Local Control of Excitation-Contraction Coupling in Human Embryonic Stem Cell-Derived Cardiomyocytes |
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Authors: | Wei-Zhong Zhu Luis F Santana Michael A Laflamme |
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Institution: | 1. Department of Pathology, University of Washington, Seattle, Washington, United States of America.; 2. Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, Washington, United States of America.; 3. Department of Physiology & Biophysics, University of Washington, Seattle, Washington, United States of America.;University of Cincinnati, United States of America |
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Abstract: | We investigated the mechanisms of excitation-contraction (EC) coupling in human embryonic stem cell-derived cardiomyocytes (hESC-CMs) and fetal ventricular myocytes (hFVMs) using patch-clamp electrophysiology and confocal microscopy. We tested the hypothesis that Ca2+ influx via voltage-gated L-type Ca2+ channels activates Ca2+ release from the sarcoplasmic reticulum (SR) via a local control mechanism in hESC-CMs and hFVMs. Field-stimulated, whole-cell Ca2+]i transients in hESC-CMs required Ca2+ entry through L-type Ca2+ channels, as evidenced by the elimination of such transients by either removal of extracellular Ca2+ or treatment with diltiazem, an L-type channel inhibitor. Ca2+ release from the SR also contributes to the Ca2+]i transient in these cells, as evidenced by studies with drugs interfering with either SR Ca2+ release (i.e. ryanodine and caffeine) or reuptake (i.e. thapsigargin and cyclopiazonic acid). As in adult ventricular myocytes, membrane depolarization evoked large L-type Ca2+ currents (I
Ca) and corresponding whole-cell Ca2+]i transients in hESC-CMs and hFVMs, and the amplitude of both I
Ca and the Ca2+]i transients were finely graded by the magnitude of the depolarization. hESC-CMs exhibit a decreasing EC coupling gain with depolarization to more positive test potentials, “tail” Ca2+]i transients upon repolarization from extremely positive test potentials, and co-localized ryanodine and sarcolemmal L-type Ca2+ channels, all findings that are consistent with the local control hypothesis. Finally, we recorded Ca2+ sparks in hESC-CMs and hFVMs. Collectively, these data support a model in which tight, local control of SR Ca2+ release by the I
Ca during EC coupling develops early in human cardiomyocytes. |
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