Characterization of the Ptychodiscus brevis Polyether Neurotoxin Binding Component in Excitable Membranes

The polyether lipid-soluble toxins isolated from the marine dinoflagellate Ptychodiscus brevis (formerly Gymnodinium breve) bind to a unique site associated with rat brain synaptosomes. Using tritiated brevetoxin PbTx-3 as a specific probe, binding was determined at 4 C in synaptosomes using a rapid centrifugation technique. Rosenthal analysis yields a K sub D of 2.9 nM and a B sub max of 6.8 pmoles toxin bound/mg synaptosomal protein. Labeled toxin can be displaced by unlabeled PbTx-3, PbTx-2, or synthetic PbTx-3 (reduced PbTx-2) but not by a nontoxic synthetic oxidized derivative of PbTx-2. Competition experiments using natural toxins specific for Sites 1-4 of the voltage-sensitive sodium channel have illustrated that PbTx-3 does not bind to any of the previously-described sites. A fifth site is proposed. In addition, because of the varied nomenclature associated with the brevetoxins, a new toxin notation system is proposed.