Flow system fluorescence polarization measurements on fluorescein diacetate-stained EL4 cells

We have adapted a multiparameter cell sorter to measure the distribution of fluorescence polarization in cell populations. Measurements carried out on EL4 cells show that the percent polarization of fluorescein fluorescence decreases with increasing fluorescence intensity. This inverse relationship between polarization and intensity is shown both within the cell population and by the average values of the two quantities during both the increase and decrease of fluorescence intensity. The quantitative relation between intensity and polarization is different in hypertonic than in isotonic media. These results suggest that polarization measurements carried out at a fixed time after incubation of cells with fluorescein diacetate, which is converted to fluorescein within the cells, may depend in part on the rate of fluorescein accumulation, and that agents that have been reported to change the polarization of fluorescein in living cells may do so by changing the kinetics of fluorescein accumulation.