Temperature- and dose-dependent internalization of concanavalin A in monolayer culture

When rat hepatoma cells (R117-21B) were incubated for 20 h at 37 degrees C with 125I-labeled concanavalin A at low concentrations (0.5-10 micrograms/ml), only 20-30% of the cell-associated radioactivity was released by alpha-methyl-D-mannoside, but at high concentrations (50-500 micrograms/ml), 60-80% of the cell-associated radioactivity was released. At 4 degrees C, the cell-associated radioactivity decreased with the increase in concentration of concanavalin A, and more than 80% of the cell-associated radioactivity was released by alpha-methyl-D-mannoside. These results suggest that the amount of cell-associated concanavalin A is related to the physicochemical state of the plasma membrane, which can be altered by the incubation temperature or by the concentration of concanavalin A, the transitional concentration being 5-10 micrograms/ml.