batrachotoxinin-a-20-alpha-benzoate and protopanaxadiol

A [(3)H]batrachotoxinin A-20alpha-benzoate ([(3)H]BTX-B) binding assay was used to investigate the interaction of two ginseng aglycones (20(S)protopanaxadiol and 20(S)protopanaxatriol) and Rh(2) (a monoglucoside of 20(S)protopanaxadiol) with voltage-gated sodium channels in mouse brain. All compounds inhibited the binding of [(3)H]BTX-B and IC(50)s were established at 42 microM (20(S)protopanaxadiol), 79 microM (20(S)protopanaxatriol) and 162 microM (Rh(2)). Scatchard analysis confirmed that 20(S)protopanaxadiol and Rh-2 reduced the B(max) of [(3)H]BTX-B binding while Rh(2) also increased the K(d). At IC(50) concentrations and above, 20(S)protopanaxadiol and Rh(2) increased the dissociation of the [(3)H]BTX-B:sodium channel complex above that produced by a saturating concentration of veratridine, but failed to reduce the rate of association of [(3)H]BTX-B with sodium channels. Reversal of the inhibition of [(3)H]BTX-B binding by 20(S)protopanaxadiol and Rh(2) occurred slowly. We conclude that the 20(S)protopanaxadiol and the less potent inhibitor Rh(2) destabilize BTX-B-activated sodium channels through non-covalent allosteric modification of neurotoxin binding site 2.

Topics: Animals; Batrachotoxins; Binding, Competitive; Cell Membrane; Cerebral Cortex; Dose-Response Relationship, Drug; Ginsenosides; Kinetics; Male; Mice; Molecular Structure; Neurons; Panax; Plant Extracts; Radioligand Assay; Sapogenins; Sodium Channels; Solubility; Synaptosomes; Triterpenes; Tritium