Charge-selective permeability of dermo-epidermal junction: tracer studies with cationic and anionic ferritins

To investigate quantitatively the charge-selective permeability of the basement membrane (BM) of the dermo-epidermal junction (DEJ), tracer experiments using anionic and cationic ferritins were performed on an epidermal sheet, whose lamina densa was exposed on the dermal surface; its dermis was removed with forceps after the treatment of newborn rat skin with 10 mM dithiothreitol. The lamina densa and epidermal components of the sheets were electron microscopically well preserved, and anionic sites were ultrastructurally demonstrated on both the dermal and epidermal aspects of the lamina densa in the DEJ as clusters of cationic ferritins (CF) [isoelectric point (pI) greater than 9.5] or polyethyleneimine particles, indicating that the epidermal sheets were suitable for study of permeability. In tracer experiments, a large number of CF (pI 8.0-9.4) passed the lamina densa and formed clusters on both aspects of the lamina densa and in the intercellular space. The number of native anionic ferritins (NF) (pI 4.1-4.6) passing it was apparently much smaller than that of CF. When the epidermal sheets were pre-treated with protamine sulfate to neutralize the negative charges in the tissue, the number of NF penetrating the lamina densa was significantly larger than the number of those in the untreated sheet. These results indicate that the BM of the DEJ plays a role in a charge-selective filtration, although it is not as selective a barrier as the glomerular basement membrane.