WPB EGFP-CD63 microdomains are secreted as discrete particles during exocytosis. (A-D) Examples of image montages taken from dual-color live-cell videos (supplemental Videos 8-11, respectively) of WPBs containing EGFP-CD63 (top panels; green in color merge) and VWFpp-mRFP (middle panels) prior to (frame 1) and during (frames 2-9) exocytosis evoked by histamine stimulation (100 µM). Scale bars, 2 µm. In each case, the WPB indicated by the arrow undergoes a morphological transition from rod to spheroid shape, accompanied by expulsion of VWFpp-EGFP and release of the EGFP-CD63 ILV as a discrete particle. (A-C) The EGFP-CD63 particle diffuses out of the field of view. (D) The particle remains trapped within the patch of secreted VWF. Images were acquired sequentially on a wide-field microscope equipped with an Olympus UPLSAPO 100× 1.4NA objective, an OptoLED epifluorescence excitation system, and an Andor iXon3 EMCCD camera operating at 30 frames per second.