (CaM-M [a loss-of-function CaM mutation with all 4 EF-hand motifs mutated]), PKA, and Ca2+/CaMKII (CaM-dependent protein kinase II) reduced the termination threshold. The S2030L mutation abolished the actions of CaM-wild-type, CaM-M, and PKA, but not CaMKII, in Ca2+ release termination. Moreover, we showed that isoproterenol and CaM-M suppressed pacing-induced Ca2+ alternans and accelerated Ca2+ transient recovery in intact working hearts, whereas CaM-wild-type exerted an opposite effect. The impact of isoproterenol was partially and fully reversed by the PKA inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline-sulfonamide and the CaMKII inhibitor N-[2-[N-(4-chlorocinnamyl)-N-methylaminomethyl]phenyl]-N-(2-hydroxyethyl)-4-methoxybenzenesulfonamide individually and together, respectively. S2030L abolished the impact of CaM-wild-type, CaM-M, and N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline-sulfonamide-sensitive component, but not the N-[2-[N-(4-chlorocinnamyl)-N-methylaminomethyl]phenyl]-N-(2-hydroxyethyl)-4-methoxybenzenesulfonamide-sensitive component, of isoproterenol.
Collapse
Affiliation(s)
- Jinhong Wei
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta T2N 4N1, Canada (J.W., W.G., R.W., J.P.E., D.B., Y.-X.C., S.R.W.C.).,School of Medicine, Northwest University, Xi 'an, China (J.W.)
| | - Wenting Guo
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta T2N 4N1, Canada (J.W., W.G., R.W., J.P.E., D.B., Y.-X.C., S.R.W.C.)
| | - Ruiwu Wang
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta T2N 4N1, Canada (J.W., W.G., R.W., J.P.E., D.B., Y.-X.C., S.R.W.C.)
| | - John Paul Estillore
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta T2N 4N1, Canada (J.W., W.G., R.W., J.P.E., D.B., Y.-X.C., S.R.W.C.)
| | - Darrell Belke
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta T2N 4N1, Canada (J.W., W.G., R.W., J.P.E., D.B., Y.-X.C., S.R.W.C.)
| | - Yong-Xiang Chen
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta T2N 4N1, Canada (J.W., W.G., R.W., J.P.E., D.B., Y.-X.C., S.R.W.C.)
| | | | - Raul Benitez
- Department of Automatic Control, Universitat Politècnica de Catalunya, 08034 Barcelona, Spain (A.V., R.B.)
| | - Leif Hove-Madsen
- Biomedical Research Institute Barcelona IIBB-CSIC, IIB Sant Pau and CIBERCV, Hospital de Sant Pau, 08025, Barcelona, Spain (L.H.-M.)
| | - S R Wayne Chen
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta T2N 4N1, Canada (J.W., W.G., R.W., J.P.E., D.B., Y.-X.C., S.R.W.C.)
| |
Collapse
|
4
|
Qu Z, Yan D, Song Z. Modeling Calcium Cycling in the Heart: Progress, Pitfalls, and Challenges. Biomolecules 2022; 12:1686. [PMID: 36421700 PMCID: PMC9687412 DOI: 10.3390/biom12111686] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Revised: 11/08/2022] [Accepted: 11/11/2022] [Indexed: 11/16/2022] Open
Abstract
Intracellular calcium (Ca) cycling in the heart plays key roles in excitation-contraction coupling and arrhythmogenesis. In cardiac myocytes, the Ca release channels, i.e., the ryanodine receptors (RyRs), are clustered in the sarcoplasmic reticulum membrane, forming Ca release units (CRUs). The RyRs in a CRU act collectively to give rise to discrete Ca release events, called Ca sparks. A cell contains hundreds to thousands of CRUs, diffusively coupled via Ca to form a CRU network. A rich spectrum of spatiotemporal Ca dynamics is observed in cardiac myocytes, including Ca sparks, spark clusters, mini-waves, persistent whole-cell waves, and oscillations. Models of different temporal and spatial scales have been developed to investigate these dynamics. Due to the complexities of the CRU network and the spatiotemporal Ca dynamics, it is challenging to model the Ca cycling dynamics in the cardiac system, particularly at the tissue sales. In this article, we review the progress of modeling of Ca cycling in cardiac systems from single RyRs to the tissue scale, the pros and cons of the current models and different modeling approaches, and the challenges to be tackled in the future.
Collapse
Affiliation(s)
- Zhilin Qu
- Department of Medicine, David Geffen School of Medicine, University of California, A2-237 CHS, 650 Charles E. Young Drive South, Los Angeles, CA 90095, USA
- Department of Computational Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | - Dasen Yan
- Peng Cheng Laboratory, Shenzhen 518066, China
| | - Zhen Song
- Peng Cheng Laboratory, Shenzhen 518066, China
| |
Collapse
|
5
|
Iaparov B, Baglaeva I, Zahradník I, Zahradníková A. Magnesium Ions Moderate Calcium-Induced Calcium Release in Cardiac Calcium Release Sites by Binding to Ryanodine Receptor Activation and Inhibition Sites. Front Physiol 2022; 12:805956. [PMID: 35145426 PMCID: PMC8821920 DOI: 10.3389/fphys.2021.805956] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2021] [Accepted: 12/21/2021] [Indexed: 12/13/2022] Open
Abstract
Ryanodine receptor channels at calcium release sites of cardiac myocytes operate on the principle of calcium-induced calcium release. In vitro experiments revealed competition of Ca2+ and Mg2+ in the activation of ryanodine receptors (RyRs) as well as inhibition of RyRs by Mg2+. The impact of RyR modulation by Mg2+ on calcium release is not well understood due to the technical limitations of in situ experiments. We turned instead to an in silico model of a calcium release site (CRS), based on a homotetrameric model of RyR gating with kinetic parameters determined from in vitro measurements. We inspected changes in the activity of the CRS model in response to a random opening of one of 20 realistically distributed RyRs, arising from Ca2+/Mg2+ interactions at RyR channels. Calcium release events (CREs) were simulated at a range of Mg2+-binding parameters at near-physiological Mg2+ and ATP concentrations. Facilitation of Mg2+ binding to the RyR activation site inhibited the formation of sparks and slowed down their activation. Impeding Mg-binding to the RyR activation site enhanced spark formation and speeded up their activation. Varying Mg2+ binding to the RyR inhibition site also dramatically affected calcium release events. Facilitation of Mg2+ binding to the RyR inhibition site reduced the amplitude, relative occurrence, and the time-to-end of sparks, and vice versa. The characteristics of CREs correlated dose-dependently with the effective coupling strength between RyRs, defined as a function of RyR vicinity, single-channel calcium current, and Mg-binding parameters of the RyR channels. These findings postulate the role of Mg2+ in calcium release as a negative modulator of the coupling strength among RyRs in a CRS, translating to damping of the positive feedback of the calcium-induced calcium-release mechanism.
Collapse
Affiliation(s)
| | | | | | - Alexandra Zahradníková
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center of the Slovak Academy of Sciences, Bratislava, Slovakia
| |
Collapse
|
6
|
Li X, Tian G, Xu L, Sun L, Tao R, Zhang S, Cong Z, Deng F, Chen J, Yu Y, Du W, Zhao H. Wenxin Keli for the Treatment of Arrhythmia-Systems Pharmacology and In Vivo Pharmacological Assessment. Front Pharmacol 2021; 12:704622. [PMID: 34512338 PMCID: PMC8426352 DOI: 10.3389/fphar.2021.704622] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Accepted: 07/21/2021] [Indexed: 12/13/2022] Open
Abstract
This study employed a systems pharmacology approach to identify the active compounds and action mechanisms of Wenxin Keli for arrhythmia treatment. Sixty-eight components identified in vivo and in vitro by UPLC/Q-TOF-MS were considered the potential active components of Wenxin Keli. Network pharmacology further revealed 33 key targets and 75 KEGG pathways as possible pathways and targets involved in WK-mediated treatment, with the CaMKII/CNCA1C/Ca2+ pathway being the most significantly affected. This finding was validated using an AC-induced rat arrhythmias model. Pretreatment with Wenxin Keli reduced the malignant arrhythmias and shortened RR, PR, and the QT interval. Wenxin Keli exerted some antiarrhythmic effects by inhibiting p-CaMKII and intracellular Ca2+ transients and overexpressing CNCA1C. Thus, suppressing SR Ca2+ release and maintaining intracellular Ca2+ balance may be the primary mechanism of Wenxin Keli against arrhythmia. In view of the significance of CaMKII and NCX identified in this experiment, we suggest that CaMKII and NCX are essential targets for treating arrhythmias.
Collapse
Affiliation(s)
- Xiaofeng Li
- Department of Cardiology, The Second Affiliated Hospital of Tianjin University of TCM, Tianjin, China
| | - Gang Tian
- Department of Cardiology, Teda International Cardiovascular Hospital, Tianjin, China
| | - Liang Xu
- School of Pharmacy, Tianjin Medical University, Tianjin, China.,Tianjin Medical College, Tianjin, China
| | - Lili Sun
- Department of TCM, Tianjin University of TCM, Tianjin, China
| | - Rui Tao
- Department of TCM, Tianjin University of TCM, Tianjin, China
| | - Shaoqiang Zhang
- Department of Cardiology, The Second Affiliated Hospital of Tianjin University of TCM, Tianjin, China
| | - Zidong Cong
- Department of Cardiology, The Second Affiliated Hospital of Tianjin University of TCM, Tianjin, China
| | - Fangjun Deng
- Department of TCM, Tianjin University of TCM, Tianjin, China
| | - Jinhong Chen
- Department of TCM, Tianjin University of TCM, Tianjin, China
| | - Yang Yu
- Department of Aeronautics and Astronautics, Tsinghua University, Beijing, China
| | - Wuxun Du
- Department of Cardiology, The Second Affiliated Hospital of Tianjin University of TCM, Tianjin, China
| | - Hucheng Zhao
- Department of Aeronautics and Astronautics, Tsinghua University, Beijing, China
| |
Collapse
|
7
|
Parks SZ, Gao T, Jimenez Awuapura N, Ayathamattam J, Chabosseau PL, Kalvakolanu DV, Valdivia HH, Rutter GA, Leclerc I. The Ca 2+ -binding protein sorcin stimulates transcriptional activity of the unfolded protein response mediator ATF6. FEBS Lett 2021; 595:1782-1796. [PMID: 33960419 DOI: 10.1002/1873-3468.14101] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Revised: 04/19/2021] [Accepted: 04/21/2021] [Indexed: 12/13/2022]
Abstract
Sorcin is a calcium-binding protein involved in maintaining endoplasmic reticulum (ER) Ca2+ stores. We have previously shown that overexpressing sorcin under the rat insulin promoter was protective against high-fat diet-induced pancreatic beta-cell dysfunction in vivo. Activating transcription factor 6 (ATF6) is a key mediator of the unfolded protein response (UPR) that provides cellular protection during the progression of ER stress. Here, using nonexcitable HEK293 cells, we show that sorcin overexpression increased ATF6 signalling, whereas sorcin knock out caused a reduction in ATF6 transcriptional activity and increased ER stress. Altogether, our data suggest that sorcin downregulation during lipotoxic stress may prevent full ATF6 activation and a normal UPR during the progression of obesity and insulin resistance.
Collapse
Affiliation(s)
- Steven Z Parks
- Section of Cell Biology and Functional Genomics, Department of Metabolism, Digestion & Reproduction, Imperial College London, UK
| | - Tian Gao
- Section of Cell Biology and Functional Genomics, Department of Metabolism, Digestion & Reproduction, Imperial College London, UK
| | - Natalia Jimenez Awuapura
- Section of Cell Biology and Functional Genomics, Department of Metabolism, Digestion & Reproduction, Imperial College London, UK
| | - Joseph Ayathamattam
- Section of Cell Biology and Functional Genomics, Department of Metabolism, Digestion & Reproduction, Imperial College London, UK
| | - Pauline L Chabosseau
- Section of Cell Biology and Functional Genomics, Department of Metabolism, Digestion & Reproduction, Imperial College London, UK
| | - Dhananjaya V Kalvakolanu
- Departments of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Héctor H Valdivia
- Cardiovascular Research Center, University of Wisconsin-Madison, WI, USA
| | - Guy A Rutter
- Section of Cell Biology and Functional Genomics, Department of Metabolism, Digestion & Reproduction, Imperial College London, UK
| | - Isabelle Leclerc
- Section of Cell Biology and Functional Genomics, Department of Metabolism, Digestion & Reproduction, Imperial College London, UK
| |
Collapse
|
8
|
Protasi F, Pietrangelo L, Boncompagni S. Improper Remodeling of Organelles Deputed to Ca 2+ Handling and Aerobic ATP Production Underlies Muscle Dysfunction in Ageing. Int J Mol Sci 2021; 22:6195. [PMID: 34201319 PMCID: PMC8228829 DOI: 10.3390/ijms22126195] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 06/01/2021] [Accepted: 06/02/2021] [Indexed: 12/28/2022] Open
Abstract
Proper skeletal muscle function is controlled by intracellular Ca2+ concentration and by efficient production of energy (ATP), which, in turn, depend on: (a) the release and re-uptake of Ca2+ from sarcoplasmic-reticulum (SR) during excitation-contraction (EC) coupling, which controls the contraction and relaxation of sarcomeres; (b) the uptake of Ca2+ into the mitochondrial matrix, which stimulates aerobic ATP production; and finally (c) the entry of Ca2+ from the extracellular space via store-operated Ca2+ entry (SOCE), a mechanism that is important to limit/delay muscle fatigue. Abnormalities in Ca2+ handling underlie many physio-pathological conditions, including dysfunction in ageing. The specific focus of this review is to discuss the importance of the proper architecture of organelles and membrane systems involved in the mechanisms introduced above for the correct skeletal muscle function. We reviewed the existing literature about EC coupling, mitochondrial Ca2+ uptake, SOCE and about the structural membranes and organelles deputed to those functions and finally, we summarized the data collected in different, but complementary, projects studying changes caused by denervation and ageing to the structure and positioning of those organelles: a. denervation of muscle fibers-an event that contributes, to some degree, to muscle loss in ageing (known as sarcopenia)-causes misplacement and damage: (i) of membrane structures involved in EC coupling (calcium release units, CRUs) and (ii) of the mitochondrial network; b. sedentary ageing causes partial disarray/damage of CRUs and of calcium entry units (CEUs, structures involved in SOCE) and loss/misplacement of mitochondria; c. functional electrical stimulation (FES) and regular exercise promote the rescue/maintenance of the proper architecture of CRUs, CEUs, and of mitochondria in both denervation and ageing. All these structural changes were accompanied by related functional changes, i.e., loss/decay in function caused by denervation and ageing, and improved function following FES or exercise. These data suggest that the integrity and proper disposition of intracellular organelles deputed to Ca2+ handling and aerobic generation of ATP is challenged by inactivity (or reduced activity); modifications in the architecture of these intracellular membrane systems may contribute to muscle dysfunction in ageing and sarcopenia.
Collapse
Affiliation(s)
- Feliciano Protasi
- CAST, Center for Advanced Studies and Technology, University G. d’Annunzio of Chieti-Pescara, I-66100 Chieti, Italy; (L.P.); (S.B.)
- DMSI, Department of Medicine and Aging Sciences, University G. d’Annunzio of Chieti-Pescara, I-66100 Chieti, Italy
| | - Laura Pietrangelo
- CAST, Center for Advanced Studies and Technology, University G. d’Annunzio of Chieti-Pescara, I-66100 Chieti, Italy; (L.P.); (S.B.)
- DMSI, Department of Medicine and Aging Sciences, University G. d’Annunzio of Chieti-Pescara, I-66100 Chieti, Italy
| | - Simona Boncompagni
- CAST, Center for Advanced Studies and Technology, University G. d’Annunzio of Chieti-Pescara, I-66100 Chieti, Italy; (L.P.); (S.B.)
- DNICS, Department of Neuroscience and Clinical Sciences, University G. d’Annunzio of Chieti-Pescara, I-66100 Chieti, Italy
| |
Collapse
|
9
|
Wei J, Yao J, Belke D, Guo W, Zhong X, Sun B, Wang R, Paul Estillore J, Vallmitjana A, Benitez R, Hove-Madsen L, Alvarez-Lacalle E, Echebarria B, Chen SRW. Ca 2+-CaM Dependent Inactivation of RyR2 Underlies Ca 2+ Alternans in Intact Heart. Circ Res 2020; 128:e63-e83. [PMID: 33375811 DOI: 10.1161/circresaha.120.318429] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
RATIONALE Ca2+ alternans plays an essential role in cardiac alternans that can lead to ventricular fibrillation, but the mechanism underlying Ca2+ alternans remains undefined. Increasing evidence suggests that Ca2+ alternans results from alternations in the inactivation of cardiac RyR2 (ryanodine receptor 2). However, what inactivates RyR2 and how RyR2 inactivation leads to Ca2+ alternans are unknown. OBJECTIVE To determine the role of CaM (calmodulin) on Ca2+ alternans in intact working mouse hearts. METHODS AND RESULTS We used an in vivo local gene delivery approach to alter CaM function by directly injecting adenoviruses expressing CaM-wild type, a loss-of-function CaM mutation, CaM (1-4), and a gain-of-function mutation, CaM-M37Q, into the anterior wall of the left ventricle of RyR2 wild type or mutant mouse hearts. We monitored Ca2+ transients in ventricular myocytes near the adenovirus-injection sites in Langendorff-perfused intact working hearts using confocal Ca2+ imaging. We found that CaM-wild type and CaM-M37Q promoted Ca2+ alternans and prolonged Ca2+ transient recovery in intact RyR2 wild type and mutant hearts, whereas CaM (1-4) exerted opposite effects. Altered CaM function also affected the recovery from inactivation of the L-type Ca2+ current but had no significant impact on sarcoplasmic reticulum Ca2+ content. Furthermore, we developed a novel numerical myocyte model of Ca2+ alternans that incorporates Ca2+-CaM-dependent regulation of RyR2 and the L-type Ca2+ channel. Remarkably, the new model recapitulates the impact on Ca2+ alternans of altered CaM and RyR2 functions under 9 different experimental conditions. Our simulations reveal that diastolic cytosolic Ca2+ elevation as a result of rapid pacing triggers Ca2+-CaM dependent inactivation of RyR2. The resultant RyR2 inactivation diminishes sarcoplasmic reticulum Ca2+ release, which, in turn, reduces diastolic cytosolic Ca2+, leading to alternations in diastolic cytosolic Ca2+, RyR2 inactivation, and sarcoplasmic reticulum Ca2+ release (ie, Ca2+ alternans). CONCLUSIONS Our results demonstrate that inactivation of RyR2 by Ca2+-CaM is a major determinant of Ca2+ alternans, making Ca2+-CaM dependent regulation of RyR2 an important therapeutic target for cardiac alternans.
Collapse
Affiliation(s)
- Jinhong Wei
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta, Canada (J.W., J.Y., D.B., W.G., X.Z., B.S., R.W., J.P.E., S.R.W.C.)
| | - Jinjing Yao
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta, Canada (J.W., J.Y., D.B., W.G., X.Z., B.S., R.W., J.P.E., S.R.W.C.)
| | - Darrell Belke
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta, Canada (J.W., J.Y., D.B., W.G., X.Z., B.S., R.W., J.P.E., S.R.W.C.)
| | - Wenting Guo
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta, Canada (J.W., J.Y., D.B., W.G., X.Z., B.S., R.W., J.P.E., S.R.W.C.)
| | - Xiaowei Zhong
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta, Canada (J.W., J.Y., D.B., W.G., X.Z., B.S., R.W., J.P.E., S.R.W.C.)
| | - Bo Sun
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta, Canada (J.W., J.Y., D.B., W.G., X.Z., B.S., R.W., J.P.E., S.R.W.C.)
| | - Ruiwu Wang
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta, Canada (J.W., J.Y., D.B., W.G., X.Z., B.S., R.W., J.P.E., S.R.W.C.)
| | - John Paul Estillore
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta, Canada (J.W., J.Y., D.B., W.G., X.Z., B.S., R.W., J.P.E., S.R.W.C.)
| | - Alexander Vallmitjana
- Department of Automatic Control, Universitat Politècnica de Catalunya, Barcelona, Spain (A.V., R.B.)
| | - Raul Benitez
- Department of Automatic Control, Universitat Politècnica de Catalunya, Barcelona, Spain (A.V., R.B.).,Institut de Recerca Sant Joan de Déu (IRSJD), Barcelona, Spain (R.B.)
| | - Leif Hove-Madsen
- Biomedical Research Institute Barcelona IIBB-CSIC, CIBERCV and IIB Sant Pau, Hospital de Sant Pau, Barcelona, Spain (L.H.-M.)
| | - Enrique Alvarez-Lacalle
- Department of Physics, Universitat Politècnica de Catalunya, Barcelona, Spain (E.A.-L., B.E.)
| | - Blas Echebarria
- Department of Physics, Universitat Politècnica de Catalunya, Barcelona, Spain (E.A.-L., B.E.)
| | - S R Wayne Chen
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Alberta, Canada (J.W., J.Y., D.B., W.G., X.Z., B.S., R.W., J.P.E., S.R.W.C.)
| |
Collapse
|
10
|
Pathophysiology of Calcium Mediated Ventricular Arrhythmias and Novel Therapeutic Options with Focus on Gene Therapy. Int J Mol Sci 2019; 20:ijms20215304. [PMID: 31653119 PMCID: PMC6862059 DOI: 10.3390/ijms20215304] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2019] [Revised: 10/16/2019] [Accepted: 10/21/2019] [Indexed: 12/19/2022] Open
Abstract
Cardiac arrhythmias constitute a major health problem with a huge impact on mortality rates and health care costs. Despite ongoing research efforts, the understanding of the molecular mechanisms and processes responsible for arrhythmogenesis remains incomplete. Given the crucial role of Ca2+-handling in action potential generation and cardiac contraction, Ca2+ channels and Ca2+ handling proteins represent promising targets for suppression of ventricular arrhythmias. Accordingly, we report the different roles of Ca2+-handling in the development of congenital as well as acquired ventricular arrhythmia syndromes. We highlight the therapeutic potential of gene therapy as a novel and innovative approach for future arrhythmia therapy. Furthermore, we discuss various promising cellular and mitochondrial targets for therapeutic gene transfer currently under investigation.
Collapse
|
11
|
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.
Collapse
Affiliation(s)
- Derek R Laver
- School of Biomedical Sciences and Pharmacy, University of Newcastle and Hunter Medical Research Institute, Callaghan, NSW, 2308, Australia.
| |
Collapse
|
12
|
Xiao L, Gurrola GB, Zhang J, Valdivia CR, SanMartin M, Zamudio FZ, Zhang L, Possani LD, Valdivia HH. Structure-function relationships of peptides forming the calcin family of ryanodine receptor ligands. J Gen Physiol 2017; 147:375-94. [PMID: 27114612 PMCID: PMC4845687 DOI: 10.1085/jgp.201511499] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Accepted: 03/21/2016] [Indexed: 12/22/2022] Open
Abstract
Calcins are a novel family of scorpion peptides that bind with high affinity to ryanodine receptors (RyRs) and increase their activity by inducing subconductance states. Here, we provide a comprehensive analysis of the structure-function relationships of the eight calcins known to date, based on their primary sequence, three-dimensional modeling, and functional effects on skeletal RyRs (RyR1). Primary sequence alignment and evolutionary analysis show high similarity among all calcins (≥78.8% identity). Other common characteristics include an inhibitor cysteine knot (ICK) motif stabilized by three pairs of disulfide bridges and a dipole moment (DM) formed by positively charged residues clustering on one side of the molecule and neutral and negatively charged residues segregating on the opposite side. [(3)H]Ryanodine binding assays, used as an index of the open probability of RyRs, reveal that all eight calcins activate RyR1 dose-dependently with Kd values spanning approximately three orders of magnitude and in the following rank order: opicalcin1 > opicalcin2 > vejocalcin > hemicalcin > imperacalcin > hadrucalcin > maurocalcin >> urocalcin. All calcins significantly augment the bell-shaped [Ca(2+)]-[(3)H]ryanodine binding curve with variable effects on the affinity constants for Ca(2+) activation and inactivation. In single channel recordings, calcins induce the appearance of a subconductance state in RyR1 that has a unique fractional value (∼20% to ∼60% of the full conductance state) but bears no relationship to binding affinity, DM, or capacity to stimulate Ca(2+) release. Except for urocalcin, all calcins at 100 nM concentration stimulate Ca(2+) release and deplete Ca(2+) load from skeletal sarcoplasmic reticulum. The natural variation within the calcin family of peptides offers a diversified set of high-affinity ligands with the capacity to modulate RyRs with high dynamic range and potency.
Collapse
Affiliation(s)
- Liang Xiao
- Department of Marine Biotechnology, Faculty of Naval Medicine, Second Military Medical University, Shanghai 200433, China Center for Arrhythmia Research, Cardiovascular Division, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109
| | - Georgina B Gurrola
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62271, México Center for Arrhythmia Research, Cardiovascular Division, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109
| | - Jing Zhang
- Center for Arrhythmia Research, Cardiovascular Division, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109
| | - Carmen R Valdivia
- Center for Arrhythmia Research, Cardiovascular Division, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109
| | - Mario SanMartin
- Center for Arrhythmia Research, Cardiovascular Division, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109
| | - Fernando Z Zamudio
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62271, México Center for Arrhythmia Research, Cardiovascular Division, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109
| | - Liming Zhang
- Department of Marine Biotechnology, Faculty of Naval Medicine, Second Military Medical University, Shanghai 200433, China
| | - Lourival D Possani
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62271, México
| | - Héctor H Valdivia
- Center for Arrhythmia Research, Cardiovascular Division, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109
| |
Collapse
|
13
|
Cantalapiedra IR, Alvarez-Lacalle E, Peñaranda A, Echebarria B. Minimal model for calcium alternans due to SR release refractoriness. CHAOS (WOODBURY, N.Y.) 2017; 27:093928. [PMID: 28964152 DOI: 10.1063/1.5000709] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In the heart, rapid pacing rates may induce alternations in the strength of cardiac contraction, termed pulsus alternans. Often, this is due to an instability in the dynamics of the intracellular calcium concentration, whose transients become larger and smaller at consecutive beats. This alternation has been linked experimentally and theoretically to two different mechanisms: an instability due to (1) a strong dependence of calcium release on sarcoplasmic reticulum (SR) load, together with a slow calcium reuptake into the SR or (2) to SR release refractoriness, due to a slow recovery of the ryanodine receptors (RyR2) from inactivation. The relationship between calcium alternans and refractoriness of the RyR2 has been more elusive than the corresponding SR Ca load mechanism. To study the former, we reduce a general calcium model, which mimics the deterministic evolution of a calcium release unit, to its most basic elements. We show that calcium alternans can be understood using a simple nonlinear equation for calcium concentration at the dyadic space, coupled to a relaxation equation for the number of recovered RyR2s. Depending on the number of RyR2s that are recovered at the beginning of a stimulation, the increase in calcium concentration may pass, or not, over an excitability threshold that limits the occurrence of a large calcium transient. When the recovery of the RyR2 is slow, this produces naturally a period doubling bifurcation, resulting in calcium alternans. We then study the effects of inactivation, calcium diffusion, and release conductance for the onset of alternans. We find that the development of alternans requires a well-defined value of diffusion while it is less sensitive to the values of inactivation or release conductance.
Collapse
Affiliation(s)
- Inma R Cantalapiedra
- Departament de Física. Universitat Politècnica de Catalunya, Av Dr. Marañon 50 (EPSEB), Barcelona, Spain
| | - Enrique Alvarez-Lacalle
- Departament de Física. Universitat Politècnica de Catalunya, Av Dr. Marañon 50 (EPSEB), Barcelona, Spain
| | - Angelina Peñaranda
- Departament de Física. Universitat Politècnica de Catalunya, Av Dr. Marañon 50 (EPSEB), Barcelona, Spain
| | - Blas Echebarria
- Departament de Física. Universitat Politècnica de Catalunya, Av Dr. Marañon 50 (EPSEB), Barcelona, Spain
| |
Collapse
|
14
|
Cannell MB, Kong CHT. Quenching the spark: Termination of CICR in the submicroscopic space of the dyad. J Gen Physiol 2017; 149:837-845. [PMID: 28798280 PMCID: PMC5583711 DOI: 10.1085/jgp.201711807] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Accepted: 07/21/2017] [Indexed: 12/20/2022] Open
Abstract
Cannell and Kong discuss the different termination mechanisms proposed for CICR in cardiac myocytes.
Collapse
Affiliation(s)
- Mark B Cannell
- School of Physiology, Pharmacology, and Neuroscience, University of Bristol, Bristol, England, UK
| | - Cherrie H T Kong
- School of Physiology, Pharmacology, and Neuroscience, University of Bristol, Bristol, England, UK
| |
Collapse
|
15
|
Györke S, Belevych AE, Liu B, Kubasov IV, Carnes CA, Radwański PB. The role of luminal Ca regulation in Ca signaling refractoriness and cardiac arrhythmogenesis. J Gen Physiol 2017; 149:877-888. [PMID: 28798279 PMCID: PMC5583712 DOI: 10.1085/jgp.201711808] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2017] [Revised: 06/19/2017] [Accepted: 07/12/2017] [Indexed: 01/05/2023] Open
Abstract
Györke et al. discuss the role of sarcoplasmic reticulum Ca2+ in cardiac refractoriness and pathological implications.
Collapse
Affiliation(s)
- Sándor Györke
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH .,Davis Heart and Lung Research Institute, Columbus, OH
| | - Andriy E Belevych
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH.,Davis Heart and Lung Research Institute, Columbus, OH
| | - Bin Liu
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH.,Davis Heart and Lung Research Institute, Columbus, OH
| | - Igor V Kubasov
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Cynthia A Carnes
- College of Pharmacy, The Ohio State University, Columbus, OH.,Davis Heart and Lung Research Institute, Columbus, OH
| | - Przemysław B Radwański
- College of Pharmacy, The Ohio State University, Columbus, OH.,Davis Heart and Lung Research Institute, Columbus, OH
| |
Collapse
|
16
|
Calcium dynamics in cardiac excitatory and non-excitatory cells and the role of gap junction. Math Biosci 2017; 289:51-68. [PMID: 28457965 DOI: 10.1016/j.mbs.2017.04.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2016] [Revised: 11/12/2016] [Accepted: 04/26/2017] [Indexed: 11/21/2022]
Abstract
Calcium ions aid in the generation of action potential in myocytes and are responsible for the excitation-contraction coupling of heart. The heart muscle has specialized patches of cells, called excitatory cells (EC) such as the Sino-atrial node cells capable of auto-generation of action potential and cells which receive signals from the excitatory cells, called non-excitatory cells (NEC) such as cells of the ventricular and auricular walls. In order to understand cardiac calcium homeostasis, it is, therefore, important to study the calcium dynamics taking into account both types of cardiac cells. Here we have developed a model to capture the calcium dynamics in excitatory and non-excitatory cells taking into consideration the gap junction mediated calcium ion transfer from excitatory cell to non-excitatory cell. Our study revealed that the gap junctional coupling between excitatory and non-excitatory cells plays important role in the calcium dynamics. It is observed that any reduction in the functioning of gap junction may result in abnormal calcium oscillations in NEC, even when the calcium dynamics is normal in EC cell. Sensitivity of gap junction is observed to be independent of the pacing rate and hence a careful monitoring is required to maintain normal cardiomyocyte condition. It also highlights that sarcoplasmic reticulum may not be always able to control the amount of cytoplasmic calcium under the condition of calcium overload.
Collapse
|
17
|
FKBPs facilitate the termination of spontaneous Ca2+ release in wild-type RyR2 but not CPVT mutant RyR2. Biochem J 2016; 473:2049-60. [PMID: 27154203 DOI: 10.1042/bcj20160389] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Accepted: 05/06/2016] [Indexed: 01/08/2023]
Abstract
FK506-binding proteins 12.6 (FKBP12.6) and 12 (FKBP12) tightly associate with the cardiac ryanodine receptor (RyR2). Studies suggest that dissociation of FKBP12.6 from mutant forms of RyR2 contributes to store overload-induced Ca(2+) release (SOICR) and Ca(2+)-triggered arrhythmias. However, these findings are controversial. Previous studies focused on the effect of FKBP12.6 on the initiation of SOICR and did not explore changes in the termination of Ca(2+) release. Less is known about FKBP12. We aimed to determine the effect of FKBP12.6 and FKBP12 on the termination of SOICR. Using single-cell imaging, in cells expressing wild-type RyR2, we found that FKBP12.6 and FKBP12 significantly increase the termination threshold of SOICR without changing the activation threshold of SOICR. This effect, dependent on the association of each FKBP with RyR2, reduced the magnitude of Ca(2+) release but had no effect on the propensity for SOICR. In contrast, neither FKBP12.6 nor FKBP12 was able to regulate an arrhythmogenic variant of RyR2, despite a conserved protein interaction. Our results suggest that both FKBP12.6 and FKBP12 play critical roles in regulating RyR2 function by facilitating the termination of SOICR. The inability of FKBPs to mediate a similar effect on the mutant RyR2 represents a novel mechanism by which mutations within RyR2 lead to arrhythmia.
Collapse
|
18
|
Himeno Y, Asakura K, Cha CY, Memida H, Powell T, Amano A, Noma A. A human ventricular myocyte model with a refined representation of excitation-contraction coupling. Biophys J 2016. [PMID: 26200878 DOI: 10.1016/j.bpj.2015.06.017] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cardiac Ca(2+)-induced Ca(2+) release (CICR) occurs by a regenerative activation of ryanodine receptors (RyRs) within each Ca(2+)-releasing unit, triggered by the activation of L-type Ca(2+) channels (LCCs). CICR is then terminated, most probably by depletion of Ca(2+) in the junctional sarcoplasmic reticulum (SR). Hinch et al. previously developed a tightly coupled LCC-RyR mathematical model, known as the Hinch model, that enables simulations to deal with a variety of functional states of whole-cell populations of a Ca(2+)-releasing unit using a personal computer. In this study, we developed a membrane excitation-contraction model of the human ventricular myocyte, which we call the human ventricular cell (HuVEC) model. This model is a hybrid of the most recent HuVEC models and the Hinch model. We modified the Hinch model to reproduce the regenerative activation and termination of CICR. In particular, we removed the inactivated RyR state and separated the single step of RyR activation by LCCs into triggering and regenerative steps. More importantly, we included the experimental measurement of a transient rise in Ca(2+) concentrations ([Ca(2+)], 10-15 μM) during CICR in the vicinity of Ca(2+)-releasing sites, and thereby calculated the effects of the local Ca(2+) gradient on CICR as well as membrane excitation. This HuVEC model successfully reconstructed both membrane excitation and key properties of CICR. The time course of CICR evoked by an action potential was accounted for by autonomous changes in an instantaneous equilibrium open probability of couplons. This autonomous time course was driven by a core feedback loop including the pivotal local [Ca(2+)], influenced by a time-dependent decay in the SR Ca(2+) content during CICR.
Collapse
Affiliation(s)
- Yukiko Himeno
- Biosimulation Research Center, College of Life Sciences, Ritsumeikan University, Shiga, Japan
| | - Keiichi Asakura
- Biosimulation Research Center, College of Life Sciences, Ritsumeikan University, Shiga, Japan; Nippon Shinyaku Co., Ltd., Kyoto, Japan
| | - Chae Young Cha
- Biosimulation Research Center, College of Life Sciences, Ritsumeikan University, Shiga, Japan; Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, UK
| | - Hiraku Memida
- Biosimulation Research Center, College of Life Sciences, Ritsumeikan University, Shiga, Japan
| | - Trevor Powell
- Department of Pharmacology, University of Oxford, Oxford, UK
| | - Akira Amano
- Biosimulation Research Center, College of Life Sciences, Ritsumeikan University, Shiga, Japan
| | - Akinori Noma
- Biosimulation Research Center, College of Life Sciences, Ritsumeikan University, Shiga, Japan.
| |
Collapse
|
19
|
Marmugi A, Parnis J, Chen X, Carmichael L, Hardy J, Mannan N, Marchetti P, Piemonti L, Bosco D, Johnson P, Shapiro JAM, Cruciani-Guglielmacci C, Magnan C, Ibberson M, Thorens B, Valdivia HH, Rutter GA, Leclerc I. Sorcin Links Pancreatic β-Cell Lipotoxicity to ER Ca2+ Stores. Diabetes 2016; 65:1009-21. [PMID: 26822088 PMCID: PMC4806657 DOI: 10.2337/db15-1334] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 01/18/2016] [Indexed: 01/02/2023]
Abstract
Preserving β-cell function during the development of obesity and insulin resistance would limit the worldwide epidemic of type 2 diabetes. Endoplasmic reticulum (ER) calcium (Ca(2+)) depletion induced by saturated free fatty acids and cytokines causes β-cell ER stress and apoptosis, but the molecular mechanisms behind these phenomena are still poorly understood. Here, we demonstrate that palmitate-induced sorcin downregulation and subsequent increases in glucose-6-phosphatase catalytic subunit-2 (G6PC2) levels contribute to lipotoxicity. Sorcin is a calcium sensor protein involved in maintaining ER Ca(2+) by inhibiting ryanodine receptor activity and playing a role in terminating Ca(2+)-induced Ca(2+) release. G6PC2, a genome-wide association study gene associated with fasting blood glucose, is a negative regulator of glucose-stimulated insulin secretion (GSIS). High-fat feeding in mice and chronic exposure of human islets to palmitate decreases endogenous sorcin expression while levels of G6PC2 mRNA increase. Sorcin-null mice are glucose intolerant, with markedly impaired GSIS and increased expression of G6pc2 Under high-fat diet, mice overexpressing sorcin in the β-cell display improved glucose tolerance, fasting blood glucose, and GSIS, whereas G6PC2 levels are decreased and cytosolic and ER Ca(2+) are increased in transgenic islets. Sorcin may thus provide a target for intervention in type 2 diabetes.
Collapse
Affiliation(s)
- Alice Marmugi
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology & Metabolism, Department of Medicine, Imperial College London, London, U.K
| | - Julia Parnis
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology & Metabolism, Department of Medicine, Imperial College London, London, U.K
| | - Xi Chen
- Center for Arrhythmia Research, University of Michigan, Ann Arbor, MI
| | - LeAnne Carmichael
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology & Metabolism, Department of Medicine, Imperial College London, London, U.K
| | - Julie Hardy
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology & Metabolism, Department of Medicine, Imperial College London, London, U.K
| | - Naila Mannan
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology & Metabolism, Department of Medicine, Imperial College London, London, U.K
| | - Piero Marchetti
- Department of Endocrinology and Metabolism, University of Pisa, Pisa, Italy
| | - Lorenzo Piemonti
- Diabetes Research Institute (HSR-DRI), San Raffaele Scientific Institute, Milan, Italy
| | - Domenico Bosco
- Cell Isolation and Transplantation Center, Department of Surgery, Geneva University Hospitals and University of Geneva, Geneva, Switzerland
| | - Paul Johnson
- Nuffield Department of Surgical Sciences, University of Oxford, Oxford, U.K
| | - James A M Shapiro
- Clinical Islet Laboratory and Clinical Islet Transplant Program, University of Alberta, Edmonton, Alberta, Canada
| | | | - Christophe Magnan
- Unit of Functional and Adaptive Biology, Paris Diderot University-Paris 7, Paris, France
| | - Mark Ibberson
- Vital-IT Group, SIB Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Bernard Thorens
- Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland
| | - Héctor H Valdivia
- Center for Arrhythmia Research, University of Michigan, Ann Arbor, MI
| | - Guy A Rutter
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology & Metabolism, Department of Medicine, Imperial College London, London, U.K.
| | - Isabelle Leclerc
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology & Metabolism, Department of Medicine, Imperial College London, London, U.K.
| |
Collapse
|
20
|
Song Z, Karma A, Weiss JN, Qu Z. Long-Lasting Sparks: Multi-Metastability and Release Competition in the Calcium Release Unit Network. PLoS Comput Biol 2016; 12:e1004671. [PMID: 26730593 PMCID: PMC4701461 DOI: 10.1371/journal.pcbi.1004671] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 11/23/2015] [Indexed: 11/20/2022] Open
Abstract
Calcium (Ca) sparks are elementary events of biological Ca signaling. A normal Ca spark has a brief duration in the range of 10 to 100 ms, but long-lasting sparks with durations of several hundred milliseconds to seconds are also widely observed. Experiments have shown that the transition from normal to long-lasting sparks can occur when ryanodine receptor (RyR) open probability is either increased or decreased. Here, we demonstrate theoretically and computationally that long-lasting sparks emerge as a collective dynamical behavior of the network of diffusively coupled Ca release units (CRUs). We show that normal sparks occur when the CRU network is monostable and excitable, while long-lasting sparks occur when the network dynamics possesses multiple metastable attractors, each attractor corresponding to a different spatial firing pattern of sparks. We further highlight the mechanisms and conditions that produce long-lasting sparks, demonstrating the existence of an optimal range of RyR open probability favoring long-lasting sparks. We find that when CRU firings are sparse and sarcoplasmic reticulum (SR) Ca load is high, increasing RyR open probability promotes long-lasting sparks by potentiating Ca-induced Ca release (CICR). In contrast, when CICR is already strong enough to produce frequent firings, decreasing RyR open probability counter-intuitively promotes long-lasting sparks by decreasing spark frequency. The decrease in spark frequency promotes intra-SR Ca diffusion from neighboring non-firing CRUs to the firing CRUs, which helps to maintain the local SR Ca concentration of the firing CRUs above a critical level to sustain firing. In this setting, decreasing RyR open probability further suppresses long-lasting sparks by weakening CICR. Since a long-lasting spark terminates via the Kramers’ escape process over a potential barrier, its duration exhibits an exponential distribution determined by the barrier height and noise strength, which is modulated differently by different ways of altering the Ca release flux strength. Calcium (Ca) sparks, resulting from Ca-induced Ca release, are elementary events of biological Ca signaling. Sparks are normally brief, but long-lasting sparks have been widely observed experimentally under various conditions. The underlying mechanisms of spark duration or termination and the corresponding determinants remain a topic of debate. In this study, we demonstrate theoretically and computationally that normal brief sparks are excitable transients, while long-lasting sparks are multiple metastable states emerging in the diffusively coupled Ca release unit network, as a result of cooperativity and release competition among the Ca release units. Termination of a long-lasting spark is a Kramers’ escape process over a potential barrier, and the spark duration is the first-passage time, exhibiting an exponential distribution.
Collapse
Affiliation(s)
- Zhen Song
- The UCLA Cardiovascular Research Laboratory, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States of America
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States of America
| | - Alain Karma
- Department of Physics, Northeastern University, Boston, Massachusetts, United States of America
| | - James N. Weiss
- The UCLA Cardiovascular Research Laboratory, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States of America
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States of America
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States of America
| | - Zhilin Qu
- The UCLA Cardiovascular Research Laboratory, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States of America
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States of America
- * E-mail:
| |
Collapse
|
21
|
Functional Impact of Ryanodine Receptor Oxidation on Intracellular Calcium Regulation in the Heart. Rev Physiol Biochem Pharmacol 2016; 171:39-62. [PMID: 27251471 DOI: 10.1007/112_2016_2] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Type 2 ryanodine receptor (RyR2) serves as the major intracellular Ca2+ release channel that drives heart contraction. RyR2 is activated by cytosolic Ca2+ via the process of Ca2+-induced Ca2+ release (CICR). To ensure stability of Ca2+ dynamics, the self-reinforcing CICR must be tightly controlled. Defects in this control cause sarcoplasmic reticulum (SR) Ca2+ mishandling, which manifests in a variety of cardiac pathologies that include myocardial infarction and heart failure. These pathologies are also associated with oxidative stress. Given that RyR2 contains a large number of cysteine residues, it is no surprise that RyR2 plays a key role in the cellular response to oxidative stress. RyR's many cysteine residues pose an experimental limitation in defining a specific target or mechanism of action for oxidative stress. As a result, the current understanding of redox-mediated RyR2 dysfunction remains incomplete. Several oxidative modifications, including S-glutathionylation and S-nitrosylation, have been suggested playing an important role in the regulation of RyR2 activity. Moreover, oxidative stress can increase RyR2 activity by forming disulfide bonds between two neighboring subunits (intersubunit cross-linking). Since intersubunit interactions within the RyR2 homotetramer complex dictate the channel gating, such posttranslational modification of RyR2 would have a significant impact on RyR2 function and Ca2+ regulation. This review summarizes recent findings on oxidative modifications of RyR2 and discusses contributions of these RyR2 modifications to SR Ca2+ mishandling during cardiac pathologies.
Collapse
|
22
|
Troczka BJ, Williams AJ, Williamson MS, Field LM, Lüemmen P, Davies TGE. Stable expression and functional characterisation of the diamondback moth ryanodine receptor G4946E variant conferring resistance to diamide insecticides. Sci Rep 2015; 5:14680. [PMID: 26424584 PMCID: PMC5289073 DOI: 10.1038/srep14680] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Accepted: 09/07/2015] [Indexed: 11/09/2022] Open
Abstract
Diamides, such as flubendiamide and chlorantraniliprole, belong to a new chemical class of insecticides that act as conformation-sensitive activators of insect ryanodine receptors (RyRs). Both compounds are registered for use against lepidopteran species such as the diamondback moth, Plutella xylostella, a notorious global pest of cruciferous crops. Recently acquired resistance to diamide insecticides in this species is thought to be due to a target-site mutation conferring an amino acid substitution (G4946E), located within the trans-membrane domain of the RyR, though the exact role of this mutation has not yet been fully determined. To address this we have cloned a full-length cDNA encoding the P. xylostella RyR and established clonal Sf9 cell lines stably expressing either the wildtype RyR or the G4946E variant, in order to test the sensitivity to flubendiamide and chlorantraniliprole on the recombinant receptor. We report that the efficacy of both diamides was dramatically reduced in clonal Sf9 cells stably expressing the G4946E modified RyR, providing clear functional evidence that the G4946E RyR mutation impairs diamide insecticide binding.
Collapse
Affiliation(s)
- Bartlomiej J Troczka
- Biological Chemistry and Crop Protection Department, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
| | - Alan J Williams
- Institute of Molecular &Experimental Medicine, Cardiff University School of Medicine, Wales Heart Research Institute, Heath Park, Cardiff CF14 4XN, UK
| | - Martin S Williamson
- Biological Chemistry and Crop Protection Department, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
| | - Linda M Field
- Biological Chemistry and Crop Protection Department, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
| | | | - T G Emyr Davies
- Biological Chemistry and Crop Protection Department, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
| |
Collapse
|
23
|
Ca2+-activation kinetics modulate successive puff/spark amplitude, duration and inter-event-interval correlations in a Langevin model of stochastic Ca2+ release. Math Biosci 2015; 264:101-7. [DOI: 10.1016/j.mbs.2015.03.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Revised: 03/16/2015] [Accepted: 03/27/2015] [Indexed: 01/12/2023]
|
24
|
Abstract
In a normal human life span, the heart beats about 2 to 3 billion times. Under diseased conditions, a heart may lose its normal rhythm and degenerate suddenly into much faster and irregular rhythms, called arrhythmias, which may lead to sudden death. The transition from a normal rhythm to an arrhythmia is a transition from regular electrical wave conduction to irregular or turbulent wave conduction in the heart, and thus this medical problem is also a problem of physics and mathematics. In the last century, clinical, experimental, and theoretical studies have shown that dynamical theories play fundamental roles in understanding the mechanisms of the genesis of the normal heart rhythm as well as lethal arrhythmias. In this article, we summarize in detail the nonlinear and stochastic dynamics occurring in the heart and their links to normal cardiac functions and arrhythmias, providing a holistic view through integrating dynamics from the molecular (microscopic) scale, to the organelle (mesoscopic) scale, to the cellular, tissue, and organ (macroscopic) scales. We discuss what existing problems and challenges are waiting to be solved and how multi-scale mathematical modeling and nonlinear dynamics may be helpful for solving these problems.
Collapse
Affiliation(s)
- Zhilin Qu
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA
- Correspondence to: Zhilin Qu, PhD, Department of Medicine, Division of Cardiology, David Geffen School of Medicine at UCLA, A2-237 CHS, 650 Charles E. Young Drive South, Los Angeles, CA 90095, Tel: 310-794-6050, Fax: 310-206-9133,
| | - Gang Hu
- Department of Physics, Beijing Normal University, Beijing 100875, China
| | - Alan Garfinkel
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA
- Department of Integrative Biology and Physiology, University of California, Los Angeles, California 90095, USA
| | - James N. Weiss
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA
| |
Collapse
|
25
|
Zorov DB, Juhaszova M, Sollott SJ. Mitochondrial reactive oxygen species (ROS) and ROS-induced ROS release. Physiol Rev 2014; 94:909-50. [PMID: 24987008 DOI: 10.1152/physrev.00026.2013] [Citation(s) in RCA: 3328] [Impact Index Per Article: 332.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Byproducts of normal mitochondrial metabolism and homeostasis include the buildup of potentially damaging levels of reactive oxygen species (ROS), Ca(2+), etc., which must be normalized. Evidence suggests that brief mitochondrial permeability transition pore (mPTP) openings play an important physiological role maintaining healthy mitochondria homeostasis. Adaptive and maladaptive responses to redox stress may involve mitochondrial channels such as mPTP and inner membrane anion channel (IMAC). Their activation causes intra- and intermitochondrial redox-environment changes leading to ROS release. This regenerative cycle of mitochondrial ROS formation and release was named ROS-induced ROS release (RIRR). Brief, reversible mPTP opening-associated ROS release apparently constitutes an adaptive housekeeping function by the timely release from mitochondria of accumulated potentially toxic levels of ROS (and Ca(2+)). At higher ROS levels, longer mPTP openings may release a ROS burst leading to destruction of mitochondria, and if propagated from mitochondrion to mitochondrion, of the cell itself. The destructive function of RIRR may serve a physiological role by removal of unwanted cells or damaged mitochondria, or cause the pathological elimination of vital and essential mitochondria and cells. The adaptive release of sufficient ROS into the vicinity of mitochondria may also activate local pools of redox-sensitive enzymes involved in protective signaling pathways that limit ischemic damage to mitochondria and cells in that area. Maladaptive mPTP- or IMAC-related RIRR may also be playing a role in aging. Because the mechanism of mitochondrial RIRR highlights the central role of mitochondria-formed ROS, we discuss all of the known ROS-producing sites (shown in vitro) and their relevance to the mitochondrial ROS production in vivo.
Collapse
Affiliation(s)
- Dmitry B Zorov
- A. N. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia; and Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
| | - Magdalena Juhaszova
- A. N. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia; and Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
| | - Steven J Sollott
- A. N. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia; and Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
| |
Collapse
|
26
|
Rueda A, de Alba-Aguayo DR, Valdivia HH. [Ryanodine receptor, calcium leak and arrhythmias]. ARCHIVOS DE CARDIOLOGIA DE MEXICO 2014; 84:191-201. [PMID: 25103920 DOI: 10.1016/j.acmx.2013.12.008] [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: 07/30/2013] [Revised: 10/30/2013] [Accepted: 12/02/2013] [Indexed: 11/28/2022] Open
Abstract
The participation of the ionic Ca(2+) release channel/ryanodine receptor in cardiac excitation-contraction coupling is well known since the late '80s, when various seminal papers communicated its purification for the first time and its identity with the "foot" structures located at the terminal cisternae of the sarcoplasmic reticulum. In addition to its main role as the Ca(2+) channel responsible for the transient Ca(2+) increase that activates the contractile machinery of the cardiomyocytes, the ryanodine receptor releases Ca(2+) during the relaxation phase of the cardiac cycle, giving rise to a diastolic Ca(2+) leak. In normal physiological conditions, diastolic Ca(2+) leak regulates the proper level of luminal Ca(2+), but in pathological conditions it participates in the generation of both, acquired and hereditary arrhythmias. Very recently, several groups have focused their efforts into the development of pharmacological tools to control the altered diastolic Ca(2+) leak via ryanodine receptors. In this review, we focus our interest on describing the participation of cardiac ryanodine receptor in the diastolic Ca(2+) leak under physiological or pathological conditions and also on the therapeutic approaches to control its undesired exacerbated activity during diastole.
Collapse
Affiliation(s)
- Angélica Rueda
- Departamento de Bioquímica, Centro de Investigación y de Estudios Avanzados del IPN, Unidad Zacatenco, México D.F., México.
| | - David R de Alba-Aguayo
- Departamento de Bioquímica, Centro de Investigación y de Estudios Avanzados del IPN, Unidad Zacatenco, México D.F., México
| | - Héctor H Valdivia
- Center for Arrhythmia Research, University of Michigan, Ann Arbor, MI, Estados Unidos
| |
Collapse
|
27
|
Termination of calcium puffs and coupled closings of inositol trisphosphate receptor channels. Cell Calcium 2014; 56:157-68. [PMID: 25016315 DOI: 10.1016/j.ceca.2014.06.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Revised: 06/06/2014] [Accepted: 06/16/2014] [Indexed: 11/22/2022]
Abstract
Calcium puffs are localized Ca(2+) signals mediated by Ca(2+) release from the endoplasmic reticulum (ER) through clusters of inositol trisphosphate receptor (IP3R) channels. The recruitment of IP3R channels during puffs depends on Ca(2+)-induced Ca(2+) release, a regenerative process that must be terminated to maintain control of cell signaling and prevent Ca(2+) cytotoxicity. Here, we studied puff termination using total internal reflection microscopy to resolve the gating of individual IP3R channels during puffs in intact SH-SY5Y neuroblastoma cells. We find that the kinetics of IP3R channel closing differ from that expected for independent, stochastic gating, in that multiple channels tend to remain open together longer than predicted from their individual open lifetimes and then close in near-synchrony. This behavior cannot readily be explained by previously proposed termination mechanisms, including Ca(2+)-inhibition of IP3Rs and local depletion of Ca(2+) in the ER lumen. Instead, we postulate that the gating of closely adjacent IP3Rs is coupled, possibly via allosteric interactions, suggesting an important mechanism to ensure robust puff termination in addition to Ca(2+)-inactivation.
Collapse
|
28
|
Abstract
Calcium sparks in cardiac myocytes are brief, localized calcium releases from the sarcoplasmic reticulum (SR) believed to be caused by locally regenerative calcium-induced calcium release (CICR) via couplons, clusters of ryanodine receptors (RyRs). How such regeneration is terminated is uncertain. We performed numerical simulations of an idealized stochastic model of spark production, assuming a RyR gating scheme with only two states (open and closed). Local depletion of calcium in the SR was inevitable during a spark, and this could terminate sparks by interrupting CICR, with or without assumed modulation of RyR gating by SR lumenal calcium. Spark termination by local SR depletion was not robust: under some conditions, sparks could be greatly and variably prolonged, terminating by stochastic attrition-a phenomenon we dub "spark metastability." Spark fluorescence rise time was not a good surrogate for the duration of calcium release. Using a highly simplified, deterministic model of the dynamics of a couplon, we show that spark metastability depends on the kinetic relationship of RyR gating and junctional SR refilling rates. The conditions for spark metastability resemble those produced by known mutations of RyR2 and CASQ2 that cause life-threatening triggered arrhythmias, and spark metastability may be mitigated by altering the kinetics of the RyR in a manner similar to the effects of drugs known to prevent those arrhythmias. The model was unable to explain the distributions of spark amplitudes and rise times seen in chemically skinned cat atrial myocytes, suggesting that such sparks may be more complex events involving heterogeneity of couplons or local propagation among sub-clusters of RyRs.
Collapse
Affiliation(s)
- Michael D Stern
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.
| | | | | |
Collapse
|
29
|
Zima AV, Bovo E, Mazurek SR, Rochira JA, Li W, Terentyev D. Ca handling during excitation-contraction coupling in heart failure. Pflugers Arch 2014; 466:1129-37. [PMID: 24515294 DOI: 10.1007/s00424-014-1469-3] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Revised: 01/29/2014] [Accepted: 01/30/2014] [Indexed: 12/22/2022]
Abstract
In the heart, coupling between excitation of the surface membrane and activation of contractile apparatus is mediated by Ca released from the sarcoplasmic reticulum (SR). Several components of Ca machinery are perfectly arranged within the SR network and the T-tubular system to generate a regular Ca cycling and thereby rhythmic beating activity of the heart. Among these components, ryanodine receptor (RyR) and SR Ca ATPase (SERCA) complexes play a particularly important role and their dysfunction largely underlies abnormal Ca homeostasis in diseased hearts such as in heart failure. The abnormalities in Ca regulation occur at practically all main steps of Ca cycling in the failing heart, including activation and termination of SR Ca release, diastolic SR Ca leak, and SR Ca uptake. The contributions of these different mechanisms to depressed contractile function and enhanced arrhythmogenesis may vary in different HF models. This brief review will therefore focus on modifications in RyR and SERCA structure that occur in the failing heart and how these molecular modifications affect SR Ca regulation and excitation-contraction coupling.
Collapse
Affiliation(s)
- Aleksey V Zima
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Avenue, Maywood, IL, 60153, USA,
| | | | | | | | | | | |
Collapse
|
30
|
Calmodulin modulates the termination threshold for cardiac ryanodine receptor-mediated Ca2+ release. Biochem J 2014; 455:367-75. [PMID: 23992453 DOI: 10.1042/bj20130805] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
RyR2 (cardiac ryanodine receptor)-mediated Ca2+ release in cardiomyocytes terminates when the sarcoplasmic reticulum Ca2+ content depletes to a threshold level, known as the termination threshold. Despite its importance, little is known about the mechanism that regulates the termination threshold. CaM (calmodulin), by inhibiting RyR2, has been implicated in Ca2+-release termination, but whether CaM modulates the termination threshold is unknown. To this end, we monitored the endoplasmic reticulum Ca2+ dynamics in RyR2-expressing HEK (human embryonic kidney)-293 cells transfected with WT (wild-type) CaM or mutants. We found that WT CaM or CaM mutations which abolish Ca2+ binding to the N-lobe (N-terminal lobe) of CaM increased the termination threshold (i.e. facilitated termination), but had no effect on the activation threshold at which spontaneous Ca2+ release occurs. On the other hand, CaM mutations that diminish Ca2+ binding to both the N-lobe and C-lobe (C-terminal lobe), or the C-lobe only, decreased the termination threshold (i.e. delayed termination) with a similar activation threshold. Furthermore, deletion of residues 3583-3603 or point mutations (W3587A/L3591D/F3603A, W3587A, or L3591D) in the CaM-binding domain of RyR2 that are known to abolish or retain CaM binding all reduced the termination threshold without having a significant impact on the activation threshold. Interestingly, the RyR2-F3603A mutation affected both the activation and termination threshold. Collectively, these data indicate that CaM facilitates the termination of Ca2+ release by increasing the termination threshold, and that this action of CaM depends on Ca2+ binding to the C-lobe, but not to the N-lobe, of CaM. The results of the present study also suggest that the CaM-binding domain of RyR2 is an important determinant of Ca2+-release termination and activation.
Collapse
|
31
|
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: 84] [Impact Index Per Article: 7.6] [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.
Collapse
Affiliation(s)
- M B Cannell
- Department of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.
| | | | | | | |
Collapse
|
32
|
Huang X, Liu Y, Wang R, Zhong X, Liu Y, Koop A, Chen SRW, Wagenknecht T, Liu Z. Two potential calmodulin-binding sequences in the ryanodine receptor contribute to a mobile, intra-subunit calmodulin-binding domain. J Cell Sci 2013; 126:4527-35. [PMID: 23868982 DOI: 10.1242/jcs.133454] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Calmodulin (CaM), a 16 kDa ubiquitous calcium-sensing protein, is known to bind tightly to the calcium release channel/ryanodine receptor (RyR), and modulate RyR function. CaM binding studies using RyR fragments or synthetic peptides have revealed the presence of multiple, potential CaM-binding regions in the primary sequence of RyR. In the present study, we inserted GFP into two of these proposed CaM-binding sequences and mapped them onto the three-dimensional structure of intact cardiac RyR2 by cryo-electron microscopy. Interestingly, we found that the two potential CaM-binding regions encompassing, Arg3595 and Lys4269, respectively, are in close proximity and are adjacent to the previously mapped CaM-binding sites. To monitor the conformational dynamics of these CaM-binding regions, we generated a fluorescence resonance energy transfer (FRET) pair, a dual CFP- and YFP-labeled RyR2 (RyR2R3595-CFP/K4269-YFP) with CFP inserted after Arg3595 and YFP inserted after Lys4269. We transfected HEK293 cells with the RyR2R3595-CFP/K4269-YFP cDNA, and examined their FRET signal in live cells. We detected significant FRET signals in transfected cells that are sensitive to the channel activator caffeine, suggesting that caffeine is able to induce conformational changes in these CaM-binding regions. Importantly, no significant FRET signals were detected in cells co-transfected with cDNAs encoding the single CFP (RyR2R3595-CFP) and single YFP (RyR2K4269-YFP) insertions, indicating that the FRET signal stemmed from the interaction between R3595-CFP and K4269-YFP that are in the same RyR subunit. These observations suggest that multiple regions in the RyR2 sequence may contribute to an intra-subunit CaM-binding pocket that undergoes conformational changes during channel gating.
Collapse
Affiliation(s)
- Xiaojun Huang
- Wadsworth Center, New York State Department of Health, Albany, New York 12201, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
33
|
Bers DM, Shannon TR. Calcium movements inside the sarcoplasmic reticulum of cardiac myocytes. J Mol Cell Cardiol 2013; 58:59-66. [PMID: 23321551 PMCID: PMC3628081 DOI: 10.1016/j.yjmcc.2013.01.002] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Revised: 12/17/2012] [Accepted: 01/04/2013] [Indexed: 02/03/2023]
Abstract
Sarcoplasmic reticulum (SR) Ca content ([Ca]SRT) is critical to both normal cardiac function and electrophysiology, and changes associated with pathology contribute to systolic and diastolic dysfunction and arrhythmias. The intra-SR free [Ca] ([Ca]SR) dictates the [Ca]SRT, the driving force for Ca release and regulates release channel gating. We discuss measurement of [Ca]SR and [Ca]SRT, how [Ca]SR regulates activation and termination of release, and how Ca diffuses within the SR and influences SR Ca release during excitation-contraction coupling, Ca sparks and Cac waves. The entire SR network is connected and its lumen is also continuous with the nuclear envelope. Rapid Ca diffusion within the SR could stabilize and balance local [Ca]SR within the myocyte, but restrictions to diffusion can create spatial inhomogeneities. Experimental measurements and mathematical models of [Ca]SR to date have greatly enriched our understanding of these [Ca]SR dynamics, but controversies exist and may stimulate new measurements and analysis.
Collapse
Affiliation(s)
- Donald M Bers
- Department of Pharmacology, University of California, Davis, Davis, CA, USA.
| | | |
Collapse
|
34
|
Extraction of sub-microscopic Ca fluxes from blurred and noisy fluorescent indicator images with a detailed model fitting approach. PLoS Comput Biol 2013; 9:e1002931. [PMID: 23468614 PMCID: PMC3585382 DOI: 10.1371/journal.pcbi.1002931] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Accepted: 01/07/2013] [Indexed: 11/25/2022] Open
Abstract
The release of Ca from intracellular stores is key to cardiac muscle function; however, the molecular control of intracellular Ca release remains unclear. Depletion of the intracellular Ca store (sarcoplasmic reticulum, SR) may play an important role, but the ability to measure local SR Ca with fluorescent Ca indicators is limited by the microscope optical resolution and properties of the indicator. This leads to an uncertain degree of spatio-temporal blurring, which is not easily corrected (by deconvolution methods) due to the low signal-to-noise ratio of the recorded signals. In this study, a 3D computer model was constructed to calculate local Ca fluxes and consequent dye signals, which were then blurred by a measured microscope point spread function. Parameter fitting was employed to adjust a release basis function until the model output fitted recorded (2D) Ca spark data. This ‘forward method’ allowed us to obtain estimates of the time-course of Ca release flux and depletion within the sub-microscopic local SR associated with a number of Ca sparks. While variability in focal position relative to Ca spark sites causes more out-of-focus events to have smaller calculated fluxes (and less SR depletion), the average SR depletion was to 20±10% (s.d.) of the resting level. This focus problem implies that the actual SR depletion is likely to be larger and the five largest depletions analyzed were to 8±6% of the resting level. This profound depletion limits SR release flux during a Ca spark, which peaked at 8±3 pA and declined with a half time of 7±2 ms. By comparison, RyR open probability declined more slowly, suggesting release termination is dominated by neither SR Ca depletion nor intrinsic RyR gating, but results from an interaction of these processes. Calcium levels inside myocytes regulate the heart's force of contraction. Calcium is released from the primary intracellular store called the sarcoplasmic reticulum. Calcium release was directly observed as ‘calcium sparks’ using fluorescent calcium indicators inside the cell. More recently, calcium levels inside the store have been measured as calcium ‘blinks’. These suggest that some depletion of store calcium occurs during cell excitation; however, the actual extent of depletion is made uncertain by the complex sarcoplasmic reticulum shape, dye saturation and optical properties of the microscope. While previous studies have assumed idealized microscope properties, we measured microscope blurring and applied it to a computer model of calcium movements inside the cell. In this model, calcium release was adjusted to match the simulated blurred calcium signals to experimental results. The calculations show that the depth of local sarcoplasmic reticulum calcium depletion is much greater than inferred from calcium blinks and that the time-course of calcium release is affected by this depletion. An estimate for the time-course of gating of the ion channels that regulate calcium release inside the cell was also calculated. We suggest that the time-course of SR Ca release arises from a complex interaction of Ca depletion and channel gating.
Collapse
|
35
|
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.
Collapse
Affiliation(s)
- Angela F Dulhunty
- Department of Translational Biosciences, John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory, Australia.
| | | | | | | | | | | | | | | |
Collapse
|
36
|
Gez LS, Hagalili Y, Shainberg A, Atlas D. Voltage-driven Ca(2+) binding at the L-type Ca(2+) channel triggers cardiac excitation-contraction coupling prior to Ca(2+) influx. Biochemistry 2012; 51:9658-66. [PMID: 23145875 DOI: 10.1021/bi301124a] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The activation of the ryanodine Ca(2+) release channels (RyR2) by the entry of Ca(2+) through the L-type Ca(2+) channels (Cav1.2) is believed to be the primary mechanism of excitation-contraction (EC) coupling in cardiac cells. This proposed mechanism of Ca(2+)-induced Ca(2+) release (CICR) cannot fully account for the lack of a termination signal for this positive feedback process. Using Cav1.2 channel mutants, we demonstrate that the Ca(2+)-impermeable α(1)1.2/L775P/T1066Y mutant introduced through lentiviral infection into neonate cardiomyocytes triggers Ca(2+) transients in a manner independent of Ca(2+) influx. In contrast, the α(1)1.2/L775P/T1066Y/4A mutant, in which the Ca(2+)-binding site of the channel was destroyed, supports neither the spontaneous nor the electrically evoked contractions. Ca(2+) bound at the channel selectivity filter appears to initiate a signal that is conveyed directly from the channel pore to RyR2, triggering contraction of cardiomyocytes prior to Ca(2+) influx. Thus, RyR2 is activated in response to a conformational change in the L-type channel during membrane depolarization and not through interaction with Ca(2+) ions diffusing in the junctional gap space. Accordingly, termination of the RyR2 activity is achieved when the signal stops upon the return of the L-channel to the resting state. We propose a new model in which the physical link between Cav1.2 and RyR2 allows propagation of a conformational change induced at the open pore of the channel to directly activate RyR2. These results highlight Cav1.2 as a signaling protein and provide a mechanism for terminating the release of Ca(2+) from RyR2 through protein-protein interactions. In this model, the L-type channel is a master regulator of both initiation and termination of EC coupling in neonate cardiomyocytes.
Collapse
Affiliation(s)
- Liron S Gez
- Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | | | | | | |
Collapse
|
37
|
Laver DR, Kong CHT, Imtiaz MS, Cannell MB. Termination of calcium-induced calcium release by induction decay: an emergent property of stochastic channel gating and molecular scale architecture. J Mol Cell Cardiol 2012; 54:98-100. [PMID: 23123322 DOI: 10.1016/j.yjmcc.2012.10.009] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2012] [Revised: 09/25/2012] [Accepted: 10/22/2012] [Indexed: 10/27/2022]
Abstract
Calcium-induced calcium release (CICR) is an inherently regenerative process due to the Ca(2+)-dependent gating of ryanodine receptors (RyRs) in the sarco/endoplasmic reticulum (SR) and is critical for cardiac excitation-contraction coupling. This process is seen as Ca(2+) sparks, which reflect the concerted gating of groups of RyRs in the dyad, a specialised junctional signalling domain between the SR and surface membrane. However, the mechanism(s) responsible for the termination of regenerative CICR during the evolution of Ca(2+) sparks remain uncertain. Rat cardiac RyR gating 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. Model CICR termination was robust, relatively insensitive to the number of dyadic RyRs and automatic. This emergent behaviour arose from the rapid development and dissolution of nanoscopic Ca(2+) gradients within the dyad. These simulations show that CICR does not require intrinsic inactivation or SR calcium sensing mechanisms for stability and cessation of regeneration that arises from local control at the molecular scale via a process we call 'induction decay'.
Collapse
Affiliation(s)
- D R Laver
- Department of Physiology and Pharmacology, University of Bristol, Bristol BS9 1TH, UK
| | | | | | | |
Collapse
|
38
|
Store-dependent deactivation: cooling the chain-reaction of myocardial calcium signaling. J Mol Cell Cardiol 2012; 58:77-83. [PMID: 23108187 DOI: 10.1016/j.yjmcc.2012.10.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2012] [Revised: 10/11/2012] [Accepted: 10/21/2012] [Indexed: 01/08/2023]
Abstract
In heart cells, Ca(2+) released from the internal storage unit, the sarcoplasmic reticulum (SR) through ryanodine receptor (RyR2) channels is the predominant determinant of cardiac contractility. Evidence obtained in recent years suggests that SR Ca(2+) release is tightly regulated not only by cytosolic Ca(2+) but also by intra-store Ca(2+) concentration. Specifically, Ca(2+)-induced Ca(2+) release (CICR) that relies on auto-catalytic action of Ca(2+) at the cytosolic side of RyR2s is precisely balanced and counteracted by RyR2 deactivation dependent on a reciprocal decrease of Ca(2+) at the luminal side of RyR2s. Dysregulation of this inherently unstable Ca(2+) signaling is considered to be an underlying cause of triggered arrhythmias, and is associated with genetic and acquired forms of sudden cardiac death. In this article, we present an overview of recent advances in our understanding of the regulatory role luminal Ca(2+) plays in Ca(2+) handling, with a particular emphasis on the role of Ca(2+)release refractoriness in aberrant Ca(2+) release.
Collapse
|
39
|
Porta M, Diaz-Sylvester PL, Neumann JT, Escobar AL, Fleischer S, Copello JA. Coupled gating of skeletal muscle ryanodine receptors is modulated by Ca2+, Mg2+, and ATP. Am J Physiol Cell Physiol 2012; 303:C682-97. [PMID: 22785120 DOI: 10.1152/ajpcell.00150.2012] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Coupled gating (synchronous openings and closures) of groups of skeletal muscle ryanodine receptors (RyR1), which mimics RyR1-mediated Ca(2+) release underlying Ca(2+) sparks, was first described by Marx et al. (Marx SO, Ondrias K, Marks AR. Science 281: 818-821, 1998). The nature of the RyR1-RyR1 interactions for coupled gating still needs to be characterized. Consequently, we defined planar lipid bilayer conditions where ∼25% of multichannel reconstitutions contain mixtures of coupled and independently gating RyR1. In ∼10% of the cases, all RyRs (2-10 channels; most frequently 3-4) gated in coupled fashion, allowing for quantification. Our results indicated that coupling required cytosolic solutions containing ATP/Mg(2+) and high (50 mM) luminal Ca(2+) (Ca(lum)) or Sr(2+) solutions. Bursts of coupled activity (events) started and ended abruptly, with all channels activating/deactivating within ∼300 μs. Coupled RyR1 were heterogeneous, where highly active RyR1 ("drivers") seemed open during the entire coupled event (P(o) = 1), while other RyR1s ("followers") displayed abundant flickering and smaller amplitude. Drivers mean open time increased with cytosolic Ca(2+) (Ca(cyt)) or caffeine, whereas followers flicker frequency was Ca(cyt) independent and more sensitive to inhibition by cytosolic Mg(2+). Coupled events were insensitive to varying lumen-to-cytosol Ca(2+) fluxes from ∼1 to 8 pA, which does not corroborate coupling of neighboring RyR1 by local Ca(2+)-induced Ca(2+) release. However, coupling requires specific Ca(lum) sites, as it was lost when Ca(lum) was replaced by luminal Ba(2+) or Mg(2+). In summary, coupled events reveal complex interactions among heterogeneous RyR1, differentially modulated by cytosolic ATP/Mg(2+), Ca(cyt), and Ca(lum,) which under cell-like ionic conditions may parallel synchronous RyR1 gating during Ca(2+) sparks.
Collapse
Affiliation(s)
- Maura Porta
- Dept. of Pharmacology, Southern Illinois Univ. School of Medicine, Springfield, IL 62794-962, USA
| | | | | | | | | | | |
Collapse
|
40
|
Venetucci L, Denegri M, Napolitano C, Priori SG. Inherited calcium channelopathies in the pathophysiology of arrhythmias. Nat Rev Cardiol 2012; 9:561-75. [DOI: 10.1038/nrcardio.2012.93] [Citation(s) in RCA: 141] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
|
41
|
Abstract
Carbohydrate-responsive element binding protein (ChREBP (MLXIPL)) is emerging as an important mediator of glucotoxity both in the liver and in the pancreatic β-cells. Although the regulation of its nuclear translocation and transcriptional activation by glucose has been the subject of intensive research, it is still not fully understood. We have recently uncovered a novel mechanism in the excitable pancreatic β-cell where ChREBP interacts with sorcin, a penta-EF-hand Ca(2)(+)-binding protein, and is sequestered in the cytosol at low glucose concentrations. Upon stimulation with glucose and activation of Ca(2)(+) influx, or application of ATP as an intracellular Ca(2)(+)-mobilising agent, ChREBP rapidly translocates to the nucleus. In sorcin-silenced cells, ChREBP is constitutively present in the nucleus, and both glucose and Ca(2)(+) are ineffective in stimulating further ChREBP nuclear shuttling. Whether an active Ca(2)(+)-sorcin element of ChREBP activation also exists in non-excitable cells is discussed.
Collapse
Affiliation(s)
- Isabelle Leclerc
- Division of Diabetes, Endocrinology and Metabolism, Section of Cell Biology, Department of Medicine, Imperial College London, SW7 2AZ London, UK.
| | | | | | | |
Collapse
|
42
|
Tonic signaling from O₂ sensors sets neural circuit activity and behavioral state. Nat Neurosci 2012; 15:581-91. [PMID: 22388961 PMCID: PMC3564487 DOI: 10.1038/nn.3061] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Accepted: 01/31/2012] [Indexed: 12/15/2022]
Abstract
Tonic receptors convey stimulus duration and intensity and are implicated in homeostatic control. However, how tonic homeostatic signals are generated and how they reconfigure neural circuits and modify animal behavior is poorly understood. Here we show that Caenorhabditis elegans O(2)-sensing neurons are tonic receptors that continuously signal ambient [O(2)] to set the animal's behavioral state. Sustained signaling relied on a Ca(2+) relay involving L-type voltage-gated Ca(2+) channels, the ryanodine and the inositol-1,4,5-trisphosphate receptors. Tonic activity evoked continuous neuropeptide release, which helps elicit the enduring behavioral state associated with high [O(2)]. Sustained O(2) receptor signaling was propagated to downstream neural circuits, including the hub interneuron RMG. O(2) receptors evoked similar locomotory states at particular O(2) concentrations, regardless of previous d[O(2)]/dt. However, a phasic component of the URX receptors' response to high d[O(2)]/dt, as well as tonic-to-phasic transformations in downstream interneurons, enabled transient reorientation movements shaped by d[O(2)]/dt. Our results highlight how tonic homeostatic signals can generate both transient and enduring behavioral change.
Collapse
|
43
|
Noordeen NA, Meur G, Rutter GA, Leclerc I. Glucose-induced nuclear shuttling of ChREBP is mediated by sorcin and Ca(2+) ions in pancreatic β-cells. Diabetes 2012; 61:574-85. [PMID: 22338092 PMCID: PMC3282809 DOI: 10.2337/db10-1329] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Carbohydrate-responsive element-binding protein (ChREBP) is a regulator of pancreatic β-cell gene expression and an important mediator of glucotoxicity. Glucose increases the activity and nuclear localization of ChREBP by still ill-defined mechanisms. Here we reveal, using both MIN6 and primary mouse β-cells, a unique mechanism behind ChREBP nuclear translocation. At low glucose concentrations, ChREBP interacts with sorcin, a penta EF hand Ca(2+) binding protein, and is sequestered in the cytosol. Sorcin overexpression inhibits ChREBP nuclear accumulation at high glucose and reduced the activity of L-type pyruvate kinase (L-PK) and TxNIP promoters, two well-characterized ChREBP target genes. Sorcin inactivation by RNA interference increases ChREBP nuclear localization and in vivo binding to the L-PK promoter at low glucose concentrations. Ca(2+) influx was essential for this process since Ca(2+) chelation with EGTA, or pharmacological inhibition with diazoxide and nifedipine, blocked the effects of glucose. Conversely, mobilization of intracellular Ca(2+) with ATP caused the nuclear accumulation of ChREBP. Finally, sorcin silencing inhibited ATP-induced increases in intracellular Ca(2+) and glucose-stimulated insulin secretion. We therefore conclude that sorcin retains ChREBP in the cytosol at low glucose concentrations and may act as a Ca(2+) sensor for glucose-induced nuclear translocation and the activation of ChREBP-dependent genes.
Collapse
Affiliation(s)
| | | | - Guy A. Rutter
- Corresponding authors: Guy A. Rutter, , and Isabelle Leclerc,
| | | |
Collapse
|
44
|
Tang Y, Tian X, Wang R, Fill M, Chen SRW. Abnormal termination of Ca2+ release is a common defect of RyR2 mutations associated with cardiomyopathies. Circ Res 2012; 110:968-77. [PMID: 22374134 DOI: 10.1161/circresaha.111.256560] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Naturally occurring mutations in the cardiac ryanodine receptor (RyR2) have been associated with both cardiac arrhythmias and cardiomyopathies. It is clear that delayed afterdepolarization resulting from abnormal activation of sarcoplasmic reticulum Ca2+ release is the primary cause of RyR2-associated cardiac arrhythmias. However, the mechanism underlying RyR2-associated cardiomyopathies is completely unknown. OBJECTIVE In the present study, we investigate the role of the NH2-terminal region of RyR2 in and the impact of a number of cardiomyopathy-associated RyR2 mutations on the termination of Ca2+ release. METHODS AND RESULTS The 35-residue exon-3 region of RyR2 is associated with dilated cardiomyopathy. Single-cell luminal Ca2+ imaging revealed that the deletion of the first 305 NH2-terminal residues encompassing exon-3 or the deletion of exon-3 itself markedly reduced the luminal Ca2+ threshold at which Ca2+ release terminates and increased the fractional Ca2+ release. Single-cell cytosolic Ca2+ imaging also showed that both RyR2 deletions enhanced the amplitude of store overload-induced Ca2+ transients in HEK293 cells or HL-1 cardiac cells. Furthermore, the RyR2 NH2-terminal mutations, A77V, R176Q/T2504M, R420W, and L433P, which are associated with arrhythmogenic right ventricular displasia type 2, also reduced the threshold for Ca2+ release termination and increased fractional release. The RyR2 A1107M mutation associated with hypertrophic cardiomyopathy had the opposite action (i.e., increased the threshold for Ca2+ release termination and reduced fractional release). CONCLUSIONS These results provide the first evidence that the NH2-terminal region of RyR2 is an important determinant of Ca2+ release termination, and that abnormal fractional Ca2+ release attributable to aberrant termination of Ca2+ release is a common defect in RyR2-associated cardiomyopathies.
Collapse
Affiliation(s)
- Yijun Tang
- Department of Physiology and Pharmacology, the Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
| | | | | | | | | |
Collapse
|
45
|
Sobie EA, Lederer WJ. Dynamic local changes in sarcoplasmic reticulum calcium: physiological and pathophysiological roles. J Mol Cell Cardiol 2012; 52:304-11. [PMID: 21767546 PMCID: PMC3217160 DOI: 10.1016/j.yjmcc.2011.06.024] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/07/2011] [Revised: 06/24/2011] [Accepted: 06/30/2011] [Indexed: 10/18/2022]
Abstract
Evidence obtained in recent years indicates that, in cardiac myocytes, release of Ca(2+) from the sarcoplasmic reticulum (SR) is regulated by changes in the concentration of Ca(2+) within the SR. In this review, we summarize recent advances in our understanding of this regulatory role, with a particular emphasis on dynamic and local changes in SR [Ca(2+)]. We focus on five important questions that are to some extent unresolved and controversial. These questions concern: (1) the importance of SR [Ca(2+)] depletion in the termination of Ca(2+) release; (2) the quantitative extent of depletion during local release events such as Ca(2+) sparks; (3) the influence of SR [Ca(2+)] refilling on release refractoriness and the propensity for pathological Ca(2+) release; (4) dynamic changes in SR [Ca(2+)] during propagating Ca(2+) waves; and (5) the speed of Ca(2+) diffusion within the SR. With each issue, we discuss data supporting alternative viewpoints, and we identify fundamental questions that are being actively investigated. We conclude with a discussion of experimental and computational advances that will help to resolve controversies. This article is part of a special issue entitled "Local Signaling in Myocytes."
Collapse
Affiliation(s)
- Eric A Sobie
- Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, NY, USA.
| | | |
Collapse
|
46
|
Koivumäki JT, Korhonen T, Tavi P. Impact of sarcoplasmic reticulum calcium release on calcium dynamics and action potential morphology in human atrial myocytes: a computational study. PLoS Comput Biol 2011; 7:e1001067. [PMID: 21298076 PMCID: PMC3029229 DOI: 10.1371/journal.pcbi.1001067] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Accepted: 12/21/2010] [Indexed: 02/02/2023] Open
Abstract
Electrophysiological studies of the human heart face the fundamental challenge that experimental data can be acquired only from patients with underlying heart disease. Regarding human atria, there exist sizable gaps in the understanding of the functional role of cellular Ca²+ dynamics, which differ crucially from that of ventricular cells, in the modulation of excitation-contraction coupling. Accordingly, the objective of this study was to develop a mathematical model of the human atrial myocyte that, in addition to the sarcolemmal (SL) ion currents, accounts for the heterogeneity of intracellular Ca²+ dynamics emerging from a structurally detailed sarcoplasmic reticulum (SR). Based on the simulation results, our model convincingly reproduces the principal characteristics of Ca²+ dynamics: 1) the biphasic increment during the upstroke of the Ca²+ transient resulting from the delay between the peripheral and central SR Ca²+ release, and 2) the relative contribution of SL Ca²+ current and SR Ca²+ release to the Ca²+ transient. In line with experimental findings, the model also replicates the strong impact of intracellular Ca²+ dynamics on the shape of the action potential. The simulation results suggest that the peripheral SR Ca²+ release sites define the interface between Ca²+ and AP, whereas the central release sites are important for the fire-diffuse-fire propagation of Ca²+ diffusion. Furthermore, our analysis predicts that the modulation of the action potential duration due to increasing heart rate is largely mediated by changes in the intracellular Na+ concentration. Finally, the results indicate that the SR Ca²+ release is a strong modulator of AP duration and, consequently, myocyte refractoriness/excitability. We conclude that the developed model is robust and reproduces many fundamental aspects of the tight coupling between SL ion currents and intracellular Ca²+ signaling. Thus, the model provides a useful framework for future studies of excitation-contraction coupling in human atrial myocytes.
Collapse
Affiliation(s)
- Jussi T. Koivumäki
- Department of Biotechnology and Molecular Medicine, A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland
| | - Topi Korhonen
- Department of Biotechnology and Molecular Medicine, A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland
| | - Pasi Tavi
- Department of Biotechnology and Molecular Medicine, A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland
| |
Collapse
|
47
|
Neumann JT, Diaz-Sylvester PL, Fleischer S, Copello JA. CGP-37157 inhibits the sarcoplasmic reticulum Ca²+ ATPase and activates ryanodine receptor channels in striated muscle. Mol Pharmacol 2010; 79:141-7. [PMID: 20923851 DOI: 10.1124/mol.110.067165] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
7-Chloro-5-(2-chlorophenyl)-1,5-dihydro-4,1-benzothiazepin-2(3H)-one [CGP-37157 (CGP)], a benzothiazepine derivative of clonazepam, is commonly used as a blocker of the mitochondrial Na+/Ca²+ exchanger. However, evidence suggests that CGP could also affect other targets, such as L-type Ca²+ channels and plasmalemma Na+/Ca²+ exchanger. Here, we tested the possibility of a direct modulation of ryanodine receptor channels (RyRs) and/or sarco/endoplasmic reticulum Ca²+-stimulated ATPase (SERCA) by CGP. In the presence of ruthenium red (inhibitor of RyRs), CGP decreased SERCA-mediated Ca²+ uptake of cardiac and skeletal sarcoplasmic reticulum (SR) microsomes (IC₅₀ values of 6.6 and 9.9 μM, respectively). The CGP effects on SERCA activity correlated with a decreased V(max) of ATPase activity of SERCA-enriched skeletal SR fractions. CGP (≥ 5 μM) also increased RyR-mediated Ca²+ leak from skeletal SR microsomes. Planar bilayer studies confirmed that both cardiac and skeletal RyRs are directly activated by CGP (EC(50) values of 9.4 and 12.0 μM, respectively). In summary, we found that CGP inhibits SERCA and activates RyR channels. Hence, the action of CGP on cellular Ca²+ homeostasis reported in the literature of cardiac, skeletal muscle, and other nonmuscle systems requires further analysis to take into account the contribution of all CGP-sensitive Ca²+ transporters.
Collapse
Affiliation(s)
- Jake T Neumann
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, USA
| | | | | | | |
Collapse
|
48
|
Grabner M, Dayal A. Crosstalk via the Sarcoplasmic Gap: The DHPR-RyR Interaction. CURRENT TOPICS IN MEMBRANES 2010; 66:115-38. [PMID: 22353478 DOI: 10.1016/s1063-5823(10)66006-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
|
49
|
Williams GSB, Smith GD, Sobie EA, Jafri MS. Models of cardiac excitation-contraction coupling in ventricular myocytes. Math Biosci 2010; 226:1-15. [PMID: 20346962 PMCID: PMC5499386 DOI: 10.1016/j.mbs.2010.03.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2009] [Revised: 03/09/2010] [Accepted: 03/12/2010] [Indexed: 01/27/2023]
Abstract
Mathematical and computational modeling of cardiac excitation-contraction coupling has produced considerable insights into how the heart muscle contracts. With the increase in biophysical and physiological data available, the modeling has become more sophisticated with investigations spanning in scale from molecular components to whole cells. These modeling efforts have provided insight into cardiac excitation-contraction coupling that advanced and complemented experimental studies. One goal is to extend these detailed cellular models to model the whole heart. While this has been done with mechanical and electrophysiological models, the complexity and fast time course of calcium dynamics have made inclusion of detailed calcium dynamics in whole heart models impractical. Novel methods such as the probability density approach and moment closure technique which increase computational efficiency might make this tractable.
Collapse
Affiliation(s)
- George S B Williams
- The Department of Bionformatics and Computational Biology, George Mason University, VA, USA.
| | | | | | | |
Collapse
|
50
|
Jiménez-Moreno R, Wang ZM, Messi ML, Delbono O. Sarcoplasmic reticulum Ca2+ depletion in adult skeletal muscle fibres measured with the biosensor D1ER. Pflugers Arch 2010; 459:725-35. [PMID: 20069312 PMCID: PMC2864504 DOI: 10.1007/s00424-009-0778-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Accepted: 12/16/2009] [Indexed: 01/21/2023]
Abstract
The endoplasmic/sarcoplasmic reticulum (ER/SR) plays a crucial role in cytoplasmic signalling in a variety of cells. It is particularly relevant to skeletal muscle fibres, where this organelle constitutes the main Ca2+ store for essential functions, such as contraction. In this work, we expressed the cameleon biosensor D1ER by in vivo electroporation in the mouse flexor digitorum brevis (FDB) muscle to directly assess SR Ca2+ depletion in response to electrical and pharmacological stimulation. The main conclusions are: (1) D1ER is expressed in the SR of FDB fibres according to both di-8-(amino naphthyl ethenyl pyridinium) staining experiments and reductions in the Förster resonance energy transfer signal consequent to SR Ca2+ release; (2) the amplitude of D1ER citrine/cyan fluorescent protein (CFP) ratio evoked by either 4-chloro-m-cresol (4-CmC) or electrical stimulation is directly proportional to the basal citrine/CFP ratio, which indicates that SR Ca2+ modulates ryanodine-receptor-isoform-1-mediated SR Ca2+ release in the intact muscle fibre; (3) SR Ca2+ release, measured as D1ER citrine/CFP signal, is voltage-dependent and follows a Boltzmann function; and (4) average SR Ca2+ depletion is 20% in response to 4-CmC and 6.4% in response to prolonged sarcolemmal depolarization. These results indicate that significantly depleting SR Ca2+ content under physiological conditions is difficult.
Collapse
Affiliation(s)
- Ramón Jiménez-Moreno
- Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA
| | | | | | | |
Collapse
|