An elevated free cytosolic Ca2+ wave follows fertilization in eggs of the frog, Xenopus laevis.
The eggs of most or all animals are thought to be activated after fertilization by a transient increase in free cytosolic Ca2+ concentration ([Ca2+]i). We have applied Ca2+-selective microelectrodes to detect such an increase in fertilized eggs of the frog, Xenopus laevis. As observed with an electrode in the animal hemisphere, [Ca2+]i increased from 0.4 to 1.2 microM over the course of 2 min after fertilization, and returned to its original value during the next 10 min. No further changes in [Ca2+]i were detected through the first cleavage division. In eggs impaled with two Ca2+ electrodes, the Ca2+ pulse was observed to travel as a wave from the animal to the vegetal hemisphere, propagating at a rate of approximately 10 microns/s across the animal hemisphere. The apparent delay between the start of the fertilization potential and initiation of the Ca2+ wave at the sperm entry site as approximately 1 min. Through these observations describe only the behavior of subcortical [Ca2+]i, we suggest that our data represent the subcortical extension of the cortical Ca2+ wave thought to trigger cortical granule exocytosis, and we present evidence that both the timing and magnitude of the Ca2+ pulse we observed are consistent with this identity. This first quantification of subcortical [Ca2+]i during fertilization indicates that the Ca2+ transient is available to regulate processes (e.g., protein synthesis) in the subcortical cytosol.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005260:Female; D005306:Fertilization; D007700:Kinetics; D008839:Microelectrodes; D010063:Ovum / Q000378:metabolism*; D014982:Xenopus laevis
D002118:Calcium