Deviating flux ratios for Na+ in ouabain-treated frog skin

Unidirectional Na+ fluxes across ouabain-treated frog skins were measured at different applied voltages. The calculated influx/efflux ratios appear to deviate markedly from Ussing's flux-ratio equation. This means that interactions of Na+ ions with some component in the system occur. Possible mechanisms, responsible for this phenomenon, are indicated.