A quantitative relationship between Cl- enhanced [3H]flunitrazepam and [35S]t-butylbicyclophosphorothionate binding to the benzodiazepine/GABA receptor chloride ionophore complex.

A quantitative relationship between the efficacy (i.e. maximum enhancement) of Cl- to increase [3H]flunitrazepam binding and the density of [35S]t-butylbicyclophosphorothionate binding sites was observed in well-washed membrane fragments of rat cerebral cortex previously exposed to phospholipase A2. This relationship (described by the equation y = ABx) was maintained when [3H]flunitrazepam was assayed at Cl- concentrations between 100 and 600 mM, and was not qualitatively altered by the presence of 100 microM pentobarbital. However, under experimental conditions that reduced the ratio of [35S]TBPS binding sites/benzodiazepine receptors, the effects of pentobarbital suggest that the conductance state of benzodiazepine receptor-coupled chloride channels may be the primary determinant of Cl- enhanced [3H]flunitrazepam binding.