Effects of divalent cations on chloride movement across amphibian skin

Effects of the divalent heavy metal ions Cd2+, Co2+, Cu2+, Mn2+, Ni2+, and Zn2+ on pathways for sodium and chloride were assessed on isolated amphibian skin (Rana temporaria and esculenta, Bufo marinus and viridis). It was observed that these agents, in addition to the previously reported stimulation of sodium transport, inhibit chloride-related tissue conductance (gCl) in frog skin with spontaneously high gCl when added to the external incubation medium. Serosal application was ineffective. Half-maximal inhibition of gt occurred at approximately 0.2 mmol/l Ni2+ and Zn2+, 0.5 mmol/l Co2+ and Cd2+, and more than 3 mmol/l Mn2+. The onset of inhibition was rapid, steady state values being reached within 3 min; reversibility was complete with approximately similar time course. Cu2+, which could not be tested at concentrations above 0.1 mmol/l, had only minimal and poorly reversible effect on gCl. Skin of Bufo was virtually insensitive to these metal ions. Microelectrode determinations demonstrate that the decrease of conductance was restricted to a pathway distinct from the principal cells which show, on the contrary, increase of apical membrane conductance originating from stimulation of sodium permeability. The metal ions might be valuable for characterization of the pathway and the mechanism of transepithelial conductive chloride transport.