The influence of transferin binding to L2C guinea pig leukemic lymphocytes on the endocytosis cycle kinetics of its receptor

Abstract

The parameters regulating the internalization and recycling of transferrin‐specific receptors were determined in guinea pig leukemic B lymphocytes, in the absence or presence of ligand. We show that after the cells were purified, 45–56% of the total receptors were on the cell surface. In the absence of transferin, unoccupied receptors are quickly internalized (rate constant, 0.12 min−1) whereas their recycling is much slower (rate constant, 0.026 min−1). This difference between endocytosis and recycling rates leads to a balanced receptor distribution with only 22% of the total receptors outside after incubation of the cells for 20–30 min at 37°C. The internalization rate of occupied receptors, measured in the presence of transferrin is faster (rate constant, 0.21 min−1) than that of unoccupied receptors calculated in the absence of transferrin (0.12 min−1; see above). On the other hand, mere binding of transferrin to its receptor, without internalization, arrested by cytoplasm acidification, is sufficient to induce a large increase (by a factor of seven) in the recycling rate of unoccupied internal receptors from 0.026 min−1 to 0.17 min−1. Thus, in these lymphocytes, transferrin mobilizes internal receptors by modifying the kinetic rates of internalization and recycling, leading to a new equilibrium between external and internal receptors. Copyright © 1991, Wiley Blackwell. All rights reserved