Model of subunit composition of gamma-aminobutyric acid A receptor subtypes expressed in rat cerebellum with respect to their alpha and gamma/delta subunits.

Antibodies specific for subunits of the gamma-aminobutyric acid A (GABAA) receptor have been used to immunoprecipitate [3H]muscimol, [3H]Ro 15-4513, and [3H]Ro 15-1788 binding sites from deoxycholate-solubilized preparations of rat cerebellum. Of the antisera raised against alpha subunits, those specific for alpha 6 immunoprecipitated the largest proportion of receptors. Two populations of alpha 6-containing GABAA receptors were identified. The first was labeled with [3H]Ro 15-4513 and exhibited a pharmacological profile consistent with that observed for alpha 6 beta 2 gamma 2 in transfected cells (Lüddens, H., Pritchett, D. B., Kohler, M., Killisch, I., Keinanen, K., Monyer, H., Sprengel, R., and Seeberg, P. H. (1990) Nature 346, 648-651). The second population was labeled only with [3H]muscimol and was deduced, from quantitative immunoprecipitation studies using combinations of antibodies, to contain both alpha 6 and delta subunits. The alpha 6 subunit was not observed to be present in combination with other alpha subunits or the gamma 1 subunit. Each of the other alpha subunits was found to be present in only one population of receptors in the cerebellum. Some subunits (alpha 4, alpha 5, and gamma 3) were not detectable. By combining information from quantitative immunoprecipitation experiments and Western blot analysis, a model describing the composition of all GABAA receptors in the cerebellum was constructed that defined the following alpha and gamma/delta combinations (percentage of cerebellar GABAA receptors): alpha 6 gamma 2 (36%), alpha 6 delta (23%), alpha 1 gamma 2 (28%), alpha 2 gamma 1 (8%), and alpha 3 gamma 2 (5%).