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

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^® 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.

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^® 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^® CMs and 2D monolayers, and predicted pending arrhythmias better than action-potential prolongation.

Taking their ion-current characteristics and Ca²⁺ handling into account, Pluricyte^® 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.