Electrophysiological Properties of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes Cultured on a Flexible Matrigel Substrate

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Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) provide a unique tool to evaluate cellular properties in disease models, investigate underlying mechanisms and optimize cell-based therapies. We recently reported that after plating 30 day old single hiPSC-CMs on undiluted Matrigel “Mattress” (thickness ∼0.5 mm) for 5 days, mattress hiPSC-CMs developed a rod-like cell shape, aligned myofilament structure, increased sarcomere length and exhibited robust cell shortening. Here, we compared the electrophysiological properties of mattress hiPSC-CMs to hiPSC-CMs cultured on standard substrates (control) and acutely-isolated adult rabbit CMs. The action potentials of mattress hiPSC-CMs were comparable to rabbit CMs. Compared to control, mattress hiPSC-CMs had significantly increased the action potential upstroke velocity due to two-fold increase in sodium current (INa) (−68.61±11.63 pA·pF-1 in mattress vs. −29.66±7.50 pA·pF-1 in control at −30mV). The inward rectifier current (IK1) is responsible for the maintenance of resting membrane potential and contributes to phase 3 of the action potential. Although resting potential and action potential duration was not different from rabbit CMs, IK1 density in mattress hiPSC-CMs was nine-time smaller than in rabbit CMs, but there was no difference between mattress and control hiPSC-CMs (−4.86±0.66 pA·pF-1 in mattress vs. −43.75±4.13 pA·pF-1 in rabbit vs. −3.98±0.83 pA·pF-1 in control at −120 mV). The funny current (If) is an inward current activating at hyperpolarized membrane potential, which is detectable in the developing heart but absent in the adult ventricle and contributes to the spontaneous beating of hiPSC-CMs. Mattress hiPSC-CMs exhibit robust If that was not significantly different from control (−6.22±1.31 pA·pF-1 in mattress vs.-5.60±1.43 pA·pF-1 in control at −120 mV). In summary, the matrigel mattress method enables the rapid generation of robustly contracting single hiPSC-CMs and increases INa, with negligible effect on IK1 or If.