Contribution of potassium channels to action potential repolarization of human embryonic stem cell‐derived cardiomyocytes

Background and Purpose The electrophysiological properties of human pluripotent stem cell‐derived cardiomyocytes (CMs) have not yet been characterized in a syncytial context. This study systematically characterized the contributions of different repolarizing potassium currents in human embryonic stem cell‐derived CMs (hESC‐CMs) during long‐term culture as cell monolayers. Experimental Approach The H9 hESC line was differentiated to CMs and plated to form confluent cell monolayers. Optical mapping was used to record the action potentials (APs) and conduction velocity (CV) during electrophysiological and pharmacological experiments. RT‐PCR and Western blot were used to detect the presence and expression levels of ion channel subunits. Key Results Long‐term culture of hESC‐CMs led to shortened AP duration (APD), faster repolarization rate, and increased CV. Selective block of IKr, IKs, IK1, and IKur significantly affected AP repolarization and APD in a concentration‐ and culture time‐dependent manner. Baseline variations in APD led to either positive or negative APD dependence of drug response. Chromanol 293B produced greater relative AP prolongation in mid‐ and late‐stage cultures, while DPO‐1 had more effect in early‐stage cultures. CV in cell monolayers in early‐ and late‐stage cultures was most susceptible to slowing by E‐4031 and BaCl2 respectively. Conclusions and Implications IKr, IKs, IK1, and IKur all play an essential role in the regulation of APD and CV in hESC‐CMs. During time in culture, increased expression of IKr and IK1 helps to accelerate repolarization, shorten APD, and increase CV. We identified a new pro‐arrhythmic parameter, positive APD dependence of ion channel block, which can increase APD and repolarization gradients.