Fine structure of horny cells of the vermilion border of the lip compared with skin

Abstract

The formation and ultrastructure of the thick cellular envelope, i.e., the marginal band, of the cornified cells and the intercellular substances of the stratum corneum of the vermilion border were studied with the aid of ruthenium red-staining and a high resolution electron microscope. The marginal band was precipitated on the cytoplasmic side of the plasma membrane. This process was rather abrupt in other parts of the body, appearing first in the lowermost horny cell as an 160Å-thick dense band, but was gradual in the vermilion border of the lip. In spite of the discharge of the membrane-coating granules, the original 80Å-thick trilaminar plasma membranes were observed outside the marginal band and often desquamated as such in the upper stratum corneum. This observation was thought to be evidence against the theory that the membrane-coating granule coats the plasma membrane and thickens it. Instead, this seemed to support the concept that the thickened cellular envelope of the cornified cells is a de novo product. In the upper horny layers, ribbon-like lamellar structures, laminated fibrils and occluding zonule-like structures were found in the intercellular spaces. They were interpreted as an admixture of ruthenium red-positive component of the membrane-coating granules and cell-surface coat (glycocalyx), decomposed lipid substance derived from the membrane-coating granules and from shed plasma membranes, and probably peeled off occluding zonules of horny cells or subjacent cells respectively.