High molecular weight polymers block cortical granule exocytosis in sea urchin eggs at the level of granule matrix disassembly.
Open Access
- 1 September 1989
- journal article
- research article
- Published by Rockefeller University Press in The Journal of cell biology
- Vol. 109 (3), 1269-1278
- https://doi.org/10.1083/jcb.109.3.1269
Abstract
Recently, we have shown that high molecular weight polymers inhibit cortical granule exocytosis at total osmolalities only slightly higher than that of sea water (Whitaker, M., and J. Zimmerberg, 1987. J. Physiol. 389:527-539). In this study, we visualize the step at which this inhibition occurs. Lytechinus pictus and Stronglyocentrotus purpuratus eggs were exposed to 0.8 M stachyrose or 40% (wt/vol) dextran (average molecular mass of 10 kD) in artificial sea water, activated with 60 .mu.M of the calcium ionophore A23187, and then either fixed with glutaraldehyde and embedded or quick-frozen and freeze-fractured. Stachyose (2.6 osmol/kg) appears to inhibit cortical granule exocytosis by eliciting formation of a granule-free zone (GFZ) in the egg cortex which pushes granules away from the plasma membrane thus preventing their fusion. In contrast, 40% dextran (1.58 osmol/kg) does not result in a GFZ and cortical granules undergo fusion. In some specimens, the pores joining granule and plasma membranes are relatively small; in other cases, the exocytotic pocket has been stabilized in an omega configuration and the granule matrix remains intact. These observations suggest that high molecular weight polymers block exocytosis because of their inability to enter the granule matrix: they retard the water entry that is needed for matrix dispersal.This publication has 31 references indexed in Scilit:
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