Functional modulation of cerebral gamma-aminobutyric acidA receptor/benzodiazepine receptor/chloride ion channel complex with ethyl beta-carboline-3-carboxylate: presence of independent binding site for ethyl beta-carboline-3-carboxylate.
Effect of ethyl beta-carboline-3-carboxylate (beta-CCE) on the function of gamma-aminobutyric acid (GABA)A receptor/benzodiazepine receptor/chloride ion channel complex was studied. Beta-CCE noncompetitively and competitively inhibited [3H]flunitrazepam binding to benzodiazepine receptor, but not [3H]muscimol binding to GABAA receptor as well as t-[3H]butylbicycloorthobenzoate [( 3H] TBOB) binding to chloride ion channel, in particulate fraction of the mouse brain. Ro15-1788 also inhibited competitively [3H] flunitrazepam binding. On the other hand, the binding of beta-[3H]CCE was inhibited noncompetitively and competitively by clonazepam and competitively by Ro15-1788. In agreement with these results, benzodiazepines-stimulated [3H]muscimol binding was antagonized by beta-CCE and Ro15-1788. Gel column chromatography for the solubilized fraction from cerebral particulate fraction by 0.2% sodium deoxycholate (DOC-Na) in the presence of 1 M KCl indicated that beta-[3H]CCE binding site was eluted in the same fraction (molecular weight, 250,000) as the binding sites for [3H]flunitrazepam, [3H]muscimol and [3H]TBOB. GABA-stimulated 36Cl- influx into membrane vesicles prepared from the bovine cerebral cortex was stimulated and attenuated by flunitrazepam and beta-CCE, respectively. These effects of flunitrazepam and beta-CCE on the GABA-stimulated 36Cl- influx were antagonized by Ro15-1788. The present results suggest that the binding site for beta-CCE, which resides on GABAA receptor/benzodiazepine receptor/chloride ion channel complex, may be different from that for benzodiazepine. Possible roles of beta-CCE binding site in the allosteric inhibitions on benzodiazepine binding site as well as on the functional coupling between chloride ion channel and GABAA receptor are also suggested.
Taguchi
J
J
Department of Pharmacology, Kyoto Prefectural University of Medicine, Japan.
Kuriyama
K
K
D000818:Animals; D001418:Baclofen / Q000378:metabolism / Q000494:pharmacology; D001665:Binding Sites; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002243:Carbolines / Q000378:metabolism / Q000494:pharmacology*; D002478:Cells, Cultured; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism; D004347:Drug Interactions; D005445:Flunitrazepam / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D009118:Muscimol / Q000378:metabolism / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000378:metabolism; D014316:Tritium
D002243:Carbolines; D018118:Chloride Channels; D002712:Chlorides; D008565:Membrane Proteins; D011963:Receptors, GABA-A; D014316:Tritium; D009118:Muscimol; D005445:Flunitrazepam; C024915:beta-carboline-3-carboxylic acid ethyl ester; D001418:Baclofen