HISTOCHEMICAL MARKERS REVEAL AN UNEXPECTED HETEROGENEOUS COMPOSITION OF THE RENAL EMBRYONIC COLLECTING DUCT EPITHELIUM

The ampullary collecting duct epithelium acts as an inductor in the em bryonic and neonatal kidney. It induces the formation of all nephron g enerations and thus determines the whole architecture of the kidney. A s the organ matures, the collecting duct epithelium itself transdiffer entiates. The ampullary inductor epithelium, which appears homogeneous as revealed by light microscopy, develops into the well-known heterog eneous epithelium of the mature collecting duct consisting of light pr incipal and dark intercalated cells. Up to now the mechanisms initiati ng and regulating this transdifferentiation step are unknown. Only ver y few data are available concerning functional characteristics of the ampullary epithelial cells of neonatal rabbit kidney. Therefore, a cha racterization of the collecting duct ampullary cells was carried out b y means of immunohistological techniques using a set of different mono clonal antibodies and the lectin peanut agglutinin. All epithelial cel ls within the ampullary tip and neck were positive for cytokeratin 19, an intermediate filament protein. On the other hand, the monoclonal a ntibody CD 7 revealed a clear cut boundary between the ampullary neck and the ampullary tip region. Furthermore, after incubation with the m onoclonal antibody BO-7 specifically reacting with intercalated cells of the mature collecting duct, both labeled and unlabeled cells were o bserved within the whole ampullary epithelium. These results were conf irmed by scanning electron microscopical investigations which revealed two distinct epithelial cell populations. Thus, an unexpected heterog eneity of the ampullary epithelium could be demonstrated.