scholarly journals Regulation of AQP0 water permeability is enhanced by cooperativity

2013 ◽  
Vol 141 (3) ◽  
pp. 287-295 ◽  
Author(s):  
Karin L. Németh-Cahalan ◽  
Daniel M. Clemens ◽  
James E. Hall
Keyword(s):  
Water Permeability ◽  
Calcium Concentration ◽  
Functional Unit ◽  
Water Channel ◽  
Regulatory Change ◽  
Xenopus Laevis Oocytes ◽  
Hydrogen Ions ◽  
External Ph ◽  
Concentration Signal ◽  
Permeability Regulation

Aquaporin 0 (AQP0), essential for lens clarity, is a tetrameric protein composed of four identical monomers, each of which has its own water pore. The water permeability of AQP0 expressed in Xenopus laevis oocytes can be approximately doubled by changes in calcium concentration or pH. Although each monomer pore functions as a water channel, under certain conditions the pores act cooperatively. In other words, the tetramer is the functional unit. In this paper, we show that changes in external pH and calcium can induce an increase in water permeability that exhibits either a positive cooperativity switch-like increase in water permeability or an increase in water permeability in which each monomer acts independently and additively. Because the concentrations of calcium and hydrogen ions increase toward the center of the lens, a concentration signal could trigger a regulatory change in AQP0 water permeability. It thus seems plausible that the cooperative modes of water permeability regulation by AQP0 tetramers mediated by decreased pH and elevated calcium are the physiologically important ones in the living lens.

Cloning and functional expression of an MIP (AQP0) homolog from killifish (Fundulus heteroclitus) lens

2001 ◽  
Vol 281 (6) ◽  
pp. R1994-R2003 ◽  
Author(s):  
Leila V. Virkki ◽  
Gordon J. Cooper ◽  
Walter F. Boron
Keyword(s):  
Water Permeability ◽  
Fundulus Heteroclitus ◽  
Water Channel ◽  
Fold Increase ◽  
Functional Expression ◽  
Xenopus Laevis Oocytes ◽  
Lens Fiber ◽  
Fiber Cells ◽  
Aqp1 Expression ◽  
Very High

The major intrinsic protein (MIP) of lens fiber cells is a member of the aquaporin (AQP) water channel family. The protein is expressed at very high levels in lens fiber cells, but its physiological function is unclear. By homology to known AQPs, we have cloned a full-length cDNA encoding an MIP from the lens of killifish ( Fundulus heteroclitus). The predicted protein (263 amino acids; GenBank accession no. AF191906 ) shows 77% identity to amphibian MIPs, 70% identity to mammalian MIPs, and 46% identity to mammalian AQP1. Expression of MIPfun in Xenopus laevis oocytes causes an ∼40-fold increase in oocyte water permeability. This stimulation is comparable to that seen with AQP1 and substantially larger than that seen with other MIPs. The mercurials HgCl2 and p-chloromercuribenzenesulfonate inhibit the water permeability of MIPfun by ∼25%. MIPfun is not permeable to glycerol, urea, or formic acid but is weakly permeable to CO2.

Molecular and functional characterization of a vasotocin-sensitive aquaporin water channel in quail kidney

2004 ◽  
Vol 287 (4) ◽  
pp. R915-R924 ◽  
Author(s):  
Y. Yang ◽  
Y. Cui ◽  
W. Wang ◽  
L. Zhang ◽  
L. Bufford ◽  
...  
Keyword(s):  
Water Permeability ◽  
Early Stage ◽  
Collecting Duct ◽  
Functional Characterization ◽  
Water Channel ◽  
Arginine Vasotocin ◽  
Mercury Chloride ◽  
Xenopus Laevis Oocytes ◽  
Mrna Levels ◽  
Rt Pcr

Both mammals and birds can concentrate urine hyperosmotic to plasma via a countercurrent multiplier mechanism, although evolutionary lines leading to mammals and birds diverged at an early stage of tetrapod evolution. We reported earlier (Nishimura H, Koseki C, and Patel TB. Am J Physiol Regul Integr Comp Physiol 271: R1535–R1543, 1996) that arginine vasotocin (AVT; avian antidiuretic hormone) increases diffusional water permeability in the isolated, perfused medullary collecting duct (CD) of the quail kidney. In the present study, we have identified an aquaporin (AQP) 2 homolog water channel in the medullary cones of Japanese quail, Coturnix coturnix (qAQP2), by RT-PCR-based cloning techniques. A full-length cDNA contains an 822-bp open reading frame that encodes a 274-amino acid sequence with 75.5% identity to rat AQP2. The qAQP2 has six transmembrane domains, two asparagine-proline-alanine (NPA) sequences, and putative N-glycosylation (asparagine-124) and phosphorylation sites (serine-257) for cAMP-dependent protein kinase. qAQP2 is expressed in the membrane of Xenopus laevis oocytes and significantly increased its osmotic water permeability (Pf), inhibitable ( P < 0.01) by mercury chloride. qAQP2 mRNA (RT-PCR) was detected in the kidney; medullary mRNA levels were higher than cortical levels. qAQP2 protein that binds to rabbit anti-rat AQP2 antibody is present in the apical/subapical regions of both cortical and medullary CDs from normally hydrated quail, and the intensity of staining increased only in the medullary CDs after water deprivation or AVT treatment. The relative density of the ∼29-kDa protein band detected by immunoblot from the medullary cones was modestly higher in water-deprived/AVT-treated quail. The results suggest that 1) medullary CDs of quail kidneys express a mercury-sensitive functioning qAQP2 water channel, and 2) qAQP2 is at least partly regulated by an AVT-dependent mechanism. This is the first clear identification of AQP2 homolog in nonmammalian vertebrates.

AQP4 plasma membrane trafficking or channel gating is not significantly modulated by phosphorylation at COOH-terminal serine residues

2014 ◽  
Vol 307 (10) ◽  
pp. C957-C965 ◽  
Author(s):  
Mette Assentoft ◽  
Brian R. Larsen ◽  
Emma T. B. Olesen ◽  
Robert A. Fenton ◽  
Nanna MacAulay
Keyword(s):  
Plasma Membrane ◽  
Water Permeability ◽  
Membrane Trafficking ◽  
Water Channel ◽  
Mammalian Brain ◽  
Membrane Localization ◽  
Xenopus Laevis Oocytes ◽  
Phosphorylation Sites ◽  
C6 Cells ◽  
Plasma Membrane Localization

Aquaporin 4 (AQP4) is the predominant water channel in the mammalian brain and is mainly expressed in the perivascular glial endfeet at the brain-blood interface. AQP4 serves as a water entry site during brain edema formation, and regulation of AQP4 may therefore be of therapeutic interest. Phosphorylation of aquaporins can regulate plasma membrane localization and, possibly, the unit water permeability via gating of the AQP channel itself. In vivo phosphorylation of six serine residues in the COOH terminus of AQP4 has been detected by mass spectrometry: Ser276, Ser285, Ser315, Ser316, Ser321, and Ser322. To address the role of these phosphorylation sites for AQP4 function, serine-to-alanine mutants were created to abolish the phosphorylation sites. All mutants were detected at the plasma membrane of transfected C6 cells, with the fraction of the total cellular AQP4 expressed at the plasma membrane of transfected C6 cells being similar between the wild-type (WT) and mutant forms of AQP4. Activation of protein kinases A, C, and G in primary astrocytic cultures did not affect the plasma membrane abundance of AQP4. The unit water permeability was determined for the mutant AQP4s upon heterologous expression in Xenopus laevis oocytes (along with serine-to-aspartate mutants of the same residues to mimic a phosphorylation). None of the mutant AQP4 constructs displayed alterations in the unit water permeability. Thus phosphorylation of six different serine residues in the COOH terminus of AQP4 appears not to be required for proper plasma membrane localization of AQP4 or to act as a molecular switch to gate the water channel.

Progesterone inhibition of water permeability in Bufo arenarum oocytes and urinary bladder

1996 ◽  
Vol 270 (5) ◽  
pp. F880-F885 ◽  
Author(s):  
P. Ford ◽  
G. Amodeo ◽  
C. Capurro ◽  
C. Ibarra ◽  
R. Dorr ◽  
...  
Keyword(s):  
Urinary Bladder ◽  
Xenopus Laevis ◽  
Water Permeability ◽  
Water Channel ◽  
Water Channels ◽  
Toad Urinary Bladder ◽  
Osmotic Permeability ◽  
Bufo Arenarum ◽  
Mrna Extraction

The ovarian oocytes from Bufo arenarum (BAO) but not those from Xenopus laevis (XLO) would have water channels (WC). We now report that the injection of the mRNA from BAO into the oocytes from XLO increased their water osmotic permeability (Pi) (reduced by 0.3 mM HgCl2 and reversed by 5 mM beta-mercaptoethanol). A 30-min challenge with progesterone induced, 18 h later, a reduction of the mercury-sensitive fraction of Pf in the BAO (but not in XLO). The mRNA from BAO pretreated with progesterone lost its capacity to induce WC in the XLO, but the hormone did not affect the expression of the WC in XLO previously injected with the mRNA from BAO. Pf was also measured in urinary bladders of BAO. Eighteen hours after a challenge with progesterone, a reduction in the hydrosmotic response to oxytocin was observed. Finally, the mRNA from the urinary bladder of BAO was injected into XLO. An increase in Pf was observed. This was not the case if, before the mRNA extraction, the bladders were treated with progesterone. We conclude that the BAO WC share progesterone sensitivity with the oxytocin-regulated water channel present in the toad urinary bladder.

Cloning of an aquaporin homologue present in water channel containing endosomes of toad urinary bladder

1996 ◽  
Vol 270 (1) ◽  
pp. C372-C381 ◽  
Author(s):  
J. Siner ◽  
A. Paredes ◽  
C. Hosselet ◽  
T. Hammond ◽  
K. Strange ◽  
...  
Keyword(s):  
Urinary Bladder ◽  
Water Channel ◽  
Structural Features ◽  
Xenopus Laevis Oocytes ◽  
Sequence Motif ◽  
Toad Urinary Bladder ◽  
Cytoplasmic Vesicles ◽  
Terrestrial Habitats ◽  
Total Body

Regulation of total body water balance in amphibians by antidiuretic hormone (ADH) contributed to their successful colonization of terrestrial habitats approximately 200-300 million years ago. In the mammalian kidney, ADH modulates epithelial cell apical membrane water permeability (Pf) by fusion and retrieval of cytoplasmic vesicles containing water channel proteins called aquaporins (AQPs). To determine the role of AQPs in ADH-elicited Pf in amphibians, we have identified and characterized a unique AQP from Bufo marinus called AQP toad bladder (AQP-TB). AQP-TB possesses many structural features common to other AQPs, AQP-TB is expressed abundantly in ADH-responsive tissues, including toad urinary bladder and skin as well as lung, skeletal muscle, kidney, and brain. In a manner identical to that reported for the mammalian ADH-elicited water channel AQP2, AQP-TB expression is increased significantly by intervals of dehydration or chronic ADH stimulation. However, expression of AQP-TB protein in Xenopus laevis oocytes does not significantly increase oocyte Pf. The lack of expression of functional AQP-TB water channels in oocytes may result from intracellular sequestration of AQP-TB due to the presence of a YXRF sequence motif present in its carboxyterminal domain.

scholarly journals The Vasopressin Receptor 2 Mutant R137L Linked to the Nephrogenic Syndrome of Inappropriate Antidiuresis (NSIAD) Signals through an Alternative Pathway that Increases AQP2 Membrane Targeting Independently of S256 Phosphorylation

Cells ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 1354
Author(s):  
Marianna Ranieri ◽  
Maria Venneri ◽  
Tommaso Pellegrino ◽  
Mariangela Centrone ◽  
Annarita Di Mise ◽  
...  
Keyword(s):  
Water Permeability ◽  
Collecting Duct ◽  
Alternative Pathway ◽  
Water Channel ◽  
Rho Kinase ◽  
Membrane Targeting ◽  
Rock Inhibitor ◽  
Activating Mutations ◽  
Osmotic Water

NSIAD is a rare X-linked condition, caused by activating mutations in the AVPR2 gene coding for the vasopressin V2 receptor (V2R) associated with hyponatremia, despite undetectable plasma vasopressin levels. We have recently provided in vitro evidence that, compared to V2R-wt, expression of activating V2R mutations R137L, R137C and F229V cause a constitutive redistribution of the AQP2 water channel to the plasma membrane, higher basal water permeability and significantly higher basal levels of p256-AQP2 in the F229V mutant but not in R137L or R137C. In this study, V2R mutations were expressed in collecting duct principal cells and the associated signalling was dissected. V2R-R137L and R137C mutants had significantly higher basal pT269-AQP2 levels -independently of S256 and PKA-which were reduced to control by treatment with Rho kinase (ROCK) inhibitor. Interestingly, ROCK activity was found significantly higher in V2R-R137L along with activation of the Gα12/13–Rho–ROCK pathway. Of note, inhibition of ROCK reduced the basal elevated osmotic water permeability to control. To conclude, our data demonstrate for the first time that the gain-of-function mutation of the V2R, R137L causing NSIAD, signals through an alternative PKA-independent pathway that increases AQP2 membrane targeting through ROCK-induced phosphorylation at S/T269 independently of S256 of AQP2.

Expression of Aquaporin-1 in the Peritoneal Tissues: Localization and Regulation by Hyperosmolality

2002 ◽  
Vol 22 (3) ◽  
pp. 307-315 ◽  
Author(s):  
Tomoko Ota ◽  
Michio Kuwahara ◽  
Shuling Fan ◽  
Yoshio Terada ◽  
Takashi Akiba ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Water Permeability ◽  
Water Channel ◽  
Mesothelial Cells ◽  
Scattering Method ◽  
Osmotic Water Permeability ◽  
Peritoneal Mesothelial Cells ◽  
Aquaporin 1 ◽  
Osmotic Water ◽  
Aqp1 Expression

Objective The purpose of this study was to determine the localization of the aquaporin-1 (AQP1) water channel in peritoneal tissues and the effect of hyperosmolality on the peritoneal expression and function of AQP1. Methods Immunohistochemical localization of AQP1 was identified in rat peritoneal tissues. Cultured rat peritoneal mesothelial cells (RPMCs) were exposed to hyperosmolality by adding 4% glucose to the culture medium. After 1 hour, 4 hours, 24 hours, and 48 hours, AQP1 was identified by semiquantitative immunoblot and immunocytochemistry. Osmotic water permeability was measured using a light-scattering method. Results Immunohistochemistry of rat peritoneal tissues showed the presence of AQP1 in mesothelial cells, venular endothelial cells, and capillary endothelial cells, but not in arteriole and interstitial cells. Semiquantitative immunoblot revealed that exposure to hyperosmolality significantly increased AQP1 expression after 24 hours in whole RPMC lysates (3.3-fold at 24 hours and 3.9-fold at 48 hours). Consistent with the immunoblot, osmotic water permeability of RPMC was augmented 1.7-fold and 2.7-fold after 1 hour and 24 hours, respectively, in a hyperosmotic environment. In RPMC membrane fractions, AQP1 expression was significantly increased after 1 hour of exposure to hyperosmolality (3.9-fold at 1 hour, 7.1-fold at 4 hours, and 8.7-fold at 24 hours). Immunocytochemistry of RPMCs showed that AQP1 was gradually redistributed from the perinuclear area to the peripheral cytoplasm, and then to the plasma membrane after a 1-hour hyperosmotic challenge, suggesting hyperosmolality-induced translocation of AQP1. Upregulation of AQP1 was also observed in the omentum of rats loaded intraperitoneally with hyperosmotic dialysate every day for 10 weeks. Conclusion AQP1 is widely distributed in the peritoneal cavity and may provide the major aqueous pathway across the peritoneal barrier. In addition, our findings suggested that hyperosmolality increases AQP1-dependent water permeability in peritoneal tissues by regulating the translocation and synthesis of AQP1 protein.

scholarly journals Water Permeability in Resting and Stimulated Crayfish Nerve

1969 ◽  
Vol 54 (4) ◽  
pp. 462-478 ◽  
Author(s):  
B. Gunnar Wallin
Keyword(s):  
Hydrostatic Pressure ◽  
Hydraulic Conductivity ◽  
Water Permeability ◽  
Calcium Concentration ◽  
Procambarus Clarkii ◽  
Silicone Oil ◽  
Ionic Conductance ◽  
Volume Increase ◽  
External Calcium

The hydraulic conductivity, Lp, was determined in single axons of the crayfish, Procambarus clarkii, by injecting a hypertonic sample between two drops of silicone oil and photographing the volume increase of the sample. The method has the advantage of minimizing errors due to hydrostatic pressure differences across the membrane. In resting axons an Lp of 0.236 x 10-8 cm/ sec per cm H2O was found and similar values were obtained with low external calcium concentration and when the nerve was continuously stimulated at 20–30 impulses/sec. Thus the experiments have failed to demonstrate any change of water permeability in cases in which the ionic conductance is known to change. Some possible implications of this are discussed.

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