RO5-4864 inhibits the binding of [³⁵S]t-butylbicyclophosphorothionate to rat brain membranes

RO5-4864, a 1, 4-benzodiazepine, has recently been shown to possess anticonvulsant, convulsant and anxiogenic properties and to inhibit Ca⁺⁺-calmodulin-stimulated membrane phosphorylation. RO5-4864 inhibited the binding of [³⁵S]t-butylbicyclophosphorothionate (TBPT) to cerebral cortex, cerebellar and hippocampus membranes, with an IC₅₀ value of ∼ 20 μM. TBPT binds apparently to the picrotoxinin site of the benzodiazepine-GABA receptor-ionophore complex and appears to be a site of action for several classes of convulsant, depressant and anxiolytic drugs that modulate GABAergic transmission. RO5-4864 inhibited [³⁵S]TBPT binding in cerebral cortex, apparently competitively. Antagonists of GABA and central benzodiazepine sites did not interfere with the ability of RO5-4864 to inhibit [³⁵S]TBPT binding. The properties of RO5-4864 to inhibit TBPT binding are similar to other convulsants and GABA antagonists (except bicuculline) which inhibit TBPT binding. These results suggest that RO5-4864 interacts with the TBPT binding sites of the oligomeric GABA receptor complex.