Effects of in vivo and in vitro alkali treatment on intracellular pH regulation of OMCD(is) cells

To examine functional changes of the transporters in the inner stripe of the outer medullary collecting ducts (OMCD(is)) by the peritubular acid-base status, in vitro microperfusion using the acetoxymethyl ester of 2',7'- bis(2-carboxyethyl)-5(6)-carboxyfluorescein was performed. Cell alkalinization systems were assessed by the recovery rate (dpH(i)/dt) of intracellular pH (pH(i)) after intracellular acid loading by NH₄/⁺-NH₃ prepulse with bath amiloride. In alkali-loaded rabbits (0.15 M NaHCO₃ drinking for 14 days), dpH(i)/dt showed a significant decrease (1.80 ± 0.29 pH units/s x 10³) compared with either control (3.30 ± 0.59) or acid- loaded rabbits (0.15 M NH₄Cl drinking for 14 days, 3.05 ± 0.46). The difference of dpH(i)/dt between control and alkali-loaded rabbits was eliminated by lumen N-ethylmaleimide (NEM), suggesting that H⁺ pump activity was decreased. The effect of in vitro alkali treatment (50 mM HCO₃/^-, pH 7.7) for 3-4 h was also examined. This incubation significantly decreased the dpH(i)/dt (1.83 ± 0.35) compared with the time control experiments (3.18 ± 0.28), whereas no significant difference was seen in the presence of lumen NEM. Anion exchanger activity, as determined from the pH, changes after Cl^- addition to the bath, showed no significant change with in vivo or in vitro alkali treatment. The results indicate that cell function of the OMCD(is) is regulated in response to the peritubular acid-base environment via changes in the H⁺-adenosinetriphosphatase.