Binding of [ 3H]Ro 5-4864 and [ 3H]PK 11195 to cerebral cortex and peripheral tissues of various species: Species differences and heterogeneity in peripheral benzodiazepine binding sites

Abstract

: The binding of [3H]PK 11195 and [3H]Ro 5–4864 to membrane preparations from cerebral cortex and peripheral tissues of various species was studied. [3H]PK 11195 (0.05–10 nM) bound with high affinity to rat and alf cerebral cortical and kidney membranes. [3H]Ro 5–4864 (0.05–30 nM) also successfully labeled rat cerebral cortical and kidney membranes, but in calf cerebral cortical and kidney membranes, its binding capacity was only 3 and 4%, respectively, of that of [3H]PK 11195. Displacement studies showed that unlabeled Ro 5–4864, diazepam, and flunitrazepam were much more potent in displacing [3H]PK 11195 from rat cerebral cortex and kidney membranes than from calf, tissues. The potency of unlabeled Ro 5–4864 in displacing [3H]PK 11195 from the cerebral cortex of various other species was also tested, and the rank order of potency was rat = guinea pig < cat = dog < rabbit < calf. Analysis of these displacement curves revealed that Ro 5–4864 bound to two populations of binding sites from rat and calf kidney and from rat, guinea pig, rabbit, and calf cerebral cortex but to a single population of binding sites from cat and dog cerebral cortex. Using [3H]PK 11195 as a ligand, the rank order of binding capacity in cerebral cortex of various species was cat < calf < guinea pig < rabbit < dog < rat, whereas when [3H]Ro 5–4864 was used, the rank order of binding capacity was cat < guinea pig < rat < rabbit < calf < dog. These results further demonstrate species differences of “peripheral-type” benzodiazepine binding sites and also provide evidence of their heterogeneity in the kidney of rat and calf and in the cerebral cortex of rat, guinea pig, rabbit, and calf.