Objectives: To explore the role of blood flow in red blood cell deformability and determine whether it is associated with the release of ATP by red cells.
Methods: A perfusion system was employed to mimic the blood flow conditions. Red cell treatment in vitro with dipyridamole or aspirin, either alone or combined, was performed either on red cells alone prior to blood reconstitution or on already reconstituted blood. Blood viscosity at shear rates of 90 and 450 s-1 was measured, before and after perfusion, by means of a cone/plate viscometer. Red cell deformability was estimated as the magnitude of the slope between these two values of viscosity. ATP level in platelet-free plasma was measured by the firefly luciferase assay, and was used to monitor dipyridamole-induced blockade of ATP efflux by red cells.
Results: In control experiments, red cells became more rigid after perfusion (slope values: 0.62 +/- 0.09 vs 0.40 +/- 0.04; P < 0.05). Absence of platelets or treatment of red cells with aspirin and/or dipyridamole prevented dipyridamole prevented the increased stiffness of red cells observed after exposure of blood to flow conditions. Moreover, a significant increase in red cell deformability was observed when blood was treated with dipyridamole alone or combined with aspirin (0.69 +/- 0.07 and 0.65 +/- 0.05 respectively vs. 0.40 +/- 0.04; P < 0.05). Treatment with dipyridamole alone or combined with aspirin caused a decrease in ATP levels. Statistical significance was reached when red cells alone were treated with dipyridamole alone (45.8 +/- 2.8 vs. 173.3 +/- 47.6 ng ATP/ml; P < 0.05).
Conclusions: Flow stress induced a decrease in red cell deformability probably linked to platelet activation. Treatment with dipyridamole alone or associated with aspirin eliminated the effect of flow, increasing red cell deformability. Under our experimental conditions, modifications could not be ascribed to red cell-released ATP. Our results emphasize the importance of blood flow conditions to evaluate RBC deformability.