Intrinsic stiffening and dynamic softening by cholesterol

The stiffness of a lipid bilayer is the key mechanical constant for understanding membrane reshaping in the cell. Cholesterol, present in the plasma membrane at high levels, has ambiguous effects on stiffness that appears to depend strongly on the lipid matrix. Inferred from long length and time scale experiments (e.g., X-ray diffraction and GUV fluctuations) cholesterol has little effect on a simple di-oleoyl-phosphatidylcholine (DOPC) bilayer. Inferred from dynamic experiments limited to nanosecond timescales (e.g., neutron spin echo) DOPC bilayers appear stiffer. In a saturated chain matrix like DMPC, both x-ray and neutron spin echo experiments indicate stiffening.