Surface adsorption of dextrans on human red cell membrane

Abstract

The adsorption isotherms of dextrans with molecular weights of 40,000 (Dx 40), 74,000 (Dx 70), and 450,000 (Dx 500) were studied on normal red blood cells (RBCs) and RBCs with surface charge depleted by neuraminidase treatment. The adsorption curves on neuraminidase-treated RBCs showed a two-step behavior with secondary adsorption commencing at a bulk concentration of approximately 5 g/100 ml. A plateau adsorption of approximately 9 × 10 −14 g/RBC was attained with bulk concentrations between 12 and 20 g/100 ml. Normal RBCs showed similar adsorption curves as neuraminidase-treated RBCs in Dx 70, as well as in Dx 500, with bulk concentrations up to 5 g/100 ml. Further increases in bulk concentration of Dx 70 or Dx 500 caused greater adsorption on normal RBCs than on neuraminidase-treated RBCs, with a plateau concentration of approximately 15 × 10 −14 g/RBC. Adsorption of Dx 40 on normal RBCs was higher than that on neuraminidase-treated RBCs at all bulk concentrations. These results on surface adsorption have been correlated with the aggregation behavior of the same cell systems. The data offer evidence in support of the hypothesis that surface adsorption of dextrans leads to RBC aggregation by bridging adjacent cell surfaces. The results also indicate that the adsorption of dextrans to RBC surface is a dynamic, reversible process in which the adsorbed molecules exchange readily with the molecules in the bulk or those attached to another cell surface. RBC aggregation is associated with an apparent decrease in surface adsorption as the opposing cell surfaces in the aggregate share their adsorption sites via the same dextran molecules.