GABA-A RECEPTOR SUBTYPES IMMUNOPURIFIED FROM RAT-BRAIN WITH ALPHA SUBUNIT-SPECIFIC ANTIBODIES HAVE UNIQUE PHARMACOLOGICAL PROPERTIES

The unique cytoplasmic loop regions of the alpha-1, alpha-2, alpha-3, and alpha-5 subunits of the GABA(A) receptor were expressed in bacteria and used to produce subunit-specific polyclonal antisera. Antibodies immobilized on protein A-Sepharose were used to isolate naturally occurring alpha-specific populations of GABA(A) receptors from rat brain that retained the ability to bind [H-3]muscimol, [H-3]flunitrazepam, [H-3]Ro15-1788, and [I-125]iodoclonazepam with high affinity. Pharmacological characterization of these subtypes revealed marked differences between the isolated receptor populations and was generally in agreement with the reported pharmacological profiles of GABA(A) receptors in cells transiently transfected with alpha-1-beta-1-gamma-2, alpha-2-beta-1-gamma-2, alpha-3-beta-1-gamma-2, and alpha-5-beta-1-gamma-2 combinations of subunits. Additional subtypes were also identified that bind [H-3]muscimol but do not bind benzodiazepines with high affinity. The majority of GABA(A) receptor oligomers contains only a single type of alpha-subunit, and we conclude that alpha-1, alpha-2, alpha-3, and alpha-5 subunits exist in vivo in combination with the beta-subunit and gamma-2 subunit.