Bertrand D, Galzi J L, Devillers-Thiéry A, Bertrand S, Changeux J P
Département de Physiologie, Centre Médical Universitaire (Faculté de Médecine), Geneva, Switzerland.
Proc Natl Acad Sci U S A. 1993 Aug 1;90(15):6971-5. doi: 10.1073/pnas.90.15.6971.
The relative permeability for sodium, potassium, and calcium of chicken alpha 7 neuronal nicotinic receptor was investigated by mutagenesis of the channel domain M2. Mutations in the "intermediate ring" of negatively charged residues, located at the cytoplasmic end of M2 (site 1), reduce calcium permeability without significantly modifying other functional properties (activation and desensitization) of the receptor; a similar change of ion selectivity is also noticed when mutations at site 1 are done in the context of a receptor mutant that conducts ions in a desensitized state. Moreover, mutations of two adjacent rings of leucines at the synaptic end of M2 (site 2) have multiple effects. They abolish calcium permeability, increase the apparent affinity for acetylcholine by 10- to 100-fold, augment Hill numbers (up to 4.6-5.0) of acetylcholine dose-response relationships, slow rates of ionic response onset, and lower the extent of desensitization. Mutations at these two topographically distinct sites within M2 selectively alter calcium transport without affecting the relative permeabilities for sodium and potassium.
通过对通道结构域M2进行诱变，研究了鸡α7神经元烟碱型受体对钠、钾和钙的相对通透性。位于M2胞质端的带负电荷残基的“中间环”（位点1）发生突变，可降低钙通透性，而不会显著改变受体的其他功能特性（激活和脱敏）；当在处于脱敏状态下传导离子的受体突变体背景下进行位点1的突变时，也会观察到类似的离子选择性变化。此外，M2突触端两个相邻亮氨酸环（位点2）的突变具有多种效应。它们消除了钙通透性，使对乙酰胆碱的表观亲和力增加10至100倍，增加了乙酰胆碱剂量反应关系的希尔系数（高达4.6 - 5.0），减缓了离子反应起始速率，并降低了脱敏程度。M2内这两个拓扑结构不同的位点发生突变可选择性地改变钙转运，而不影响钠和钾的相对通透性。
