Effect of MTX on vital dye uptake in BAECs. Panel A. Ethidium bromide (EB) uptake in BAECs was determined from the increase in fluorescence as a function of time as described in Material and Methods. Five traces are shown superimposed. EB was added at 50 sec to BAECs suspended in HBS. At the time indicated by the arrow (2 min), MTX was added at the final concentration indicated to the right of each trace. Values shown are normalized to the maximum fluorescence obtained by addition of digitonin at the end of each trace. Panels B and C. Same as in panel A with YO-PRO-1 (blue) or POPO-3 (red) added at 50 sec. Panels D and E. Comparison of EB (black), YO-PRO (blue), and POPO-3 (red) uptake data for 1.0 and 0.3 nM MTX; note expanded fluorescence scale and time base. Results shown are representative of 5 individual experiments.