Internalization of cationized ferritin receptors by rat hepatoma ascites cells.

Cationized ferritin (CF) was used to label the cell surface anionic sites of Chang rat hepatoma ascites cells. If the hepatoma cells were fixed with glutaraldehyde and treated with CF, the label was distributed evenly over the external surface of the plasma membrane. Treatment of unfixed ascites cells with CF yielded clusters of ferritin particles separated by label-free areas of the plasma membrane. Some unfixed ascites cells were treated firstly with CF, then incubated in veronal buffered saline at 37 °C for 10, 20, 30 and 45 min, subsequently fixed in glutaraldehyde and re-exposed to CF. After 10 min of incubation, the label was arranged into large clusters with the remaining areas of the plasma membrane lightly labelled with CF. At 20 min, only clusters of ferritin were present on the plasma membrane; the remaining area of the cell surface was totally free of label. The ability of the plasma membrane to bind additional CF was completely restored after 45 min of incubation. These results suggest that for some period of time after internalization of CF label on cell surface the plasma membrane is devoid of any detectable negative charge.