DOMINANT GABA(A) RECEPTOR CL- CHANNEL KINETICS CORRELATE WITH THE RELATIVE EXPRESSIONS OF ALPHA(2),ALPHA(3),ALPHA(5) AND BETA(3) SUBUNITS IN EMBRYONIC RAT NEURONS/

The embryonic appearance of GABAergic cells and signals in the rat ner vous system coincides with the appearance of transcripts encoding some but not all of the subunits forming GABA(A) receptor/Cl- channels. Qu antitative in situ hybridization studies reveal higher variabilities i n alpha(2) and alpha(3) subunit transcripts relative to others examine d (alpha(5), beta(2), beta(3) and gamma(2)) in six spinal and supraspi nal regions. Immunocytochemistry of cells dissociated from the embryon ic CNS shows that alpha(2) and alpha 3 subunits are detectable in diff erentiating neurones. FAGS analyses of dissociated cells immunostained with alpha(2)- -or alpha(3)-antibodies reveal immunopositive subpopul ations of variable size in each region. Whole-cell recordings of acute ly adherent neurones show that GABA activates Cl- currents whose fluct uations characteristically vary depending on a neurone's region of ori gin. Spectral analyses indicate a predominance of the low frequency (< 5 Hz) components, which vary regionally. Regression analyses reveal t hat (i) channel properties correlate with subunit transcript levels an d (ii) dominant channel kinetics correlate with alpha(2) and alpha(3) subunit transcripts indexed as a ratio and with coexpressions of alpha (5) and beta(3). The correlations strongly suggest that alpha(3) subun its in embryonic neurones are expressed in native receptor/channel com plexes with slower kinetics than those containing alpha(2) without alp ha 3 subunits, Thus, GABA(A) receptor/Cl- channels in these embryonic neurones may be encoded by the six transcripts (alpha(2), alpha(3), al pha(5), and beta(2), beta(3), and gamma(2)) with proportions of alpha 2, alpha(3), alpha(5), and beta(3) subunits critical in determining th eir dominant kinetics.