title: Structure of the saxitoxin binding site at sodium channels in nerve membranes. Exchange of tritium from bound toxin molecules.
abstract: The exchange of tritium into water from saxitoxin molecules that were radiolabeled at the C-11 methylene position was measured at 37 degrees in solution and in suspensions of brain membranes. High concentrations of membrane receptors were used to assure that more than 80% of the total saxitoxin (STX) present was specifically bound. The amount of back-exchanged tritium was determined either by measuring the radioactivity remaining in the STX, using a second binding assay, or by measuring the tritium in water using ion-exchange chromatography. The results show that the back-exchange is accelerated in the presence of the membranes, and that this is attributable solely to the nonspecific toxin binding. Little change in the back-exchange rate over that in solution occurs in specifically bound toxin molecules. These results place certain restrictions on the possible bonds and configurations of receptor-toxin complexes.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D011894:Rana pipiens; D012530:Saxitoxin / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
chemical_list: D007473:Ion Channels; D012530:Saxitoxin; D012964:Sodium