Plasma membrane disruption is more common than one might think: around 20%of muscle cells can suffer lesions during exercise, and wounding also affects irreplaceable cells, such as neurons. Small holes in the plasma membrane might`self-seal' because of the inherent thermodynamic properties of lipids. Large holes, by contrast, require a dynamic cellular mechanism. Paul McNeil discusses our understanding of this resealing mechanism. Some forty years ago,external Ca2+ was found to be required for resealing. More recent work in sea urchin eggs has revealed that Ca2+ influx stimulates fusion of internal vesicles to form abnormally large vesicles that `patch up'the plasma membrane by exocytosis. Analysis of surface markers from wounded cells indicates that these vesicles are in fact lysosomes. Because these organelles lie below the cell cortex, Ca2+-dependent depolymerization of cortical actin is a crucial step in resealing. The cytoskeleton might also have a positive role in resealing,...

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