Water binding and mobility in the phosphatidylchlone/cholesterol/water lamellar phase.

Measurements of hydration and water self diffusion in lamellar phases of the ternary system: phosphatidylcholine/cholesterol/water have been made using pulse NMR relaxation methods. Systems containing phosphatidylcholine and cholesterol in a 1:1 mol ratio with varying water contents are studied at 20.5 degrees C. The results indicate that 12 water molecules corresponds to complete hydration of the phosphatidylcholine/cholesterol unit, and in the region of this hydration a 4-fold decrease in water diffusion occurs. The nature of the bound water and its relationship to phase stability and overall water mobility in the system are discussed. It is concluded that at the stoichiometric composition the diffusion decreases due to the relative immobility of the bound water. The implications in terms of permeability regulation in the aqueous channels by water content and hydration are cited.