<prompt> Which drug acts through alpha subunit of GABA?BenzodiazepineBarbiturateHaloperidolTCA  <response>: The exact subunit structures of native GABA receptors are still unknown, but it is thought that most GABA receptor are composed of α, β and γ subunits that coassemble with some uncertain stoichiometry.Binding site of GABA is on β -subunit.Benzodiazepine site is located on the a subunit but the stabilization or completion of that site in the assembled structure requires also the γ subunit.The photo - affinity labeling of the benzodiazepine site has confirmed, using isoform - antibodies, to be on an α and not a γ subunit.So, BZD binding site is present on α subunit at α - γ interface, and both α γ units are required for BZDs action.Barbiturates act on Picrotoxin site that is located usually on β- subunit at α -β interface. Both α β subunit are required for barbiturates action.GABA β - subunit.BZD α subunit at α - γ interface, i.e. α γ site.Barbiturate β subunit at α - β interface, i.e. α β site. 