Department of Biological Sciences, University at Albany, State University of New York, Albany, New York, USA.
FASEB J. 2018 Jun;32(6):3047-3057. doi: 10.1096/fj.201701260R. Epub 2018 Jan 12.
Spontaneous rhythmic action potential or pacemaking activity of pacemaker cells controls rhythmic signaling such as heartbeat. The mechanism underlying the origin of pacemaking activity is not well understood. In this study, we created human embryonic kidney (HEK) 293 cells that show pacemaking activity through heterologous expression of strong inward rectifier K subfamily 2 isoform 1 (Kir2.1) channels, hyperpolarization-activated cyclic nucleotide-gated isoform 2 (HCN2) nonselective cation channels, and voltage-gated Na subfamily 1 isoform 5 or Ca subfamily 3 isoform 1 (Na1.5 or Ca3.1) channels. A range of relative levels of Kir2.1 and HCN2 currents dynamically counterbalance, generating spontaneous rhythmic oscillation of resting membrane potential between -64 and -34 mV and determining oscillation rates. Each oscillation cycle begins with an autodepolarization phase, which slowly proceeds to the threshold potential that activates Na1.5 or Ca3.1 channels and triggers action potential, causing engineered HEK293 cells to exhibit pacemaking activity at a rate of ≤67 beats/min. Engineered HEK293 cells with Kir2.1 and either HCN3 or HCN4 also show the oscillation. Engineered HEK293 cells expressing HCN2 and other Kir2 channels, which lack Kir2.1-like complete inward rectification, do not show the oscillation. Therefore, Kir2.1-like inward rectification-controlled precise and dynamic balances between Kir2 and HCN currents initiate spontaneous rhythmic action potential and form an origin of pacemaking activity; Kir2 and HCN channels play essential roles in pacemaking activity.-Chen, K., Zuo, D., Wang, S.-Y. Chen, H. Kir2 inward rectification-controlled precise and dynamic balances between Kir2 and HCN currents initiate pacemaking activity.
自发节律性动作电位或起搏细胞的起搏活动控制着节律信号，如心跳。起搏活动起源的机制尚不清楚。在这项研究中，我们通过异源表达强内向整流钾亚家族 2 亚型 1（Kir2.1）通道、超极化激活环核苷酸门控亚型 2（HCN2）非选择性阳离子通道以及电压门控钠亚家族 1 亚型 5 或钙亚家族 3 亚型 1（Na1.5 或 Ca3.1）通道，创建了表现起搏活性的人胚肾（HEK）293 细胞。Kir2.1 和 HCN2 电流的相对水平在动态上相互平衡，产生了-64 至-34 mV 的静息膜电位的自发节律性振荡，并决定了振荡频率。每个振荡周期都以自动去极化阶段开始，该阶段缓慢进展到激活 Na1.5 或 Ca3.1 通道并引发动作电位的阈电位，导致工程化 HEK293 细胞以≤67 次/分钟的速率表现出起搏活性。表达 Kir2.1 和 HCN3 或 HCN4 的工程化 HEK293 细胞也显示出这种振荡。表达 HCN2 和其他缺乏 Kir2.1 样完全内向整流的 Kir2 通道的工程化 HEK293 细胞则不会显示这种振荡。因此，Kir2.1 样内向整流控制的 Kir2 和 HCN 电流之间的精确和动态平衡引发了自发节律性动作电位，并形成了起搏活动的起源；Kir2 和 HCN 通道在起搏活性中发挥着重要作用。
