Receptor Up-regulation, Internalization, and Interconverting Receptor States

Abstract

High resolution kinetic data of the binding of fluores- cent peptide to the N-formyl peptide receptor of neutro- phils at 37 °C has allowed for the development of a li- gand binding model that predicts statistically larger binding rate constants than those previously reported for intact neutrophils. The new model accounts for li- gand association and dissociation, receptor up-regula- tion, ligand-receptor complex internalization, a change in receptor affinity, and the quenching of internalized fluorescent ligand. We determined that receptor up-reg- ulation is both agonist- and temperature-induced and is inhibited by both phenylarsine oxide and pertussis toxin treatment. Model fits of ligand association to per- tussis toxin-treated cells show that while receptor up- regulation was inhibited, rate constants for ligand bind- ing, receptor affinity conversion, and internalization of ligand-receptor complexes were unaffected. Results suggest Gi-protein-mediated receptor up-regulation and Gi-protein-independent receptor affinity conversion. Simulation of ligand infusion using our model gives in- sight into the quantitative and dynamic relationship between the low affinity ligand-receptor complex and the actin polymerization response.