Low aquaporin-2 levels in polyuric di +/+ severe mice with
constitutively high camp-phosphodiesterase activity.
Fr_kiaer, J_rgen, ), David Marples, ), Heinz Valtin ), John F. Morris
), Mark A. Knepper ) and S_ren Nielsen ).
1) Department of Clinical Physiology, Aarhus University Hospital
and Institute of Experimental Clinical Research, University of
Aarhus, DK-8000 Aarhus, Denmark; 2) Department of Cell Biology,
Institute of Anatomy, University of Aarhus, DK-8000 Aarhus, Denmark;
3) Department of Physiology, University of Leeds, LS2 9NQ, Leeds, UK;
4) Department of Physiology, Dartmouth Medical School, Hanover, New
Hampshire 03755-3836; 5) Department of Anatomy, University of Oxford,
Oxford OX1 3QX, UK and 6) Laboratory of Kidney and Electrolyte
Metabolism, NHLBI, National Institutes of Health, Bethesda, Maryland
20892, USA.
APStracts 5:0174F, 1998.
In the renal collecting duct, vasopressin acutely activates cAMP
production, resulting in trafficking of aquaporin-2 water channels
(AQP2) to the apical plasma membrane, thereby increasing water
permeability. This acute response is modulated by long-term changes
in AQP2 expression. Recently a cAMP-responsive element has been
identified in the AQP2 gene raising the possibility that changes in
cAMP levels may control AQP2 expression. To investigate this
possibility, we determined AQP2 protein levels in a strain of mice,
DI +/+ Severe (DI), which have genetically high levels of cyclic AMP
-phosphodiesterase activity, and hence low cellular cAMP levels, and
severe polyuria. Semiquantitative immunoblotting of membrane
fractions prepared from whole kidneys revealed that AQP2 levels in DI
mice were only 26 [angstrom]a 7 (SE) % of those in control mice
(n=10, p<0.01). In addition semiquantitative Northern blotting
revealed a significantly lower AQP2 mRNA expression in kidneys from
DI +/+ Severe mice compared to control mice (43 [angstrom]a 6% vs 100
[angstrom]a 10%, n=6 in each group, p<0.05). AQP3 levels were also
reduced. The mice were polyuric and urine osmolalities were
accordingly substantially lower in the DI mice than in controls (496
[angstrom]a 53 vs 1696 [angstrom]a 105 mOsm/kg H2O, respectively).
Moreover, there was a linear correlation between urine osmolalities
and AQP2 levels (p<0.05). Immunoelectron microscopy confirmed the
markedly lower expression of AQP2 in collecting duct principal cells
in kidneys of DI mice, and furthermore demonstrated that AQP2 was
almost completely absent from the apical plasma membrane. Thus,
expression of AQP2 and AQP2 trafficking were severely impaired in DI
mice. These results are consistent with the view that in vivo
regulation of AQP2 expression by vasopressin is mediated by cyclic
AMP.
Received 5 March 1998; accepted in final form 24 September 1998.
APS Manuscript Number F52-8.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 20 October 1998