Immunohistochemical and Scanning Electron Microscopic Study of Cytokeratin Distribution in the Collecting Tubule of the Rat Kidney

Cytokeratin distribution in the collecting tubules (CTs) of the rat kidney was studied by immunohistochemistry and scanning electron microscopy (SEM). After preparation of sections from formalin-fixed, paraffin-embedded tissue for immunohistochemistry, the remaining tissue was prepared for SEM. The cut surfaces of the tissue were examined by SEM and compared with sections stained with anti-cytokeratin antibody. The immunostained sections revealed positive staining along the entire CTs. However, in addition to diffusely stained cells, unstained and partially stained cells were seen. The latter were not distributed in inner medullary CTs, whereas the diffusely stained cells were observed in cortical, outer medullary and inner medullary CTs. This immunohistochemical heterogeneity of cytokeratin reactivity was prominent in the outer medullary and cortical CTs. From this comparative study of immunostained sections and SEM specimens, it was concluded that the heterogeneously stained cells correspond to intercalated cells, whereas the diffusely stained cells represent most principal cells. These results suggest that the difference in cytokeratin density among CT cells may represent different functional states, at least in intercalated cells.