Gonnella P A, Neutra M R
J Cell Biol. 1984 Sep;99(3):909-17. doi: 10.1083/jcb.99.3.909.
The absorptive cell of the suckling rat ileum is specialized for the uptake and digestion of milk macromolecules from the intestinal lumen. The apical cytoplasm contains an extensive tubulocisternal system, a variety of vesicles and multivesicular bodies (MVB), and a giant phagolysosomal vacuole where digestion is completed. To determine if sorting of membrane-bound and fluid-phase macromolecules occurs in this elaborate endocytic system, we infused adsorptive and soluble tracers into ligated intestinal loops in vivo and examined their fates. Lysosomal compartments were identified by acid phosphatase histochemistry. Native ferritin and two ferritin-lectin conjugates that do not bind to ileal membranes (Con A, UEAI) served as soluble tracers. Horseradish peroxidase binds to ileal membranes and thus was not useful as a fluid-phase tracer in this system. Cationized ferritin and a lectin that binds to terminal B-D-galactosyl sites on ileal membranes (Ricinus communis agglutinin [RCAI]-ferritin) were used as tracer ligands. All tracers entered the wide apical invaginations of the luminal cell surface and were transported intracellularly. Membrane-bound tracers were found in coated pits and vesicles, and throughout the tubulocisternal system (where cationized ferritin is released from the membrane) and later, in large clear vesicles and MVB. In contrast, fluid-phase tracers appeared within 5 min in vesicles of various sizes and were not transported through the tubulocisternae, rather, they were concentrated in a separate population of vesicles of increasing size that contained amorphous dense material. Large clear vesicles, large dense vesicles, and MVB eventually fused with the giant supranuclear vacuole. Acid phosphatase activity was present in MVB and in the giant vacuole but was not present in most large vesicles or in the tubulocisternae. These results demonstrate that membrane-bound and soluble protein are transported to a common lysosomal destination via separate intracellular routes involving several distinct prelysosomal compartments.
哺乳大鼠回肠的吸收细胞专门用于从肠腔摄取和消化乳大分子。顶端细胞质含有广泛的管状囊泡系统、各种囊泡和多泡体（MVB），以及一个用于完成消化的巨大吞噬溶酶体空泡。为了确定在这个复杂的内吞系统中是否发生膜结合和液相大分子的分选，我们在体内将吸附性和可溶性示踪剂注入结扎的肠袢中，并检查它们的去向。通过酸性磷酸酶组织化学鉴定溶酶体区室。天然铁蛋白和两种不与回肠膜结合的铁蛋白-凝集素缀合物（伴刀豆球蛋白A、UEAI）用作可溶性示踪剂。辣根过氧化物酶与回肠膜结合，因此在该系统中不能用作液相示踪剂。阳离子化铁蛋白和一种与回肠膜上的末端B-D-半乳糖基位点结合的凝集素（蓖麻凝集素[RCAI]-铁蛋白）用作示踪配体。所有示踪剂都进入管腔细胞表面宽阔的顶端内陷，并在细胞内运输。膜结合示踪剂存在于被膜小窝和囊泡中，以及整个管状囊泡系统（阳离子化铁蛋白从膜上释放的地方），随后存在于大的清亮囊泡和MVB中。相比之下，液相示踪剂在5分钟内出现在各种大小的囊泡中，并且不通过管状囊泡运输，相反，它们集中在一群大小不断增加的单独囊泡中，这些囊泡含有无定形致密物质。大的清亮囊泡、大的致密囊泡和MVB最终与巨大的核上空泡融合。酸性磷酸酶活性存在于MVB和巨大空泡中，但不存在于大多数大囊泡或管状囊泡中。这些结果表明，膜结合蛋白和可溶性蛋白通过涉及几个不同的前溶酶体区室的单独细胞内途径被运输到共同的溶酶体目的地。
