Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P41181 (collecting duct)
 5,183 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Congenital nephrogenic diabetes insipidus is a recessive hereditary disorder characterized by the inability of the kidney to concentrate urine in response to vasopressin. Recently, we reported mutations in the gene encoding the water channel of the collecting duct, aquaporin-2 (AQP-2) causing an autosomal recessive form of nephrogenic diabetes insipidus (NDI). Expression of these mutant AQP-2 proteins (Gly64Arg, Arg187Cys, Ser216Pro) in Xenopus oocytes revealed nonfunctional water channels. Here we report further studies into the inability of these missense AQP-2 proteins to facilitate water transport in Xenopus oocytes. cRNAs encoding the missense AQPs were translated with equal efficiency as cRNAs encoding wild-type AQP-2 and were equally stable. Arg187Cys AQP2 was more stable and Gly6-4Arg and Ser216Pro AQP2 were less stable when compared to wild-type AQP2 protein. On immunoblots, oocytes expressing missense AQP-2 showed, besides the wild-type 29 kDa band, an endoplasmic reticulum-retarded form of AQP-2 of approximately 32 kD. Immunoblots and immunocytochemistry demonstrated only intense labeling of the plasma membranes of oocytes expressing wild-type AQP-2. Therefore, we conclude that in Xenopus oocytes the inability of Gly64-Arg, Arg187Cys or Ser216Pro substituted AQP-2 proteins to facilitate water transport is caused by an impaired routing to the plasma membrane.
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PMID:Water channels encoded by mutant aquaporin-2 genes in nephrogenic diabetes insipidus are impaired in their cellular routing. 753 61

Aquaporin 2 is a collecting duct water channel that is located in apical vesicles and in the apical plasma membrane of collecting duct principal cells. It shares 42% identity with the proximal tubule/thin descending limb water channel, CHIP28. The present study was aimed at addressing three questions concerning the location and behavior of the AQP2 protein under different conditions. First, does the AQP2 channel relocate to the apical membrane after vasopressin treatment? Our results show that AQP2 is diffusely distributed in cytoplasmic vesicles in collecting duct principal cells of homozygous Brattleboro rats that lack vasopressin. In rats injected with exogenous vasopressin, however, AQP2 became concentrated in the apical plasma membrane of principal cells, as determined by immunofluorescence and immunogold electron microscopy. This behavior is consistent with the idea that AQP2 is the vasopressin-sensitive water channel. Second, is the cellular location of AQP2 modified by microtubule disruption? In normal rats, AQP2 has a mainly apical and subapical location in principal cells, but in colchicine-treated rats, it is distributed on vesicles that are scattered throughout the entire cytoplasm. This is consistent with the dependence on microtubules of apical protein targeting in many cell types, and explains the inhibitory effect of microtubule disruption on the hydroosmotic response to vasopressin in sensitive epithelia, including the collecting duct. Third, is AQP2 present in neonatal rat kidneys? We show that AQP2 is abundant in principal cells from neonatal rats at all days after birth. The detection of AQP2 in early neonatal kidneys indicates that a lack of this protein is not responsible for the relatively weak urinary concentrating response to vasopressin seen in neonatal rats.
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PMID:The AQP2 water channel: effect of vasopressin treatment, microtubule disruption, and distribution in neonatal rats. 753 96

Aquaporin-2 (AQP2) is the predominant vasopressin-regulated water channel of the renal collecting duct. We tested whether vasopressin induces translocation of AQP2 from intracellular vesicles into the apical plasma membrane. AQP2 was quantitated in plasma membrane and intracellular vesicle fractions prepared from the inner medulla of one kidney from each rat before or 20 min after intravenous 1-desamino-8-D-arginine vasopressin (DDAVP) treatment, using immunoblotting and densitometry. Contralateral kidneys were prepared for immunofluorescence and immunoelectron microscopy. Immunoblotting revealed that, compared with untreated controls, DDAVP treatment significantly increased the fraction of AQP2 protein associated with the plasma membrane fraction relative to intracellular vesicles. This increase averaged 2.0-fold in untreated rats and 2.9-fold in rats water loaded for 12 h. Water loading, presumably by suppressing circulating vasopressin levels, decreased the fraction of AQP2 associated with the plasma membrane by 55%, suggesting retrieval of AQP2 from the plasma membrane. In rats sequentially thirsted for 48 h to increase expression and then water loaded for 72 h to minimize plasma membrane labeling, DDAVP caused a 12-fold increase in the plasma membrane to intracellular vesicle labeling ratio. The accentuation of the DDAVP response seen after water loading is consistent with the observed increase in the fraction of AQP2 in the intracellular pool available for insertion. Immunofluorescence confirmed a marked DDAVP-induced redistribution of AQP2 from intracellular to plasma membrane domains. Furthermore, quantitative immunoelectron microscopy demonstrated a 3.4-fold increase in apical plasma membrane to intracellular vesicle labeling ratio. These results provide a direct in vivo demonstration of vasopressin-induced translocation of AQP2 into the apical plasma membrane.
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PMID:Redistribution of aquaporin-2 water channels induced by vasopressin in rat kidney inner medullary collecting duct. 757 95

The mRNA expression and localization of the aquaporin (AQP) family in rat kidney were examined by ribonuclease protection assay and immunohistochemistry. AQP1, AQP2, AQP3, and AQP4 mRNA were hardly detectable in 16-day gestation fetuses. AQP1 mRNA was explosively expressed at 1 wk, keeping the level throughout life. AQP2 mRNA expression was apparently noticed in 18-day fetuses and was enhanced gradually with age to reach a plateau at 4 wk. AQP3 and AQP4 mRNA expression was significantly found at birth but was not changed remarkably thereafter. AQP2 protein appeared first at the apical side of collecting duct cells in 18-day fetuses. The staining intensity at the site increased with age, and basolateral staining was added in adult rats. AQP3 was distinctly demonstrated at the basolateral side of collecting duct cells after birth, and the staining intensity was almost stable throughout life. The progressive induction of AQP2 expression in the first 4 wk after birth is presumed to contribute to the maturation of urinary concentrating capacity during the kidney development.
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PMID:Expression of AQP family in rat kidneys during development and maturation. 912 96

In bilateral ureteral obstruction, both aquaporin-2 (AQP2) levels and urinary concentrating capacity are markedly reduced. However, the mechanisms involved in AQP2 downregulation are unknown. In rats with unilateral ureteral obstruction (UUO) the relative role of intrarenal and systemic factors can be evaluated. Semiquantitative immunoblotting revealed a marked decrease in AQP2 in obstructed kidneys to 23 +/- 7% (n = 9) of sham levels. This downregulation persisted 24 h after release of UUO. Furthermore, there was a significant but less extensive downregulation of AQP2 in the nonobstructed kidneys to 75 +/- 7% (n = 9) of sham levels. Consistent with impairment of collecting duct water reabsorption, free water clearance was greatly elevated in the obstructed kidneys (-2 +/- 1 microliter-min-1.kg-1, determined immediately after release) and only moderately elevated in nonobstructed kidneys (-44 +/- 5 microliters.min-1.kg-1) compared with sham-operated controls (-59 +/- 3 microliters.min-1.kg-1). Also AQP2 mRNA levels were reduced in obstructed kidneys. Immunocytochemistry confirmed the marked decrease in AQP2 expression in obstructed kidneys. In nonobstructed kidneys AQP2 was predominantly found in intracellular vesicles, which together with the reduced expression and elevated free water clearance strongly suggests a role of AQP2 in the observed compensatory diuresis from nonobstructed kidneys. The much lower AQP2 protein and mRNA levels in obstructed vs. nonobstructed kidneys are consistent with intrarenal factors playing a major role for downregulation of AQP2.
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PMID:Downregulation of aquaporin-2 parallels changes in renal water excretion in unilateral ureteral obstruction. 927 82

Water retention is characteristic of pregnancy but the mechanism(s) of the altered water metabolism has yet to be elucidated. The collecting duct water channel, aquaporin 2 (AQP2), plays a pivotal role in the renal water regulation, and we hypothesized that AQP2 expression could be modified during pregnancy. Sprague-Dawley female rats were studied on days 7 (P7), 14 (P14), and 20 (P20) of pregnancy, and expression of AQP2 in papillae was examined. Nonpregnant (NP) littermates were used as controls. Plasma osmolalities were significantly lower in pregnant rats by day 7 of gestation (P7 283.8+/-1.82, P14 284.3+/-1.64, P < 0.001, P20 282. 4+/-1.32, P < 0.0001, vs. NP 291.8+/-1.06 mosmol/kgH2O). However, plasma vasopressin concentrations in pregnant rats were not significantly different than in nonpregnant rats (NP 1.03+/-0.14, P7 1.11+/-0.21, P14 1.15+/-0.21, P20 1.36+/-0.24 pg/ml, NS). The mRNA of AQP2 was increased early during pregnancy: AQP2/beta actin: P7 196+/-17.9, P14 200+/-6.8, and P20 208+/-15.5%, P < 0.005 vs. NP (100+/-11.1%). AQP2 protein was also increased during pregnancy: AQP2 protein: P7 269+/-10.0, P14 251+/-12.0, P < 0.0001, and P20 250+/-13.6%, P < 0.001 vs. NP (100+/-12.5%). The effect of V2 vasopressin receptor antagonist, OPC-31260, was then investigated. AQP2 mRNA was suppressed significantly by OPC-31260 administration to P14 rats (AQP2/beta actin: P14 with OPC-31260 39.6+/-1.7%, P < 0.001 vs. P14 with vehicle) and was decreased to the same level of expression as NP rats receiving OPC-31260. Similar findings were found with the analysis of AQP2 protein. The decreased plasma osmolality of P14 rats was not modified by OPC-31260. The results of the study indicate that upregulation of AQP2 contributes to the water retention in pregnancy through a V2 receptor-mediated effect. In addition to vasopressin, other factors may be involved in this upregulation.
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PMID:Upregulation of aquaporin 2 water channel expression in pregnant rats. 948 78

To examine the involvement of vasopressin and dehydration in the regulation of aquaporin-2 (AQP2) expression in rat kidney, we investigated the effects of treatment for 60 h with the specific V2-receptor antagonist OPC-31260 (OPC), alone and in conjunction with dehydration for the last 12 h. Changes in AQP2 protein and mRNA expression in kidney inner medulla were determined by Western and Northern blotting, and AQP2 distribution was analyzed by immunocytochemistry and immunoelectron microscopy. Treatment with OPC increased urine output fourfold, with a reciprocal decrease in urine osmolality. AQP2 expression decreased to 52 +/- 11% of control levels (n = 12, P < 0.05), and AQP2 was found predominantly in intracellular vesicles in collecting duct principal cells. This is consistent with efficient blockade of the vasopressin-induced AQP2 delivery to the plasma membrane and with the observed increased diuresis. Consistent with this, AQP2 mRNA levels were also reduced in response to prolonged OPC treatment (30 +/- 10% of control levels, n = 9). Five days of treatment with furosemide, despite producing even greater polyuria than OPC, was not associated with downregulation of AQP2 levels, demonstrating that AQP2 downregulation is not secondary to increased urine flow rate or loss of medullary hypertonicity. During 12-h thirsting in the continued presence of OPC, urine output dropped dramatically, to levels not significantly different from that seen in (nonthirsted) control animals. In parallel with this, AQP2 levels rose to control levels. Control experiments confirmed continued effective receptor blockade. These results indicate that the V2-receptor antagonist causes a modest decrease in AQP2 expression that is not a consequence of increased urine flow rate or washout of medullary hypertonicity. However, this decrease is much less marked than that seen in some forms of acquired nephrogenic diabetes insipidus. In conjunction with the effects of thirsting, this suggests that modulation of AQP2 expression is mediated partly, but not exclusively, via V2 receptors.
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PMID:Dehydration reverses vasopressin antagonist-induced diuresis and aquaporin-2 downregulation in rats. 972 13

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 cAMP-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 +/- 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 mice compared with control mice (43 +/- 6% vs. 100 +/- 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 +/- 53 vs. 1,696 +/- 105 mosmol/kgH2O, 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 cAMP.
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PMID:Low aquaporin-2 levels in polyuric DI +/+ severe mice with constitutively high cAMP-phosphodiesterase activity. 995 Sep 48

Three aquaporins (AQP) are present in the membrane of the principal collecting duct cells. On the apical side, the levels of AQP2 protein are increased in response to both arginine vasopressin and water deprivation. However, whether this change parallels changes in the abundance of AQP3 and AQP4 in the basolateral membrane is less well known. This study evaluates the effect of either dehydration or water loading on the rat kidney mRNA expression of AQP2, AQP3, and AQP4. Poly(A+)RNA was prepared from renal cortex and medulla of control, water-deprived, well hydrated, and water-deprived rats treated with OPC31260, a V2 receptor antagonist. Northern blots were done and mRNA levels were quantified using a PhosphorImager system. Relative to control, water deprivation increased the expression of cortical AQP2, -3, and -4, whereas water loading decreased the cortical and medullar expression of AQP2, -3, and -4. Therefore, in addition to AQP2 and -3, AQP4 expression is also regulated by water intake. Treatment with OPC31260 (40 mg/kg of weight per d) inhibited up to 20 to 30% the upregulation of AQP-mRNA induced by water deprivation. Blood values of arginine vasopressin and aldosterone were significantly increased by water deprivation, whereas they were unchanged by water overloading. Taken together, these results indicate that renal AQP2, -3, and -4 expression is regulated in a coordinated manner. Simultaneous up- or downregulation of the three transcripts occurred upon either water deprivation or water loading of animals, respectively. However, the signaling mechanism for the two long-term adaptive processes may be different, and, in addition to arginine vasopressin, other factors may be involved in the transcriptional regulatory processes.
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PMID:Regulation of aquaporin mRNA expression in rat kidney by water intake. 1020 52

Aquaporin-2 (AQP2) water channel mutations cause autosomal recessive and dominant nephrogenic diabetes insipidus. Expressed in oocytes, a mutant in dominant (AQP2-E258K), but not in recessive (AQP2-R187C), NDI conferred a specific dominant-negative effect (DNE) on wild-type (WT) AQP2 water permeability (P(f)) but only at low expression levels. Here, we determined the cell biological basis for this requirement. Injection of different amounts of WT-AQP2 cRNAs revealed that a correlation between AQP2 protein levels and P(f) is only obtained with low expression levels. In coexpression studies of WT- and mutant AQP2 proteins, higher expression levels of AQP2-R187C also exerted a DNE on the P(f) of WT-AQP2. Immunoblot and immunoprecipitation analysis revealed that this DNE was caused by competitive inhibition of WT-AQP2 expression and escape of AQP2-R187C from the endoplasmic reticulum, resulting in oligomerization with WT-AQP2. Because many disease-related mutants of multimeric renal membrane transporters and channels are likely to be identified, our data provide important information for studying the effects of such mutants on the activity of WT transporters and channels in oocytes.
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PMID:Importance of aquaporin-2 expression levels in genotype -phenotype studies in nephrogenic diabetes insipidus. 1099 28


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