title: Stimulation of benzodiazepine receptor binding by gamma-aminobutyric acid.
abstract: The effect of the neurotransmitter gamma-aminobutyric acid (GABA) on high-affinity binding of benzodiazepines to brain membranes has been investigated. GABA stimulated [3H]diazepam binding by more than 100% when extensively washed membranes from brain tissue were used. This GABA-stimulated benzodiazepine binding occurred in all brain regions examined. The stimulation was specific for GABA agonist. It was inhibited by the GABA receptor blocker bicuculline methiodide. A large number of compounds structurally closely related to GABA but without direct effect on the GABA receptor failed to enhance [3H]diazepam binding. The stimulation of benzodiazepine binding was caused by an increase in affinity; the number of binding sites remained unchanged. Half-maximal activation of [3H]diazepam binding occurred in the presence of 300 nM muscimol or 900 nM GABA. beta-Guanidinopropionic acid and imidazoleacetic acid were much weaker activators. It is suggested that the described stimulation of benzodiazepine high-affinity binding is mediated by a receptor for GABA. This site of GABA action exhibits different properties when compared to GABA receptors, as characterized by high-affinity binding of GABA agonists.
mesh_terms: D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D001921:Brain / Q000378:metabolism*; D002540:Cerebral Cortex / Q000378:metabolism; D003975:Diazepam / Q000378:metabolism*; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D009118:Muscimol / Q000494:pharmacology; D051381:Rats; D011955:Receptors, Drug / Q000187:drug effects / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D011955:Receptors, Drug; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; D003975:Diazepam; D001640:Bicuculline