Summary Descriptions of the acidic surface pH of mammalian keratinizing epithelia, the "acid mantle”, extend back over a century (Heuss, 1892). With minor racial and species differences (Berardesca et al., 1998), tape stripping reveals that the pH in the upper stratum corneum (SC) approximates 5.0, while the pH of the lower SC (above the outermost nucleated cell layer) approaches neutrality. Thus, the SC develops a progressively acidic environment over a vertical space of less than 100 microns in both human (Ohman and Vahlquist, 1994) and in rodent (Turner et al., 1998) skin. Nevertheless, the function of the acidic pH of the SC is not well understood, and its origin has been attributed to a variety of pathways (Krien and Kermici 2000; Ohman and Vahlquist 1998). Because keratinocytes are known to possess several ion transporters and channels, such as the chloride/bicarbonate antiport (Mauro 1995), which are known to regulate intracellular pH, we asked whether ion transporter(s) could contribute to (extracellular) SC acidification.
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