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.

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The hypothesis that the internal viscosity of erythrocytes is governed by the intracellular hemoglobin (Hb) concentration is examined. Here viscosity is determined by labeling of the cytoplasmic reduced glutathione with the spin label maleimido-Tempo. Erythrocyte populations with different Hb concentrations in isosmotic conditions were obtained through incomplete lysis, followed by cell resealing, and discontinuous density gradient separation. This procedure maintains normal cell shape and volume. Microviscosity of membrane-free Hb solutions was measured by addition of spin labeled glutathione. It was found that microviscosity values are similar for the erythrocyte cytoplasm and for Hb solutions of equivalent concentrations, showing that the erythrocyte membrane does not have any influence on internal microviscosity. The dependence of the microviscosity on the concentration of Hb solutions was compared with results of macroscopic viscosity obtained by other authors. It is concluded that microviscosity is sensitive to individual properties of the Hb molecule (intrinsic viscosity), but that it is not sensitive to intermolecular interactions. As the microviscosity behavior as a function of Hb concentration is the same in Hb solutions as in the erythrocyte cytoplasm, the inferences regarding macroscopic viscosity in Hb solutions could be translated to the rheological properties of the erythrocyte cytoplasm. Thus, these properties could be predicted from the values of the mean corpuscular Hb concentration.

Increase in erythrocyte aggregation (EA) is pathognomonic for rheumatoid arthritis (RA), and its estimation through erythrocyte sedimentation rate (ESR) is part of DAS 28-4 activity diagnosis, with low correlation with EA and that does not discriminate the contribution of cell factors that increase aggregation.Objective: To analyse cell and plasma factors that might be involved in EA increase, to understand how RA affects blood components, thus modifying blood fluid behavior.Methodology: One hundred women presenting active RA were compared with age-matched controls (C). EA was measured by transmitted light, obtaining two parameters: 2k 2 n 0 , characterizing the aggregation process kinetics and s 0 /n 0 , estimating aggregates size. Cell factors assays: erythrocyte deformability, by filtration through nucleopore membranes, cell shape, by microscopy, and membrane fluidity by EPR. Plasma: total proteins and CRP, albumin, fibrinogen (Fb), by gravimetry, and IgG and IgM by single radial immuno-diffusion.Results: AR and C (x ± SE). 2k 2 n 0 : 31.83 ± 2.84, 23.75 ± 1.91; s 0 /n 0 : 0.92 ± 0.05, 0.87 ± 0.04. Rigidity index (RI):