Effects of anion transport inhibitors and ion substitution on Cl- transport in TAL of Henle's loop.

To identify the mechanism of Cl- transport across the thin ascending limb of Henle's loop (TAL), we examined effects of anion transport inhibitors and ionic substitution in the isolated segments of hamsters using the in vitro microperfusion technique. 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) at 10(-3) M changed the NaCl diffusion voltage (Vt) to the orientation that corresponds to the decrease in the Cl(-)-Na+ permeability ratio when it was added either to the bath or to the lumen. DIDS, added to the bath or to the lumen decreased the lumen-to-bath flux coefficient for 36Cl, KCl-(1----b) (X10(-7) cm2/s), from 74.5 +/- 2.1 to 17.9 +/- 3.6 and from 77.7 +/- 3.6 to 51.1 +/- 5.4, respectively, whereas it had little effect on the flux coefficient for 22Na, KNa+(1----b). Elimination of HCO3- slightly increased rather than decreased both NaCl diffusion potential and KCl-(1----b), indicating that Cl- transport is independent of HCO3- transport. Phloretin at 10(-3) M inhibited both diffusion potential and KCl-(1----b) to a similar extent as DIDS did. KNa+(1----b) was also changed little. The inhibitory effect of phloretin was rapid and reversible. Phloridzin was ineffective. Furosemide added to the bath at 10(-3) M decreased Vt and KCl-(1----b) from 29 +/- 0.9 to 5.3 +/- 0.7 mV and from 75.7 +/- 3.9 to 62.8 +/- 4.1 X 10(-7) cm2/s, respectively; but it was ineffective when added to the lumen. Elimination of Na+ caused only a small decrease in KCl-(1----b) from 119.2 +/- 6.9 to 107.3 +/- 8.5 X 10(-7) cm2/s. Elimination of K+ and addition of Ba2+ did not change KCl-(1----b). From these observations, we conclude that Cl- transport across the TAL is distinct from Na+ and is not coupled with Na+, K+, or HCO3-.