Open AccessActivation of Sea-Urchin Eggs by a Calcium Ionophore
Author(s) -
Richard A. Steinhardt,
David Epel
Publication year - 1974
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.71.5.1915
Subject(s) - ionophore , calcium , divalent , sea urchin , biophysics , strongylocentrotus purpuratus , biochemistry , human fertilization , intracellular , chemistry , magnesium , biology , microbiology and biotechnology , membrane , anatomy , organic chemistry
Micromolar amounts of the divalent ionophore A23187 can activate echinoderm eggs. The activations by ionophore A23187 were examined in terms of membrane elevation, the program of membrane conductance changes, the respiratory burst, and the increases in protein and DNA synthesis which normally accompany activation by sperm. In all these respects activation by the ionophore was fairly normal although subsequent cleavage and embryonic development was limited. Ionophore A23187 activations of the cortex ofLytechinus pictus andStrongylocentrotus purpuratus eggs were compared in various ionic media and were found to be completely independent of the ionic composition of the external solution. Respiration and protein synthesis ofL. pictus eggs in singly substituted ionic media also indicated that these activations were independent of external sodium, calcium, or magnesium. These results suggest that the ionophore acts by releasing intracellular Ca++ . Consistent with this interpretation is the finding that eggs preloaded with45 Ca show a 20-fold increase in45 Ca-efflux when activated by ionophore A23187 or fertilization. Measurements of the “free” and “bound” calcium and magnesium in homogenates of the unfertilized eggs show that most of the Mg++ is already available in the soluble form, whereas Ca++ is sequestered but available for release.We propose that both normal fertilization and ionophore activation affect the metabolism of the egg by releasing Ca++ sequestered in intracellular stores.