Picrotoxinin and diazepam bind to two distinct proteins: further evidence that pentobarbital may act at the picrotoxinin site.
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.
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003975:Diazepam / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008970:Molecular Weight; D010424:Pentobarbital / Q000494:pharmacology*; D010852:Picrotoxin / Q000031:analogs & derivatives* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011955:Receptors, Drug / Q000302:isolation & purification / Q000378:metabolism*; D011963:Receptors, GABA-A; D054830:Sesterterpenes
D003975:Diazepam; D010424:Pentobarbital; D010852:Picrotoxin; D011955:Receptors, Drug; D011963:Receptors, GABA-A; D054830:Sesterterpenes; C031012:dihydropicrotoxinin receptor; C017230:dihydropicrotoxinin; C022961:picrotoxinin