Expansion of phosphatidylcholine and phosphatidylserine/phosphatidylcholine monolayers by differently charged amphiphiles

The degree and time-course of expansion of palmitoyloleoylphosphatidylcholi ne (PC) and bovine brain phosphatidylserine (PS)/PC (75:25, mol/mol) monola yers at 32 mN/m caused by differently charged amphiphiles (detergents) adde d to the sub-phase buffer (pH 7.4, 22 degreesC) were followed. Amphiphiles were added to the sub-phase at a concentration/monolayer area corresponding to the concentration/erythrocytes surface area where sphero-echinocytic or sphero-stomatocytic shapes are induced (0.46-14.6 muM). Nonionic, cationic and anionic amphiphiles expanded the PS/PC monolayer significantly more (1 .7-4.2 times) than the PC monolayer. A zwitterionic amphiphile expanded bot h monolayers to a similar extent. The initial rate of monolayer-expansion w as higher for all amphiphiles (1.7-20.4 times) in the PS/PC monolayer than in the PC monolayer. It is suggested that hydrophobic interactions govern the intercalation of a mphiphiles into monolayers, and that monolayer packing, modulated by phosph olipid head group interactions and alkyl chain saturation, strongly influen ce amphiphile intercalation. A possible relation between the monolayer-expa nding effect of amphiphiles and their effect on erythrocyte shape is discus sed.