FURTHER EVIDENCE FOR THE EXISTENCE OF ALPHA-SUBUNIT HETEROGENEITY WITHIN DISCRETE GAMMA-AMINOBUTYRIC ACIDA-RECEPTOR SUBPOPULATIONS

The alpha subunit complements of natural gamma-aminobutyric acid(A) (GABA(A)) receptor subpopulations were investigated by their purification from mammalian cerebral cortex and cerebellum by immunoaffinity chromatography using antibodies raised against peptide sequences unique to the alpha1, alpha2, alpha3, and alpha6 subunits. Receptors purified from cerebral cortex by anti-Cys alpha2 414-424 and anti-Cys alpha3 454-467 antibody affinity columns in series had immunoreactivity with alpha2 and alpha3 but not alpha1 subunit-specific antibodies. Receptors purified from cerebellum by a new affinity column matrix, anti-alpha6 1-16 Cys whole antibody, or the Fab fragment thereof, enriched for alpha6 subunit immunoreactivity. A further series of experiments demonstrated the partial coexistence of this alpha6 subunit immunoreactivity with that for the alpha1 but not the alpha2 and alpha3 subunits. These results provide additional evidence for the existence of GABA(A) receptor subpopulations with heterogeneous alpha subunit complements yielding increased structural diversity of natural GABA(A) receptors. Furthermore, they substantiate previous findings implicating the presence of two alpha subunits per receptor oligomer.