The role of contractile filaments in secretion.

Fig. 1. Endocytotic fusion processes in mast cells and neutrophils afer rapid freezing 1. Unreleased granule in a mast cell quick-frozen 10s after stimulation with 48/80. x 66000.2. Granule-plasma membrane fusion in a mast cell quick-frozen 200s after stimulation with 48/80. x 36000. 3. Release of granule contents in a cell quickfrozen 15s after stimulation. Interior granules have formed minute contacts with the released granule membrane (arrow). x 32000. 4. High magnification view of pedestal-like contacts seen between granules in 3 (arrows). Note also the small vesicle joined to the granule membrane (asterisk). x 75000. 5. Multiple contacts between interior granules of a mast cell quick-frozen 17s after stimulation. x 75000. 6. Narrow tubules connect interior granules in a mast cell frozen 17s after stimulation (solid arrows); crossfractured tubules are seen as craters (open arrows). x 67000. 7. Compound exocytosis in a rabbit neutrophil fixed 10s after stimulation with FMLP and cytochalasin B results in finger-like invaginations directed toward the cell centre. x 62000. 8. The narrow tips of these invaginations (arrow) may undergo fusion with the small vesicles (V) nearby. This cell was fixed 30s after stimulation with FMLP. x 54000. 9. Compound exocytosis results in a ‘ribbon’ of fused granule membrane in a neutrophil fixed 30s after stimulation with FMLP at 37°C. x24OOO.