CHARACTERIZATION OF PERIPHERAL BENZODIAZEPINE TYPE SITES IN A CULTURED MURINE BV-2 MICROGLIAL CELL-LINE

It is known that the density of peripheral benzodiazepine receptors (P BR) increases after brain damage. Astrocytes are among the cell types where PBR ligand binding has been detected and may be involved in the response to neuronal injury and regeneration. Consistent with the hypo thesis, the apparent density of PER sites in astrocytes is increased b y both cytokines and neurotoxins. However, microglia, the resident mac rophages which represent 5-15% of glial cell populations have not been evaluated for the presence of the PER. In the present study, we repor t the presence of [H-3]Ro5-4864 binding in microglial cells. In partic ular, we used BV-2 cells, an immortalized cell line of murine microgli al cells. High affinity binding of [H-3]Ro5-4864 to a single site was detected in membranes prepared from BV-2 cells (K-D = 4.4 nM, B-max = 3,800 fmoles/mg protein). Various ligands for the PER displaced [H-3]R o5-4864 binding with the following rank order of potencies: PK11195 = Ro5-4864 > FGIN-1-27 > triazolam = diazepam > beta-pro-pyl-beta-carbol ine-3-carboxylate = clonazepam > lorazepam = flurazepam >> chloridazep oxide = clorazepate. Subcellular fractionationstudies indicate that th e majority of the Ro5-4864 binding sites is in the mitochondrial fract ion. The remainder is found in nonmitochondrial cell fractions. The [H -3]Ro5-4864 binding observed on intact cells had characteristics simil ar to those found on membranes. The presence of a high density of PBRs in these cells establish the basis for additional investigations into their possible functional role, if any, in the microglial response to neuronal injury. (C) 1996 Wiley-Liss, Inc.