Endocytic apparatus and transcytosis in epithelial cells of the vas deferens in the rat

Abstract

The apex of the principal epithelial cells lining the vas deferens of the rat contains coated pits in continuity with the apical plasma membrane and large subsurface-coated vesicles (100-125 nm). In the apical cytoplasm, large, pale, uncoated vesicles (150-300 nm), small coated and uncoated vesicles (50-60 nm), uncoated vesicles about 75-90 nm, and membranous apical tubules are present, in addition to large, vacuolar, pale, multivesicular bodies, dense multivesicular bodies, and secondary lysosomes seen deeper in the cytoplasm amongst numerous ER cisternae, saccules of the Golgi apparatus, and mitochondria. The endocytic activity of these cells was investigated by using cationic ferritin (CF) as a marker of adsorptive endocytosis and native ferritin (NF) for demonstrating fluid-phase endocytosis. These tracers were injected separately into the lumen of the vas deferens, and the animals were killed at various time intervals thereafter from 2 to 90 minutes. At 2 minutes CF was seen bound predominantly to microvilli and to areas of the apical plasma membrane delimiting coated pits as well as in large, coated vesicles. At 5 and 15 minutes the tracers were seen in apical tubules and pale multivesicular bodies; at 30 minutes moderately dense multivesicular bodies were labeled. At 1 hour and longer time intervals dense multivesicular bodies and secondary lysosomes were labeled. NF followed the same pathway as CF; however, no binding to microvilli or areas delimiting coated pits was observed. The numerous other vesicular structures, i.e., the large uncoated vesicles (150-300 nm) and the small coated and uncoated vesicles (50-60 nm), never became labeled with the tracers and therefore were not involved in the endocytic process. There was, however, an exception in the case of several small (75-90 nm) uncoated vesicles seen deeper in the apical cytoplasm of these cells which were labeled exclusively with CF. With time such vesicles appeared along the lateral and basal surfaces of these cells and discharged their content of CF into the lateral intercellular space or the connective tissue space at the base of these cells. Thus the principal epithelial cells in addition to sequestering the endocytosed tracers within secondary lysosomes where they are presumably degraded also appear to be involved in the transcytosis of material from the lumen of the vas deferens to the underlying lamina propria.