The membrane contact seam in adhesion of erythrocytes by polymers

Abstract

The influence of polymers on human erythrocyte membrane-membrane interactions has been examined. Particular attention was paid to the contact seam, i.e. whether the membranes formed spatially periodic local contact points or lay parallel to each other in a continuous seam. Exposure to the polycation poly- l-lysine resulted in a spatially periodic contact seam for all normal control cells. The lateral separation distance of contact points decreased from 1.6 μm to a lower limiting value of 0.8 μm as the concentration of 220 kDa polycation was increased threefold from the adhesion threshold value. Reduction of the glycocalyx sialic acid content by neuraminidase pretreatment decreased polycation interaction sites, reduced cell adhesion and resulted in an increased lateral separation of contact points. Normal cells agglutinated by the neutral polymer dextran showed a plane parallel contact seam, in contrast to the results with polylysine. Cells pretreated with pronase and then exposed to 72 kDa dextran in 145 mM saline showed a mode response of lateral contact separations in the range 0.8–1.2 μm. Suspensions of such pretreated cells in 120 mM saline, where electrostatic repulsion was increased, showed a change towards longer contact spacings. The experiments identify situations where either electrostatic or glycocalyx repulsion can dominate membrane interaction. The results show that changes in physicochemical conditions which increase net attraction lead to shorter lateral contact separation. The results are consistent with the interfacial instability model for the generation of local contacts.