FIGURE 8.

Zn²⁺ promotes protein C activation. A, endothelial cells were incubated with protein C (80 nm) and thrombin (2 nm) with varying concentrations (0–100 μm) of ZnCl₂ in the presence (●) or absence (○) of CaCl₂ (5 mm) at 37 °C for 2 h. At the end of 2 h, thrombin in the reaction mixture was inhibited by adding hirudin (4 units/ml), and the amount of APC generated was measured in an amidolytic activity assay using chromogenic substrate S-2366 (500 μm). B, endothelial cells were incubated with protein C (80 nm) and thrombin (2 nm) for 1 h at 37 °C in the presence of one or more divalent cations as listed on the x axis. The amount of APC generated was measured as described above. The results are presented as the means ± S.E. of three or more experiments. *, the values are statistically significantly higher compared with the values obtained in the reaction mixture containing only Ca²⁺ (p < 0.01). #, the values are statistically significantly lower compared with the values obtained in the reaction mixture containing Ca²⁺ and Mg²⁺ (p < 0.05).