The pharmacology of the benzodiazepine site of the GABA-A receptor is dependent on the type of gamma-subunit present.

The pharmacology of native and recombinant GABA-A receptors containing either gamma1, gamma2 or gamma3 subunits has been investigated. The pharmacology of native receptors has been investigated by immunoprecipitating receptors from solubilised preparations of rat brain with antisera specific for individual gamma-subunits and analysing their radioligand binding characteristics. Receptors containing a gamma1-subunit do not bind benzodiazepine radioligands with high affinity. Those containing either a gamma2 or gamma3 subunit bind [3H]flumazenil with high affinity. Some compounds compete for these binding sites with multiple affinities, reflecting the presence of populations of receptors containing several different types of alpha-subunit. Photoaffinity-labelling of GABA-A receptors from a cell line stably expressing GABA-A receptors of composition alpha1beta3gamma2 followed by immunoprecipitation of individual subunits revealed that the alpha and gamma but not the beta-subunit could be irreversibly labelled by [3H]flunitrazepam. The properties of recombinant receptors have been investigated in oocytes expressing gamma1, gamma2, or gamma3 subunits in combination with an alpha and a beta-subunit. Some compounds such as zolpidem, DMCM and flunitrazepam show selectivity for receptors containing different gamma-subunits. Others such as CL 218,872 show no selectivity between receptors containing different gamma-subunits but exhibit selectivity for receptors containing different alpha-subunits. These data taken together suggest that the benzodiazepine site of the GABA-A receptor is formed with contributions from both the alpha and gamma-subunits.