The interaction of Na+ and K+ in voltage-gated potassium channels. Evidence for cation binding sites of different affinity.
The interaction of Na+ and K+ in voltage-gated potassium channels. Evidence for cation binding sites of different affinity.
复制标题
DOI：
10.1085/jgp.111.2.195
复制
发表时间：
1998-02
期刊：
影响因子：
--
通讯作者：
Korn SJ
中科院分区：
文献类型：
--
作者：
Kiss L;Immke D;LoTurco J;Korn SJ
电压门控钾（K+）通道是多离子孔。最近的研究表明，类似于钙通道，离子物种之间的竞争，孔内结合位点可能有助于离子的选择性，至少在一些K+通道。分子研究表明，一个假定的收缩区域的孔，这大概是网站的选择性，可能是一个离子直径的长度短。总之，这些结果表明，选择性可能发生在孔中的一个单一的结合位点。我们正在研究一种嵌合的K+通道，它在生理溶液中对K+的选择性高于Na+，但在没有K+的情况下传导Na+。Na+和K+电流都显示缓慢（C型）失活，但有显着不同的失活和失活动力学; Na+电流失活更快，失活更慢比K+电流。160 mM Na+携带的电流被外部K+抑制，表观IC 50 <30 μM。K+在这些低浓度下也改变了Na+电流的失活和失活动力学。在补充实验中，3 mM K+携带的电流被外部Na+抑制，表观IC 50为100 mM。与低[K+]对Na+电流动力学的影响相反，Na+不影响K+电流动力学，即使在抑制K+电流40- 50%的浓度下。这些数据表明，Na+阻断K+电流并不涉及从门控动力学中涉及的高亲和力位点置换K+。我们提出了一个模型，描述了渗透途径作为一个单一的高亲和力，阳离子选择性结合位点，两侧低亲和力，非选择性网站。该模型定量地预测了在两个不同的K+通道中观察到的异常摩尔分数行为，微分K+和Na+电导，以及Na+电流的K+阻断和K+电流的Na+阻断的浓度依赖性。基于我们的研究结果，我们假设渗透途径包含一个单一的高亲和力结合位点，在那里发生选择性和离子调制门控。
Voltage-gated potassium (K+) channels are multi-ion pores. Recent studies suggest that, similar to calcium channels, competition between ionic species for intrapore binding sites may contribute to ionic selectivity in at least some K+ channels. Molecular studies suggest that a putative constricted region of the pore, which is presumably the site of selectivity, may be as short as one ionic diameter in length. Taken together, these results suggest that selectivity may occur at just a single binding site in the pore. We are studying a chimeric K+ channel that is highly selective for K+ over Na+ in physiological solutions, but conducts Na+ in the absence of K+. Na+ and K+ currents both display slow (C-type) inactivation, but had markedly different inactivation and deactivation kinetics; Na+ currents inactivated more rapidly and deactivated more slowly than K+ currents. Currents carried by 160 mM Na+ were inhibited by external K+ with an apparent IC50 <30 μM. K+ also altered both inactivation and deactivation kinetics of Na+ currents at these low concentrations. In the complementary experiment, currents carried by 3 mM K+ were inhibited by external Na+, with an apparent IC50 of ∼100 mM. In contrast to the effects of low [K+] on Na+ current kinetics, Na+ did not affect K+ current kinetics, even at concentrations that inhibited K+ currents by 40–50%. These data suggest that Na+ block of K+ currents did not involve displacement of K+ from the high affinity site involved in gating kinetics. We present a model that describes the permeation pathway as a single high affinity, cation-selective binding site, flanked by low affinity, nonselective sites. This model quantitatively predicts the anomalous mole fraction behavior observed in two different K+ channels, differential K+ and Na+ conductance, and the concentration dependence of K+ block of Na+ currents and Na+ block of K+ currents. Based on our results, we hypothesize that the permeation pathway contains a single high affinity binding site, where selectivity and ionic modulation of gating occur.