Cell surface localization of the peripheral-type benzodiazepine receptor (PBR) in adrenal cortex

Previous studies demonstrated that the mitochondrial peripheral-type benzodiazepine receptor (PBR) regulates steroid biosynthesis. In this study we investigate further PBR action by examining its subcellular localization in mouse adrenal gland using anti-peptide PBR antiserum and employing biotin-strep-tavidin peroxidase immunocytochemistry. Results demonstrated PBR immunostaining exclusively in the cortex. Within this region, however, PBR staining was homogeneously distributed in cells of the zona glomerulosa, whereas in cells of the zona fasciculata both cytoplasmic and prominent plasma membrane immunostaining was evident. Next, PBR distribution was examined using confocal microscopy. Confocal optical sections were obtained, 3-D reconstructions of these sections generated, and vertical, z-sections of the 3-D reconstruction recreated. The immunostaining pattern observed was consistent with a cell surface distribution of PBR. The demonstration of a subset of PBR at the plasma membrane may account for actions of PBR ligands not related to mitochondrial function.