Mutations in M2 alter the selectivity of the mouse nicotinic acetylcholine receptor for organic and alkali metal cations.
Mutations in M2 alter the selectivity of the mouse nicotinic acetylcholine receptor for organic and alkali metal cations.
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DOI：
10.1085/jgp.100.3.373
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发表时间：
1992-09
期刊：
影响因子：
--
通讯作者：
Lester HA
中科院分区：
文献类型：
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作者：
Cohen BN;Labarca C;Davidson N;Lester HA
我们利用宏观电流的双离子反转电位的变化，测量了非洲爪蟾卵母细胞中表达的 3 种野生型、1 种杂交型、2 种亚基缺陷型和 22 种突变型烟碱受体对碱金属和有机阳离子的渗透率比 (PX/PNa)。 M2 中三个位置（2'、6'、10'）的突变影响离子选择性。 M2 细胞内末端附近的位置 2'（α Thr244、β Gly255、γ Thr253、δ Ser258）处的突变使有机阳离子渗透性比率改变两倍，并使 PCs/PNa 和 PK/PNa 降低 16-18%。 6'和10'位置的突变增加了甘氨酸乙酯/Na+和甘氨酸甲酯/Na+的渗透性比率。两个亚基的改变也影响了选择性：缺失 delta 亚基使 PCs/PNa 减少了 16%，用 Xenopus delta 替代小鼠 delta 使 Pguanidinium/PNa 增加了两倍以上，并使 PCs/PNa 减少了 34%，PLi/PNa 减少了 20%。野生型小鼠受体与伯铵阳离子表现出令人惊讶的相互作用；相对渗透性在链长等于四个碳时达到峰值。对野生型小鼠受体的有机物渗透率比值分析表明：(a)孔最窄处的直径为8.4 A； (b) 小鼠受体对单价有机阳离子的尺寸选择性显着偏离； (c)降低温度使 Pguanidinium/PNa 减少 38%，对丁铵/PNa 减少两倍以上。结果强化了目前的观点，即位置-1'和2'是孔隙最窄的部分，并表明位置6'和10'以与通道阻断剂QX-222类似的相互作用排列孔隙中的一些渗透性有机阳离子。
We measured the permeability ratios (PX/PNa) of 3 wild-type, 1 hybrid, 2 subunit-deficient, and 22 mutant nicotinic receptors expressed in Xenopus oocytes for alkali metal and organic cations using shifts in the bi-ionic reversal potential of the macroscopic current. Mutations at three positions (2', 6', 10') in M2 affected ion selectivity. Mutations at position 2' (alpha Thr244, beta Gly255, gamma Thr253, delta Ser258) near the intracellular end of M2 changed the organic cation permeability ratios as much as twofold and reduced PCs/PNa and PK/PNa by 16-18%. Mutations at positions 6' and 10' increased the glycine ethyl ester/Na+ and glycine methyl ester/Na+ permeability ratios. Two subunit alterations also affected selectivity: omission of the delta subunit reduced PCs/PNa by 16%, and substitution of Xenopus delta for mouse delta increased Pguanidinium/PNa more than twofold and reduced PCs/PNa by 34% and PLi/PNa by 20%. The wild-type mouse receptor displayed a surprising interaction with the primary ammonium cations; relative permeability peaked at a chain length equal to four carbons. Analysis of the organic permeability ratios for the wild-type mouse receptor shows that (a) the diameter of the narrowest part of the pore is 8.4 A; (b) the mouse receptor departs significantly from size selectivity for monovalent organic cations; and (c) lowering the temperature reduces Pguanidinium/PNa by 38% and Pbutylammonium/PNa more than twofold. The results reinforce present views that positions -1' and 2' are the narrowest part of the pore and suggest that positions 6' and 10' align some permeant organic cations in the pore in an interaction similar to that with channel blocker, QX-222.