Time-dependent ultrastructural changes to porcine stratum corneum following an electric pulse

The morphological changes to heat-stripped porcine stratum corneum following an electroporating pulse were studied by time-resolved freeze fracture electron microscopy. Pulses at a supra-electroporation threshold of 80 volts and 300 microseconds were applied across the stratum corneum with a pair of copper plate electrodes, which also served as cooling contacts. Multilamellar vesicles of 0.1-5.5 mm in diameter in the intercellular lipid bilayers of the stratum corneum appeared in less than milliseconds after pulsing. Pulsed samples exhibited aggregations of vesicles, whereas only occasional single vesicles were seen in the unpulsed samples. Aggregates form in less than a millisecond and disappear within minutes after the pulse. Their size ranged from 0.3 to 700 mm2. The size of individual vesicles, aggregate density, and size were analyzed as functions of postpulse time. These aggregate formations seem to be a secondary reaction to the pulse-induced skin permeabilization, determined by the resistance drop and recovery after the pulse. Heating the samples to 65 degrees C also caused vesicle aggregates of similar appearance to form, suggesting that these aggregations are related to the heating effect of the pulse. Hydration is thought to play an important role in aggregate formation.