Kinetic analysis of chemotactic peptide receptor modulation

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Abstract
The dynamics of the chemotactic peptide receptor on rabbit peritoneal polymorphonuclear leukocytes were followed using the tritiated peptide N-formylnorleucylleucylphenylalanine (FNLLP). A kinetic analysis was used to examine the possible interrelationships between receptor loss (down-regulation), receptor-mediated peptide uptake and receptor recycling. Cells incubated with FNLLP show a dose-dependent reduction in the number of receptors available on the surface. This receptor down-regulation is complete within 20 min and then the number of receptors available for binding remains at a plateau level. Peptide continues to be taken up in a receptor-mediated manner even after down-regulation is complete. If peptide is removed, receptor recovery occurs and does not require protein synthesis. The kinetics of these processes was studied. The plateau receptor level apparently is a steady state in which receptor internalization and return occur continuously. The rate of receptor-mediated peptide uptake is approximately equal to the rate of receptor recovery measured after peptide removal. The rate of receptor recovery is proportional to the number of receptors missing from the surface, suggesting receptor recycling may be occurring.