Hyperosmolality inhibits exocytosis in sea urchin eggs by formation of a granule-free zone and arrest of pore widening
- 1 December 1989
- journal article
- research article
- Published by Springer Nature in The Journal of Membrane Biology
- Vol. 112 (3), 223-232
- https://doi.org/10.1007/bf01870953
Abstract
Hyperosmolality is known to inhibit membrane fusion during exocytosis. In this study cortical granule exocytosis in sea urchin eggs is used as a model system to determine at what step this inhibition occurs.Strongylocentrotus purpuratus eggs were incubated in hyperosmotic seawater (Na2SO4, sucrose or sodium HEPES used as osmoticants), the eggs activated with 20 μm A23187 to trigger exocytosis, and then quick frozen or chemically fixed for electron microscopy. Thin sections and freeze-fracture replicas show that at high osmolality (2.31 osmol/kg), there is a decrease in cortical granule size, a 90% reduction in granule-plasma membrane fusion, and formation of a granulefree zone between the plasma membrane and cortical granules. This zone averages 0.64 μm in thickness and prevents the majority of granules from docking at the plasma membrane. The remaining granules (∼10%) exhibit early stages of fusion which appear to have been stabilized; the matrix of these granules remains intact. We conclude that exocytosis is blocked by two separate mechanisms. First, the granule-free zone prevents granule-plasma membrane contact required for fusion. Second, in cases where fusion does occur, opening of the pocket and dispersal of the granule contents are slowed in hyperosmotic media.This publication has 29 references indexed in Scilit:
- Osmotic Swelling of Vesicles: Its Role in the Fusion of Vesicles with Planar Phospholipid Bilayer Membranes and its Possible Role in ExocytosisAnnual Review of Physiology, 1986
- The Role of Osmotic Forces in Exocytosis from Adrenal Chromaffin CellsAnnual Review of Physiology, 1986
- Exocytosis of sea urchin egg cortical vesicles in vitro is retarded by hyperosmotic sucrose: kinetics of fusion monitored by quantitative light-scattering microscopy.The Journal of cell biology, 1985
- Osmotic and phorbol ester-induced activation of Na+/H+ exchange: possible role of protein phosphorylation in lymphocyte volume regulation.The Journal of cell biology, 1985
- Parameters affecting the fusion of unilamellar phospholipid vesicles with planar bilayer membranes.The Journal of cell biology, 1984
- Freeze-fracture studies of chemotactic peptide-induced exocytosis in neutrophils: evidence for two patterns of secretory granule fusionJournal of Ultrastructure Research, 1983
- Secretory protein decondensation as a distinct, Ca2+-mediated event during the final steps of exocytosis in Paramecium cells.The Journal of cell biology, 1981
- pH regulates the polymerization of actin in the sea urchin egg cortex.The Journal of cell biology, 1979
- Synaptic vesicle exocytosis captured by quick freezing and correlated with quantal transmitter release.The Journal of cell biology, 1979
- Bivalent-cation-stimulated ATPase activity at preformed exocytosis sites in Paramecium coincides with membrane-intercalated particle aggregatesNature, 1977