Karin R Sipido

University of Leuven, Louvain, Flemish, Belgium

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Publications (167)998.33 Total impact

  • Diane Gal · Wouter Vandevelde · Karin R Sipido ·

    Cardiovascular Research 10/2015; 108(3). DOI:10.1093/cvr/cvv245 · 5.94 Impact Factor
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    ABSTRACT: Aims: In atrial fibrillation (AF), abnormalities in Ca(2+) release contribute to arrhythmia generation and contractile dysfunction. We explore whether RyR cluster ultrastructure is altered and is associated with functional abnormalities in AF. Methods and results: Using high resolution confocal microscopy (STED) we examined RyR cluster morphology in fixed atrial myocytes from sheep with persistent AF (N=6) and control (Ctrl; N=6) animals. RyR clusters on average contained 15 contiguous RyRs; this did not differ between AF and Ctrl. However, the distance between clusters was significantly reduced in AF (288±12 nm vs. 376±17 nm). When RyR clusters were grouped into Ca(2+) release units (CRUs), i.e. clusters separated by <150 nm), CRUs in AF had more clusters (3.43±0.10 vs. 2.95±0.02 in Ctrl), which were more dispersed. Furthermore, in AF cells, more RyR clusters were found between Z lines.In parallel experiments, Ca(2+) sparks were monitored in live permeabilized myocytes. In AF, myocytes had: (i) >50% higher spark frequency with (ii) increased spark time-to-peak (TTP) and duration and (iii) a higher incidence of macrosparks.A computational model of the CRU was used to simulate the morphological alterations observed in AF cells. Increasing cluster fragmentation to the level observed in AF cells caused the observed changes i.e. higher spark frequency, increased TTP and duration; RyR clusters dispersed between Z-lines increased the occurrence of macrosparks. Conclusion: In persistent AF, ultrastructural reorganization of RyR clusters within CRUs is associated with overactive Ca(2+) release, increasing the likelihood of propagating Ca(2+) release.
    Cardiovascular Research 10/2015; 108(3). DOI:10.1093/cvr/cvv231 · 5.94 Impact Factor
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    ABSTRACT: Beat-to-beat variability of ventricular repolarization (BVR) has been proposed as a strong predictor of Torsades de Pointes (TdP). BVR is also observed at the myocyte level, and a number of studies have shown the importance of calcium handling in influencing this parameter. The chronic AV block (CAVB) dog is a model of TdP arrhythmia in cardiac hypertrophy, and myocytes from these animals show extensive remodeling, including of Ca(2+) handling. This remodeling process also leads to increased BVR. We aimed to determine the role that (local) Ca(2+) handling plays in BVR. In isolated LV myocytes an exponential relationship was observed between BVR magnitude and action potential duration (APD) at baseline. Inhibition of Ca(2+) release from sarcoplasmic reticulum (SR) with thapsigargin resulted in a reduction of [Ca(2+)]i, and of both BVR and APD. Increasing ICaL in the presence of thapsigargin restored APD but BVR remained low. In contrast, increasing ICaL with preserved Ca(2+) release increased both APD and BVR. Inhibition of Ca(2+) release with caffeine, as with thapsigargin, reduced BVR despite maintained APD. Simultaneous inhibition of Na(+)/Ca(2+) exchange and ICaL decreased APD and BVR to similar degrees, whilst increasing diastolic Ca(2+). Buffering of Ca(2+) transients with BAPTA reduced BVR for a given APD to a greater extent than buffering with EGTA, suggesting subsarcolemmal Ca(2+) transients modulated BVR to a larger extent than the cytosolic Ca(2+) transient. In conclusion, BVR in hypertrophied dog myocytes, at any APD, is strongly dependent on SR Ca(2+) release, which may act through modulation of the l-type Ca(2+) current in a subsarcolemmal microdomain.
    Journal of Molecular and Cellular Cardiology 10/2015; DOI:10.1016/J.YJMCC.2015.10.008 · 4.66 Impact Factor
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    ABSTRACT: The purpose of this study is to investigate the relationship between T-wave alternans (TWA), infarct size and microvascular obstruction (MVO) and recurrent cardiac morbidity after ST elevation myocardial infarction (STEMI). One hundred six patients underwent TWA testing 1-12 months and 57 patients underwent cardiac magnetic resonance imaging (MRI) in the first 2-4 days after STEMI. During follow-up (3.5 ± 0.5 years), death (n = 2), ventricular tachycardia (n = 3), supraventricular tachycardia (n = 4), heart failure (n = 3) and recurrent coronary ischemia (n = 25) were observed. After multivariate analysis, positive TWA (HR2.59, CI1.10-6.11, p0.024) and larger MVO (HR1.08, CI1.01-1.16, p0.034) were associated with recurrent angina or ACS. Presence of MVO was correlated with TWA (Spearman rho 0.404, p0.002) and the impairment of LVEF (-0.524, p < 0.001). Patients after STEMI remain at a high risk of symptoms of coronary ischemia. The presence of MVO and TWA 1-12 months after STEMI is related to each other and to recurrent angina or ACS.
    Journal of Cardiovascular Translational Research 09/2015; 8(8). DOI:10.1007/s12265-015-9649-x · 3.02 Impact Factor
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  • D Gal · Karin R Sipido · Wolfgang Glanzel ·
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    ABSTRACT: A hybrid search strategy, using lexical and citation based methods, is presented in this paper as a robust method to delineate the broad field of cardiovascular research. Overall, this study aims to provide scientifically reliable and accurate data driven evidence about cardiovascular research by establishing a dataset of published research in this field. A workflow is presented that outlines the methods carried out to establish a core dataset based on a core set of journals, to identify and use search terms to detect a broader dataset, and then to apply measures of similarities between the citations of these two datasets to ensure relevance of the final dataset. The final core set of journals established comprises of 120 unique journals covered in Thomson Reuters Web of Science Core Collection (WoS) database including a total of 320,647 documents from 1991 to 2013. The search terms utilised include 107 cardio-specific terms that initially identify 1.8 million unique documents when searching the title, abstract and keywords. Upon application of the citation-based similarity measures the final combined dataset consists of 845,071 publications. Overall, establishing a relevant dataset of cardiovascular research means placing a greater emphasis on having a precise dataset, reducing recall in the process.
    Proceedings of ISSI 2015 Istanbul; 07/2015
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    ABSTRACT: An acute increase in blood pressure is associated with the occurrence of premature ventricular complexes (PVCs). To study the timing of these PVCs in respect to afterload-induced changes in myocardial deformation in a controlled, pre-clinical relevant, novel closed-chest pig model. An acute left ventricular (LV) afterload challenge was applied by partial balloon inflation in the descending aorta, lasting 5 to 10 heartbeats (8 pigs;396 inflations). The balloon inflation enhanced the reflected wave (augmentation index 30±8% vs 59±6%; p<0.001), increasing systolic central blood pressure by 35±4%. This challenge resulted in a more abrupt LV pressure decline which was delayed beyond ventricular repolarization (rate of pressure decline 0.16±0.01 vs 0.27±0.04 mmHg/ms; p<0.001 and interval T-wave to peak-pressure 1±12ms vs. 36±9ms; p=0.008), during which the velocity of shortening at the basal septum abruptly increased (i.e. post-systolic shortening) (peak strain rate of -0.6±0.5s(-1) vs -2.5±0.8s(-1); p<0.001). It is exactly at this time of LV pressure decline, with increased post-systolic shortening, and not at peak pressure, that PVCs arose (22% of inflations). These PVCs preferentially occurred at the basal and apical segments. In the same regions, monophasic action potentials demonstrated the appearance of DAD-like transient depolarizations as origin for the PVCs. An acute blood pressure increase results in a more abrupt LV pressure decline, delayed after ventricular repolarization, which has a profound effect on myocardial mechanics, with enhanced post-systolic shortening. Coincidence with induced transient depolarizations and PVCs provides support for the mechano-electrical origin of pressure induced premature beats. Copyright © 2015. Published by Elsevier Inc.
    Heart rhythm: the official journal of the Heart Rhythm Society 06/2015; 12(11). DOI:10.1016/j.hrthm.2015.06.037 · 5.08 Impact Factor
  • Karin R Sipido · Niall Macquaide · Virginie Bito ·
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    ABSTRACT: In cardiac myocytes, Ca(2+) release from the sarcoplasmic reticulum (SR) Ca(2+) store through the opening of ryanodine receptors (RyRs) is the major source of Ca(2+) for activation of myofilaments and contraction. Over the past 20 years, tools have become available to study this release process in detail, allowing new insights into the regulation of SR Ca(2+) release and RyR function. To assess these processes, we recommend and here review a systematic approach that evaluates the essential transport mechanisms and Ca(2+) fluxes in isolated single cardiac myocytes by using fluorescent Ca(2+) indicators and whole-cell recording of membrane voltage and ionic currents under voltage clamp. The approach includes an assessment of the L-type Ca(2+) current as a trigger for opening of RyRs and release of SR Ca(2+), of the SR Ca(2+) content, of intrinsic properties of RyRs, and of Ca(2+)-removal systems. © 2015 Cold Spring Harbor Laboratory Press.
    Cold Spring Harbor Protocols 05/2015; 2015(5):pdb.top066142. DOI:10.1101/pdb.top066142 · 4.63 Impact Factor
  • Niall Macquaide · Virginie Bito · Karin R Sipido ·
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    ABSTRACT: This protocol describes the measurement of Ca(2+) sparks in intact myocytes by using a Ca(2+)-sensitive dye and imaging using laser scanning confocal microscopy. It takes advantage of spontaneous Ca(2+)-release events-sparks-using them as a measure of the activity of ryanodine receptors (RyRs). Two methodologies are described: One requires that cardiomyocytes be stimulated, preferably under voltage clamp by depolarizing pulses, until steady-state is reached, and then stimulation is stopped and Ca(2+) sparks are recorded. The second requires that cells be permeabilized and bathed in a solution to load the cell with Ca(2+) sufficient to elicit Ca(2+) sparks, but not Ca(2+) waves. These are then analyzed offline to quantify spark frequency and morphology. The advantages and disadvantages of each approach are discussed. © 2015 Cold Spring Harbor Laboratory Press.
    Cold Spring Harbor Protocols 05/2015; 2015(5):pdb.prot076984. DOI:10.1101/pdb.prot076984 · 4.63 Impact Factor
  • Virginie Bito · Karin R Sipido · Niall Macquaide ·
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    ABSTRACT: The decline of an intracellular calcium ([Ca(2+)]i) transient during a single excitation-contraction coupling (ECC) cycle reflects the combined activity of the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) pump and the sarcolemmal Na(+)-Ca(2+) exchanger (NCX), along with minor contributions of the plasma membrane Ca(2+)-ATPase and mitochondrial Ca(2+) uniporter, in removing Ca(2+) from the cytosol. A traditional approach for assessing the individual components is to fit the decline of the [Ca(2+)]i transient evoked during electrical stimulation with an exponential. This reflects mostly the SERCA-dependent rate of uptake, which can be properly deduced after correcting for a component of NCX removal. As NCX function is an important determinant of the membrane potential as well as the Ca(2+) balance, we present here several detailed protocols for assessing NCX function. As the reversal potential and the amplitudes of the current are highly dependent on the prevailing concentrations of Na(+) and Ca(2+), we show how NCX function can be assessed under highly controlled conditions, with Ca(2+) and Na(+) clamped, as well as under more physiological conditions, with freely changing Ca(2+) and Na(+). © 2015 Cold Spring Harbor Laboratory Press.
    Cold Spring Harbor Protocols 05/2015; 2015(5):pdb.prot076992. DOI:10.1101/pdb.prot076992 · 4.63 Impact Factor
  • Virginie Bito · Niall Macquaide · Karin R Sipido ·
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    ABSTRACT: Here, we describe a method for characterizing the L-type Ca(2+) current, ICaL, which is a major trigger for Ca(2+) release from the sarcoplasmic reticulum (SR). The protocol includes measuring ICaL amplitude and voltage dependence and the elicited SR Ca(2+) release. The procedure for measuring ICaL activity is performed using solutions (internal and external) and voltage control such that other ionic currents are eliminated. The resultant relationship between the Ca(2+) current and the associated internal [Ca(2+)]i transient is a first approach for evaluating coupling gain. We discuss which parameters are most appropriate for this analysis and how an evaluation of gain needs to be further explored by measuring the SR Ca(2+) content. © 2015 Cold Spring Harbor Laboratory Press.
    Cold Spring Harbor Protocols 04/2015; 2015(4):pdb.prot076968. DOI:10.1101/pdb.prot076968 · 4.63 Impact Factor
  • Virginie Bito · Karin R Sipido · Niall Macquaide ·
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    ABSTRACT: In cardiac myocytes, the physiological increase of intracellular calcium, the [Ca(2+)]i transient, elicited during excitation-contraction coupling typically reaches a peak amplitude of up to 1 µm, from a resting value of ∼100 nm, within 50-100 msec, depending on the species. Various conditions will affect the amplitude and rise time of the [Ca(2+)]i transient and, depending on the nature of the Ca(2+) signals under study, a variety of different probes are available for monitoring changes in intracellular Ca(2+). In this protocol, we focus on Fluo-3, which exists in the cytosol in its salt form K5Fluo-3. This form is practically nonfluorescent in the absence of Ca(2+), but the fluorescence increases dramatically on Ca(2+) binding. Although Fluo-3 is a single excitation-emission dye, it has a number of advantages for investigators, including an ideal dissociation constant (Kd) value and high quantum yield, meaning that it can be used at low concentrations that introduce minimal buffering. Here, we describe the basic setup and methodology for recording the global cytosolic [Ca(2+)]i transient with this probe during simultaneous patch-clamp and whole-cell recording of membrane voltage or of ionic currents under voltage clamp. © 2015 Cold Spring Harbor Laboratory Press.
    Cold Spring Harbor Protocols 04/2015; 2015(4):pdb.prot076950. DOI:10.1101/pdb.prot076950 · 4.63 Impact Factor
  • Niall Macquaide · Virginie Bito · Karin R Sipido ·
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    ABSTRACT: Here, we describe a protocol for the reliable measurement of the amount of Ca(2+) in the sarcoplasmic reticulum (SR) Ca(2+) store of cardiac myocytes. The whole-cell patch-clamp method is used to provide controlled loading of the SR during conditioning depolarizing pulses, followed by rapid application of a high dose of caffeine to release all SR Ca(2+) and to prevent Ca(2+) reuptake by the SR. Simultaneous measurement of membrane currents records Ca(2+) extruded through the Na(+)-Ca(2+) exchanger. The integral of the caffeine-induced Na(+)-Ca(2+) exchange current is then used as a measure of the SR Ca(2+). Derived measurements include the Ca(2+) buffering capacity and measurement of fractional release as an indicator of coupling gain. Caveats, advantages, and disadvantages of this method and alternative methods are discussed. © 2015 Cold Spring Harbor Laboratory Press.
    Cold Spring Harbor Protocols 04/2015; 2015(4):pdb.prot076976. DOI:10.1101/pdb.prot076976 · 4.63 Impact Factor
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    ABSTRACT: This paper is the third in a series of reviews published in this issue resulting from the University of California Davis Cardiovascular Symposium 2014: Systems approach to understanding cardiac excitation–contraction coupling and arrhythmias: Na+ channel and Na+ transport. The goal of the symposium was to bring together experts in the field to discuss points of consensus and controversy on the topic of sodium in the heart. The present review focuses on cardiac Na+/Ca2+ exchange (NCX) and Na+/K+-ATPase (NKA). While the relevance of Ca2+ homeostasis in cardiac function has been extensively investigated, the role of Na+ regulation in shaping heart function is often overlooked. Small changes in the cytoplasmic Na+ content have multiple effects on the heart by influencing intracellular Ca2+ and pH levels thereby modulating heart contractility. Therefore it is essential for heart cells to maintain Na+ homeostasis. Among the proteins that accomplish this task are the Na+/Ca2+ exchanger (NCX) and the Na+/K+ pump (NKA). By transporting three Na+ ions into the cytoplasm in exchange for one Ca2+ moved out, NCX is one of the main Na+ influx mechanisms in cardiomyocytes. Acting in the opposite direction, NKA moves Na+ ions from the cytoplasm to the extracellular space against their gradient by utilizing the energy released from ATP hydrolysis. A fine balance between these two processes controls the net amount of intracellular Na+ and aberrations in either of these two systems can have a large impact on cardiac contractility. Due to the relevant role of these two proteins in Na+ homeostasis, the emphasis of this review is on recent developments regarding the cardiac Na+/Ca2+ exchanger (NCX1) and Na+/K+ pump and the controversies that still persist in the field.
    The Journal of Physiology 03/2015; 593(6). DOI:10.1113/jphysiol.2014.282319 · 5.04 Impact Factor
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    ABSTRACT: Postconditioning and cyclosporine A prevent mitochondrial permeability transition pore opening providing cardioprotection during ischemia/reperfusion. Whether microvascular obstruction is affected by these interventions is largely unknown. Pigs subjected to coronary occlusion for 1 h followed by 3 h of reperfusion were assigned to control (n = 8), postconditioning (n = 9) or cyclosporine A intravenous infusion 10–15 min before the end of ischemia (n = 8). Postconditioning was induced by 8 cycles of repeated 30-s balloon inflation and deflation. After 3 h of reperfusion magnetic resonance imaging, triphenyltetrazolium chloride/Evans blue staining and histopathology were performed. Microvascular obstruction (MVO, percentage of gadolinium-hyperenhanced area) was measured early (3 min) and late (12 min) after contrast injection. Infarct size with double staining was smaller in cyclosporine (46.2 ± 3.1 %, P = 0.016) and postconditioning pigs (47.6 ± 3.9 %, P = 0.008) versus controls (53.8 ± 4.1 %). Late MVO was significantly reduced by cyclosporine (13.9 ± 9.6 %, P = 0.047) but not postconditioning (23.6 ± 11.7 %, P = 0.66) when compared with controls (32.0 ± 16.9 %). Myocardial blood flow in the late MVO was improved with cyclosporine versus controls (0.30 ± 0.06 vs 0.21 ± 0.03 ml/g/min, P = 0.002) and was inversely correlated with late-MVO extent (R 2 = 0.93, P
    Archiv für Kreislaufforschung 03/2015; 110(2):475. DOI:10.1007/s00395-015-0475-8 · 5.41 Impact Factor
  • Demetrio J. Santiago · Eef Dries · Ilse Lenaerts · Karin R. Sipido ·

    Biophysical Journal 01/2015; 108(2):567a. DOI:10.1016/j.bpj.2014.11.3105 · 3.97 Impact Factor

  • Cardiovascular Research 12/2014; 105(1):1-2. DOI:10.1093/cvr/cvu253 · 5.94 Impact Factor
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    ABSTRACT: There is strong need to develop the current stratified practice of CVD management into a better personalized cardiovascular medicine, within a broad framework of global patient care. Clinical information obtained from history and physical examination, functional and imaging studies, biochemical biomarkers, genetic/epigenetic data, and pathophysiological insights into disease-driving processes need to be integrated into a new taxonomy of CVDs to allow personalized disease management. This has the potential for major health benefits for the population suffering from cardiovascular diseases.
    European Heart Journal 12/2014; 35(46):3250-3257. DOI:10.1093/eurheartj/ehu312 · 15.20 Impact Factor
  • Diane Gal · Wouter Vandevelde · Heping Cheng · Karin R Sipido ·

    Cardiovascular Research 11/2014; 104(3). DOI:10.1093/cvr/cvu238 · 5.94 Impact Factor
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Publication Stats

4k Citations
998.33 Total Impact Points


  • 1993-2015
    • University of Leuven
      • • Department of Cardiovascular Sciences
      • • Division of Experimental Cardiology
      Louvain, Flemish, Belgium
  • 2004-2013
    • Catholic University of Louvain
      Лувен-ла-Нев, Walloon, Belgium
  • 2011
    • Sahlgrenska University Hospital
      Goeteborg, Västra Götaland, Sweden
  • 2007
    • Universitair Ziekenhuis Leuven
      • Department of Cardiovascular diseases
      Louvain, Flanders, Belgium
  • 2005
    • The University of Manchester
      Manchester, England, United Kingdom
  • 1998
    • Maastricht University
      • Department of Cardiology
      Maestricht, Limburg, Netherlands
  • 1992
    • Johns Hopkins University
      • Department of Medicine
      Baltimore, Maryland, United States