Wang F, Imoto K
Department of Medical Chemistry, Kyoto University Faculty of Medicine, Japan.
Proc Biol Sci. 1992 Oct 22;250(1327):11-7. doi: 10.1098/rspb.1992.0124.
To gain an insight into the molecular basis of ion permeation mechanism through the nicotinic acetylcholine receptor (AChR) channel, we have determined permeability ratios of organic cations relative to Na+ of specifically mutated Torpedo californica AChR channels expressed in Xenopus oocytes. The mutations involved mainly the side chains of the amino acid residues in the intermediate ring, where mutations have been found to exert strong effects on single-channel conductance and ion selectivity among alkali metal cations. The results obtained reveal that both the size and the net charge of the side chains of the intermediate ring are involved in determining the permeability, and provide experimental evidence that the pore size at the intermediate ring is a critical determinant of permeability. Our findings further suggest that changes in net charge exert effects on permeability by affecting the pore size of the channel.
为深入了解离子通过烟碱型乙酰胆碱受体（AChR）通道的渗透机制的分子基础，我们测定了非洲爪蟾卵母细胞中表达的特定突变的加州电鳐AChR通道的有机阳离子相对于Na⁺的渗透率比值。这些突变主要涉及中间环中氨基酸残基的侧链，在中间环处的突变已被发现对单通道电导以及碱金属阳离子之间的离子选择性有强烈影响。所获得的结果表明，中间环侧链的大小和净电荷都参与了渗透率的决定，并提供了实验证据，即中间环处的孔径是渗透率的关键决定因素。我们的研究结果进一步表明，净电荷的变化通过影响通道的孔径对渗透率产生影响。
