CHARACTERIZATION OF BENZODIAZEPINE BINDING SITES IN CULTURED CELLS OF NEURAL ORIGIN

— The binding of [ 3 H]diazepam to benzodiazepine receptors was investigated in cultured cell lines of neural origin. Two cell lines, the rat C6 glioma and mouse NB41A3 neuroblastoma possess large numbers of benzodiazepine binding sites, while the other neural cell lines examined had significantly fewer benzodiazepine binding sites. [ 3 H]diazepam binding to membranes prepared from C6 or NB41A3 cells was saturable and of a relatively high affinity ( K D ± 12 and 20 n m , respectively) when compared with rat cerebral cortex ( K D ± 4.6 n m ). A single class of binding sites in both cell lines was demonstrated by Scatchard analysis. The maximum binding capacities ( B max ) in the C6 and NB41A3 cell lines were found to be 10 and 3.5 fold higher than in rat cerebral cortex, respectively. In contrast to the rat cerebral cortex, binding of [ 3 H]diazepam in cultured cells was not displaced by the clinically active benzodiazepines clonazepam and oxazepam while the clinically inactive benzodiazepine Ro 5‐4864 potently inhibited the binding of [ 3 H]diazepam in both neural cell lines. In toto , this data suggests a change in the benzodiazepine binding sites in cultured cells of neural origin to that found in peripheral (kidney) tissue. The observation that cell lines derived from both neuronal and glial elements contain large numbers of benzodiazepine binding sites also suggests benzodiazepine receptors in the central nervous system may not be confined to a single cell type.