弱向内整流K+通道中外部K+和内部阻滞剂的相互作用。

Lei Yang, Johan Edvinsson, Lawrence G Palmer
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引用次数: 8

摘要

我们研究了改变细胞外K(+)浓度对三种细胞内阳离子Mg(2+)、Na(+)和TEA(+)阻断弱内向整流K(+)通道Kir1.1b (ROMK2)的影响。用表达通道的非洲爪蟾卵母细胞制成的由内到外的贴片监测单通道电流。这三种阳离子在细胞质内溶液中K(+)为110 mM,在细胞外溶液中K(+)为11 mM,它们阻断K(+)电流的表观亲和力范围不同(Mg(2+)的K(i) (0) = 1.6 mM, Na(+)为160 mM, TEA(+)为1.8 mM),但它们具有相似的电压依赖性(Mg(2+)的zδ = 0.58, Na(+)为0.71,TEA(+)为0.61),尽管它们具有不同的价。当外部K(+)增加到110 mM时,所有三种阻滞剂的表观亲和力降低了约三倍,而阻滞剂的电压依赖性没有显著变化。跨膜腔是阻滞位点的可能性是通过在N152残基上进行突变来探索的,N152残基先前被证明会影响Kir通道的纠正。N152D增加了对Mg(2+)的亲和力,但对Na(+)和TEA(+)没有亲和力。相反,N152Y突变增加了对TEA(+)阻滞的亲和力,但对Na(+)或Mg(2+)没有亲和力。用强向内整流Kir2.1取代通道的C端增加了Mg(2+)对阻滞的亲和力,但对Na(+)的亲和力影响不大。TEA(+)阻滞增强,具有更大的电压依赖性。我们用一个八态动力学模型来模拟这些结果。电压和外部K(+)的影响可以用一个模型来解释,在这个模型中,阻滞剂占据了一个位置,大概是在跨膜腔中,在很大程度上不受电场变化的影响。电压和细胞外K(+)的影响可以通过K(+)离子在选择性过滤器内占据位置的变化来解释。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Interactions of external K+ and internal blockers in a weak inward-rectifier K+ channel.

Interactions of external K+ and internal blockers in a weak inward-rectifier K+ channel.

Interactions of external K+ and internal blockers in a weak inward-rectifier K+ channel.

Interactions of external K+ and internal blockers in a weak inward-rectifier K+ channel.

We investigated the effects of changing extracellular K(+) concentrations on block of the weak inward-rectifier K(+) channel Kir1.1b (ROMK2) by the three intracellular cations Mg(2+), Na(+), and TEA(+). Single-channel currents were monitored in inside-out patches made from Xenopus laevis oocytes expressing the channels. With 110 mM K(+) in the inside (cytoplasmic) solution and 11 mM K(+) in the outside (extracellular) solution, these three cations blocked K(+) currents with a range of apparent affinities (K(i) (0) = 1.6 mM for Mg(2+), 160 mM for Na(+), and 1.8 mM for TEA(+)) but with similar voltage dependence (zδ = 0.58 for Mg(2+), 0.71 for Na(+), and 0.61 for TEA(+)) despite having different valences. When external K(+) was increased to 110 mM, the apparent affinity of all three blockers was decreased approximately threefold with no significant change in the voltage dependence of block. The possibility that the transmembrane cavity is the site of block was explored by making mutations at the N152 residue, a position previously shown to affect rectification in Kir channels. N152D increased the affinity for block by Mg(2+) but not for Na(+) or TEA(+). In contrast, the N152Y mutation increased the affinity for block by TEA(+) but not for Na(+) or Mg(2+). Replacing the C terminus of the channel with that of the strong inward-rectifier Kir2.1 increased the affinity of block by Mg(2+) but had a small effect on that by Na(+). TEA(+) block was enhanced and had a larger voltage dependence. We used an eight-state kinetic model to simulate these results. The effects of voltage and external K(+) could be explained by a model in which the blockers occupy a site, presumably in the transmembrane cavity, at a position that is largely unaffected by changes in the electric field. The effects of voltage and extracellular K(+) are explained by shifts in the occupancy of sites within the selectivity filter by K(+) ions.

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