Neurosteroid analogues. 4. The effect of methyl substitution at the C-5 and C-10 positions of neurosteroids on electrophysiological activity at GABAA receptors.
A series of analogues of the neuroactive steroids 3 alpha-hydroxy-5 alpha-pregnan-20-one and 3 alpha-hydroxy-5 beta-pregnan-20-one were studied to elucidate the mode of binding of 5 alpha-and 5 beta-reduced steroids to steroid binding sites on GABAA receptors. Analogues which were either 3 alpha-hydroxy-20-ketosteroids or 3 alpha-hydroxysteroid-17 beta-carbonitriles and which contained various methyl group substitution patterns at C-5 and C-10 were prepared. Evaluations utilized whole-cell patch clamp electrophysiological methods carried out on cultured rat hippocampal neurons, and the results obtained with the rigid 17 beta-carbonitrile analogs were analyzed using molecular modeling methods. The molecular modeling results provide a rationale for the observation that the configuration of the hydroxyl group at C-3 is a greater determinant of anesthetic potency than the configuration of the A,B ring fusion at C-5. The electrophysiological results identify steric restrictions for the space that can be occupied in 5 alpha- and 5 beta-reduced steroid modulators of GABAA receptors in the regions of space proximate to the steroid C-5, C-10, and possibly C-4 positions. This information is useful for the development of nonsteroidal analogues that can modulate GABAA receptors via interactions at steroid binding sites.
Han
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Department of Molecular Biology & Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Zorumski
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Covey
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D000818:Animals; D002478:Cells, Cultured; D004594:Electrophysiology; D006531:HEPES; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008745:Methylation; D008958:Models, Molecular; D011280:Pregnanolone / Q000737:chemistry / Q000494:pharmacology*; D051381:Rats; D018079:Receptors, GABA / Q000187:drug effects* / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
D018079:Receptors, GABA; D013779:Tetrodotoxin; D011280:Pregnanolone; D006531:HEPES