Effects of Cd++ on short-circuit current across epithelial membranes. I. Interactions with Ca++ and vasopressin on frog skin.

Cadmium ion (Cd++) significantly increased potential difference (PD) and short-circuit current (SCC) across isolated frog skin when added to the outside Ringer's solution at 10(-4), 10(-3) and 5 X 10(-3) M concentration. Resistance was reduced by 10(-4) 7 cd++ but not significantly changed by the higher concentrations. When SCC was first stimulated by vasopressin, 10(-4) and 10(-3) M Cd++ produced additive stimulation which was reversible by washing with Cd++-free Ringer's. If SCC was first stimulated by Cd++, further stimulation by vasopressin was additive with 10(-4)M Cd++ but dompletely inhibited by 10(-3)M Cd++. Elevating the calcium ion (Ca++) concentration of the outer Ringer's from 10(-3) M to 5 X 10(-3)M or 10(-2)M prior to Cd++ treatment did not reduce the magnitude of SCC stimulation by Cd++. Removal of Ca++ from the outside Ringer's with 2 X 10%-3)M EDTA increased SCC as predicted. Subsequent addition of 5 X 10(-3) M Cd++ drastically reduced SCC below control levels while equimolar concentrations of Cd++ and EDTA reduced SCC only to control levels. These results suggest that Cd++ interacts with the components of the apical plasma membranes of epithelial cells which are associated with the stimulation of SCC by vasopressin and Ca++ removal and may be a useful probe for elucidating these components.