Immunoreactive kallikrein localization in the rat kidney: an immuno-electron-microscopic study

The cellular and subcellular localization of immunoreactive kallikrein was studied in the rat kidney using the peroxidase-antiperoxidase (PAP) method for the electron microscope. The effect of various tissue-processing protocols on ultrastructural preservation and immunocytochemical staining was evaluated by fixing kidneys with four different mixtures. The tissues were immunostained and further stained with OsO4 or silver methenamine. The best ultrastructural and immunocytochemical staining was obtained with Zamboni's-glutaraldehyde fixative. The kallikrein-immunoreactive cell type was identified, according to its localization and ultrastructural features, as the connecting-tubule cell. Immunoreactive kallikrein was concentrated mainly in the upper one-third of the cell and at both sides of the nuclei, and to a less extent was associated with the plasma membranes and basolateral infoldings. The immunoreactivity was related to free polyribosomes, the rough endoplasmic reticulum (RER), and the Golgi complex, suggesting that kallikrein is actively synthesized in this particular type of cell.