Mechanical properties of sickle cell membranes

Abstract

The mechanical properties of sickle erythrocyte membranes were evaluated in the ektacytometer. When ghosts from the total red blood cell population were examined, the rigidity of the resealed ghosts and their rate of fragmentation by shear stress (t1/2) were normal. However, fractionation on Stractan density gradients revealed that sickle cells were heterogenous in their membrane mechanical properties. The ghosts from dense cell fractions exhibited both increased rigidity and decreased stability. Presumably, these altered mechanical properties are a reflection of the well-documented biochemical damage found in irreversibly sickle cell membranes. Nevertheless, neither of the alterations in mechanical properties are likely to be significant elements in the hemolysis of sickle cell anemia. Earlier studies of abnormal erythrocytes suggest that increases in membrane rigidity per se do not increase hemolysis, and they are, therefore, unlikely to do so in this case. The stability of membranes from the dense cell fractions was reduced to about two thirds of the control value. Comparison with the results of studies of red blood cell membranes with genetically defective or deficient spectrin suggests that a reduction in t 1/2 of 50% is not associated with significant increases in the rate of hemolysis. Although altered ghost stability and flexibility can be demonstrated in dense sickle cells, these changes in membrane mechanical properties are not likely to be significant factors in the hemolytic process.

Rheological properties of sickle erythrocytes in patients with sickle‐cell anemia: The effect of hydroxyurea, fetal hemoglobin, and α‐thalassemia

“…Sickle RBCs are mechanically fragile, and dense sickle RBCs are particularly susceptible to mechanical damage, probably because of decreased membrane stability . Because patients with SS and α‐thalassemia have decreased numbers of dense cells, it is likely that their RBCs are less mechanically fragile.…”

Sickle Red Cell Microrheology and Sickle Blood Rheology

“…They found that cellular dehydration and the consequent increase in cytoplasmic viscosity are major determinants of the abnormal rheologic behavior of oxygenated sickle cell anemia RBC. Studies on resealed ghosts showed that membrane changes of sickle cell anemia RBC, such as altered material properties, increased extensional rigidity, and decreased membrane stability (53,89), contribute to the abnormal deformability of sickle cell anemia RBC.…”

The biophysics and mechanics of blood from a materials perspective

“…For example, in patients with sickle cell disease 125 (BOX 1), mutated haemoglobin polymerizes in low oxygen conditions leading to an increase in cell stiffness and reduced deformability. In addition, as the red cell continuously travels between low and high oxygen concentrations, the fluctuating mechanical loads to the membrane applied by polymerizing haemoglobin contribute to the aforementioned haemolysis 126 . Similarly, in the early stages of malaria infection, red blood cells that contain the parasite become stiffer 127,128 and more adhesive, allowing them to stick to the wall of small blood vessels and evade detection by the immune system 129 .…”

“…Effect on haemostasis and the immune system-A change in the collective cell number may also impair haemostatic function 126,132 . For example, abnormally high numbers of white blood cells can lead to leukostasis, a medical condition in which cells block blood flow, which can cause a transient ischemic attack and a stroke 143 .…”