Fig. 4. Endocytosis of wild-type and GDI1^– cells. (A) Pinocytosis of FITC-dextran. Cells were resuspended in fresh axenic medium at 5 × 10⁶ cells/ml in the presence of 2 mg/ml FITC-dextran. Fluorescence from the internalized marker was measured at selected time points. (B) Fluid-phase exocytosis of FITC-dextran. Cells were pulsed with FITC-dextran (2 mg/ml) for 3 h, washed and resuspended in fresh axenic medium. Fluorescence from the marker remaining in the cell was measured. (C) Phagocytosis of TRITC-labeled yeast cells. Dictyostelium cells were resuspended at 2 × 10⁶ cells/ml in fresh axenic medium and challenged with a 5-fold excess fluorescent yeast cells. Fluorescence from internalized yeasts was measured at the designated time points. Data are presented as relative fluorescence, AX2 being considered 100%, and all values are the average ± standard deviation of at least three independent experiments.