Solubilization of the picrotoxinin binding receptor from mammalian brain

The binding sites for alpha-dihydropicrotoxinin (DHP), which is a ligand for the picrotoxin-sensitive component at the benzodiazepine-gamma-aminobutyric acid-receptor-ionophore complex, has been solubilized from rat brain, using 1% Lubrol. A new assay, which involves precipitation of the [3H]DHP-soluble protein complex by gamma-globulin and polyethylene glycol (PEG), followed by centrifugation, is described. The solubilized material bound DHP to two sites with apparent affinities of 0.038 and 1.85 microM. The binding of DHP to the solubilized receptors was inhibited by convulsant and depressant drugs with potencies similar to those required for membrane receptors. The ability of barbiturates to inhibit DHP binding to both solubilized and membrane receptors strongly suggests that barbiturates may interact with the picrotoxin binding component. These data suggest that ligand recognition properties of the picrotoxinin binding are not altered by solubilization. The binding was abolished by urea and partially destroyed by heating the soluble extract at 65 degrees C for 30 min. This new method of measuring the binding of ligands to the solubilized receptors by PEG centrifugation might be used successfully in other solubilization studies.