Specific binding of 1-[3H]-O-alkyl-2-acetyl-sn-glyceryl-3-phosphoryl choline (platelet-activating factor, PAF) by human polymorphonuclear neutrophils

1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (PAF) is a potent activator of polymorphonuclear neutrophil (PMN) aggregation, exocytosis and chemotaxis. Specific desensitization of PMN to PAF suggests a receptor-mediated interaction. The binding of 1-[³H]-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (³H-PAF) to human PMN and platelets was analysed and compared. Binding was saturable at 0.6 n M and 0.1 n M for 2×10⁶ PMN and 5×10⁷ platelets, respectively. The time course of binding at 22°C and 37°C for both cell types reached the plateau at 2 min. The average K_d was 45.0±1.7 n M (mean ±1 SD of 4 experiments) for PMN (27.391±1381 sites for PMN) and 20.1±6.3 n M (4 experiments) for platelets (1577±461 sites for platelets). The Scatchard plot analysis revealed two distinct binding sites both on PMN and platelets: a high affinity binding site and a non-saturable binding site.