Fig. 3. Internalized anti-PRL was located in structures with multiple dense cores. (A-C) Electron micrographs of cells stimulated in the presence of anti-PRL antibodies and then fixed at the 20 minute time point as described in Fig. 1, were then stained with gold-labeled secondary antibodies. (A) Low power image acquired at 4000 magnification of a section containing six gold-labeled clusters (location highlighted with boxes, box marked `b' is displayed at high magnification in B) demonstrates that the internalized anti-PRL was throughout the cell. (B) The gold-labeled dense cores often clustered together or (C) appeared to have begun to coalesce. (D,E) Control cells processed as for above except that anti-PRL primary antibody was omitted from the stimulation solution. Note the presence of multi-granule clusters containing small cores (arrows). For B-E micrographs were acquired at 30,000 magnification. Bars, 300 nm (A); 200 nm (B-E).