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Assay Method Information

Assay Name:  NATIVE RECEPTOR BINDING ASSA
Description:  The binding of 125I-CGRP to receptors in SK-N-MC cell membranes was carried out essentially as described (Edvinsson et al. (2001) Eur. J. Pharmacol. 415, 39-44). Briefly, membranes (25 μg) were incubated in 1 mL of binding buffer [10 mM HEPES, pH 7.4, 5 mM MgCl2 and 0.2% bovine serum albumin (BSA)] containing 10 pM 125I-CGRP and antagonist. After incubation at room temperature for 3 h, the assay was terminated by filtration through GFB glass fibre filter plates (PerkinElmer) that had been blocked with 0.5% polyethyleneimine for 3 h. The filters were washed three times with ice-cold assay buffer (10 mM HEPES, pH 7.4 and 5 mM MgCl2), then the plates were air dried. Scintillation fluid (50 μL) was added and the radioactivity was counted on a Topcount (Packard Instrument). Data analysis was carried out by using Prism and the Ki was determined by using the Cheng-Prusoff equation (Cheng & Prusoff (1973) Biochem. Pharmacol. 22, 3099-3108).Cells expressing recombinant human CL receptor/RAMP1 were washed with PBS and harvested in harvest buffer containing 50 mM HEPES, 1 mM EDTA and Complete™ protease inhibitors (Roche). The cell suspension was disrupted with a laboratory homogenizer and centrifuged at 48,000 g to isolate membranes. The pellets were resuspended in harvest buffer plus 250 mM sucrose and stored at −70° C. For binding assays, 20 μg of membranes were incubated in 1 mL binding buffer (10 mM HEPES, pH 7.4, 5 mM MgCl2, and 0.2% BSA) for 3 h at room temperature containing 10 pM 125I-hCGRP (GE Healthcare) and antagonist. The assay was terminated by filtration through 96-well GFB glass fiber filter plates (PerkinElmer) that had been blocked with 0.05% polyethyleneimine. The filters were washed 3 times with ice-cold assay buffer (10 mM HEPES, pH 7.4, and 5 mM MgCl2). Scintillation fluid was added and the plates were counted on a Topcount (Packard). Non-specific binding was determined and the data analysis was carried out with the apparent dissociation constant (Ki) determined by using a non-linear least squares fitting the bound CPM data to the equation below:Y obsd = ( Y max - Y min ) ⁢ ( % ⁢ ⁢ I max - % ⁢ Imin ⁢ / ⁢ 100 ) + Y min + ( Y max - Y min ) ⁢ ( 100 - % ⁢ ⁢ I max ⁢ / ⁢ 100 ) 1 + ( [ Drug ] ⁢ / ⁢ K i ⁡ ( 1 + [ Radiolabel ] ⁢ / ⁢ K d ) nH Where Y is observed CPM bound, Ymax is total bound counts, Ymin is non specific bound counts, (Ymax−Ymin) is specific bound counts, % Imax is the maximum percent inhibition, % I min is the minimum percent inhibition, radiolabel is the probe, and the Kd is the apparent dissociation constant for the radioligand for the receptor as determined by hot saturation experiments.
Affinity data for this assay
 

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Last update November 1, 2007
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