Abstract
GABA(A) receptors containing alpha(5)-subunit have an important role in cognitive function. As the agonistic effect of 3alpha-hydroxy ring-A reduced steroids depends on subunit combinations of the GABA(A) receptor, the antagonistic effect of pregnenolone sulfate and 3beta-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 3alpha-OH-5alpha-pregnan-20-one (3alpha5alphaP), 5alpha-pregnan-3alpha,21-diol-20-one (3alpha5alphaTHDOC) and 5alpha-androstane-3alpha,17beta-diol (3alpha5alphaADL) 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 3alpha5alphaTHDOC was significantly higher than 3alpha5alphaP and 3alpha5alphaADL. The efficacies of 5beta-pregnan-3beta,21-diol-20-one(UC1015) and 5alpha-pregnan-3beta,20alpha-diol(UC1019) to inhibit 30 microM GABA response, and the efficacies of 3beta-OH-5beta-pregnan-20-one (UC1014) and 5beta-pregnan-3beta, 20beta-diol (UC1020) to inhibit 3 microM 3alpha5alphaTHDOC+3 microM 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 3beta-hydroxypregnane steroids to inhibit the GABA response and the 3alpha5alphaTHDOC+GABA response did not vary between two receptors. Interestingly, the potencies and efficacies of pregnenolone sulfate and 3beta-hydroxypregnane steroids to inhibit the GABA response were positively correlated to their potencies and efficacies to inhibit the 3alpha5alphaTHDOC+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.
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