Allen R D, Staehelin L A
J Cell Biol. 1981 Apr;89(1):9-20. doi: 10.1083/jcb.89.1.9.
Freeze-fractured membranes of digestive vacuoles of randomly feeding Paramecium caudatum exhibit dramatic differences in intramembrane particle (IMP) number and distribution on both E- and P-fracture faces. By pulse-feeding latex spheres to cells we have demonstrated that these differences are related to the age of the digestive vacuoles, and that the membranes of such vacuoles undergo a specific sequence of changes during the digestive cycle. Young digestive vacuoles (DV-I; less than or equal to 6 min), nascent vacuoles still connected to the cytopharynx, and discoidal vesicles, from which vacuole membrane is derived, all have a highly particulate E face and a less particulate P face. As early as 3 min after feeding, a second category of digestive vacuoles (DV-II) can be recognized, which are both considerably smaller in diameter and lack particles on their E face. These findings suggest that the endocytic removal of DV-I membrane material associated with the formation of DV-II vacuoles involves a concomitant and selective removal of E-face particles, as essentially no changes are seen in the density of P-face particles on the two types of vacuoles. Beginning at 10 min the first DV-III vacuoles are encountered. These are both larger than the DV-II vacuoles and possess very prominent E-face particles, which resemble those on the E face of the numerous lysosomes bordering the digestive vacuoles. DV-III vacuoles also exhibit a substantial increase in P-face particles. These membrane changes closely parallel, and are probably correlated with, the physiological events occurring within the vacuole lumen: concentration of food, killing of prey, and digestion. Calculations of the amount of membrane removed from DV-I to form DV-II and of the increase in membrane surface area during the transition from DV-II to DV-III indicate that as much as 90% of the initial phagosome (DV-I) membrane can be removed before digestion begins. The enlargment of DV-II must be caused by fusion with adjacent lysosomes which also contribute the new populations of IMPs to the DV-III membrane. The appearance of numerous endocytic structures on older DV-III vacuoles suggests that membrane is retrieved from DV-III before defecation.
随机取食的尾草履虫消化泡的冷冻断裂膜在 E 面和 P 面的膜内颗粒（IMP）数量及分布上呈现出显著差异。通过向细胞脉冲投喂乳胶球，我们证明了这些差异与消化泡的年龄有关，并且此类消化泡的膜在消化周期中会经历特定的变化序列。年轻的消化泡（DV-I；小于或等于 6 分钟）、仍与胞咽相连的新生泡以及形成泡膜的盘状小泡，其 E 面都具有高度颗粒状，而 P 面颗粒较少。进食后 3 分钟内，就可识别出第二类消化泡（DV-II），其直径明显更小，E 面上没有颗粒。这些发现表明，与 DV-II 泡形成相关的 DV-I 膜物质的内吞去除涉及 E 面颗粒的伴随性和选择性去除，因为在这两种类型的泡上，P 面颗粒的密度基本没有变化。从 10 分钟开始出现第一批 DV-III 泡。这些泡比 DV-II 泡更大，并且具有非常突出的 E 面颗粒，类似于与消化泡相邻的众多溶酶体 E 面上的颗粒。DV-III 泡的 P 面颗粒也显著增加。这些膜变化与泡腔内发生的生理事件密切平行，并且可能与之相关：食物浓缩、猎物杀死和消化。从 DV-I 形成 DV-II 时去除的膜量以及从 DV-II 转变为 DV-III 过程中膜表面积增加的计算表明，在消化开始前，初始吞噬体（DV-I）膜的多达 90%可被去除。DV-II 的扩大必定是由与相邻溶酶体的融合引起的，溶酶体也为 DV-III 膜贡献了新的 IMP 群体。较老的 DV-III 泡上出现大量内吞结构表明，在排便前膜从 DV-III 被回收。
