Properties of a high affinity binding site for [3H]avermectin B1a.

The specific high affinity binding of [3H]avermectin B1a was investigated in membranes from several rat brain regions. Binding occurred rapidly, was reversible and partially dependent on the presence of chloride ions in the incubation medium. Specific high affinity binding of [3H]avermectin B1a was partially inhibited by GABA receptor agonists and this effect was blocked by GABA receptor antagonists. Pentobarbital and etazolate inhibited, and picrotoxin, picrotoxinin and IPTBO stimulated high affinity binding of [3H]avermectin B1a. All these effects were influenced by the presence of chloride ions in the incubation medium. The results indicate that the high affinity binding site of [3H]avermectin B1a is associated with the GABA-benzodiazepine receptor-chloride ion channel complex.