title: Diazepam-insensitive [3H]Ro 15-4513 binding in intact cultured cerebellar granule cells.
abstract: [3H]Ro 15-4513, a partial inverse agonist at the benzodiazepine receptor, binds to two sites in the rat cerebellum, only one of which is sensitive to diazepam. The diazepam-insensitive component, whose identity is unknown, is unique to this brain area. We studied the binding of [3H]Ro 15-4513 in cultured cerebellar granule cells to characterize its binding sites in a specified neuronal cell population and to determine the effects of ethanol on the binding. We also compared the properties of [3H]Ro 15-4513 binding in washed membranes of cultured cells and 14-day-old rat cerebella. [3H]Ro 15-4513 had two binding components in intact granule cells, one sensitive to diazepam, that probably represents binding to the benzodiazepine agonist site, the other sensitive to an antagonist (Ro 15-1788) and two inverse agonists (ethyl-beta-carboline-3-carboxylate, beta CCE and methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, DMCM) of the benzodiazepine receptor (diazepam-insensitive binding). This diazepam-insensitive binding was stimulated by GABA; the maximal increase in binding was about 60% with an EC50 of 0.3 microM. The effect of GABA (10 microM) on the diazepam-insensitive binding was unaffected by 100 microM nipecotic acid but was partially inhibited by 100 microM bicuculline. The stimulation by GABA was also seen at 37 degrees C with washed membranes of 14-day-old rat whole cerebella in the presence of micromolar diazepam.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: University of Tampere, Finland.
authors.forename: O
authors.initials: O
authors.lastname: Malminiemi
authors.forename: E R
authors.initials: ER
authors.lastname: Korpi
mesh_terms: D000818:Animals; D001386:Azides / Q000378:metabolism*; D001569:Benzodiazepines / Q000378:metabolism*; D001667:Binding, Competitive / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000378:metabolism*; D003975:Diazepam / Q000494:pharmacology*; D004347:Drug Interactions; D051381:Rats
chemical_list: D001386:Azides; D001569:Benzodiazepines; C042957:Ro 15-4513; D003975:Diazepam