A freeze-fracture study of exocytosis and reflexive gap junctions in human ovarian decidual cells

Fine-structural features of ovarian decidual cells and their mode of secretion were examined by means of freeze-fracture microscopy. Unique cortical peduncular processes contained secretory vesicles within the expanded peduncle tip, the membrane-leaflets of which exhibited a particle-poor E face adjacent to the vesicle lumen and a P face containing a greater particle number. Exocytosis from attached peduncles involved release of vesicular profiles 40-55 nm in diameter; small particles 8.5-11.5 nm in diameter were also observed at degranulation sites. In fractures revealing the E face of the plasmalemma, cytoplasmic portals at the bases of peduncular stalks were distinguishable from endocytic vesicles. The frequent occurrence of reflexive gap junctions associated with peduncles was shown by freeze-fracture. However, there appeared to be no consistent spatial relationship between gap junctions, secretory peduncles, or sites of exocytosis. Freeze-fracture analysis of the topography of reflexive gap junctional profiles revealed that such gap junctions share basic similarities with intercellular gap jum particle-free aisles. The finding in the present study of reflexive gap junctions occurring between peduncles and the cell soma, as well as between peduncles, suggests that the original definitiof the same cell should be broadened to include any gap junctional specialization formed between portions of the plasma membrane of one cell.