Molecular models of the intercellular lipid lamellae from epidermal stratum corneum

The purpose of the present study was to test the hypothesis that the 13 nm trilamellar repeat units within the intercellular spaces of epidermal stratum corneum are composed of lamellae with alternating 5-3-5 nm dimensions as presented in previous models [J. Invest. Dermatol. 92 (1989) 251, P.W. Wertz, Integral lipids in hair and stratum corneum, in: P. Jolles, H. Zahn, H. Hocker (Eds.), Hair: Biology And Structure, Birkhauser Verlag, Basel, 1996, pp. 227-238, Acta Derm.-Venereol., Suppl. 208 (2000) 23]. Electron density profiles were measured from transmission electron micrographs of porcine stratum corneum prepared using ruthenium tetroxide [J. Invest. Dermatol. 92 (1989) 251]. Center-to-center distances of adjacent electron-dense bands as well as adjacent lucent bands were measured. Dense band center-to-center measurements were consistent with a 5-3-5 nm arrangement. However, lucent band center-to-center measurements revealed uniform lamellar thickness. It is suggested that linoleate chains in the central lamella reduce more ruthenium than the predominantly saturated chains in the outer lamellae and that this additional reduced ruthenium accumulates under the polar head group regions. A similar phenomenon involving the sphingosine moieties of the covalently bound omega-hydroxyceramide molecules accounts for the three-band pattern seen between the ends of adjacent corneocytes. It is concluded that the component lamellae of the several types of 13 nm trilamellar units of the stratum corneum are all of equal thickness.