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The Journal of Neuroscience, May 1, 2002, 22(9):3366-3375
3 -Hydroxypregnane Steroids Are Pregnenolone Sulfate-Like
GABAA Receptor Antagonists
Mingde
Wang1,
Yejun
He1,
Lawrence N.
Eisenman5,
Christopher
Fields1,
Chun-Min
Zeng3,
Jose
Mathews1,
Ann
Benz1,
Tao
Fu1,
Erik
Zorumski1,
Joe Henry
Steinbach2,
Douglas F.
Covey3,
Charles F.
Zorumski1, 4, and
Steven
Mennerick1, 4
Departments of 1 Psychiatry,
2 Anesthesiology, 3 Molecular Biology and
Pharmacology, 4 Anatomy and Neurobiology, and
5 Neurology, Washington University School of Medicine, St.
Louis, Missouri 63110
Endogenous neurosteroids have rapid actions on ion
channels, particularly GABAA receptors, which are
potentiated by nanomolar concentrations of 3 -hydroxypregnane
neurosteroids. Previous evidence suggests that 3 -hydroxypregnane
steroids may competitively antagonize potentiation induced by their
3 diastereomers. Because of the potential importance of antagonists
as experimental and clinical tools, we characterized the functional
effect of 3 -hydroxysteroids. Although 3 -hydroxysteroids reduced
the potentiation induced by 3 -hydroxysteroids, 3 -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
3 -hydroxysteroids. 3 -Hydroxysteroids are also direct,
noncompetitive GABAA receptor antagonists.
3 -Hydroxysteroids coapplied with GABA significantly inhibited
responses to 15 µM GABA. The profile of block was
similar to that exhibited by sulfated steroids, known blockers of
GABAA receptors. This direct, noncompetitive effect of
3 -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 3 -hydroxysteroids on GABAA
responses and the reduction of potentiating steroid effects. At
concentrations that had little effect on GABAergic synaptic currents,
3 -hydroxysteroids and low concentrations of sulfated steroids
significantly reversed the potentiation of synaptic currents induced by
3 -hydroxysteroids. We conclude that 3 -hydroxypregnane steroids
are not direct antagonists of potentiating steroids but rather are
noncompetitive, likely state-dependent, blockers of GABAA
receptors. Nevertheless, these steroids may be useful functional
blockers of potentiating steroids when used at concentrations that do
not affect baseline neurotransmission.
Key words:
neurosteroids; inhibitory postsynaptic current; GABAA receptors; pregnenolone sulfate; anesthetic; hippocampal culture
Copyright © 2002 Society for Neuroscience 0270-6474/02/2293366-10$05.00/0
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