Abstract 261: Human IPS-Derived Cardiac Myocytes (hiPSC-CMs): How Good Are They as a Model for Cardiac Pacing and E-C Coupling?

Abstract

Derivation of cardiomyocytes from human induced pluripotent stem cells has opened a new field of biology where hiPSC-CM are being used as electrophysiological models of human cardiovascular physiology and pathology. Whether hiPS-CM represent also reliable Ca 2+ signaling and pacemaking models for the mammalian myocytes remains to be determined. Here we evaluate the EC-coupling and spontaneous pacemaking properties of human iPS-CM in detail and compare them to those of native mammalian myocytes. iPS-CMs, dissociated after ~40 days of differentiation and voltage-clamped at -50 mV, showed spontaneous beating and Ca 2+ oscillations that activated in-phase I NCX oscillations at holding potentials between -60 and +20mV, while I f activated negative to -75mV. Withdrawal of [Ca 2+ ] o and application of NCX-blocker (KBR- 7943) or tetracaine rapidly and reversibly inhibited spontaneous Ca 2+ -oscillations. Nifedipine and NO-synthase inhibitor L-NAME failed to alter spontaneous beating. Identical sets of data as these were also obtained from neonatal rat myocytes (NRM), suggesting that SR Ca 2+ release and uptake, and not I f , were responsible for spontaneous beating in NRM and hiPS-CM. Ca 2+ signaling parameters of hiPS-CM were also similar to those of adult atrial myocytes with Ca 2+ currents averaging ~8 pA/pF and I Ca -induced Ca 2+ -transients having a bell-shaped voltage-dependence similar to that of I Ca , consistent with Ca 2+ -induced Ca 2+ -release (CICR) mechanism. The ratio of I Ca -activated to caffeine-triggered Ca 2+ -transients was ~0.3, similar to the value in rat atria, but significantly smaller than the value of >0.8 in ventricle. The gain of CICR was voltage-dependent as in adult cardiomyocytes. Adrenergic agonists enhanced I Ca , but elevated diastolic Ca 2+ . Ca 2+ -sparks were sporadic and brief in duration (< 25ms). Our data suggest that hiPS-CM have all the specific characteristics of adult cardiomyocytes and the mechanisms of their spontaneous pacing are similar to those found in NRM, and involve Ca 2+ cross-talk between NCX, RyR/SR, and possibly mitochondria.