Urea transport processes are induced in rat imcd subsegments when
urine concentrating ability is reduced.
Kato, Akihiko, and Jeff M. Sands.
Renal Division, Department of Medicine, Emory University School of
Medicine, Atlanta, GA 30322 USA
APStracts 5:0167F, 1998.
Infusing urea into low-protein fed mammals increases urine
concentration within 5-10 minutes. To determine which urea
transporter may be responsible, urea transport was measured in
perfused IMCD3s from low-protein fed rats. Basal facilitated urea
permeability increased 78% while active urea secretion was completely
inhibited. This suggests that up-regulation of facilitated urea
transport may mediate the rapid increase in urine concentration.
Next, expression of active urea transporter(s) in perfused IMCDs was
determined in rats with other causes of reduced urine concentrating
ability. In untreated and water diuretic rats, IMCD1s showed no
active urea transport, nor did IMCD2s from untreated or hypercalcemic
rats. In IMCD1s from hypercalcemic rats, active urea reabsorption was
induced. The induced active urea reabsorption was completely
inhibited by replacing perfusate Na+ with NMDG+. Active urea
secretion was completely inhibited in IMCD3s from hypercalcemic rats.
In contrast, water diuresis stimulated active urea secretion in
IMCD2s. The induced active urea secretion was inhibited by:
phloretin; ouabain; triamterene; or replacing perfusate Na+ with
NMDG+. In conclusion, the response of active urea transporters to
reductions in urine concentrating ability follows 2 paradigms: one
occurs with hypercalcemia or a low-protein diet while the second
occurs only in water diuresis.
Received 20 July 1998; accepted in final form 17 September 1998.
APS Manuscript Number F174-8.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 20 October 1998