Publications (5)29.85 Total impact
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Article: Identification and characterization of a transient outward K(+) current in human induced pluripotent stem cell-derived cardiomyocytes.
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ABSTRACT: BACKGROUND: The ability to recapitulate mature adult phenotypes is critical to development of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) as models of disease. The present study examines the characteristics of the transient outward current (Ito) and its contribution to the hiPSC-CM action potential (AP). METHOD: Embryoid bodies were made from a hiPS cell line reprogrammed with Oct4, Nanog, Lin28 and Sox2. Sharp microelectrodes were used to record APs from beating-clusters (BC) and patch-clamp techniques were used to record Ito in single hiPSC-CM. mRNA levels of Kv1.4, KChIP2 and Kv4.3 were quantified from BCs. RESULTS: BCs exhibited spontaneous beating (60.5±2.6 bpm) and maximum-diastolic-potential (MDP) of 67.8±0.8 mV (n=155). A small 4-aminopyridine-sensitive phase-1-repolarization was observed in only 6/155 BCs. A robust Ito was recorded in the majority of cells (13.7±1.9 pA/pF at +40 mV; n=14). Recovery of Ito from inactivation (at -80 mV) showed slow kinetics (τ1=200±110 ms (12%) and τ2=2380±240 ms (80%)) accounting for its minimal contribution to the AP. Transcript data revealed relatively high expression of Kv1.4 and low expression of KChIP2 compared to human native ventricular tissues. Mathematical modeling predicted that restoration of IK1 to normal levels would result in a more negative MDP and a prominent phase-1-repolarization. CONCLUSION: The slow recovery kinetics of Ito coupled with a depolarized MDP account for the lack of an AP notch in the majority of hiPSC-CM. These characteristics reveal a deficiency for the development of in vitro models of inherited cardiac arrhythmia syndromes in which Ito-induced AP notch is central to the disease phenotype.Journal of Molecular and Cellular Cardiology 03/2013; · 5.17 Impact Factor -
Article: Maximum diastolic potential of human induced pluripotent stem cell-derived cardiomyocytes depends critically on I(Kr).
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ABSTRACT: Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) hold promise for therapeutic applications. To serve these functions, the hiPSC-CM must recapitulate the electrophysiologic properties of native adult cardiomyocytes. This study examines the electrophysiologic characteristics of hiPSC-CM between 11 and 121 days of maturity. Embryoid bodies (EBs) were generated from hiPS cell line reprogrammed with Oct4, Nanog, Lin28 and Sox2. Sharp microelectrodes were used to record action potentials (AP) from spontaneously beating clusters (BC) micro-dissected from the EBs (n = 103; 37°C) and to examine the response to 5 µM E-4031 (n = 21) or BaCl(2) (n = 22). Patch-clamp techniques were used to record I(Kr) and I(K1) from cells enzymatically dissociated from BC (n = 49; 36°C). Spontaneous cycle length (CL) and AP characteristics varied widely among the 103 preparations. E-4031 (5 µM; n = 21) increased Bazett-corrected AP duration from 291.8±81.2 to 426.4±120.2 msec (p<0.001) and generated early afterdepolarizations in 8/21 preparations. In 13/21 BC, E-4031 rapidly depolarized the clusters leading to inexcitability. BaCl(2), at concentrations that selectively block I(K1) (50-100 µM), failed to depolarize the majority of clusters (13/22). Patch-clamp experiments revealed very low or negligible I(K1) in 53% (20/38) of the cells studied, but presence of I(Kr) in all (11/11). Consistent with the electrophysiological data, RT-PCR and immunohistochemistry studies showed relatively poor mRNA and protein expression of I(K1) in the majority of cells, but robust expression of I(Kr.) In contrast to recently reported studies, our data point to major deficiencies of hiPSC-CM, with remarkable diversity of electrophysiologic phenotypes as well as pharmacologic responsiveness among beating clusters and cells up to 121 days post-differentiation (dpd). The vast majority have a maximum diastolic potential that depends critically on I(Kr) due to the absence of I(K1). Thus, efforts should be directed at producing more specialized and mature hiPSC-CM for future therapeutic applications.PLoS ONE 01/2012; 7(7):e40288. · 4.09 Impact Factor -
Article: Cellular basis for the electrocardiographic and arrhythmic manifestations of Timothy syndrome: effects of ranolazine.
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ABSTRACT: Timothy syndrome is a multisystem disorder associated with QT interval prolongation and ventricular cardiac arrhythmias. The syndrome has been linked to mutations in Ca(V)1.2 resulting in gain of function of the L-type calcium current (I(Ca,L)). Ranolazine is an antianginal agent shown to exert an antiarrhythmic effect in experimental models of long QT syndrome. The purpose of this study was to develop and characterize an experimental model of Timothy syndrome by using BayK8644 to mimic the gain of function of I(Ca,L) and to examine the effects of ranolazine. Action potentials from epicardial and M regions and a pseudo-electrocardiogram (ECG) were simultaneously recorded from coronary-perfused left ventricular wedge preparations, before and after addition of BayK8644 (1 microM). BayK8644 preferentially prolonged action potential duration of the M cell, leading to prolongation of the QT interval and an increase in transmural dispersion of repolarization (from 44.3 +/- 7 ms to 86.5 +/- 25 ms). Stimulation at cycle lengths of 250-500 ms led to ST-T wave alternans due to alternation of the plateau voltage of the M cell action potential as well as development of delayed afterdepolarizations in epicardial and M cell action potentials. Ventricular extrasystoles and tachycardia (monomorphic, bidirectional, or torsades de pointes) developed spontaneously or after rapid pacing. Peak and late I(Na) were unaffected by BayK8644. Clinically relevant concentrations of ranolazine (10 microM) suppressed all actions of BayK8644. A left ventricular wedge model of long QT syndrome created by augmentation of I(Ca,L) recapitulates the ECG and arrhythmic manifestations of Timothy syndrome, which can be suppressed by ranolazine.Heart Rhythm 06/2007; 4(5):638-47. · 4.10 Impact Factor -
Article: Electrophysiologic properties and antiarrhythmic actions of a novel antianginal agent.
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ABSTRACT: Ranolazine is a novel antianginal agent capable of producing anti-ischemic effects at plasma concentrations of 2 to 6 microM without a significant reduction of heart rate or blood pressure. This review summarizes the electrophysiologic properties of ranolazine. Ranolazine significantly blocks I(Kr) (IC(50) = 12 microM), late I(Na), late I(Ca), peak I(Ca), I(Na-Ca) (IC(50) = 5.9, 50, 296, and 91 microM, respectively) and I(Ks) (17% at 30 microM), but causes little or no inhibition of I(to) or I(K1). In left ventricular tissue and wedge preparations, ranolazine produces a concentration-dependent prolongation of action potential duration (APD) in epicardium, but abbreviation of APD of M cells, leading to either no change or a reduction in transmural dispersion of repolarization (TDR). The result is a modest prolongation of the QT interval. Prolongation of APD and QT by ranolazine is fundamentally different from that of other drugs that block I(Kr) and induce torsade de pointes in that APD prolongation is rate-independent (ie, does not display reverse rate-dependent prolongation of APD) and is not associated with early after depolarizations, triggered activity, increased spatial dispersion of repolarization, or polymorphic ventricular tachycardia. Torsade de pointes arrhythmias were not observed spontaneously nor could they be induced with programmed electrical stimulation in the presence of ranolazine at concentrations as high as 100 microM. Indeed, ranolazine was found to possess significant antiarrhythmic activity, acting to suppress the arrhythmogenic effects of other QT-prolonging drugs. Ranolazine produces ion channel effects similar to those observed after chronic exposure to amiodarone (reduced late I(Na), I(Kr), I(Ks), and I(Ca)). Ranolazine's actions to reduce TDR and suppress early after depolarization suggest that in addition to its anti-anginal actions, the drug possesses antiarrhythmic activity.Journal of Cardiovascular Pharmacology and Therapeutics 10/2004; 9 Suppl 1:S65-83. · 1.75 Impact Factor -
Article: Ionic and cellular basis for the predominance of the Brugada syndrome phenotype in males.
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ABSTRACT: The Brugada syndrome displays an autosomal dominant mode of transmission with low penetrance. Despite equal genetic transmission of the disease, the clinical phenotype is 8 to 10 times more prevalent in males than in females. The basis for this intriguing sex-related distinction is unknown. The present study tests the hypothesis that the disparity in expression of the Brugada phenotype is a result of a more prominent I(to)-mediated action potential notch in the right ventricular (RV) epicardium of males versus females. We studied epicardial tissue slices, arterially perfused wedge preparations, and dissociated epicardial myocytes isolated from male and female canine hearts. RV epicardium action potential phase 1 amplitude was 64.8+/-2.0% of that of phase 2 in males compared with 73.8+/-4.4% in females (P<0.05) at a cycle length of 2000 ms. I(to) density was 26% smaller and time constant for inactivation 17% smaller at +40 mV in female versus male RV epicardial cells (P<0.05). The other functional characteristics of I(to), including the voltage dependence of inactivation and time course of reactivation, were no different between the sexes. Pinacidil caused loss of action potential dome in male, but not female, RV epicardial tissue slices. Terfenadine (5 micromol/L) induced phase 2 reentry in 6 of 7 male but only 2 of 7 female arterially perfused wedge preparations. Two of 6 male and 1 of 2 female preparations developed polymorphic ventricular tachycardia/ventricular fibrillation. Our results suggest that the predominance of the Brugada phenotype in males is a result of the presence of a more prominent I(to) in males versus females.Circulation 10/2002; 106(15):2004-11. · 14.74 Impact Factor
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2002–2012
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Masonic Medical Research Laboratory
Utica, NY, USA
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