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Baglaeva I, Iaparov B, Zahradník I, Zahradníková A. Analysis of noisy transient signals based on Gaussian process regression. Biophys J 2023; 122:451-459. [PMID: 36609141 PMCID: PMC9941716 DOI: 10.1016/j.bpj.2023.01.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Revised: 11/26/2022] [Accepted: 01/04/2023] [Indexed: 01/07/2023] Open
Abstract
Dynamic systems such as cells or tissues generate, either spontaneously or in response to stimuli, transient signals that carry information about the system. Characterization of recorded transients is often hampered by a low signal-to-noise ratio (SNR). Reduction of the noise by filtering has limited use due to partial signal distortion. Occasionally, transients can be approximated by a mathematical function, but such a function may not hold correctly if recording conditions change. We introduce here the model-independent approximation method for general noisy transient signals based on the Gaussian process regression. The method was implemented in the software TransientAnalyzer, which detects transients in a record, finds their best approximation by the Gaussian process, constructs a surrogate spline function, and estimates specified signal parameters. The method and software were tested on a cellular model of the calcium concentration transient corrupted by various SNR levels and recorded at a low sampling frequency. Statistical analysis of the model data sets provided the error of estimation <7.5% and the coefficient of variation of estimates <17% for peak SNR = 5. The performance of Gaussian process regression on signals of diverse experimental origin was even better than fitting by a function. The software and its description are available on GitHub.
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Affiliation(s)
- Iuliia Baglaeva
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Bogdan Iaparov
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Ivan Zahradník
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Alexandra Zahradníková
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, Slovak Academy of Sciences, Bratislava, Slovakia.
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2
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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.
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Affiliation(s)
| | | | | | - Alexandra Zahradníková
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center of the Slovak Academy of Sciences, Bratislava, Slovakia
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3
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Janicek R, Agarwal H, Gómez AM, Egger M, Ellis-Davies GCR, Niggli E. Local recovery of cardiac calcium-induced calcium release interrogated by ultra-effective, two-photon uncaging of calcium. J Physiol 2021; 599:3841-3852. [PMID: 34245001 PMCID: PMC8456848 DOI: 10.1113/jp281482] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2021] [Accepted: 07/09/2021] [Indexed: 11/09/2022] Open
Abstract
Key points In cardiac myocytes, subcellular local calcium release signals, calcium sparks, are recruited to form each cellular calcium transient and activate the contractile machinery. Abnormal timing of recovery of sparks after their termination may contribute to arrhythmias. We developed a method to interrogate recovery of calcium spark trigger probabilities and their amplitude over time using two‐photon photolysis of a new ultra‐effective caged calcium compound. The findings confirm the utility of the technique to define an elevated sensitivity of the calcium release mechanism in situ and to follow hastened recovery of spark trigger probabilities in a mouse model of an inherited cardiac arrhythmia, which was used for validation. Analogous methods are likely to be applicable to investigate other microscopic subcellular signalling systems in a variety of cell types.
Abstract In cardiac myocytes Ca2+‐induced Ca2+ release (CICR) from the sarcoplasmic reticulum (SR) through ryanodine receptors (RyRs) governs activation of contraction. Ca2+ release occurs via subcellular Ca2+ signalling events, Ca2+ sparks. Local recovery of Ca2+ release depends on both SR refilling and restoration of Ca2+ sensitivity of the RyRs. We used two‐photon (2P) photolysis of the ultra‐effective caged Ca2+ compound BIST‐2EGTA and laser‐scanning confocal Ca2+ imaging to probe refractoriness of local Ca2+ release in control conditions and in the presence of cAMP or low‐dose caffeine (to stimulate CICR) or cyclopiazonic acid (CPA; to slow SR refilling). Permeabilized cardiomyocytes were loaded with BIST‐2EGTA and rhod‐2. Pairs of short 2P photolytic pulses (1 ms, 810 nm) were applied with different intervals to test Ca2+ release amplitude recovery and trigger probability for the second spark in a pair. Photolytic and biological events were distinguished by classification with a self‐learning support vector machine (SVM) algorithm. In permeabilized myocytes data recorded in the presence of CPA showed a lower probability of triggering a second spark compared to control or cAMP conditions. Cardiomyocytes from a mouse model harbouring the arrhythmogenic RyRR420Q mutation were used for further validation and revealed a higher Ca2+ sensitivity of CICR. This new 2P approach provides composite information of Ca2+ release amplitude and trigger probability recovery reflecting both SR refilling and restoration of CICR and RyR Ca2+ sensitivity. It can be used to measure the kinetics of local CICR recovery, alterations of which may be related to premature heart beats and arrhythmias. In cardiac myocytes, subcellular local calcium release signals, calcium sparks, are recruited to form each cellular calcium transient and activate the contractile machinery. Abnormal timing of recovery of sparks after their termination may contribute to arrhythmias. We developed a method to interrogate recovery of calcium spark trigger probabilities and their amplitude over time using two‐photon photolysis of a new ultra‐effective caged calcium compound. The findings confirm the utility of the technique to define an elevated sensitivity of the calcium release mechanism in situ and to follow hastened recovery of spark trigger probabilities in a mouse model of an inherited cardiac arrhythmia, which was used for validation. Analogous methods are likely to be applicable to investigate other microscopic subcellular signalling systems in a variety of cell types.
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Affiliation(s)
| | - Hitesh Agarwal
- Department of Neuroscience, Mount Sinai School of Medicine, New York, NY, USA
| | - Ana M Gómez
- Signaling and cardiovascular pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay, Châtenay-Malabry, France
| | - Marcel Egger
- Department of Physiology, University of Bern, Bern, Switzerland
| | | | - Ernst Niggli
- Department of Physiology, University of Bern, Bern, Switzerland
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4
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Iaparov BI, Zahradnik I, Moskvin AS, Zahradníková A. In silico simulations reveal that RYR distribution affects the dynamics of calcium release in cardiac myocytes. J Gen Physiol 2021; 153:211900. [PMID: 33735373 PMCID: PMC7980188 DOI: 10.1085/jgp.202012685] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2020] [Accepted: 02/08/2021] [Indexed: 11/20/2022] Open
Abstract
The dyads of cardiac myocytes contain ryanodine receptors (RYRs) that generate calcium sparks upon activation. To test how geometric factors of RYR distribution contribute to the formation of calcium sparks, which cannot be addressed experimentally, we performed in silico simulations on a large set of models of calcium release sites (CRSs). Our models covered the observed range of RYR number, density, and spatial arrangement. The calcium release function of CRSs was modeled by RYR openings, with an open probability dependent on concentrations of free Ca2+ and Mg2+ ions, in a rapidly buffered system, with a constant open RYR calcium current. We found that simulations of spontaneous sparks by repeatedly opening one of the RYRs in a CRS produced three different types of calcium release events (CREs) in any of the models. Transformation of simulated CREs into fluorescence signals yielded calcium sparks with characteristics close to the observed ones. CRE occurrence varied broadly with the spatial distribution of RYRs in the CRS but did not consistently correlate with RYR number, surface density, or calcium current. However, it correlated with RYR coupling strength, defined as the weighted product of RYR vicinity and calcium current, so that CRE characteristics of all models followed the same state-response function. This finding revealed the synergy between structure and function of CRSs in shaping dyad function. Lastly, rearrangements of RYRs simulating hypothetical experiments on splitting and compaction of a dyad revealed an increased propensity to generate spontaneous sparks and an overall increase in calcium release in smaller and more compact dyads, thus underlying the importance and physiological role of RYR arrangement in cardiac myocytes.
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Affiliation(s)
- Bogdan I Iaparov
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, Slovak Academy of Sciences, Bratislava, Slovakia.,Research Institute of Physics and Applied Mathematics, and Department of Theoretical and Mathematical Physics, Ural Federal University, Ekaterinburg, Russia
| | - Ivan Zahradnik
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Alexander S Moskvin
- Research Institute of Physics and Applied Mathematics, and Department of Theoretical and Mathematical Physics, Ural Federal University, Ekaterinburg, Russia
| | - Alexandra Zahradníková
- Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, Slovak Academy of Sciences, Bratislava, Slovakia
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5
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Structural variability of dyads relates to calcium release in rat ventricular myocytes. Sci Rep 2020; 10:8076. [PMID: 32415205 PMCID: PMC7229197 DOI: 10.1038/s41598-020-64840-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Accepted: 04/11/2020] [Indexed: 12/30/2022] Open
Abstract
Cardiac excitation-contraction coupling relies on dyads, the intracellular calcium synapses of cardiac myocytes, where the plasma membrane contacts sarcoplasmic reticulum and where electrical excitation triggers calcium release. The morphology of dyads and dynamics of local calcium release vary substantially. To better understand the correspondence between the structure and the functionality of dyads, we estimated incidences of structurally different dyads and of kinetically different calcium release sites and tested their responsiveness to experimental myocardial injury in left ventricular myocytes of rats. According to the structure of dyads estimated in random electron microscopic images of myocardial tissue, the dyads were sorted into 'compact' or 'loose' types. The calcium release fluxes, triggered at local calcium release sites in patch-clamped ventricular myocytes and recorded by laser scanning confocal fluorescence microscopy, were decomposed into 'early' and 'late' components. ANOVA tests revealed very high correlation between the relative amplitudes of early and late calcium release flux components and the relative occurrences of compact and loose dyads in the control and in the injured myocardium. This finding ascertained the relationship between the structure of dyads and the functionality of calcium release sites and the responsiveness of calcium release sites to physical load in cardiac myocytes.
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6
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Stochastic and deterministic approaches to modelling calcium release in cardiac myocytes at different spatial arrangements of ryanodine receptors. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2019; 48:579-584. [PMID: 31236612 DOI: 10.1007/s00249-019-01378-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Revised: 05/22/2019] [Accepted: 06/09/2019] [Indexed: 10/26/2022]
Abstract
Calcium release sites (CRSs) play a key role in excitation-contraction coupling of cardiac myocytes. Recent studies based on electron tomography and super-resolution imaging revealed that CRSs are not completely filled with ryanodine receptors (RyRs) and that the spatial arrangement of RyRs is neither uniform nor static. In this work, we studied the effect of spatial arrangement of RyRs on RyR activation using simulations based on Monte Carlo (MC) and mean-field (MF) approaches. Both approaches showed that activation of RyRs is sensitive to the arrangement of RyRs in the CRS. However, the MF simulations did not reproduce results of MC simulations for non-compact CRSs, suggesting that the approximations used in the MF approach are not suitable for simulation studies of RyRs arrangements observed experimentally. MC simulations revealed the importance of realistic spatial arrangement of RyRs for adequate modelling of calcium release in cardiac myocytes.
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7
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Calcium Activity Dynamics Correlate with Neuronal Phenotype at a Single Cell Level and in a Threshold-Dependent Manner. Int J Mol Sci 2019; 20:ijms20081880. [PMID: 30995769 PMCID: PMC6515432 DOI: 10.3390/ijms20081880] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Revised: 04/08/2019] [Accepted: 04/10/2019] [Indexed: 12/23/2022] Open
Abstract
Calcium is a ubiquitous signaling molecule that plays a vital role in many physiological processes. Recent work has shown that calcium activity is especially critical in vertebrate neural development. Here, we investigated if calcium activity and neuronal phenotype are correlated only on a population level or on the level of single cells. Using Xenopus primary cell culture in which individual cells can be unambiguously identified and associated with a molecular phenotype, we correlated calcium activity with neuronal phenotype on the single-cell level. This analysis revealed that, at the neural plate stage, a high frequency of low-amplitude spiking activity correlates with an excitatory, glutamatergic phenotype, while high-amplitude spiking activity correlates with an inhibitory, GABAergic phenotype. Surprisingly, we also found that high-frequency, low-amplitude spiking activity correlates with neural progenitor cells and that differentiating cells exhibit higher spike amplitude. Additional methods of analysis suggested that differentiating marker tubb2b-expressing cells exhibit relatively persistent and predictable calcium activity compared to the irregular activity of neural progenitor cells. Our study highlights the value of using a range of thresholds for analyzing calcium activity data and underscores the importance of employing multiple methods to characterize the often irregular, complex patterns of calcium activity during early neural development.
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8
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Molecular mechanisms of detection and discrimination of dynamic signals. Sci Rep 2018; 8:2480. [PMID: 29410522 PMCID: PMC5802782 DOI: 10.1038/s41598-018-20842-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Accepted: 01/24/2018] [Indexed: 12/25/2022] Open
Abstract
Many molecules decode not only the concentration of cellular signals, but also their temporal dynamics. However, little is known about the mechanisms that underlie the detection and discrimination of dynamic signals. We used computational modelling of the interaction of a ligand with multiple targets to investigate how kinetic and thermodynamic parameters regulate their capabilities to respond to dynamic signals. Our results demonstrated that the detection and discrimination of temporal features of signal inputs occur for reactions proceeding outside mass-action equilibrium. For these reactions, thermodynamic parameters such as affinity do not predict their outcomes. Additionally, we showed that, at non-equilibrium, the association rate constants determine the amount of product formed in reversible reactions. In contrast, the dissociation rate constants regulate the time interval required for reversible reactions to achieve equilibrium and, consequently, control their ability to detect and discriminate dynamic features of cellular signals.
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9
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Tian Q, Kaestner L, Schröder L, Guo J, Lipp P. An adaptation of astronomical image processing enables characterization and functional 3D mapping of individual sites of excitation-contraction coupling in rat cardiac muscle. eLife 2017; 6:30425. [PMID: 29135437 PMCID: PMC5703646 DOI: 10.7554/elife.30425] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Accepted: 11/03/2017] [Indexed: 01/06/2023] Open
Abstract
In beating cardiomyocytes, synchronized localized Ca2+ transients from thousands of active excitation-contraction coupling sites (ECC couplons) comprising plasma and sarcoplasmic reticulum membrane calcium channels are important determinants of the heart's performance. Nevertheless, our knowledge about the properties of ECC couplons is limited by the lack of appropriate experimental and analysis strategies. We designed CaCLEAN to untangle the fundamental characteristics of ECC couplons by combining the astronomer's CLEAN algorithm with known properties of calcium diffusion. CaCLEAN empowers the investigation of fundamental properties of ECC couplons in beating cardiomyocytes without pharmacological interventions. Upon examining individual ECC couplons at the nanoscopic level, we reveal their roles in the negative amplitude-frequency relationship and in β-adrenergic stimulation, including decreasing and increasing firing reliability, respectively. CaCLEAN combined with 3D confocal imaging of beating cardiomyocytes provides a functional 3D map of active ECC couplons (on average, 17,000 per myocyte). CaCLEAN will further enlighten the ECC-couplon-remodelling processes that underlie cardiac diseases.
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Affiliation(s)
- Qinghai Tian
- Institute for Molecular Cell Biology, Center for Molecular Signaling (PZMS), Medical Faculty, Saarland University, Homburg, Germany
| | - Lars Kaestner
- Institute for Molecular Cell Biology, Center for Molecular Signaling (PZMS), Medical Faculty, Saarland University, Homburg, Germany
| | - Laura Schröder
- Institute for Molecular Cell Biology, Center for Molecular Signaling (PZMS), Medical Faculty, Saarland University, Homburg, Germany
| | - Jia Guo
- Institute for Molecular Cell Biology, Center for Molecular Signaling (PZMS), Medical Faculty, Saarland University, Homburg, Germany
| | - Peter Lipp
- Institute for Molecular Cell Biology, Center for Molecular Signaling (PZMS), Medical Faculty, Saarland University, Homburg, Germany
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10
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Hansen KJ, Favreau JT, Gershlak JR, Laflamme MA, Albrecht DR, Gaudette GR. Optical Method to Quantify Mechanical Contraction and Calcium Transients of Human Pluripotent Stem Cell-Derived Cardiomyocytes. Tissue Eng Part C Methods 2017; 23:445-454. [PMID: 28562232 DOI: 10.1089/ten.tec.2017.0190] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Differentiation of human pluripotent stem cells into cardiomyocytes (hPS-CMs) holds promise for myocardial regeneration therapies, drug discovery, and models of cardiac disease. Potential cardiotoxicities may affect hPS-CM mechanical contraction independent of calcium signaling. Herein, a method using an image capture system is described to measure hPS-CM contractility and intracellular calcium concurrently, with high spatial and temporal resolution. The image capture system rapidly alternates between brightfield and epifluorescent illumination of contracting cells. Mechanical contraction is quantified by a speckle tracking algorithm applied to brightfield image pairs, whereas calcium transients are measured by a fluorescent calcium reporter. This technique captured changes in contractile strain, calcium transients, and beat frequency of hPS-CMs over 21 days in culture, as well as acute responses to isoproterenol and Cytochalasin D. The technique described above can be applied without the need to alter the culture platform, allowing for determination of hPS-CM behavior over weeks in culture for drug discovery and myocardial regeneration applications.
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Affiliation(s)
- Katrina J Hansen
- 1 Department of Biomedical Engineering, Worcester Polytechnic Institute , Worcester, Massachusetts
| | - John T Favreau
- 1 Department of Biomedical Engineering, Worcester Polytechnic Institute , Worcester, Massachusetts
| | - Joshua R Gershlak
- 1 Department of Biomedical Engineering, Worcester Polytechnic Institute , Worcester, Massachusetts
| | - Michael A Laflamme
- 2 Toronto General Research Institute, McEwen Centre for Regenerative Medicine, University Health Network , Toronto, Canada
| | - Dirk R Albrecht
- 1 Department of Biomedical Engineering, Worcester Polytechnic Institute , Worcester, Massachusetts
| | - Glenn R Gaudette
- 1 Department of Biomedical Engineering, Worcester Polytechnic Institute , Worcester, Massachusetts
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11
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Petrovič P, Valent I, Cocherová E, Pavelková J, Zahradníková A. Ryanodine receptor gating controls generation of diastolic calcium waves in cardiac myocytes. ACTA ACUST UNITED AC 2016; 145:489-511. [PMID: 26009544 PMCID: PMC4442793 DOI: 10.1085/jgp.201411281] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Calcium waves can form and propagate at low frequencies of spontaneous calcium sparks if the calcium dependence of spark frequency is sufficiently steep, or the number of open RyRs is sufficiently large. The role of cardiac ryanodine receptor (RyR) gating in the initiation and propagation of calcium waves was investigated using a mathematical model comprising a stochastic description of RyR gating and a deterministic description of calcium diffusion and sequestration. We used a one-dimensional array of equidistantly spaced RyR clusters, representing the confocal scanning line, to simulate the formation of calcium sparks. Our model provided an excellent description of the calcium dependence of the frequency of diastolic calcium sparks and of the increased tendency for the production of calcium waves after a decrease in cytosolic calcium buffering. We developed a hypothesis relating changes in the propensity to form calcium waves to changes of RyR gating and tested it by simulation. With a realistic RyR gating model, increased ability of RyR to be activated by Ca2+ strongly increased the propensity for generation of calcium waves at low (0.05–0.1-µM) calcium concentrations but only slightly at high (0.2–0.4-µM) calcium concentrations. Changes in RyR gating altered calcium wave formation by changing the calcium sensitivity of spontaneous calcium spark activation and/or the average number of open RyRs in spontaneous calcium sparks. Gating changes that did not affect RyR activation by Ca2+ had only a weak effect on the propensity to form calcium waves, even if they strongly increased calcium spark frequency. Calcium waves induced by modulating the properties of the RyR activation site could be suppressed by inhibiting the spontaneous opening of the RyR. These data can explain the increased tendency for production of calcium waves under conditions when RyR gating is altered in cardiac diseases.
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Affiliation(s)
- Pavol Petrovič
- Department of Physical and Theoretical Chemistry, Faculty of Natural Sciences, Comenius University, 842 15 Bratislava, Slovak Republic
| | - Ivan Valent
- Department of Physical and Theoretical Chemistry, Faculty of Natural Sciences, Comenius University, 842 15 Bratislava, Slovak Republic Department of Muscle Cell Research, Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic
| | - Elena Cocherová
- Department of Muscle Cell Research, Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic Institute of Electronics and Photonics, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology, 812 19 Bratislava, Slovak Republic
| | - Jana Pavelková
- Department of Muscle Cell Research, Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic
| | - Alexandra Zahradníková
- Department of Muscle Cell Research, Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic
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12
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Janicek R, Hotka M, Zahradníková A, Zahradníková A, Zahradník I. Quantitative analysis of calcium spikes in noisy fluorescent background. PLoS One 2013; 8:e64394. [PMID: 23741324 PMCID: PMC3669300 DOI: 10.1371/journal.pone.0064394] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2013] [Accepted: 04/12/2013] [Indexed: 12/25/2022] Open
Abstract
Intracellular calcium signals are studied by laser-scanning confocal fluorescence microscopy. The required spatio-temporal resolution makes description of calcium signals difficult because of the low signal-to-noise ratio. We designed a new procedure of calcium spike analysis based on their fitting with a model. The accuracy and precision of calcium spike description were tested on synthetic datasets generated either with randomly varied spike parameters and Gaussian noise of constant amplitude, or with constant spike parameters and Gaussian noise of various amplitudes. Statistical analysis was used to evaluate the performance of spike fitting algorithms. The procedure was optimized for reliable estimation of calcium spike parameters and for dismissal of false events. A new algorithm was introduced that corrects the acquisition time of pixels in line-scan images that is in error due to sequential acquisition of individual pixels along the space coordinate. New software was developed in Matlab and provided for general use. It allows interactive dissection of temporal profiles of calcium spikes from x-t images, their fitting with predefined function(s) and acceptance of results on statistical grounds, thus allowing efficient analysis and reliable description of calcium signaling in cardiac myocytes down to the in situ function of ryanodine receptors.
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Affiliation(s)
- Radoslav Janicek
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Matej Hotka
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
- Department of Biophysics, Faculty of Natural Sciences, Pavol Jozef Šafárik University, Košice, Slovakia
| | - Alexandra Zahradníková
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Alexandra Zahradníková
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Ivan Zahradník
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
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13
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Janiek R, Zahradníková A, Poláková E, Pavelková J, Zahradník I, Zahradníková A. Calcium spike variability in cardiac myocytes results from activation of small cohorts of ryanodine receptor 2 channels. J Physiol 2012; 590:5091-106. [PMID: 22890710 DOI: 10.1113/jphysiol.2012.234823] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
In mammalian cardiac myocytes, the elementary calcium releases triggered by step voltage stimuli manifest either as solitary or as twin spikes that vary widely in kinetics and amplitude for unknown reasons. Here we examined the variability of calcium spikes measured using line-scanning confocal microscopy in patch-clamped rat ventricular myocytes. Amplitude distributions of the single and of the first of twin spikes were broader than those of the second spikes. All could be best approximated by a sum of a few elementary Gaussian probability distribution functions. The latency distributions of the single and the first spikes were identical, much shorter and less variable than those of the second spikes. The multimodal distribution of spike amplitudes and the probability of occurrence of twin spikes were stochastically congruent with activation of only a few of the many RyR2 channels present in the release site cluster. The occurrence of twin release events was rare due to refractoriness of release, induced with a probability proportional to the number of RyR2s activated in the primary release event. We conclude that the variability of the elementary calcium release events supports a calcium signalling mechanism that arises from stochastics of RyR2 gating and from inactivation of local origin.
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Affiliation(s)
- Radoslav Janiek
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vl´arska 5, 833 34 Bratislava, Slovak Republic
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14
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Techniques and Methodologies to Study the Ryanodine Receptor at the Molecular, Subcellular and Cellular Level. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:183-215. [DOI: 10.1007/978-94-007-2888-2_8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Baartscheer A, Schumacher CA, Coronel R, Fiolet JWT. The Driving Force of the Na/Ca-Exchanger during Metabolic Inhibition. Front Physiol 2011; 2:10. [PMID: 21483726 PMCID: PMC3070476 DOI: 10.3389/fphys.2011.00010] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Accepted: 02/28/2011] [Indexed: 11/13/2022] Open
Abstract
OBJECTIVE Metabolic inhibition causes a decline in mechanical performance and, if prolonged, myocardial contracture and cell death. The decline in mechanical performance is mainly due to altered intracellular calcium handling, which is under control of the Na(+)/Ca(2+)-exchanger (NCX) The driving force of the NCX (ΔG(ncx)) determines the activity of NCX. The aim of this study was to describe the relation between ΔG(ncx) and calcium homeostasis during metabolic inhibition. METHODS In left ventricular rabbit myocytes, during metabolic inhibition (2 mmol/L sodium cyanide), sodium ([Na(+)](i)), calcium ([Ca(2+);](i)), and action potentials were determined with SBFI, indo-1, and the patch clamp technique. Changes of ΔG(ncx) were calculated. RESULTS During metabolic inhibition: The first 8 min [Na(+)](i) remained constant, systolic calcium decreased from 532 ± 28 to 82 ± 13 nM, diastolic calcium decreased from 121 ± 12 to 36 ± 10 nM and the sarcoplasmic reticulum (SR) calcium content was depleted for 85 ± 3%. After 8 min [Na(+);](i) and diastolic calcium started to increase to 30 ± 1.3 mmol/L and 500 ± 31 nM after 30 min respectively. The action potential duration shortened biphasically. In the first 5 min it shortened from 225 ± 12 to 153 ± 11 ms and remained almost constant until it shortened again after 10 min. After 14 min action potential and calcium transients disappeared due to unexcitability of the myocytes. This resulted in an increased of the time average of ΔG(ncx) from 6.2 ± 0.2 to 7.7 ± 0.3 kJ/mol during the first 3 min, where after it decreased and became negative after about 15 min. CONCLUSION Metabolic inhibition caused an early increase of ΔG(ncx) caused by shortening of the action potential. The increase of ΔG(ncx) contributed to decrease of diastolic calcium, calcium transient amplitude, SR calcium content, and contractility. The increase of diastolic calcium started after ΔG(ncx) became lower than under aerobic conditions.
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Affiliation(s)
- Antonius Baartscheer
- Experimental Cardiology, Heart Failure Research Center, Academic Medical Center, University of AmsterdamAmsterdam, Netherlands
| | - Cees A. Schumacher
- Experimental Cardiology, Heart Failure Research Center, Academic Medical Center, University of AmsterdamAmsterdam, Netherlands
| | - Ruben Coronel
- Experimental Cardiology, Heart Failure Research Center, Academic Medical Center, University of AmsterdamAmsterdam, Netherlands
| | - Jan W. T. Fiolet
- Experimental Cardiology, Heart Failure Research Center, Academic Medical Center, University of AmsterdamAmsterdam, Netherlands
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Neco P, Rose B, Huynh N, Zhang R, Bridge JHB, Philipson KD, Goldhaber JI. Sodium-calcium exchange is essential for effective triggering of calcium release in mouse heart. Biophys J 2010; 99:755-64. [PMID: 20682252 DOI: 10.1016/j.bpj.2010.04.071] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2009] [Revised: 03/26/2010] [Accepted: 04/30/2010] [Indexed: 11/30/2022] Open
Abstract
In cardiac myocytes, excitation-contraction coupling depends upon sarcoplasmic reticular Ca2+ release triggered by Ca2+ influx through L-type Ca2+ channels. Although Na+-Ca2+ exchange (NCX) is essential for Ca2+ extrusion, its participation in the trigger process of excitation-contraction coupling is controversial. To investigate the role of NCX in triggering, we examined Ca2+ sparks in ventricular cardiomyocytes isolated from wild-type (WT) and cardiac-specific NCX knockout (KO) mice. Myocytes from young NCX KO mice are known to exhibit normal resting cytosolic Ca2+ and normal Ca2+ transients despite reduced L-type Ca2+ current. We loaded myocytes with fluo-3 to image Ca2+ sparks using confocal microscopy in line-scan mode. The frequency of spontaneous Ca2+ sparks was reduced in KO myocytes compared with WT. However, spark amplitude and width were increased in KO mice. Permeabilizing the myocytes with saponin eliminated differences between spontaneous sparks in WT and KO mice. These results suggest that sarcolemmal processes are responsible for the reduced spark frequency and increased spark width and amplitude in KO mice. When myocytes were loaded with 1 mM fluo-3 and 3 mM EGTA via the patch pipette to buffer diadic cleft Ca2+, the number of sparks triggered by action potentials was reduced by 60% in KO cells compared to WT cells, despite similar SR Ca2+ content in both cell types. When EGTA was omitted from the pipette solution, the number of sparks triggered in KO and WT myocytes was similar. Although the number of sparks was restored in KO cells, Ca2+ release was asynchronous. These results suggest that high subsarcolemmal Ca2+ is required to ensure synchronous triggering with short spark latency in the absence of NCX. In WT mice, high subsarcolemmal Ca2+ is not required for synchronous triggering, because NCX is capable of priming the diadic cleft with sufficient Ca2+ for normal triggering, even when subsarcolemmal Ca(2+) is lowered by EGTA. Thus, reducing subsarcolemmal Ca2+ with EGTA in NCX KO mice reveals the dependence of Ca2+ release on NCX.
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Affiliation(s)
- Patricia Neco
- Departments of Medicine (Cardiology) and Physiology and the Cardiovascular Research Laboratories, David Geffen School of Medicine at UCLA, Los Angeles, California, USA
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Zahradníková A, Valent I, Zahradník I. Frequency and release flux of calcium sparks in rat cardiac myocytes: a relation to RYR gating. ACTA ACUST UNITED AC 2010; 136:101-16. [PMID: 20548054 PMCID: PMC2894546 DOI: 10.1085/jgp.200910380] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cytosolic calcium concentration in resting cardiac myocytes locally fluctuates as a result of spontaneous microscopic Ca2+ releases or abruptly rises as a result of an external trigger. These processes, observed as calcium sparks, are fundamental for proper function of cardiac muscle. In this study, we analyze how the characteristics of spontaneous and triggered calcium sparks are related to cardiac ryanodine receptor (RYR) gating. We show that the frequency of spontaneous sparks and the probability distribution of calcium release flux quanta of triggered sparks correspond quantitatively to predictions of an allosteric homotetrameric model of RYR gating. This model includes competitive binding of Ca2+ and Mg2+ ions to the RYR activation sites and allosteric interaction between divalent ion binding and channel opening. It turns out that at rest, RYRs are almost fully occupied by Mg2+. Therefore, spontaneous sparks are most frequently evoked by random openings of the highly populated but rarely opening Mg4RYR and CaMg3RYR forms, whereas triggered sparks are most frequently evoked by random openings of the less populated but much more readily opening Ca2Mg2RYR and Ca3MgRYR forms. In both the spontaneous and the triggered sparks, only a small fraction of RYRs in the calcium release unit manages to open during the spark because of the limited rate of Mg2+ unbinding. This mechanism clarifies the unexpectedly low calcium release flux during elementary release events and unifies the theory of calcium signaling in resting and contracting cardiac myocytes.
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Affiliation(s)
- Alexandra Zahradníková
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, 833 34 Bratislava, Slovak Republic.
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Rankovic V, Ehling P, Coulon P, Landgraf P, Kreutz MR, Munsch T, Budde T. Intracellular Ca2+release-dependent inactivation of Ca2+currents in thalamocortical relay neurons. Eur J Neurosci 2010; 31:439-49. [DOI: 10.1111/j.1460-9568.2010.07081.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Fowler MR. Local is as local does: the unitary nature of SR Ca2+ release in cardiac ventricular myocytes. J Physiol 2009; 587:301-2. [PMID: 19015191 DOI: 10.1113/jphysiol.2008.164608] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Mark R Fowler
- Faculty of Biomedical and Life Science, West Medical Building, University of Glasgow, Glasgow, UK.
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Poláková E, Zahradníková A, Pavelková J, Zahradník I, Zahradníková A. Local calcium release activation by DHPR calcium channel openings in rat cardiac myocytes. J Physiol 2008; 586:3839-54. [PMID: 18591191 DOI: 10.1113/jphysiol.2007.149989] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The principal role of calcium current in the triggering of calcium release in cardiac myocytes is well recognized. The mechanism of how calcium current (I(Ca)) controls the intensity of calcium release is not clear because of the stochastic nature of voltage-dependent gating of calcium channels (DHPRs) and of calcium-dependent gating of ryanodine receptors (RyRs). To disclose the relation between DHPR openings and the probability of calcium release, local calcium release activation by I(Ca) was investigated in rat ventricular myocytes using patch-clamp and confocal microscopy. Calcium spikes were activated by temporally synchronized DHPR calcium current triggers, generated by instantaneous 'tail' I(Ca) and modulated by prepulse duration, by tail potential, and by the DHPR agonist BayK 8644. The DHPR-RyR coupling fidelity was determined from the temporal distribution of calcium spike latencies using a model based on exponentially distributed DHPR open times. The analysis provided a DHPR mean open time of approximately 0.5 ms, RyR activation time constant of approximately 0.6 ms, and RyR activation kinetics of the 4th order. The coupling fidelity was low due to the inherent prevalence of very short DHPR openings but was increased when DHPR openings were prolonged by BayK 8644. The probability of calcium release activation was high, despite low coupling fidelity, due to the activation of many DHPRs at individual release sites. We conclude that the control of calcium release intensity by physiological stimuli can be achieved by modulating the number and duration of DHPR openings at low coupling fidelity, thus avoiding the danger of inadvertently triggering calcium release events.
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Affiliation(s)
- Eva Poláková
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlárska 5, 833 34 Bratislava, Slovakia
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Local Calcium Signaling. Biophys J 2008. [DOI: 10.1016/s0006-3495(08)79069-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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Abstract
We investigated the effect of combined inhibition of oxidative and glycolytic metabolism on L-type Ca(2+) channels (LCCs) and Ca(2+) spikes in isolated patch-clamped rabbit ventricular myocytes. Metabolic inhibition (MI) reduced LCC open probability, increased null probability, increased first latency, and decreased open time but left conductance unchanged. These results explain the reduction in macroscopic Ca(2+) current observed during MI. MI also produced a gradual reduction in action potential duration at 90% repolarization (APD(90)), a clear decline in spike probability, and an increase in spike latency and variance. These effects are consistent with the changes we observed in LCC activity. MI had no effect on the amplitude or time to peak of Ca(2+) spikes until APD(90) reached 10% of control, suggesting preserved sarcoplasmic reticulum Ca(2+) stores and ryanodine receptor (RyR) conductance in those couplons that remained functioning. Ca(2+) spikes disappeared completely when APD(90) reached <2% of control, although in two cells, spikes were reactivated in a highly synchronized fashion by very short action potentials. This reactivation is probably due to the increased driving force for Ca(2+) entry through a reduced number of LCCs that remain open during early repolarization. The enlarged single channel flux produced by rapid repolarization is apparently sufficient to trigger RyRs whose Ca(2+) sensitivity is likely reduced by MI. We suggest that loss of coupling fidelity during MI is explained by loss of LCC activity (possibly mediated by Ca(2+)-calmodulin kinase II activity). In addition, the results are consistent with loss of RyR activity, which can be mitigated under conditions likely to enlarge the trigger.
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