title: Study of water permeability through phospholipid vesicle membranes by 17O NMR.
abstract: Vesicle suspensions of up to 5% egg lecithin and 2.5% cholesterol have been found to have no effect on the NMR relaxation times of 17O from water. Addition of 1-5 mM Mn2+ to an equimolar vesicle suspension of egg lecithin and cholesterol permitted resolution of the free induction decay into two exponential components, a fast one arising from the external water and a slow one arising from the intravesicular fluid.  From the rates of relaxation the mean life time of the water molecules within the vesicles was calculated to be 1+/- 0.1 ms at 22 degrees C. The size of the vesicle was estimated from electron micrographs to be about 500 A in diameter. These data yield an equilibrium water permeability, Pw, of about 8 mus-1 for the vesicle membranes. From the temperature dependence of Pw an activation energy of 12+/-2 kcal/mol was obtained. The longitudinal relaxation time (T1) of water within vesicles remained the same as in pure water.
mesh_terms: D001665:Binding Sites; D001692:Biological Transport; D002784:Cholesterol; D009682:Magnetic Resonance Spectroscopy; D008345:Manganese; D008433:Mathematics; D008567:Membranes, Artificial; D008854:Microscopy, Electron; D008954:Models, Biological; D008968:Molecular Conformation; D010539:Permeability; D010713:Phosphatidylcholines; D013696:Temperature; D013816:Thermodynamics; D014867:Water
chemical_list: D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D014867:Water; D008345:Manganese; D002784:Cholesterol