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

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Abstract
Unidirectional Cl- fluxes across the short-circuited skin of Rana pipiens varied between 0.06 and 2.29 .mu.eq/h .cntdot. cm2. 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 Cl- fluxes by about 50% while reducing the stimulated SCC to zero. Cl- fluxes may be mainly transcellular. Theophylline increases Cl- fluxes possibly by increasing cellular permeability. Amiloride may reduce passive Cl- fluxes across a cellular pathway by altering the electrochemical potential of the cell compartment.

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