Proarrhythmogenic Ca2 Research Articles

Cardiac-Specific Overexpression of Caveolin-1 in Rats With Ischemic Cardiomyopathy Improves Arrhythmogenicity and Cardiac Remodelling.

Ischemic cardiomyopathy (ICM) is associated with electrical and structural remodelling, leading to arrhythmias. Caveolin-1 (Cav1) is a membrane protein involved in the pathogenesis of ischemic injury. Cav1 deficiency has been associated with arrhythmogenicity. The current study aimed to determine how Cav1 overexpression inhibits arrhythmias and cardiac remodelling in ICM. ICM was modelled using left anterior descending (LAD) artery ligation for 4 weeks. Cardiac-specific Cav1 overexpression in ICM on arrhythmias, excitation-contraction coupling, and cardiac remodelling were investigated using the intramyocardial injection of an adeno-associated virus serotype 9 (AAV-9) system, carrying a specific sequence expressing Cav1 (AAVCav1) under the cardiac troponin T (cTnT) promoter. Cav1 overexpression decreased susceptibility to arrhythmias by upregulating gap junction connexin 43 (CX43) and reducing spontaneous irregular proarrhythmogenic Ca2+ waves in ventricular cardiomyocytes. It also alleviated ischemic injury-induced contractility weakness by improving Ca2+ cycling through normalizing Ca2+-handling protein levels and improving Ca2+ homeostasis. Masson stain and immunoblotting revealed that the deposition of excessive fibrosis was attenuated by Cav1 overexpression, inhibiting the transforming growth factor-β (TGF-β)/Smad2 signalling pathway. Coimmunoprecipitation assays demonstrated that the interaction between Cav1 and cSrc modulated CX43 expression and Ca2+-handling protein levels. Cardiac-specific overexpression of Cav1 attenuated ventricular arrhythmia, improved Ca2+ cycling, and attenuated cardiac remodelling. These effects were attributed to modulation of CX43, normalized Ca2+-handling protein levels, improved Ca2+ homeostasis, and attenuated cardiac fibrosis.

Abstract 12554: Hipsc Derived Cardiomyocytes for Mechanistic, Patient Tailored Treatment in a Novel Mutation Linked to Cpvt

Background: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a disease related to altered ryanodine receptor (RyR) mediated SR Ca 2+ leak and associated with sudden cardiac death in young adults. We recently identified a family with a mixed phenotype of CPVT and long-QT-syndrome (CPVT3*) related to a novel mutation in the trans-2.3-enyol-CoA reductase-like (TECRL) gene. Ventricular arrhythmia burden varies greatly between individual CPVT3* patients. Methods/Results: We generated human induced pluripotent stem cell derived cardiomyocytes (iPSc-CM) from a control and CPVT3* patient to explore underlying mechanisms and individualize pharmacological treatment. iPSc-CM were studied using confocal Ca 2+ imaging (fluo-4). Ca 2+ signaling during excitation-contraction coupling was studied in the presence of different clinically available modulators of RyR mediated SR Ca 2+ leak. In particular, cardiomyocyte function and arrythmias were tested upon addition of the class Ic antiarrhythmic flecainide (10μM), the RyR stabilizer dantrolene (1μM), the betablocker R-Carvedilol (1μM), the kinase inhibitor Rimacalib (10μM) and the RyR-Calstabin interaction stabilizer S107 (10μM). Under baseline conditions, CPVT3* iPSc-CM showed significantly decreased Ca 2+ transient (CaT) amplitudes and increased CaT duration. Upon addition of the beta-agonist isoproterenol (ISO, 100nM), CaT amplitudes and pro-arrhythmogenic Ca 2+ release (i.e. Ca 2+ sparks) significantly increased in CPVT3* as compared to control. All pharmaceuticals altered Ca 2+ signaling in CPVT3* in a substance dependent manner and pro-arrhythmogenic Ca 2+ release was particularly mitigated upon addition of flecainide. Treatment of the CPVT3* patient with flecainide significantly reduced ventricular premature beats as determined by 24 hour holter-ECG monitoring. Conclusion: We quantitatively assessed drugs targeting RyR mediated SR Ca 2+ leak in a CPVT3* patient with a novel TECRL mutation using iPSc-CM. Favorable in-vitro results of flecainide were mirrored in a significant reduction of ventricular arrhythmia in-vivo. Our results underscore the potential of iPSc-CM for the development of patient-tailored treatment in genetic arrhythmia syndromes.

Inhibition of sodium glucose cotransporter 1 reduces arrhythmogenesis in diabetic rats

Type-2 diabetes (T2D) is associated with a higher risk for arrhythmias, but the underlying mechanisms are incompletely elucidated. The Na+-glucose cotransporter 1 (SGLT1) is upregulated in T2D hearts, resulting in larger myocyte Na+ concentration ([Na+]i), which promotes the occurrence of pro-arrhythmogenic Ca2+ sparks. Moreover, SGLT1 is electrogenic and may depolarize the myocytes at rest. To test the effect of SGLT1 inhibition on diabetic hearts. Rats expressing human amylin in the pancreatic β-cells (HIP rats) were used as a model of late-onset T2D and their WT littermates served as controls.

Interplay between mineral bone disorder and cardiac damage in acute kidney injury: from Ca2+ mishandling and preventive role of Klotho in mice to its potential mortality prediction in human

Biomarkers of mineral bone disorders (MBD) including phosphorus, fibroblast growth factor (FGF)-23 and Klotho are strongly altered in patients with acute kidney injury (AKI) who have high cardiac outcomes and mortality rates. However, the crosslink between MBD and cardiac damage after an AKI episode still remains unclear. We tested MBD and cardiac biomarkers in an experimental AKI model after 24 or 72 hours of folic acid injection and we analyzed structural cardiac remodeling, intracellular calcium (Ca2+) dynamics in cardiomyocytes and cardiac rhythm. AKI mice presented high levels of FGF-23, phosphorus and cardiac troponin T and exhibited a cardiac hypertrophy phenotype accompanied by an increase in systolic Ca2+ release 24 hours after AKI. Ca2+ transients and contractile dysfunction were reduced 72 hours after AKI while diastolic sarcoplasmic reticulum Ca2+ leak, pro-arrhythmogenic Ca2+ events and ventricular arrhythmias were increased. These cardiac events were linked to the activation of the calcium/calmodulin-dependent kinase II pathway through the increased phosphorylation of ryanodine receptors and phospholamban specific sites after AKI. Cardiac hypertrophy and the altered intracellular Ca2+ dynamics were prevented in transgenic mice overexpressing Klotho after AKI induction. In a translational retrospective longitudinal clinical study, we determined that combining FGF-23 and phosphorus with cardiac troponin T levels achieved a better prediction of mortality in AKI patients at hospital admission. Thus, monitoring MBD and cardiac damage biomarkers could be crucial to prevent mortality in AKI patients. In this setting, Klotho might be considered as a new cardioprotective therapeutic tool to prevent deleterious cardiac events in AKI conditions.

The effect of canakinumab on COVID19-associated cardiomyocyte contractile dysfunction and arrhythmias

Abstract Background Cardiac injury associated with cytokine release occurs in almost 20% of SARS-CoV-2 positive patients during hospitalization and mortality is particularly high in these patients. Cardiac enzyme (e.g. troponin or creatinine kinase (CK)) elevations are a frequently reported finding, indicating myocardial damage and arrhythmias are the cause for ICU transfer in up to 12% of patients. However, the mechanistic role of COVID19 associated cytokine-storm for the concomitant cardiac dysfunction and associated arrhythmias is unclear. In addition, the role of anti-inflammatory therapy approaches to mitigate this cardiac dysfunction remains elusive. Methods We investigated the effects of COVID19-associated inflammatory response on cardiac cellular function as well as its cardiac arrhythmogenic potential in rat and induced pluripotent stem cell derived cardiomyocytes (iPSc-CM). Moreover, we evaluated the therapeutic potential of the IL1-beta antagonist Canakinumab using state of the art in-vitro confocal and ratiometric high-throughput microscopy. Results Isolated rat ventricular cardiomyocytes were exposed to control or COVID19 plasma from intensive care unit patients with severe ARDS and impaired cardiac function (LVEF 41±5%; 1/3 of patients on veno-venous extracorporeal membrane oxygenation; CK 154±43 U/l). Cardiomyocytes showed decreased Ca2+ transient amplitudes and altered baseline Ca2+ concentrations leading to impaired cellular contractile function upon electrical field-stimulation and exposure to patient plasma (n=276 control and 359 COVID19 cells; Fura). In addition, we used iPSc-CM to explore the long-term effect of patient plasma on cardiac electrical and mechanical function in a translational setting (24h incubation; Fluo). In iPSc, spontaneous Ca2+ release events (i.e. Ca2+ waves and Ca2+ sparks) were more likely to occur upon incubation with COVID19 plasma and nuclear as well as cytosolic Ca2+ release were altered. Co-incubation with Canakinumab had no effect on pro-arrhythmogenic Ca2+ release or Ca2+ signaling during excitation-contraction coupling but influenced cellular automaticity upon prolonged electrical stimulation. Conclusion Plasma derived from COVID19 patients exerts acute cardio-depressant and chronic pro-arrhythmogenic effects in rat and iPS-derived cardiomyocytes. Chronic co-incubation with Canakinumab had no beneficial effect on cellular Ca2+ signaling during excitation-contraction coupling. Funding Acknowledgement Type of funding sources: None.

COVID19-associated cardiomyocyte dysfunction, arrhythmias and the effect of Canakinumab.

BackgroundCardiac injury associated with cytokine release frequently occurs in SARS-CoV-2 mediated coronavirus disease (COVID19) and mortality is particularly high in these patients. The mechanistic role of the COVID19 associated cytokine-storm for the concomitant cardiac dysfunction and associated arrhythmias is unclear. Moreover, the role of anti-inflammatory therapy to mitigate cardiac dysfunction remains elusive.Aims and methodsWe investigated the effects of COVID19-associated inflammatory response on cardiac cellular function as well as its cardiac arrhythmogenic potential in rat and induced pluripotent stem cell derived cardiomyocytes (iPS-CM). In addition, we evaluated the therapeutic potential of the IL-1β antagonist Canakinumab using state of the art in-vitro confocal and ratiometric high-throughput microscopy.ResultsIsolated rat ventricular cardiomyocytes were exposed to control or COVID19 serum from intensive care unit (ICU) patients with severe ARDS and impaired cardiac function (LVEF 41±5%; 1/3 of patients on veno-venous extracorporeal membrane oxygenation; CK 154±43 U/l). Rat cardiomyocytes showed an early increase of myofilament sensitivity, a decrease of Ca2+ transient amplitudes and altered baseline [Ca2+] upon exposure to patient serum. In addition, we used iPS-CM to explore the long-term effect of patient serum on cardiac electrical and mechanical function. In iPS-CM, spontaneous Ca2+ release events were more likely to occur upon incubation with COVID19 serum and nuclear as well as cytosolic Ca2+ release were altered. Co-incubation with Canakinumab had no effect on pro-arrhythmogenic Ca2+ release or Ca2+ signaling during excitation-contraction coupling, nor significantly influenced cellular automaticity.ConclusionSerum derived from COVID19 patients exerts acute cardio-depressant and chronic pro-arrhythmogenic effects in rat and iPS-derived cardiomyocytes. Canakinumab had no beneficial effect on cellular Ca2+ signaling during excitation-contraction coupling. The presented method utilizing iPS-CM and in-vitro Ca2+ imaging might serve as a novel tool for precision medicine. It allows to investigate cytokine related cardiac dysfunction and pharmacological approaches useful therein.

Effects of different exercise modalities on cardiac dysfunction in heart failure with preserved ejection fraction.

AimsHeart failure with preserved ejection fraction (HFpEF) is an increasingly prevalent disease. Physical exercise has been shown to alter disease progression in HFpEF. We examined cardiomyocyte Ca2+ homeostasis and left ventricular function in a metabolic HFpEF model in sedentary and trained rats following 8 weeks of moderate‐intensity continuous training (MICT) or high‐intensity interval training (HIIT).Methods and resultsLeft ventricular in vivo function (echocardiography) and cardiomyocyte Ca2+ transients (CaTs) (Fluo‐4, confocal) were compared in ZSF‐1 obese (metabolic syndrome, HFpEF) and ZSF‐1 lean (control) 21‐ and 28‐week‐old rats. At 21 weeks, cardiomyocytes from HFpEF rats showed prolonged Ca2+ reuptake in cytosolic and nuclear CaTs and impaired Ca2+ release kinetics in nuclear CaTs. At 28 weeks, HFpEF cardiomyocytes had depressed CaT amplitudes, decreased sarcoplasmic reticulum (SR) Ca2+ content, increased SR Ca2+ leak, and elevated diastolic [Ca2+] following increased pacing rate (5 Hz). In trained HFpEF rats (HIIT or MICT), cardiomyocyte SR Ca2+ leak was significantly reduced. While HIIT had no effects on the CaTs (1–5 Hz), MICT accelerated early Ca2+ release, reduced the amplitude, and prolonged the CaT without increasing diastolic [Ca2+] or cytosolic Ca2+ load at basal or increased pacing rate (1–5 Hz). MICT lowered pro‐arrhythmogenic Ca2+ sparks and attenuated Ca2+‐wave propagation in cardiomyocytes. MICT was associated with increased stroke volume in HFpEF.ConclusionsIn this metabolic rat model of HFpEF at an advanced stage, Ca2+ release was impaired under baseline conditions. HIIT and MICT differentially affected Ca2+ homeostasis with positive effects of MICT on stroke volume, end‐diastolic volume, and cellular arrhythmogenicity.

Moderate FKBP12.6 overexpression mitigates β-adrenergic-associated pro-arrhythmogenic Ca2+ events, but a higher expression level leads to a cardiomyopathic phenotype

Cardiac ryanodine receptors RyR2 have a crucial role in excitation-contraction coupling by releasing Ca2+ from the sarcoplasmic reticulum (SR). In cardiomyocytes, two FK506 binding proteins (FKBP) of 12 and 12.6 kDa bind and stabilize RyR2 in a closed state. Despite its lower concentration, FKBP12.6 has a stronger affinity for RyR2 than FKBP12. In heart failure (HF), the expression of both isoforms decreases, associated with a high incidence of arrhythmias. By contrast, cardiac FKBP12.6 overexpression protects against β-adrenergic-activated arrhythmias, but the underlying molecular mechanism remains elusive. We wanted to understand the anti-arrhythmic mechanism of FKBP12.6 overexpression, with the hypothesis of dose-effect anti-adrenergic properties. Accordingly, we developed two transgenic mouse lines with cardiac-specific moderate- ( × 10, TG1) and high- ( × 40, TG2) FKBP12.6 overexpression. We characterized cardiac function, [Ca2 + ]i cycling, and its response to sympathetic stimulation in both mouse lines. TG2 mice died prematurely and exhibited marked cardiac hypertrophy with nonsignificant pulmonary congestion, whereas TG1 mice had a normal phenotype. At 2-3 months, TG1 mice had a normal cardiac function, whereas TG2 had a collapsed heart rate and a dilated and hypertrophied left ventricle with unaltered fractional shortening. TG1 cardiomyocytes had higher [Ca2 + ]i transient amplitude and less pro-arrhythmogenic Ca2+ release events than WT mice, without modification of the SR Ca2+ load, and an attenuated response to β-adrenergic stimulation. In contrast, TG2 mice showed [Ca2 + ]i handling characteristics similar to HF with slower [Ca2 + ]i transient relaxation, although pro-arrhythmogenic Ca2+ release events were reduced. These results confirm that FKBP12.6 overexpression interferes with pro-arrhythmic sympathetic signaling, and demonstrate that high level of FKBP12.6 has a deleterious cardiac effect.

P3510Cardiac function and Ca2+-cycling are different according to the level of cardiac-specific FKBP12.6 overexpression

Abstract Cardiac ryanodine receptors (RyR2) have a key role in excitation-contraction coupling by releasing Ca2+ from sarcoplasmic reticulum (SR). In cardiomyocytes, two FK506 binding protein (FKBP) isoforms have been shown to bind and to stabilize RyR2 opening: FKBP12 and FKBP12.6, the later having a stronger affinity for RyR2 despite its lower abundance. Cardiac-specific FKBP12.6 overexpressing mice have fewer arrhythmias induced by β-adrenergic stimulation than wild type (WT) mice, suggesting an implication of FKBP12.6 in an antiarrhythmic mechanism. Heart failure (HF) syndrome has a high incidence of arrhythmias, which may be explained by a decrease of FKBP isoform expression. The precise mechanism of the antiarrhythmic effect of FKBP12.6 overexpression remains unknown. To gain insight into this mechanism, we developed 2 transgenic mouse lines with cardiac-specific moderate- (TG1) and high- (TG2) FKBP12.6 overexpression levels. We characterized cardiac function, [Ca2+]i cycling and its response to β-adrenergic stimulation in both mouse lines. TG1 and TG2 mice developed mild and marked cardiac hypertrophy, respectively, associated with basal cardiac function increase in TG1 mice only. In stimulated cardiomyocytes, [Ca2+]i transient amplitude, measured by confocal microscopy, was higher in TG1 than in WT mice, without a significant difference in their SR Ca2+ content. The effect of β-adrenergic stimulation (50 nM isoproterenol) was attenuated in TG1 mice compared to WT mice, in association with the prevention of pro-arrhythmogenic Ca2+ release events, such as Ca2+ waves. In contrast, TG2 mice showed [Ca2+]i handling characteristics similar to HF, with slower [Ca2+]i transient relaxation. Interestingly, and contrary to HF, pro-arrhythmogenic Ca2+ release events were also reduced in TG2. These results indicate that the level of FKBP12.6 overexpression has distinct effects on cardiac function and on Ca2+-cycling and its response to β-adrenergic stimulation.

P3832Dantrolene reduces CaMKII-mediated arrhythmogenesis

Abstract Rationale In atrial and ventricular rhythm disorders, an increased diastolic sarcoplasmatic reticulum (SR) calcium leak can induce a depolarizing transient inward current, serving as a trigger for cellular arrhythmias. Dantrolene has been shown to also stabilize the cardiac ryanodine receptor. However, the detailed mechanism of the mode of action remains unknown. This study aims to investigate the effects of dantrolene on calcium/calmodulin-dependent kinase II (CaMKII) mediated arrhythmogenesis. Methods and results Right atrial cardiomyocytes (CM) were isolated from patients with atrial fibrillation. To investigate SR Ca2+ leak, measurements of diastolic SR Ca2+ sparks were performed by confocal microscopy using Fluo-4 AM. Dantrolene (10 μmol/l) potently reduced Ca2+-spark-frequency (CaSpF) by 90±26% (p<0.05, n=21 cells dantrolene vs. 19 cells control) leading to a reduction of the calculated diastolic SR-Ca2+-leak by 91±31% (p<0.05, n=21 vs. 19). Interestingly, CaMKII-inhibition using Autocamtide-2-Related Inhibitory Peptide (AIP) did not further reduced SR Ca2+ leak compared to dantrolene alone in human cardiomyocytes. This observation may suggest (secondary) inhibitory effects of dantrolene on CaMKII. To elucidate the role of CaMKII in dantrolene-mediated antiarrhythmic effects, we investigated atrial CM from mice overexpressing CaMKII (TG) and respective wildtype controls (WT). CaSpF and SR Ca2+ leak were reduced by dantrolene in both TG and WT mice (p<0.005, TG: dantrolene vs. vehicle n=132 vs 127 cells (9 mice); WT: dantrolene vs. vehicle n=61 vs 61 cells (5 mice)). However, proarrhythmogenic Ca2+ waves were only significantly reduced by dantrolene in TG mice (p<0.05, TG: dantrolene vs. vehicle 10.8% vs. 26.2%, n=154 vs 164 cells). Correspondingly, the incidence of delayed afterdepolarizations (DADs) in TG cells was significantly diminished by dantrolene (p<0.05, TG: dantrolene vs. vehicle 1/14 vs. 9/15 cells, n=5 mice). In contrast, DADs were not reduced by dantrolene in WT cells without increased CaMKII activity (p=n.s., WT: dantrolene vs vehicle 3/16 vs 2/13 cells, n=5 mice). In preliminary in vivo experiments, intraperitoneal injection of 40 mg/kg body weight dantrolene reduced the inducibility of arrhythmias by ventricular burst stimulation in CaMKII TG mice compared to vehicle (dantrolene 0/2 mice vs. vehicle 2/2 mice, p<0.05 Chi-Square). Conclusion Dantrolene beneficially altered Ca2+ homeostasis in human AF CM and murine CM. Dantrolene seems to exert its antiarrhythmic potential in a CaMKII-dependent manner. Thus, dantrolene as an already clinically approved compound might be a potential antiarrhythmic drug that merits clinical investigation. Acknowledgement/Funding Deutsche Forschungsgemeinschaft (MA 1981/5-1 and 7-1 to LSM). Marga und Walter Boll-Stiftung (SS).

Progression of excitation-contraction coupling defects in doxorubicin cardiotoxicity

Cardiac failure is a common complication in cancer survivors treated with anthracyclines. Here we followed up cardiac function and excitation-contraction (EC) coupling in an in vivo doxorubicin (Dox) treated mice model (iv, total dose of 10 mg/Kg divided once every three days). Cardiac function was evaluated by echocardiography at 2, 6 and 15 weeks after the last injection. While normal at 2 and 6 weeks, ejection fraction was significantly reduced at 15 weeks. In order to evaluate the underlying mechanisms, we measured [Ca2+]i transients by confocal microscopy and action potentials (AP) by patch-clamp technique in cardiomyocytes isolated at these times. Three phases were observed: 1/depression and slowing of the [Ca2+]i transients at 2 weeks after treatment, with occurrence of proarrhythmogenic Ca2+ waves, 2/compensatory state at 6 weeks, and 3/depression on [Ca2+]i transients and cell contraction at 15 weeks, concomitant with in-vivo defects. These [Ca2+]i transient alterations were observed without cellular hypertrophy or AP prolongation and mirrored the sarcoplasmic reticulum (SR) Ca2+ load variations. At the molecular level, this was associated with a decrease in the sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) expression and enhanced RyR2 phosphorylation at the protein kinase A (PKA, pS2808) site (2 and 15 weeks). RyR2 phosphorylation at the Ca2+/calmodulin dependent protein kinase II (CaMKII, pS2814) site was enhanced only at 2 weeks, coinciding with the higher incidence of proarrhythmogenic Ca2+ waves. Our study highlighted, for the first time, the progression of Dox treatment-induced alterations in Ca2+ handling and identified key components of the underlying Dox cardiotoxicity. These findings should be helpful to understand the early-, intermediate-, and late- cardiotoxicity already recorded in clinic in order to prevent or treat at the subclinical level.

FKBP12.6 overexpression protects the cardiac myocyte from β-adrenergic stimulated proarrhythmogenic Ca2+ release in mice cardiomyocytes

FKBP12.6 overexpression protects the cardiac myocyte from β-adrenergic stimulated proarrhythmogenic Ca2+ release in mice cardiomyocytes

β-Adrenergic blockade combined with subcutaneous B-type natriuretic peptide: a promising approach to reduce ventricular arrhythmia in heart failure?

AimsClinical studies failed to prove convincingly efficiency of intravenous infusion of neseritide during heart failure and evidence suggested a pro-adrenergic action of B-type natriuretic peptide (BNP). However, subcutaneous BNP therapy...

Camkii Exacerbates Calcium Waves During Reperfusion of Ischemic Heart

Cardiac dysfunction is associated with an abnormal intracellular Ca2+ cycling, particularly during the setting of ischemia/reperfusion (I/R). Hearts submitted to ischemia suffer an increase in diastolic Ca2+, accompanied with an increase in sarcoplasmic reticulum (SR) Ca2+ load. At the onset of reperfusion there is a massive increase in cytosolic Ca2+, associated with an abrupt release of Ca2+ from the SR (Cardiovasc Res, 2006,2010). In a previous work we showed that arrhythmogenic Ca2+ waves are the subcellular events associated with this SR-Ca2+ release (Circulation, 2013). Moreover, Ca2+/calmodulin-dependent protein kinase II (CaMKII) has been associated with reperfusion arrhythmias, particularly associated with a CaMKII-dependent phosphorylation of Ser2814 site of ryanodine receptors (RyR2) (JMCC,2011). The aim of the present work was to evaluate the role of CaMKII on the abrupt SR-Ca2+ release and enhanced frequency of Ca2+ waves during reperfusion. The experiments were done in perfused mouse (C57BL/6) hearts loaded with the Ca2+ indicator Fluo-4, on an upright confocal microscope. Hearts were submitted to ischemia and reperfusion (15/30 min) at 32°C, in the presence and absence of a CaMKII inhibitor (KN-93, 2.5 μM). We evaluated Ca2+ waves at the epicardial layer of the heart. Inhibition of CaMKII did not prevent the increase in Ca2+ wave frequency (0.15±0.05 pre-ischemia vs. 0.29±0.04 waves/100μm/s, ischemia) nor the velocity of the Ca2+ wave propagation (122.01±4.62 vs. 126.06±1.02 μm/s). During reperfusion in the presence of KN-93, we observed a reduction in Ca2+ waves frequency (0.28±0.06 vs. 0.14±0.02 waves/μm/s, control vs. KN-93), and also in the velocity of its propagation (114.99±3.02 vs. 94.75±1.45 μm/s, control vs. KN-93). The results indicate that the increase in the proarrhythmogenic Ca2+ waves at the onset of reperfusion are mainly mediated by a CaMKII-dependent phosphorylation.

20 Increased activity of mitochondrial complex II in rabbit heart failure is associated with reactive oxygen species generation and impaired excitation-contraction coupling

BackgroundIn heart failure (HF), the increase in cardiac adrenergic tone, while initially beneficial, ultimately contributes to damage to the failing heart. The aim of this study was to evaluate the...