Imaging regions of transport across human stratum corneum
during high-voltage and low-voltage exposures.
Prausnitz MR; Gimm JA; Guy RH; Langer R; Weaver JC; Cullander C
J Pharm Sci (JO7), 1996 Dec; 85 (12): 1363-70
Scanning confocal fluorescence microscopy was used to image
localized regions of calcein transport across human stratum
corneum during constant low-voltage (iontophoresis) and
pulsed high-voltage exposures. Following an electrical
protocol, imaging revealed regions of fluorescence which
were interpreted as sites where transport of a fluorescent
probe (calcein) into the stratum corneum had taken place.
Electrically-assisted 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 corneum that are
not associated with appendages. Uniquely associated with the
highest voltage pulses used (300 V across the skin) was the
appearance of small, brightly fluorescent areas containing
nonfluorescent interiors, i.e., fluorescent
"rings". We present evidence which suggests that
the dark interiors represent sites through which transport
occurred during pulsing, but where calcein was no longer
present at the time of imaging. Transport of charged
microspheres into the stratum corneum was also observed.