Effects of X-rays on cell membranes. II. Changes of permeability measured by fluorescein efflux.

The effect of irradiation on the permeability of cell membranes of L-929 cells was investigated. Efflux of fluorescein, accumulated by hydrolysis of fluoresceindiacetate in the cells, was measured using flow cytometry. The changes of rate constants for the permeation of florescein through the cell membrane at different temperatures and after various X-ray doses were studied. Decreasing temperatures yielded substantially slower efflux of fluorescein. After irradiation of cells, the rate constant of fluorescein efflux increased linearly with dose; 180 Gy are required to cause an increase by a factor of 2. The results are discussed with respect to radiation damage of active and passive transport mechanisms.