Dog left ventricular midmyocardial myocytes for assessment of drug‐induced delayed repolarization: short‐term variability and proarrhythmic potential

Abstract

Background and purpose: Evaluation of the potential for delayed ventricular repolarization and proarrhythmia by new drugs is essential. We investigated if dog left ventricular midmyocardial myocytes (LVMMs) that can be used as a preclinical model to assess drug effects on action potential duration (APD) and whether in these cells, short-term variability (STV) or triangulation could predict proarrhythmic potential. Experimental approach: Beagle LVMMs and Purkinje fibres (PFs) were used to record APs. Effects of six reference drugs were assessed on APD at 50% (APD50) and 90% (APD90) of repolarization, STV(APD), triangulation (ratio APD90/APD50) and incidence of early afterdepolarizations (EADs) at 1 and 0.5 Hz. Key results: LVMMs provided stable recordings of AP, which were not affected by four sequential additions of dimethyl sulphoxide. Effects of dofetilide, d-sotalol, cisapride, pinacidil and diltiazem, but not of terfenadine, on APD in LVMMs were found to be comparable with those recorded in PFs. LVMMs, but not PFs, exhibited a proarrhythmic response to IKr blockers. Incidence of EADs was not related to differences in AP prolongation or triangulation, but corresponded to beat-to-beat variability of repolarization, here quantified as STV of APD. Conclusions and implications:LVMMs provide a suitable preclinical model to assess the effects of new drugs on APD and also yield additional information about putative indicators of proarrhythmia that add value to an integrated QT/TdP risk assessment. Our findings support the concept that increased STV(APD) may predict drug-induced proarrhythmia.

In vitroModel for Assessing Arrhythmogenic Properties of Drugs Based on High-resolution Impedance Measurements

“…Studies involving the mechanisms underlying these cardiotoxicities revealed that TER blocks the human ether-a-go-go related gene (hERG), which is involved in expression of ion channels (e.g. K [37,38]. Defects in hERG lead to prolongation of the QT interval.…”

Contribution of ion currents to beat-to-beat variability of action potential duration in canine ventricular myocytes

“…In spite of the fact that SV is considered one of the best proarrhythmic predictors [1,11,22] (but see also Michael et al 2007 [17]), its exact ionic mechanism is poorly understood. Involvement of many factors, such as stochastic gating of ion channels [14,18], cell-to-cell coupling [27], action potential duration and morphology [6], stimulation frequency [12] and intracellular calcium handling [13] in modulation of SV have been reported, however, neither their relative contribution, nor the role of the specific cardiac ion currents have been identified in a well defined experimental model.…”

“…Therefore, in absence of relevant human cellular electrophysiological data, canine ventricular myocytes were chosen to analyze experimentally the determinants of SV in the present study due to two reasons. (1) Canine ventricular myocytes are believed to resemble human ventricular cells regarding their action potential morphology and kinetics of the underlying ion currents [19,20]; and (2) a large mass of in vitro and in vivo experimental data on beat-to-beat variability have been obtained in this species [1,12,13,15,22,23]. Here is to be mentioned that all action potentials analyzed in the present study were normally driven ones, records taken in myocytes displaying early or delayed afterdepolarizations were excluded from evaluation.…”

Beat-to-Beat Variability in Field Potential Duration in Human Embryonic Stem Cell-Derived Cardiomyocyte Clusters for Assessment of Arrhythmogenic Risk, and a Case Study of Its Application

“…In this hES-CMC system, we record the field potential duration (FPD)-as QT-like intervals-of clusters treated with a compound; we then calculate the corrected FPD (FPDc) and examine whether or not the compound prolongs FPDc. However, there have been reports that the QT interval is not a good surrogate marker of TdP and ventricular fibrillation [9][10][11][12][13][14][15][16][17][18]; the beat-to-beat variability of QT or QTc is suggested to be a better parameter [14,15]. It would therefore be of interest to investigate whether short-term variability in FPDc (STV FPDc ), as beat-to-beat variability, is increased along with FPDc prolongation in hES-CMCs treated with torsadogenic agents.…”