Dominant GABA A receptor/Cl – channel kinetics correlate with the relative expressions of α 2 , α 3 , α 5 and β 3 subunits in embryonic rat neurones

The embryonic appearance of GABAergic cells and signals in the rat nervous system coincides with the appearance of transcripts encoding some but not all of the subunits forming GABA A receptor/Cl – channels. Quantitative in situ hybridization studies reveal higher variabilities in α 2 and α 3 subunit transcripts relative to others examined (α 5 , β 2 , β 3 and γ 2 ) in six spinal and supraspinal regions. Immunocytochemistry of cells dissociated from the embryonic CNS shows that α 2 and α 3 subunits are detectable in differentiating neurones. FACS analyses of dissociated cells immunostained with α 2 ‐ or α 3 ‐ antibodies reveal immunopositive subpopulations of variable size in each region. Whole‐cell recordings of acutely adherent neurones show that GABA activates Cl – currents whose fluctuations characteristically vary depending on a neurone’s region of origin. Spectral analyses indicate a predominance of the low frequency (< 5 Hz) components, which vary regionally. Regression analyses reveal that (i) channel properties correlate with subunit transcript levels and (ii) dominant channel kinetics correlate with α 2 and α 3 subunit transcripts indexed as a ratio and with coexpressions of α 5 and β 3 . The correlations strongly suggest that α 3 subunits in embryonic neurones are expressed in native receptor/channel complexes with slower kinetics than those containing α 2 without α 3 subunits. Thus, GABA A receptor/Cl – channels in these embryonic neurones may be encoded by the six transcripts (α 2 , α 3 , α 5 , and β 2 , β 3 , and γ 2 ) with proportions of α 2 , α 3 , α 5 , and β 3 subunits critical in determining their dominant kinetics.