Nature 286, 185 - 186 (10 July 1980); doi:10.1038/286185a0

Calcium-induced decrease in membrane fluidity of sea urchin egg cortex after fertilization

Judith Campisi^* & Carl J. Scandella

Department of Biochemistry, State University of New York, Stony Brook, New York 11794
^*Present address: Laboratory of Tumor Biology, Sidney Farber Cancer Institute, 44 Binney Street, Boston, Massachusetts 02115.

Fertilization of the sea urchin egg is a dramatic example of cell activation resulting from the interaction of an external stimulus, the spermatozoon, with the cell surface¹. Growing and quiescent cells may have different membrane states². Here we report membrane fluidity measurements on a surface membrane fraction, the cortex, isolated from unfertilized and fertilized eggs. The fluidity of the fertilized egg cortex, measured by electron spin resonance (ESR) spectroscopy using 5-doxy 1st ear at e as a probe, is less than that of the unfertilized cortex. In the intact egg the intracellular Ca²⁺ concentration increases after fertilization and this transient rise seems to be localized in the cortex³. The addition of Ca²⁺ to the cortex fraction isolated from unfertilized eggs triggers a fluidity decrease in vitro. The fluidity decrease seems to represent a Ca²⁺-induced change in membrane structure rather than a direct interaction of Ca²⁺ with phospholipid headgroups.

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