Fig. 2. scar^- cells are defective in fluid phase exocytosis. To examine exocytosis, wild-type and scar^- cells were loaded with FITC-dextran for 3 hours, washed and allowed to efflux FITC-dextran for the indicated times prior to harvesting and fluorescence measurement. The percentage FITC-dextran remaining inside the cell was calculating by comparing the fluorescence values at each of the time points to the value at time T=0. (A) The average of four independent experiments, showing that scar^- cells are defective in exocytosis. Whereas wild-type cells have released 50% of the FITC-dextran from the cell by 50 minutes, scar^- cells required nearly twice as long (90 minutes) to exocytose 50% of the FITC-dextran. (B) The vesicular pH was calculated over time as described in Materials and Methods. Fluid phase entered acidic vesicles rapidly (within 10 minutes into the chase period in both control Ax3 and scar^- cells). However, the fluid phase only slowly left lysosomes in scar^- cells and did not reach more neutral pH post-lysosomes until after 60 minutes into the chase period, whereas, in wild-type cells, the fluid phase entered the post-lysosomes within 45 minutes.