Detection of the electrical surface charge induced by treatment of the membrane lipid bilayer of human erythrocytes.

Abstract

ABSTRACT.The lipid bilayer of the membrane of human erythrocytes from which most sialic acid residues on the outer surface had been removed was digested by phospholipase from outside the medium or treated by the incorpora- We reported previously that a change in the shape of human erythrocytes is induced by in vitro treatments of the membrane lipid bilayer (1,8) and that after some treatments which liberate or form anionic head groups in the lipid molecules exposed on the outer surface of the membrane, the degree of the change in shape became markedly dependent on the pH of the medium (8, 9). We assumed that the dissociation of these polar head groups in an appropriate pH range might increase the repulsion among the charged groups or increase the hydration around these groups. This in turn would result in the asymmetric expansion of the outer half of the lipid bilayer, relative to the inner half because the mechanism for the change in the shape of the erythrocytes can be explained by the asymmetric expansion of one half of the bilayer according to the "bilayer couple hypothesis" (7) . To prove the validity of our assumption, we have demonstrated by cell electrophoresis that these treatments do cause the increased exposure of dissociable head groups on the bilayer outer surface, and that these groups become negatively charged in the pH range of their dissociation. We used desialydated erythrocytes which had been treated with neuraminidase to remove most of the sialic acid residues on their outer surfaces because the abundant negative charges of these residues must prevent the electrophoretic detection of the relatively weak negative charges contributed by the polar head groups of the membrane lipids.

Electrostatic Contributions to Carcinogenesis

“…This surface charge density σ C/m 2 (Coulombs per square meter) is due largely to ionized carboxyl groups of sialic acid residues [7] [8] [9]. Net surface negativity is primarily a function of the density of these anionic groups anchored in the membrane at the cell surface, but it also depends on the pH and ionic strength of the surrounding medium [10]. Other acidic groups may reside at the cell surface [11], and some cells have anionic groups associated with RNA at their periphery [12].…”