The Human "Peripheral-Type" Benzodiazepine Receptor: Regional Mapping of the Gene and Characterization of the Receptor Expressed from cDNA

A cDNA for the human "peripheral-type" benzodiazepine receptor (PBR) was isolated from a liver cDNA library. The 851-nucleotide probe hybridized with a ∼1 kb mRNA in Northern blots of RNA extracted from various human tissues and cell lines. The human PBR probe was hybridized to DNA from a somatic cell hybrid mapping panel to determine that the gene maps to chromosome 22. With a regional mapping panel for chromosome 22, we localized the gene within band 22q13.31. The ligand-binding properties of the receptor expressed from the cDNA were examined in transient expression experiments and compared to the endogenous human PBR. The PBR ligand [³H]PK 11195 had high affinity for the expressed receptor in COS-1 cells, but the affinities of a pair of isoquinoline propanamide enantiomers differed remarkably in expressed and endogenous human PBR. These findings reveal that the host cell and/or post-translational modification may have an important influence on PBR function.