INTERFACIAL HYDRATION OF CERAMIDE IN STRATUM-CORNEUM MODEL MEMBRANE MEASURED BY H-2 NMR OF D2O

H-2 NMR of D2O was used to determine the interfacial hydration of bila yers modelizing the stratum corneum lamellar sheets. Our model membran es are composed of equimolar amounts of ceramide and cholesterol sulfa te and the study was realized at 70 degrees C, temperature for which t he system is in a lamellar phase. The two-site exchange theory applied to the spin lattice relaxation rate, 1/T-1Z, led us to conclude that 1 molecule of ceramide and 1 molecule of cholesterol sulfate bind ca. 11 molecules of D2O. The comparison of this value to previous works re porting that cholesterol sulfate binds ca. 12 molecules of water (Faur e et al., 1996, Biophysical J., 70, 1380-1390), indicates that ceramid e is little hydrated. This result provides a basis to account for the non-existence of a pure lamellar phase with ceramide-water or ceramide -cholesterol-water systems.