Repolarization instability and arrhythmia by I-Kr block in single human-induced pluripotent stem cell-derived cardiomyocytes and 2D monolayers

Aims Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have proven valuable for studies in drug discovery and safety, although limitations regarding their structural and electrophysiological characteristics persist. In this study, we investigated the electrophysiological properties of Pluricyte (R) CMs, a commercially available hiPSC-CMs line with a ventricular phenotype, and assessed arrhythmia incidence by I-Kr block at the single-cell and 2D monolayer level.Methods and results Action potentials were measured at different pacing frequencies, using dynamic clamp. Through voltage-clamp experiments, we determined the properties of I-Na, I-Kr, and I-CaL. Intracellular Ca2+ measurements included Ca2+-transients at baseline and during caffeine perfusion. Effects of I-Kr block were assessed in single hiPSC-CMs and 2D monolayers (multi-electrode arrays). Action-potential duration (APD) and its rate dependence in Pluricyte (R) CMs were comparable to those reported for native human CMs. I-Na, I-Kr, and I-CaL revealed amplitudes, kinetics, and voltage dependence of activation/inactivation similar to other hiPSC-CM lines and, to some extent, to native CMs. Near-physiological Ca2+-induced Ca2+ release, response to caffeine and excitation-contraction coupling gain characterized the cellular Ca2+-handling. Dofetilide prolonged the APD and field-potential duration, and induced early afterdepolarizations. Beat-to-beat variability of repolarization duration increased significantly before the first arrhythmic events in single Pluricyte (R) CMs and 2D monolayers, and predicted pending arrhythmias better than action-potential prolongation.Conclusion Taking their ion-current characteristics and Ca2+ handling into account, Pluricyte (R) CMs are suitable for in vitro studies on action potentials and field potentials. Beat-to-beat variability of repolarization duration proved useful to evaluate the dynamics of repolarization instability and demonstrated its significance as proarrhythmic marker in hiPSC-CMs during I-Kr block.Stem cells & developmental biolog