Molecular and functional development of cardiomyocytes differentiated from human embryonic stem cells.

Cardiomyocytes derived from human embryonic stem cells constitute a promising cell source for the regeneration of damaged hearts. The assessment of their in vitro functional properties is mandatory to envisage appropriate cardiac cell-based therapies. In this study, we characterized human embryonic stem cell-derived cardiomyocytes over a three-month period, using patch-clamp or intracellular recordings to assess their functional maturation and RT-PCR to evaluate the expression of ion channel-encoding subunits. The transient outward (Ito1) and inward rectifier (IK1) potassium currents were present in cardiomyocytes only, whereas, the rapid delayed rectifier potassium current(IKr), the pacemaker current (If) and the L-type calcium current(ICa,L) could be recorded both in undifferentiated human embryonic stem cells and cardiomyocytes. Most of the currents underwent developmental maturation in cardiomyocytes, as assessed by modifications in current density (Ito1, IK1 and ICa,L) and properties (If). Ion channel mRNAs were always present when the current was recorded. Quantitative RT-PCR showed a significant correlation between IK1 or If properties and mRNA levels of corresponding genes. Intracellular recordings in spontaneously beating clusters of cardiomyocytes revealed changes in action potential parameters and in response to pharmacological tools according to time of differentiation. In summary, human embryonic stem cell-derived cardiomyocytes mature over time during in vitro differentiation, approaching an adult phenotype.