The effect of cholesterol on the bending modulus of DOPC bilayers: re-analysis of NSE data

The effect of cholesterol on the bending modulus K_C of DOPC lipid bilayers has been controversial. Previous analysis of dynamic neutron spin echo (NSE) data reported that 50% cholesterol increased K_C by a factor of three in contrast to earlier studies using four different static methods that reported essentially no increase. We reanalyzed the previous NSE data using new developments in NSE analysis. We find that the same NSE data require non-zero viscosity in pure DOPC and they are consistent with no increases in K_C with cholesterol. Instead, we find more than a five-fold increase in the membrane viscosity η_m. We have further added diffusional softening dynamical theory to the basic phenomenological model. This generally decreases the 5-fold increase in viscosity, but the NSE data are not sufficient to determine by how much.