Important Physical Regulatory Roles of Erythrocytes on Platelet Adhesion Under Blood Flow Conditions.

Abstract

Aim: Functional roles of erythrocytes on platelet adhesion to vessel wall under blood flow condition is still to be elucidated. Methods: Blood specimens containing native, biochemically fixed, or artificial erythrocytes, at various hematocrits were perfused on immobilized von Willebrand factor (VWF) at a shear rate of 1,500 s− 1. Number of platelets adhered on VWF within the region of interest (ROI: 5x103 µm2) was serially measured for 2 minutes using the fluorescent microscopy system. Regression analyses were conducted to evaluate the relationship between the rates of platelet adhesion and the hematocrit values. Computer simulation of platelet adhesion on the wall of von Willebrand factor (VWF) at a shear rate of 1,500 s− 1 was conducted by solving governing equations with a finite-difference method on K-computer. Calculations were conducted at various hematocrits conditions in the computational domain of 100 µm (x-axis) x 400 µm (y-axis) x 100 µm (z-axis). Results: Biological experiments demonstrated the positive correlations between the rates of platelet adhesion and hematocrit values in native, fixed, and artificial erythrocytes. (r = 0.992, 0.934, and 0.825, p < 0.05 for all) The number of platelets adhered after 2 minutes blood perfusion at 24% hematocrit of 221.7 ± 22.6/5x103 µm2 (fixed erythrocytes) and 208.0 ± 26.5/5x103 µm2(artificial ones), respectively, were comparable to that with native ones of 195.9 ± 28.3/5x103 µm2. The simulation results demonstrated the hematocrit dependent increase in platelet adhesion rates (94.3/sec at 10%, 185.2/sec at 20%, and 327.9/sec at 30%, respectively) suggesting the importance of augmented z-axis fluctuation of flowing platelet by erythrocytes as the cause of platelet adhesion. Conclusions: Our experimental results indicate the importance of the physical roles of erythrocytes inducing wall-normal fluctuations of flowing platelets on their vessel adhesion under blood flow conditions.