Evidence that the M2 membrane-spanning region lines the ion channel pore of the nicotinic receptor.
Site-directed mutagenesis and expression in Xenopus oocytes were used to study acetylcholine receptors in which serine residues (i) were replaced by alanines (alpha, delta subunits) or (ii) replaced a phenylalanine (beta subunit) at a postulated polar site within the M2 transmembrane helix. As the number of serines decreased, there were decreases in the residence time and consequently the equilibrium binding affinity of QX-222, a quaternary ammonium anesthetic derivative thought to bind within the open channel. Receptors with three serine-to-alanine mutations also displayed a selective decrease in outward single-channel currents. Both the direction of this rectification and the voltage dependence of QX-222 blockade suggest that the residues mutated are within the aqueous pore of the receptor and near its cytoplasmic (inner) surface.
Leonard
R J
RJ
Division of Biology, California Institute of Technology, Pasadena 91125.
Labarca
C G
CG
Charnet
P
P
Davidson
N
N
Lester
H A
HA
D000818:Animals; D002462:Cell Membrane / Q000502:physiology*; D003001:Cloning, Molecular; D004553:Electric Conductivity; D005260:Female; D007473:Ion Channels / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials; D009154:Mutation; D009865:Oocytes / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics; D011978:Receptors, Nicotinic / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic; D014981:Xenopus
D007473:Ion Channels; D012333:RNA, Messenger; D011978:Receptors, Nicotinic