The keratinization of epidermal cells of normal guinea pig skin as revealed by electron microscopy

Abstract

A considerable improvement in the contrast-effect of Araldite-embedded material has been achieved through the staining of ultra-thin sections of the horny layer of normal guinea pig skin with uranyl acetate at 40–70°C. The stratum corneum can be subdivided into three cell layers. Almost the entire cytoplasm of the cells of the basal layer shows a characteristic structural pattern consisting of bundles of unstained filaments embedded in a stained amorphous material. The filament bundles traverse the cell in different directions more or less parallel to the plane in which the relatively flat cells extend. In the intermediate layer this pattern becomes to a great extent irregular. In the superficial layer the typical regular pattern appears in regions irregularly scattered over the cell body and separated by more or less wide, empty spaces. Mitochondria-like structures are demonstrated throughout the stratum corneum. The opacity of the broad cell boundaries increases towards the surface of the skin. The cell surfaces show a wavy course, most pronounced in the superficial layer. An intercellular space separates the cells and is filled with a substance of fairly low opacity. In this substance intercellular bodies are found at short intervals. They are opaque and diffusely outlined in the basal and intermediate layers. In the superficial layer they appear as vesicular structures bounded by a very opaque membrane. A hypothesis is advanced according to which the keratin is formed from tonofilaments and keratohyalin granule-material, partly through a gradual incorporation of tonofilaments into the keratohyalin granules. The specific keratohyalin material would then form the interfilamentous component.