Effects of Na+ and K+ on protein adsorption on red blood cell surface

Effects of Na+ and K+ in plasma on the protein adsorption on red blood cells (RBCs) were studied using fresh human blood and human plasma albumin labeled with a radioactive isotope. Crystalline NaCl and/or KCl were added to blood samples containing labeled albumin so that the plasma osmolarity was increased to final values of 350, 400, and 450 mosmol. The number of albumin molecules adsorbed on the RBCs increased markedly with increases in Na+ but remained unaltered or increased only slightly with increases in K+. The distribution of Na+ and K+ around the RBC membrane was considered to contribute to increasing the adsorption of albumin on the outer surface and to restricting the deposition of hemoglobin on the inner surface with a consequent positive effect on maintaining the stiffness and flexibility of the membrane. In support of this hypothesis the ouabain treatment of RBCs resulted in a decrease in the cellular deformability.