Hightime-resolution analysis of the secretory dynamics of tPA-CD-GFP. (A) Molecular structure of tPA. (B) Epi-F and TIR-F images in tPA-CD-GFP–expressing cells. The bars represent 10 μm. (C) Representative 32 frames per second sequences of the single tPA-CD-GFP secretory granule indicated by a white box in panel B. Time 0 shows the point of granule opening. (D) Changes in F/F₀ in each single secretory granule plotted as a function of the time after opening (time 0) of tPA-CD-GFP–containing granules (▲, 31 granules from 6 cells) compared with tPA-GFP–containing granules (●, 8 granules from 3 cells). Data are shown as mean plus or minus SE.