3beta -hydroxypregnane steroids are pregnenolone sulfate-like GABA(A) receptor antagonists.
Endogenous neurosteroids have rapid actions on ion channels, particularly GABA(A) receptors, which are potentiated by nanomolar concentrations of 3alpha-hydroxypregnane neurosteroids. Previous evidence suggests that 3beta-hydroxypregnane steroids may competitively antagonize potentiation induced by their 3alpha diastereomers. Because of the potential importance of antagonists as experimental and clinical tools, we characterized the functional effect of 3beta-hydroxysteroids. Although 3beta-hydroxysteroids reduced the potentiation induced by 3alpha-hydroxysteroids, 3beta-hydroxysteroids acted noncompetitively with respect to potentiating steroids and inhibited the largest degrees of potentiation most effectively. Potentiation by high concentrations of barbiturates was also reduced by 3beta-hydroxysteroids. 3beta-Hydroxysteroids are also direct, noncompetitive GABA(A) receptor antagonists. 3beta-Hydroxysteroids coapplied with GABA significantly inhibited responses to > or =15 microm GABA. The profile of block was similar to that exhibited by sulfated steroids, known blockers of GABA(A) receptors. This direct, noncompetitive effect of 3beta-hydroxysteroids was sufficient to account for the apparent antagonism of potentiating steroids. Mutated receptors exhibiting decreased sensitivity to sulfated steroid block were insensitive to both the direct effects of 3beta-hydroxysteroids on GABA(A) responses and the reduction of potentiating steroid effects. At concentrations that had little effect on GABAergic synaptic currents, 3beta-hydroxysteroids and low concentrations of sulfated steroids significantly reversed the potentiation of synaptic currents induced by 3alpha-hydroxysteroids. We conclude that 3beta-hydroxypregnane steroids are not direct antagonists of potentiating steroids but rather are noncompetitive, likely state-dependent, blockers of GABA(A) receptors. Nevertheless, these steroids may be useful functional blockers of potentiating steroids when used at concentrations that do not affect baseline neurotransmission.
Wang
Mingde
M
Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
He
Yejun
Y
Eisenman
Lawrence N
LN
Fields
Christopher
C
Zeng
Chun-Min
CM
Mathews
Jose
J
Benz
Ann
A
Fu
Tao
T
Zorumski
Erik
E
Steinbach
Joe Henry
JH
Covey
Douglas F
DF
Zorumski
Charles F
CF
Mennerick
Steven
S
D019943:Amino Acid Substitution; D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005442:Flumazenil / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology*; D018757:GABA Modulators / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists; D006914:Hydroxysteroids / Q000494:pharmacology*; D008140:Lorazepam / Q000494:pharmacology; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011278:Pregnanes / Q000494:pharmacology*; D011284:Pregnenolone / Q000494:pharmacology*; D021122:Protein Subunits; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000235:genetics; D013329:Structure-Activity Relationship; D013569:Synapses / Q000187:drug effects / Q000378:metabolism; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000494:pharmacology
D018756:GABA Antagonists; D018757:GABA Modulators; D058787:GABA-A Receptor Antagonists; D006914:Hydroxysteroids; D011278:Pregnanes; D021122:Protein Subunits; D011963:Receptors, GABA-A; C018370:pregnenolone sulfate; D005442:Flumazenil; D005680:gamma-Aminobutyric Acid; D011284:Pregnenolone; D008140:Lorazepam