Journal of Neuroscience, Vol 1, 1036-1042, Copyright © 1981 by Society for Neuroscience
Picrotoxinin and diazepam bind to two distinct proteins: further evidence that pentobarbital may act at the picrotoxinin site
WC Davis and MK Ticku
alpha-[3H]Dihydropicrotoxinin (DHP) and [3H]diazepam binding proteins were
solubilized from rat brain membranes with 1% Lubrol-Px. Gel filtration of
the Lubrol-solubilized fraction revealed that [3H]DHP and [3H]diazepam bind
to two distinct peaks with apparent molecular weights of 185,000 and
61,000, respectively. The signal-to-noise ratio of [3H]DHP binding to
185,000-dalton fractions was improved significantly. [3H]DHP bound to the
185,000-dalton fraction with two binding constants. Muscimol and
pentobarbital, while enhancing [3H]diazepam binding to membrane and crude
Lubrol-solubilized fractions, failed to enhance [3H]diazepam binding to the
61,000-dalton fraction. Pentobarbital inhibited the binding of [3H]DHP to
the 185,000-dalton fraction with an IC50 value of 60 +/- 12 micro M. The
binding of [3H]DHP alos was inhibited by several depressant and convulsant
drugs which affect gamma-aminobutyric acid (GABA)-mediated transmission.
These results provide strong evidence that picrotoxinin and diazepam bind
to two distinct proteins and that pentobarbital may act at the
picrotoxinin-sensitive site of the benzodiazepine . GABA receptor .
ionophore complex.