期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1998
卷号：95
期号：5
页码：2653-2658
DOI：10.1073/pnas.95.5.2653
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Batrachotoxin (BTX) is a steroidal alkaloid that causes Na+ channels to open persistently. This toxin has been used widely as a tool for studying Na+ channel gating processes and for estimating Na+ channel density. In this report we used point mutations to identify critical residues involved in BTX binding and to examine if such mutations affect channel gating. We show that a single asparagine [->] lysine substitution of the rat muscle Na+ channel -subunit, {micro}1-N434K, renders the channel completely insensitive to 5 {micro}M BTX when expressed in mammalian cells. This mutant channel nonetheless displays normal current kinetics with minimal changes in gating properties. Another substitution, {micro}1-N434A, yields a partial BTX-sensitive mutant. Unlike wild-type currents, the BTX-modified {micro}1-N434A currents continue to undergo fast and slow inactivation as if the inactivation processes remain functional. This finding implies that the {micro}1-N434 residue upon binding with BTX is critical for subsequent changes on gating; alanine at the {micro}1-434 position apparently diminishes the efficacy of BTX on eliminating Na+ channel inactivation. Mutants of two adjacent residues, {micro}1-I433K and {micro}1-L437K, also were found to exhibit the identical BTX-resistant phenotype. We propose that the {micro}1-I433, {micro}1-N434, and {micro}1-L437 residues in transmembrane segment I-S6 probably form a part of the BTX receptor.
