| Assay Method Information | |
| | Biological Assays |
| Description: | For measuring Npt2a activity in a cell based assay, a stable CHO cell line with inducible Npt2a expression was generated. Therefore, CHO T-Rex cells (life technologies cat. R718-07) were stably transfected with doxycycline-inducible human NPT2a (pcDNA5TO-hNpt2a). The obtained CHO T-REx hNpt2a cells were routinely cultured in Dulbecco's MEM/F12 (4.5 g/l Glucose, Gibco cat. 21331-020; 500 mL) supplemented with 10 ml Glutamax 100×, Sodium pyruvate (7 mL of 100 mM solution), HEPES (10 mL of 1 M solution), Sodium bicarbonate (10 mL of 7.5% solution), 10% Fetal Bovine Serum Tetracycline free (Clontech cat. 631106, 500 ml), Penicillin-Streptomycin (5 mL of 100× Solution), Blasticidin 10 μg/mL and 400 μg/mL Hygromycin.Activity of Npt2a was detected by following depolarization of cellular membrane potential by influx of sodium phosphate using fluorescent membrane potential dye kit BLUE (Molecular devices cat. R8034). For Npt2a activity measurements, CHO T-Rex hNpt2a cells were seeded into 1536 well microtiter plates (GREINER Bio-One cat. 782092) with 750 cells/well in 7 μL/w of complete medium (2% Tetracycline-free FBS, 2% Poly-D-Lysine) without selective agents+Doxycycline 0.5 μg/mL to induce Npt2a gene expression, and grown for 24 h at 37° C., 5% carbon dioxide.On the day of experiment a 1×MPdye Loading Solution was freshly prepared by re-suspending 15 mg of Blue MPdye powder in 10 mL of NHE buffer sodium-free (140 mM N-Methyl-D-glucamine, 5.4 mM KCl, 1 mM CaCl2, 11 mM D(±)-Glucose water free, 1.2 mM MgCl2, 10 mM HEPES; pH 7.4 (adjusted with hydrochloric acid); sterile filtered). 5 μl medium was removed from plates by robotic manipulation, then 5 μL/well of sodium-free NHE buffer was added. After incubation for 2 min, this washing step was repeated once. Then, 5 μL/w of buffer was removed from plates and cells were incubated for 5 min at room temperature with 5 μL/w of MPdye Loading Solution (1× in Sodium-free NHE Buffer). Test compounds were added to the cells at final test concentrations between 50 μM and 1 nM (0.6 μL/well, final DMSO 0.6%, prepared in MPDye Loading Solution) and incubated for 5 min at room temperature.Plates were analyzed with an in house CCD camera device using a λexc 510-545 nm/λem 565-625 nm filter. Fluorescence was detected for 15 sec (background measurement M1). Activity of Npt2a was triggered by addition of 2 μL/well of 30 mM Na+ and 1 mM phosphate (prepared in a mixture of NHE Buffer Na+ free and NHE Buffer 140 mM Na+). Fluorescence was followed for 2-3 min (depolarization measurement M2). Data was normalized to cell number and dye loading efficiency by calculating M2/M1. This quotient was plotted against test compound concentration. Graph Pad Prism or equivalent in house software was used to create sigmoidal dose-response curves (variable slope) and determine IC50 values. |
| Affinity data for this assay | |
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