CNS depressants accelerate the dissociation of 35S-TBPS binding and GABA enhances their displacing potencies.

The specific binding of 35S-t-butylbicyclophosphorothionate (TBPS) was studied in synaptosomal membranes of rat cerebral cortex. The displacing potencies of eleven CNS depressants and three convulsants were determined in the presence of 1 microM GABA and 10 nM R 5135. GABA enhanced the displacing potencies of depressants of most diverse chemical structures: diaryltriazine (LY 81067), pyrazolopyridine (etazolate), cinnamide, glutarimide, 2,3-benzodiazepine (tofizopam) and alcohol derivatives, barbiturates, (+)etomidate, methaqualone and meprobamate. In contrast, the IC50 values of convulsants (picrotoxinin, pentetrazol and the barbiturate enantiomer S(+) MPPB) were not significantly affected. The depressants accelerated either basal or GABA-augmented dissociation of 35-TBPS mainly by increasing the contribution of its rapid first phase.