Inositol lipid hydrolysis contributes to the Ca2+ wave in the activating egg of Xenopus laevis.
We have used fluorescence ratio-imaging of fura-2 in the activating egg of Xenopus laevis to study the wave of increased intracellular free Ca2+ concentration ([Ca2+]i) while monitoring that of cortical granule exocytosis. Naturally matured eggs were dejellied, injected with fura-2, and activated by the iontophoresis of 1-30 nCoul of inositol-1,4,5-trisphosphate which triggers an immediate increase in free [Ca2+]i at the injection site. The Ca2+ rise spreads throughout the egg, reaching the opposite side in 5-8 min, and is followed by elevation of the fertilization envelope about 20-30 sec behind the [Ca2+]i wave. [Ca2+]i returns to preactivation levels within about 20 min after activation. We further studied the role of phosphatidylinositol-4,5-bisphosphate (PIP2) hydrolysis by microinjecting antibodies to PIP2 into the egg. PIP2 antibodies did not alter the propagation velocity of the wave but greatly reduced the amount of Ca2+ released in the egg cortex. These data suggest that PIP2 hydrolysis plays a role in the release of [Ca2+]i in the outer regions of the egg following activation.
Larabell
C
C
Department of Zoology, University of California, Davis 95616.
Nuccitelli
R
R
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005089:Exocytosis; D005260:Female; D016257:Fura-2; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008297:Male; D010063:Ovum / Q000378:metabolism*; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates / Q000032:analysis / Q000378:metabolism*; D013084:Sperm-Ovum Interactions; D014982:Xenopus laevis
D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium; D016257:Fura-2