IONTOPHORETIC TRANSPORT ACROSS A SYNTHETIC MEMBRANE AND HUMAN EPIDERMAL MEMBRANE - A STUDY OF THE EFFECTS OF PERMEANT CHARGE

The effects of permeant charge (z) on iontophoretic-enhanced transport were investigated with synthetic Nuclepore membranes and with human e pidermal membranes using a four-electrode potentiostat with side-by-si de diffusion cells. The modified Nernst-Planck model (Nernst-Planck th eory with an additional transport term to correct for the effect of th e convective solvent flow due to electroosmosis) was first examined in a Nuclepore membrane system with model permeants calcein (z = -4), sa licylate (z = -1), and a series of polystyrene sulfonates (from monome r to molecular weight of similar to 8000 with a z range of -1 to simil ar to -40). The flux enhancement (E) for each permeant was determined at 470 mV. Mannitol (a neutral molecule) was used as a probe to determ ine a correction for convective solvent flow under the same applied vo ltage conditions. Good agreement between the experimental results and the predictions from the modified Nernst-Planck model was found for ca lcein, salicylate, and polystyrene sulfonates up to molecular weight o f similar to 1800 (z similar to -8). The flux enhancements for the hig her molecular weight polystyrene sulfonates with greater z values were more than a factor of three lower than theoretical predictions; the e lectrophoretic effect and counterion binding to the permeants are prop osed as possible explanations for these discrepancies between experime nt and the modified Nernst-Planck theory. In the studies with human ep idermal membranes, iontophoretic flux enhancements for calcein, salicy late, and taurocholate were determined at 250 and/or 470 mV. The flux enhancements were generally consistent with the results calculated fro m the modified Nernst-Planck model.