Mechanism for attenuated outward conductance induced by mutations in the cytoplasmic pore of Kir2.1 channels.
Mechanism for attenuated outward conductance induced by mutations in the cytoplasmic pore of Kir2.1 channels.
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DOI：
10.1038/srep18404
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发表时间：
2015-12-18
影响因子：
4.6
通讯作者：
Shieh RC
中科院分区：
文献类型：
--
作者：
Chang HK;Iwamoto M;Oiki S;Shieh RC
通过Kir2.1通道的外向电流调节可兴奋细胞的电特性。这些电流受到电压依赖性衰减的多胺结合到高和低亲和力的网站，这导致向内整流，从而控制细胞的兴奋性。为了研究细胞质孔中低亲和力位点的正电荷对内向整流的影响，我们研究了突变的Kir通道（E224 K/H226 E）并测量了单通道电流和流动电位（Vstream），后者提供了选择性过滤器中单列渗透过程中排队的水与离子的比率。对于野生型通道，在高K+浓度（[K+]）下水-离子耦合比接近1，并且随着[K+]降低而显著增加。另一方面，更少的离子占据的选择性过滤器中的突变体在所有[K+]。介绍了一个在宽孔中含有K+结合位点的Kir通道模型。模型分析表明，与结合和释放到和从宽孔K+结合位点的速率常数被修改的突变体。这些效应导致传统的双离子渗透模式对总电导的贡献减少，特别是在正电位下，从而向内整流。
Outward currents through Kir2.1 channels regulate the electrical properties of excitable cells. These currents are subject to voltage-dependent attenuation by the binding of polyamines to high- and low-affinity sites, which leads to inward rectification, thereby controlling cell excitability. To examine the effects of positive charges at the low-affinity site in the cytoplasmic pore on inward rectification, we studied a mutant Kir channel (E224K/H226E) and measured single-channel currents and streaming potentials (Vstream), the latter provide the ratio of water to ions queued in a single-file permeation process in the selectivity filter. The water-ion coupling ratio was near one at a high K+ concentration ([K+]) for the wild-type channel and increased substantially as [K+] decreased. On the other hand, fewer ions occupied the selectivity filter in the mutant at all [K+]. A model for the Kir channel involving a K+ binding site in the wide pore was introduced. Model analyses revealed that the rate constants associated with the binding and release to and from the wide-pore K+ binding site was modified in the mutant. These effects lead to the reduced contribution of a conventional two-ion permeation mode to total conductance, especially at positive potentials, thereby inward rectification.