Sphingomyelin/phosphatidylcholine/cholesterol monolayers – analysis of the interactions in model membranes and Brewster Angle Microscopy experiments

In this work the properties of two ternary sphingomyelin/phosphatidylcholine/cholesterol monolayers imitating erythrocyte membrane were studied at various content of sterol. Phosphatidylcholines chosen for experiments differ in the length of sn-1 saturated chain in the molecule (1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine–SOPC vs. 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine – POPC). Langmuir monolayer experiments combined with Brewster Angle Microscopy prove that for both investigated systems the most favorable effect of cholesterol appears at 30% of sterol in the film. However, the interactions between molecules at 50% of sterol are only slightly weaker as compared to those for 1:1:1 films. It was also found that only at higher sterol concentration appear differences in the ordering effect of cholesterol on the systems containing PC molecules of various length of sn-1 saturated chain. Although the differences in the properties of POPC versus SOPC-containing monolayers were found, similarities in the morphology of the respective systems and stoichiometry of thermodynamically the most favorable mixture allow one to conclude that both SM/POPC/Chol as well as SM/SOPC/Chol monolayer can be used to mimic raft systems.

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► Influence of cholesterol on sphingomyelin/phosphtidylcholines films was studied.
► The most favorable properties of the studied ternary systems occur at 30% of sterol.
► Phosphatidylcholines strongly determine the properties of the investigated films.
► Sterol/phosphatidylcholine forces contribute to the overall effect for ternary film.
► Differences in ordering effect of sterol on both films only at higher sterol range.