Freeze-fracture immunocytochemical study of the expression of native and recombinant GABAA receptors

To assess the density and distribution of native and recombinant GABA_A receptors we used label-fracture and fracture-flip technologies combined with immunocytochemistry using monoclonal and polyclonal Abs directed against the extracellular domain of the GABA_A receptor protein located in the freeze-fracture replicas. In cortical neurons there is a high density of GABA_A receptors on both soma and dendrites with some areas were the density of receptors is higher, but there are no well defined clusters. In cerebellar granule cells most of the receptors are distributed in round clusters both in neurites and soma. In astroglial cells the receptor density is lower than in neurons and only occasionally they appear in clusters. In cells transfected with cDNAs encoding for various molecular forms of GABA_A receptor subunits, the receptor density is moderate when cDNAs for α, β and γ subnits are cotransfected; however, on cells cotransfected with cDNAs for β and γ subunits the receptor density is significantly lower. Recombinant receptors appear randomly distributed and occasionally they aggregate in small groups.