Effects of cadmium on the active transport of sodium by the abdominal skin of a bullfrog (Rana catesbeiana).

Effects of Cd on the active transport of Na in SO4-Ringer's solution on the abdominal skin of a bullfrog (Rana catesbeiana) were investigated. The short circuit current (SCC), potential difference (PD), and Na flux were determined. The skin resistance (Rm), the electromotive force of active Na transport (Ena), and the resistance to the active Na current (Rna) were calculated from the measured data. The application of Cd to the epidermal side at 2 mM was more effective in increasing SCC than that to the dermal side at the same concentration. The time course of changes in SCC induced by Cd were classified into three types: (I) a simple increase in SCC during Cd application, (II) an early decrease followed by an increase in SCC, and (III) a decrease in SCC except for a small increase in the initial short period. Type I response was observed in the majority of cases (about two-thirds). Types II and III were observed in 7 and 32 percent of 28 cases, respectively. The Cd-induced changes in SCC were analyzed on the basis of changes in ENa and RNa. In Type I, the increase in SCC was due to a remarkable decrease in RNa without an appreciable change in ENa (since SCC = ENa/RNa). In Types II and III, the changes in SCC in the early and the later stages could be explained by the differences in the extents to which ENa and RNa decreased. The experimental and calculated ratios of PDcd to PDcontrol in these stages were in good agreement with each other.