title: Mapping the site of block by tetrodotoxin and saxitoxin of sodium channel II.
abstract: The SS2 and adjacent regions of the 4 internal repeats of sodium channel II were subjected to single mutations involving, mainly, charged amino acid residues. These sodium channel mutants, expressed in Xenopus oocytes by microinjection of cDNA-derived mRNAs, were tested for sensitivity to tetrodotoxin and saxitoxin and for single-channel conductance. The results obtained show that mutations involving 2 clusters of predominantly negatively charged residues, located at equivalent positions in the SS2 segment of the 4 repeats, strongly reduce toxin sensitivity, whereas mutations of adjacent residues exert much smaller or no effects. This suggests that the 2 clusters of residues, probably forming ring structures, take part in the extracellular mouth and/or the pore wall of the sodium channel. This view is further supported by our finding that all mutations reducing net negative charge in these amino acid clusters cause a marked decrease in single-channel conductance.
authors.affiliation: Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Terlau
authors.forename: S H
authors.initials: SH
authors.lastname: Heinemann
authors.forename: W
authors.initials: W
authors.lastname: Stühmer
authors.forename: M
authors.initials: M
authors.lastname: Pusch
authors.forename: F
authors.initials: F
authors.lastname: Conti
authors.forename: K
authors.initials: K
authors.lastname: Imoto
authors.forename: S
authors.initials: S
authors.lastname: Numa
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000595:Amino Acid Sequence; D000818:Animals; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010449:Peptide Mapping; D051381:Rats; D012530:Saxitoxin / Q000235:genetics* / Q000494:pharmacology; D015222:Sodium Channels / Q000737:chemistry* / Q000187:drug effects; D013779:Tetrodotoxin / Q000235:genetics* / Q000494:pharmacology
chemical_list: D015222:Sodium Channels; D012530:Saxitoxin; D013779:Tetrodotoxin