Electrophoretic and aggregation behavior of bovine, horse and human red blood cells in plasma and in polymer solutions

The electrophoretic mobility of native and glutaraldehyde-fixed bovine, hum an. and horse red blood cells (RBC) was investigated as a function of ionic strength (5-150 mM) and concentration of 464 kDa dextran (2 and 3 g/dl); R BC aggregation in autologous plasma and in dextran solutions was also measu red. In agreement with previous observations, human and horse RBC form stab le rouleaux whereas bovine RBC do not aggregate in either plasma or in dext ran 464 kDa solutions. Electrophoretic measurements showed a species-depend ent adsorption and depletion of dextran that can be theoretically evaluated . Adsorption of polymer is not a prerequisite for RBC aggregation (bovine R BC show the highest amount of adsorbed dextran yet do not aggregate). Aggre gate formation thus occurs as long as the Gibbs free energy difference, giv en by the osmotic pressure difference between the bulk phase and the polyme r-depleted region between two RBC, is larger than the steric and electrosta tic repulsive energy contributed by the macromolecules present on the RBC s urface. With increasing bulk-phase polymer concentration the depletion laye r thickness decreases and the amount of adsorbed macromolecules increases, thereby resulting in an increase of the repulsive component of the interact ion energy and decreased aggregation. We thus view electrophoretic measurem ents of RBC in various media as an important tool for understanding polymer behavior near the red cell surface and hence the mechanisms involved in RB C aggregation.