Homy cell membranes

Lipid transitions in the skin have been studied by Guia et al. [2] using DSC experiments on fractionated skin samples and solvent extracts. Three major transitions were observed in all samples at 65, 80 and 95 °C as shown in Figure 2, while a small peak (not observed in all samples) is seen at 35 °C. When these samples were cooled and reheated, the transitions at 35 and 65 °C remained unchanged and the peak at 95 °C disappeared, while the peak at 80 C was decreased in size and shifted to a lower temperature. To explain these observations, fractionated samples and samples extracted using solvents were studied. On extraction, all transitions below 90°C disappeared, while the transition at 95 C remained in the extracted sample. On concentration of the extracts, a peak remained at 65 C [2]. When homy cell membranes are prepared from the stratum comeum, the thermal profile shows 2 peaks at 65 and 75 °C (as shown in Figure 3), while a reheat of this sample shows a peak at 65 C and a minor peak at 70 C. 

Figure 3. DSC trace of the homy cell membrane. (Adapted fi-om [2]).

The skin covers a surface area of more than 1 m and is the most readily accessible organ in terms of drug delivery. However, the skin is also the most impermeable of all the epithelial membranes, and, owing to the multiple layers of homy cells in the stratum comeum, it is an excellent barrier to the penetration of hydrophilic substances. Therefore, the rate of passive permeation of proteins is far too slow to be therapeutically significant. 

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