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, we 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 (PCl/PNa) was reduced from 2.77 +/- 0.21 to 0.48 +/- 0.02 (n = 7, P less than 0.01) or from 2.55 +/- 0.15 to 0.81 +/- 0.11 (n = 6, P less than 0.01), respectively. At 37 degrees C, when the pH of the bathing fluid was reduced from 7.4 to 6.2, the lumen-to-bath flux coefficient for 36Cl (X10(-7) cm2/s) was reduced from 84.8 +/- 7.5 to 20.4 +/- 3.2 (n = 7, P less than 0.01), whereas the value for 22Na was unchanged (27.3 +/- 2.9 vs. 25.3 +/- 2.5, n = 5). 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. Alkalinization had little or no effect on the Cl- permeability. At room temperature, the acid pH did not affect the Cl- permeability. Intracellular acidification with o-nitrophenylacetate also decreased the Cl- permeability.(ABSTRACT TRUNCATED AT 250 WORDS)