Influence of constant current iontophoresis on the impedance and passive Na+ permeability of excised nude mouse skin.

The impedance of excised nude mouse skin was determined over the frequency range 0.2-2500 Hz. Impedance versus frequency plots were obtained for skin which had undergone progressive hydration over a period of 8 h, and for similarly hydrated skin which, during the hydration period, was also exposed to a current density of 0.16 mA cm-2 for 1 h. The parallel frequency-dependent skin resistance and capacitance were then calculated from the impedance data. The skin resistance, at 0.2 Hz, for skin exposed to the iontophoretic current decreased by a factor of approximately 5 compared with that observed for skin which had undergone hydration, implying that the current had altered the ion conducting pathways of the skin. In addition, the Na+ flux was measured and shown to be linearly correlated (r = 0.99) with the inverse of the impedance of the skin at 0.2 Hz. This implies that the low frequency impedance of the skin is a measure of the passive ion permeability of the skin, and that this technique can be used as a noninvasive way to assess the relative effects of different types of iontophoretic current on the skin.