Purification of the GABA/benzodiazepine/barbiturate receptor complex

The post synaptic receptor for the inhibitory neurotransmitter γ-aminobutyric acid (GABA) is a complex protein containing a chloride channel and modulatory sites for two classes of drugs, the benzodiazepines (BZ) and convulsants/barbiturates. Barbiturates which enhance GABA-activated chloride permeability at the tissue and cellular level also are able to enhance benzodiazepine and GABA receptor binding at the molecular level. Convulsant/barbiturate sites can be assayed directly with [ 35S]t-butyl bicyclophosphorothionate (TBPS). This activity was solubilized with the detergent CHAPS and shown to co-migrate with BZ and GABA receptor binding activity during protein fractionation as a single protein complex, which could be purified intact by over 1000-fold on benzodiazepine affinity columns.