Fig. 4. Comparison of pH_DV in D10' parasites at the early trophozoite stage (16-22 hours post-invasion) and at the mature trophozoite stage (32-38 hours post-invasion) as determined using either 40 µM Fluorescein (open symbols) or 70 µM Oregon Green 514 (closed symbols) (i.e. 28 µM dextran in the loading solution in each case), calibrated using the nigericin/high-K⁺ method. For both dyes, the reported pH_DV changed significantly as the intraerythrocytic parasites developed from the early to the mature stage (P<0.05). The data represent the means (± s.e.m.) of at least three independent experiments, each derived from at least three replicate measurements per experiment.