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J Mol Cell Cardiol. 2015 Apr;81:81-93. doi: 10.1016/j.yjmcc.2015.01.013. Epub 2015 Jan 30.

Mechanism of automaticity in cardiomyocytes derived from human induced pluripotent stem cells.

Author information

1
Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261, USA; Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA.
2
Department of Developmental Biology, University of Pittsburgh, Pittsburgh, PA 15261, USA.
3
University of Iowa, Carver College of Medicine, Division of Cardiovascular Medicine, Iowa City, IA 52242, USA.
4
Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA.
5
Center for Cellular and Systems Electrophysiology, University at Buffalo, State University of New York, Buffalo, NY 14214, USA.
6
Center for Cellular and Systems Electrophysiology, University at Buffalo, State University of New York, Buffalo, NY 14214, USA; Departments of Physiology and Biophysics, University at Buffalo, State University of New York, Buffalo, NY 14214, USA; Departments of Gynecology-Obstetrics, University at Buffalo, State University of New York, Buffalo, NY 14214, USA.
7
Center for Cellular and Systems Electrophysiology, University at Buffalo, State University of New York, Buffalo, NY 14214, USA; Departments of Physiology and Biophysics, University at Buffalo, State University of New York, Buffalo, NY 14214, USA.
8
Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261, USA; Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA. Electronic address: gsalama@pitt.edu.

Abstract

BACKGROUND AND OBJECTIVES:

The creation of cardiomyocytes derived from human induced pluripotent stem cells (hiPS-CMs) has spawned broad excitement borne out of the prospects to diagnose and treat cardiovascular diseases based on personalized medicine. A common feature of hiPS-CMs is their spontaneous contractions but the mechanism(s) remain uncertain.

METHODS:

Intrinsic activity was investigated by the voltage-clamp technique, optical mapping of action potentials (APs) and intracellular Ca(2+) (Cai) transients (CaiT) at subcellular-resolution and pharmacological interventions.

RESULTS:

The frequency of spontaneous CaiT (sCaiT) in monolayers of hiPS-CMs was not altered by ivabradine, an inhibitor of the pacemaker current, If despite high levels of HCN transcripts (1-4). HiPS-CMs had negligible If and IK1 (inwardly-rectifying K(+)-current) and a minimum diastolic potential of -59.1±3.3mV (n=18). APs upstrokes were preceded by a depolarizing-foot coincident with a rise of Cai. Subcellular Cai wavelets varied in amplitude, propagated and died-off; larger Cai-waves triggered cellular sCaTs and APs. SCaiTs increased in frequency with [Ca(2+)]out (0.05-to-1.8mM), isoproterenol (1μM) or caffeine (100μM) (n≥5, p<0.05). HiPS-CMs became quiescent with ryanodine receptor stabilizers (K201=2μM); tetracaine; Na-Ca exchange (NCX) inhibition (SEA0400=2μM); higher [K(+)]out (5→8mM), and thiol-reducing agents but could still be electrically stimulated to elicit CaiTs. Cell-cell coupling of hiPS-CM in monolayers was evident from connexin-43 expression and CaiT propagation. SCaiTs from an ensemble of dispersed hiPS-CMs were out-of-phase but became synchronous through the outgrowth of inter-connecting microtubules.

CONCLUSIONS:

Automaticity in hiPS-CMs originates from a Ca(2+)-clock mechanism involving Ca(2+) cycling across the sarcoplasmic reticulum linked to NCX to trigger APs.

KEYWORDS:

Cell–cell coupling; Funny current; Human myocytes from stem cells; Optical mapping of calcium and action potentials; Spontaneous activity; Subcellular calcium waves

PMID:
25644533
PMCID:
PMC4409767
DOI:
10.1016/j.yjmcc.2015.01.013
[Indexed for MEDLINE]
Free PMC Article

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