Anisatin modulation of temperature-dependent inhibition [3H]muscimol binding by chloride ion

We investigated the effects of anisatin, a pure toxic substance isolated from Illicium anisatum, and chloride ion on [3H]muscimol binding to rat brain membranes at various temperatures (0-16 degrees C). Chloride ion (100 mM) itself slightly inhibited specific [3H]muscimol binding at 0-4 degrees C and this inhibition was more marked at 10 or 16 degrees C than at 0-4 degrees C. Anisatin further decreased [3H]muscimol binding inhibited by 100 mM chloride at 16 degrees C without affecting the basal specific binding. These effects of anisatin were also dependent on the temperature. Scatchard analysis revealed that the effects of chloride and chloride plus anisatin on [3H]muscimol binding were mainly due to reduction in the number of binding sites. The temperature- and chloride-dependent effects of anisatin were similar to those of picrotoxinin. Pre-treatment of membranes with 0.05% Triton X-100 markedly decreased the inhibitory effects of chloride and chloride plus anisatin. Our results indicate that anisatin affects the number of GABA receptor sites probably through the picrotoxin sensitive sites and that chloride ion not only modifies the GABA receptors but also plays an important role in the action of anisatin and picrotoxinin.