Yolk platelets in Xenopus oocytes maintain an acidic internal pH which may be essential for sodium accumulation.
Yolk platelets in Xenopus oocytes maintain an acidic internal pH which may be essential for sodium accumulation.
复制标题
DOI：
10.1083/jcb.125.5.1047
复制
发表时间：
1994-06
期刊：
影响因子：
--
通讯作者：
Maxfield FR
中科院分区：
文献类型：
--
作者：
Fagotto F;Maxfield FR
卵黄血小板构成胚胎内吞室，储存母体合成的营养物质。通过对内吞 FITC-卵黄原蛋白的整个卵母细胞进行光度测定，发现非洲爪蟾卵黄血小板的 pH 值呈酸性（pH 值约为 5.6）。对洋地黄皂苷通透的卵母细胞进行的实验表明，酸化是由于 NEM 和巴弗洛霉素 A1 敏感的液泡质子 ATP 酶的活性所致。质子泵需要氯化物，但不受钾或钠的影响。被动质子泄漏很慢，可能是由于卵黄的缓冲能力，并且取决于细胞质单价阳离子的存在。特别是，钠可以通过阿米洛利敏感的 Na+/H+ 交换器驱动质子流出。 8-溴环-AMP被发现可以增加酸化，表明pH值可以通过细胞内第二信使来调节。中等酸性的 pH 值不会促进卵黄血小板的降解，卵黄血小板在卵母细胞中可稳定数周，但可能需要维持这些细胞器的完整性。此外，当与 Na+/H+ 交换器耦合时，质子泵产生的 pH 梯度可能是卵子发生过程中钠在卵黄血小板中积累和储存的原因。
Yolk platelets constitute an embryonic endocytic compartment that stores maternally synthesized nutrients. The pH of Xenopus yolk platelets, measured by photometry on whole oocytes which had endocytosed FITC-vitellogenin, was found to be acidic (around pH 5.6). Experiments on digitonin-permeabilized oocytes showed that acidification was due to the activity of an NEM- and bafilomycin A1- sensitive vacuolar proton-ATPase. Proton pumping required chloride, but was not influenced by potassium or sodium. Passive proton leakage was slow, probably due to the buffer capacity of the yolk, and was dependent on the presence of cytoplasmic monovalent cations. In particular, sodium could drive proton efflux through an amiloride- sensitive Na+/H+ exchanger. 8-Bromo-cyclic-AMP was found to increase acidification, suggesting that pH can be regulated by intracellular second messengers. The moderately acidic pH does not promote degradation of the yolk platelets, which in oocytes are stable for weeks, but it is likely to be required to maintain the integrity of these organelles. Furthermore, the pH gradient created by the proton pump, when coupled with the Na+/H+ exchanger, is probably responsible for the accumulation and storage of sodium into the yolk platelets during oogenesis.