Fig. 1.

Neurosteroid affinity of recombinant GABA_ARs containing α1 or α2 subunit. Two distinct receptor compositions of the rat GABA_AR were tested for their apparent affinity for 3α-OH-DHP using a [³⁵S]TBPS binding assay. 3α-OH-DHP inhibited binding of the radioactive ligand in a concentration-dependent manner. In the absence of GABA (top 2 traces), the apparent affinity for 3α-OH-DHP was significantly higher for α1-containing receptors. However, in the presence of GABA (1 μm;bottom 2 traces), there was no such difference. All data were normalized to the control [³⁵S]TBPS binding in the absence of GABA and 3α-OH-DHP.