Angiotensin II increases vasopressin-stimulated facilitated urea permeability in rat terminal IMCDs

Kwon, Tae-Hwan, Jakob Nielsen, Mark A. Knepper, Jørgen Frøkiaer, and Søren Nielsen. Angiotensin II AT 1 receptor blockade decreases vasopressin-induced water reabsorption and AQP2 levels in NaCl-restricted rats. Am J Physiol Renal Physiol 288: F673-F684, 2005. First published December 7, 2004; doi:10.1152/ajprenal.00304. 2004.-Vasopressin and ANG II, which are known to play a major role in renal water and sodium reabsorption, are mainly coupled to the cAMP/PKA and phosphoinositide pathways, respectively. There is evidence for cross talk between these intracellular signaling pathways. We therefore hypothesized that vasopressin-induced water reabsorption could be attenuated by ANG II AT 1 receptor blockade in rats. To address this, three protocols were used: 1) DDAVP treatment (20 ng/h sc for 7 days, n ϭ 8); 2) DDAVP (20 ng/h sc for 7 days) and candesartan (1 mg ⅐ kg Ϫ1 ⅐ day Ϫ1 sc for 7 days) cotreatment (n ϭ 8); and 3) vehicle infusion as the control (n ϭ 8). All rats were maintained on a NaCl-deficient diet (0.1 meq Na ϩ ⅐ 200 g body wt Ϫ1 ⅐ day Ϫ1 ) during the experiment. DDAVP treatment alone resulted in a significant decrease in urine output (3.1 Ϯ 0.2 ml/day) compared with controls (11.5 Ϯ 2.2 ml/day, P Ͻ 0.05), whereas the urine output was significantly increased in response to DDAVP and candesartan cotreatment (9.8 Ϯ 1.0 ml/day, P Ͻ 0.05). Consistent with this, rats cotreated with DDAVP and candesartan demonstrated decreased urine osmolality (1,319 Ϯ 172 mosmol/kgH2O) compared with rats treated with DDAVP alone (3,476 Ϯ 182 mosmol/kgH2O, P Ͻ 0.05). Semiquantitative immunoblotting revealed significantly decreased expression of medullary aquaporin-2 (AQP2) and AQP2 phosphorylated in the PKA phosphorylation consensus site Ser-256 (p-AQP2) in response to DDAVP and candesartan cotreatment compared with DDAVP treatment alone. In addition, cortical and medullary AQP1 was also downregulated. Fractional sodium excretion (FENa) and plasma potassium levels were markedly increased, and the expressions of the cortical type 3 Na ϩ /H ϩ exchanger (NHE3), thiazidesensitive Na-Cl cotransporter (NCC), and Na-K-ATPase were significantly decreased in response to DDAVP and candesartan cotreatment. Moreover, medullary type 1 bumetanide-sensitive Na-K-2Cl cotransporter expression showed a marked gel mobility shift from 160 to ϳ180 kDa corresponding to enhanced glycosylation, whereas expression was unchanged. In conclusion, ANG II AT 1 receptor blockade in DDAVP-treated rats was associated with decreased urine concentration and decreased AQP2 and AQP1 expression. Moreover, FENa was increased in parallel with decreased expression of NHE3, NCC, and Na-K-ATPase. These results suggest that ANG II AT1 receptor activation plays a significant role in regulating aquaporin and sodium transporter expression and modulating urine concentration in vivo.aquaporin; calcium; cAMP; type 1 bumetanide-sensitive Na-K-2Cl cotransporter; urine concentration VASOPRESSIN AND ANG II are importantly involved in the renal conservation of water and sodiu...

Section: Discussionsupporting

confidence: 70%

Section: )-2clmentioning

confidence: 75%

Section: Potential Role Of Ang II In Urea Equlibration and Urinary Comentioning

confidence: 82%

See 1 more Smart Citation

Angiotensin II AT₁receptor blockade decreases vasopressin-induced water reabsorption and AQP2 levels in NaCl-restricted rats

Kwon

Nielsen²,

Knepper³

et al. 2005

“…In normal rats, angiotensin II (in the presence of vasopressin) increases the phosphorylation of UT-A1 and urea permeability in perfused terminal IMCDs (10). Thus the lack of angiotensin II in the ACE.2 mice may also result in submaximal function of the small amount of UT-A1 protein that is present in their inner medulla.…”

Section: Discussionmentioning

confidence: 99%

Impaired urine concentration and absence of tissue ACE: involvement of medullary transport proteins

Klein¹,

Quach²,

Cole³

et al. 2002

Self Cite

mice lack all tissue angiotensin-converting enzyme (ACE) but have 33% of normal plasma ACE activity. They exhibit the urine-concentrating defect and hyperkalemia present in mice that lack all ACE, but in contrast to the complete knockout, ACE.2 mice have normal medullary histology and creatinine clearance. To explore the urine-concentrating defect in ACE.2 mice, renal medullary transport proteins were analyzed using Western blot analysis. In the inner medulla, UT-A1, ClC-K1, and aquaporin-1 (AQP1) were significantly reduced to 28 Ϯ 5, 6 Ϯ 6, and 39 Ϯ 5% of the level in wild-type mice, respectively, whereas AQP2 and UT-B were unchanged. In the outer medulla, NaϪ cotransporter (NKCC2/BSC1) and AQP1 were significantly reduced to 56 Ϯ 11 and 29 Ϯ 6%, respectively, whereas Na ϩ -K ϩ -ATPase, UT-A2, UT-B, and AQP2 were unchanged, and renal outer medullary potassium channel was significantly increased to 711 Ϯ 187% of the level in wild-type mice. The abnormal expression of these transporters was similar in ACE.2 mice backcrossed onto a C57BL/6 or a Swiss background and was not rescued by ANG II infusion. We conclude that the urine-concentrating defect in ACE.2 mice is associated with, and may result from, downregulation of some or all of these key urea, salt, and water transport proteins.

“…NaCl was used to induce hypertonicity, similar to the perfused tubule studies. Following treatments, pieces were washed free of unincorporated 32 P with phosphatefree DMEM, and 32 P-labeled UT-A1 was immunoprecipitated as previously described (6). Precipitated proteins were separated by SDS-PAGE and radiolabeled UT-A1 was determined by autoradiography of the dried gel.…”

Section: Animalsmentioning

confidence: 99%

Role of protein kinase C-α in hypertonicity-stimulated urea permeability in mouse inner medullary collecting ducts

Wang

Klein

Froehlich

et al. 2013

Self Cite

The kidney's ability to concentrate urine is vitally important to our quality of life. In the hypertonic environment of the kidney, urea transporters must be regulated to optimize function. We previously showed that hypertonicity increases urea permeability and that the protein kinase C (PKC) blockers chelerythrine and rottlerin decreased hypertonicity-stimulated urea permeability in rat inner medullary collecting ducts (IMCDs). Because PKCα knockout (PKCα−/−) mice have a urine-concentrating defect, we tested the effect of hypertonicity on urea permeability in isolated perfused mouse IMCDs. Increasing the osmolality of perfusate and bath from 290 to 690 mosmol/kgH2O did not change urea permeability in PKCα−/− mice but significantly increased urea permeability in wild-type mice. To determine whether the response to protein kinase A was also missing in IMCDs of PKCα−/− mice, tubules were treated with vasopressin and subsequently with the PKC stimulator phorbol dibutyrate (PDBu). Vasopressin stimulated urea permeability in PKCα−/− mice. Like vasopressin, forskolin stimulated urea permeability in PKCα−/− mice. We previously showed that, in rats, vasopressin and PDBu have additive stimulatory effects on urea permeability. In contrast, in PKCα−/− mice, PDBu did not further increase vasopressin-stimulated urea permeability. Western blot analysis showed that expression of the UT-A1 urea transporter in IMCDs was increased in response to vasopressin in wild-type mice as well as PKCα−/− mice. Hypertonicity increased UT-A1 phosphorylation in wild-type mice but not in PKCα−/− mice. We conclude that PKCα mediates hypertonicity-stimulated urea transport but is not necessary for vasopressin stimulation of urea permeability in mouse IMCDs.