REGULATION OF INTRACELLULAR PH IN PROXIMAL TUBULES OF AVIAN LOOPLESS REPTILIAN-TYPE NEPHRONS

In proximal tubules isolated from chicken superficial loopless reptili an-type nephrons, intracellular pH (pH(i)), measured with pH-sensitive fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, was similar to 7.1-7.2 under control conditions (N-2-hydroxyethylpiperazin e-N'-2-ethanesulfonic acid-buffered medium with pH 7.4 at 37 degrees C ), and was reduced to similar to 6.9 in response to NH4Cl pulse. The r ate of recovery of pH(i) (control value congruent to 5 x 10(-3) pH U/s ) from this acid level was I) significantly decreased by removal of Na + or both Na+ and Cl- from the bath or addition of 4,4'-diisothiocyano stilbene-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 B a2+ (5 mM) to the bath. Resting pH(i) was 1) significantly decreased b y 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 pH(i) regulation by the most commo nly suggested basolateral transporters (Na+/H+ exchanger, Na+-dependen t and Na+-independent Cl-/HCO3- exchangers, or Na+-HCO3--CO32- cotrans porter).