Fusion of a granzyme B-mCherry containing lytic granule with the plasma membrane.

(A) Consecutive frames from the TIRF video imaging are shown. The video frame numbers are shown below the images. The arrowhead indicates a lytic granule which decreased in fluorescence and generated a cloud of fluorescence while fusing. (B) The fluorescent intensity (arbitrary units) of the fusing granule (filled circles) indicated by the arrow in A was plotted versus frame number. The intensity of the juxtagranular region (halo, open circles) is included. As the granule fused its intensity increased briefly (frame 534) and it then disappeared. At frame 535 the juxtagranular area brightened. In subsequent frames the fluorescence dissipated (frame 537). (C) The whole-cell membrane capacitance trace (C_m, upper trace) and the camera trigger voltage are shown (lower trace, positive steps indicate shutter opening) versus time. The capacitance step in the C_m trace at time 48.2 s occurs at video frame 535 (arrow).