Lipid monolayer expansion by calcium-chlorotetracycline at the air/water interface and, as inferred from cell shape changes, in the human erythrocyte membrane

Chemically induced shape changes of the human erythrocyte may result from cell membrane bending by surface tension changes at the lipid bilayer (Evans, E.A. (1947) Biophys. J. 14, 923-931) implicating differential expansion of the monolayers coupled to form the red cell membrane (Sheetz, M.P. and Singer, S.J. (1974) Proc. Natl. Acad. Sci. U.S.A. 71, 4457-4461). Interacting with calcium, the antibiotic chlorotetracycline (CTC) transforms crenated cells (echinocytes) into cup-shaped ones (stomatocytes), presumably expanding thereby the red cell membrane inner leaflet relative to the outer one (Behn, C., Lübbemeier, A. and Weskamp, P. (1977) Pflügers Arch. 372, 259-268). Whether the Ca-CTC interaction with lipid monolayers may in fact expand the latter, has now been examined by surface tension measurements at the air/water interface. CTC and lipids appeared to compete for the available sites at the air/water interface, contributing additively to its surface pressure. Ca increased both th