Electric Stimulus Opens Intercellular Spaces in SkinThis work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas, Nanomedicine Molecular Science (No. 2306) from Ministry of Education, Culture, Sports, Science, and Technology of Japan

Iontophoresis is a technology for transdermal delivery of ionic small medicines by faint electricity. Since iontophoresis can noninvasively deliver charged molecules into the skin, this technology could be a useful administration method that may enhance patient comfort. Previously, we succeeded in the transdermal penetration of positively charged liposomes (diameters: 200–400 nm) encapsulating insulin by iontophoresis (Kajimoto, K., Yamamoto, M., Watanabe, M., Kigasawa, K., Kanamura, K., Harashima, H., and Kogure, K. (2011) Int. J. Pharm. 403, 57–65). However, the mechanism by which these liposomes penetrated the skin was difficult to define based on general knowledge of principles such as electro-repulsion and electro-osmosis. In the present study, we confirmed that rigid nanoparticles could penetrate into the epidermis by iontophoresis. We further found that levels of the gap junction protein connexin 43 protein significantly decreased after faint electric stimulus (ES) treatment, although occludin, CLD-4, and ZO-1 levels were unchanged. Moreover, connexin 43 phosphorylation and filamentous actin depolymerization in vivo and in vitro were observed when permeation of charged liposomes through intercellular spaces was induced by ES. Ca2+ inflow into cells was promoted by ES with charged liposomes, while a protein kinase C inhibitor prevented ES-induced permeation of macromolecules. Consequently, we demonstrate that ES treatment with charged liposomes induced dissociation of intercellular junctions via cell signaling pathways. These findings suggest that ES could be used to regulate skin physiology. Background: Although skin is a tight barrier, transdermal liposome delivery is achievable by faint electric stimulus (ES). Results: ES caused rigid nanoparticle penetration into the epidermis, and induced connexin 43 phosphorylation, actin fiber depolymerization and Ca2+-influx. Conclusion: Our data indicate that ES opens epidermis intercellular spaces via intracellular signaling activation. Significance: Skin barrier permeability could be controlled by ES via changes in cutaneous physiological properties.