WATER INCREASES THE FLUIDITY OF INTERCELLULAR MEMBRANES OF STRATUM-CORNEUM - CORRELATION WITH WATER PERMEABILITY, ELASTIC, AND ELECTRICAL-RESISTANCE PROPERTIES

We used the spin label electron spin resonance technique to monitor th e hydration effect on the molecular dynamics of lipids at C-5, C-12, a nd C-16 positions of the allkyl chain. Increase in water content of ne onatal rat SC leads to an increase in membrane fluidity, especially in the region near the membrane-water interface. The effect is less pron ounced deeper inside the hydrophobic core. The reorientational correla tion time at the C-16 position of hydrocarbon chains showed a higher c hange up to similar to 18% (w/w) of water content. This behavior was a ccompanied by an exponential decay both in elastic modulus and electri cal resistance with water content. On the contrary, the segmental moti on at C-5 and C-12 positions of the chain and the permeability constan t increased in the range of around 18% (w/w) up to the fully hydrated condition (58 +/- 7%). Our results give a better characterization of t he fluidity of SC and show that it is the principal parameter involved in the mechanism of the permeability of different compounds through s kin.