Mehlmann L M, Kline D
Department of Biological Sciences, Kent State University, Ohio 44242.
Biol Reprod. 1994 Dec;51(6):1088-98. doi: 10.1095/biolreprod51.6.1088.
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.
未成熟的、处于减数分裂前期I阻滞的小鼠卵母细胞受精后会产生多个钙瞬变，类似于成熟的、处于减数分裂中期II的卵子；然而，第一个钙瞬变的幅度要低得多，持续时间也更短。与处于减数分裂前期I阻滞的卵母细胞不同，在生发泡破裂后受精的成熟卵母细胞的第一个钙瞬变与成熟受精卵的相似。未成熟的、处于前期阻滞的卵母细胞对注射肌醇1,4,5-三磷酸（IP3）的反应释放的钙比卵子少。在高浓度下，巯基试剂硫柳汞（200微摩尔）会导致卵子中的钙振荡，并在卵母细胞中产生类似的振荡。较低浓度的硫柳汞（25微摩尔）不会引起钙振荡，但会使卵子和卵母细胞中IP3诱导的钙释放敏感，因为在25微摩尔硫柳汞存在的情况下，IP3诱导的钙释放会增强。在注射2.2微摩尔IP3之前，将卵母细胞在25微摩尔硫柳汞中孵育，会使卵母细胞释放的钙与注射2.2微摩尔IP3的卵子释放的钙一样多。这些结果表明，未成熟的小鼠卵母细胞拥有与卵子中可释放钙大小相似的细胞内钙储存；然而，这些储存对IP3的敏感性较低。IP3诱导的钙释放机制的发育可能是成熟的一个重要组成部分；在卵子受精时，钙必须升高到足以激活进一步发育并建立多精受精阻断的水平。小鼠卵母细胞在卵母细胞成熟过程中似乎对IP3的敏感性增加。
