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

GABAA receptors containing alpha(5)-subunit have an important role in cognitive function. As the agonistic effect of 3 alpha-hydroxy ring-A reduced steroids depends on subunit combinations of the GABAA receptor, the antagonistic effect of pregnenolone sulfate and 3 beta-hydroxypregnane steroids may vary between alpha(5)-subunit and alpha(1)-subunit containing receptors. We investigated the effect of agonist and antagonist steroids in the recombinant rat alpha(1)beta(2)gamma(2L) and alpha(5)beta(2)gamma(2L) 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 alpha(1)beta(2)gamma(2L) and alpha(5)beta(2)gamma(2L) receptors. Compared to the alpha(1)beta(2)gamma(2L) receptor, a significantly lower degree of desensitization was observed in the alpha(5)beta(2)gamma(2L) receptor. In addition, the potencies of 3 alpha-OH-5 alpha-pregnan-20-one (3 alpha 5 alpha P), 5 alpha-pregnan-3 alpha,21-diol-20-one (3 alpha 5 alpha THDOC) and 5 alpha-androstane-3 alpha,17 beta-diol (3 alpha 5 alpha ADL) to enhance GABA response were significantly higher in the alpha(5)beta(2)gamma(2L) receptor, whereas their efficacies remained unchanged between two receptors. In either receptor, the efficacy of 3 alpha 5 alpha THDOC was significantly higher than 3 alpha 5 alpha P and 3 alpha 5 alpha ADL. The efficacies of 5 beta-pregnan-3,21-diol-20-one(UC1015) and 5 alpha-pregnan-3 beta,20 alpha-diol(UC1019) to inhibit 30 mu M GABA response, and the efficacies of 3 beta-OH-5 beta-pregnan-20-one (UC1014) and 5 beta-pregnan-3 beta, 20 beta-diol (UC1020) to inhibit 3 mu M 3 alpha 5 alpha THDOC+3 mu M GABA response were higher in the alpha(5)beta(2)gamma(2L) receptor compared to the alpha(1)beta(2)gamma(2L) receptor. The potencies of pregnenolone sulfate and 3 beta-hydroxypregnane steroids to inhibit the GABA response and the 3 alpha 5 alpha THDOC+GABA response did not vary between two receptors. Interestingly, the potencies and efficacies of pregnenolone sulfate and 3 beta-hydroxypregnane steroids to inhibit the GABA response were positively correlated to their potencies and efficacies to inhibit the 3 alpha 5 alpha THDOC+GABA response. Results from the current study revealed a different modulation pattern by neurosteroids between the alpha(1)beta(2)gamma(2L) and alpha(5)beta(2)gamma(2L) receptor. (c) 2006 Elsevier B.V. All rights reserved.