Effect of cadmium on active sodium transport by the abdominal skin and the isolated epidermis of the bullfrog: differences in effects between epidermal and dermal cadmium applications.

Epidermal application of 2 mM-cadmium (Cd2+) to the SO42---Ringer's solution bathing the whole frog skin increased its short circuit current (SCC) significantly, whereas the dermal application did not, in most cases. When Cd2+ was applied to the epidermal side, the uptake of cadmium by the skin was approximately 150 microM/kg wet weight, but the uptake by the skin from the dermal side was about eight times as large. In the isolated epidermis, the epidermal application of Cd2+ increased the SCC, whereas the dermal application decreased it. The amount of cadmium taken up by the isolated epidermis was approximately the same when the cation was applied to either epidermal or dermal side. These seemingly contradictory results can probably be explained by the barrier-hypothesis which is supported by the results of an electron probe X-ray microanalysis. In the case of the epidermal application, the junction between s. corneum and s. granulosum may act as an outside barrier for cadmium translocation. For the dermal application of Cd2+, the sieve layer in the dermis, where a large amount of calcium is deposited, may probably exert its effects as an inside barrier by the mechanism of Cd-Ca exchange process. Tela subcutanea, the basement membrane and its adjacent tissue may be also inside barriers, though their role as a diffusion barrier may be considered to be weaker than that of the sieve layer.