Ion mobility across human stratum corneum in vivo

The aim of this study was to develop methods to determine ionic transport p arameters, in particular ionic mobilities across human stratum corneum (SC) in vivo. It has been shown previously that the SC, a structurally heteroge neous biomembrane, behaves as a homogeneous barrier to water transport; tha t is, water diffusivity does not vary as a function of position within the SC; in this work, therefore, the question posed was whether ion motion beha ved similarly. Low-frequency impedance measurements (1.61 Hz) reported on t he decrease of SC impedance as the barrier was progressively removed by ser ial adhesive tape stripping. This corresponded to an increase in ion mobili ty of approximately 2 orders of magnitude across the SG (from the external surface to the interior). Therefore, an algorithm was developed from the ab solute impedance data to calculate ion mobility as a function of position w ithin (i.e., depth into) the SC. The mobilities deduced from the algorithm correlated well with water permeability across the SC. The data presented h ere are thought to be the first measurements of ionic mobility across human skin in vivo.