The junctions of normal human epidermis: A freeze-fracture study

Abstract

Freeze-fracture has confirmed the presence of desmosomes, gap junctions, and tight junctions in fixed human epidermis. On the basal cell plasma membrane directed toward the dermis structures are detected that are reminescent of the hemidesmosome. On the lateral and apical plasma membrane of the basal cell and in the spinous and granular layers the desmosome, when cross-fractured, possesses a simple structure. Fine filaments are observed where the attachment plaque is seen in thin section. When the fracture reveals the apposed membranes “en face,” the desmosome appears as an aggregate of particles on both the P and E membrane faces. The area occupied by the junctions is at a different level than that of the adjacent nonjunctional membrane. In the horny layer the desmosome appears as an elevated plaque on the E face and a cluster of particles on the P face. Gap junctions are rather small and are found in a limited number from the basal to the granular layers. Tight junctions as well are rarely observed in the intermediate layers. Both types of junctions are never observed in the horny layer. Freeze-fracture demonstrates the presence of an extensive network of grooves on the P fracture face and ridges on the E fracture face of the plasma membrane of the first cells of the horny layer. The ridges and the grooves are in close relation with the desmosomes.