TRIS+/NA+ PERMEABILITY RATIOS OF NICOTINIC ACETYLCHOLINE-RECEPTORS ARE REDUCED BY MUTATIONS NEAR THE INTRACELLULAR END OF THE M2 REGION
TRIS+/NA+ PERMEABILITY RATIOS OF NICOTINIC ACETYLCHOLINE-RECEPTORS ARE REDUCED BY MUTATIONS NEAR THE INTRACELLULAR END OF THE M2 REGION
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DOI：
10.1085/jgp.99.4.545
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发表时间：
1992-04-01
影响因子：
3.8
通讯作者：
LESTER, HA
中科院分区：
文献类型：
--
作者：
COHEN, BN;LABARCA, C;LESTER, HA
三羟甲基氨基甲烷/Na+渗透率的变化进行了测量从宏观乙酰胆碱诱导的电流为3野生型（WT），1杂交，2亚基缺陷，和25突变体烟碱受体在非洲爪蟾卵母细胞中表达的双离子反转电位。 在M2的推定细胞内末端附近的两个位置，2'（α-Thr 244、β-Gly 255、γ-Thr 253、δ-Ser 258）和-1'，点突变使小鼠受体的相对Tris+渗透性降低多达三倍。 其他几个位置的可比突变对相对Tris+渗透性没有影响。 δ突变对相对Tris+渗透性的影响大于γ突变;省略小鼠δ亚基（δ（0）受体）或用爪蟾δ替代小鼠δ显著降低了相对Tris+渗透性。 WT小鼠肌肉受体（α-β-γ-δ）对Tris+的相对渗透性高于野生型Torpedo受体。 数据分析表明，（a）突变产生的Tris+/Na+渗透率比的变化与M2中氨基酸残基的疏水性的相关性优于与其体积的相关性;（B）混合Na+/Tris+溶液中反转电位的摩尔分数依赖性与Goldman-Hodgkin-Katz电压方程大致一致。 结果表明，ACh受体通道中大的单价阳离子的主要离子选择性过滤器是由M2螺旋的细胞内末端附近的位置-1'和2'限定的区域。
Tris+/Na+ permeability ratios were measured from shifts in the biionic reversal potentials of the macroscopic ACh-induced currents for 3 wild-type (WT), 1 hybrid, 2 subunit-deficient, and 25 mutant nicotinic receptors expressed in Xenopus oocytes. At two positions near the putative intracellular end of M2, 2' (alpha-Thr244, beta-Gly255, gamma-Thr253, delta-Ser258) and -1', point mutations reduced the relative Tris+ permeability of the mouse receptor as much as threefold. Comparable mutations at several other positions had no effects on relative Tris+ permeability. Mutations in delta had a greater effect on relative Tris+ permeability than did comparable mutations in gamma; omission of the mouse delta-subunit (delta(0) receptor) or replacement of mouse delta with Xenopus delta-dramatically reduced relative Tris+ permeability. The WT mouse muscle receptor (alpha-beta-gamma-delta) had a higher relative permeability to Tris+ than the wild-type Torpedo receptor. Analyses of the data show that (a) changes in the Tris+/Na+ permeability ratio produced by mutations correlate better with the hydrophobicity of the amino acid residues in M2 than with their volume; and (b) the mole-fraction dependence of the reversal potential in mixed Na+/Tris+ solutions is approximately consistent with the Goldman-Hodgkin-Katz voltage equation. The results suggest that the main ion selectivity filter for large monovalent cations in the ACh receptor channel is the region delimited by positions -1' and 2' near the intracellular end of the M2 helix.