Fig. 2. Tracking of insulin granules in ßTC3 cells reveals two granule populations. (A-C) Three representative frames, at different time points, from a time-lapse movie of secretory granules labeled with phogrin-EGFP before and after KCl stimulation. The first 60 frames (120 seconds) were taken under unstimulated condition before 30 mM KCl was added, and the movie continued for another 120 frames to record KCl-stimulated granule movement. Several granules are manually tracked through 30 frames to show their paths in D-F. The movie can be viewed in the supplementary material. Bar, 10 µm.