Some ultrastructural observations on keratohyalin granules of guinea pig epidermis.

Abstract

Keratohyalin in the cavy back and plantar epidermis was examined by transmission electron microscopy. These cytoplasmic aggregates are made up of numerous fine particles uniformly stained by osmium, probably the protein component. Phospholipid in the interstices is removable in lipid solvents before osmium post-fixation. After glutaraldehyde fixation without osmium, tissue stained in uranyl acetate showed keratohyalin aggregates composed of mixtures of darkly stained and weakly stained groups of fine particles which indicate heterogeneity in composition. More weakly stained aggregates of keratohyalin composed of these particles were found in the interiors of keratinized cells in the lower part of the stratum corneum not previously demonstrated at this level. Oxidation in peracetic acid followed by staining in uranyl acetate showed dark areas in keratohyalin aggregates, which it is thought contain cystine. Keratohyalin aggregates are not surrounded by a membrane and they are not organelles. Their heterogeneous composition suggests different derivations and destinies of component substances, some of which may be synthetic and others autolytic products. It is suggested that keratohyalin is a cytoplasmic coacervate of protein, phospholipid, and bound calcium precipitated under unstable physiochemical conditions associated with keratinization involving extensive cytolysis.