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.