Urea transport in initial imcd of rats fed a low-protein diet:
functional properties and mrna abundance.
Ashkar, Ziad M., Sonia Martial, Taisuke Isozaki, and Jeff M. Sands.
Renal Division, Department of Medicine, Emory University School of
Medicine, Atlanta, GA 30322
APStracts 2:0045F, 1995.
Feeding rats a low (8%) protein diet (LPD) for 2 weeks induces a
facilitated urea transporter in rat initial IMCDs. To determine if
this is preceded by an increase in mRNA abundance, we designed
degenerate PCR primers to the rabbit facilitated urea transporter
(UT2, You et al., Nature, 365: 844, 1993) and amplified a 716 bp cDNA
fragment to perform Northern analysis of the base or tip of rat inner
medulla (IM). In the base, the predominant transcript was a 2.9 kb
band which increased 55% after 1 week on a LPD; there was no change
in a 4 kb band. In the tip, the 4 kb band predominated but neither
band varied with a LPD. Next, we functionally characterized the
induced urea transporter using microperfused initial IMCDs from rats
fed a LPD for 2 weeks. First, 100 pM AVP stimulated urea permeability
(Purea); 10 nM AVP increased Purea further. Second, raising perfusate
and bath osmolality to 690 mOsm/kg H2O (NaCl added) stimulated Purea;
adding AVP (10 nM) increased Purea further. Third, thiourea
reversibly inhibited AVP-stimulated Purea. In conclusion: 1) 1 week
on a LPD increases mRNA abundance of rat UT2 in the IM base; 2) a LPD
does not change mRNA abundance of rat UT2 in the IM tip; and 3)
although the predominant rat UT2 transcript differs between base and
tip regions, the facilitated urea transporter induced in initial
IMCDs by a LPD has the same functional properties as the urea
transporter normally expressed in terminal IMCDs, suggesting that
both transcripts encode the same urea transporter.
Received 1 February 1995; accepted in final form 21 March 1995.
APS Manuscript Number F34-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 4 April 1995.