Sperm-induced calcium oscillations of human oocytes show distinct features in oocyte center and periphery.
Temporal and spatial characteristics of explosive periodic increases (spikes) of intracellular free Ca2+ concentration ([Ca2+]i) induced by sperm in human oocytes (Ca2+ oscillations) were analyzed by confocal laser scanning microscopy and compared to Ca2+ oscillations induced in oocytes by the thiol reagent thimerosal. During the steady-state period of sperm-induced Ca2+ oscillations, each individual [Ca2+]i spike invariably began from a focus in oocyte periphery and spread throughout the entire peripheral region before propagating to the central ooplasm. This peripheral Ca2+ wave was immediately followed by an explosive [Ca2+]i increase in the central ooplasm. However, this central [Ca2+]i rise only peaked when [Ca2+]i in the peripheral ooplasm was already on the decline. Moreover, the peak [Ca2+]i values were always considerably higher in the oocyte center than in the periphery. In contrast, thimerosal-induced Ca2+ oscillations did not show this particular form of propagation. These data show that sperm-induced Ca2+ oscillations have a unique pattern of spatial dynamics and suggest that the bulk of Ca2+ mobilized during each spike is released from stores that have a relatively high threshold for Ca(2+)-induced Ca2+ release (CICR). These stores are poorly developed, if not absent, in the oocyte cortex, and CICR from them is triggered by previous CICR from another type of store with a lower threshold that are preferentially located in the oocyte cortex and act as a detonator.
Tesarik
J
J
Center of Reproductive Biology and Medicine, American Hospital of Paris, Neuilly sur Seine, France.
Sousa
M
M
Mendoza
C
C
D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation; D005260:Female; D006801:Humans; D008297:Male; D018613:Microscopy, Confocal; D009865:Oocytes / Q000378:metabolism*; D013084:Sperm-Ovum Interactions
D002118:Calcium