Computational Study of the Excitation of Human Induced Pluripotent Stem-Cell Derived Cardiomyocytes

Human induced pluripotent stem-cell derived cardiomyocytes (hiPSC-CMs) have proven to be a revolutionary advance for tissue engineering, disease modeling, and drug testing and discovery. Computational modeling enables a detailed electrophysiological analysis that is otherwise difficult or impossible to achieve under strictly experimental settings. Action potential characteristics of hiPSC-CMs measured in our lab at four different pacing rates were used it to modify the computational Kernik-Clancy hiPSC-CM model. The modified model was used to compare the excitation of single hiPSC-CMs with that of single human ventricular cardiomyocytes (hV-CMs) under varying conditions, including at stimulation at different strengths, rates and pulse durations. The physiological stimulation of both hiPSC-CMs and hV-CMs embedded within a tissue strand involves a biphasic waveform during which time excitatory currents (particularly INa, but also ICaT and ICaL for hiPSC-CMs and INaL and ICaL for hV-CMs) are activated during both phases of the waveform. INa in particular activated more slowly and with diminished amplitude under conditions of increasing pacing rate or increasing intracellular resistance. Lastly, histograms characterizing the relative amounts of excitatory currents in a population of hiPSC-CMs become broader with increasing levels of INa block, with ICaT and ICaL working in tandem to excite cells where INa has failed to activate. In general, hiPSC-CMs were found to be more excitable from rest compared with hV-CMs owing to their more depolarized resting potential and intrinsic automaticity despite a lower sodium channel density. Such a mismatch should be taken into consideration for applications using these cells, particularly for cardiac repair.