A Novel Screening Assay of the Na+-Dependent Cl-/HCO-3 Exchanger (NCBE) and Its Inhibitors

Abstract
A mouse fibroblast L cell line defective in Na+/H+ antiport activity (LAP1) was used to develop a screening assay for the Na+-dependent Cl-/HCO3 exchanger (NCBE). Regulation of intracellular pH (pHi) via NCBE was studied in suspended LAP1 cells using the pH-sensitive fluorescent dye 2’, 7’-bis(2-carboxyethyl)-5,6-carboxyfluorescein. Besides the well-known irreversible NCBE blocker 4,4’-diisothiocyanatostilbene-2,2’-disulfonic acid (DIDS), different compounds were tested. None of these had any higher effect than DIDS. Nevertheless, 3’,5-dichlorodiphenylamine-2-carboxylic acid and the corresponding 3’-trifluoromethyl derivative were found to be approximately as potent as DIDS with IC50 values of 29.2 ± 2.5 and 21.7 ± 5.7 µM.

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