Surface pressure-molecular area isotherms for mixed monolayers of
oxysterols and DOPC or DPPC. DOPC and DPPC monolayer mixtures were
prepared containing 25-HC (A), 27-HC (B), 7α-HC
(C), 7β-HC (D), 7-KC (E), and cholesterol
(F). Molecular areas are plotted versus the mole fraction of
sterol at a constant surface pressure of 5 millinewtons/m (solid
lines). Dashed lines represent the theoretical ideal
(non-interacting) mixture of the pure components. Increased mean molecular
area versus ideal isotherm indicates membrane expansion effects of
sterols, whereas decreased mean molecular area versus ideal isotherm
indicates membrane-condensing effects of sterols.