Red blood cell shape as a function of medium’s ionic strength and pH

Abstract

Glycocalyx, the characteristic first line of interaction between membrane and environment, can be visualized as a polyelectrolyte anchored to a bending-resistant matrix. This structure has an amazing resemblance with the ionized monolayers, in which, the cohesion among hydrocarbon chains is counteracted by the repulsion among similarly charged ionic heads, and thus the balance determines the curvature of the membrane. Likewise, it could be assumed that in biological membranes, repulsion among similarly charged groups in the glycocalyx could generate different curving trends. Hence, the factors directly influencing the electrostatic interaction among surface charged groups were studied, assessing the effect of the medium's ionic strength (mu) and pH, in an extensive range of values around the physiological one. The results point out mu variations inducing different shapes, depending on whether mu values were lower or higher than the physiological ones; which could be explained by the polyelectrolyte theory. The occurrence of more invaginated shapes as the medium's pH decreases, and the opposite event, when the pH increases, could be attributed to the coupling between the dissociation of the glycocalyx ionic groups and the H+ concentration. The behavior of the cells with reduced surface charges (by neuraminidase degradation) supports the hypothesis that the observed mu and the pH effect on erythrocyte shape could be mediated by glycocalyx charged groups.

On the mechanism of stomatocyte–echinocyte transformations of red blood cells: experiment and theoretical model

“…This is expected to affect the tension of the outer leaflet of the membrane and to influence the shape index of the cells [7]. Our data (Fig.…”

“…As this electrostatic repulsion can be quantitatively predicted by the electric double layer theory [36], the coupling of the latter with a membrane-mechanical model, like that in [33], would lead to the construction of a complete quantitative theory of the stomatocyte-echinocyte transformation. Unfortunately, it seems that the experimental observations contradict the predictions of the double-layer theory: with the rise of the outer medium's ionic strength the experiment shows a shifting of the stomatocytes toward echinocytes [3], whereas exactly the opposite trend follows from the double layer theory insofar as the repulsion between the charges at the outer membrane surface should be screened by the increased electrolyte concentration; consequently the area of the outer leaflet should diminish [7].…”

“…Nine shapes were considered in accordance with the following classification [7,14]: biconcave disc (shape index 0); three types of stomatocytes (indexes −1, −2 and −3) to spherostomatocyte (index −4); and three degrees of echinocytes (indexes 1, 2 and 3) to spheroechinocyte (index 4). At least 150 cells were classified and labeled for each processed frame.…”

“…1) upon variation of the electrolyte concentration [1][2][3][4][5][6][7], increase of the medium's pH [7][8][9][10][11][12], addition of amphiphiles and other agents [1,[13][14][15][16][17][18], and changes in temperature [19,20]. A general correlation was found between the erythrocyte shape and the transmembrane electric potential [21][22][23][24][25].…”

“…The effect of pH and other agents could be also attributed to their influence on the transmembrane potential [25]. Detailed reviews, different viewpoints and discussions on the molecular origin of the observed phenomena can be found in [7,12,18,[24][25][26]. Some authors have established correlations between the stomatocyte-echinocyte transition and the effect of additives on the conformation of the anion-exchange protein band 3, including inhibition of the anion transport effectuated by this protein [27][28][29][30].…”