title: Activation of frog (Xenopus laevis) eggs by inositol trisphosphate. I. Characterization of Ca2+ release from intracellular stores.
abstract: Iontophoresis of inositol 1, 4, 5-triphosphate into frog (Xenopus laevis) eggs activated early developmental events such as membrane depolarization, cortical contraction, cortical granule exocytosis, and abortive cleavage furrow formation (pseudocleavage). Inositol 1, 4-bisphosphate also triggered these events, but only at doses approximately 100-fold higher, whereas no level of fructose-1, 6-bisphosphate tested activated eggs. Using Ca2+-selective microelectrodes, we observed that activating doses of inositol 1, 4, 5-trisphosphate triggered a Ca2+ release from intracellular stores that was indistinguishable from that previously observed at fertilization (Busa, W. B., and R. Nuccitelli, 1985, J. Cell Biol., 100:1325-1329), whereas subthreshold doses triggered only a localized Ca2+ release at the site of injection. The subthreshold IP3 response could be distinguished from the major Ca2+ release at activation with respect to their dose-response characteristics, relative timing, sensitivity to external Ca2+ levels, additivity, and behavior in the activated egg, suggesting that the Xenopus egg may possess two functionally distinct Ca2+ pools mobilized by different effectors. In light of these differences, we suggest a model for intracellular Ca2+ mobilization by sperm-egg interaction.
mesh_terms: D000818:Animals; D001826:Body Fluids / Q000378:metabolism*; D002118:Calcium / Q000096:biosynthesis / Q000378:metabolism*; D004594:Electrophysiology; D005260:Female; D005306:Fertilization / Q000187:drug effects; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology*; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D007478:Iontophoresis / Q000295:instrumentation; D008839:Microelectrodes; D008845:Microinjections; D010063:Ovum / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D013403:Sugar Phosphates / Q000494:pharmacology*; D014982:Xenopus laevis
chemical_list: D007295:Inositol Phosphates; D013403:Sugar Phosphates; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium