Steroid modulation of the concatameric receptors activated by GABA
The table shows the effect of coapplication of 1 μM allopregnanolone with a submaximal concentration of GABA. Given are the effect of steroid (mean ± S.D.) in the presence of a low concentration of GABA as the ratio of the response in the presence of 1 μM allopregnanolone to the response of that cell (third column) in the absence of steroid (1 stands for no effect) the ratio of the peak responses to that concentration of GABA alone and saturating GABA (fourth column). The first row (αβγ) gives the results obtained from receptors containing free α1, β2, and γ2L subunits. Receptors containing two mutated β subunits showed negligible currents in the presence of GABA. Accordingly, steroid potentiation of GABA-elicited currents was not examined.
| Receptor | Configuration | Potentiation by Allopregnanolone | Fractional GABA Response | No of Cells |
|---|---|---|---|---|
| αβγ | GS/GS | 2.9 ± 0.5 | 0.26 ± 0.03 | 7 |
| βαγ-βα | GS/GS | 4.2 ± 1.6 | 0.22 ± 0.09 | 5 |
| βαγ-β*α | GS/–S | 10.4 ± 2.6 | 0.23 ± 0.03 | 5 |
| βαγ-βα* | GS/G– | 2.2 ± 0.3 | 0.27 ± 0.05 | 4 |
| βαγ-β*α* | GS/– – | 4.4 ± 0.5 | 0.23 ± 0.04 | 5 |
| βα*γ-βα | G–/GS | 3.4 ± 0.6 | 0.19 ± 0.04 | 4 |
| βα*γ-β*α | G–/–S | 2.7 ± 0.3 | 0.28 ± 0.05 | 5 |
| βα*γ-βα* | G–/G– | 1.0 ± 0.1 | 0.24 ± 0.15 | 4 |
| βα*γ-β*α* | G–/– – | 1.2 ± 0.2 | 0.27 ± 0.01 | 4 |
| β*αγ-βα | –S/GS | 4.9 ± 0.6 | 0.21 ± 0.05 | 5 |
| β*αγ-β*α | –S/–S | N.D. | N.D. | N.D. |
| β*αγ-βα* | –S/G– | 2.5 ± 0.6 | 0.29 ± 0.04 | 6 |
| β*αγ-β*α* | –S/– – | N.D. | N.D. | N.D. |
| β*α*γ-βα | – –/GS | 4.2 ± 2.0 | 0.26 ± 0.08 | 3 |
| β*α*γ-β*α | – –/–S | N.D. | N.D. | N.D. |
| β*α*γ-βα* | – –/G– | 1.1 ± 0.1 | 0.26 ± 0.03 | 4 |
| β*α*γ-β*α* | – –/– – | N.D. | N.D. | N.D. |
β*, β(Y205S); α*, α(Q241L); G, intact GABA site; S, intact steroid site; N.D., not determined.