Effects of specific modifications of several hydroxyls of tetrodotoxin on its affinity to rat brain membrane

Mari Yotsu-Yamashita, Atsuko Sugimoto, Akira Takai, Takeshi Yasumoto

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    65 Citations (Scopus)


    The widely used sodium channel blocker tetrodotoxin (TTX) is a compound that has six hydroxyl residues at the C-4, C-6, C-8, C-9, C-10, and C-11 positions in addition to a guanidinium group, which is positively charged in biological pH range. Thirteen analogs of this toxin with structural modifications involving one or more of these hydroxyls were examined on their affinity to a rat brain membrane preparation, which is known to contain sodium channels abundantly. The equilibrium dissociation constants associated with the binding of TTX and its analogs to the sodium channels were estimated, from their ability to inhibit the binding of [3H]saxitoxin, as follows (in nM): TTX, 1.8; chiriquitoxin, 1.0; 11-oxo-I-FX, 1.5; 11-nor-TTX- 6,6-diol, 1.6; 11-nor-TTX6(S)-ol, 23; 11-norTTX-6(R)-ol, 31; 11-deoxy-TTX, 37; 6-ep/TTX, 39; 4-ep/TTX, 68; 4,9-anhydro-TTX, 180; TTX-8-O-hemisuccinate, >380; TTX-11-carboxylic acid, >2300; tetrodonic acid, >3600; 5,6,11-trideoxy- TTX, >5000. The reduction of the affinity observed with the analogs involving reduction or translocation of the hydroxyls at C-6 and C-11 is indicative of the contribution of these residues to the binding to sodium channels as hydrogen bond donors. The especially large value of the dissociation constant for TTX-11-carboxylic acid is consistent with the idea that the C-11-hydroxyl forms a hydrogen bond with a carboxylic acid residue of the channel protein. The markedly low affinity of TTX-8-O-hemisuccinate may possibly be ascribable to intramolecular salt-bridge formation, which neutralizes the positive charge of the guanidinium group.

    Original languageEnglish
    Pages (from-to)1688-1696
    Number of pages9
    JournalJournal of Pharmacology and Experimental Therapeutics
    Issue number3
    Publication statusPublished - 1999 Jun

    ASJC Scopus subject areas

    • Molecular Medicine
    • Pharmacology


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