Immunoelectron microscopy of fodrin in the rat uriniferous and collecting tubular epithelium.

We examined the localization of fodrin in epithelial cells of rat uriniferous and collecting tubules by immunofluorescence and immunoelectron microscopy of frozen sections. In the uriniferous tubule, fodrin was found along the cell membrane and in the well-developed terminal web, as previously reported in other epithelial cells: in the terminal web and along the basolateral cell membrane in the proximal tubule; all around the cell surface in the thin limb of Henle; along the basolateral surface in the thick limb of Henle's thick segment and the distal tubule. In the intercalated cells of the collecting tubule, fodrin was found not only along the basolateral cell membrane but also in the apical cytoplasm. The most peculiar labeling was obtained in the principal cells of the collecting tubule. In addition to labeling in the basolateral cell membrane, fodrin was found diffusely in the cytoplasmic matrix. Association of fodrin with any particular structure could not be identified, but the Golgi area was apparently free of labeling. Cytoplasmic labeling was more conspicuous in the principal cells of the medulla than in those of the cortex. The present results show that fodrin need not always exist in association with the cell membrane or the cytoskeleton but can occur in the cytoplasmic matrix, at least in epithelial cells. We discuss the possible physiological significance of the latter distribution.