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Laboratoire de Physiologie et Endocrinologie Cellulaire Rénale, Institut National de la Santé et de la Recherche Médicale Unité 356, Université Pierre et Marie Curie, Centre Hospitalo-Universitaire Broussais, 75270 Paris Cedex 06, France
The present studies examined the effects of
chronic NaCl administration and metabolic alkalosis on NHE-3, an apical
Na+/H+
exchanger of the rat medullary thick ascending limb of Henle (MTAL).
NaCl administration had no effect on NHE-3 mRNA abundance as assessed
by competitive RT-PCR, as well as on NHE-3 transport activity estimated from the
Na+-dependent cell pH recovery of
Na+-depleted acidified MTAL cells,
in the presence of 50 µM Hoe-694, which specifically blocks NHE-1 and
NHE-2. Two models of metabolic alkalosis were studied, one associated
with high sodium intake, i.e.,
NaHCO3 administration, and one not
associated with high sodium intake, i.e., chloride depletion alkalosis
(CDA). In both cases, the treatment induced a significant metabolic
alkalosis that was associated with a decrease in NHE-3 transport
activity (
27% and
25%, respectively). Negative linear
relationships were observed between NHE-3 activity and plasma pH or
bicarbonate concentration. NHE-3 mRNA abundance and NHE-3 protein
abundance, assessed by Western blot analysis, also decreased by 35 and
25%, respectively, during
NaHCO3-induced alkalosis, and by
47 and 33%, respectively, during CDA. These studies demonstrate that
high sodium intake has per se no effect on MTAL NHE-3. In contrast,
chronic metabolic alkalosis, regardless of whether it is associated
with high sodium intake or not, leads to an appropriate adaptation of
NHE-3 activity, which involves a decrease in NHE-3 protein and mRNA abundance.
sodium/proton exchange; NHE-3; kidney; sodium chloride administration
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