Neuroactive Steroid Interactions with Voltage-Dependent Anion Channels: Lack of Relationship to GABAA Receptor Modulation and Anesthesia

Ramin Darbandi-Tonkabon, Brad D. Manion, William R. Hastings, William J. Craigen, Gustav Akk, John R. Bracamontes, Yejun He, Tatiana V. Sheiko, Joseph H. Steinbach, Steven J. Mennerick, Douglas F. Covey, Alex S. Evers

Research output: Contribution to journalArticle

27 Scopus citations

Abstract

Neuroactive steroids modulate the function of γ-aminobutyric acid type A (GABAA) receptors in brain; this is the presumed basis of their action as anesthetics. In a previous study using the neuroactive steroid analog, (3α,5β)-6-azi-3-hydroxypregnan-20-one (6-AziP), as a photoaffinity-labeling reagent, we showed that voltage-dependent anion channel-1 (VDAC-1) was the predominant protein labeled in brain. Antisera to VDAC-1 were shown to coimmunoprecipitate GABAA receptors, suggesting a functional relationship between steroid binding to VDAC-1 and modulation of GABAA receptor function. This study examines the contribution of steroid binding to VDAC proteins to modulation of GABAA receptor function and anesthesia. Photolabeling of 35-kDa protein with [ 3H]6-AziP was reduced 85% in brain membranes prepared from VDAC-1-deficient mice but was unaffected by deficiency of VDAC-3. The photolabeled 35-kDa protein in membranes from VDAC-1-deficient mice was identified by two-dimensional electrophoresis and electrospray ionization-tandem mass spectrometry as VDAC-2. The absence of VDAC-1 or VDAC-3 had no effect on the ability of neuroactive steroids to modulate GABA A receptor function as evidenced by radioligand ([35S] t-butylbicyclophosphorothionate) binding or by electrophysiological studies. Electrophysiological studies also showed that neuroactive steroids modulate GABAA receptor function normally in VDAC-2-deficient fibroblasts transfected with α1β2γ2 GABAA receptor subunits. Finally, the neuroactive steroid pregnanolone [(3α5β)-3-hydroxypregnan-20-one] produced anesthesia (loss of righting reflex) in VDAC-1- and VDAC-3-deficient mice, and there was no difference in the recovery time between the VDAC-deficient mice and wild-type controls. These data indicate that neuroactive steroid binding to VDAC-1, -2, or -3 is unlikely to mediate GABAA receptor modulation or anesthesia.

Original languageEnglish
Pages (from-to)502-511
Number of pages10
JournalJournal of Pharmacology and Experimental Therapeutics
Volume308
Issue number2
DOIs
StatePublished - Feb 1 2004

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