Fig. 7. Endosomal pH in wild-type, rtoA^-, mdrA1^-/mdrA2^- and rtoA^-/mdrA1^-/mdrA2^- cells. Cells were fed FITC-dextran for 10 minutes, collected, and resuspended in buffer. At the indicated times, aliquots of cells were removed, centrifuged, and resuspended in assay buffer, and fluorescence was measured using excitation at 450 and 495 nm. The pH values were obtained from a standard curve of the FITC dextran fluorescence ratio as a function of pH. Values are mean±s.e.m.