Neurosteroid modulation of recombinant rat α5β2γ2L and α1β2γ2L GABAA receptors in Xenopus oocyte

GABAA receptors containing α5-subunit have an important role in cognitive function. As the agonistic effect of 3α-hydroxy ring-A reduced steroids depends on subunit combinations of the GABAA receptor, the antagonistic effect of pregnenolone sulfate and 3β-hydroxypregnane steroids may vary between α5-subunit and α1-subunit containing receptors. We investigated the effect of agonist and antagonist steroids in the recombinant rat α1β2γ2L and α5β2γ2L receptors expressed in Xenopus oocytes using a two electrodes voltage-clamp technique. We did not find any significant difference in potency and efficacy of GABA response between α1β2γ2L and α5β2γ2L receptors. Compared to the α1β2γ2L receptor, a significantly lower degree of desensitization was observed in the α5β2γ2L receptor. In addition, the potencies of 3α-OH-5α-pregnan-20-one (3α5αP), 5α-pregnan-3α,21-diol-20-one (3α5αTHDOC) and 5α-androstane-3α,17β-diol (3α5αADL) to enhance GABA response were significantly higher in the α5β2γ2L receptor, whereas their efficacies remained unchanged between two receptors. In either receptor, the efficacy of 3α5αTHDOC was significantly higher than 3α5αP and 3α5αADL. The efficacies of 5β-pregnan-3β,21-diol-20-one(UC1015) and 5α-pregnan-3β,20α-diol(UC1019) to inhibit 30 μM GABA response, and the efficacies of 3β-OH-5β-pregnan-20-one (UC1014) and 5β-pregnan-3β, 20β-diol (UC1020) to inhibit 3 μM 3α5αTHDOC + 3 μM GABA response were higher in the α5β2γ2L receptor compared to the α1β2γ2L receptor. The potencies of pregnenolone sulfate and 3β-hydroxypregnane steroids to inhibit the GABA response and the 3α5αTHDOC + GABA response did not vary between two receptors. Interestingly, the potencies and efficacies of pregnenolone sulfate and 3β-hydroxypregnane steroids to inhibit the GABA response were positively correlated to their potencies and efficacies to inhibit the 3α5αTHDOC + GABA response. Results from the current study revealed a different modulation pattern by neurosteroids between the α1β2γ2L and α5β2γ2L receptor.