The inwardly rectifying potassium current (IK1), encode by Kir2 family, is responsible for maintaining the negative resting potential, and contributes to phase 3 repolarization of the cardiac action potential. IK1 was generally thought to suppress cardiac automaticity, while the suppression of IK1 in adult ventricular cardiomyocytes (CMs) could engineer bio-artificial pacemaker-like cells to spontaneously fire action potential. Our studies also showed that overexpressed the gene of Kir2.1 could facilitate the electrophysiological maturing of mouse and human embryonic stem cell-differentiated CMs (ESC-CMs), which have the high degree of automaticity with nearly 50% of cells that can spontaneously fire action potential. In this study, we extensively analyzed the electrophysiology of mouse and human ESC-CMs, and found that the maximum diastolic potential in spontaneously firing ESC-CMs, -72.1±1.3 mV in atrial cells and -75.0±2.1 mV in ventricular cells, were significantly more hyperpolarized than that in quiescent ESC-CMs (-64.4±2.1 mV in atrial cells and -67.1±3.2 mV in ventricular cells). Applying a small amount of IK1 to hyperpolarize the membrane potential could enable those quiescent ESC-CMs to spontaneously fire action potential, indicating the enhancement of cardiac automaticity, while a large amount of IK1 could quiet those spontaneously firing cells down. By combining computational and experimental analyses, we confirmed that the synergistic interaction of IK1 and pacemaker current (If) could efficiently regulate cardiac automaticity during the differentiation. Our studies disclosed a dose-dependent role of IK1 on cardiac automaticity that a small amount of IK1 enhances and a large amount of IK1 suppresses cardiac automaticity in ESC-CMs during differentiation.
Rescuing cardiac automaticity in L-type Cav1.3 channelopathies and beyond
