The Benzodiazepine Receptor in Rat Brain and Its Interaction with Ethyl /3-Carboline-3-Carboxylate

[³H]Ethyl β-carboline-3-carboxylate ([³H]β-CCE) binds to a homogeneous population of recognition sites in rat whole brain membranes with high affinity. The [³H]β-CCE binding is completely displaceable by low concentrations of a number of benzodiazepines with similar potencies found when using a ³H-benzodiazepine as the ligand. This suggests that the recognition sites for β-CCE and the benzodiazepines are identical or that they are involved in a close interaction. The binding of [³H]β-CCE does not obey simple mass-action kinetics. [³H]Flunitrazepam dissociation from its receptor population is biphasic, and different methods of initiation of this dissociation indicate that cooperative interactions take place within the receptor population. We conclude that the benzodiazepine receptor is a single entity that can exist in two conformations, the equilibrium between which may be controlled by some as yet unidentified factor.