Electrophysiological Characteristics of Embryonic Stem Cell-Derived Cardiomyocytes are Cell Line-Dependent

Background: Modelling of cardiac development, physiology and pharmacology by differentiation of embryonic stem cells (ESCs) requires comparability of cardiac differentiation between different ESC lines. To investigate whether the outcome of cardiac differentiation is consistent between different ESC lines, we compared electrophysiological properties of ESC-derived cardiomyocytes (ESC-CMs) of different murine ESC lines. Methods: Two wild-type (D3 and R1) and two transgenic ESC lines (D3/aPIG44 and CGR8/AMPIGX-7) were differentiated under identical culture conditions. The transgenic cell lines expressed enhanced green fluorescent protein (eGFP) and puromycin-N-acetyltransferase under control of the cardiac specific α-myosin heavy chain (αMHC) promoter. Action potentials (APs) were recorded using sharp electrodes and multielectrode arrays in beating clusters of ESC-CMs. Results: Spontaneous AP frequency and AP duration (APD) as well as maximal upstroke velocity differed markedly between unpurified CMs of the four ESC lines. APD heterogeneity was negligible in D3/aPIG44, moderate in D3 and R1 and extensive in CGR8/AMPIGX-7. Interspike intervals calculated from long-term recordings showed a high degree of variability within and between recordings in CGR8/AMPIGX-7, but not in D3/aPIG44. Purification of the αMHC+ population by puromycin treatment posed only minor changes to APD in D3/aPIG44, but significantly shortened APD in CGR8/AMPIGX-7. Conclusion: Electrophysiological properties of ESC-CMs are strongly cell line-dependent and can be influenced by purification of cardiomyocytes by antibiotic selection. Thus, conclusions on cardiac development, physiology and pharmacology derived from single stem cell lines have to be interpreted carefully.