Fok A K, Ueno M S, Azada E A, Allen R D
Eur J Cell Biol. 1987 Jun;43(3):412-20.
Phagosomes of paramecia and amoeba and endosomes of fibroblasts and other mammalian cells are acidified prior to lysosomal fusion. The question, whether the phagosomal acidification process in paramecia is required for phagosome-lysosome fusion, was studied using ionophores, weak bases, and cytochalasin B (CB) in combination with monoclonal antibodies, acid phosphatase (AcPase) cytochemistry, and lysosome morphometry. Digestive vacuoles (DVs) of known ages were treated and examined. In untreated cells, lysosome binding to the membrane of the acidified DV increased linearly with age and reached a maximum before lysosome-DV fusion. When the fusion of the acidosomes with the very young DVs was prevented by CB, causing a block in the normal vacuole-pH drop, lysosome binding to the DVs as well as the rate and extent of lysosome-DV fusion were all greatly reduced. These effects of CB were reversible. When present prior to acidification, three ionophores and two weak bases did not inhibit the acidosome-DV fusion but raised the phagosomal pH and reduced both the rates of DV acidification and of lysosome-DV fusion. However, when added after acidification but prior to lysosome-DV fusion, five of the six perturbants studied did not inhibit this fusion but prolonged the period when DVs remained AcPase positive. Lastly, lysosome-DV fusion rates were found to be related to acidification rates. We conclude that an inhibition in acidosome-DV fusion or a reduction in both the acidification rate and vacuolar-pH drop would inhibit lysosome-DV fusion.
草履虫和变形虫的吞噬体以及成纤维细胞和其他哺乳动物细胞的内体在与溶酶体融合之前会发生酸化。本研究使用离子载体、弱碱和细胞松弛素B（CB），结合单克隆抗体、酸性磷酸酶（AcPase）细胞化学和溶酶体形态计量学，探讨了草履虫吞噬体酸化过程对于吞噬体 - 溶酶体融合是否必要。对已知年龄的消化泡（DVs）进行处理并检查。在未处理的细胞中，溶酶体与酸化的DV膜的结合随年龄呈线性增加，并在溶酶体 - DV融合之前达到最大值。当CB阻止酸性小体与非常年轻的DVs融合，导致正常液泡pH下降受阻时，溶酶体与DVs的结合以及溶酶体 - DV融合的速率和程度均大大降低。CB的这些作用是可逆的。在酸化之前存在时，三种离子载体和两种弱碱不会抑制酸性小体 - DV融合，但会提高吞噬体pH，并降低DV酸化速率和溶酶体 - DV融合速率。然而，在酸化后但在溶酶体 - DV融合之前添加时，所研究的六种干扰物中的五种不会抑制这种融合，但会延长DVs保持AcPase阳性的时间。最后，发现溶酶体 - DV融合速率与酸化速率有关。我们得出结论，酸性小体 - DV融合的抑制或酸化速率和液泡pH下降的降低都会抑制溶酶体 - DV融合。
