Lateral segregation of membrane lipids and formation of stable rod-shaped membrane projections in erythrocytes treated with long-chain alcohols.

Human erythrocytes, incubated with sonicated dispersions of phosphatidylcholine, cholesterol and saturated straight-chain alcohols (C16-C18) develop stiff, rod-shaped, hemoglobin-containing membrane projections within 120 min. The number of these 'rods' varies (1-3 per cell), they reach a length of up to 14 microns (twice the cell diameter) and a thickness of 0.3-1.0 microns. 'Rods' may be separated from 'residual cells' by shear flow and centrifugation without severe hemolysis. Lipid analyses carried out on residual cells and rods indicate lateral segregation of the phospholipids of the outer leaf of the membrane lipid bilayer (phosphatidylcholine and sphingomyelin) and of the alcohol applied. Phosphatidylcholine accumulates in the residual cells, sphingomyelin and the alcohol in the rods. No differences in membrane protein patterns were observed between rods and residual cells. The rod-shape is dependent on the presence of the alcohol, extraction of the alcohol converts rods into hemoglobin-containing spheres without lysis. The formation of rods, which is indicative of a lateral phase separation, is discussed in terms of lipid-lipid interactions and with respect to parameters determining the shape of cells.