Binding of concanavalin A to isolated hepatocytes and its effect on uptake and degradation of asialo-fetuin by the cells.

Abstract

1. The binding of 125I-labelled concanavalin A to isolated rat hepatocytes was studied at temperatures between 4 degrees C and 37 degrees C. At the latter temperature, concentrations of concanavalin A from 0.01 to 0.4 mg/ml were used. In all of these experiments, binding reached a plateau after 40--60 min, when 28--35% of the concanavalin A added was bound to the cells (cell density 8 x 10(6) cells/ml). 2. The rate of uptake of 125I-labelled asialo-fetuin by the hepatocytes was lowered to 30% of control values when the cells were preincubated with 0.1 mg of concanavalin A/ml. This decrease could be accounted for by a decrease in the rate of binding of asialo-fetuin to the beta-galactoside receptor of the cells. The binding capacity of the cells was not influenced by preincubation with concanavalin A. 3. Degradation of asialo-fetuin was decreased only if concanavalin A was present during the uptake of asialo-fetuin by the cells. Subcellular fractionation revealed that concanavalin A lowered the rate of entry of endocytosed asialo-fetuin into the lysosomes. The effect of concanavalin A on degradation is distinct from its effect on the rate of uptake of asialo-fetuin by hepatocytes.