Effect of amiloride on chloride transport across amphibian epithelia

Amiloride is found to inhibit chloride exchange diffusion in toad skin and passive chloride transport in frog skin. In both tissues, chloride transport is reactivated by substituting with KCl-Ringer's on the inside, so the effect of amiloride on chloride transport is secondary to its well-known inhibition of sodium transport. Removal of chloride from the outside bathing solution inhibits chloride outflux in both tissues. This is easy to explain in the case of the toad skin where chloride transport under short-circuit conditions occurs as exchange diffusion. In the frog skin this transeffect indicates that the chloride concentration at a location very near the outer surface is of significance for chloride permeability. The possibility is discussed that the chloride concentration in the outward facing membrane, or in compartments near to it, regulates chloride fluxes across frog skin.