Regulation of ae2 mrna expression in the cortical collecting duct
by acid/base balance.
Fejes T th, Gza, Erzsbet Rusvai, Emily S. Cleaveland, and Anik Nray
Fejes T th.
Department of Physiology, Dartmouth Medical School, Lebanon, NH
03756
APStracts 5:0001F, 1998.
AE2 mRNA and protein is expressed in several nephron segments, among
them in the cortical collecting duct (CCD). However, the distribution
of AE2 among the different cell types of the CCD, and its function in
the kidney are not known. The purpose of this study was to determine
the distribution of AE2 mRNA among the three CCD cell types, and to
examine the effects of changes in acid/base balance on its
expression. Following NH4Cl (acid) or NaHCO3 (base) loading of
rabbits for 18 hr., CCD cells were isolated by immunodissection. AE2
mRNA levels were determined by RT-PCR, and were normalized for -actin
levels. We found that CCD cells express high levels of AE2 mRNA ( 500
copies/cell). AE2 mRNA levels were significantly higher in CCD cells
originating from base-loaded than acid-loaded rabbits, with an
average increase of 3.7 +/- 1.07-fold. The effect of pH on AE2 mRNA
levels was also tested directly using primary cultures of CCD cells.
CCD cells incubated in acidic media expressed significantly lower
levels of AE2 mRNA than those in normal or alkaline media.
Experiments with isolated principal cells, [alpha]-intercalated cells
and -intercalated cells (separated by fluorescence-activated cell
sorting) demonstrated that AE2 mRNA levels are comparable in the
three collecting duct cell subtypes, and are similarly regulated by
changes in acid/base balance. Based on these results we conclude that
adaptation to changes in extracellular H+ concentration is
accompanied by opposite changes in AE2 mRNA expression. The
observations that AE2 mRNA is not expressed in a cell-type specific
manner, and that changes in acid/base balance have similar effects on
each CCD cell subtype suggest that AE2 might serve a housekeeping
function rather than being the apical anion exchanger of
-intercalated cells.
Received 3 July 1997; accepted in final form 18 December 1997.
APS Manuscript Number F215-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 9 January 1998