K+-permeability of the outer border of the frog skin (R. temporaria).

Skins from Rana temporaria, investigated with microelectrode techniques in the absence of Na uptake across the outer border (Na-free epithelial solution or amiloride), were found to be permeable to K+ at the apical membrane in 10-20% of the experiments. Full development of the K+-permeable state requires the absence of Na+ uptake for certain periods of time, which suggests that the K+-permeability of the apical membrane is higher at lower intracellular [Na]. The addition of Ba++ reduces the K+-permeability of the apical membrane. These skins may provide a model for the study of transcellular K+ movements.