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Effects of Clobazam and Its Active Metabolite on GABA‐Activated Currents in Rat Cerebral Neurons in Culture
Author(s) -
Nakamura Fumihiro,
Suzuki Setsuo,
Nishimura Shigeko,
Yagi Kazuichi,
Seino Masakazu
Publication year - 1996
Publication title -
epilepsia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.687
H-Index - 191
eISSN - 1528-1167
pISSN - 0013-9580
DOI - 10.1111/j.1528-1157.1996.tb00643.x
Subject(s) - clobazam , metabolite , pharmacology , flumazenil , chemistry , gabaa receptor , gabaergic , benzodiazepine , antagonist , active metabolite , anticonvulsant , inhibitory postsynaptic potential , receptor , medicine , neuroscience , endocrinology , biology , biochemistry , epilepsy
Summary:Purpose : The antiepileptic effects of clobazam, a 1,5‐benzodiazepine, have been well documented in animal experiments and clinical trials. However, the drug's mechanisms of antiepileptic actions are still undetermined. The purpose of this study was to learn how clobazam and its active metabolite modulate γ‐aminobutyric acid (GABA)‐activated currents in rat cerebral neurons in culture. Methods : Whole‐cell voltage‐clamp recordings were performed on cultured cerebral neurons of the rat. Clobazam or its metabolite N ‐desmethylclobazam was dissolved in the extracellular solution and applied for 2 s by pressure ejection from a micropipette. To maintain GABA‐activated currents, 2 m M Mg adenosine triphosphate (ATP) was added to the intracellular solution. Results : GABA elicited outward currents that were mediated by GABA A receptor‐coupled Cl ‐ channels. Applying clobazam with 10 μ M GABA elicited enhanced outward currents. Flumazenil, an antagonist of the benzodiazepine receptor, inhibited the enhancing effect of clobazam. The enhancement ratio increased as much as 2.28‐fold in a dose‐dependent manner at a concentration of 3 μ M clobazam. However, it started to decrease at a concentration of 10 μ M clobazam. The metabolite N ‐desmethylclobazam was tested in the same manner, and exhibited an identical dose‐dependent enhancement of GABA‐activated currents. Conclusions : The antiepileptic effects of the 1,5‐ benzodiazepines are attributed to the enhancement of GABAergic inhibitory neurotransmission. The antiepileptic effects of clobazam are thought to depend mainly on its active metabolite N ‐desmethylclobazam, which is present in high concentrations in patients who receive long‐term clobazam. Clobazam's enhancement of GABAactivated currents was most marked on weaker GABA currents. We therefore infer that clobazam acts more efficiently on tissues in which the release of GABA is diminished.