DIRECT IMAGING OF IONIC PATHWAYS IN STRATUM-CORNEUM USING SCANNING ELECTROCHEMICAL MICROSCOPY

We have used a scanning electrochemical microscope (SECM) to identify the routes of iontophoretic flux of ionic species (Fe2+ and Fe3+) across excised hairless mouse skin. SECM has been used both in the imaging mode, where large two-dimensional areas (approximately 1 mm2) are surveyed to identify regions of high ionic flux, and in the quantitative single trace mode, where flux profiles over a fixed feature are repeatedly measured along one dimension. SECM images indicate that a significant portion of ion flux occurs through shunt pathways in the skin- Images reveal that the spatial density of shunt pathways is greater than that of hair follicles, by up to an order of magnitude, indicating that hair follicles represent a minor contribution to shunt pathways in the skin. A quantitative comparison of the relative fluxes of Fe2+ and Fe3+ through a single pore indicates that Fe2+ is transported at a significantly larger rate than Fe3+. These data represent, to our knowledge, the first direct, chemical-specific identification of transport pathways in skin.