Selectivity of ion permeability across ascending thin limb of Henle's loop: interaction of Cl- and other halogens with anion transport system.

In hamster ascending thin limb of Henle's loop (ATL) perfused in vitro, we examined halogen selective permeability and effects on Cl- transport. Relative permeabilities for halogens to sodium (PX/PNa) were determined by single salt dilution voltage. (PF/PNA, PCl/PNa, PBr/PNa and PI/PNa were 0.47 +/- 0.09, 3.23 +/- 0.22, 3.23 +/- 0.26, and 0.47 +/- 0.09, respectively. Simultaneous determination of 36Cl and 125I fluxes confirmed that addition of 10(-4) M 5-nitro-2-(3-phenyl-propylamino)-benzoate (NPPB), a Cl- channel blocker, to the bath decreased the flux coefficient for 36Cl (10(-7) cm2/s) from 67.0 +/- 11.7 to 29.5 +/- 7.9 without affecting that for 125I. NPPB also reduced both PCl/PNa and PBr/PNa from 2.67 +/- 0.20 to 0.95 +/- 0.12 and from 2.33 +/- 0.24 to 1.32 +/- 0.12, respectively. Addition of 100 mM Cl- or I- decreased 36Cl flux coefficient from 124.8 +/- 14.3 to 87.7 +/- 13.0 or to 41.0 +/- 11.6 without affecting that for 125I. All other halogens and SCN- also exhibited inhibitory effects on 36Cl flux. These findings support the hypothesis that the putative Cl- channel in the ATL is highly permeable to both Cl- and Br- but less permeable to I-, F-, and SCN-. They suggest that there are at least two functionally distinct components in the process of Cl- transport across the ATL, the binding site and the selective barrier. All halogens may compete against Cl- at the binding site.