High-affinity peripheral benzgdiazepine receptors are expressed on nuclei of rat liver cells and a murine macrophage cell line

Peripheral benzodiazepine receptors (PBDZR) are abundant in liver and macrophages, with well-characterized localization to mitochondria This study investigated the nucleus as a possible site of PBDZR. METHODS: Isolated nuclei from liver homogenates of SpragueDawley rat and a murine macrophage cell line, WLG5, were separated on a 2.3 mol/L sucrose gradient. Specific nuclear binding of varying concentrations of peripheral benzodiazepine (BDZ) ligand, [3H]PK11195. was determined with or without excess unlabeled ligand (100 uM) incubated for 2 hrs. RESULTS: PK11195 showed specific nuclear binding of 77.6 ±0.9% (± SEM. n=60) in rat liver cells and 96.0 ±0.38% (n=30) in WLG5. The binding was saturable, with high-affinity, at an apparent single binding site, Kd 3.14 nM and Bmax 320 firiol/ mg protein. A known PBDZr ligand, diazepam, showed 75.2 ±2.2% (n=21) specific binding, but a central BDZ ligand, chlorodiazepoxide, showed no binding. SUMMARY AND CONCLUSION: A high-affinity PBDZ receptor on nuclei of liver cells and macrophages has been demonstrated. These findings suggest that BDZ, and possibly endogenous ligands, can bind to these sites and may effect nuclear events, such as gene regulation