| Assay Method Information | |
| | Cell-Based Assay of NHE3 Activity under Persistent Conditions |
| Description: | The ability of compounds to inhibit Rat NHE3-mediated Na+-dependent H+ antiport after application and washout was measured using a modification of the pH sensitive dye method described above. Opossum kidney (OK) cells were obtained from the ATCC and propagated per their instructions. The rat NHE3 gene was introduced into OK cells via electroporation, and cells were seeded into 96 well plates and grown overnight. Medium was aspirated from the wells, cells were washed twice with NaCl-HEPES buffer (100 mM NaCl, 50 mM HEPES, 10 mM glucose, 5 mM KCl, 2 mM CaCl2, 1 mM MgCl2, pH 7.4), then overlayed with NaCl-HEPES buffer containing 0-30 μM test compound.After a 60 min incubation, the test drug containing buffer was aspirated from the cells, cells were washed twice with NaCl-HEPES buffer without drug, then incubated for 30 min at room temperature with NH4Cl-HEPES buffer (20 mM NH4Cl, 80 mM NaCl, 50 mM HEPES, 5 mM KCl, 2 mM CaCl2, 1 mM MgCl2, pH 7.4) containing 5 uM BCECF-AM. Cells were washed twice with Ammonium free, Natfree HEPES (100 mM choline, 50 mM HEPES, 10 mM glucose, 5 mM KCl, 2 mM CaCl2, 1 mM MgCl2, pH 7.4) and incubated in the same buffer for 10 minutes at room temperature to lower intracellular pH. NHE3-mediated recovery of neutral intracellular pH was initiated (40 min after compound washout) by addition of Na-HEPES buffer containing 0.4 uM ethyl isopropyl amiloride (EIPA, a selective antagonist of NHE-1 activity that does not inhibit NHE3), and monitoring the pH sensitive changes in BCECF fluorescence (λex 505 nm, λem, 538 nm) normalized to the pH insensitive BCECF fluorescence (λex 439 nm, λem, 538 nm). Initial rates were plotted as the average 2 or more replicates, and pIC50 values w |
| Affinity data for this assay | |
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