Fig. 5. Fluorometer traces of mature trophozoite-stage D10' parasites isolated from erythrocytes loaded with (A) 150 µM Fluorescein, (B) 10 µM Fluorescein, (C) 70 µM Oregon Green 514, or (D) 4 µM Oregon Green 514. Cells were suspended in minimal saline solution at pH 7.1. Black arrowheads indicate the point of addition of concanamycin A (75 nM), a potent and specific inhibitor of the digestive vacuole V-type H⁺ pump (Saliba et al., 2003). Numbered traces indicate the pH of calibration samples (nigericin/high-K⁺ method). The traces are from single experiments, and are representative of those obtained in at least three separate experiments for each dye concentration. Note that the dynamic range of Oregon Green 514 (see Fig. 3) precluded accurate measurement of the endpoint of digestive vacuole alkalinisation by concanamycin A.