Journal of Neuroscience, Vol 1, 409-418, Copyright © 1981 by Society for Neuroscience
Characterization of benzodiazepine and gamma-aminobutyric recognition sites and their endogenous modulators
M Massotti, A Guidotti and E Costa
The solubilization and partial purification from rat brain cortex
homogenates of [3H]gamma-aminobutyric acid (GABA) and [3H]diazepam
recognition sites and of their endogenous modulators (GABA-modulin and an
endogenous compound which specifically bound [3H]diazepam) are reported. A
high percentage of GABA binding sites (virtually free of benzodiazepine
binding sites) was solubilized from homogenates of rat brain cortex
incubated at 0 degree C with 1% Triton X-100 and a mixture of protease
inhibitors. A large proportion of benzodiazepine binding sites was
solubilized in the absence of apparent GABA binding capacity by incubating
crude synaptic membrane preparations at 37 degree C with 0.05% Triton
X-100. The characteristics of these two solubilized binding sites resemble
those of the membrane-bound binding sites. However, unlike the
membrane-bound sites, solubilized GABA and benzodiazepine binding sites are
insensitive to GABA stimulation, while solubilized GABA binding sites are
no longer protected by the benzodiazepines against heat inactivation. These
results indicate that GABA and benzodiazepine recognition sites reside in
two different molecules which, when bound to membranes, can interact
reciprocally and modulate their binding affinity for specific ligands.