Intracellular Transport Pathways in Endodermal Cells of the Rat Visceral Yolk Sac

摘要

Using horse radish peroxidase (HRP) and HRP-labeled concanavalin A, we examined intracellular transport pathways in endodermal cells of the rat visceral yolk sac. Morphologically, membrane-bound structures in these cells were regarded as coated vesicles, apical vacuoles, lysosome and apical canaliculi. The coated vesicles were further classified into three groups; large, medium-sized and small coated vesicles. Those of large size were found only in the supranuclear cytoplasm, while those of the medium-size, only in the basolateral cytoplasm. Small vesicles were found in the supranuclear and basolateral cytoplasm and in the Golgi areas. It is well known that the large coated vesicles, apical vacuoles and lysosmes are directly involved in endocytosis which occurs at the apical surface, and the apical canaliculi, in membrane recyling from the apical vacuoles and lysosmes to the apical cell membrane. Histochemically, by 30 min, the membrane-bound structures labeled with these tracers were found only in the supranuclear cytoplasm, but at 60 min, some small labeled vesicles were noted also in the basolateral cytoplasm and in the Golgi areas. These findings suggest that though most substances and membrames endocytosing at the apical surface are transported to the lysosmes, some might be transported to the basolateral cytoplasm and Golgi areas in the form of the small coated vesicles. The medium-sized coated vesicles were not labeled with the histochemical tracers, suggesting that they might be endocytosed at the basolateral cell membrane.