Domain turnover of junctional membrane areas in the epidermis.

To investigate the turnover of complete junctional membrane areas ("domain turnover"), psoriatic epidermis, keratoacanthoma, and squamous cell carcinoma were studied with an electron microscope and compared with the normal epidermis. Three types of domain turnover of junctions were observed. First, the uptake of intact intercellular junctions, which occurred as complete or incomplete annular junctions in the cytoplasm. Mainly gap junctions were involved. Second, the formation of autojunctions bridging an infolding at the surface of a cell, which is then incorporated and occurs partly with an attached saccule in the cytoplasm. This type was confined to desmosomes. Finally, the loss of intercellular desmosomes into the intercellular space was observed. Proliferating epidermis was associated with an increased domain turnover of gap junctional membrane areas. Domain turnover of desmosomes prevailed in tumors.