Characterization of [3H]Ro 5‐4864 Binding Sites in Rat Vas Deferens

Publisher Website
Google Scholar
Abstract
The presence of benzodiazepine binding sites in rat vas deferens was detected using [3H]Ro 5‐4864 as a radioligand. The binding of [3H]Ro 5‐4864 to the mitochondrial sites is saturable, reversible, and temperature and time dependent. The association rate constant (k1) was 8.7 ± 0.7 × 107M−1 min−1, and the dissociation rate constant (k‐1) was 0.031 ± 0.003 min−1. The dissociation constant (KD) determined by saturation binding was 5.22 ± 0.56 nM. The density of binding was 4,926 ± 565 fmol/mg of protein. The Hill coefficient of binding was 0.99 ± 0.01, an indication that [3H]Ro 5‐4864 binds to a single site. The [3H]Ro 5‐4864 binding was inhibited competitively by Ro 5‐4864 and 2‐hydroxy‐5‐nitrobenzyl‐6‐thioguanosine and noncompetitively by PK 11195, nitrendipine, α,β‐methylene‐ATP, and carboxyatractyloside and was not affected by clonazepam, dicyclohexylcarbodiimide, or protoporphyrin IX. Our data indicate that [3H]Ro 5‐4864 binding sites are not identical to those labeled by PK 11195. These binding sites are modulated by the ADP/ATP mitochondrial carrier, and an interaction of dihydropyridines and [3H]Ro 5‐4864 binding sites in rat vas deferens is suggested.