Na+/Ca2+ Exchanger is a Determinant of Excitation–Contraction Coupling in Human Embryonic Stem Cell–Derived Ventricular Cardiomyocytes

In adult cardiomyocytes (CMs), the Na+/Ca2+ exchanger (NCX) is a well-defined determinant of Ca2+ homeostasis. Developmentally, global NCX knockout in mice leads to abnormal myofibrillar organization, electrical defects, and early embryonic death. Little is known about the expression and function of NCX in human heart development. Self-renewable, pluripotent human embryonic stem cells (hESCs) can serve as an excellent experimental model. However, hESC-derived CMs are highly heterogeneous. A stably lentivirus-transduced hESC line (MLC2v-dsRed) was generated to express dsRed under the transcriptional control of the ventricular-restricted myosin light chain-2v (MLC2v) promoter. Electrophysiologically, dsRed+ cells differentiated from MLC2v-dsRed hESCs displayed ventricular action potentials (AP), exclusively. Neither atrial nor pacemaker APs were observed. While ICa-L, If, and IKr were robustly expressed, IKs and IK1 were absent in dsRed+ ventricular hESC-CMs. Upon differentiation (7+40 to +90 days), the bas...