2′,7′-Bis-(carboxyethyl)-5-(6′)-carboxyfluorescein (BCECF) as a probe for intracellular fluorescence polarization measurements

The utility of 2′,7′-bis-(carboxyethyl)-5-(6′)-carboxyfluorescein (BCECF) for the execution of the structuredness of the cytoplasmic matrix (SCM) measurement for lymphocyte activation is investigated. Cells were incubated with BCECF/AM [2′,7′-bis-(carboxyethyl)-5(6′)-carboxyfluorescein acetoxymethylester], a nonfluorescent lipophilic acetoxymethylester that readily enters cells and is enzymatically hydrolyzed to fluorescent BCECF once inside. Leakage of BCECF out of cells is negligible in comparison to that observed with fluorescein, greatly reducing one source of background fluorescence. However, spontaneous hydrolysis of BCECF/AM in aqueous solution does contribute significant background fluorescence, which can be minimized by staining at relatively high concentrations of cells and subsequent dilution. As is the case with fluorescein, the polarization spectrum of intracellular BCECF shows a wavelength dependence not seen in the spectrum of the dye in homogeneous media of various viscosities. The more pronounced wavelength dependence of the polarization observed with BCECF compared with fluorescein suggests that BCECF might be preferable to fluorescein as a marker for the SCM test.