PASSIVE ELECTRICAL-PROPERTIES OF HUMAN STRATUM-CORNEUM IN-VITRO DEPENDING ON TIME AFTER SEPARATION

The passive electrical properties of human skin after separation from the body are predominated by the stratum corneum. Skin within a bath m edium (150 mM phosphate buffered saline) at constant temperature (37 d egrees C) exhibits a characteristic change of the passive electrical p roperties with time. Independent of the time the locus in the Z-plane is a depressed semicircular are. The angle between the lines from the center of the are to the points where the locus reaches the real axis remains unchanged. The difference between the high and low frequency r esistivity (R(0) - R(x)) increases over 10 h, reaches a plateau and de cays after 20 h exponentially with a time constant of about 40 h. As m odel for the impedance we used a 5 element electrical circuit (R(0), R (1), R(2), C-1, C-2), describing 3 pathways, (0) the de path (appendag es; R(0)), (1) tortuous pathways around the cell structures (R(1), C-1 ) and (2) direct pathways involving the corneocytes (R(2), C-2). There are characteristic changes with time in the elements of the equivalen t circuit up to about 200 h after excision. Dramatic changes in C-1 an d R(2) at about this time after separation strongly suggests destructi on of the lipid structures. It will be suggested that the use of separ ated human stratum corneum as model for in vivo yields unreliable resu lts after this time.