Figure 4.

Secretion depletes mobile secretory vesicles viewed by TIRFM in growth cones. (A) Image processing was used to display vesicles that took large steps (“mobile”) or that were stationary. Note that after depolarization, mobile vesicles are depleted whereas stationary vesicles show little change. (Bar = 2 μm.) (B) Quantitation from five experiments. Sustained depolarization started at 0 min. Mobile vesicle depletion was greater than stationary vesicle depletion. Furthermore, mobile vesicle depletion was at least as rapid as for stationary vesicles. Finally, although the measurement of mobile vesicles is not prone to contamination by slow, “immobile” vesicles, mobile vesicles occasionally stop and, hence, contribute to the measurement of stationary vesicles.