Multiple mechanisms underlying rectification in retinal cyclic nucleotide-gated (CNGA1) channels.
Multiple mechanisms underlying rectification in retinal cyclic nucleotide-gated (CNGA1) channels.
复制标题
DOI：
10.1002/phy2.148
复制
发表时间：
2013-11
影响因子：
2.5
通讯作者：
Torre, Vincent
中科院分区：
文献类型：
--
作者：
Arcangeletti, Manuel;Marchesi, Arin;Mazzolini, Monica;Torre, Vincent
在环核苷酸门控(CNGA1)通道中，在对称离子条件下，电流-电压(I-V)关系复杂地依赖于离子渗透半径。有人认为，孔和S4螺旋对观察到的整流都有贡献。在目前的手稿中，使用尾电流和门控电流测量在非洲爪哇卵母细胞中表达的同源四聚体CNGA1通道，我们澄清和量化了毛孔和S4螺旋的作用。结果表明，在对称的Rb+和Cs+离子中，宏观电流以单通道电流整流为主，而在对称的乙胺和二甲基铵中，电压相关的门控电流变大，其开通几率强烈依赖于电压。二甲基铵的等时尾电流分析表明，至少有两个电压相关的转变是观察到的整流的基础。只有第一个电压依赖的转变对S4螺旋中电荷残基的突变敏感。此外，对尾部电流和门控电流的分析表明，在K+通道中，当基元电荷数约为12个时，每个通道通过膜的基元电荷数小于2。这些结果表明，CNG通道存在不同的整流机制。S4螺旋的受限运动以及与通道门的低效耦合使CNGA1通道在生理Na+和K+存在的情况下对电压的敏感性较差。
In cyclic nucleotide-gated (CNGA1) channels, in the presence of symmetrical ionic conditions, current–voltage (I-V) relationship depends, in a complex way, on the radius of permeating ion. It has been suggested that both the pore and S4 helix contribute to the observed rectification. In the present manuscript, using tail and gating current measurements from homotetrameric CNGA1 channels expressed in Xenopus oocytes, we clarify and quantify the role of the pore and of the S4 helix. We show that in symmetrical Rb+ and Cs+ single-channel current rectification dominates macroscopic currents while voltage-dependent gating becomes larger in symmetrical ethylammonium and dimethylammonium, where the open probability strongly depends on voltage. Isochronal tail currents analysis in dimethylammonium shows that at least two voltage-dependent transitions underlie the observed rectification. Only the first voltage-dependent transition is sensible to mutation of charge residues in the S4 helix. Moreover, analysis of tail and gating currents indicates that the number of elementary charges per channel moving across the membrane is less than 2, when they are about 12 in K+ channels. These results indicate the existence of distinct mechanisms underlying rectification in CNG channels. A restricted motion of the S4 helix together with an inefficient coupling to the channel gate render CNGA1 channels poorly sensitive to voltage in the presence of physiological Na+ and K+.