Influence of extracellular Cl concentration on Cl transport across isolated skin ofRana pipiens

Summary

The effect of changes in Cl concentration in the external and/or serosal bath on Cl transport across short-circuited frog skin was studied by measurements of transepithelial Cl influx (J ^Cl₁₃ ) and efflux (J ^Cl₃₁ ), short-circuit current, transepithelial potential, and conductance (G _m).J ^Cl₁₃ as well asJ ^Cl₃₁ were found to have a saturating component and a component which is apparently linear with Cl concentration. The linear component ofJ ^Cl₃₁ appears only upon addition of Cl to external medium, and about 3/4 of this component does not contribute toG _m. The saturating component ofJ ^Cl₃₁ is only 5% of totalJ ^Cl₃₁ with 115mm Cl in the serosal medium. Replacement of 115mm Cl⁻ in external medium by SO ⁼₄ , NO ⁻₃ , HCO ⁻₃ or I⁻ results in 87–97% reduction ofJ ^Cl₃₁ , whereas replacement with Br⁻ has no effect. As external Cl concentration is raised in steps from 2 to 115mm,J ^Cl₁₃ andJ ^Cl₃₁ increase by the same amount butJ ^Cl₁₃ is persistently 0.15 μeq/cm² hr larger thanJ ^Cl₃₁ . These results indicate that at least 3/4 of linear components ofJ ^Cl₁₃ andJ ^Cl₃₁ proceed via an exchange diffusion mechanism which seems to be located at the outer cell border. The saturating component ofJ ^Cl₁₃ is involved in active Cl transport in an inward direction, and there is evidence suggesting that Cl uptake across outer cell border, which proceeds against an electrochemical gradient, is electroneutral but not directly linked to Na.