Intracellular pH in isolated rat renal papillary thin limbs of Henle's loop

Intracellular pH (pH(i)) was measured in isolated, nonperfused and perfused rat papillary thin limbs of Henle's loops in N-2- hydroxyethylpiperazine-N'-2-ethansulfonic acid (HEPES)- or HEPES/bicarbonate- buffered medium at pH 7.4 using the pH-sensitive fluorescent dye 2',7'-bis(2- carboxyethyl)-5,6-carboxyfluorescein (BCECF). Resting pH(i) was about 6.7 in descending thin limbs (DTL) and about 6.9 in ascending thin limbs (ATL), even with a medium pH of 7.4. These values appeared to reflect the acid pH of the blood in the neighboring vasa recta found in vivo. The resting pH(i) did not differ whether or not the medium contained bicarbonate although the total buffering capacity of the tubule cells was increased in the presence of bicarbonate. In nonperfused DTL and ATL, pH(i) was further acidified following an NH₄Cl pulse. The rate of recovery of pH(i) from this level to the resting pH(i) was reduced by Na⁺ removal from the bath in both DTL and ATL and by the addition of ethylisopropylamiloride (EIPA) to the bath in the presence of Na⁺ in DTL. The rate of recovery was not affected by Cl^- removal from the bath or K⁺ (75 mM) or 4,4'-diisothiocyanostilbene-2,2'- disulfonate (DIDS) addition to the bath in either DTL or ATL. These results suggest that the common, amiloride-sensitive, basolateral Na⁺/H⁺ exchanger plays a role in the regulation of pH(i) in rat papillary DTL but that a different basolateral Na⁺/H⁺ exchanger or a luminal Na⁺/H⁺ exchanger is important in rat papillary ATL.