Evidence for platelet-activating factor receptor subtypes on human polymorphonuclear leukocyte membranes

• Published in: Biochemical pharmacology 1997-11, Vol.54 (9), p.1007-1012
• Main Authors: LeVan, Tricia D., Dow, Scan B., Chase, Peter B., Bloom, John W., Regan, John W., Cunningham, Eve, Halonen, Marilyn
• Format: Article
• Language: English
• Subjects: Animals; Azepines - metabolism; Biological and medical sciences; Cell receptors; Cell structures and functions; COS Cells; Fundamental and applied biological sciences. Psychology; G-protein coupled receptor; Humans; Miscellaneous; Molecular and cellular biology; Neutrophils - chemistry; Platelet Membrane Glycoproteins - classification; platelet-activating factor; polymorphonuclear leukocytes; radioligand binding; Receptors, Cell Surface; Receptors, G-Protein-Coupled; Triazoles - metabolism
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/S0006-2952(97)00249-9

Platelet-activatmg factor (PAF) is a potent phospholipid mediator that acts through specific cell surface receptors. The existence of PAF receptor subtypes has been suggested by functional and radioligand binding studies in a variety of cells and tissues. This report addresses this issue more directly and demonstrates differences between specific PAF receptors in human polymorphonuclear leukocytes (PMNs) and COS-7 cells transfected with the cloned human PAF receptor gene. The presence of more than one receptor in human PMNs is supported by three different studies. First, the K d from the saturation isotherms for the binding of [ 3H]WEB 2086 on PMNs was 7-fold larger ( K d = 29.2 nM) than the kinetic K d (4.2 nM). Second, the pseudo-Hill slope determined from the saturation experiments with PMNs was significantly lower than unity (0.69 ± 0.05 SEM), and the saturation K d values for transfected COS-7 ( K d = 9.6 nM) and PMN membranes were significantly different. These results contrasted with those for the transfected COS-7 cells, which showed a K d from the saturation isotherms similar to that of the kinetic K d (3.2 nM) and a pseudo-Hill slope that was not different from 1.0. Third, when the radiolabeled ligand [ 3H]WEB 2086 was increased in concentration from 10 to 50 nM in inhibition experiments with the human PMN membranes, the K i increased, indicative of binding mainly to receptors with lower affinity. These results suggest that PAF receptor subtypes exist in human PMNs based on distinct radioligand binding characteristics from the human cloned PAF receptor.