Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA.
Department of Internal Medicine, University of California, Davis, CA, USA.
Stem Cell Rev Rep. 2017 Oct;13(5):631-643. doi: 10.1007/s12015-017-9745-1.
The inward rectifier potassium current (I) is generally thought to suppress cardiac automaticity by hyperpolarizing membrane potential (MP). We recently observed that I could promote the spontaneously-firing automaticity induced by upregulation of pacemaker funny current (I) in adult ventricular cardiomyocytes (CMs). However, the intriguing ability of I to activate I and thereby promote automaticity has not been explored. In this study, we combined mathematical and experimental assays and found that only I and I, at a proper-ratio of densities, were sufficient to generate rhythmic MP-oscillations even in unexcitable cells (i.e. HEK293T cells and undifferentiated mouse embryonic stem cells [ESCs]). We termed this effect I-induced I activation. Consistent with previous findings, our electrophysiological recordings observed that around 50% of mouse (m) and human (h) ESC-differentiated CMs could spontaneously fire action potentials (APs). We found that spontaneously-firing ESC-CMs displayed more hyperpolarized maximum diastolic potential and more outward I current than quiescent-yet-excitable m/hESC-CMs. Rather than classical depolarization pacing, quiescent mESC-CMs were able to fire APs spontaneously with an electrode-injected small outward-current that hyperpolarizes MP. The automaticity to spontaneously fire APs was also promoted in quiescent hESC-CMs by an I-specific agonist zacopride. In addition, we found that the number of spontaneously-firing m/hESC-CMs was significantly decreased when I was acutely upregulated by Ad-CGI-HCN infection. Our study reveals a novel role of I promoting the development of cardiac automaticity in m/hESC-CMs through a mechanism of I-induced I activation and demonstrates a synergistic interaction between I and I that regulates cardiac automaticity.
内向整流钾电流（I）通常被认为通过超极化膜电位（MP）来抑制心脏自律性。我们最近观察到，I 可以促进由起搏滑稽电流（I）上调诱导的成年心室心肌细胞（CM）的自发性自动兴奋。然而，I 激活 I 从而促进自动兴奋的有趣能力尚未得到探索。在这项研究中，我们结合了数学和实验检测，发现只有 I 和 I，在适当密度的比例下，即使在非兴奋细胞（即 HEK293T 细胞和未分化的小鼠胚胎干细胞[ESCs]）中，也足以产生节律性的 MP 振荡。我们将这种效应称为 I 诱导的 I 激活。与先前的发现一致，我们的电生理记录观察到，大约 50%的小鼠（m）和人类（h）ESC 分化的 CM 可以自发地产生动作电位（AP）。我们发现，自发兴奋的 ESC-CM 比静止但可兴奋的 m/hESC-CM 显示出更超极化的最大舒张电位和更多的外向 I 电流。与经典的去极化起搏不同，静止的 mESC-CM 可以通过注入电极的小外向电流自发地产生 AP，该电流使 MP 超极化。通过 I 特异性激动剂 zacopride，也可以促进静止的 hESC-CM 中的自动 AP 发放。此外，我们发现，当通过 Ad-CGI-HCN 感染急性上调 I 时，自发兴奋的 m/hESC-CM 的数量明显减少。我们的研究揭示了 I 通过 I 诱导的 I 激活机制促进 m/hESC-CM 心脏自律性发展的新作用，并证明了 I 和 I 之间调节心脏自律性的协同相互作用。
