title: Brevetoxins bind to multiple classes of sites in rat brain synaptosomes.
abstract: The brevetoxins (PbTx series), neurotoxins produced by the marine dinoflagellate Ptychodiscus brevis, cause dose-dependent activation of the voltage-sensitive sodium channel (VSSC). Saturation binding studies employing adult rat brain synaptosomes suggest the existence of a high affinity/low capacity (HA/LC) and a second, lower affinity/higher capacity (LA/HC) class of binding site. LIGAND analysis of saxitoxin and brevetoxin saturation binding data yields a statistically identical Bmax for the brevetoxin high affinity/low capacity (HA/LC) site (1.9 +/- 0.98 pmol/mg protein) and for saxitoxin (1.72 +/- 0.78 pmol/mg protein; P less than 0.001). The stoichiometry of HA/LC brevetoxin binding and saxitoxin binding approaches 1:1. Covalent modification of synaptosomes with a brevetoxin photoaffinity probe preferentially blocks the HA/LC binding site. Hill plots of saturation binding data yield a coefficient of 1.0 +/- 0.02, demonstrating a lack of cooperativity between brevetoxin binding site classes. Kd and Bmax for toxin binding are independent of membrane polarity, intimating that the observed low affinity/high capacity (LA/HC) binding characteristics are not due to modification of the HA/LC site, and strongly argue for the presence of multiple brevetoxin binding site classes. Half-maximal binding at the LA/HC site, and strongly argue for the presence of multiple brevetoxin binding site classes. Half-maximal binding at the LA/HC site occurs at concentration ranges for which the brevetoxins allosterically modulate binding of other natural toxins to their specific sites.
authors.affiliation: University of Miami, Rosenstiel School of Marine and Atmospheric Science, NIEHS Marine and Freshwater Biomedical Sciences Center, FL 33149.
authors.forename: R A
authors.initials: RA
authors.lastname: Edwards
authors.forename: V L
authors.initials: VL
authors.lastname: Trainer
authors.forename: D G
authors.initials: DG
authors.lastname: Baden
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D008297:Male; D008387:Marine Toxins / Q000378:metabolism*; D015394:Molecular Structure; D009498:Neurotoxins / Q000378:metabolism*; D035964:Oxocins; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012530:Saxitoxin / Q000378:metabolism; D015222:Sodium Channels; D013574:Synaptosomes / Q000378:metabolism*; D000095702:Polyether Toxins
chemical_list: D008387:Marine Toxins; D009498:Neurotoxins; D035964:Oxocins; D011956:Receptors, Cell Surface; D012530:Saxitoxin; D015222:Sodium Channels; C072089:brevetoxin receptor; C053342:brevetoxin; D000095702:Polyether Toxins