Complex interactions between the steroid derivative RU 5135 and the GABAA-receptor complex.
The modulation of [35S]t-butylbicyclophosporothionate ([35S]TBPS) binding was used to evaluate the actions of the steroid derivative RU 5135 at the gamma-aminobutyric acidA (GABAA) receptor complex. The inhibition of [35S]TBPS binding by GABA in the presence of various concentrations of RU 5135 was consistent with the hypothesis that RU 5135 is a competitive antagonist at the GABAA receptor. Despite common structural features (i.e., 3 alpha-hydroxylated, 5 beta-reduced A ring) with GABAA receptor-active neurosteroids, RU 5135 did not appear to be competitive at the putative steroid site on the GABAA receptor-active, as demonstrated by Schild analysis of 5 alpha-pregnane-3 alpha-ol-20-one (3 alpha,5 alpha-P) modulation of [35S]TBPS binding in the presence of different concentrations of RU 5135. On the other hand, the reduced potency of 3 alpha,5 alpha-P as an inhibitor of [35S]TBPS binding in the presence of RU 5135, as well as blockade of 5 alpha-pregnane-3 alpha-20 alpha-diol (5 alpha-pregnanediol) inhibition of [35S]TBPS binding by RU 5135 provide further support for the GABAA receptor antagonist properties of RU 5135. Moreover, this amidine steroid was able to partially inhibit [35S]TBPS binding independent of GABA with nanomolar potency; yet the mechanism by which this occurs remains to be determined.
Cadoni
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Department of Pharmacology, College of Medicine, University of California, Irvine 92717.
Gee
K W
KW
D000731:Androstanes / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001378:Azasteroids / Q000378:metabolism / Q000494:pharmacology*; D001667:Binding, Competitive; D001643:Bridged Bicyclo Compounds / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002540:Cerebral Cortex / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D058787:GABA-A Receptor Antagonists; D066298:In Vitro Techniques; D008297:Male; D011276:Pregnanediol / Q000378:metabolism / Q000494:pharmacology; D011280:Pregnanolone / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism*; D013237:Stereoisomerism; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D000731:Androstanes; D001378:Azasteroids; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D058787:GABA-A Receptor Antagonists; D011963:Receptors, GABA-A; C016836:allopregnane-3,20-diol; D005680:gamma-Aminobutyric Acid; C037476:tert-butylbicyclophosphorothionate; D011280:Pregnanolone; D011276:Pregnanediol; C032061:RU 5135