Biophysical and molecular mechanisms underlying the modulation of heteromeric Kir4.1-Kir5.1 channels by CO2 and pH.
Biophysical and molecular mechanisms underlying the modulation of heteromeric Kir4.1-Kir5.1 channels by CO2 and pH.
复制标题
二氧化碳和pH调制的杂体Kir4.1-KIR5.1通道的生物物理和分子机制。
DOI：
10.1085/jgp.116.1.33
复制
发表时间：
2000-07-01
期刊：
影响因子：
--
通讯作者：
Jiang C
中科院分区：
文献类型：
--
作者：
Yang Z;Xu H;Cui N;Qu Z;Chanchevalap S;Shen W;Jiang C
CO2化学感受可能与脑干神经元内向整流钾通道（Kir通道）的调节有关。Kir4.1主要在脑干中表达，并在高碳酸血症期间被抑制。虽然同聚Kir4.1只响应于严重的细胞内酸化，Kir4.1与Kir5.1的共表达大大增强了通道对CO2和pH的敏感性。为了了解CO2和pH对这些电流的调制的生物物理和分子机制，异聚Kir4.1-Kir5.1进行了研究，在由内而外的补丁。这些Kir4.1-Kir5.1电流显示在pH 7.4时具有59 pS的单通道电导，其中开放状态概率（P open）为0.4。通道活性在pH 8.5时达到最大值，在pH 6.5时完全抑制，pKa为7.45。低pH对这些电流的影响是由于选择性抑制P开放而对单通道电导没有明显影响，导致通道平均开放时间减少和平均关闭时间增加。在pH 8.5时，单通道电流在最大开口的1/4和3/4处表现出两个亚水平的电导。它们都没有受到影响，降低pH值。Kir4.1-Kir5.1电流调制磷脂酰肌醇-4，5-二磷酸（PIP 2），增强基线P开放和降低通道敏感性细胞内质子。在10 μM PIP 2存在下，Kir4.1-Kir5.1显示pKa值为7.22。然而，PIP 2的作用在同聚Kir4.1电流中未观察到。CO2/pH敏感性与Kir4.1的NH 2末端的赖氨酸残基有关。该残基的突变（K67 M，K67 Q）完全消除了同聚Kir4.1和异聚Kir4.1-Kir5.1的CO2敏感性。有趣的是，在切除的斑块中，携带K67 M突变的Kir4.1-Kir5.1对低pHi保持敏感。然而，这种pH敏感性在PIP 2存在下消失。当Kir5.1中的Arg 178突变时，PIP 2对野生型和突变型通道的滴定曲线移动的作用被完全消除。因此，这些研究证明了可以通过酸性和碱性pH调节的异聚Kir通道，显示了通过PIP 2调节Kir通道的pH敏感性，并提供了细胞内质子调节Kir的生物物理和分子机制的信息。
CO2 chemoreception may be related to modulation of inward rectifier K+ channels (Kir channels) in brainstem neurons. Kir4.1 is expressed predominantly in the brainstem and inhibited during hypercapnia. Although the homomeric Kir4.1 only responds to severe intracellular acidification, coexpression of Kir4.1 with Kir5.1 greatly enhances channel sensitivities to CO2 and pH. To understand the biophysical and molecular mechanisms underlying the modulation of these currents by CO2 and pH, heteromeric Kir4.1–Kir5.1 were studied in inside-out patches. These Kir4.1–Kir5.1 currents showed a single channel conductance of 59 pS with open-state probability (P open) ∼ 0.4 at pH 7.4. Channel activity reached the maximum at pH 8.5 and was completely suppressed at pH 6.5 with pKa 7.45. The effect of low pH on these currents was due to selective suppression of P open without evident effects on single channel conductance, leading to a decrease in the channel mean open time and an increase in the mean closed time. At pH 8.5, single-channel currents showed two sublevels of conductance at ∼1/4 and 3/4 of the maximal openings. None of them was affected by lowering pH. The Kir4.1–Kir5.1 currents were modulated by phosphatidylinositol-4,5-bisphosphate (PIP2) that enhanced baseline P open and reduced channel sensitivity to intracellular protons. In the presence of 10 μM PIP2, the Kir4.1–Kir5.1 showed a pKa value of 7.22. The effect of PIP2, however, was not seen in homomeric Kir4.1 currents. The CO2/pH sensitivities were related to a lysine residue in the NH2 terminus of Kir4.1. Mutation of this residue (K67M, K67Q) completely eliminated the CO2 sensitivity of both homomeric Kir4.1 and heteromeric Kir4.1–Kir5.1. In excised patches, interestingly, the Kir4.1–Kir5.1 carrying K67M mutation remained sensitive to low pHi. Such pH sensitivity, however, disappeared in the presence of PIP2. The effect of PIP2 on shifting the titration curve of wild-type and mutant channels was totally abolished when Arg178 in Kir5.1 was mutated. Thus, these studies demonstrate a heteromeric Kir channel that can be modulated by both acidic and alkaline pH, show the modulation of pH sensitivity of Kir channels by PIP2, and provide information of the biophysical and molecular mechanisms underlying the Kir modulation by intracellular protons.
登录
查看更多内容
影响因子：
4.8
作者：
Chanchevalap, S;Yang, ZJ;Jiang, C
通讯作者：
Jiang, C
DOI：
10.1073/pnas.96.26.15298
发表时间：
1999-12-21
影响因子：
11.1
作者：
Schulte, U;Hahn, H;Ludwig, J
通讯作者：
Ludwig, J
DOI：
10.1073/pnas.92.15.6753
发表时间：
1995-07-18
影响因子：
11.1
作者：
BREDT, DS;WANG, TL;SNYDER, SH
通讯作者：
SNYDER, SH
DOI：
10.1152/ajprenal.1997.273.4.f516
发表时间：
1997-10-01
影响因子：
4.2
作者：
Choe, H;Zhou, H;Sackin, H
通讯作者：
Sackin, H
影响因子：
56.9
作者：
Baukrowitz, T;Schulte, U;Fakler, B
通讯作者：
Fakler, B