Role of electrical and mechanical properties of red blood cells for their aggregation

In previous investigations using a novel electro-optical technique, we found that red blood cells (RBC) orientation and disorientation in an alternating electric field (1 kHz) is influenced by their deformability, conformational state of their glycocalyx and by the concentration and molecular weight of neutral macromolecules (dextran and polyethylene glycol) in the suspending medium. In the present study, we have altered the surface charge density of the RBC by treatment with neuraminidase and their deformability by fixing them with glutaraldehyde. We quantified these changes by means of electro-optics and observed their influence on the aggregation behaviour of the RBC in phosphate buffered saline, containing dextran 70 000 using the zeta sedimentation ratio technique (ZSR). For comparison, the electrical properties of RBC were also estimated by cell electrophoresis and by biochemical analysis of sialic acid content of their membranes. A negative linear relationship with near-equal slopes between cell electrical polarizability estimated electro-optically, membrane sialic acid content, cell electrophoretic mobility and the aggregation indices was found. The quantification of RBC deformability (rigidity) with the electro-optical method resulted in a linear relationship between aggregation indices and mechanical property. The comparison of the relative influence of mechanical and electrical factors clearly indicates the stronger influence of the electrical components on the aggregation of the RBC for the present experimental setup. The obtained results are discussed from the viewpoints of the two mechanisms proposed for dextran induced aggregation, i.e. the bridging model and the depletion model.