title: Determination of the pH gradient across the stratum corneum.
abstract: The objective of this work was to determine the pH gradient profile across hairless mouse stratum corneum (SC) using ratiometric laser scanning confocal microscopy imaging and direct pH measurement with a flat surface electrode. Dual-emission ratiometric imaging used the fluorophore, carboxy seminaphthorhodafluor-1, which displays a pH-dependent shift in its emission spectrum. The assay developed was unsuccessful, however, because (i) the pKa of seminaphthorhodafluor (approximately 7.5) makes it insufficiently sensitive to the normal pH gradient (4-7.4) across mammalian SC, and (ii) the unexpectedly high buffering capacity of the skin precluded a meaningful calibration of the system. In the second method, pH measurements with a flat surface electrode were recorded as the hairless mouse SC was progressively tape stripped. In the superficial SC, the pH remained relatively constant (approximately 5.9); further removal of the barrier resulted in a steady increase in pH to approximately 7. In conclusion, improved methodology is clearly required to characterize precisely the pH profile across the SC.
authors.affiliation: Department of Biopharmaceutical Sciences, University of California, San Francisco, USA.
authors.forename: N G
authors.initials: NG
authors.lastname: Turner
authors.forename: C
authors.initials: C
authors.lastname: Cullander
authors.forename: R H
authors.initials: RH
authors.lastname: Guy
mesh_terms: D000818:Animals; D001578:Benzopyrans; D004563:Electrochemistry; D004817:Epidermis / Q000378:metabolism*; D005260:Female; D005456:Fluorescent Dyes; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008812:Mice, Hairless; D018613:Microscopy, Confocal; D009284:Naphthols; D012235:Rhodamines
chemical_list: D001578:Benzopyrans; D005456:Fluorescent Dyes; D009284:Naphthols; D012235:Rhodamines; C091666:seminaphthorhodaminefluoride; D006859:Hydrogen