FunctionaI eflects oltryptophan substitutions in the M4 (ransmemhrane domain ol the nicolinic aeclykholine receptor

• Published in: Japanese Journal of Pharmacology Vol. 82; no. suppl.1; p. 135
• Main Authors: Shiori Tamamizu-Kato, Hiroyuki Kato, Tsutomu Nakada, Maho Mizowaki, Jose A. Lasalde, Mark G. McNamee, Kazuo Toriizuka, Toshihiko Hanawa
• Format: Journal Article
• Language: Japanese
• Published: The Japanese Pharmacological Society 2000
• ISSN: 0021-5198

The nicotinic acetylcholine receptor (nAChR) is a ligand-gated ion channel composed of four different homologous subunits. Each subunit contains four hydrophobic putative transmembrane domains (M1-M4). In this study, we introduced tryptophan substitutions at twelve positions along the M4 segment of Torpedo calijbrnica nAChR and expressed them in Xenopus laevis oocytes in order to examine functional consequences of the substitutions. The expression levels of mutants, C412W, G421W, S424W and V425W, were almost as same as that of the wild type whereas other mutants (M415W, L416W, C418W, I419W, I420W, T422W, and V423W) had relatively lower expression levels compared to the wild type as measured by alphabungarotoxin binding (^^125 I-BgTx). I417W gave no detectable ^^125 I-BgTx binding on the surface of oocytes. These results indicated that the position I417 might be involved in the nAChR assembly, oligomerization or transport to the cell membrane. In voltageclamped oocytes, C418W, G421W and V425W produced increases in normalized macroscopic response to acetyleholine. Single channel study of the C418W, G421W and V425W showed a significant increase in the open channel probability.