Regulation of intracellular pH in proximal tubules of avian loopless reptilian-type nephrons.

In proximal tubules isolated from chicken superficial loopless reptilian-type nephrons, intracellular pH (pHi), measured with pH-sensitive fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, was ∼7.1-7.2 under control conditions ( N-2-hydroxyethylpiperazine- N'-2-ethanesulfonic acid-buffered medium with pH 7.4 at 37°C), and was reduced to ∼6.9 in response to NH4Cl pulse. The rate of recovery of pHi(control value ≅ 5 × 10-3 pH U/s) from this acid level was 1) significantly decreased by removal of Na+ or both Na+ and Cl- from the bath or addition of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (0.25 mM) to the bath, 2) significantly increased by high bath K+ (75 mM), and 3) unchanged by removal of Cl- alone from the bath or addition of ethylisopropylamiloride (1 mM) or Ba2+ (5 mM) to the bath. Resting pHi was 1) significantly decreased by Na+ or simultaneous Na+ and Cl- removal, 2) significantly increased by high K+, and 3) unchanged by Cl- removal alone or addition of Ba2+. The data do not fit the concept of pHi regulation by the most commonly suggested basolateral transporters (Na+/H+exchanger, Na+-dependent and Na+-independent Cl-/[Formula: see text]exchangers, or Na+-[Formula: see text]-[Formula: see text]cotransporter).