Retention of major WPB core proteins during lingering kiss fusion events. (A) The fate of VWF-EGFP and Proregion-mRFP, co-packaged within the same WPB, following a complete exocytotic event (Ai,iii) or following fusion-evoked collapse (Aii,iv). Ai and ii show montages of images of VWF-EGFP (top panels) and Proregion-mRFP (bottom panels) fluorescence from time-lapse sequences, and Aiii and iv show the time-course for the fluorescence changes for VWF-EGFP (black traces) and Proregion-mRFP (gray traces) during the 2 distinct fusion events. Scale bars are 2 μm, dual-color images were acquired at 0.83 frames per second. (B) A montage of images of a single Proregion-EGFP containing WPBs undergoing fusion in the presence of 7 μM extracellular FM 4-64. FM4-64 labels the WPB membrane only following formation of a fusion pore. The top panel shows Proregion-EGFP fluorescence, the lower panel shows FM 4-64 fluorescence. Images were acquired simultaneously on a Leica SP2 confocal microscope at 7.4 frames per second. The cell was stimulated with histamine (100 μM), the scale bar is 2 μm. (C) In the same format as Panel A, examples of complete exocytosis and collapsed WPB structures containing Proregion-EGFP alone. Images were acquired at 30 frames per second on an epi-fluorescence microscope. For display, images were resampled to a frame every 2 seconds. Frames indicated by the white asterisks correspond to the point on the time-course plot indicated by the black asterisk.