AJP - Renal Physiology, Vol 265, Issue 5 729-F735, Copyright © 1993 by American Physiological Society
Effects of in vivo and in vitro alkali treatment on intracellular pH regulation of OMCDis cells
M. Hayashi, M. Iyori, Y. Yamaji and T. Saruta
Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan.
To examine functional changes of the transporters in the inner stripe of
the outer medullary collecting ducts (OMCDis) 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 (dpHi/dt) of
intracellular pH (pHi) after intracellular acid loading by NH(4+)-NH3
prepulse with bath amiloride. In alkali-loaded rabbits (0.15 M NaHCO3
drinking for 14 days), dpHi/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 dpHi/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 dpHi/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
pHi 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 OMCDis is regulated in response to the peritubular
acid-base environment via changes in the H(+)-adenosinetriphosphatase.
