Abstract:
:Neuroactive steroids bind to a unique site on the gamma-aminobutyric acidA (GABAA) receptor complex and allosterically modulate the binding of convulsant ([35S]t-butylbicyclophosphorothionate, [35S]TBPS), GABA ([3H]muscimol), and benzodiazepine ([3H]flunitrazepam) site ligands. In rat cortical membranes, 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha, 5 alpha-P) is a full agonist at the steroid site, inhibiting 96% of specific [35S]TBPS binding and enhancing [3H]flunitrazepam and [3H]muscimol binding 95% and 69% above control levels, respectively. In contrast, the synthetic steroid 3 alpha-hydroxy-3 beta-trifluoromethyl-5 alpha-pregnan-20-one (Co 2-1970) has limited efficacy for modulating the binding of [35S]TBPS (44% inhibition), [3H]flunitrazepam (41% enhancement), and [3H]muscimol (< 10% enhancement). In competition experiments, Co 2-1970 (10 microM) reduced the apparent potency of 3 alpha, 5 alpha-P by 7-17-fold for modulating the binding of these radioligands in rat cortical membranes, suggesting that it has partial agonist properties. Because cortical membranes contain a heterogeneous population of receptors, Co 2-1970 was examined in recombinant GABAA receptors stably expressed in human embryonic kidney 293 cells. Co 2-1970 inhibited [35S]TBPS binding with limited efficacy (39-65% inhibition) in the five receptor combinations examined and, at 10 microM, reduced the apparent potency of 3 alpha, 5 alpha-P 57-fold for inhibiting [35S]TBPS binding to alpha 1 beta 1 gamma 2L receptors. To verify these findings functionally, the effects of 3 alpha, 5 alpha-P and Co 2-1970 were examined electrophysiologically in Xenopus oo-cytes expressing alpha 1 beta 1 gamma 2L receptors. Co 2-1970 showed limited efficacy potentiation of GABA-evoked chloride currents relative to 3 alpha, 5 alpha-P (28% and 86% of the GABA maximum current, respectively). Moreover, Co 2-1970 produced a concentration-dependent antagonism of the 3 alpha, 5 alpha-P-induced potentiation that was associated with a reduction in the apparent affinity of 3 alpha, 5 alpha-P (11-fold at 10 microM Co 2-1970). Taken together, these data indicate that Co 2-1970 is a partial agonist at the neuroactive steroid site associated with GABAA receptors.
journal_name
Mol Pharmacoljournal_title
Molecular pharmacologyauthors
Hawkinson JE,Drewe JA,Kimbrough CL,Chen JS,Hogenkamp DJ,Lan NC,Gee KW,Shen KZ,Whittemore ER,Woodward RMsubject
Has Abstractpub_date
1996-05-01 00:00:00pages
897-906issue
5eissn
0026-895Xissn
1521-0111journal_volume
49pub_type
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journal_title:Molecular pharmacology
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journal_title:Molecular pharmacology
pub_type: 杂志文章
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更新日期:1995-07-01 00:00:00
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journal_title:Molecular pharmacology
pub_type: 杂志文章
doi:
更新日期:1996-01-01 00:00:00
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