Differential effect of detergents on [3H]Ro 5-4864 and [3H]PK 11195 binding to peripheral-type benzodiazepine-binding sites

The present study demonstrates a differential effect of various detergent treatments on 3H]Ro 5-4864 and 3H]PK 11195 binding to peripheral benzodiazepine binding sites (PBS). Triton X-100 (0.0125%) caused a decrease of about 70% in 3H]Ro 5-4864 binding to membranes from various peripheral tissues of rat, but had only a negligible effect on 3H]PK 11195 binding. A similar effect of Triton X-100 was observed on guinea pig and rabbit kidney membranes. The decrease in 3H]Ro 5-4864 binding after treatment with Triton X-100 was apparently due to a decrease in the density of PBS, since the affinity remained unaltered. The detergents 3-(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate (CHAPS), Tween 20, deoxycholic acid, or digitonin (0.0125%) caused only a minor change in 3H]Ro 5-4864 and 3H]PK 11195 binding to rat kidney membranes; but when concentrations were substantially increased (0.1%), all detergents caused a decrease of at least 50% in 3H]Ro 5-4864 binding, while 3H]PK 11195 binding to rat kidney membranes remained unaffected by the first three detergents, with only a minor decrease (15%) after treatment with digitonin. These results may further support the assumption that Ro 5-4864 and PK 11195 are agonist and antagonist, respectively, of PBS and interact with two different conformations or domains in the peripheral-type benzodiazepine binding site molecule.