Regulation of intracellular calcium in the mouse egg: calcium release in response to sperm or inositol trisphosphate is enhanced after meiotic maturation.
Fertilization of the immature, prophase I-arrested mouse oocyte produces multiple Ca2+ transients similar to those of the mature, metaphase II egg; however, the first Ca2+ transient is much lower in amplitude and shorter in duration. In contrast to prophase I-arrested oocytes, maturing oocytes fertilized after germinal vesicle breakdown have first Ca2+ transients similar to those of mature fertilized eggs. Immature, prophase-arrested oocytes release less Ca2+ in response to injection of inositol 1,4,5-trisphosphate (IP3) than eggs. At high concentrations, the sulfhydryl reagent, thimerosal (200 microM), causes Ca2+ oscillations in eggs and produces similar oscillations in oocytes. A lower concentration of thimerosal (25 microM) does not cause Ca2+ oscillations, but does sensitize IP3-induced Ca2+ release in both eggs and oocytes, since IP3-induced Ca2+ release is enhanced in the presence of 25 microM thimerosal. Incubation of oocytes in 25 microM thimerosal before injection of 2.2 microM IP3 causes oocytes to release as much Ca2+ as is released in eggs injected with 2.2 microM IP3. These results indicate that immature mouse oocytes possess intracellular stores of releasable Ca2+ similar in size to Ca2+ stores in eggs; however, these stores are less sensitive to IP3. Development of the IP3-induced Ca2+ release mechanism may be an important component of maturation; at fertilization of the egg, Ca2+ must be elevated to levels sufficient to activate further development and establish a block to polyspermy. Mouse oocytes appear to develop an increased sensitivity to IP3 during the course of oocyte maturation.
Mehlmann
L M
LM
Department of Biological Sciences, Kent State University, Ohio 44242.
Kline
D
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D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005306:Fertilization / Q000187:drug effects / Q000502:physiology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008540:Meiosis / Q000502:physiology*; D051379:Mice; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009866:Oogenesis / Q000187:drug effects / Q000502:physiology; D010063:Ovum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013084:Sperm-Ovum Interactions / Q000502:physiology; D013094:Spermatozoa / Q000502:physiology*; D013849:Thimerosal / Q000494:pharmacology
D007476:Ionophores; D013849:Thimerosal; D015759:Ionomycin; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium