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 este r of 2',7'-bis(2-carboxyethyl)5(6)-carboxyfluorescein was performed. C ell alkalinization systems were assessed by the recovery rate (dpH(i)/ dt) of intracellular pH (pH(i)) after intracellular acid loading by NH 4+-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 10(3)) 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), suggest ing 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 in cubation significantly decreased the dpH(i)/dt (1.83 +/- 0.35) compare d with the time control experiments (3.18 +/- 0.28), whereas no signif icant difference was seen in the presence of lumen NEM. Anion exchange r activity, as determined from the pH(i) changes after Cl- addition to the bath, showed no significant change with in vivo or in vitro alkal i treatment. The results indicate that cell function of the OMCD(is) i s regulated in response to the peritubular acid-base environment via c hanges in the H+-adenosinetriphosphatase.