Publications
174 results found
Wang BX, Kane C, Couch L, et al., 2017, Arginine-Glycine-Aspartic Acid-Motif Containing Peptides and Integrin Binding Modulate Human Induced Pluripotent Stem-Cell Derived Cardiomyocyte Calcium Cycling, Scientific Sessions of the American-Heart-Association / Resuscitation Science Symposium, Publisher: LIPPINCOTT WILLIAMS & WILKINS, ISSN: 0009-7322
Wang B, Terracciano C, Macleod K, 2017, Regulation of cardiac excitation-contraction coupling by fibroblasts in health and disease, ISHR-NAS Annual Meeting, Publisher: ELSEVIER SCI LTD, Pages: 161-161, ISSN: 0022-2828
Rowlands C, Owen T, Lawal S, et al., 2017, Age and strain related aberrant Ca2+ release is associated with sudden cardiac death in the ACTC E99K mouse model of hypertrophic cardiomyopathy, American Journal of Physiology: Heart and Circulatory Physiology, Vol: 313, Pages: H1213-H1226, ISSN: 1522-1539
Patients with hypertrophic cardiomyopathy, particularly young adults, can die from arrhythmia, but the mechanism underlying abnormal rhythm formation remains unknown. C57Bl6 × CBA/Ca mice carrying a cardiac actin (ACTC) E99K (Glu99Lys) mutation reproduce many aspects of human hypertrophic cardiomyopathy, including increased myofilament Ca2+ sensitivity and sudden death in a proportion (up to 40%) of young (28−40 day old) animals. We studied the hearts of transgenic (TG; ACTC E99K) mice and their non-TG (NTG) littermates when they were in their vulnerable period (28–40 days old) and when they were adult (8–12 wk old). Ventricular myocytes were isolated from the hearts of TG and NTG mice at these two time points. We also examined the hearts of mice that died suddenly (SCD). SCD animals had approximately four times more collagen compared with age-matched NTG mice, yet myocyte cell size was normal. Young TG mice had double the collagen content of NTG mice. Contraction and Ca2+ transients were greater in cells from young TG mice compared with their NTG littermates but not in cells from adult mice (TG or NTG). Cells from young TG mice had a greater propensity for Ca2+ waves than NTG littermates, and, despite similar sarcoplasmic reticulum Ca2+ content, a proportion of these cells had larger Ca2+ spark mass. We found that the probability of SCD in young TG mice was increased when the mutation was expressed in animals with a CBA/Ca2+ background and almost eliminated in mice bred on a C57Bl6 background. The latter TG mice had normal cellular Ca2+ homeostasis.
Sikkel MB, Francis DP, Howard J, et al., 2017, Hierarchical statistical techniques are necessary to draw reliable conclusions from analysis of isolated cardiomyocyte studies, Cardiovascular Research, Vol: 113, Pages: 1743-1752, ISSN: 1755-3245
AimsIt is generally accepted that post-MI heart failure (HF) changes a variety of aspects of sarcoplasmic reticular Ca2+ fluxes but for some aspects there is disagreement over whether there is an increase or decrease. The commonest statistical approach is to treat data collected from each cell as independent, even though they are really clustered with multiple likely similar cells from each heart. In this study, we test whether this statistical assumption of independence can lead the investigator to draw conclusions that would be considered erroneous if the analysis handled clustering with specific statistical techniques (hierarchical tests).Methods and resultsCa2+ transients were recorded in cells loaded with Fura-2AM and sparks were recorded in cells loaded with Fluo-4AM. Data were analysed twice, once with the common statistical approach (assumption of independence) and once with hierarchical statistical methodologies designed to allow for any clustering. The statistical tests found that there was significant hierarchical clustering. This caused the common statistical approach to underestimate the standard error and report artificially small P values. For example, this would have led to the erroneous conclusion that time to 50% peak transient amplitude was significantly prolonged in HF.Spark analysis showed clustering, both within each cell and also within each rat, for morphological variables. This means that a three-level hierarchical model is sometimes required for such measures. Standard statistical methodologies, if used instead, erroneously suggest that spark amplitude is significantly greater in HF and spark duration is reduced in HF.ConclusionCa2+ fluxes in isolated cardiomyocytes show so much clustering that the common statistical approach that assumes independence of each data point will frequently give the false appearance of statistically significant changes. Hierarchical statistical methodologies need a little more effort, but are necessary for relia
Yang H-Y, Firth JM, Francis AJ, et al., 2017, The effect of ovariectomy on intracellular calcium (Ca2+) regulation in guinea pig cardiomyocytes, American Journal of Physiology-Heart and Circulatory Physiology, Vol: 313, Pages: H1031-H1043, ISSN: 1522-1539
This study addressed the hypothesis that long-term deficiency of ovarian hormones alters cellular calcium (Ca2+) handling mechanisms in the heart resulting in the formation of a pro-arrhythmic substrate. It also tested if estrogen supplementation to ovariectomised guinea pigs reverses any alterations to cardiac Ca2+ handling and rescues pro-arrhythmic behaviour. Ovariectomy (OVx) or sham operations were performed on female guinea pigs using appropriate anaesthetic and analgesic regimes. Pellets containing 17β-estradiol (1mg, 60-day release), were placed subcutaneously in selected OVx animals (OVx+E). Cardiac myocytes were enzymatically isolated and electrophysiological measurements were conducted with a switch clamp system. In Fluo-4 loaded cells, Ca2+ transients were 20% larger and fractional sarcoplasmic reticulum (SR) Ca2+ release was 7% greater in the OVx group compared with the sham group. Peak L-type Ca2+ current (ICa,L) was 16% larger in OVx myocytes with channel inactivation shifting to more positive membrane potentials creating a larger "window" current. SR Ca2+ stores were 22% greater in the OVx group and these cells showed a higher frequency of Ca2+ sparks and waves and shorter wave-free intervals. OVx myocytes showed higher frequencies of early afterdepolarizations (EADs) and a greater percentage of these cells showed delayed afterdepolarizations (DADs) following exposure to isoprenaline (ISO) compared to sham. The altered Ca2+ regulation occurring in the OVx group was not observed in the OVx+E group. These findings suggest that long-term deprivation of ovarian hormones in guinea pig lead to changes in myocyte Ca2+ handling mechanisms that are considered pro-arrhythmogenic. 17β-estradiol replacement prevented these adverse effects.
Sikkel MB, Kumar S, Maioli V, et al., 2017, Erratum: High speed sCMOS-based oblique plane microscopy applied to the study of calcium dynamics in cardiac myocytes: [J. Biophotonics 9, No. 3, 311-323 (2016)]., J Biophotonics, Vol: 10, Pages: 744-745
In the article by M.B. Sikkel et al. (doi: 10.1002/jbio.201500193), published in J. Biophotonics 9, 311-323 (2016), an error occurred in the computer code that was used to generate Figure 3. This erratum is published to correct Figure 3, the calculated value of tgeom and the experimentally determined value of toptics in the text of the article.
Shattock MJ, Park KC, Yang H-Y, et al., 2017, Restitution slope is principally determined by steady-state action potential duration, Cardiovascular Research, Vol: 113, Pages: 817-828, ISSN: 1755-3245
AimsThe steepness of the action potential duration (APD) restitution curve and local tissue refractoriness are both thought to play important roles in arrhythmogenesis. Despite this, there has been little recognition of the apparent association between steady-state APD and the slope of the restitution curve. The objective of this study was to test the hypothesis that restitution slope is determined by APD and to examine the relationship between restitution slope, refractoriness and susceptibility to VF.Methods and resultsExperiments were conducted in isolated hearts and ventricular myocytes from adult guinea pigs and rabbits. Restitution curves were measured under control conditions and following intervention to prolong (clofilium, veratridine, bretylium, low [Ca]e, chronic transverse aortic constriction) or shorten (catecholamines, rapid pacing) ventricular APD. Despite markedly differing mechanisms of action, all interventions that prolonged the action potential led to a steepening of the restitution curve (and vice versa). Normalizing the restitution curve as a % of steady-state APD abolished the difference in restitution curves with all interventions. Effects on restitution were preserved when APD was modulated by current injection in myocytes pre-treated with the calcium chelator BAPTA-AM – to abolish the intracellular calcium transient. The non-linear relation between APD and the rate of repolarization of the action potential is shown to underpin the common influence of APD on the slope of the restitution curve. Susceptibility to VF was found to parallel changes in APD/refractoriness, rather than restitution slope.Conclusion(s)Steady-state APD is the principal determinant of the slope of the ventricular electrical restitution curve. In the absence of post-repolarization refractoriness, factors that prolong the action potential would be expected to steepen the restitution curve. However, concomitant changes in tissue refractoriness act to reduce susceptib
Yang H-Y, Alvarez-Laviada A, Firth JM, et al., 2017, The Effect of Ovariectomy on Calcium (Ca2+) Handling in Guinea Pig Cardiomyocytes, 61st Annual Meeting of the Biophysical-Society, Publisher: CELL PRESS, Pages: 101A-101A, ISSN: 0006-3495
Thomas NM, Gray R, Fry CH, et al., 2016, Functional consequences of co-expressing connexin40 or connexin45 with connexin43 on intercellular electrical coupling, Biochemical and Biophysical Research Communications, Vol: 483, Pages: 191-196, ISSN: 0006-291X
The functional characteristics of the co-expression of connexin43, connexin40, and connexin45 proteins in human myocardium are thought to play an important role in governing normal propagation of the cardiac electrical impulse and in generating the myocardial substrate for some arrhythmias and conduction disturbances.A rat liver epithelial cell line, that endogenously expresses connexin43, was used to induce also expression of connexin40 or connexin45 after stable transfection using an inducible ecdysone system. Electrical coupling was estimated from measurement of the input resistance of transfected cells using an intracellular microelectrode to inject current and record changes to membrane potential.However, varied expression of the transfected connexin40 or connexin45 did not change electrical coupling, although connexin43/40 co-expression led to better coupling than connexin43/45 co-expression. Quantification of endogenous connexin43 expression, at both mRNA and protein levels, showed that it was altered in a manner dependent on the transfected connexin isotype.The data using rat liver epithelial cells indicate an increased electrical coupling upon expression of connexin40 and connexin43 but decreased coupling with connexin45 and connexin43 co-expression.
Williams AJ, Bannister ML, Thomas NL, et al., 2016, Questioning flecainide's mechanism of action in the treatment of catecholaminergic polymorphic ventricular tachycardia, Journal of Physiology, Vol: 594, Pages: 6431-6432, ISSN: 1469-7793
MacLeod KT, 2016, Recent advances in understanding cardiac contractility in health and disease, F1000 Research, Vol: 5, ISSN: 2046-1402
The aim of this review is to provide the reader with a synopsis of some of the emerging ideas and experimental findings in cardiac physiology and pathophysiology that were published in 2015. To provide context for the non-specialist, a brief summary of cardiac contraction and calcium (Ca) regulation in the heart in health and disease is provided. Thereafter, some recently published articles are introduced that indicate the current thinking on (1) the Ca regulatory pathways modulated by Ca/calmodulin-dependent protein kinase II, (2) the potential influences of nitrosylation by nitric oxide or S-nitrosated proteins, (3) newly observed effects of reactive oxygen species (ROS) on contraction and Ca regulation following myocardial infarction and a possible link with changes in mitochondrial Ca, and (4) the effects of some of these signaling pathways on late Na current and pro-arrhythmic afterdepolarizations as well as the effects of transverse tubule disturbances.
Bannister ML, Alvarez-Laviada A, Thomas NL, et al., 2016, Effect of flecainide derivatives on sarcoplasmic reticulum calcium release suggests a lack of direct action on the cardiac ryanodine receptor, British Journal of Pharmacology, Vol: 173, Pages: 2446-2459, ISSN: 1476-5381
Background and PurposeFlecainide is a use-dependent blocker of cardiac Na+ channels. Mechanistic analysis of this block showed that the cationic form of flecainide enters the cytosolic vestibule of the open Na+ channel. Flecainide is also effective in the treatment of catecholaminergic polymorphic ventricular tachycardia but, in this condition, its mechanism of action is contentious. We investigated how flecainide derivatives influence Ca2+-release from the sarcoplasmic reticulum through the ryanodine receptor channel (RyR2) and whether this correlates with their effectiveness as blockers of Na+ and/or RyR2 channels.Experimental ApproachWe compared the ability of fully charged (QX-FL) and neutral (NU-FL) derivatives of flecainide to block individual recombinant human RyR2 channels incorporated into planar phospholipid bilayers, and their effects on the properties of Ca2+ sparks in intact adult rat cardiac myocytes.Key ResultsBoth QX-FL and NU-FL were partial blockers of the non-physiological cytosolic to luminal flux of cations through RyR2 channels but were significantly less effective than flecainide. None of the compounds influenced the physiologically relevant luminal to cytosol cation flux through RyR2 channels. Intracellular flecainide or QX-FL, but not NU-FL, reduced Ca2+ spark frequency.Conclusions and ImplicationsGiven its inability to block physiologically relevant cation flux through RyR2 channels, and its lack of efficacy in blocking the cytosolic-to-luminal current, the effect of QX-FL on Ca2+ sparks is likely, by analogy with flecainide, to result from Na+ channel block. Our data reveal important differences in the interaction of flecainide with sites in the cytosolic vestibules of Na+ and RyR2 channels.
Toepfer CN, Sikkel MB, Caorsi V, et al., 2016, A post-MI power struggle: adaptations in cardiac power occur at the sarcomere level alongside MyBP-C and RLC phosphorylation., American Journal of Physiology - Heart and Circulatory Physiology, Vol: 311, Pages: H465-H475, ISSN: 0363-6135
Myocardial remodeling in response to chronic myocardial infarction (CMI) progresses through two phases, hypertrophic 'compensation' and congestive 'decompensation'. Nothing is known about the ability of un-infarcted myocardium to produce force, velocity, and power during these clinical phases, even though adaptation in these regions likely drive progression of compensation. We hypothesized that enhanced crossbridge-level contractility underlies mechanical compensation and is controlled in part by changes in the phosphorylation states of myosin regulatory proteins. We induced CMI in rats by left anterior descending coronary artery ligation. We then measured mechanical performance in permeabilized ventricular trabecula taken distant from the infarct zone and assayed myosin regulatory protein phosphorylation in each individual trabecula. During full activation, the compensated myocardium produced twice as much power and 31% greater isometric force compared to non-infarcted controls. Isometric force during submaximal activations was raised >2.4-fold, whilst power was 2-fold greater. EM and confocal microscopy demonstrated that these mechanical changes were not a result of increased density of contractile protein, and therefore not an effect of tissue hypertrophy. Hence, sarcomere-level contractile adaptations are key determinants of enhanced trabecular mechanics and of the overall cardiac compensatory response. Phosphorylation of myosin regulatory light chain (RLC) increased and remained elevated post-MI, while phosphorylation of myosin binding protein-C (MyBP-C) was initially depressed but then increased as the hearts became decompensated. These sensitivities to CMI are in accordance with phosphorylation-dependent regulatory roles for RLC and MyBP-C in crossbridge function and with compensatory adaptation in force and power that we observed in post-CMI trabeculae.
Sikkel MB, Kumar S, Maioli V, et al., 2016, High speed sCMOS-based oblique plane microscopy applied to the study of calcium dynamics in cardiac myocytes, Journal of Biophotonics, Vol: 9, Pages: 311-323, ISSN: 1864-0648
blique plane microscopy (OPM) is a form of light sheet microscopy that uses a single high numerical aperture microscope objective for both fluorescence excitation and collection. In this paper, measurements of the relative collection efficiency of OPM are presented. An OPM system incorporating two sCMOS cameras is then introduced that enables single isolated cardiac myocytes to be studied continuously for 22 seconds in two dimensions at 667 frames per second with 960 × 200 pixels and for 30 seconds with 960 × 200 × 20 voxels at 25 volumes per second. In both cases OPM is able to record in two spectral channels, enabling intracellular calcium to be studied via the probe Fluo-4 AM simultaneously with the sarcolemma and transverse tubule network via the membrane dye Cellmask Orange. The OPM system was then applied to determine the spatial origin of spontaneous calcium waves for the first time and to measure the cell transverse tubule structure at their point of origin. Further results are presented to demonstrate that the OPM system can also be used to study calcium spark parameters depending on their relationship to the transverse tubule structure.
Alvarez-Laviada A, Bannister ML, Thomas NL, et al., 2016, Effect of Flecainide Derivatives on Sarcoplasmic Reticulum Ca<SUP>2+</SUP> Release Confirms a Lack of Direct Action on the Cardiac Ryanodine Receptor, 60th Annual Meeting of the Biophysical-Society, Publisher: CELL PRESS, Pages: 450A-451A, ISSN: 0006-3495
Alvarez-Laviada A, Bannister ML, Lowri Thomas N, et al., 2016, Effect of Flecainide Derivatives on Sarcoplasmic Reticulum Ca2+ Release Confirms a Lack of Direct Action on the Cardiac Ryanodine Receptor, Biophysical Journal, Vol: 110, Pages: 450a-451a, ISSN: 0006-3495
Bannister ML, Thomas NL, Sikkel MB, et al., 2015, The mechanism of flecainide action in CPVT does not involve a direct effect on RyR2, Circulation Research, Vol: 116, Pages: 1324-1335, ISSN: 1524-4571
Rationale: Flecainide, a class 1c antiarrhythmic, has emerged as an effective therapy in preventing arrhythmias in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT) refractory to β-adrenergic receptor blockade. It has been proposed that the clinical efficacy of flecainide in CPVT is because of the combined actions of direct blockade of ryanodine receptors (RyR2) and Na+ channel inhibition. However, there is presently no direct evidence to support the notion that flecainide blocks RyR2 Ca2+ flux in the physiologically relevant (luminal-to-cytoplasmic) direction. The mechanism of flecainide action remains controversial.Objective: To examine, in detail, the effect of flecainide on the human RyR2 channel and to establish whether the direct blockade of physiologically relevant RyR2 ion flow by the drug contributes to its therapeutic efficacy in the clinical management of CPVT.Methods and Results: Using single-channel analysis, we show that, even at supraphysiological concentrations, flecainide did not inhibit the physiologically relevant, luminal-to-cytosolic flux of cations through the channel. Moreover, flecainide did not alter RyR2 channel gating and had negligible effect on the mechanisms responsible for the sarcoplasmic reticulum charge-compensating counter current. Using permeabilized cardiac myocytes to eliminate any contribution of plasmalemmal Na+ channels to the observed actions of the drug at the cellular level, flecainide did not inhibit RyR2-dependent sarcoplasmic reticulum Ca2+ release.Conclusions: The principal action of flecainide in CPVT is not via a direct interaction with RyR2. Our data support a model of flecainide action in which Na+-dependent modulation of intracellular Ca2+ handling attenuates RyR2 dysfunction in CPVT.
Taggart MJ, Hume R, Lartey J, et al., 2014, Cardiac remodelling during pregnancy: whither the guinea pig?, CARDIOVASCULAR RESEARCH, Vol: 104, Pages: 226-227, ISSN: 0008-6363
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- Citations: 4
Mills AM, Sikkel MB, Kumarswamy R, et al., 2014, miR-1: a link between SERCA2a and the Beta-Adrenoceptor in the failing heart?, CARDIOVASCULAR RESEARCH, Vol: 103, ISSN: 0008-6363
Zollner J, Ke H-Y, Sooranna SR, et al., 2014, The Expression of the Sodium Potassium ATPases in Cardiac Myocytes in a Guinea Pig Model of Transaortic Constriction, REPRODUCTIVE SCIENCES, Vol: 21, Pages: 384A-384A, ISSN: 1933-7191
Dias P, Desplantez T, El-Harasis MA, et al., 2014, Characterisation of Connexin Expression and Electrophysiological Properties in Stable Clones of the HL-1 Myocyte Cell Line, PLOS ONE, Vol: 9, ISSN: 1932-6203
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Alvarez-Laviada A, Sikkel M, Al-khayatt B, et al., 2014, Effects of Flecainide and Ranolazine on Intracellular Calcium Handling and Sarcolemmal Sodium Current, 58th Annual Meeting of the Biophysical-Society, Publisher: CELL PRESS, Pages: 324A-324A, ISSN: 0006-3495
Al-Khayatt BM, Sikkel MB, Laviada AA, et al., 2014, Ranolazine Reduces Arrhythmogenic Calcium Waves in Ventricular Cardiomyocytes, 58th Annual Meeting of the Biophysical-Society, Publisher: CELL PRESS, Pages: 721A-721A, ISSN: 0006-3495
Ke H-Y, Collins TP, Alvarez-Laviada A, et al., 2014, Na/K ATPase Function Declines Before Changes to Calcium Handling in a Guinea-Pig Model of Progressive Heart Failure, 58th Annual Meeting of the Biophysical-Society, Publisher: CELL PRESS, Pages: 763A-763A, ISSN: 0006-3495
Rowlands CT, Marston SB, MacLeod KT, 2014, Calcium Handling is Altered in the Actc E99K Transgenic Mouse Model of Hypertrophic Cardiomyopathy, 58th Annual Meeting of the Biophysical-Society, Publisher: CELL PRESS, Pages: 323A-323A, ISSN: 0006-3495
Toepfer C, Sikkel M, Caorsi V, et al., 2014, Effects of Chronic Myocardial Infarction on Cardiac Muscle Performance and Structure In-Vivo and In-Vitro, 58th Annual Meeting of the Biophysical-Society, Publisher: CELL PRESS, Pages: 343A-344A, ISSN: 0006-3495
Sikkel MB, Hayward C, MacLeod KT, et al., 2014, SERCA2a gene therapy in heart failure: an anti-arrhythmic positive inotrope, BRITISH JOURNAL OF PHARMACOLOGY, Vol: 171, Pages: 38-54, ISSN: 0007-1188
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Sikkel MB, MacLeod KT, Gordon F, 2013, Letter by Sikkel et al Regarding Article, "Late Sodium Current Inhibition Reverses Electromechanical Dysfunction in Human Hypertrophic Cardiomyopathy", CIRCULATION, Vol: 128, Pages: e156-e156, ISSN: 0009-7322
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Caorsi V, Toepfer C, Sikkel M, et al., 2013, Collagen fibrosis quantified by non linear optical microscopy to study cardiac disease progression, 9th European-Biophysical-Societies-Association Congress, Publisher: SPRINGER, Pages: S99-S99, ISSN: 0175-7571
Song W, Vikhorev PG, Kashyap MN, et al., 2013, Mechanical and energetic properties of papillary muscle from <i>ACTC</i> E99K transgenic mouse models of hypertrophic cardiomyopathy, AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, Vol: 304, Pages: H1513-H1524, ISSN: 0363-6135
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- Citations: 20
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