Differential localization of GABA-dependent and GABA-independent benzodiazepine binding sites within synapses of rat cerebral cortex.

Fractions containing non-junctional membranes (fraction 1) could be separated from those enriched in junctional complexes (fraction 2) by sucrose gradient centrifugation of osmotically disrupted rat cerebral cortex synaptosomes. [3H]flunitrazepam binding sites were found to be homogeneous characterized by Kd = 0.65 nM, Bmax = 13 pM for fraction 1; and Kd = 2 nM, Bmax = 45 pM for fraction 2. GABA-dependent benzodiazepine receptor sites were found to be localized to the junctional complex fraction, while non-junctional membranes showed GABA-independent receptor and acceptor binding sites.