Effect of pH on Cl- transport in TAL of Henle's loop

To further characterize the mechanism of Cl- transport across the hamster thin ascending limb (TAL) of Henle's loop, the authors examined effects of pH on Cl- permeability as determined by either the choline chloride diffusion voltage or the lumen-to-bath 36Cl flux in the isolated segments perfused in vitro. When pH of the bathing fluid or the perfusate was reduced from 7.4 to 5.8, the Cl--Na+ permeability ratio was reduced from 2.77 ± 0.21 to 0.48 ± 0.02 or from 2.55 ± 0.15 to 0.81 ± 0.11, respectively. At 37 degree C, when the pH of the bathing fluid was reduced from 7.4 to 6.2, the lumen-to-bath flux coefficient for 36Cl was reduced from 84.8 ± 7.5 to 20.4 ± 3.2, whereas the value for 22Na was unchanged. From the pH titration curves for PCl/PNa, pKa values for proton binding were 6.31 and 5.78, and Hill's coefficients were 2.1 and 2.3 on the basolateral side and on the luminal side, respectively. Intracellular acidification with o-nitrophenylacetate also decreased the Cl- permeability. They conclude that (1) Cl- transport across the TAL is mediated by a process that is sensitive to ambient pH, (2) the basolateral side is more sensitive to pH, (3) the proton binding exhibits positive cooperativity in the modulation of Cl- transport, and (4) intracellular pH might also modulate Cl- transport