Cholesterol Suppresses Pressure-induced Interdigitation of Dipalmitoylphosphatidylcholine Bilayer Membrane

We investigated the effect of cholesterol on the pressure-induced interdigitation of dipalmitoylphosphatidylcholine (DPPC) bilayer membrane by fluorescence technique using 6-propionyl-2-(dimethylamino)naphthalene (Prodan) as a probe. The interdigitation pressure (IP), minimum pressure required for the bilayer interdigitation, was elevated with increasing cholesterol composition (Cch) up to ca. 2 mol %. Further increase of Cch did not give any effect on the IP value. Finally, the interdigitation could not be observed at Cch=8 mol %. Constructed pressure–Cch phase diagram at 50 °C suggests that the retardation and the abolition of the interdigitation are attributable to an interference effect and eventual formation of ordered molecular orientation induced by cholesterol.