Efflux of Bis-carboxyethyl-carboxyfluorescein (BCECF) by a Novel ATP-dependent Transport Mechanism in Epithelial Cells

The efflux of the intracellular pH fluorochrome 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) was quantified in four cultured epithelial cell lines; HCT-8, T84, HGT-1 and MDCK. BCECF efflux was time-dependent, and after 5 h 45-91% of the initial BCECF loaded was extracellular, efflux being greatest in MDCK cells. Depletion of cellular ATP approximately halved BCECF efflux. BCECF efflux was inhibited by indomethacin, vinblastine and verapamil, but not by nifedipine or reserpine. Certain features of BCECF efflux resemble drug efflux in multidrug resistant cells, but inhibition of efflux displays a distinct pharmacological profile suggesting BCECF is a substrate for a novel ATP-dependent transport system.