Papers by Eleonora Galimberti
Heart Rhythm, Nov 1, 2011
Compared to the sham mice, the left ventricular volume was enlarged (105.5 Ϯ 4.4 vs 91.6 Ϯ 4.0 L,... more Compared to the sham mice, the left ventricular volume was enlarged (105.5 Ϯ 4.4 vs 91.6 Ϯ 4.0 L, P Ͻ.05), and the ejection fraction was reduced (39.2 Ϯ 1.6% vs 48.7 Ϯ 1.6%, P Ͻ.05) in DOCA mice, showing significant systolic dysfunction. Myocyte NADH level was increased and I Na was decreased (2.8 Ϯ 0.7-fold and 59 Ϯ 8% of sham respectively, P Ͻ.01) in DOCA mice vs sham. Mitochondrial ROS overproduction was observed in DOCA mice (2.9 Ϯ 0.3-fold of sham; P Ͻ.01). Treatment of NAD ϩ or mitoTEMPO, either to myocytes (500 or 10 M) or to mice (100 or 0.7 mg/kg), recovered I Na and decreased ROS in DOCA mice myocytes back to the level of sham. Conclusions: In this nonischemic cardiomyopathy model DOCA mice, NADH and mitochondrial ROS were elevated, and I Na was decreased. Maneuvers that reduced ROS restored I Na. In contradistinction to the prevailing pharmaceutical antiarrhythmic approaches, this work explores the utility of using Na ϩ channel upregulation with NAD ϩ and mitochondrial anti-oxidants as an antiarrhythmic strategy.
Circulation, Nov 22, 2011
Journal of Molecular and Cellular Cardiology, Nov 1, 2011
Background-Ca 2+ waves can trigger ventricular arrhythmias such as catecholaminergicpolymorphic v... more Background-Ca 2+ waves can trigger ventricular arrhythmias such as catecholaminergicpolymorphic ventricular tachycardia (CPVT). Drugs that prevent Ca 2+ waves may have antiarrhythmic properties. Here, we use permeabilized ventricular myocytes from a CPVT mouse model lacking calsequestrin (casq2) to screen all clinically available class I antiarrhythmic drugs and selected other antiarrhythmic agents for activity against Ca 2+ waves. Methods and Results-Casq2−/− myocytes were imaged in line-scan mode and the following Ca 2+ wave parameters analyzed: wave incidence, amplitude, frequency, and propagation speed. IC 50 (potency) and maximum inhibition (efficacy) were calculated for each drug. Drugs fell into 3 distinct categories. Category 1 drugs (flecainide, R-propafenone) suppressed wave parameters with the highest potency (IC 50 < 10 μM) and efficacy (> 50% maximum wave inhibition). Category 2 drugs (encainide, quinidine, lidocaine, verapamil) had intermediate potency (IC 50 20 μ 40 μM) and efficacy (20%-40% maximum wave inhibition). Category 3 drugs (procainamide, disopyramide, mexilitine, cibenzoline, ranolazine) had no significant effects on Ca 2+ waves at the highest concentration tested (100 μM). Propafenone was stereoselective, with R-propafenone suppressing waves more potently than S-propafenone (IC 50 : R-propafenone 2±0.2 μM vs. Spropafenone 54±18 μM). Both flecainide and R-propafenone decreased Ca 2+ spark mass and converted propagated Ca 2+ waves into non-propagated wavelets and frequent sparks, suggesting that reduction in spark mass, not spark frequency, was responsible for wave suppression. Conclusions-Among all class I antiarrhythmic drugs, flecainide and R-propafenone inhibit Ca 2+ waves with the highest potency and efficacy. Permeabilized casq2−/− myocytes are a simple in-vitro assay for finding drugs with activity against Ca 2+ waves.
Biophysical Journal, Feb 1, 2011
2þ ] SR) at rest in rabbit ventricular myocytes. We compared the rate of [Ca 2þ ] SR decline (wit... more 2þ ] SR) at rest in rabbit ventricular myocytes. We compared the rate of [Ca 2þ ] SR decline (with Fluo-5N) after rest from electrical pacing in control conditions and after SERCA inhibition with thapsigargin (TG; 10 mM). We found that the rate of [Ca 2þ ] SR decline increased only~30% after SERCA blockade compared to control conditions (from 10.9 in control to 14.1 mM/s in the presence of TG). Similar results were obtained by measuring the rate of decline of total SR Ca 2þ content, estimated from caffeine-induced Ca 2þ transient amplitude (with Fluo-4). Inhibition of NCX by Ni 2þ (5 mM) or by 0 [Na þ ]/0[Ca 2þ ] solution significantly slowed [Ca 2þ ] SR decline during rest (by 3.4 times), but did not prevent it. Simultaneous inhibition of NCX with 0 [Na þ ]/0[Ca 2þ ] solution and plasmalemmal Ca 2þ ATPase with La 3þ (1 mM) completely prevented [Ca 2þ ] SR decline during rest. These results indicate that in rabbit ventricular myocytes the predominant mechanism for cytosolic Ca 2þ removal during rest is NCX but not SERCA-mediated Ca 2þ uptake. These data are compatible with a model in which the majority of SR Ca 2þ leak occurs through clusters of ryanodine receptors in the junctional SR that closely oppose NCX in the dyadic cleft.
Heart Rhythm, Nov 1, 2014
Obesity Surgery, Nov 10, 2013
Introduction/Purpose-While AF is a disease of the elderly, it can occur earlier in the presence o... more Introduction/Purpose-While AF is a disease of the elderly, it can occur earlier in the presence of risk factors such as obesity. Bariatric surgery patients are significantly younger and more obese than previously described populations with AF. Therefore, it remains to be determined whether current estimates of the prevalence and predictors for AF remain true in the bariatric surgery population. Materials and Methods-We performed a cross-sectional analysis of 1341 consecutive patients who underwent bariatric surgery from 1/2008 to 10/2012. Baseline characteristics were compared between patients with and without AF. For additional comparison, 176 patients with AF and body mass index (BMI) >40 kg/m 2 were identified from the Vanderbilt AF Registry. A multivariable logistic regression was performed to identify predictors of AF within the bariatric surgery cohort. Results-The prevalence of AF in the bariatric surgery cohort was 1.9% (25/1341). Patients with AF were older (median 56 years (Interquartile range [52-64) vs.46 [38-56] years, p<0.001), were more often male (48% vs. 23%, p=0.004), had more comorbidities, but had no difference in BMI (50 kg/m 2 [44-58] vs. 48 [43-54], p=0.4). In multivariable analysis, the odds of AF increased 2.2fold by age per decade (95% CI: 1.4-3.5, p<0.001) and 2.4-fold by male gender (1.1-5.4, p=0.03) when adjusted for BMI. BMI was not independently associated with AF (OR 1.15 [95% CI: 0.98-1.41], p=0.09). Conclusions-The prevalence of AF is 1.9% among patients undergoing bariatric surgery. Risk of AF was found to increase with age and male gender, but not with higher BMI.
Circulation-arrhythmia and Electrophysiology, Oct 1, 2013
A trial fibrillation (AF) is the most common sustained cardiac arrhythmia in adults. The prevalen... more A trial fibrillation (AF) is the most common sustained cardiac arrhythmia in adults. The prevalence of AF rises exponentially with age, and because of the aging population, the number of people with AF in the United States is projected to increase to 12 million by 2050. 1 Importantly, AF confers a 6-fold increased risk for thromboembolic disease including stroke, predisposes to heart failure, and is associated with premature death. 2 The incremental healthcare costs directly related to the diagnosis and management of AF in the United States have been estimated at $6 billion. 3 Clinical Perspective on p 966 Most often, AF occurs within the context of structural heart disease with onset after 65 years of age. However, an estimated 10% to 30% of AF, designated as lone AF, arises in the absence of overt heart disease and has a younger age of onset. 4-7 Genetic predisposition to AF has been demonstrated in populations 8,9 and families with monogenic forms of the disease. 10 AF-associated mutations have been identified in potassium channels, 11-16 sodium channels, 17-19 and other genes. 20 The mutation KCNQ1-S140G was the first identified mutation and remains the best-studied genetic variant associated with autosomal dominant AF. 11,21-23 KCNQ1 encodes a pore-forming voltage-gated potassium channel (Kv7.1 or KCNQ1) that combines with the auxiliary subunit KCNE1 to generate the slow component of the delayed rectifier potassium current (I Ks), critical for cardiac action potential repolarization. Coexpression of KCNQ1-S140G with KCNE1 (S140G-I Ks) demonstrated a gain of function with larger and more instantaneous current activation. 11,23 A similar gain-offunction effect occurs with the AF-associated mutation KCNQ1-V141M. 12 These in vitro data are consistent with the notion that increased repolarizing potassium current evoked by these mutations causes shortening of atrial action potentials in myocytes
Heart Rhythm, Nov 1, 2012
Circulation, Nov 22, 2011
Background- Mutations in the genes that encode either the ryanodine receptors (RyR2) or calseques... more Background- Mutations in the genes that encode either the ryanodine receptors (RyR2) or calsequestrin (casq2) can lead to catecholaminergic-polymorphic ventricular tachycardia (CPVT), a Ca 2+ -triggered arrhythmia. We recently reported that the RyR2 open-channel blockers flecainide (FLEC) and R-propafenone (RPROP) reduce spark mass and prevent Ca 2+ waves in intact myocytes and CPVT in mice lacking calsequestrin (casq2-/-). We hypothesized that by decreasing spark mass FLEC and RPROP lead to a sub-threshold Ca 2+ signal that reduces the likelihood of activating neighboring RyR2, thereby reducing the number of initiation sites and, thus, the generation of Ca 2+ waves. Methods and results- To test this hypothesis, we characterized the initiation sites in an experimental model of Ca 2+ waves - permeabilized casq2-/- myocytes, and compared it against wild-type (WT) cells. We also quantified the effects of FLEC and RPROP on Ca 2+ wave initiation sites in casq2-/- cells. Myocytes were imaged in 2D mode using confocal microscopy. Initiation sites were defined as the sites where the initial burst and fusion of sparks originates a propagated Ca 2+ wave. Under control conditions ([EGTA]=0.05 mM, [Ca 2+ ] t =0.06 mM), casq2-/- myocytes exhibit initiation sites ranged between 1 and 4 (2.3±0.1 (n=21)), localized at the ends as well as on the lateral sides of the cell. The simultaneous activation of various initiation sites determines the confluence of robust Ca 2+ waves that enhances the propagation of the wave along the entire myocyte. In contrast, WT cells depict a significantly smaller number of initiation sites (between 1 and 2 (1.3±0.1 (n=15)). In WT the sites are localized predominantly at one end of the myocyte and their frequency of discharge is ~ 40 % lower compared to casq2-/-. When casq2-/- cells are exposed either FLEC (25 µM) or RPROP (25 µM) the number of initiation sites significantly decreased to approximately 60% of control values (FLEC=1.3±0.1 (n=15), RPROP=1.4±0.1 (n=9), p Conclusion- The data presented here suggest that the decrease in the number of initiation sites is an underlying mechanism responsible for the annihilation of Ca 2+ waves by FLEC or RPROP and, thus, for preventing delayed-after-depolarizations and ventricular arrhythmias.
Circulation, Nov 22, 2011
Background- Myocytes lacking calsequestrin (casq2-/-) exhibit frequent spontaneous RyR2 channel o... more Background- Myocytes lacking calsequestrin (casq2-/-) exhibit frequent spontaneous RyR2 channel openings and Ca2+ waves that can trigger delayed afterdepolarizations and ventricular arrhythmias. We...
Circulation, Nov 20, 2012
Introduction: Mutations in natriuretic peptide precursor A (NPPA) gene, which encodes atrial natr... more Introduction: Mutations in natriuretic peptide precursor A (NPPA) gene, which encodes atrial natriuretic peptide (ANP), have been linked with familial atrial fibrillation (AF). Although the precise...
Circulation, Oct 16, 2007
<jats:p> We tested the hypothesis that sarcoplasmic reticulum (SR) Ca release triggered by ... more <jats:p> We tested the hypothesis that sarcoplasmic reticulum (SR) Ca release triggered by cardiac action potentials is significantly affected by Na influx through brain isoforms of the Na channel. These channels are reportedly located in the t-tubules and could therefore activate reverse Na-Ca exchanger (NCX) and contribute to triggered release. In the complete absence of a Na gradient (Li replacement) Ca transients evoked by action potentials were delayed, their upstrokes slowed and their peak values diminished (SR Ca content not depleted under these conditions). Ca spikes recorded under these conditions occurred at significantly lower probability and became asynchronous (see figure <jats:xref ref-type="fig" /> ). Tetrodotoxin 200 nM (this concentration selectively blocks brain Na channel isoforms Nav 1.1, 1.3 and 1.6) reduced the magnitude and rate of rise of Ca transients in a way that resembled the effect of removing the Na gradient. We suggest that early activation of brain type Na channels leads to elevation of Na in the dyadic cleft. This causes reverse NCX, which primes the junction with Ca before L-type Ca channels (LCC) have opened. Since the junction has been primed with Ca, short LCC openings can effectively gate ryanodine receptors (RyRs). Because these LCC openings have short latencies and occur with high probability they produce spikes with short latencies at high probability. In the absence of a Na gradient longer LCC openings are required to fill the junction and gate RyRs. These occur with lower probability and greater latency. We conclude that brain Na channels together with NCX significantly increase LCC-RyR coupling fidelity and synchronize spikes. </jats:p> <jats:p> <jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" orientation="portrait" position="anchor" xlink:href="zhc141070009396g.jpeg" /> </jats:p>
Circulation, 2013
Introduction: SCN10A encodes the sodium channel isoform Nav1.8, which is variably expressed in at... more Introduction: SCN10A encodes the sodium channel isoform Nav1.8, which is variably expressed in atria and has been linked to altered cardiac conduction and atrial fibrillation (AF). We resequenced S...
Handbook of experimental pharmacology, 2017
The voltage-gated cardiac sodium channel (Nav1.5) is a mega-complex comprised of a pore-forming α... more The voltage-gated cardiac sodium channel (Nav1.5) is a mega-complex comprised of a pore-forming α subunit and 4 ancillary β-subunits together with numerous protein partners. Genetic defects in the form of rare variants in one or more sodium channel-related genes can cause a loss- or gain-of-function of sodium channel current (INa) leading to the manifestation of various disease phenotypes, including Brugada syndrome, long QT syndrome, progressive cardiac conduction disease, sick sinus syndrome, multifocal ectopic Purkinje-related premature contractions, and atrial fibrillation. Some sodium channelopathies have also been shown to be responsible for sudden infant death syndrome (SIDS). Although these genetic defects often present as pure electrical diseases, recent studies point to a contribution of structural abnormalities to the electrocardiographic and arrhythmic manifestation in some cases, such as dilated cardiomyopathy. The same rare variants in SCN5A or related genes may presen...
Circulation, Nov 22, 2011
AJP: Heart and Circulatory Physiology, 2004
Chagasic (Ch) and nonchagasic (NCh) IgG fraction (20 μg/ml) effects on cardiac performance of adu... more Chagasic (Ch) and nonchagasic (NCh) IgG fraction (20 μg/ml) effects on cardiac performance of adult Wistar rat ventricles were studied with a novel approach applying a microcalorimetric technique. Resting heat ( Hr) was significantly decreased by Ch antibodies (Δ HrCh = 4.8 ± 0.9 mW/g). Although the Hr decrease can be associated with diminished activity of the Na+/K+ pump, the magnitude of the effect (25% of control Hr) indicates that additional processes may also be affected. Ch antibodies induced an initial increase in developed pressure (P), which was associated with a decreased contractile economy. However, after 30 min of Ch antibody perfusion, P reached a significantly lower level (ΔPCh = 3.8 ± 1.2 mN/mm2) without changes in active heat per beat ( Ha). Consequently, Ha/P ratio increased, indicating that the energetic cost per unit of P was higher. In contrast, P and Ha were both significantly and reversibly decreased by NCh antibodies (ΔPNCh = 4.4 ± 1.2 mN/mm2; Δ HaNCh = 9.7 ±...
Biophysical Journal, 2010
situ (an SCR) occurs in a synchronized fashion; however, the mechanism responsible for synchroniz... more situ (an SCR) occurs in a synchronized fashion; however, the mechanism responsible for synchronizing SCR activity in coupled myocardium is unknown. Since others have reported that Ca can diffuse through gap junctions (GJ), we hypothesize that uncoupling cells by blocking GJ will desynchronize, and attenuate SCR activity. Methods: To test this hypothesis high resolution optical mapping of Ca (Indo-1AM) from the anterior surface of the Langendorff perfused guinea pig heart (n=5) was performed in hearts under high Ca conditions ([Ca2þ]e=5.5mM), with and without carbonoxolone (CBX, 50mM) to reduce GJ coupling. Endocardial cryoablation were performed to eliminate Purkinje fibers and cytochalasin-D (7mM) was administered to remove motion artifact. Fifteen seconds of rapid pacing (350-160 ms cycle length) followed by a pause was used to induce SCR activity. Results: In all preparations, SCR activity was observed across the entire mapping field before and after CBX. With CBX, the amplitude of SCR activity increased (þ14.8%, p < 0.05) and its time to peak occurred earlier (À11.2%, p < 0.01) compared to no CBX. CBX also decreased the range of local SCR time to peaks across the mapping field (À17.2%, p < 0.05), suggesting that uncoupling myocytes synchronizes spontaneous calcium release across cells. There was no statistical difference in the occurrence of triggered activity before and during CBX. Conclusions: These results demonstrate that the occurrence of spontaneous calcium release in tissue (an SCR) does not require Ca diffusion though GJs. In fact, spontaneous calcium release in tissue is paradoxically enhanced during GJ inhibition.
Circulation, 2015
Introduction: Atrial fibrillation (AF), the most common sustained arrhythmia worldwide, is associ... more Introduction: Atrial fibrillation (AF), the most common sustained arrhythmia worldwide, is associated with increased morbidity and mortality. Obesity is increasingly recognized as an important risk factor to develop AF and heart disease with a diet rich in fats leading to morbid obesity. Melanocortin-4 receptor (MC4R) gene is a critical regulator of energy homeostasis, and homozygous loss-of-function mutations cause hyperphagia and morbid obesity. Hypothesis: We hypothesized that obesity and its comorbidities can create a profibrillatory substrate for AF in high fat diet-induced obese (DIO) and MC4R knock-out (MC4R-KO) mice, and that this substrate can be reversed by weight loss. Methods: Transesophageal rapid pacing was performed using atrial burst pacing (cycle length: 50-15 ms, for 15 s) to determine AF inducibility (% of mice that develop AF) and AF burden (number of AF episodes and total AF duration/mouse) in lightly anesthesized normotensive mice (C57bl6 mice [LEAN], DIO, and ...
PLOS ONE, 2015
<p>A. Representative LS of Ca<sup><b>2+</b></sup> waves in permeabi... more <p>A. Representative LS of Ca<sup><b>2+</b></sup> waves in permeabilized WT myocytes, WT cells sensitized with 150 μM caffeine (WT+CAFF 150μM) and Casq2<sup><b>-/-</b></sup> myocytes under control condition (VEH) and in the presence of FLEC 10 μM. B. CRCs for wave parameters (incidence, amplitude, frequency, and propagation speed) as a function of the concentration of FLEC (in μM) in WT, WT+CAFF 150μM, and Casq2<sup><b>-/-</b></sup> cells. FLEC effect on Ca<sup><b>2+</b></sup> wave parameters is dose-dependent, with a strongest effect on Ca<sup><b>2+</b></sup> waves in Casq2<sup><b>-/-</b></sup> myocytes. FLEC effects on Ca<sup><b>2+</b></sup> waves in WT cells are partially restored by sensitizing the cells with CAFF 150 μM. Mean±SE for each concentration and each parameter. For each group: n = 20 cells, N = 3 mice/condition tested.</p
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Papers by Eleonora Galimberti