The effect of neutral polymers on the electrokinetic potential of cells and other charged particles: IV. Electrostatic effects in dextran-mediated cellular interactions☆

Abstract Expressions previously developed to describe the electrostatic potential distribution adjacent to a charged surface in the presence of adsorbed neutral polymer are used to derive an expression for the electrostatic repulsive pressure acting between two such surfaces. The repulsion is predicted to increase, to a degree greater than if the potential increase associated with the presence of neutral polymer were due to an equivalent surface charge change. Addition of dextran to erythrocytes suspended in saline can cause cellular aggregation, probably by the mechanism of polymer bridging. Increasing the polymer concentration past that required for aggregation initially increases, then decreases the degree of aggregation until at a critical level of dextran, and a critical zeta potential, the cells dissociate. The disaggregation concentration, but not that required to induce aggregation, is a strong function of ionic strength. The critical zeta potential remains approximately constant, however. Since dextran adsorption is independent of ionic strength, steric stabilization is probably not important here. The data are consistent with a model in which intercellular electrostatic repulsion can be sufficiently enhanced by the presence of adsorbed neutral polymer to overcome the tendency of polymer bridging to aggregate cells.