Unbuffered osmium staining in pars recta of the proximal tubule from rat kidney studied by thin and semi-thin section cytochemistry.

Abstract

Using semi-thin (0.5 μm thick) and conventional thin sections, observations have been made on the pattern of unbuffered OsO4 staining in the pars recta of the proximal tubule (thick descending limb of Henle) from rat kidney. The cisternae limiting autophagic vacuoles and Golgi cisternae located at the apical aspect of the stack were heavily stained in most cells. Sometimes a progressive diminution of stain was seen across the Golgi stack from apical to basal aspects. In many cells the endoplasmic reticulum stained although the degree of staining varied. Plasma membranes were unreactive. Transformation of membranes from endoplasmic reticulum-like to plasma membrane-like (i.e., endoplasmic to exoplasmic transformation) is thought to occur across the Golgi stack (deDuve, 1969; Morre et al., 1971) and presumably also occurs at the membranes limiting autophagic vacuoles, when these membranes are derived from endoplasmic reticulum. It is interesting that both sites of membrane transformation were heavily stained with unbuffered OsO4 in pars recta cells and a similar staining distribution has been reported by others in several different cell types. These observations suggest that OsO4 staining is associated with the membrane transformation phenomenon.