Abstract 261: Human IPS-Derived Cardiac Myocytes (hiPSC-CMs): How Good Are They as a Model for Cardiac Pacing and E-C Coupling?
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 Ca2+ 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 Ca2+ oscillations that activated in-phase INCX oscillations at holding potentials between -60 and +20mV, while If activated negative to -75mV. Withdrawal of [Ca2+]o and application of NCX-blocker (KBR- 7943) or tetracaine rapidly and reversibly inhibited spontaneous Ca2+-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 Ca2+ release and uptake, and not If, were responsible for spontaneous beating in NRM and hiPS-CM. Ca2+ signaling parameters of hiPS-CM were also similar to those of adult atrial myocytes with Ca2+ currents averaging ~8 pA/pF and ICa-induced Ca2+-transients having a bell-shaped voltage-dependence similar to that of ICa, consistent with Ca2+-induced Ca2+-release (CICR) mechanism. The ratio of ICa-activated to caffeine-triggered Ca2+-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 ICa, but elevated diastolic Ca2+. Ca2+-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 Ca2+cross-talk between NCX, RyR/SR, and possibly mitochondria.
- © 2013 by American Heart Association, Inc.