Nephrology Dialysis Transplantation, Vol 14, Issue 6 1435-1440, Copyright © 1999 by Oxford University Press
M Bailey, G Capasso, S Agulian, G Giebisch and R Unwin
Background: Dietary potassium depletion is associated
with elevated plasma bicarbonate concentration and enhanced bicarbonate
reabsorption in the distal tubule. The relationship between distal proton
secretion and potassium status was investigated by in
vivo microperfusion of the superficial distal tubule.
Methods: Experiments were performed on anaesthetized
rats that had been maintained on either a low-potassium or control diet for
3-5 weks prior to experimentation. The distal tubules were perfused at 10
nl/min with either a standard or a barium chloride-containing solution, and
the late distal tubular transepithelial potential difference (Vte) and pH
of the luminal fluid were recorded using a double-barrelled voltage and
ion-sensitive microelectrode. Results: In control
rats, the Vte was -40.7 ± 2.4 mV and the tubular fluid pH was
6.44 ± 0.07; in potassium-depleted animals, the Vte was -15.0
± 1.4 mV and the pH was 6.76 ± 0.03. The pH values in
both groups of animals were significantly lower than would be predicted
from the Vte and systemic pH for passive H+
distribution, indicating active proton secretion. Moreover, in hypokalaemic
rats, this difference from predicted pH was significantly greater than in
control animals (control=0.27 ± 0.06 vs
low-potassium= 0.46 ± 0.003; P <0.01), suggesting
enhanced active proton secretion. During perfusion with a solution
containing BaCl2, the late distal tubule Vte became lumen positive in
potassium-depleted rats, contrasting with an increased lumen negativity in
potassium-replete controls. The barium-induced lumen-positive potential
difference observed in the hypokalaemic rats was abolished by intravenous
administration of acetazolamide. Conclusion: These
data are consistent with enhanced electrogenic proton secretion
(H+-ATPase) during dietary potassium deprivation.
Key words: late distal tubule; potassium depletion;
proton secretion
ORIGINAL ARTICLES
The relationship between distal tubular proton secretion and dietary potassium depletion: evidence for up-regulation of H+-ATPase
Centre for Nephrology, Department of Medicine, The Rayne Institute, University College London, 5 University Street, London WC1E 6JJ, UK; Chair of Nephrology, Second University of Naples, Naples, Italy; Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT, USA; Corresponding author
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