Membrane lipid bilayers classification

Mammalian stratum comeum (SC) consists of highly comified cells embedded in a matrix of lipid bilayers (Matoltsy, 1976). These extracellular lipids are arranged in the form of multiple lamellae that are believed to constitute the major barrier to percutaneous penetration (Michaels et al., 1975 Elias, 1983). As discussed, the SC lipid membranes are made up predominantly of ceramides, cholesterol, free fatty acids, cholesteryl sulfate, and small amounts of some less well-defined nonpolar components (Gray et al., 1982 Yardley and Summerly, 1981). Six groups of ceramides have been characterized in porcine SC, as shown in Fig. 4 (Wertz et al., 1983). This classification was based on the polarity of the ceramides, with ceramide 1 being the least polar. 

The structural classification of synthetic ion channels and pores differentiates between (macro)molecules and different classes of supramolecules [2]. Unimolec-ular synthetic ion channels and pores are usually hollow, often helical (macro)mol-ecules that are long enough to span common lipid bilayer membranes (2-4 nm). 

---