CHANGES IN THE PASSIVE ELECTRICAL-PROPERTIES OF HUMAN STRATUM-CORNEUMDUE TO ELECTROPORATION

The stratum corneum (SC) is the main barrier to molecular and ionic tr ansport across mammalian skin and has been extensively studied by othe rs at low voltages (U-skin(t) < 10 V) in order to partially characteri ze the skin. Here we used one or more exponential pulses (tau(pulse) = 1 ms) and a temperature of 25 +/- 2 degrees C acid found that the low voltage passive electrical properties (impedance) change rapidly and significantly if these pulses result in U-skin,U-0 > 40 V. In contrast , the dynamic resistance (describing passive electrical behavior in a nonlinear range) changes dramatically by application of pulses between 40 V and 80 V and then it settles at levels between 50 Ohm and 100 Oh m. we also found that recovery of the low voltage electrical parameter s after pulsing depends mainly on the voltage, and, for multiple pulse protocols, on the number of pulses. For single pulses of U-skin,U-0 a pproximate to 90 V or less the electrical recovery was almost complete , returning to within 0.90 of the pre-pulse value. In contrast, larger pulses result progressively in decreased recovery. The recovery for p ulses > 90 V revealed several characteristic times, suggesting the inv olvement of different processes. For multiple pulses with U-skin,U-0 > 130 V almost no recovery of the transdermal resistance, R(skin), was evident (returning to < 0.10 of pre-pulse values), i.e., essentially p ermanent changes in the stratum comeum occurred. This is similar to th at of single bilayer membrane electroporation, for which a transition from reversible to irreversible behavior occurs as transmembrane volta ge is increased. Thus, these results are consistent with the hypothesi s that 'high-voltage' pulses cause electroporation within the SC, i.e. , that elevated transmembrane voltages result in creation of new aqueo us pathways ('pores') across SC lipid regions.