Inhibition Of Late Sodium Current Research Articles

Discovery of triazolopyridine GS-458967, a late sodium current inhibitor (Late INai) of the cardiac NaV 1.5 channel with improved efficacy and potency relative to ranolazine

We started with a medium throughput screen of heterocyclic compounds without basic amine groups to avoid hERG and β-blocker activity and identified [1,2,4]triazolo[4,3-a]pyridine as an early lead. Optimization of substituents for Late INa current inhibition and lack of Peak INa inhibition led to the discovery of 4h (GS-458967) with improved anti-arrhythmic activity relative to ranolazine. Unfortunately, 4h demonstrated use dependent block across the sodium isoforms including the central and peripheral nervous system isoforms that is consistent with its low therapeutic index (approximately 5-fold in rat, 3-fold in dog). Compound 4h represents our initial foray into a 2nd generation Late INa inhibitor program and is an important proof-of-concept compound. We will provide additional reports on addressing the CNS challenge in a follow-up communication.

Discovery of triazolopyridinone GS-462808, a late sodium current inhibitor (Late INai) of the cardiac Nav1.5 channel with improved efficacy and potency relative to ranolazine

Previously we disclosed the discovery of potent Late INa current inhibitor 2 (GS-458967, IC50 of 333nM) that has a good separation of late versus peak Nav1.5 current, but did not have a favorable CNS safety window due to high brain penetration (3-fold higher partitioning into brain vs plasma) coupled with potent inhibition of brain sodium channel isoforms (Nav1.1, 1.2, 1.3). We increased the polar surface area from 50 to 84Å2 by adding a carbonyl to the core and an oxadiazole ring resulting in 3 GS-462808 that had lower brain penetration and serendipitously lower activity at the brain isoforms. Compound 3 has an improved CNS window (>20 rat and dog) relative to 2, and improved anti-ischemic potency relative to ranolazine. The development of 3 was not pursued due to liver lesions in 7day rat toxicology studies.

Novel Approach Targeting the Complex Pathophysiology of Hypertrophic Cardiomyopathy: The Impact of Late Sodium Current Inhibition on Exercise Capacity in Subjects with Symptomatic Hypertrophic Cardiomyopathy (LIBERTY-HCM) Trial.

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disorder, with an overall prevalence of at least 1:500 in the adult population although only a fraction of affected patients come to clinical recognition. It is also the most common cause of sudden cardiac death in young adults and a major cause of morbidity caused by chronic heart failure symptoms. However, more than half a century since the original description of the disease, there is no currently approved therapy for the treatment of patients with HCM, and to date there have been only 5 randomized studies of medical therapies in HCM. As such, unmet medical need in HCM has been highlighted by the National Heart, Lung, and Blood Institute (NHLBI) as a research priority. Encouragingly, the infrastructure needed to conduct rigorous clinical trials in HCM has recently emerged because of the heightened awareness and understanding of the disease, development of clinical centers of excellence, and advances in diagnostic imaging. In this article, we will discuss the complex pathophysiology of HCM, review the current therapeutic landscape, describe new mechanistic insights into the central role of the late sodium current in HCM, and introduce the scientific rationale and execution of the Impact of Late Sodium Current Inhibition on Exercise Capacity in Subjects with Symptomatic Hypertrophic Cardiomyopathy (LIBERTY-HCM) trial, the largest randomized, double-blind, placebo controlled clinical trial, now underway, designed to evaluate the effect of a novel pharmacological approach in patients with symptomatic HCM. URL: http://www.clinicaltrials.gov. Unique identifier: NCT02291237.

Effect of late sodium current inhibition on MRI measured diastolic dysfunction in aortic stenosis: a pilot study

BackgroundRanolazine is a new anti-anginal drug that acts via late sodium current inhibition, and has been shown to improve diastolic dysfunction in isolated myocytes. Diastolic dysfuntion is common in patients with aortic stenosis (AS), and precedes symptom development and systolic dysfunction. The purpose of this study was to assess the effects of ranolazine on peak early diastolic strain rate (PEDSR) and exercise capacity in patients with AS.MethodsPatients with asymptomatic moderate to severe AS and diastolic dysfunction underwent trans-thoracic echocardiography, exercise testing and cardiac magnetic resonance (CMR) imaging at baseline, 6 weeks after commencing ranolazine and at 10 weeks (4 weeks after discontinuation). Diastolic function was assessed using PEDSR measured on tagged CMR images.ResultsFifteen patients (peak pressure gradient 48.8 ± 12.4 mmHg, mean pressure gradient 27.1 ± 7.5 mmHg, aortic valve area 1.26 ± 0.31 cm2) completed the week-6 visit and 13 completed the final visit. Global PEDSR did not significantly increase from baseline (0.79 ± 0.15) to week-6 (0.86 ± 0.18, p = 0.198). There was a borderline significant increase in total exercise duration from 10.47 ± 3.68 min to 11.60 ± 3.25 min (p = 0.06).ConclusionThis small pilot study did not show a significant improvement in diastolic function with the use of ranolazine in asymptomatic patients with moderate-severe AS. Further studies with a larger population may be indicated.EduraCT number 2011-000111-26Electronic supplementary materialThe online version of this article (doi:10.1186/s13104-016-1874-0) contains supplementary material, which is available to authorized users.

A randomized, placebo-controlled trial of late Na current inhibition (ranolazine) in coronary microvascular dysfunction (CMD): impact on angina and myocardial perfusion reserve.

AimsThe mechanistic basis of the symptoms and signs of myocardial ischaemia in patients without obstructive coronary artery disease (CAD) and evidence of coronary microvascular dysfunction (CMD) is unclear. The aim of this study was to mechanistically test short-term late sodium current inhibition (ranolazine) in such subjects on angina, myocardial perfusion reserve index, and diastolic filling.Materials and resultsRandomized, double-blind, placebo-controlled, crossover, mechanistic trial in subjects with evidence of CMD [invasive coronary reactivity testing or non-invasive cardiac magnetic resonance imaging myocardial perfusion reserve index (MPRI)]. Short-term oral ranolazine 500–1000 mg twice daily for 2 weeks vs. placebo. Angina measured by Seattle Angina Questionnaire (SAQ) and SAQ-7 (co-primaries), diary angina (secondary), stress MPRI, diastolic filling, quality of life (QoL). Of 128 (96% women) subjects, no treatment differences in the outcomes were observed. Peak heart rate was lower during pharmacological stress during ranolazine (−3.55 b.p.m., P < 0.001). The change in SAQ-7 directly correlated with the change in MPRI (correlation 0.25, P = 0.005). The change in MPRI predicted the change in SAQ QoL, adjusted for body mass index (BMI), prior myocardial infarction, and site (P = 0.0032). Low coronary flow reserve (CFR <2.5) subjects improved MPRI (P < 0.0137), SAQ angina frequency (P = 0.027), and SAQ-7 (P = 0.041).ConclusionsIn this mechanistic trial among symptomatic subjects, no obstructive CAD, short-term late sodium current inhibition was not generally effective for SAQ angina. Angina and myocardial perfusion reserve changes were related, supporting the notion that strategies to improve ischaemia should be tested in these subjects.Trial registrationclinicaltrials.gov Identifier: NCT01342029.

The Selective Cardiac Late Sodium Current Inhibitor GS-458967 Suppresses Autonomically Triggered Atrial Fibrillation in an Intact Porcine Model.

The anti-atrial fibrillation (AF) effects of GS-458967 (GS-967), a selective, potent inhibitor of cardiac late Na(+) current (I(Na)), were evaluated in a novel model of AF induction that does not require electrical stimuli. In 6 closed-chest anesthetized pigs, AF was induced by intrapericardial acetylcholine (1 mL of 100 mM solution) followed within 1 minute by epinephrine (20 μg/kg, i.v., bolus over 1 min). Effects of GS-967 (0.4 mg/kg, i.v., infused over 30 min) on inducibility and duration of AF were analyzed. Administration of acetylcholine followed by epinephrine elicited spontaneous AF that persisted for 12.03 ± 1.22 minutes (mean ± SEM) in all 6 pigs. Following GS-967, AF did not occur in 5 of 6 pigs when plasma concentration was 383 ± 150 nM. In the single animal in which AF could still be induced, the arrhythmia lasted 6.3 minutes. Partial return of AF inducibility occurred in 2 of 6 animals at 90 minutes, when plasma concentration of GS-967 was 228 ± 35 nM. GS-967 reduced the QT interval (P = 0.004), consistent with cardiac late I(Na) inhibition, but did not affect heart rate, mean arterial pressure, QRS duration, or PR interval. Epinephrine infusion alone, tested in a separate group (N = 6), did not provoke AF. Selective cardiac late I(Na) inhibition with GS-967 suppresses spontaneous induction of AF in a novel model that does not require provocative electrical stimuli. Because this mode of action has only a mild on effect on contractility, it offers an advantage over contemporary anti-AF agents, which can have negative inotropic actions.

GW26-e4625 Inhibitions of Wenxin Keli on ventricular arrhythmias with various underlying mechanisms

The antiarrhythmic effects of Wenxin Keli, the first state-sanctioned traditional Chinese medicine to treat cardiac arrhythmias, has been attributed to the inhibition of late sodium current. The purpose of this study was to determine the effects of Wenxin Keli on ventricular arrhythmias in rabbit

Effects of ranolazine on exercise capacity, right ventricular indices, and hemodynamic characteristics in pulmonary arterial hypertension: a pilot study.

Ranolazine, a late inward sodium current and fatty acid oxidation inhibitor, may improve right ventricular (RV) function in pulmonary arterial hypertension (PAH); however, the safety and efficacy of ranolazine in humans with PAH is unknown. Therefore, we sought to (1) determine whether ranolazine is safe and well tolerated in PAH and (2) explore ranolazine's effect on symptoms, exercise capacity, RV structure and function, and hemodynamic characteristics. We therefore conducted a 3-month, prospective, open-label pilot study involving patients with symptomatic PAH (n = 11) and echocardiographic evidence of RV dysfunction. We evaluated the safety and tolerability of ranolazine and compared symptoms, exercise capacity, exercise bicycle echocardiographic parameters, and invasive hemodynamic parameters between baseline and 3 months of ranolazine therapy using paired t tests. Of the 11 patients enrolled, one discontinued ranolazine therapy due to a drug-drug interaction after 3 days of therapy. All 10 of the remaining patients continued therapy for 3 months, and 8 (80%) of 10 completed all study tests. After 3 months, ranolazine administration was safe and associated with improvement in functional class (P = 0.0013), reduction in RV size (P = 0.015), improved RV function (improvement in RV strain during exercise at 3 months; P = 0.037), and a trend toward improved exercise time and exercise watts on bicycle echocardiography (P = 0.06 and 0.01, respectively). Ranolazine was not associated with improvement in invasive hemodynamic parameters. In conclusion, in a pilot study involving PAH, ranolazine therapy was safe and well tolerated, and it resulted in improvement in symptoms and echocardiographic parameters of RV structure and function but did not alter invasive hemodynamic parameters. ClinicalTrials.gov Identifier: NCT01174173.

Selective late INa inhibition by GS-458967 exerts parallel suppression of catecholamine-induced hemodynamically significant ventricular tachycardia and T-wave alternans in an intact porcine model

Catecholamines can elicit early and delayed afterdepolarizations (EADs and DADs), resulting in ventricular tachyarrhythmias. As inhibition of the cardiac late sodium current (I(Na)) suppresses EADs and DADs, we examined whether GS-458967 (GS-967), a potent inhibitor of this current that is devoid of beta-adrenergic blocking action, can prevent epinephrine-induced ventricular tachycardia (VT) induction in an intact porcine model. In 12 closed-chest anesthetized pigs, spontaneous VT was induced by epinephrine administration (2.0 µg/kg, intravenous, bolus over 1 minute). Effects of GS-967 (0.4 mg/kg, intravenous, infused over 30 minutes) on VT incidence, T-wave alternans (TWA) level, and hemodynamic and electrophysiologic parameters before and after epinephrine were analyzed (N = 6). Effects of vehicle control were investigated in 6 animals. TWA was measured using the Modified Moving Average method. Epinephrine elicited spontaneous hemodynamically significant nonsustained VT in all 6 pigs and increased TWA by 28-fold compared to baseline (P < .001). GS-967 reduced mean 3- to 7-beat VT incidence by 55% (from 9.5 ± 2.72 to 4.3 ± 0.76 beats/min, P = .020) and ≥8-beat VT incidence by 56% (from 1.6 ± 0.47 to 0.7 ± 0.42 beats/2 min, P = .033) and eliminated the VT-associated hypotension, with no changes in chronotropic and minimal attenuation of the inotropic responses to epinephrine. Concurrently, GS-967 at 30, 60, and 90 minutes reduced the magnitude of the epinephrine-induced surge in TWA by 56% (from 140 ± 13.2 to 62 ± 12.1 µV, P < .01), 62% (to 53 ± 8.3 µV, P < .01), and 51% (to 69 ± 14.0 µV, P < .01) (means ± SEM), respectively. Selective cardiac late INa inhibition with GS-967 confers significant protection against catecholamine-induced VT and TWA.

Effect of Ranolazine Monotherapy on Glycemic Control in Subjects With Type 2 Diabetes.

OBJECTIVERanolazine is an antianginal drug that mediates its effects by inhibition of cardiac late sodium current. Although ranolazine is not approved for the treatment of type 2 diabetes, in post hoc analyses of pivotal angina trials, ranolazine was associated with reductions in percent glycosylated hemoglobin (HbA1c) in subjects with type 2 diabetes. The study prospectively assessed the safety and efficacy of ranolazine in subjects with type 2 diabetes with inadequate glycemic control managed by lifestyle alone.RESEARCH DESIGN AND METHODSThe study was conducted worldwide in 465 subjects, with baseline HbA1c of 7–10% (53–86 mmol/mol) and fasting serum glucose of 130–240 mg/dL, randomized to placebo versus ranolazine.RESULTSCompared with placebo, there was a greater decline in HbA1c at week 24 from baseline (primary end point) in subjects taking ranolazine (mean difference −0.56% [−6.1 mmol/mol]; P < 0.0001). Moreover, the proportion of subjects achieving an HbA1c <7.0% was greater with ranolazine (25.6% vs. 41.2%; P = 0.0004). Ranolazine was associated with reductions in fasting (mean difference −8 mg/dL; P = 0.0266) and 2-h postprandial glucose (mean difference −19 mg/dL; P = 0.0008 vs. placebo). Subjects taking ranolazine trended toward a greater decrease from baseline in fasting insulin (P = 0.0507), a greater decrease in fasting glucagon (P = 0.0003), and a lower postprandial 3-h glucagon area under the curve (P = 0.0031 vs. placebo). Ranolazine was safe and well tolerated.CONCLUSIONSCompared with placebo, use of ranolazine monotherapy over 24 weeks, in subjects with type 2 diabetes and inadequate glycemic control on diet and exercise alone, significantly reduced HbA1c and other measures of glycemic control.

99 Effect of Late Sodium Current Inhibition on MRI Measured Diastolic Dysfunction and Myocardial Perfusion Reserve in Aortic Stenosis: A Pilot Study: Abstract 99 Table 1

Introduction Aortic Stenosis (AS) is characterised by pressure overload left ventricular hypertrophy (LVH) and associated diastolic dysfunction. Important determinants of exercise capacity in AS may include the presence of LVH, diastolic dysfunction and microvascular dysfunction. There are no medical therapies in AS of proven value. Ranolazine is licenced for the treatment of angina. It inhibits late sodium channel activation and has been shown to improve diastolic dysfunction in isolated myocytes. Methods In this prospective, open label pilot study with blinded endpoint analysis, we recruited patients with asymptomatic moderate/severe AS and diastolic dysfunction or LVH. They underwent trans-thoracic echocardiography, exercise testing and adenosine stress cardiac magnetic resonance imaging at baseline, 6 weeks after commencing Ranolazine (maximum dose 750 mg BD) and again at 10 weeks (4 weeks after discontinuation). Tagged images were acquired at three short-axis slices on a 3T platform (Siemens Skyra). Myocardial perfusion reserve was calculated from stress and resting blood flow. The primary hypothesis was that Ranolazine would improve peak early diastolic strain rate (PEDSR) on tagged MRI. Results Fifteen patients (PPG 48.8 ± 12.4 mmHg, MPG 27.1 ± 7.5 mmHg, AVA 1.26 ± 0.31 cm 2 , LV mass index 66.72 ± 15.35 g/m 2 ) completed the week-6 visit and 13 completed the final visit. There was a trend for the global PEDSR to increase from the baseline to week-6 (0.79 ± 0.15 to 0.86 ± 0.18, p = 0.198, n = 15). For those who completed the final visit (n = 13), PEDSR increased from baseline to week-6 and then returned close to the baseline value at week-10 (Table 1). There was no significant change in MPR or echocardiographic measures of diastolic dysfunction. The total exercise duration increased from 10.47 ± 3.68 min to 11.60 ± 3.25 min (n = 15, p = 0.06), with a trend for the maximal HR and SBP to be lower at week-6, resulting in a reduction in exercise LV rate-pressure product (LVRPP), suggesting improved myocardial efficiency. On splitting the patients into low and high-MPR subgroups based on the median MPR, the trend for the improvement in PEDSR (0.88 ± 0.80, 1.03 ± 0. 30, 0.86 ± 0.15) and reduction in exercise LVRPP was maintained in the low-MPR subgroup only. Conclusions This pilot hypothesis-generating study has shown some signals towards Ranolazine improving diastolic function and exercise myocardial efficiency in patients with AS, particularly in those with a lower MPR. The current results would support a larger study in patients with diastolic dysfunction. Funding This study was funded and sponsored by Menarini International Operation, Luxembourg with support from the NIHR Leicester Cardiovascular Biomedical Research Unit (CVBRU).

Antiarrhythmic ionic mechanism of Guanfu base A—Selective inhibition of late sodium current in isolated ventricular myocytes from guinea pigs

The present study was designed to determine the effects of Guanfu base A (GFA) on the late sodium current (INa.L), transient sodium current (INa.T), HERG current (IHERG), and Kv1.5 current (IKv1.5). The values of INa.L, INa.T, IHERG and IKv1.5 were recorded using the whole-cell patch clamp technique. Compared with other channels, GFA showed selective blocking activity in late sodium channel. It inhibited INa.L in a concentration-dependent manner with an IC50 of (1.57 ± 0.14) μmol·L−1, which was significantly lower than its IC50 values of (21.17 ± 4.51) μmol·L−1 for the INa.T. The inhibitory effect of GFA on INa,L was not affected by 200 μmol·L−1 H2O2. It inhibited IHERG with an IC50 of (273 ± 34) μmol·L−1 and has slight blocking effect on IKv1.5, decreasing IKv1.5 by only 20.6% at 200 μmol·L−1. In summary, GFA inhibited INa.L selectively and remained similar inhibition in presence of reactive oxygen species. These findings may suggest a novel molecular mechanism for the potential clinical application of GFA in the treatment of cardiovascular disorders.

SELECTIVE LATE INA INHIBITION BY GS967 EXERTS POTENT SUPPRESSION OF CATECHOLAMINE-INDUCED VENTRICULAR TACHYCARDIA

Catecholamines can elicit early and delayed afterdepolarizations (EADs and DADs), resulting in ventricular tachyarrhythmias. As late sodium current (INa) inhibition suppresses EADs and DADs, we examined whether GS967, a selective inhibitor of late INa that is devoid of beta-adrenergic blocking

Effect of late sodium current inhibition on MRI measured diastolic dysfunction and myocardial perfusion reserve in aortic stenosis: a pilot study

Background Aortic Stenosis (AS) is characterized by pressure overload hypertrophy (LVH) with associated diastolic dysfunction. The presence of LVH, diastolic dysfunction and microvascular dysfunction appear to be important determinants of exercise capacity in AS. There are no medical therapies in AS of proven value. Ranolazine is licenced for the treatment of angina and inhibits late sodium channel activation. Ranolazine has been shown to improve diastolic dysfunction in isolated myocytes. Methods In this prospective, open label study with blinded endpoint analysis, patients with asymptomatic moderate/severe AS and diastolic dysfunction or LVH were recruited. Patients, underwent trans-thoracic echocardiography, exercise testing and adenosine stress cardiac magnetic resonance imaging at baseline, 6 weeks after commencing Ranolazine (maximum dose 750mg BD) and again at 10 weeks (4 weeks after discontinuation). Tagged images were acquired at three short-axis slices on a 3T platform (Siemens Skyra). Myocardial perfusion reserve was calculated from stress and resting blood flow. The primary hypothesis was that Ranolazine would improve peak early diastolic strain rate (PEDSR) on tagged MRI. Results Fifteen patients (PPG 48.8±12.4 mmHg, MPG 27.1±7.5 mmHg, AVA 1.26±0.31 cm 2 , LV mass index 66.72±15.35 g/m 2 ) completed the week-6 visit and 13 completed the final visit. Results are shown in table 1. There was a trend for the global PEDSR to increase from the baseline to week-6 (0.79 ± 0.15 to 0.86 ± 0.18, p=0.198). For those who completed the final visit, PEDSR increased from baseline to week-6 and then returned close to the baseline value at week-10 (table). There was no significant change in MPR or echocardiographic measures of diastolic dysfunction. The total exercise duration increased from 10.47 ±3.68 minutes to 11.60±3.25 minutes (n=15, p=0.06), with a trend for the maximal HR and SBP to be lower at week6, resulting in a reduction in exercise LV rate-pressure product (LVRPP), suggesting improved myocardial efficiency. On splitting the patients into low and high-MPR subgroups based on the median MPR, the trend for the improvement in PEDSR (0.88 ± 0.80, 1.03 ± 0 .30, 0.86 ± 0.15) and reduction in exercise LVRPP was maintained in the low-MPR subgroup only. Conclusions This pilot hypothesis-generating study has shown some signals towards Ranolazine improving diastolic function and exercise myocardial efficiency in patients with AS, particularly in those with a lower MPR. The current results would support a larger study in patients with diastolic dysfunction. Funding

Application of Ranolazine in Stable Angina Pectoris Therapy (ARETHA): Real-World Data from an Observational Study

Objective: Ranolazine, a late sodium current inhibitor, is indicated in adults as add-on therapy for the symptomatic treatment of patients with stable angina pectoris who are inadequately controlled or intolerant to first-line antiischaemic therapies. This study was conducted to assess the use of ranolazine as well as its safety and efficacy in patients with stable angina pectoris from different causes in a real world scenario. Methods: Patients with stable angina pectoris (AP) receiving ranolazine were enrolled in this non-interventional study. Data were documented at baseline and after 3 months of ranolazine treatment. Endpoints included changes in the number of AP attacks per week, frequency of using short-acting nitrates, current status of the CCS classification, overall estimate of quality of life assessed by both, the physician and the patient, and safety. Results: In total, 1,537 patients were eligible for efficacy evaluation. After 3 months, the mean (±SD) number of AP episodes per week significantly decreased from 4.4 ± 4.0 at baseline to 1.1 ± 1.8 (p<0.0001), and the weekly use of short-acting nitrates was significantly reduced from 3.4 ± 3.4 to 0.8 ± 1.5 (p<0.0001). Improvement occurred independent of diagnosed coronary heart disease (CHD). The CCS classification improved in 69.0% of patients and remained stable in 27.1%. Quality of life, assessed on a numerical analogue scale by physicians and patients, improved significantly by 43.7% and 44.9%, respectively (p<0.0001). Safety analysis was based on 2,726 patients. A total of 63 adverse drug reactions (ADRs) occurred in 37 patients (1.4%) and led to discontinuation in 34 patients (1.2%). By the end of the observation period, all ADRs were resolved or resolving. Conclusion: The adjuvant therapy with ranolazine is an effective treatment option with a positive benefit-risk balance for patients with angina pectoris of different causes, e.g. small vessel disease, endothelial dysfunction, including those without prior CHD diagnosis.

ASSA14-03-46 Inhibition of late sodium current reduces the reverse rate dependence of action potential duration prolongation induced by L-type calcium channel activator

Objective Late sodium current (late I Na ) has been confirmed to contribute to the reverse rate dependence (RRD) of action potential duration (APD) prolongation induced by potassium inhibitor. This study is to determine the role of endogenous late sodium current in the induced RRD of APD prolongation in hearts treated with L-type calcium channel activator Bay K 8644. Methods New Zealand White rabbit isolated heart preparations were perfused with modified Krebs-Henseleit solution. Hearts were paced at increasing cycle lengths (CLs) of 400, 500, 667, 1000, 1333 and 2000 ms after atrioventricle (AV) block was introduced by themo-ablation of the AV nodal area. Epicardial monophasic action potential duration at 90% completion of an action potential (epi-MAPD 90 ) from the left ventricular free wall were recorded and measured. Tetrodotoxin (TTX) at the concentration of 1 µmol/L was used to inhibit late I Na selectively. Results At CL of 400 ms, epi-MAPD 90 was 150.5 ± 2.2 ms (n = 12). When the pacing CL was increased to 500, 667, 1000, 1333 and 2000 ms, the epi-MAPD 90 was significantly increased by 10.6 ± 2.9, 27.2 ± 3.0, 39.2 ± 3.8, 48.8 ± 3.5 and 56.6 ± 5.2 ms (n = 12, p 90 at all pacing rates (n = 12, P .01 vs control), and the increase was greater at longer CLs (72.8 ± 6.1 at CL of 2000 ms) than at shorter CLs (16.1 ± 2.4 at CL of 400 ms, p 90 and abolished the ventricular tachycardia. Conclusion Endogenous late sodium current contributes to the enhanced RRD of APD prolongation induced by L-type calcium channel activator.

ASSA14-03-45 Selective late sodium current inhibitor altered atrial electrical conduction but not atrial activation pattern

Objective Rhythm control is an important strategy to treat atrial fibrillation (AF). However, drugs currently used for rhythm control are neither sufficiently safe nor effective. Ranolazine (Ran) and dronedarone (Drone) are new drugs with efficacy to maintain sinus rhythm. Ran, a late sodium current inhibitor, but not Drone, caused no increase in mortality in patients with AF and organic heart disease. The objective of this study was to compare the effect of ranolazine and dronedarone on atrial activation pattern and interatrial conduction. Method Electrogram was recorded from two identical multielectrode recording arrays (48 channels each) placed against the left and right atria of Langendorff-perfused female rabbit isolated hearts. Continuous 5 s recordings were analysed offline. Isochronal maps were drawn from the recording data. Data were analysed with Prism version 5 and expressed as mean ± SEM. To compare values of measurements obtained from the same heart before and after a drug treatment, repeated measures one-way analysis of variance (ANOVA) was used to determine which pairs of group means was significantly different. Results Ran (1–30 μm) significantly prolonged intra-atrial activation conduction time and mean activation time in frequency- and concentration-dependent manners. At the frequency of 3.3 Hz, 4.0 Hz and 5.0 Hz, Ran (1–30 μm) increased left and right intraatrial conduction time by 5.22 ± 0.14, 7.33 ± 0.07, 9.78 ± 0.02 ms, and 6.89 ± 0.09, 8.83 ± 0.23 and 13.06 ± 0.96 ms, respectively. It also prolonged left and right atrial mean activation time by 2.85 ± 0.03, 3.92 ± 0.11, 5.23 ± 0.09 ms and 3.15 ± 0.14, 3.75 ± 0.15, 6.58 ± 0.40 ms, respectively (n = 9, p 0.05). Conclusion Compared with multichannel inhibitor dronedarone, selective late sodium current inhibitor ranolazine has obvious frequency dependence to slow the intra-atrial electrical conduction, which can partially explain the anti-AF mechanism of ranolazine.

Abstract 14727: Late Sodium Current Plays a Role in Ventricular Arrhythmias Associated With Increased Intracellular Calcium Concentration

Objective: An increase in intracellular calcium concentration is associated with the prolongation of action potential duration (APD) and polymorphic ventricular tachycardia (PVT). Recent studies indicated that late sodium current inhibitor is effective in preventing ventricular arrhythmias in patients with long QT syndrome 8. The objective of the study was to determine the role of late sodium current in calcium related ventricular arrhythmias. Methods: Hearts from New Zealand female rabbits were perfused in a Langendorff mode. The atrioventricular nodal area was thermally ablated to produce complete atrioventricular block, and then heart was paced at stated frequency. Multiple channel monophasic action potentials (MAP) and pseudo 12-lead electrocardiograms (ECGs) were recorded. Calcium transient and myocyte contraction were determined in rabbit ventricular myocytes. Results: Bay-K 8644 (10-300 nM) increased both epi- and endo- cardial MAPD90 of left ventricle in concentration dependent manners, from (176±6) to (222±13) ms, and (201±6) to (246±10) ms (n=15, p&lt;0.05 vs control), respectively. In the presence of 1 nM ATX-II, Bay-K 8644 caused a greater prolongation of epi-MAPD90 which was increased from (182±6) to (342±21) ms (n=9, p&lt;0.05 vs control). The prolongation of MAPD90 caused by Bay-K 8644 were reversed by 1 μM TTX in both absence and presence of ATX-II. Additionally, the incidence of PVT evoked by Bay-K 8644 was also greater in the presence compared to the absence of ATX-II. 200 nM Bay-K 8644 caused few arrhythmias in absence of ATX-II. In contrast, PVT occurred in 7/9 (77.78%) of hearts treated with 200 nM Bay-K 8644 in the presence of ATX-II. These arrhythmias could be abolished by 1 μM TTX in the continued presence of Bay-K 8644. TTX (1 μM) attenuated the increase by 200 nM Bay-K 8644 of intracellular calcium transient and myocyte contraction amplitude by 10.8% and 14.6%, respectively (n=6, p&lt;0.05). Conclusion: Both endogenous and enhanced late sodium current contributes to the ventricular arrhythmias with increased intracellular calcium concentration. Inhibition of late sodium current may be effective in preventing or treating calcium overload-related ventricular arrhythmias and dysfunction of myocardial contraction.

Abstract 14019: Electrophysiological Effects of the Late Sodium Current Inhibitor GS967 in Scn5a -1798insD Mouse and Human SCN5A -1795insD iPSC-derived Cardiomyocytes

Background and Aim: Selective inhibition of cardiac late sodium current (I Na,L ) is an emerging target in the treatment of ventricular arrhythmias. The electrophysiological effects of GS967, a potent I Na,L inhibitor, were investigated in an overlap syndrome model of both gain and loss of sodium channel function, comprising cardiomyocytes derived from human SCN5A -1795insD induced pluripotent stem cells (iPSC-CMs) and mice carrying the homologous mutation Scn5a -1798insD. Methods and Results: On patch-clamp analysis, isolated mouse Scn5a -1798insD cardiomyocytes and human SCN5A -1795insD iPSC-CMs showed decreased peak I Na and action potential (AP) upstroke velocity (Vmax) and increased I Na,L and AP duration at 90% repolarization (APD 90 ) as compared to wild-type. GS967 (50-300 nM) significantly decreased APD 90 in mouse Scn5a -1798insD cardiomyocytes by 8±2% (mean±SEM) at 50 nM (n=7), 13±3% at 100 nM (n=11) and 20±5% at 300 nM (n=6) (all p &lt;0.01 vs. control), without affecting Vmax. GS967 (300 nM) selectively inhibited I NaL in mouse Scn5a -1798insD cardiomyocytes (GS967-sensitive current of 0.7±0.1 pA/pF, n=6), but had no effect on peak I Na . Furthermore, GS967 (100 nM) suppressed fast (5 Hz) pacing-induced afterpotentials and triggered activity. In human SCN5A -1795insD iPSC-CMs (n=6), GS967 (300 nM) significantly reduced APD 90 without affecting the resting membrane potential or Vmax. In Langendorff-perfused, isolated mouse Scn5a -1798insD hearts (n=5), GS967 (300 nM) had no effect on ventricular activation time or conduction velocity (as assessed by epicardial mapping). Conclusion: Selective inhibition of I NaL by GS967 attenuated AP prolongation and prevented pro-arrhythmic activity in mouse Scn5a -1798insD cardiomyocytes and human SCN5A-1795insD iPSC-CMs, thus suppressing the gain-of-function features of this overlap syndrome mutation. Importantly, these beneficial actions of GS967 occurred in the absence of deleterious effects on sodium channel availability or cardiac conduction, despite a pre-existing decrease in peak I Na . Thus, selective inhibition of I Na,L constitutes a promising pharmacological treatment of cardiac channelopathies associated with enhanced I NaL , even in overlap syndromes whereby peak I Na is decreased.

Ranolazine Attenuates Hypoxia- and Hydrogen Peroxide-induced Increases in Sodium Channel Late Openings in Ventricular Myocytes

Ranolazine attenuates cardiac arrhythmic activity associated with hypoxia and hydrogen peroxide (H2O2) by inhibition of late sodium current (late INa). The mechanism of ranolazine's action on Na channels was investigated using whole-cell and single-channel recording from guinea pig isolated ventricular myocytes. Hypoxia increased whole-cell late INa from -0.48 ± 0.02 to -3.99 ± 0.07 pA/pF. Ranolazine at 3 and 9 μmol/L reduced the hypoxia-induced late INa by 16% ± 3% and 55% ± 3%, respectively. Hypoxia increased the mean open probability and open time of Na-channel late openings from 0.016 ± 0.001 to 0.064 ± 0.007 milliseconds and from 0.693 ± 0.043 to 1.081 ± 0.098 milliseconds, respectively. Ranolazine at 3 and 9 μmol/L attenuated the hypoxia-induced increase of open probability by 19% ± 7% and 61% ± 1%, and increase of open time by 26% ± 19% and 74 ± 21%, respectively. H2O2 increased the mean open probability and open time of Na-channel late openings from 0.013 ± 0.002 to 0.107 ± 0.015 milliseconds and from 0.689 ± 0.075 to 1.487 ± 0.072 milliseconds, respectively. Ranolazine at 3 and 6 μmol/L reduced the H2O2-induced increase of mean open probability by 60% ± 7% and 95% ± 2%, and the increase of mean open time by 31% ± 21% and 82% ± 8%. In conclusion, the inhibition by ranolazine of hypoxia- and H2O2-stimulated late INa is due to reduction of both the open probability and open time of Na-channel late openings.