Permeability parameters of the toad isolatedstratum corneum

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Abstract
A technique for isolating thestratum corneum from the subjacent layers of the epithelium was developed which permits studying thestratum corneum as an isolated membrane mounted between half-chambers. The method basically consists of an osmotic shock induced by immersing a piece of skin in distilled water at 50°C for 2 min. When the membrane is bathed on each surface by NaCl-Ringer's solution, its electrical resistance is 14.1±1.3 Ω cm2 (n=10). This value is about 1/100 of the whole skin resistance in the presence of the same solution. The hydraulic filtration coefficient (L p ) measured by a hydrostatic pressure method, with identical solutions on each side of the membrane, is 8.8×10−5±1.5×10−5 cm sec−1 atm−1 (n=10) in distilled water and 9.2×10−5±1.4×10−5 cm sec−1 atm−1 (n=10) in NaCl-Ringer's solution. These values are not statistically different and are within the range of 1/80 to 1/120 of the whole skinL p . Thestratum corneum shows an amphoteric character when studied by KCl diffusion potentials at different pH's. The membrane presents an isoelectric pH of 4.6±0.3 (n=10). Above the isoelectric pH the potassium transport number is higher than the chloride transport number; below it, the reverse situation is valid. Divalent cations (Ca++ or Cu++) reduce membrane ionic discrimination when the membrane is negatively charged and are ineffective when the membrane fixed charges are protonated at low pH.