Long-term regulation of four renal aquaporins in rats .
Terris, James, Carolyn A. Ecelbarger, S[stod]oren Nielsen, and Mark A.
Knepper.
Laboratory of Kidney and Electrolyte Metabolism, National Heart,
Lung and Blood Institute, National Institutes of Health, Bethesda,
MD, Department of Cell Biology, Institute of Anatomy, University of
Aarhus, Aarhus, DK, Department of Physiology, Uniformed Services
University of the Health Sciences, Bethesda, MD
APStracts 3:0063F, 1996.
The aquaporins (AQPs) are molecular water channels expressed in the
kidney and other organs. To investigate long-term regulation of renal
expression of these water channels, we carried out immunoblotting
studies using membrane fractions from rat renal cortex and medulla.
Both 48-hour water restriction in Sprague-Dawley rats and 5-day
vasopressin infusion in Brattleboro rats caused significant increases
in the expression levels of two aquaporins, aquaporin-2 and
aquaporin-3, while the levels of aquaporin-1 and aquaporin-4 were
unchanged. The increases in aquaporin-2 and aquaporin-3 expression
were seen in inner and outer medulla as well as cortex. Ablation of
the corticomedullary interstitial osmotic gradient with an infusion
of furosemide did not eliminate the upregulatory response to
vasopressin infusion in Brattleboro rats. Furthermore, 5-day
furosemide infusion to Sprague-Dawley rats did not decrease
expression levels of the collecting duct aquaporins, but rather
increased them. We conclude that the expression of aquaporin-2 and
aquaporin-3, but not aquaporin-1 or aquaporin-4, is increased in
response to elevated circulating vasopressin. Because regulation of
aquaporin-2 and aquaporin-3 levels was observed in the cortex, and
because osmotic gradient ablation did not abrogate the increase, we
conclude that changes in interstitial osmolality are not necessary
for the vasopressin-induced upregulation of aquaporin-2 and
aquaporin-3 expression.
Received 22 December 1995; accepted in final form 15 March 1996.
APS Manuscript Number F424-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 April 96