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Assay Method Information

Assay Name:  competition binding assay
Description:  The human V1a receptor was cloned by RT-PCR from total human liver RNA. The coding sequence was subcloned in an expression vector after sequencing to confirm the identity of the amplified sequence. To demonstrate the affinity of the compounds from the present invention to the human V1a receptor binding studies were performed. Cell membranes were prepared from HEK293 cells transiently transfected with the expression vector and grown in 20 liter fermenters with the following protocol.50 g of cells are re-suspended in 30 ml freshly prepared ice cold Lysis buffer (50 mM HEPES, 1 mM EDTA, 10 mM MgCl2 adjusted to pH=7.4+complete cocktail of protease inhibitor (Roche Diagnostics)). Homogenized with Polytron for 1 min and sonicated on ice for 22 minutes at 80% intensity (Vibracell sonicator). The preparation is centrifuged 20 min at 500 g at 4 C., the pellet is discarded and the supernatant centrifuged 1 hour at 43,000 g at 4 C. (19,000 rpm). The pellet is re-suspended in 12.5 ml Lysis buffer+12.5 ml Sucrose 20% and homogenized using a Polytron for 1-2 min. The protein concentration is determined by the Bradford method and aliquots are stored at −80 C. until use. For binding studies 60 mg Yttrium silicate SPA beads (Amersham) are mixed with an aliquot of membrane in binding buffer (50 mM Tris, 120 mM NaCl, 5 mM KCl, 2 mM CaCl2, 10 mM MgCl2) for 15 minutes with mixing. 50 μl of bead/membrane mixture is then added to each well of a 96 well plate, followed by 50 μl of 4 nM 3H-Vasopressin (American Radiolabeled Chemicals). For total binding measurement 100 μl of binding buffer are added to the respective wells, for non-specific binding 100 μl of 8.4 mM cold vasopressin and for compound testing 100 μl of a serial dilution of each compound in 2% DMSO. The plate is incubated 1 h at room temperature, centrifuged 1 min at 1000 g and counted on a Packard Top-Count. Non-specific binding counts are subtracted from each well and data is normalized to the maximum specific binding set at 100%. To calculate an IC 50 the curve is fitted using a non-linear regression model (XLfit) and the Ki is calculated using the Cheng-Prussoff equation.
Affinity data for this assay
 

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Last update November 1, 2007
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