Ultrastructural characterization of the extramammary Paget cell plasma membrane: a freeze-fracture study

Membrane characterization of cultured human keratinocytes by freeze-fracture electron microscopy

Human skin explants obtained from 2 to 5-year-old patients with harelips were cultured in NCTC 168 medium at 37 degrees C, in a humidified atmosphere of 5% CO2 in air. After a 2-week incubation period, plasma membranes of the newly grown cells were characterized by freeze-fracture electron microscopy. Desmosomal diameter in cultured keratinocytes was much smaller, ranging from 0.08 to 0.19 micron, than that in vivo, where it ranged from 0.3 to 0.7 micron in diameter. On the E-face of the plasma membranes, attached to the bottom of the culture dish, small particle aggregations were observed. These were thought to be half-desmosomes, each consisting of 10 to 30 particles. Small gap junctions were also observed. These ranged in size from 0.05 to 0.1 micron in diameter. Membranous structures were found adhering to the plasma membrane from the intercellular spaces. These membranous structures may be lipid vesicles, since they are similar in freeze-fracture electron-microscopic features to lamellar lipid structures seen in the intercellular spaces of horny cells in vivo.

Freeze-fracture replication technique of human skin

The freeze-fracture replication technique represents one of the most advanced methods for studying the ultrastructure of biological tissues and has given a new dimension to the ultrastructure research. This technique makes it possible to obtain a cast of a fracture surface of frozen preparations. Apart from allowing samples to be examined without being dehydrated, i.e. under conditions very close to those of living state, it has proved especially useful for the analysis of many tissue functions concerned with membrane activity and exchanges between cells and their disturbance in specific disease conditions. Even through good quality replicas had already been obtained back in 1961 (Moor et al. 1961), only after 1970, mainly thanks to the contribution made by Breathnach and his collaborators (Breathnach et al. 1972, Breathnach 1973, Breathnach et al. 1973) was the freeze-fracture replication technique successfully used in the study of the skin, since this tissue had proved especially difficult to process. In this review paper, technical principles will be summarized and the most important findings so far obtained in the study of normal and pathologic skin will be illustrated.