Grandin N, Charbonneau M
Laboratoire de Biologie et Génétique du Développement, URA CNRS No. 256, Université de Rennes I, France.
Biochim Biophys Acta. 1991 Jan 31;1091(2):242-50. doi: 10.1016/0167-4889(91)90068-9.
The aim of this work was to determine the potential relationships between rises in intracellular pH (pHi) and intracellular free calcium activity (Cai2+) during cell activation in Xenopus eggs. To do this, we used two weak bases, NH4Cl and procaine, and a weak acid, CO2, and measured Cai2+ variations in response to these imposed pHi variations. NH4Cl and procaine increased Cai2+ in both unactivated and activated eggs. Procaine was found to alkalinize the egg cytoplasm, whereas the other weak base, NH4Cl, acidified the egg cytoplasm. On the other hand, CO2 was found to acidify the cytoplasm and to substantially decrease Cai2+, also in unactivated and activated eggs. In addition, CO2 triggered an increase in the conductance of the plasma membrane to Cl- ions, similarly to what had been found previously with weak bases (Charbonneau, M. (1989) Cell Differ. Develop. 26, 39-52). These Cl- channels, similarly to the sperm-triggered Cl- channels during the fertilization potential, are supposed to be Ca2(+)-sensitive. Therefore, the changes in Ca2+ observed in response to CO2 do not seem to be responsible for the opening of these Cl- channels, which would rather be triggered by an increase in Cai2+ localized near the plasma membrane. We conclude therefore that weak acids and bases represent appropriate tools for studying cytosolic Ca2+ homeostasis, but not for dissecting the complex pathways involved in signal transduction.
本研究旨在确定非洲爪蟾卵母细胞激活过程中细胞内pH值（pHi）升高与细胞内游离钙活性（Cai2+）之间的潜在关系。为此，我们使用了两种弱碱（氯化铵和普鲁卡因）和一种弱酸（二氧化碳），并测量了Cai2+对这些人为施加的pHi变化的响应。氯化铵和普鲁卡因在未激活和激活的卵母细胞中均能增加Cai2+。发现普鲁卡因可使卵母细胞胞质碱化，而另一种弱碱氯化铵则使卵母细胞胞质酸化。另一方面，发现二氧化碳可使胞质酸化，并在未激活和激活的卵母细胞中大幅降低Cai2+。此外，二氧化碳可引发质膜对氯离子的电导增加，这与先前使用弱碱时的发现类似（Charbonneau, M. (1989) Cell Differ. Develop. 26, 39 - 52）。这些氯离子通道与受精电位期间精子触发的氯离子通道类似，被认为对Ca2(+)敏感。因此，观察到的二氧化碳引起的Ca2+变化似乎不是这些氯离子通道开放的原因，这些通道更可能是由质膜附近局部Cai2+的增加触发的。因此，我们得出结论，弱酸和弱碱是研究胞质Ca2+稳态的合适工具，但不是剖析信号转导复杂途径的合适工具。
