Rapid modulation of N-formyl chemotactic peptide receptors on the surface of human granulocytes: formation of high-affinity ligand-receptor complexes in transient association with cytoskeleton.

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Abstract
When human granulocytes were exposed to 50 nM N-formyl-Met-Leu-[3H]Phe at 37.degree. C they rapidly formed ligand-receptor complexes that dissociated 50-100 times more slowly than those on cells initially exposed to the peptide at 4.degree. C. These complexes of apparent higher affinity were stable after detergent solubilization of the cells with Triton X-100. The complexes co-isolated with the detergent insoluble cytoskeletal residues and were free of the cytosolic and Golgi markers, lactate dehydrogenase and galactosyl transferase, respectively. After 5 s of exposure to f-Met-Leu-Phe, 2000-3000 molecules of ligand/cell were trapped in such complexes. Continued exposure resulted in capture of a maximum of 14,000 molecules/cell by 5 min. Exposure at 15.degree. C, a temperature at which endocytosis of the receptor is prevented, resulted in complex formation at a linear rate for at least 20 min to levels twice those measured at 37.degree. C. At 4.degree. C, complex formation was .apprx. 10% of the maximum amount formed at 37.degree. C. Pulse-chase experiments revealed that the complex was in transient association with the cytoskeleton with a half-life ranging between 30 s to 4 min depending on the length of the original incubation. EM autoradiography indicated that after 1 min of incubation at 37.degree. C, the majority of the specific autoradiographic grains were localized to the outer circumference of the cellular cytoskeleton. After 4 min of incubation, the grains were less frequent at the cytoskeleton periphery but still 3-fold enriched over a random cellular distribution. A metabolically controlled modulation of the state of the N-formyl chemotactic peptide receptor apparently occurs in the plasma membrane which may be the result of transient association of ligand-receptor complex and the cell cytoskeleton.