Non-linearity of molecular transport through human skin due to electric stimulus

The multilamellar bilayer system of the skin's stratum corneum (SC) provide s the main barrier to transdermal transport of ions and charged molecules. Electrically driven transport of charged species at low trans-SC voltages ( U-SC<5 V) occurs predominantly via pre-existing aqueous pathways. In contra st, high voltage, (HV; U-SC>50 V) has been hypothesized to involve electrop oration within the SC's multilamellar bilayer membranes, creating new aqueo us pathways that contribute to a rapid, large increase in transport. Thus, it might be expected that HV-pulses would always increase subsequent iontop horesis. Here we show, however, that for some charged molecules the opposit e occurs, because the low skin resistance due to new aqueous pathways leads to an actual decrease in U-SC for the same applied current, and the transp ort of some, highly charged molecules has a highly nonlinear dependence on U-SC. (C) 2000 Elsevier Science B.V. All rights reserved.