In:
The Journal of Physiology, Wiley, Vol. 559, No. 2 ( 2004-09), p. 479-496
Abstract:
Human embryonic stem cell‐derived cardiomyocytes (hES‐CMs) are thought to recapitulate the embryonic development of heart cells. Given the exciting potential of hES‐CMs as replacement tissue in diseased hearts, we investigated the pharmacological sensitivity and ionic current of mid‐stage hES‐CMs (20–35 days post plating). A high‐resolution microelectrode array was used to assess conduction in multicellular preparations of hES‐CMs in spontaneously contracting embryoid bodies (EBs). TTX (10 μ m ) dramatically slowed conduction velocity from 5.1 to 3.2 cm s −1 while 100 μ m TTX caused complete cessation of spontaneous electrical activity in all EBs studied. In contrast, the Ca 2+ channel blockers nifedipine or diltiazem (1 μ m ) had a negligible effect on conduction. These results suggested a prominent Na + channel current, and therefore we patch‐clamped isolated cells to record Na + current and action potentials (APs). We found for isolated hES‐CMs a prominent Na + current (244 ± 42 pA pF −1 at 0 mV; n = 19), and a hyperpolarization‐activated current (HCN), but no inward rectifier K + current. In cell clusters, 3 μ m TTX induced longer AP interpulse intervals and 10 μ m TTX caused cessation of spontaneous APs. In contrast nifedipine (Ca 2+ channel block) and 2 m m Cs + (HCN complete block) induced shorter AP interpulse intervals. In single cells, APs stimulated by current pulses had a maximum upstroke velocity (d V /d t max ) of 118 ± 14 V s −1 in control conditions; in contrast, partial block of Na + current significantly reduced stimulated d V /d t max (38 ± 15 V s −1 ). RT‐PCR revealed Na V 1.5, Ca V 1.2, and HCN‐2 expression but we could not detect Kir2.1. We conclude that hES‐CMs at mid‐range development express prominent Na + current. The absence of background K + current creates conditions for spontaneous activity that is sensitive to TTX in the same range of partial block of Na V 1.5; thus, the Na V 1.5 Na + channel is important for initiating spontaneous excitability in hES‐derived heart cells.
Type of Medium:
Online Resource
ISSN:
0022-3751
,
1469-7793
DOI:
10.1113/jphysiol.2004.068213
Language:
English
Publisher:
Wiley
Publication Date:
2004
detail.hit.zdb_id:
1475290-6
SSG:
12
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