Reduction of chloride fluxes by amiloride across the short-circuited frog skin

Unidirectional Cl^- fluxes across the short-circuited skin of Rana pipiens varied between 0.06 and 2.29 μeq/hxcm². The Cl^- fluxes were inversely related to the open-circuit potential difference. The Na⁺ short-circuit current (SCC) was not related to the value of the Cl^- fluxes. Amiloride, 10^-4 M, reduced the SCC to near zero, and the unidirectional Cl^- fluxes to about 45% of their control value. A similar reduction in Cl^- fluxes was observed by removal of Na⁺ from the outside bathing solution. The inhibitory effect of amiloride on Cl^- fluxes was also found in skins in which edge damage was avoided. The increase in electrical resistance produced by amiloride was consistent with the blockade of Na⁺ transport plus the reduction in unidirectional Cl^- fluxes. Theophylline, 10^-3 M, increased the Cl^- fluxes previously reduced by amiloride without affecting the zero value of the SCC. Theophylline, 10^-3 M, stimulated the control SCC and increased both unidirectional Cl^- fluxes. Amiloride, 10^-4 M, also reduced the theophylline-stimulated SCC to zero. It is suggested that Cl^- fluxes are mainly transcellular. Theophylline increases Cl^- fluxes possibly by increasing cellular permeability. It is postulated that amiloride may reduce passive Cl^- fluxes across a cellular pathway by altering the electrochemical potential of the cell compartment.