A mutant of TTX-resistant cardiac sodium channels with TTX-sensitive properties.
The cardiac sodium channel alpha subunit (RHI) is less sensitive to tetrodotoxin (TTX) and saxitoxin (STX) and more sensitive to cadmium than brain and skeletal muscle (microliter) isoforms. An RHI mutant, with Tyr substituted for Cys at position 374 (as in microliter) confers three properties of TTX-sensitive channels: (i) greater sensitivity to TTX (730-fold); (ii) lower sensitivity to cadmium (28-fold); and (iii) altered additional block by toxin upon repetitive stimulation. Thus, the primary determinant of high-affinity TTX-STX binding is a critical aromatic residue at position 374, and the interaction may take place possibly through an ionized hydrogen bond. This finding requires revision of the sodium channel pore structure that has been previously suggested by homology with the potassium channel.
Satin
J
J
Department of Medicine, University of Chicago, IL 60637.
Kyle
J W
JW
Chen
M
M
Bell
P
P
Cribbs
L L
LL
Fozzard
H A
HA
Rogart
R B
RB
D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000502:physiology; D002104:Cadmium / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology; D003001:Cloning, Molecular; D004351:Drug Resistance / Q000235:genetics; D005822:Genetic Vectors; D006321:Heart / Q000502:physiology*; D007700:Kinetics; D008969:Molecular Sequence Data; D009132:Muscles / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D012313:RNA / Q000235:genetics; D051381:Rats; D015183:Restriction Mapping; D012530:Saxitoxin / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology*; D014981:Xenopus
D015222:Sodium Channels; D002104:Cadmium; D012530:Saxitoxin; D013779:Tetrodotoxin; D012313:RNA