(A through D) Effect of PF-4 on the binding of¹²⁵I–FGF-2 to receptors in cells deficient of heparan sulfates and expressing FGFR-1 (CHOm–FGFR-1), and cross-linking. CHOm–FGFR-1 cells (500,000 cells/dish) were incubated with 10 ng/mL¹²⁵I–FGF-2 with or without PF-4, 50 ng/mL heparin, or 1 μg/mL unlabeled ligand. Binding of ¹²⁵I–FGF-2 to receptors or cross-linking was performed as indicated in Materials and Methods. (A) Effect of increasing concentrations of PF-4 on high-affinity binding of ¹²⁵I–FGF-2 to receptors in the absence of heparin. (B) Effect of increasing concentrations of heparin on ¹²⁵I–FGF-2 binding in the presence (•) or absence (○) of 10 μg/mL PF-4. (C) Effect of increasing concentrations of PF-4 on ¹²⁵I–FGF-2 binding in the presence or absence of 50 ng/mL heparin. (D) Cross-linking of¹²⁵I–FGF-2 to receptors in the presence or absence of 10 μg/mL PF-4 or heparin. The differences in the amounts of¹²⁵I–FGF-2 bound between the different experiments reflect clonal variability in FGFR-1 expression. (A through C) Representative experiments done in duplicates (data points as mean; SD values: [A] 0 < SD < 0.04; [B] 0.01 < SD < 0.3; [C] 0.005 < SD < 0.09).