| Assay Method Information | |
| | Determination of Binding Affinity for CGRP Receptor by Radioligand Binding Assay in SK-N-MC Cell Membranes |
| Description: | The binding affinity assay of compounds for human CGRP receptor was carried out by inhibition of radiolabeled ligand [125I]-CGRP binding in human neuroblastoma cell line SK-N-MC cell membranes.Cell membranes prepared from SK-N-MC cells expressing CGRP receptors endogenously (Muff et al., Ann N Y Acad Sci. 1992; 657: 106-116) were used for radioligand binding assay. Radioligand binding assay was performed using 96-well microplate in a total volume of 200 μL in each well. A 2.5 μL of serial dilution of compound dissolved in dimethylsulfoxide (DMSO) was mixed with SK-N-MC cell membranes (40 μg membrane protein per well) and [125I]-CGRP (PerkinElmer NEX354, final concentration of 150 pM) in an assay buffer consisting of 50 mM Tris-HCl, 5 mM MgCl2 and 0.1% bovine serum albumin (pH 7.4). The assay plate was incubated with shaking on a plate shaker at room temperature for 90 minutes. The incubation was terminated by filtration through a GF/C glass fiber filter plate (Merck Millipore) pre-soaked with 0.3% polyethyleneimine (PEI). Filters were washed 4 times with 300 μL of ice-cold assay buffer. After drying the filter plate, 100 μL of scintillation fluid (PerkinElmer, MicroScint-20) was added to each well and the radioactivity was counted using a TopCount NXT (PerkinElmer). Non-specific binding was determined in the presence of 1.25 μM unlabelled human α-CGRP (Bachem). The radioactivity was converted to the percent of specific binding using the equation below.% of specific binding = ( Y - Y min ) ( Y max - Y min ) × 100 [ Number 1 ]In the formulae, Y is observed radioactivity, Ymax is total bound activity, and Ymin is non-specific bound activity.From these data, the concentration of compound required for 50% inhibition of radioligand binding (IC50) was determined using Prism (GraphPad Inc.). The IC50 value is then converted to the equilibrium dissociation constant (Ki) using the Cheng-Prusoff equation below (Cheng & Prusoff (1973) Biochem. Pharmacol. 22, 3099-3108).Ki = IC 50 1 + [ L ] Kd [ Number 2 ]In the formulae, [L] is the concentration of radioligand, Kd is the apparent dissociation constant of the radioligand for the receptor as determined by saturation binding assay with [125I]-CGRP. |
| Affinity data for this assay | |
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