Impact of surface-area-to-volume ratio, internal viscosity and membrane viscoelasticity on red blood cell deformability measured in isotonic condition

Céline Renoux,Lydie Da Costa,Philippe Connes,Philippe Joly,Amel Bessaa,Magalie Faivre,Alexandra Gauthier

doi:10.1038/s41598-019-43200-y

Abstract

Osmotic gradient ektacytometry is the gold standard to assess red blood cell (RBC) deformability. It has been proposed that, when measured in isotonic condition, RBC deformability at low shear stress would depend on membrane elasticity while it would be influenced by internal viscosity when measured at high shear stress, but this hypothesis needs to be further addressed. Healthy RBCs were rigidified by treatment with lysolecithine (LPC), diamide or nystatine associated with hyperosmolar solutions (OSMO), which reduces membrane surface area, decreases membrane elasticity or promotes cell dehydration, respectively. Diamide treatment resulted in a decrease in isotonic RBC deformability at all shear stresses tested (i.e. from 0.3 to 30 Pa). LPC and OSMO treatments caused a decrease in isotonic RBC deformability above 3 Pa only. Isotonic RBC deformability from patients with hereditary spherocytosis or sickle cell disease was mainly decreased above 1.69 Pa. Our findings indicate that decreased isotonic RBC deformability at shear stresses above 3 Pa would be related to a reduction in the surface-area-to-volume ratio and/or to a loss of membrane elasticity and/or to an increase in internal viscosity while a decrease of RBC deformability below 3 Pa would reflect a loss of membrane elasticity.

Highlights

Red blood cells (RBCs) are discoid shape entities with a diameter of 8 μm and a thickness of 2 μm, which play a key role in gas transport in the human body
Omin reflects the osmotic fragility and the surface-area-to-volume ratio (S/V) ratio, EImax depends on the membrane deformability and RBC surface area, and Ohyper reflects mean cell hemoglobin concentration (MCHC) and cell volume3,9
Our study demonstrates that a simple isotonic ektacytometry may provide important information regarding RBC biophysical properties

Summary

Introduction

Red blood cells (RBCs) are discoid shape entities with a diameter of 8 μm and a thickness of 2 μm, which play a key role in gas transport in the human body. While osmotic gradient ektacytometry is often used by hematologist involved in the screening of RBC membrane disorders, it is less frequently used by researchers involved in the field of blood rheology who prefers assessing RBC deformability with ektacytometer used at various shear stresses but under constant tonicity of the medium (i.e., isotonicity). This situation may be partly explained by the fact that osmotic gradient ektacytometers have not been available in the markets from the nineties to recently. We tested the effects of several molecules known to modulate surface area, cell volume, internal viscosity or membrane elasticity on healthy RBCs and we compared the RBC deformability measurements obtained with osmotic gradient ektacytometry versus isotonic ektacytometry. We used RBC from patients with HS or sickle cell disease (SCD) and compared the RBC deformability findings obtained with osmotic gradient ektacytometry versus isotonic ektacytometry to get further information on the meaning of isotonic ektacytometry results

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