The influence of subunit composition on the interaction of neurosteroids with GABAA receptors

NOTE: THE MATHEMATICAL SYMBOLS/SPECIAL CHARACTERS IN THIS ABSTRACT CANNOT BE DISPLAYED CORRECTLY ON THIS PAGE. PLEASE REFER TO THE ABSTRACT ON THE PUBLISHER’S WEBSITE FOR AN ACCURATE DISPLAY.The influence of the subunit composition of human GABAA receptors upon the GABA-modulatory properties of 5a-pregnan-3a-ol-20-one (5a,3a) has been examined using the Xenopus laevis oocyte expression system and the two electrode voltage-clamp technique. Steroid potency (EC50) is modestly influenced by the a-isoform (axß1?2L; x=1–6). a2-, a4- and a5-containing receptors are significantly less sensitive to the action of low concentrations of 5a,3a (10–100 nM) when compared to a1,3,6ß1?2L receptors. Additionally, the maximal effect of the steroid is favoured at a6-containing receptors. The ß-isoform (a1ßy?2L; y=1–3) has little influence on the GABA-modulatory effect of the neurosteroid. The EC50 of 5a,3a is only modestly influenced by the omission of the ?2 subunit (a1ß1?2L vs a1ß1): while the maximal effect is favoured by the binary complex. However, the identity of the ? subunit influences the GABAA-modulatory potency of 5a,3a with ?2- and ?1-containing receptors being the most and the least sensitive to 5a,3a, respectively. Finally, incorporation of the , or d subunit dramatically reduces and augments the GABA-enhancing actions of the steroid, respectively. These findings provide evidence that 5a,3a discriminates amongst recombinant receptors of varied subunit composition. Furthermore, this selectivity may contribute to their neuronal specificity and behavioural profile.