Influence of extracellular Cl concentration on Cl transport across isolated skin or Rana pipiens.

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 (J13Cl) and efflux (J31Cl), short-circuit current, transepithelial potential, and conductance (Gm). J14Cl as well as J31Cl were found to have a saturating component and a component which is apparently linear with Cl concentration. The linear component of J31Cl appears only upon addition of Cl to external medium, and about 3/4 of this component does not contribute to Gm. The saturating component of J31Cl is only 5% of total J31Cl with 115mM Cl in the serosal medium. Replacement of 115 mM Cl- in external medium by SO4=, NO3-, HCO3- or I- results in 87-97% reduction of J31Cl, whereas replacement with Br- has no effect. As external Cl concentration is raised in steps from 2 to 115 mM, J13Cl and J31Cl increase by the same amount but J13Cl is persistently 0.15 mueg/cm2hr larger than J31Cl. These results indicate that at least 3/4 of linear components of J13Cl and J31Cl proceed via an exchange diffusion mechanism which seems to be located at the outer cell border. The saturating component of J13Cl 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.