scholarly journals Urinary excretion of aquaporin-2 in humans: a potential marker of collecting duct responsiveness to vasopressin.

1996 ◽  
Vol 7 (3) ◽  
pp. 403-409 ◽  
Author(s):  
S Elliot ◽  
P Goldsmith ◽  
M Knepper ◽  
M Haughey ◽  
B Olson
Keyword(s):  
Urinary Excretion ◽  
Collecting Duct ◽  
Water Channel ◽  
Apical Plasma Membrane ◽  
Hydration Status ◽  
Standard Curve ◽  
Western Analysis ◽  
Aquaporin 2 ◽  
Potential Marker ◽  
Collecting Ducts

The vasopressin-sensitive water channel (aquaporin 2; AQP-2) mediates water transport across the apical plasma membrane of the renal collecting ducts and is excreted in human urine. This study presents the hypothesis that measurements of the AQP-2 excretion rate might be used as a marker of collecting-duct responsiveness to vasopressin, and therefore could be useful in the clinical evaluation of various water-balance disorders. This study presents information about the development of an antibody to human AQP-2, and measures the urinary excretion of AQP-2 by quantitative Western analysis. A standard curve of band densities was generated by using known quantities of the modified immunizing peptide to derive the amount of AQP-2 contained in aliquots of urine. AQP-2 urinary excretion changed with short-term alterations in hydration status produced either by water loading (76% decrease, P < 0.01) or by 3% sodium chloride (760% increase, P < 0.01). Steady-state 24-h urinary excretion of AQP-2 was 43 +/- 10 nmol/24 h (or 28.5 +/- 6.9 pmol/mg creatinine), and 20 +/- 6 nmol/24 h (or 18.3 +/- 7.9 pmol/mg creatinine) in men and women, respectively. Therefore, urinary AQP-2 excretion can be quantified by using Western analysis, and may serve as a marker of collecting-duct responsiveness to vasopressin in different physiologic settings.

Advances in aquaporin-2 trafficking mechanisms and their implications for treatment of water balance disorders

2020 ◽  
Vol 319 (1) ◽  
pp. C1-C10 ◽  
Author(s):  
Robert A. Fenton ◽  
Sathish K. Murali ◽  
Hanne B. Moeller
Keyword(s):  
Protein Interactions ◽  
Collecting Duct ◽  
Water Channel ◽  
Plasma Osmolality ◽  
Carboxyl Terminus ◽  
Apical Plasma Membrane ◽  
Tail Domain ◽  
Water Reabsorption ◽  
Aquaporin 2

In mammals, conservation of body water is critical for survival and is dependent on the kidneys’ ability to minimize water loss in the urine during periods of water deprivation. The collecting duct water channel aquaporin-2 (AQP2) plays an essential role in this homeostatic response by facilitating water reabsorption along osmotic gradients. The ability to increase the levels of AQP2 in the apical plasma membrane following an increase in plasma osmolality is a rate-limiting step in water reabsorption, a process that is tightly regulated by the antidiuretic hormone arginine vasopressin (AVP). In this review, the focus is on the role of the carboxyl-terminus of AQP2 as a key regulatory point for AQP2 trafficking. We provide an overview of AQP2 structure, disease-causing mutations in the AQP2 carboxyl-terminus, the role of posttranslational modifications such as phosphorylation and ubiquitylation in the tail domain, and their implications for balanced trafficking of AQP2. Finally, we discuss how various modifications of the AQP2 tail facilitate selective protein-protein interactions that modulate the AQP2 trafficking mechanism.

Aquaporin 2 is a vasopressin-independent, constitutive apical membrane protein in rat vas deferens

2000 ◽  
Vol 278 (4) ◽  
pp. C791-C802 ◽  
Author(s):  
Anna L. Stevens ◽  
Sylvie Breton ◽  
Corinne E. Gustafson ◽  
Richard Bouley ◽  
Raoul D. Nelson ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Cellular Localization ◽  
Vas Deferens ◽  
Apical Membrane ◽  
Collecting Duct ◽  
Water Channel ◽  
Sperm Concentration ◽  
Apical Plasma Membrane ◽  
Principal Cells ◽  
Aquaporin 2

Aquaporin 2 (AQP2), the vasopressin-regulated water channel, was originally identified in renal collecting duct principal cells. However, our recent description of AQP2 in the vas deferens indicated that this water channel may have extra-renal functions, possibly related to sperm concentration in the male reproductive tract. In this study, we have examined the regulation and membrane insertion pathway of AQP2 in the vas deferens. The amino acid sequence of vas deferens AQP2 showed 100% identity to the renal protein. AQP2 was highly expressed in the distal portion (ampulla) of the vas deferens, but not in the proximal portion nearest the epididymis. It was concentrated on the apical plasma membrane of vas deferens principal cells, and very little was detected on intracellular vesicles. Protein expression levels and cellular localization patterns were similar in normal rats and vasopressin-deficient Brattleboro homozygous rats, and were not changed after 36 h of dehydration, or after 3 days of vasopressin infusion into Brattleboro rats. AQP2 was not found in apical endosomes (labeled with Texas Red-dextran) in vas deferens principal cells, indicating that it is not rapidly recycling in this tissue. Finally, vasopressin receptors were not detectable on vas deferens epithelial cell membranes using a [3H]vasopressin binding assay. These data indicate that AQP2 is a constitutive apical membrane protein in the vas deferens, and that it is not vasopressin-regulated in this tissue. Thus AQP2 contains targeting information that can be interpreted in a cell-type-specific fashion in vivo.

Regulated exocytosis: Renal Aquaporin-2 3D Vesicular Network Organization and Association with F-actin

2021 ◽  
Author(s):  
Mikkel R. Holst ◽  
Louis Gammelgaard ◽  
Jesse Aaron ◽  
Frédéric H. Login ◽  
Sampavi Rajkumar ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Antidiuretic Hormone ◽  
Collecting Duct ◽  
Water Channel ◽  
Urine Concentration ◽  
Apical Plasma Membrane ◽  
Aquaporin 2 ◽  
3D Network ◽  
Vesicle Exocytosis ◽  
A Cell

Regulated vesicle exocytosis is a key response to extracellular stimuli in diverse physiological processes; including hormone regulated short-term urine concentration. In the renal collecting duct, the water channel aquaporin-2 localizes to the apical plasma membrane as well as small, sub-apical vesicles. In response to stimulation with the antidiuretic hormone, arginine vasopressin, aquaporin-2 containing vesicles fuse with the plasma membrane, which increases collecting duct water reabsorption and thus, urine concentration. The nano-scale size of these vesicles has limited analysis of their 3D organization. Using a cell system combined with 3D super resolution microscopy, we provide the first direct analysis of the 3D network of aquaporin-2 containing exocytic vesicles in a cell culture system. We show that aquaporin-2 vesicles are 43 ± 3nm in diameter, a size similar to synaptic vesicles, and that one fraction of AQP2 vesicles localized with the sub-cortical F-actin layer and the other localized in between the F-actin layer and the plasma membrane. Aquaporin-2 vesicles associated with F-actin and this association was enhanced in a serine 256 phospho-mimic of aquaporin-2, whose phosphorylation is a key event in antidiuretic hormone-mediated aquaporin-2 vesicle exocytosis.

scholarly journals Aquaporin-2 membrane targeting: still a conundrum

2017 ◽  
Vol 312 (4) ◽  
pp. F744-F747 ◽  
Author(s):  
Emma T. B. Olesen ◽  
Robert A. Fenton
Keyword(s):  
Collecting Duct ◽  
Water Channel ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Peptide Hormone ◽  
Apical Plasma Membrane ◽  
Crucial Importance ◽  
Aquaporin 2

The targeting of the water channel aquaporin-2 (AQP2) to the apical plasma membrane of kidney collecting duct principal cells is regulated mainly by the antidiuretic peptide hormone arginine vasopressin (AVP). This process is of crucial importance for the maintenance of body water homeostasis. In this brief review we assess the role of cyclic adenosine monophosphate (cAMP) and discuss the emerging concept that type 2 AVP receptor (V2R)-mediated AQP2 trafficking is cAMP-independent.

scholarly journals Lovastatin-induced cholesterol depletion affects both apical sorting and endocytosis of aquaporin-2 in renal cells

2010 ◽  
Vol 298 (2) ◽  
pp. F266-F278 ◽  
Author(s):  
G. Procino ◽  
C. Barbieri ◽  
M. Carmosino ◽  
F. Rizzo ◽  
G. Valenti ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Molecular Mechanisms ◽  
Collecting Duct ◽  
Rat Kidney ◽  
Water Channel ◽  
Membrane Rafts ◽  
Apical Plasma Membrane ◽  
Cholesterol Depletion ◽  
Aquaporin 2 ◽  
Apical Sorting

Vasopressin causes the redistribution of the water channel aquaporin-2 (AQP2) from cytoplasmic storage vesicles to the apical plasma membrane of collecting duct principal cells, leading to urine concentration. The molecular mechanisms regulating the selective apical sorting of AQP2 are only partially uncovered. In this work, we investigate whether AQP2 sorting/trafficking is regulated by its association with membrane rafts. In both MCD4 cells and rat kidney, AQP2 preferentially associated with Lubrol WX-insoluble membranes regardless of its presence in the storage compartment or at the apical membrane. Block-and-release experiments indicate that 1) AQP2 associates with detergent-resistant membranes early in the biosynthetic pathway; 2) strong cholesterol depletion delays the exit of AQP2 from the trans-Golgi network. Interestingly, mild cholesterol depletion promoted a dramatic accumulation of AQP2 at the apical plasma membrane in MCD4 cells in the absence of forskolin stimulation. An internalization assay showed that AQP2 endocytosis was clearly reduced under this experimental condition. Taken together, these data suggest that association with membrane rafts may regulate both AQP2 apical sorting and endocytosis.

scholarly journals Basolateral targeting and microtubule-dependent transcytosis of the aquaporin-2 water channel

2013 ◽  
Vol 304 (1) ◽  
pp. C38-C48 ◽  
Author(s):  
Naofumi Yui ◽  
Hua A. J. Lu ◽  
Ying Chen ◽  
Naohiro Nomura ◽  
Richard Bouley ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Cold Shock ◽  
Collecting Duct ◽  
Basolateral Membrane ◽  
Water Channel ◽  
Apical Plasma Membrane ◽  
Indirect Pathway ◽  
Basolateral Membranes ◽  
Principal Cells ◽  
Aquaporin 2

The aquaporin-2 (AQP2) water channel relocates mainly to the apical plasma membrane of collecting duct principal cells after vasopressin (VP) stimulation. AQP2 transport to this membrane domain is assumed to be a direct route involving recycling of intracellular vesicles. However, basolateral plasma membrane expression of AQP2 is observed in vivo in principal cells. Here, we asked whether there is a transcytotic pathway of AQP2 trafficking between apical and basolateral membranes. We used MDCK cells in which AQP2 normally accumulates apically after VP exposure. In contrast, both site-specific biotinylation and immunofluorescence showed that AQP2 is strongly accumulated in the basolateral membrane, along with the endocytic protein clathrin, after a brief cold shock (4°C). This suggests that AQP2 may be constitutively targeted to basolateral membranes and then retrieved by clathrin-mediated endocytosis at physiological temperatures. Rab11 does not accumulate in basolateral membranes after cold shock, suggesting that the AQP2 in this location is not associated with Rab11-positive vesicles. After rewarming (37°C), basolateral AQP2 staining is diminished and it subsequently accumulates at the apical membrane in the presence of VP/forskolin, suggesting that transcytosis can be followed by apical insertion of AQP2. This process is inhibited by treatment with colchicine. Our data suggest that the cold shock procedure reveals the presence of microtubule-dependent AQP2 transcytosis, which represents an indirect pathway of apical AQP2 delivery in these cells. Furthermore, our data indicate that protein polarity data obtained from biotinylation assays, which require cells to be cooled to 4°C during the labeling procedure, should be interpreted with caution.

scholarly journals Quantitative analysis of aquaporin-2 phosphorylation

2010 ◽  
Vol 298 (4) ◽  
pp. F1018-F1023 ◽  
Author(s):  
Luke Xie ◽  
Jason D. Hoffert ◽  
Chung-Lin Chou ◽  
Ming-Jiun Yu ◽  
Trairak Pisitkun ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Collecting Duct ◽  
Water Channel ◽  
Apical Plasma Membrane ◽  
Specific Antibodies ◽  
Protein Mass ◽  
Aquaporin 2 ◽  
Protein Mass Spectrometry ◽  
V2 Receptor ◽  
A Site

The action of vasopressin in rodent collecting ducts to regulate water permeability depends in part on increases in phosphorylation of the water channel aquaporin-2 (AQP2) at three sites: Ser256, Ser264, and Ser269. Previous studies of AQP2 phosphorylation have depended largely on qualitative data using protein mass spectrometry and phospho-specific antibodies. Here, we use a new method employing phospho-specific antibodies to determine the percentage of total AQP2 phosphorylated at each site in the presence and absence of the V2-receptor-selective vasopressin analog dDAVP in rat renal inner medullary collecting duct (IMCD) and cultured mpkCCD cells. Phosphorylation of Ser269, a site previously implicated in plasma membrane retention, was found to increase from 3 to 26% of total AQP2 in rat IMCD cells following dDAVP. Quantification of immunogold labeling of the opposite kidneys from the same rats estimated that 11% of total AQP2 is present in the apical plasma membrane (APM) without injection of dDAVP and 25% is present in the APM after dDAVP. Surprisingly, the baseline level of Ser256 phosphorylation was constitutively high, and there was no increase with dDAVP (confirmed in 2 more sets of rats). In general, Ser264 phosphorylation remained below 5% of total. The pattern of response was similar in cultured mpkCCD cells (large increase in Ser269 phosphorylation following dDAVP, but constitutively high levels of Ser256 phosphorylation). We suggest from these studies that Ser269 phosphorylation may be a more consistent indicator of vasopressin action and AQP2 membrane abundance than is Ser256 phosphorylation.

scholarly journals Molecular mechanisms regulating aquaporin-2 in kidney collecting duct

2016 ◽  
Vol 311 (6) ◽  
pp. F1318-F1328 ◽  
Author(s):  
Hyun Jun Jung ◽  
Tae-Hwan Kwon
Keyword(s):  
Molecular Mechanisms ◽  
Collecting Duct ◽  
Water Channel ◽  
Peptide Hormone ◽  
Urine Concentration ◽  
The Body ◽  
Apical Plasma Membrane ◽  
Kidney Collecting Duct ◽  
Aquaporin 2 ◽  
Aqp2 Gene

The kidney collecting duct is an important renal tubular segment for regulation of body water homeostasis and urine concentration. Water reabsorption in the collecting duct principal cells is controlled by vasopressin, a peptide hormone that induces the osmotic water transport across the collecting duct epithelia through regulation of water channel proteins aquaporin-2 (AQP2) and aquaporin-3 (AQP3). In particular, vasopressin induces both intracellular translocation of AQP2-bearing vesicles to the apical plasma membrane and transcription of the Aqp2 gene to increase AQP2 protein abundance. The signaling pathways, including AQP2 phosphorylation, RhoA phosphorylation, intracellular calcium mobilization, and actin depolymerization, play a key role in the translocation of AQP2. This review summarizes recent data demonstrating the regulation of AQP2 as the underlying molecular mechanism for the homeostasis of water balance in the body.

scholarly journals Decreased aquaporin-2 expression and apical plasma membrane delivery in kidney collecting ducts of polyuric hypercalcemic rats.

1998 ◽  
Vol 9 (12) ◽  
pp. 2181-2193 ◽  
Author(s):  
J H Earm ◽  
B M Christensen ◽  
J Frøkiaer ◽  
D Marples ◽  
J S Han ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Molecular Mechanisms ◽  
Collecting Duct ◽  
Rat Kidney ◽  
Water Channel ◽  
Urine Osmolality ◽  
Apical Plasma Membrane ◽  
Similar Reduction ◽  
Aquaporin 2 ◽  
Urine Production

Hypercalcemia is frequently associated with a urinary concentrating defect and overt polyuria. The molecular mechanisms underlying this defect are poorly understood. Dysregulation of aquaporin-2 (AQP2), the predominant vasopressin-regulated water channel, is known to be associated with a range of congenital and acquired water balance disorders including nephrogenic diabetes insipidus and states of water retention. This study examines the effect of hypercalcemia on the expression of AQP2 in rat kidney. Rats were treated orally for 7 d with dihydrotachysterol, which produced significant hypercalcemia with a 15 +/- 2% increase in plasma calcium concentration. Immunoblotting and densitometry of membrane fractions revealed a significant decrease in AQP2 expression in kidney inner medulla of hypercalcemic rats to 45.7 +/- 6.8% (n = 11) of control levels (100 +/- 12%, n = 9). A similar reduction in AQP2 expression was seen in cortex (36.9 +/- 4.2% of control levels, n = 6). Urine production increased in parallel, from 11.3 +/- 1.4 to a maximum of 25.3 +/- 1.9 ml/d (P < 0.01), whereas urine osmolality decreased from 2007 +/- 186 mosmol/kg x H2O to 925 +/- 103 mosmol/kg x H2O (P < 0.01). Immunocytochemistry confirmed a decrease in total AQP2 labeling of collecting duct principal cells from kidneys of hypercalcemic rats, and reduced apical labeling. Immunoelectron microscopy demonstrated a significant reduction in AQP2 labeling of the apical plasma membrane, consistent with the development of polyuria. In summary, the results strongly suggest that AQP2 downregulation and reduced apical plasma membrane delivery of AQP2 play important roles in the development of polyuria in association with hypercalcemia.

Redistribution of aquaporin-2 water channels induced by vasopressin in rat kidney inner medullary collecting duct

1995 ◽  
Vol 269 (3) ◽  
pp. C655-C664 ◽  
Author(s):  
D. Marples ◽  
M. A. Knepper ◽  
E. I. Christensen ◽  
S. Nielsen
Keyword(s):  
Plasma Membrane ◽  
Immunoelectron Microscopy ◽  
Collecting Duct ◽  
Water Channel ◽  
Fold Increase ◽  
Apical Plasma Membrane ◽  
Water Loading ◽  
Aquaporin 2 ◽  
Intracellular Vesicle ◽  
Intracellular Vesicles

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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