Tosti E, Dale B
Laboratory of Cell and Developmental Biology, Stazione Zoologica Anton Dohrn, Naples, Italy.
Mol Reprod Dev. 1994 Apr;37(4):473-6. doi: 10.1002/mrd.1080370416.
Neomycin, injected into ascidian oocytes to a final concentration of 10-50 mM, inhibits both the fertilization current and the surface contraction, showing that phosphoinositide hydrolysis is required for these early activation events. Sperm-activated fertilization currents are not inhibited in the presence of 100 micrograms/ml intracellular heparin, suggesting that these currents are not directly gated by InsP3. The sulfhydryl reagent thimerosal at 100 microM, in contrast, significantly increases the fertilization current presumably by sensitizing the channel receptor. Since heparin inhibits the surface contraction, InsP3 receptors are shown to play a role in the propagation of the activation response in ascidian oocyte. Depleting intracellular calcium stores by microinjecting 50 mM EGTA into oocytes does not activate fertilization channels; however, subsequent fertilization of these EGTA loaded oocytes leads to a significantly larger and faster fertilization current. Thus in contrast to somatic cells studied to date, second messenger operated plasma membrane channels in ascidian oocytes are not gated by calcium released from intracellular stores.
将新霉素注入海鞘卵母细胞，使其终浓度达到10 - 50 mM，可抑制受精电流和表面收缩，这表明磷酸肌醇水解是这些早期激活事件所必需的。在存在100微克/毫升细胞内肝素的情况下，精子激活的受精电流不受抑制，这表明这些电流不是由肌醇三磷酸（InsP3）直接门控的。相比之下，100微摩尔的巯基试剂硫柳汞可能通过使通道受体敏感而显著增加受精电流。由于肝素抑制表面收缩，表明InsP3受体在海鞘卵母细胞激活反应的传播中起作用。通过向卵母细胞显微注射50 mM乙二醇双乙胺醚四乙酸（EGTA）耗尽细胞内钙储存不会激活受精通道；然而，随后对这些加载了EGTA的卵母细胞进行受精会导致显著更大、更快的受精电流。因此，与迄今为止研究的体细胞不同，海鞘卵母细胞中第二信使操作的质膜通道不是由细胞内储存释放的钙门控的。
