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Eur J Cell Biol. 1983 Nov;32(1):31-7.

Membrane events in adrenal chromaffin cells during exocytosis: a freeze-etching analysis after rapid cryofixation.


Catecholamine-storing chromaffin cells, isolated from bovine adrenal medullae by collagenase digestion, were stimulated with carbachol at 37 degrees C; aliquots for controls were kept at 37 degrees C: Starting from this temperature, cells were ultrarapidly frozen with the use of a sandwich-propane-jet procedure and freeze-fractured. The replicas were analysed quantitatively for exocytotic activity: After stimulation the cell membrane displayed a significant increase of exo-endocytotic openings varying in size from 20 to 300 nm. The number of openings increased in parallel to the catecholamine output. At no stage could a clearing of membrane-intercalated particles (MIPs) be observed. Openings of all size classes were etchable. Results from the PF-face were comparable with those of the EF-face. We conclude that (i) exocytosis in isolated chromaffin cells starts as a focal event; the smallest possible stages are about 10 nm in size, (ii) fusion proceeds without previous rearrangement of MIPs, and (iii) the opening starts without formation of a diaphragm.

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