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| | 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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