title: Models of stratum corneum intercellular membranes: 2H NMR of macroscopically oriented multilayers.
abstract: Deuterium NMR was used to characterize model membrane systems approximating the composition of the intercellular lipid lamellae of mammalian stratum corneum (SC). The SC models, equimolar mixtures of ceramide:cholesterol:palmitic acid (CER:CHOL:PA) at pH 5.2, were contrasted with the sphingomyelin:CHOL:PA (SPM:CHOL:PA) system, where the SPM differs from the CER only in the presence of a phosphocholine headgroup. The lipids were prepared both as oriented samples and as multilamellar dispersions, and contained either perdeuterated palmitic acid (PA-d31) or [2,2,3,4,6-2H5]CHOL (CHOL-d5). SPM:CHOL:PA-d31 formed liquid-ordered membranes over a wide range of temperatures, with a maximum order parameter of approximately 0.4 at 50 degrees C for positions C3-C10 (the plateau region). The quadrupolar splitting at C2 was significantly smaller, suggesting an orientational change at this position, possibly because of hydrogen bonding with water and/or other surface components. A comparison of the longitudinal relaxation times obtained at theta = 0 degrees and 90 degrees (where theta is the angle between the normal to the glass plates and the magnetic field) revealed a significant T1Z anisotropy for all positions. In contrast to the behavior observed with the SPM system, lipid mixtures containing CER exhibited a complex polymorphism. Between 20 and 50 degrees C, a significant portion of the entire membrane (as monitored by both PA-d31 and CHOL-d5) was found to exist as a solid phase, with the remainder either a gel or liquid-ordered phase. The proportion of solid decreased as the temperature was increased and disappeared entirely above 50 degrees C. Between 50 and 70 degrees C, the membrane underwent a liquid-ordered to isotropic phase transition. These transitions were reversible but displayed considerable hysteresis, especially the conversion from a fluid phase to solid. The order profiles, relaxation behavior, and angular dependence of these parameters suggest strongly that both the liquid-ordered CER- and SPM-membranes are bilayers. The unusual phase behavior observed for the CER-system, particularly the observation of solid-phase lipid at physiological temperatures, may provide insight into the functioning of the permeability barrier of stratum corneum.
authors: Department of Biochemistry, Faculty of Medicine, University of British Columbia, Vancouver, Canada.
authors: D B
authors: DB
authors: Fenske
authors: J L
authors: JL
authors: Thewalt
authors: M
authors: M
authors: Bloom
authors: N
authors: N
authors: Kitson
mesh_terms: D000818:Animals; D002417:Cattle; D002518:Ceramides; D002784:Cholesterol; D003903:Deuterium; D004817:Epidermis / Q000648:ultrastructure*; D007425:Intracellular Membranes / Q000648:ultrastructure*; D007700:Kinetics; D008081:Liposomes; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008322:Mammals; D008563:Membrane Lipids; D019308:Palmitic Acid; D010169:Palmitic Acids; D013109:Sphingomyelins; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D002518:Ceramides; D008081:Liposomes; D008563:Membrane Lipids; D010169:Palmitic Acids; D013109:Sphingomyelins; D019308:Palmitic Acid; D002784:Cholesterol; D003903:Deuterium