Membrane bilayer balance and erythrocyte shape: a quantitative assessment

Abstract

When human erythrocytes are incubated with certain phospholipids, the cells become spiculate echinocytes, resembling red cells subjected to metabolic starvation or Ca2+ loading. The present study examines the mode of binding of saturated phosphatidylcholines and egg lysophosphatidylcholine to erythrocytes and the quantitative relationship between phospholipid incorporation and red cell shape. The phospholipids studied become intercalated into erythrocyte membranes, not simply adsorbed to the cell surface. Spin-labeling and radiolabeling data show that the incorporation of (4 .+-. 1) .times. 106 molecules of exogenous phosphatidylcholine/cell converts discocytes to stage 3 echinocytes with .apprx. 35 conical spicules. This amount of lipid incorporation is estimated to expand the red cell membrane outer monolayer by 1.7% .+-. 0.6%. Calculations of the inner and outer monolayer surface areas of model discocytes and stage 3 echinocytes yield an estimated difference of 0.7% .+-. 0.2%.