The nature of the frog skin potential.

Summary. 1. The outside of the isolated frog skin in the absence of penetrating anions behaves over a wide range of concentrations as a sodium electrode, while the inward-facing surface behaves like a potassium electrode. 2. A theory concerning the origin of the frog skin potential is put forward based on these observations and the assumption that the active transport of sodium is located at the inward-facing membrane of the epithelial cells. 3. Reasons are given for the hypothesis that the active transport of sodium in reality is a forced exchange of sodium against potassium.