The role of calcium in active regulation of erythrocyte deformability

Abstract

Red blood cell (RBC) deformability has been assumed as a passive behavior being determined by the special geometry and material properties of erythrocytes. Although the erythrocyte membrane skeleton has been accepted as an important structure influencing deformability, mechanisms related to the active regulation of this property have only been considered in the last several years. The evidence about the regulation of mechanical properties of RBC by intracellular signaling pathways has brought a new understanding to the regulation of local microcirculation. It is known that these cells are always exposed to shear forces in the circulatory system and this level of shear forces result in the activation of the intracellular signaling pathways. Activation or inhibition of these pathways can lead to changes in red cell deformability. The goal of this study is to investigate the possibility of regulation of RBC deformability by the effect of shear forces. In particular, the focus is on investigating the role of calcium-calmodulin-protein kinase C (PKC) cascade on the erythrocyte response to mechanical stress. Human RBCs in autologous plasma were incubated with calcium chloride (1–5 mM), calcium channel blocker (verapamil), nitric oxide synthase (NOS) inhibitor (L-NNA), calcium chelator (EDTA) and mechanosensitive channel blocker (gadolinium). RBCs were first exposed to a constant and homogeneous SS within the physiological range (5–10 Pascal) in a Couette-type shearing system. RBC deformability was then immediately measured via ektacytometry. Improvement in RBC deformability was observed after each level of SS exposures; it was faster with higher levels of SS and increased by 3–8% of the starting level. Increased calcium concentration in the RBC suspending medium abolished the improvement of deformability. All inhibitors significantly increased RBC deformability compared to control (p<0.01). When the inhibitors were combined with 3 mM calcium, RBC deformability was further impaired and this was significantly different than the group treated with 3mM calcium only (p<0.01). The presence of calcium (3 mM) blunted the deformability improvement in response to SS; higher concentrations of calcium (5 mM) resulted in the reversal of the effect that decreased the deformability with time during SS exposure. The novel finding of the present study is the progressive improvement of deformability during the application of physiological SS levels. These results also indicate the importance of intracellular and extracellular signaling cascades, mainly involving the activation of calcium-calmodulin-PKC pathway as a determinant of RBC deformability increment in response to SS. It can suggest that the improvement of RBC deformability should be considered as a preconditioning of RBC prior to the entrance into capillaries from the arteries. This feature may have significant effects on blood flow dynamics and may be controlled through a mechanism of mechano-sensitive signal transduction by causing phosphorylation changes which regulate the relationship between RBC membrane cytoskeletal proteins and integral membrane proteins.