Specific binding of a phenyl-pyridazinium derivative endowed with GABAA receptor antagonist activity to rat brain.

SR 95531 has been shown to be a potent, selective, reversible and competitive GABAA antagonist. In the present study we report that (3H)SR 95531 binds with high affinity and in a specific and saturable manner to rat brain membranes. Scatchard analysis revealed two binding sites (KD: 6 nM; Bmax: 0.24 pmol/mg protein and KD: 38 nM; Bmax: 0.66 pmol/mg protein). Only GABA ligands were effective displacers of (3H)SR 95531. The respective IC50 values obtained with these compounds suggests that (3H)SR 95531 labels the GABA receptor in its antagonist conformation.