Roles of charged groups on the surface of membrane lipid bilayer of human erythrocytes in induction of shape change.

Shape changes of human erythrocytes were induced by partial hydrolysis of phospholipids in the membrane lipid bilayer outer leaflet as a result of the action of exogenous phospholipase A2 or D at pH 7.4 under non-hemolytic conditions. The extent of the shape change caused by phospholipase A2 or D altered drastically when the cells were put into a medium of more alkaline or acidic pH, whereas the shape of untreated cells and cells treated with phospholipase C showed only a mild dependence on pH. These pH-dependent shape changes of intact and phospholipase-treated cells were reversible. Removal of the majority of exposed sialic acid residues from the membrane outer surface by neuraminidase treatment had no influence on the cell shape, or on the pH-dependence of the shape change. These results suggest the importance of the electric charges of polar groups located directly on the surface of the membrane lipid bilayer in inducing cell shape changes.