title: [3H]L-655,708, a novel ligand selective for the benzodiazepine site of GABAA receptors which contain the alpha 5 subunit.
abstract: A compound (L-655,708) has been identified which has at least 50-fold selectivity for the benzodiazepine site on GABAA receptors containing an alpha 5 subunit over those containing an alpha 1, alpha 2, alpha 3 or alpha 6 subunit in combination with beta 3 and gamma 2. The compound was radiolabelled with tritium and investigated as a novel radioligand which recognizes the benzodiazepine site of GABAA receptors which contain the alpha 5 subunit. [3H]L-655,708 labels one saturable and specific population of binding sites in rat hippocampus with a Kd of 2.4 +/- 0.7 nM and a Bmax of 256 +/- 42 fmol/mg protein. The pharmacology of the binding site labelled was consistent with that of receptors present in cells transfected with alpha 5, beta 2 and gamma 2 and with receptors immunoprecipitated from rat brain with an alpha 5-selective antiserum. It is concluded that [3H]L-655,708 is the first radioligand to date which is selective for any BZ2 subtype of the GABAA receptor and should provide a valuable tool for elucidating the structure and function of the alpha 5-containing GABAA receptor subtype.
authors.affiliation: Department of Biochemistry and Merck Sharp and Dohme Research Laboratories, Harlow, Essex, U.K.
authors.forename: K
authors.initials: K
authors.lastname: Quirk
authors.forename: P
authors.initials: P
authors.lastname: Blurton
authors.forename: S
authors.initials: S
authors.lastname: Fletcher
authors.forename: P
authors.initials: P
authors.lastname: Leeson
authors.forename: F
authors.initials: F
authors.lastname: Tang
authors.forename: D
authors.initials: D
authors.lastname: Mellilo
authors.forename: C I
authors.initials: CI
authors.lastname: Ragan
authors.forename: R M
authors.initials: RM
authors.lastname: McKernan
mesh_terms: D000818:Animals; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008024:Ligands; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D011233:Precipitin Tests; D011869:Radioligand Assay; D051381:Rats; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism*
chemical_list: D007093:Imidazoles; C105490:L 655,708; D008024:Ligands; D011963:Receptors, GABA-A