de Bruyn P P, Cho Y, Michelson S
J Ultrastruct Res. 1983 Dec;85(3):272-89. doi: 10.1016/s0022-5320(83)90039-4.
The present observations describe the endocystosis and intracellular transport in the endothelial cells lining the sinuses of the rat liver and occurring 3 min after intravenous administration of two protein tracers: horseradish peroxidase and ferritin. Internalization of the proteins is exclusively by bristle coated pits followed by intracellular sequestration in bristle coated vesicles (diameter 90-210 nm). No other form of endocytosis is present in the endothelial cells of the liver sinuses. The bristle coated vesicles fuse with smooth membrane lined tubules (diameter 20-70 nm) termed transfer tubules. In this way the tracers are deposited into the lumens of the transfer tubules. The transfer tubules in turn fuse with preexisting electron-lucent endosomes which then receive the protein markers. In addition, direct fusion of bristle coated vesicles with endosomes occurs in limited measure. Bristle coated vesicles may fuse with other bristle coated vesicles while losing their clathrin coat, resulting in the formation of new endosomes which may enlarge through fusion with additional bristle coated vesicles or perhaps also with transfer tubules. The sinus endothelium also contains lysosomal vesicles which appear as dense bodies or multivesicular bodies. No protein tracers have been observed in these dense bodies at the time interval (i.e., 3 min) examined. Neither has a direct fusion between endosomes and lysosomes been found. The transfer tubules may be continuous with or may be derived from cisternae of the Golgi complex. No luminal continuity between transfer tubules and endoplasmic reticulum has been observed. The sinus endothelium also contains small bristle coated vesicles (30-40 nm) often attached to Golgi cisternae. These do not participate in the transport of endocytosed protein tracer and are in this respect functionally distinct from the large bristle coated vesicles derived from the endothelial plasmalemma. Serial sections show that there are extensive connections between the endocytic transport organelles: bristle coated vesicles, transfer tubules, and endosomes, possibly forming an intracellular luminal continuum.
目前的观察结果描述了大鼠肝脏窦状隙内皮细胞中的内吞作用和细胞内运输情况，这一过程发生在静脉注射两种蛋白质示踪剂（辣根过氧化物酶和铁蛋白）3分钟后。蛋白质的内化仅通过有被小窝进行，随后在有被小泡（直径90 - 210纳米）中进行细胞内隔离。肝窦内皮细胞中不存在其他形式的内吞作用。有被小泡与称为转运小管的光滑膜内衬小管（直径20 - 70纳米）融合。通过这种方式，示踪剂被沉积到转运小管的管腔中。转运小管继而与先前存在的电子透明内体融合，然后内体接收蛋白质标记物。此外，有被小泡与内体的直接融合在一定程度上也会发生。有被小泡可能在失去其网格蛋白衣被的同时与其他有被小泡融合，导致形成新的内体，这些新内体可能通过与额外的有被小泡或也许还与转运小管融合而扩大。窦内皮细胞还含有溶酶体小泡，其表现为致密体或多泡体。在所检查的时间间隔（即3分钟）内，在这些致密体中未观察到蛋白质示踪剂。也未发现内体与溶酶体之间有直接融合。转运小管可能与高尔基体复合体的扁平囊相连或源自高尔基体复合体的扁平囊。未观察到转运小管与内质网之间有管腔连续性。窦内皮细胞还含有通常附着于高尔基体扁平囊的小有被小泡（30 - 40纳米）。这些小有被小泡不参与内吞的蛋白质示踪剂的运输，在这方面在功能上与源自内皮细胞质膜的大有被小泡不同。连续切片显示，内吞运输细胞器（有被小泡、转运小管和内体）之间存在广泛连接，可能形成细胞内管腔连续体。
