Studies of epidermal lipids using electron microscopy

Ruthenium tetroxide fixation has permitted the electron microscopic visualization of intercellular lipid lamellae in thin sections of stratum corneum. This development complements prior freeze-fracture studies of lipid lamellae and has advanced our knowledge about the ultrastructure of epidermal lipids in several ways. We have demonstrated a continuous lipid envelope that surrounds each differentiated stratum corneum cell and the presence of lipid lamellae throughout the entire stratum corneum of three mammalian species, including humans. Wherever lamellae are seen, they are present in multiples of one, two, or more pairs of bilayers, consistent with their formation from fused, flattened lipid vesicles. A unique pattern of lipid monolayers intervening between each pair of bilayers, based on sharing lipid chains between bilayers, has been proposed. In regions where there are no intercellular lamellae between corneocytes, intervening monolayers are in contact with adjacent lipid envelopes that might be involved in stratum corneum cohesion. However, limitations to the ruthenium technique must be overcome before changes in lamellar patterns can be accurately attributed to, or correlated with, changes in permeability brought about by experimental procedures or in diseased states.