Phillips K P, Baltz J M
Loeb Research Institute, Ottawa Hospital, Ottawa, Ontario, K1Y 4E9, Canada.
Dev Biol. 1999 Apr 15;208(2):392-405. doi: 10.1006/dbio.1999.9199.
We report here that at least one major pHi-regulatory mechanism, the HCO3-/Cl- exchanger, is quiescent in unfertilized mouse eggs but becomes fully activated during early development following fertilization. Zygotes (8-12 h postfertilization) exhibited a marked intracellular alkalinization upon external Cl- removal, which is indicative of active HCO3-/Cl- exchangers, in contrast to the very small response observed in eggs. In addition, efflux of Cl- from eggs upon external Cl- removal was much slower than that from zygotes, indicating additional pathways for Cl- to cross the plasma membrane in zygotes. Furthermore, while zygotes quickly recovered from an induced alkalosis, eggs exhibited only a slow, incomplete recovery. Following in vitro fertilization (IVF), increased HCO3-/Cl- exchanger activity was first detectable about 4 h postfertilization and reached the maximal level after about 8 h. The upregulation of HCO3-/Cl- exchanger activity after fertilization appeared to occur by activation of existing, inactive exchangers rather than by synthesis or transport of new exchangers, as the increase in activity following IVF was unaffected by inhibition of protein synthesis or by disruption of the Golgi apparatus or the cytoskeleton. This activation may depend on the Ca2+ transients which follow fertilization, as suppression of these transients, using the Ca2+ chelator BAPTA, reduced subsequent upregulation of HCO3-/Cl- exchanger activity by about 50%. Activation of pHi-regulatory systems may be a widespread feature of the earliest period of embryonic development, not restricted to species such as marine invertebrates as previously believed.
我们在此报告，至少一种主要的细胞内pH调节机制，即HCO₃⁻/Cl⁻交换体，在未受精的小鼠卵中处于静止状态，但在受精后的早期发育过程中会完全激活。受精卵（受精后8 - 12小时）在去除细胞外Cl⁻后表现出明显的细胞内碱化，这表明存在活跃的HCO₃⁻/Cl⁻交换体，这与在卵中观察到的非常小的反应形成对比。此外，去除细胞外Cl⁻后，卵中Cl⁻的外流比受精卵慢得多，这表明受精卵中存在Cl⁻穿过质膜的其他途径。此外，虽然受精卵能迅速从诱导的碱中毒中恢复，但卵仅表现出缓慢、不完全的恢复。体外受精（IVF）后，HCO₃⁻/Cl⁻交换体活性的增加在受精后约4小时首次可检测到，并在约8小时后达到最高水平。受精后HCO₃⁻/Cl⁻交换体活性的上调似乎是通过激活现有的无活性交换体而发生的，而不是通过新交换体的合成或运输，因为IVF后活性的增加不受蛋白质合成抑制或高尔基体或细胞骨架破坏的影响。这种激活可能依赖于受精后出现的Ca²⁺瞬变，因为使用Ca²⁺螯合剂BAPTA抑制这些瞬变会使随后HCO₃⁻/Cl⁻交换体活性的上调降低约50%。pH调节系统的激活可能是胚胎发育最早阶段的一个普遍特征，并不局限于如先前认为的海洋无脊椎动物等物种。
