PERIPHERAL-TYPE BENZODIAZEPINE RECEPTORS ARE HIGHLY CONCENTRATED IN MITOCHONDRIAL-MEMBRANES OF RAT TESTICULAR INTERSTITIAL-CELLS

The binding of 3H-RO 5-4864 to the peripheral-type benzodiazepine receptors (PBZDR) in rat testicular interstitial cells (TIC) was characterized. The binding was saturable, reversible and showed a single high-affinity (K(d) = 5.02 ± 0.86 nM) class of binding sites. The maximal binding capacity (B(max)) in crude mitochondrial fractions (77.6 ± 9.1 pmol/mg protein) represents the highest density of PBZDR in tissues thus far studied. In comparison with the crude mitochondrial fraction the subcellular fractionation of of TIC revealed a 2-fold enrichment of 3H-RO 5-4864 binding sites to the purified mitochondria (B(max) = 140 ± 23 pmol/mg protein). The ability of various drugs to displace 3H-RO 5-4864 from TIC binding sites was examined and the inhibition constants (K(i)) for RO 5-4864, PK 11195, diazepam and flunitrazepam were 3.5, 4.4, 159, and 353 nM, respectively, whereas clonazepam and RO 15-1788 were inefficient in displacing 3H-RO 5-4864 (K(i) > 10 μM). This pharmacological profile is characteristic of PBZDR described in other tissues. In conclusion, rat TIC possess a very high concentration of PBZDR primarily associated with mitochondrial membranes.