IMAGING REGIONS OF TRANSPORT ACROSS HUMAN STRATUM-CORNEUM DURING HIGH-VOLTAGE AND LOW-VOLTAGE EXPOSURES

Scanning confocal fluorescence microscopy was used to image localized regions of calcein transport across human stratum corneum during const ant low-voltage (iontophoresis) and pulsed high-voltage exposures. Fol lowing an electrical protocol, imaging revealed regions of fluorescenc e which were interpreted as sites where transport of a fluorescent pro be (calcein) into the stratum corneum had taken place. Electrically-as sisted transport of calcein, whether enhanced by iontophoresis or high -voltage pulsing, appears to occur through intercellular and, to some extent, transcellular pathways into localized regions of stratum corne um that are not associated with appendages. Uniquely associated with t he highest voltage pulses used (300 V across the skin) was the appeara nce of small, brightly fluorescent areas containing nonfluorescent int eriors, i.e., fluorescent ''rings''. We present evidence which suggest s that the dark interiors represent sites through which transport occu rred during pulsing, but where calcein was no longer present at the ti me of imaging. Transport of charged microspheres into the stratum corn eum was also observed.