Hsieh Chi-Pan, Kuo Chung-Chin, Huang Chiung-Wei
Department of Medical Education, Far Eastern Memorial Hospital, No. 21, Nan-Ya S. Rd., Ban-Chiao, New Taipei City 220, Taiwan; Department of Family Medicine, Far Eastern Memorial Hospital, No. 21, Nan-Ya S. Rd., Ban-Chiao, New Taipei City 220, Taiwan.
Department of Physiology, National Taiwan University College of Medicine, No. 1, Jen-Ai Road, 1st Section, Taipei, 100, Taiwan; Department of Neurology, National Taiwan University Hospital, No. 7, Chung-Shan S. Road, Taipei, Taiwan.
Biophys Chem. 2015 Jul;202:40-57. doi: 10.1016/j.bpc.2015.04.003. Epub 2015 Apr 15.
The Kir2.1 channel is characterized by strong inward rectification; however, the mechanism of the steep voltage dependence near the equilibrium potential remains to be investigated. Here, we studied the internal Ba(2+) block of the Kir2.1 channel expressed in Xenopus oocytes. We showed that the driving force and thus the K(+) ion flux significantly influenced the apparent affinity of the block by internal Ba(2+). Kinetic analysis revealed that the binding rate shifted with the driving force and changed steeply near the equilibrium point, either in the presence or absence of the transmembrane electrical field. The unbinding rate was determined by the intrinsic affinity of the site. Mutagenesis studies revealed that the high-affinity binding site for Ba(2+) was located near T141 at the internal entrance of the selectivity filter. The steep change of the blocking affinity near the equilibrium potential may result from the flux-coupling effect in the single-file, multi-ion cytoplasmic pore.
Kir2.1通道具有强烈的内向整流特性；然而，接近平衡电位时陡峭电压依赖性的机制仍有待研究。在此，我们研究了非洲爪蟾卵母细胞中表达的Kir2.1通道的内部Ba(2+)阻断作用。我们发现驱动力以及K(+)离子通量显著影响内部Ba(2+)对通道的表观亲和力。动力学分析表明，无论有无跨膜电场，结合速率均随驱动力而变化，并在平衡点附近急剧改变。解离速率由该位点的固有亲和力决定。诱变研究表明，Ba(2+)的高亲和力结合位点位于选择性过滤器内部入口处的T141附近。平衡电位附近阻断亲和力的急剧变化可能是由单排多离子细胞质孔中的通量耦合效应所致。
