  By means of atomistic molecular dynamics simulations, we study
cholesterol-DPPC (dipalmitoyl phosphatidylcholine) bilayers of different
composition, from pure DPPC bilayers to a 1:1 mixture of DPPC and cholesterol.
The lateral-pressure profiles through the bilayers are computed and separated
into contributions from the different components. We find that the pressure
inside the bilayer changes qualitatively for cholesterol concentrations of
about 20% or higher. The pressure profile then turns from a rather flat shape
into an alternating sequence of regions with large positive and negative
lateral pressure. The changes in the lateral-pressure profile are so
characteristic that specific interaction between cholesterol and molecules such
as membrane proteins mediated solely via the lateral-pressure profile might
become possible.
