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| | Alpha 7 UAChR Inhibition Assay |
| Description: | The [3H]-methyllycaconitine binding assay is a modification of the method described by Davies et al. in Neuropharmacol, 1999, 38, 679-690.Rat brain tissue (hippocampus or whole brain) is homogenized in aqueous homogenization buffer (10% w/v, 0.32 M sucrose, 1 mM EDTA, 0.1 mM phenylmethylsulfonyl fluoride (PMSF), 0.01% (w/v) NaN3, pH 7.4, 4° C.) at 600 rpm in a glass homogenizer. The homogenate is centrifuged (1000×g, 4° C., 10 min) and the supernatant is removed. The pellet is resuspended (20% w/v) and the suspension is centrifuged (1000×g, 4° C., 10 min). The two supernatants are combined and centrifuged (15 000×g, 4° C., 30 min). The pellet obtained in this way is referred to as the P2 fraction.The P2 pellet is suspended in binding buffer (50 mM Tris-HCl, 1 mM MgCl2, 120 mM NaCl, 5 mM KCl, 2 mM CaCl2, pH 7.4), and the suspension is centrifuged (15 000×g, 4° C., 30 min), twice.The residue is resuspended in binding buffer to a concentration of 4 mg/ml and incubated in a volume of 250 μl (amount of membrane protein 0.4 mg) in the presence of 2 nM [3H]-methyllycaconitine, 0.1% (w/v) BSA (bovine serum albumin) and various concentrations of the test substance at 21° C. for 60 min.Incubation is then carried out in the presence of 1 μM α-bungarotoxin or 100 μM nicotine or 10 μM MLA (methyllycaconitine). The incubation is stopped by adding 4 ml of PBS (20 mM Na2HPO4, 5 mM KH2PO4, 150 mM NaCl, pH 7.4, 4° C.) and filtering through type A/E glass fiber filters (Gelman Sciences) which have previously been placed in 0.3% (v/v) polyethyleneirnine (PEI) for 3 h. The filters are washed twice with 4 ml of PBS (4° C.), and the bound radioactivity is determined by scintillation measurement. All the assays are carried out in triplicate. The dissociation constant Ki of the test substance was determined from the IC50 of the compounds (concentration of the test substance at which 50% of the ligand bound to the receptor is displaced), the dissociation constant KD and the concentration L of [3H]-methyllycaconitine using the equation K1=IC50/(1+L/KD).In place of [3H]-methyllycaconitine it is also possible to employ other α7 nAChR-selective radioligands such as, for example, [125I]-α-bungarotoxin or nonselective nAChR radioligands together with inhibitors of other nAChRs.The in vitro data for the effects of the compounds of the invention show a Ki of <300 nM. |
| Affinity data for this assay | |
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