Normal red blood cells\u2019 shape stabilized by membrane\u2019s in-plane ordering

L Mesarec,A Iglič,V Kralj-Iglič,W Góźdź,E G Virga,S Kralj

doi:10.1038/s41598-019-56128-0

Abstract

Red blood cells (RBCs) are present in almost all vertebrates and their main function is to transport oxygen to the body tissues. RBCs’ shape plays a significant role in their functionality. In almost all mammals in normal conditions, RBCs adopt a disk-like (discocyte) shape, which optimizes their flow properties in vessels and capillaries. Experimentally measured values of the reduced volume (v) of stable discocyte shapes range in a relatively broad window between v ~ 0.58 and 0.8. However, these observations are not supported by existing theoretical membrane-shape models, which predict that discocytic RBC shape is stable only in a very narrow interval of v values, ranging between v ~ 0.59 and 0.65. In this study, we demonstrate that this interval is broadened if a membrane’s in-plane ordering is taken into account. We model RBC structures by using a hybrid Helfrich-Landau mesoscopic approach. We show that an extrinsic (deviatoric) curvature free energy term stabilizes the RBC discocyte shapes. In particular, we show on symmetry grounds that the role of extrinsic curvature is anomalously increased just below the nematic in-plane order-disorder phase transition temperature.

Highlights

Red blood cells (RBCs) are present in almost all vertebrates and their main function is to transport oxygen to the body tissues
The discocyte RBC shape is invaginated in the center and torus-like at the rim
Optimal RBCs flow and their carrying and transport capabilities in “healthy” conditions coincide with discocyte RBC shape[9], while in pathological conditions or in patients using drugs, a larger number of RBCs may have stomatocyte or echinocyte shapes

Summary

Introduction

Red blood cells (RBCs) are present in almost all vertebrates and their main function is to transport oxygen to the body tissues. Measured values of the reduced volume (v) of stable discocyte shapes range in a relatively broad window between v ~ 0.58 and 0.8 These observations are not supported by existing theoretical membrane-shape models, which predict that discocytic RBC shape is stable only in a very narrow interval of v values, ranging between v ~ 0.59 and 0.65. The Helfrich model predicts three qualitatively different RBC shapes upon varying of the reduced volume v: (i) stomatocytes (Fig. 1a), (ii) oblate discocytes (Fig. 1b) and (iii) prolate shapes (Fig. 1d). These shapes are stable in different regimes of v values: (i)v < v1, (ii) v1 ≤ v ≤ v2, (iii) v > v2, where v1 ~ 0.59 and v2 ~ 0.65. Because in this paper we do not consider the spiculated (echinocytic) RBC shapes, the shear elastic energy of the RBC membrane skeleton is for simplicity neglected in our theoretical approach

Methods

Results

Conclusion