Important Regulatory Roles of Erythrocytes in Platelet Adhesion to the von Willebrand Factor on the Wall under Blood Flow Conditions.

Abstract

The role of erythrocytes in platelet adhesion to von Willebrand factor (VWF) on the vessel wall through their membrane glycoprotein (GP)Ibα under blood flow conditions has not yet been elucidated. Blood specimens containing fluorescent-labeled platelets and native, biochemically fixed, or artificial erythrocytes at various hematocrits were perfused on the surface of VWF immobilized on the wall at a shear rate of 1,500 s-1. The rates of platelet adhesion were measured under each condition. The computer simulation of platelet adhesion to the VWF on the wall at the same shear rate was conducted by solving the governing equations with a finite-difference method on a K computer. The rates of platelet adhesion were calculated at various hematocrit conditions in the computational domain of 100 µm (x-axis) × 400 µm (y-axis) × 100 µm (z-axis). Biological experiments demonstrated a positive correlation between the rates of platelet adhesion and hematocrit values in native, fixed, and artificial erythrocytes. (r = 0.992, 0.934, and 0.825 respectively, p < 0.05 for all). The computer simulation results supported the hematocrit-dependent increase in platelet adhesion rates on VWF (94.3/second at 10%, 185.2/second at 20%, and 327.9/second at 30%). These results suggest that erythrocytes play an important role in platelet adhesion to VWF. The augmented z-axis fluctuation of flowing platelets caused by the physical presence of erythrocytes is speculated to be the cause of the hematocrit-dependent increase in platelet adhesion.