Abstract
Impedance spectroscopy, constant-current iontophoresis, and potentiometry are used to characterize ionic transport in human epidermis in vitro. A resistor (solution resistance) in series with a parallel combination of resistance and capacitance (membrane) is an equivalent circuit for epidermis. Membrane conduction appears to occur in free solution within a restricted volume fraction. The flux of tryptophanamide HCl across epidermis is linear with current, and the efficiency varies from 1 to 5% among skin samples. Electro-osmosis appears to be at best a second-order effect. Iontophoresis is reversible except for a long time tail in the impedance. Within the alkali metals, human epidermis is cation selective, but not size selective.
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