Unimpaired osmotic water permeability and fluid secretion in bile duct epithelia of AQP1 null mice

2002 ◽  
Vol 283 (3) ◽  
pp. G739-G746 ◽  
Author(s):  
Albert Mennone ◽  
Alan S. Verkman ◽  
James L. Boyer
Keyword(s):  
Bile Duct ◽  
Cyclic Amp ◽  
Water Permeability ◽  
Water Movement ◽  
Fluid Secretion ◽  
Osmotic Gradient ◽  
Osmotic Water Permeability ◽  
Luminal Membrane ◽  
Osmotic Water ◽  
Aqp1 Expression

The mechanisms by which fluid moves across the luminal membrane of cholangiocyte epithelia are uncertain. Previous studies suggested that aquaporin-1 (AQP1) is an important determinant of water movement in rat cholangiocytes and that cyclic AMP mediates the movement of these water channels from cytoplasm to apical membrane, thereby increasing the osmotic water permeability. To test this possibility we measured agonist-stimulated fluid secretion and osmotically driven water transport in isolated bile duct units (IBDUs) from AQP1 wild-type (+/+) and null (−/−) mice. AQP1 expression was confirmed in a mouse cholangiocyte cell line and +/+ liver. Forskolin-induced fluid secretion, measured from the kinetics of IBDU luminal expansion, was 0.05 fl/min and was not impaired in −/− mice. Osmotic water permeability (Pf), measured from the initial rate of IBDU swelling in response to a 70-mosM osmotic gradient, was 11.1 × 10−4 cm/s in +/+ mice and 11.5 × 10−4cm/s in −/− mice. Pf values increased by ∼50% in both +/+ and −/− mice following preincubation with forskolin. These findings provide direct evidence that AQP1 is not rate limiting for water movement in mouse cholangiocytes and does not appear to be regulated by cyclic AMP in this species.

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.

Evidence for transcellular osmotic water flow in rat proximal tubules

1985 ◽  
Vol 249 (1) ◽  
pp. F124-F131 ◽  
Author(s):  
P. A. Preisig ◽  
C. A. Berry
Keyword(s):  
Surface Area ◽  
Water Flow ◽  
Water Permeability ◽  
Channel Length ◽  
Osmotic Gradient ◽  
Osmotic Water Permeability ◽  
Osmotic Water ◽  
Major Route ◽  
Osmotic Water Flow

To determine the predominant pathway for transepithelial osmotic water flow, the transepithelial osmotic water permeability [Pf(TE)] and the apparent dimensions of paracellular pores and slits were determined in rat proximal convoluted tubules microperfused in vivo. To measure Pf(TE), tubules were perfused with a hyposmotic, cyanide-containing solution. Pf(TE), calculated from the observed volume flux in response to the measured log mean osmotic gradient, was 0.12-0.15 cm/s, assuming sigmaNaCl equal to 1.0-0.7, respectively. The dimensions of the paracellular pathways were determined using measured sucrose and mannitol permeabilities (nonelectrolytes confined to the extracellular space). These were 0.43 and 0.87 X 10(-5) cm/s, respectively. By using the ratio of these permeabilities, their respective free solution diffusion coefficients and molecular radii, and the Renkin equation, the radius of the nonelectrolyte-permeable pores and the total pore area/cm2 surface area/channel length were calculated to be 1.4 nm and 3.56 cm-1, respectively. Similar calculations for slits yielded a slit half-width of 0.8 nm and a total slit area/cm2 surface area/channel length of 3.16 cm-1. The osmotic water permeability of these nonelectrolyte-permeable pathways was calculated by Poiseuille's law to be 0.0018 cm/s (pores) or 0.0014 cm/s (slits), at most 2% of Pf(TE). We conclude that the nonelectrolyte-permeable pathway in the tight junctions is not the major route of transepithelial osmotic water flow in the rat proximal tubule.

Water permeability and particle aggregates in ADH-, cAMP-, and forskolin-treated toad bladder

1987 ◽  
Vol 253 (1) ◽  
pp. F120-F125 ◽  
Author(s):  
W. A. Kachadorian ◽  
R. A. Coleman ◽  
J. B. Wade
Keyword(s):  
Water Permeability ◽  
Water Movement ◽  
Toad Bladder ◽  
Intracellular Camp ◽  
Tissue Water ◽  
Membrane Area ◽  
Luminal Membrane ◽  
Osmotic Water ◽  
Particle Aggregates ◽  
The Relationship

Osmotic water flow was used to evaluate total tissue water permeability (Ptissue), and luminal membrane particle aggregates, presumed sites for transmembrane water movement, were quantified to assess luminal membrane water permeability, in bladders treated with maximally stimulating concentrations of antidiuretic hormone (ADH), adenosine 3',5'-cyclic monophosphate (cAMP), and forskolin. Aggregates were as numerous and occupied the same fractional area of the luminal membrane in response to cAMP treatment (10 mM) as treatment with ADH (20 mU/ml). Ptissue in cAMP-treated tissues, however, was only half of that induced by ADH (P less than 0.001). A similar disparity in the relationship between aggregates and Ptissue occurred for additional bladders treated with 50 microM forskolin, which is known to increase endogenous cAMP to levels much greater than caused by maximally stimulating concentrations of ADH. Although Ptissue achieved with forskolin was the same in paired bladders treated with ADH, aggregates were far more numerous (P less than 0.05) and occupied much more membrane area (P less than 0.05) with forskolin. These observations are consistent with the view that aggregate appearance in the luminal membrane is a function of intracellular cAMP. The finding that the hydrosmotic response of toad bladder to both cAMP and forskolin compared with ADH stimulation is reduced relative to measured changes in luminal membrane aggregates suggests that the effect of ADH in altering water permeability involves additional regulation via a non-cAMP-mediated mechanism. This latter event would appear to be by an effect of ADH on the permeability of a resistance at a postluminal membrane site and/or possibly on the permeability of aggregates in the luminal membrane.

scholarly journals Very high water permeability in vasopressin-induced endocytic vesicles from toad urinary bladder.

1989 ◽  
Vol 94 (6) ◽  
pp. 1101-1115 ◽  
Author(s):  
L B Shi ◽  
A S Verkman
Keyword(s):  
Urinary Bladder ◽  
Water Permeability ◽  
Time Course ◽  
Toad Urinary Bladder ◽  
Stopped Flow ◽  
Osmotic Water Permeability ◽  
Luminal Membrane ◽  
Osmotic Water ◽  
Group A ◽  
Endocytic Vesicles

The regulation of transepithelial water permeability in toad urinary bladder is believed to involve a cycling of endocytic vesicles containing water transporters between an intracellular compartment and the cell luminal membrane. Endocytic vesicles arising from luminal membrane were labeled selectively in the intact toad bladder with the impermeant fluid-phase markers 6-carboxyfluorescein (6CF) or fluorescein-dextran. A microsomal preparation containing labeled endocytic vesicles was prepared by cell scraping, homogenization, and differential centrifugation. Osmotic water permeability was measured by a stopped-flow fluorescence technique in which microsomes containing 50 mM mannitol, 5 mM K phosphate, pH 8.5 were subject to a 60-mM inwardly directed gradient of sucrose; the time course of endosome volume, representing osmotic water transport, was inferred from the time course of fluorescence self-quenching. Endocytic vesicles were prepared from toad bladders with hypoosmotic lumen solution treated with (group A) or without (group B) serosal vasopressin at 23 degrees C, and bladders in which endocytosis was inhibited by treatment with vasopressin at 0-2 degrees C (group C), or with vasopressin plus sodium azide at 23 degrees C (group D). Stopped-flow results in all four groups showed a slow rate of 6CF fluorescence decrease (time constants 1.0-1.7 s for exponential fit) indicating a component of nonendocytic 6CF entrapment into sealed vesicles. However, in vesicles from group A only, there was a very rapid 6CF fluorescence decrease (time constant 9.6 +/- 0.2 ms, SEM, 18 separate preparations) with an osmotic water permeability coefficient (Pf) of greater than 0.1 cm/s (18 degrees C) and activation energy of 3.9 +/- 0.8 kcal/mol (16 kJ/mol). Pf was inhibited reversibly by greater than 60% by 1 mM HgCl2. The rapid fluorescence decrease was absent in vesicles in groups B, C, and D. These results demonstrate the presence of functional water transporters in vasopressin-induced endocytic vesicles from toad bladder, supporting the hypothesis that water channels are cycled to and from the luminal membrane and providing a functional marker for the vasopressin-sensitive water channel. The calculated Pf in the vasopressin-induced endocytic vesicles is the highest Pf reported for any biological or artificial membrane.

Diluting segment in avian kidney. II. Water and chloride transport

1986 ◽  
Vol 250 (3) ◽  
pp. R341-R347 ◽  
Author(s):  
T. Miwa ◽  
H. Nishimura
Keyword(s):  
Water Permeability ◽  
Chloride Transport ◽  
Arginine Vasotocin ◽  
Osmotic Gradient ◽  
Thick Ascending Limb ◽  
Osmotic Water Permeability ◽  
Diluting Segment ◽  
Henle's Loop ◽  
Osmotic Water ◽  
Avian Kidney

The mammalian-type nephrons of avian kidneys contain a Henle's loop that runs parallel to the collecting ducts and the vasa recta. Thus we examined whether the thick ascending limb (TAL) of Henle's loop of the avian kidney acts as a diluting segment by measuring water and Cl transport in the isolated and perfused TAL of the quail, Coturnix coturnix. The TAL showed a lumen-positive transepithelial voltage (Vt) (+9.4 +/- 0.4 mV, n = 28). Net water flux (Jv) was nearly zero when the TAL was perfused and bathed with isosmotic solution. When the osmotic gradient was imposed, Jv increased only slightly, and thus the osmotic water permeability (Lp) was low. Arginine vasotocin (AVT) added to the hyperosmotic bath did not alter either Jv, Lp, or Vt. Cl efflux (lumen to bath, 370.4 +/- 27.7 peq X mm-1 X min-1) was higher than Cl influx (bath to lumen, 98.6 +/- 14.3 peq X mm-1 X min-1) when measured in the different tubules. AVT showed no effect on Cl efflux. These results indicate that in the TAL of the quail osmotic water permeability is low while net Cl reabsorption is present, suggesting that the TAL functions as a diluting segment.

Axial heterogeneity in the rat proximal convoluted tubule. II. Osmolality and osmotic water permeability

1984 ◽  
Vol 247 (5) ◽  
pp. F822-F826 ◽  
Author(s):  
F. Y. Liu ◽  
M. G. Cogan ◽  
F. C. Rector
Keyword(s):  
Proximal Tubule ◽  
Water Permeability ◽  
Driving Force ◽  
Wistar Rats ◽  
Proximal Convoluted Tubule ◽  
Osmotic Gradient ◽  
Osmotic Water Permeability ◽  
Water Reabsorption ◽  
Osmotic Water ◽  
Measured Water

To assess whether proximal luminal fluid becomes hypotonic with respect to plasma, free-flow micropuncture measurements were made sequentially from the end-proximal tubule to Bowman's space in 10 tubules of hydropenic Munich-Wistar rats. Osmolality in Bowman's space was 2.8 +/- 0.3 mosmol less than in plasma. Tubular fluid osmolality fell along the tubule and by the end-proximal tubule was 7.5 +/- 0.7 mosmol/kg less than in plasma or 4.7 mosmol/kg less than in Bowman's space. Since luminal fluid became hypotonic, the reabsorbate was hypertonic. The transepithelial osmotic water permeability (Pf) was calculated using simultaneously measured water reabsorption rates. The osmotic gradient responsible for water reabsorption was assumed to be either lumen-to-reabsorbate or lumen-to-peritubular plasma, with a reflection coefficient for sodium chloride of 0.7-1.0. The Pf was then estimated to be between 0.2 and 2.0 cm/s in the first millimeter of tubule and to have fallen to 0.1-0.2 cm/s by the end of the tubule. In conclusion, luminal hypotonicity develops in the rat proximal convoluted tubule and must be considered as part of the osmotic driving force for water reabsorption.

Effects of high potassium concentration on theophylline responses of toad bladder

1977 ◽  
Vol 232 (2) ◽  
pp. F173-F177
Author(s):  
S. A. Mendoza ◽  
K. K. Nakamoto
Keyword(s):  
Cyclic Amp ◽  
Water Permeability ◽  
Potassium Concentration ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Toad Bladder ◽  
Osmotic Water Permeability ◽  
High Potassium ◽  
Bathing Medium ◽  
Osmotic Water

It has been demonstrated previously that a high concentration of potassium in the serosal bathing medium (5–21.5 mM) potentiates the increase in short-circuit current caused by vasopressin or exogenous cyclic AMP. The same concentration of potassium in the bathing medium inhibited the increase in short-circuit current caused by theophylline. The increases in osmotic water permeability caused by vasopressin or cyclic AMP were unaffected by a serosal potassium concentration of 21.5 mM. The increase in osmotic water permeability caused by theophylline was inhibited by 21.5 mM potassium. The concentration of cyclic AMP in either intact total bladder or isolated toad bladder cells was increased two- or three-fold by theophylline. Increasing the concentration of potassium to 21.5 mM did not alter cyclic AMP concentration in either the absence of presence of theophylline. One interpretation of these results is that theophylline increases osmotic water flow and short-circuit current by a mechanism other than by inhibition of cyclic nucleotide phosphodiesterase.

Osmotic water permeability of rat intestinal brush border membrane vesicles: involvement of aquaporin-7 and aquaporin-8 and effect of metal ions

2007 ◽  
Vol 85 (6) ◽  
pp. 675-684 ◽  
Author(s):  
Simona Tritto ◽  
Giulia Gastaldi ◽  
Sergey Zelenin ◽  
Monica Grazioli ◽  
Maria Novella Orsenigo ◽  
...  
Keyword(s):  
Small Intestine ◽  
Epithelial Cells ◽  
Water Permeability ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Water Movement ◽  
Membrane Vesicles ◽  
Osmotic Water Permeability ◽  
Transfected Cells ◽  
Osmotic Water

Water channels AQP7 and AQP8 may be involved in transcellular water movement in the small intestine. We show that both AQP7 and AQP8 mRNA are expressed in rat small intestine. Immunoblot and immunohistochemistry experiments demonstrate that AQP7 and AQP8 proteins are present in the apical brush border membrane of intestinal epithelial cells. We investigated the effect of several metals and pH on the osmotic water permeability (Pf) of brush border membrane vesicles (BBMVs) and of AQP7 and AQP8 expressed in a cell line. Hg2+, Cu2+, and Zn2+ caused a significant decrease in the BBMV Pf, whereas Ni2+ and Li+ had no effect. AQP8-transfected cells showed a reduction in Pf in the presence of Hg2+ and Cu2+, whereas AQP7-transfected cells were insensitive to all tested metals. The Pf of both BBMVs and cells transfected with AQP7 and AQP8 was not affected by pH changes within the physiological range, and the Pf of BBMVs alone was not affected by phlorizin or amiloride. Our results indicate that AQP7 and AQP8 may play a role in water movement via the apical domain of small intestine epithelial cells. AQP8 may contribute to the water-imbalance-related clinical symptoms apparent after ingestion of high doses of Hg2+ and Cu2+.

Experimental tests of three-dimensional model of urinary concentrating mechanism.

1992 ◽  
Vol 2 (12) ◽  
pp. 1677-1688
Author(s):  
J S Han ◽  
K A Thompson ◽  
C L Chou ◽  
M A Knepper
Keyword(s):  
Water Permeability ◽  
Collecting Duct ◽  
Three Dimensional ◽  
Renal Medulla ◽  
Osmotic Gradient ◽  
Osmotic Water Permeability ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Osmotic Water ◽  
Collecting Ducts

Recently, a new model of the urinary concentrating process has been proposed that takes into account the three-dimensional architecture of the renal medulla. Under the assumptions of the model, computer simulations predicted significant axial osmolality gradients in the inner medulla without active transport by the inner medullary loop of Henle. Two of the model assumptions (which constitute hypotheses for this study) were: (1) the osmotic water permeability of the initial part of the inner medullary collecting duct (initial IMCD) is very low even in the presence of vasopressin; and (2) there is significant lateral separation of structures such that thin descending limbs are far from the collecting ducts at the same inner medullary level. The first hypothesis was addressed by perfusing rat initial IMCD segments in vitro and measuring osmotic water permeability. With the osmotic gradient oriented as predicted by the model (lumen greater than bath), vasopressin increased the osmotic water permeability from 286 to 852 microns/s. Three additional series of experiments confirmed the high water permeability in the presence of vasopressin. The second hypothesis was addressed by morphometric analysis of histologic cross-sections of the rat renal medulla. Mean distances of descending limbs to the nearest adjacent collecting duct were very small throughout the inner medulla (less than 6 microns) and substantially less than in the outer medulla (28 microns). It was concluded that the data are inconsistent with both hypotheses and therefore do not support the feasibility of the "three-dimensional" model of the renal inner medulla. The axial distributions of loops of Henle and collecting ducts in the rat renal medulla are also reported.

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