X-ray microanalysis of cryopreserved human skin to study the effect of iontophoresis on percutaneous ion transport

Purpose, To study at the ultrastructural level which part of the skin is as sociated with percutaneous iodide transport by passive diffusion and iontop horesis. Methods. Following passive diffusion or iontophoresis of iodide, the morpho logy and the ion distribution of the skin was preserved by rapid freezing. The skin was kept frozen until and during examination by transmission elect ron microscopy (TEM) and X-ray microanalysis (XRMA). The intrinsic electron absorbing characteristics of cryopreserved skin allow direct TEM examinati on without additional staining. XRMA can be used to obtain in a relatively nondestructive way in situ information on ion distributions across the skin . Results, After passive diffusion, iodide was mainly found in the stratum co rneum (SC), whereas there was little iodide in the viable epidermis. Iontop horesis up to 300 muA/cm(2) did not significantly affect this distribution. With iontophoresis at 1000 muA/cm(2). the amount of iodide increased drama tically and was equally distributed over the SC and viable epidermis. The p resence of iodide in the SC suggests that iodide is present inside corneocy tes. Conclusions. Iontophoresis up to 300 muA/cm(2) does not significantly pertu rb skin structures in contrast to iontophoresis at 1000 muA/cm(2). The pres ence of iodide inside corneocytes suggests the possibility of transcellular percutaneous iodide transport.