Late Sodium Current Research Articles

Aging-associated susceptibility to stress-induced ventricular arrhythmogenesis is attenuated by tetrodotoxin

Aging is associated with increased prevalence of life-threatening ventricular arrhythmias, but mechanisms underlying higher susceptibility to arrhythmogenesis and means to prevent such arrhythmias under stress are not fully defined. We aimed to define differences in aging-associated susceptibility to ventricular fibrillation (VF) induction between young and aged hearts. VF induction was attempted in isolated perfused hearts of young (6-month) and aged (24-month-old) male Fischer-344 rats by rapid pacing before and following isoproterenol (1 μM) or global ischemia and reperfusion (I/R) injury with or without pretreatment with low-dose tetrodotoxin, a late sodium current blocker. At baseline, VF could not be induced; however, the susceptibility to inducible VF after isoproterenol and spontaneous VF following I/R was 6-fold and 3-fold higher, respectively, in old hearts (P < 0.05). Old animals had longer epicardial monophasic action potential at 90% repolarization (APD90; P < 0.05) and displayed a loss of isoproterenol-induced shortening of APD90 present in the young. In isolated ventricular cardiomyocytes from older but not younger animals, 4-aminopyridine prolonged APD and induced early afterdepolarizations (EADs) and triggered activity with isoproterenol. Low-dose tetrodotoxin (0.5 μM) significantly shortened APD without altering action potential upstroke and prevented 4-aminopyridine-mediated APD prolongation, EADs, and triggered activity. Tetrodotoxin pretreatment prevented VF induction by pacing in isoproterenol-challenged hearts. Vulnerability to VF following I/R or catecholamine challenge is significantly increased in old hearts that display reduced repolarization reserve and increased propensity to EADs, triggered activity, and ventricular arrhythmogenesis that can be suppressed by low-dose tetrodotoxin, suggesting a role of slow sodium current in promoting arrhythmogenesis with aging.

Moricizine prevents atrial fibrillation by late sodium current inhibition in atrial myocytes.

BackgroundEnhanced late sodium current (INaL) is reportedly related to an increased risk of atrial fibrillation (AF). Moricizine, as a widely used anti-arrhythmia drug for suppressing ventricular tachycardia, has also been shown to prevent paroxysmal AF. However, the mechanism of its therapeutic effect remains poorly understood.MethodsAngiotensin II (Ang II) was induced in C57Bl/6 mice (male wild-type) for 4 weeks to increase the susceptibility of AF, and acetylcholine-calcium chloride was used to induce AF. The whole-cell patch-clamp technique was used to detect INaL from isolated atrial myocytes. The expression of proteins in atrial of mice and HL-1 cells were examined by Western-blot.ResultsThe results showed that moricizine significantly inhibited Ang II-mediated atrial enlargement and reduced AF vulnerability. We found that the densities of INaL were enhanced in Ang II-treated left and right atrial cardiomyocytes. Simultaneously, the Ang II-induced increase in INaL currents density was alleviated by the administration of moricizine, and no alteration in Nav1.5 expression was observed. In normal isolated atrial myocytes, moricizine significantly reduced Sea anemone toxin II (ATX II)-enhanced INaL density with a reduction of peak sodium currents. In addition, moricizine reduced the Ang II-induced upregulation of phosphorylated calcium/calmodulin-dependent protein kinase-II (p-CaMKII) in both the left and right atria. In HL-1 cells, moricizine also reduced the upregulation of p-CaMKII with Ang II and ATX II intervention, respectively.ConclusionsOur results indicate that Ang II enhances the INaL via activation of CaMKII. Moricizine inhibits INaL and reduces CaMKII activation, which may be one of the mechanisms of moricizine suppression of AF.

Neonatal Scn1b-null mice have sinoatrial node dysfunction, altered atrial structure, and atrial fibrillation.

Loss-of-function (LOF) variants in SCN1B, encoding the voltage-gated sodium channel β1/β1B subunits, are linked to neurological and cardiovascular diseases. Scn1b-null mice have spontaneous seizures and ventricular arrhythmias and die by approximately 21 days after birth. β1/β1B Subunits play critical roles in regulating the excitability of ventricular cardiomyocytes and maintaining ventricular rhythmicity. However, whether they also regulate atrial excitability is unknown. We used neonatal Scn1b-null mice to model the effects of SCN1B LOF on atrial physiology in pediatric patients. Scn1b deletion resulted in altered expression of genes associated with atrial dysfunction. Scn1b-null hearts had a significant accumulation of atrial collagen, increased susceptibility to pacing induced atrial fibrillation (AF), sinoatrial node (SAN) dysfunction, and increased numbers of cholinergic neurons in ganglia that innervate the SAN. Atropine reduced the incidence of AF in null animals. Action potential duration was prolonged in null atrial myocytes, with increased late sodium current density and reduced L-type calcium current density. Scn1b LOF results in altered atrial structure and AF, demonstrating the critical role played by Scn1b in atrial physiology during early postnatal mouse development. Our results suggest that SCN1B LOF variants may significantly impact the developing pediatric heart.

Differential sodium current remodelling in human left atrial appendage cardiomyocytes in paroxysmal and persistent atrial fibrillation

Abstract Funding Acknowledgements Type of funding sources: None. Background Atrial fibrillation (AF) is characterized by complex electrical, structural and metabolic remodelling. The mechanisms underlying AF progression from paroxysmal to persistent AF are not fully understood, and studies in cardiomyocytes (CMs) at the paroxysmal stage of AF are lacking. Moreover, most studies have so far investigated right atrial appendage CMs, while left atrial appendage (LAA) CMs may be more informative, as AF is predominantly a left atrial disease. Whether and to what extent electrical remodelling during various AF stages also includes alterations of the (late) sodium current (INa), remains unclear. Moreover, the functional relevance of sodium channel isoforms other than the cardiac Nav1.5, such as the "neuronal" isoform SCN10A/NaV1.8, during the various stages of AF is as yet not fully elucidated. Purpose To investigate peak and late INa remodelling in LAA CMs from patients with paroxysmal and persistent AF and patients in sinus rhythm (SR), as well as the potential contribution of NaV1.8-based current. Methods LAA were obtained from patients in SR (N=18) without a history of AF undergoing cardiac surgery, as well as from patients with paroxysmal (N=12) and persistent AF (N=30). Paroxysmal AF was defined as AF episodes terminating spontaneously within seven days and persistent as AF continuing for more than 7 days but less than 1 year. Peak INa, late INa and action potential (AP) properties were investigated through patch-clamp analysis on single LAA CMs, while qPCR was used to assess SCN5A and SCN10A expression levels in LAA tissue. Results In paroxysmal and persistent AF CMs, AP duration was shorter than in SR CMs. Compared to SR, peak INa (Figure 1A) and SCN5A expression (Figure 1B) were significantly decreased in paroxysmal AF, while they were restored to SR levels in persistent AF. Conversely, while late INa was undetectable in SR and paroxysmal AF, it was significantly increased in persistent AF (Figure 2). Peak and late INa Nav1.8-based current was not detected in persistent AF CMs. Similarly, expression of SCN10A was not observed in LAAs at any stage. Conclusions Our study is the first to show that AP shortening already occurs in LAA CMs from paroxysmal AF, potentially contributing to pro-arrhythmia in this early stage of the disease. Moreover, our findings demonstrate that INa is differentially remodelled during various stages of AF, with peak INa reduction occurring during paroxysmal AF, while late INa is increased in persistent AF only. Finally, we have shown that Nav1.8 current does not contribute to the AF-related alterations in INa. These observations are of particular relevance when considering potential pharmacological approaches targeting (late) INa in patients with distinct forms of AF.

Leveraging FHF modulation to inhibit arrhythmogenic late sodium current.

Leveraging FHF modulation to inhibit arrhythmogenic late sodium current.

Fibroblast growth factor homologous factors serve as a molecular rheostat in tuning arrhythmogenic cardiac late sodium current.

Voltage-gated sodium (Nav1.5) channels support the genesis and brisk spatial propagation of action potentials in the heart. Disruption of NaV1.5 inactivation results in a small persistent Na influx known as late Na current (I Na,L), which has emerged as a common pathogenic mechanism in both congenital and acquired cardiac arrhythmogenic syndromes. Here, using low-noise multi-channel recordings in heterologous systems, LQTS3 patient-derived iPSCs cardiomyocytes, and mouse ventricular myocytes, we demonstrate that the intracellular fibroblast growth factor homologous factors (FHF1-4) tune pathogenic I Na,L in an isoform-specific manner. This scheme suggests a complex orchestration of I Na,L in cardiomyocytes that may contribute to variable disease expressivity of NaV1.5 channelopathies. We further leverage these observations to engineer a peptide-inhibitor of I Na,L with a higher efficacy as compared to a well-established small-molecule inhibitor. Overall, these findings lend insights into molecular mechanisms underlying FHF regulation of I Na,L in pathophysiology and outline potential therapeutic avenues.

PO-614-08 SODIUM CHANNEL NAV1.6 AND NA-CA EXCHANGER REMODELING CONTRIBUTES TO ARRHYTHMOGENIC LATE SODIUM CURRENT AND CA2+ SPARKS IN THE PRESENCE OF D96V MUTANT CALMODULIN

Calmodulin (CaM) facilitates sodium channel (NaV) inactivation, thereby preventing proarrhythmic late sodium current (INa). To date, a link between arrhythmogenic mutations in CaM and NaV dysfunction is not well established. Outside of NaV1.5, dysfunctional inactivation of Nav1.6 promotes late INa-mediated arrhythmias.

Late sodium current: incomplete inactivation triggers seizures, myotonias, arrhythmias, and pain syndromes.

Acquired and inherited dysfunction in voltage-gated sodium channels underlies a wide range of diseases. In addition to defects in trafficking and expression, sodium channelopathies are caused by dysfunction in one or several gating properties, for instance activation or inactivation. Disruption of channel inactivation leads to increased late sodium current, which is a common defect in seizure disorders, cardiac arrhythmias skeletal muscle myotonia and pain. An increase in late sodium current leads to repetitive action potentials in neurons and skeletal muscles, and prolonged action potential duration in the heart. In this Topical Review, we compare the effects of late sodium current in brain, heart, skeletal muscle and peripheral nerves.

Declining Levels and Bioavailability of IGF-I in Cardiovascular Aging Associate With QT Prolongation-Results From the 1946 British Birth Cohort.

BackgroundAs people age, circulating levels of insulin-like growth factors (IGFs) and IGF binding protein 3 (IGFBP-3) decline. In rat cardiomyocytes, IGF-I has been shown to regulate sarcolemmal potassium channel activity and late sodium current thus impacting cardiac repolarization and the heart rate-corrected QT (QTc). However, the relationship between IGFs and IGFBP-3 with the QTc interval in humans, is unknown.ObjectivesTo examine the association of IGFs and IGFBP-3 with QTc interval in an older age population-based cohort.MethodsParticipants were from the 1946 Medical Research Council (MRC) National Survey of Health and Development (NSHD) British birth cohort. Biomarkers from blood samples at age 53 and 60–64 years (y, exposures) included IGF-I/II, IGFBP-3, IGF-I/IGFBP-3 ratio and the change (Δ) in marker levels between the 60–64 and 53y sampled timepoints. QTc (outcome) was recorded from electrocardiograms at the 60–64y timepoint. Generalized linear multivariable models with adjustments for relevant demographic and clinical factors, were used for complete-cases and repeated after multiple imputation.ResultsOne thousand four hundred forty-eight participants were included (48.3% men; QTc mean 414 ms interquartile range 26 ms). Univariate analysis revealed an association between low IGF-I and IGF-I/IGFBP-3 ratio at 60–64y with QTc prolongation [respectively: β −0.30 ms/nmol/L, (95% confidence intervals −0.44, −0.17), p < 0.001; β−28.9 ms/unit (-41.93, −15.50), p < 0.001], but not with IGF-II or IGFBP-3. No association with QTc was found for IGF biomarkers sampled at 53y, however both ΔIGF-I and ΔIGF-I/IGFBP-3 ratio were negatively associated with QTc [β −0.04 ms/nmol/L (−0.08, −0.008), p = 0.019; β −2.44 ms/unit (-4.17, −0.67), p = 0.007] while ΔIGF-II and ΔIGFBP-3 showed no association. In fully adjusted complete case and imputed models (reporting latter) low IGF-I and IGF-I/IGFBP-3 ratio at 60–64y [β −0.21 ms/nmol/L (−0.39, −0.04), p = 0.017; β −20.14 ms/unit (−36.28, −3.99), p = 0.015], steeper decline in ΔIGF-I [β −0.05 ms/nmol/L/10 years (−0.10, −0.002), p = 0.042] and shallower rise in ΔIGF-I/IGFBP-3 ratio over a decade [β −2.16 ms/unit/10 years (−4.23, −0.09), p = 0.041], were all independently associated with QTc prolongation. Independent associations with QTc were also confirmed for other previously known covariates: female sex [β 9.65 ms (6.65, 12.65), p < 0.001], increased left ventricular mass [β 0.04 ms/g (0.02, 0.06), p < 0.001] and blood potassium levels [β −5.70 ms/mmol/L (−10.23, −1.18) p = 0.014].ConclusionOver a decade, in an older age population-based cohort, declining levels and bioavailability of IGF-I associate with prolongation of the QTc interval. As QTc prolongation associates with increased risk for sudden death even in apparently healthy people, further research into the antiarrhythmic effects of IGF-I on cardiomyocytes is warranted.

Antiarrhythmic Effects of Vernakalant in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes from a Patient with Short QT Syndrome Type 1.

(1) Background: Short QT syndrome (SQTS) may result in sudden cardiac death. So far, no drugs, except quinidine, have been demonstrated to be effective in some patients with SQTS type 1 (SQTS1). This study was designed to examine the potential effectiveness of vernakalant for treating SQTS1 patients, using human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from a patient with SQTS1. (2) Methods: Patch clamp and calcium imaging techniques were used to examine the drug effects. (3) Results: Vernakalant prolonged the action potential duration (APD) in hiPSC-CMs from a SQTS1-patient (SQTS1-hiPSC-CMs). In spontaneously beating SQTS1-hiPSC-CMs, vernakalant reduced the arrhythmia-like events induced by carbachol plus epinephrine. Vernakalant failed to suppress the hERG channel currents but reduced the outward small-conductance calcium-activated potassium channel current. In addition, it enhanced Na/Ca exchanger currents and late sodium currents, in agreement with its APD-prolonging effect. (4) Conclusions: The results demonstrated that vernakalant can prolong APD and reduce arrhythmia-like events in SQTS1-hiPSC-CMs and may be a candidate drug for treating arrhythmias in SQTS1-patients.

Caveolin-3 and Arrhythmias: Insights into the Molecular Mechanisms.

Caveolin-3 is a muscle-specific protein on the membrane of myocytes correlated with a variety of cardiovascular diseases. It is now clear that the caveolin-3 plays a critical role in the cardiovascular system and a significant role in cardiac protective signaling. Mutations in the gene encoding caveolin-3 cause a broad spectrum of clinical phenotypes, ranging from persistent elevations in the serum levels of creatine kinase in asymptomatic humans to cardiomyopathy. The influence of Caveolin-3(CAV-3) mutations on current density parallels the effect on channel trafficking. For example, mutations in the CAV-3 gene promote ventricular arrhythmogenesis in long QT syndrome 9 by a combined decrease in the loss of the inward rectifier current (IK1) and gain of the late sodium current (INa-L). The functional significance of the caveolin-3 has proved that caveolin-3 overexpression or knockdown contributes to the occurrence and development of arrhythmias. Caveolin-3 overexpression could lead to reduced diastolic spontaneous Ca2+ waves, thus leading to the abnormal L-Type calcium channel current-induced ventricular arrhythmias. Moreover, CAV-3 knockdown resulted in a shift to more negative values in the hyperpolarization-activated cyclic nucleotide channel 4 current (IHCN4) activation curve and a significant decrease in IHCN4 whole-cell current density. Recent evidence indicates that caveolin-3 plays a significant role in adipose tissue and is related to obesity development. The role of caveolin-3 in glucose homeostasis has attracted increasing attention. This review highlights the underlining mechanisms of caveolin-3 in arrhythmia. Progress in this field may contribute to novel therapeutic approaches for patients prone to developing arrhythmia.

The insecticide β-Cyfluthrin induces acute arrhythmic cardiotoxicity through interaction with NaV1.5 and ranolazine reverses the phenotype.

β-Cyfluthrin, a class II Pyrethroid, is an insecticide used worldwide in agriculture, horticulture (field and protected crops), viticulture, and domestic applications. β-Cyfluthrin may impair the function of biological systems; however, little information is available about its potential cardiotoxic effect. Here, we explored the acute toxicity of β-Cyfluthrin in isolated heart preparations and its cellular basis, using isolated cardiomyocytes. Moreover, β-Cyfluthrin effects on the sodium current, especially late sodium current (INa-L), were investigated using human embryonic kidney cells (HEK-293) cells transiently expressing human NaV1.5 channels. We report that β-Cyfluthrin raised INa-L in a dose-dependent manner. β-Cyfluthrin prolonged the repolarization of the action potential (AP) and triggered oscillations on its duration. Cardiomyocytes contraction and calcium dynamics were disrupted by the pesticide with a marked incidence of non-electronic-stimulated contractions. The antiarrhythmic drug Ranolazine was able to reverse most of the phenotypes observed in isolated cells. Lastly, ventricular premature beats (VPBs) and long QT intervals were found during β-Cyfluthrin exposure, and Ranolazine was able to attenuate them. Overall, we demonstrated that β-Cyfluthrin can cause significant cardiac alterations and Ranolazine ameliorated the phenotype. Understanding the insecticides' impacts upon electromechanical properties of the heart is important for the development of therapeutic approaches to treat cases of pesticides intoxication.

Late Sodium Current of the Heart: Where Do We Stand and Where Are We Going?

Late sodium current has long been linked to dysrhythmia and contractile malfunction in the heart. Despite the increasing body of accumulating information on the subject, our understanding of its role in normal or pathologic states is not complete. Even though the role of late sodium current in shaping action potential under physiologic circumstances is debated, it’s unquestioned role in arrhythmogenesis keeps it in the focus of research. Transgenic mouse models and isoform-specific pharmacological tools have proved useful in understanding the mechanism of late sodium current in health and disease. This review will outline the mechanism and function of cardiac late sodium current with special focus on the recent advances of the area.

A carvedilol analogue, VK-II-86, prevents hypokalaemia-induced ventricular arrhythmia through novel multi-channel effects.

QT prolongation and intracellular Ca2+ loading with diastolic Ca2+ release via ryanodine receptors (RyR2) are the predominant mechanisms underlying hypokalaemia-induced ventricular arrhythmia. We investigated the antiarrhythmic actions of two RyR2 inhibitors: dantrolene and VK-II-86, a carvedilol analogue lacking antagonist activity at β-adrenoceptors, in hypokalaemia. Surface ECG and ventricular action potentials (APs) were recorded from whole-heart murine Langendorff preparations. Ventricular arrhythmia incidence was compared in hearts perfused with low [K+ ], and those pretreated with dantrolene or VK-II-86. Whole-cell patch clamping was used in murine and canine ventricular cardiomyocytes to study effects of dantrolene and VK-II-86 on AP parameters in low [K+ ] and effects of VK-II-86 on the inward rectifier current (IK1 ), late sodium current (INa_L ) and the L-type Ca2+ current (ICa ). Effects of VK-II-86 on IKr were investigated in transfected HEK-293 cells. A fluorogenic probe quantified the effects of VK-II-86 on oxidative stress in hypokalaemia. Dantrolene reduced the incidence of ventricular arrhythmias induced by low [K+ ] in explanted murine hearts by 94%, whereas VK-II-86 prevented all arrhythmias. VK-II-86 prevented hypokalaemia-induced AP prolongation and depolarization but did not alter AP parameters in normokalaemia. Hypokalaemia was associated with decreased IK1 and IKr , and increased INa-L , and ICa . VK-II-86 prevented all hypokalaemia-induced changes in ion channel activity and oxidative stress. VK-II-86 prevents hypokalaemia-induced arrhythmogenesis by normalizing calcium homeostasis and repolarization reserve. VK-II-86 may provide an effective treatment in hypokalaemia and other arrhythmias caused by delayed repolarization or Ca2+ overload.

Pathologically increased RyR2-Nav1.6 colocalization in db/db mouse model of diabetic cardiomyopathy

Diabetes affects more than 6% of the world population and can lead to diabetic cardiomyopathy (DCM), a condition characterized by left ventricular hypertrophy, heart failure (HF), and eventual sudden cardiac death. Linking structural remodeling with phenotype progression in DCM will enable early diagnosis and treatment, which is key for patient longevity. Previous studies have linked pathological increases in late sodium current, mediated by voltage-gated sodium channel subtype 1.6 (NaV1.6) localized near ryanodine receptor (RyR2) calcium release channels and sodium-calcium exchangers, to arrhythmogenic calcium release events in multiple cardiac disorders.

Arrhythmogenic calmodulin mutant D96V induces unexpected remodeling of cardiac nanostructure

Calmodulin facilitates normal sodium channel (NaV) inactivation that prevents proarrhythmic late sodium current (INa). NaV1.6 dysfunction has been implicated in late INa-mediated arrhythmias. Therefore we investigated NaV dysregulation by arrhythmogenic CaM mutant D96V. Chinese hamster ovary cells expressing NaV1.6 were transfected with either WT- or D96V-CaM. Superresolution STED microscopy revealed enlarged NaV1.6 clusters in cells transfected with D96V-CaM relative to WT. Therefore we explored NaV1.6 remodeling in transgenic mice with cardiac-specific expression of D96V-CaM (cD96V) with FLAG-tagged C-terminus.

The NaV1.5 accessory subunit FGF12A inhibits pro-arrhythmic late sodium current

The voltage-gated cardiac sodium channel (NaV1.5) initiates the myocyte action potential and determines conduction velocity across the myocardium. NaV1.5 dysfunction can lead to life-threatening cardiac arrhythmias. NaV1.5 is regulated by multiple accessory subunits including intracellular fibroblast growth factor (iFGF), a subfamily of FGFs comprising of FGF11-14. In human heart, the most abundant iFGF isoform is FGF12B. FGF12 gene encodes 2 variants, FGF12A and FGF12B that differ in N-terminal sequences.

Common Ancestry-Specific Ion Channel Variants Predispose to Drug-Induced Arrhythmias.

Multiple reports associate the cardiac sodium channel gene (SCN5A) variants S1103Y and R1193Q with type 3 congenital long QT syndrome and drug-induced long QT syndrome. These variants are too common in ancestral populations to be highly arrhythmogenic at baseline, however: S1103Y allele frequency is 8.1% in African Americans and R1193Q 6.1% in East Asians. R1193Q is known to increase late sodium current (INa-L) in cardiomyocytes derived from induced pluripotent stem cells but the role of these variants in modulating repolarization remains poorly understood. We determined the effect of S1103Y on QT intervals among African-American participants in a large electronic health record. Using cardiomyocytes derived from induced pluripotent stem cells carrying naturally occurring or genome-edited variants, we studied action potential durations (APDs) at baseline and after challenge with the repolarizing potassium current (IKr) blocker dofetilide and INa-L and IKr at baseline. In 1479 African-American participants with no confounding medications or diagnoses of heart disease, QT intervals in S1103Y carriers was no different from that in noncarriers. Baseline APD was no different in cells expressing the Y allele (SY, YY cells) compared with isogenic cells with the reference allele (SS cells). However, INa-L was increased in SY and YY cells and the INa-L blocker GS967 shortened APD in SY/YY but not SS cells (P<0.001). IKr was increased almost 2-fold in SY/YY cells compared with SS cells (tail current: 0.66±0.1 versus 1.2±0.1 pA/pF; P<0.001). Dofetilide challenge prolonged APD at much lower concentrations in SY (4.1 nmol/L [interquartile range, 1.5-9.3]; n=11) and YY (4.2 nmol/L [1.7-5.0]; n=5) than in SS cells (249 nmol/L [22.3-2905]; n=14; P<0.001 and P<0.01, respectively) and elicited afterdepolarizations in 8/16 SY/YY cells but only in 1/14 SS cells. R1193Q cells similarly displayed no difference in baseline APD but increased IKr and increased dofetilide sensitivity. These common ancestry-specific variants do not affect baseline repolarization, despite generating increased INa-L. We propose that increased IKr serves to maintain normal repolarization but increases the risk of manifest QT prolongation with IKr block in variant carriers. Our findings emphasize the need for inclusion of diverse populations in the study of adverse drug reactions.

Stress-induced premature senescence is associated with a prolonged QT interval and recapitulates features of cardiac aging.

Rationale: Aging in the heart is a gradual process, involving continuous changes in cardiovascular cells, including cardiomyocytes (CMs), namely cellular senescence. These changes finally lead to adverse organ remodeling and resulting in heart failure. This study exploits CMs from human induced pluripotent stem cells (iCMs) as a tool to model and characterize mechanisms involved in aging.Methods and Results: Human somatic cells were reprogrammed into human induced pluripotent stem cells and subsequently differentiated in iCMs. A senescent-like phenotype (SenCMs) was induced by short exposure (3 hours) to doxorubicin (Dox) at the sub-lethal concentration of 0.2 µM. Dox treatment induced expression of cyclin-dependent kinase inhibitors p21 and p16, and increased positivity to senescence-associated beta-galactosidase when compared to untreated iCMs. SenCMs showed increased oxidative stress, alteration in mitochondrial morphology and depolarized mitochondrial membrane potential, which resulted in decreased ATP production. Functionally, when compared to iCMs, SenCMs showed, prolonged multicellular QTc and single cell APD, with increased APD variability and delayed afterdepolarizations (DADs) incidence, two well-known arrhythmogenic indexes. These effects were largely ascribable to augmented late sodium current (INaL) and reduced delayed rectifier potassium current (Ikr). Moreover sarcoplasmic reticulum (SR) Ca2+ content was reduced because of downregulated SERCA2 and increased RyR2-mediated Ca2+ leak. Electrical and intracellular Ca2+ alterations were mostly justified by increased CaMKII activity in SenCMs. Finally, SenCMs phenotype was furtherly confirmed by analyzing physiological aging in CMs isolated from old mice in comparison to young ones.Conclusions: Overall, we showed that SenCMs recapitulate the phenotype of aged primary CMs in terms of senescence markers, electrical and Ca2+ handling properties and metabolic features. Thus, Dox-induced SenCMs can be considered a novel in vitro platform to study aging mechanisms and to envision cardiac specific anti-aging approach in humans.

NCC-3902, a novel late sodium current blocker, exhibits potent antiarrhythmic effect in isolated guinea pig pulmonary vein and canine rapid atrial pacing model

NCC-3902, a novel late sodium current blocker, exhibits potent antiarrhythmic effect in isolated guinea pig pulmonary vein and canine rapid atrial pacing model