title: Solubilization and detergent effects on interactions of some drugs and insecticides with the t-butylbicyclophosphorothionate binding site within the gamma-aminobutyric acid receptor-ionophore complex.
abstract: Specific binding of [35S]t-butylbicyclophosphorothionate (TBPS) to rat brain membranes (RBM) is enhanced nine-fold by EDTA/water dialysis and 1.3- to 4.2-fold by 50 nM ketosteroid R 5135, or 5 mM 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) or related piperazine-N-alkanesulfonate buffers, or extensive washing with NaCl/Na phosphate or Na phosphate/citrate solution. About one-fifth of the [35S]TBPS binding capacity appears in the soluble fraction whereas the rest remains in particulate form on treatment of the EDTA/water-dialyzed RBM with 20 mM CHAPS. Similar KD values (64-86 nM) are obtained for the original EDTA/water-dialyzed membranes and the CHAPS-treated and/or -solubilized preparations. The Bmax of the EDTA-treated RBM is reduced five-fold on solubilization with CHAPS. The potency for displacement of [35S]TBPS changes in the presence of CHAPS or on CHAPS solubilization: gamma-aminobutyric acid (GABA) and muscimol inhibit specific [35S]TBPS binding more strongly in the absence than in the presence of CHAPS: TBPS, picrotoxinin, and photoheptachlor epoxide are almost equally active with RBM, RBM + CHAPS, and RBM solubilized with CHAPS. Levels of (1R, alpha S)-cis-cypermethrin and dimethylbutylbarbiturate which are inhibitory with RBM are moderately stimulatory after TBPS receptor solubilization. Thus CHAPS defines three regions of the GABA receptor-ionophore complex, i.e., the GABA and benzodiazepine receptors, the TBPS/picrotoxinin/polychlorocycloalkane receptor(s), and the sites at which the alpha-cyano pyrethroid and the barbiturate interact with TBPS binding.
authors.forename: J
authors.initials: J
authors.lastname: Seifert
authors.forename: J E
authors.initials: JE
authors.lastname: Casida
mesh_terms: D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism; D001643:Bridged Bicyclo Compounds / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic; D001952:Bridged-Ring Compounds / Q000378:metabolism*; D002793:Cholic Acids / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000378:metabolism; D000077423:Polidocanol; D011092:Polyethylene Glycols / Q000494:pharmacology; D051381:Rats; D011963:Receptors, GABA-A / Q000378:metabolism*; D012995:Solubility
chemical_list: D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D001952:Bridged-Ring Compounds; D002793:Cholic Acids; D011963:Receptors, GABA-A; D000077423:Polidocanol; D011092:Polyethylene Glycols; C037476:tert-butylbicyclophosphorothionate; D004492:Edetic Acid; C028213:3-((3-cholamidopropyl)dimethylammonium)-1-propanesulfonate