Which drug acts through alpha subunit of GABA?
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.
Benzodiazepine
Barbiturate
Haloperidol
TCA