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.

Cell osmotic water permeability of isolated rabbit proximal straight tubules

1982 ◽  
Vol 242 (4) ◽  
pp. F321-F330 ◽  
Author(s):  
E. Gonzalez ◽  
P. Carpi-Medina ◽  
G. Whittembury
Keyword(s):  
Surface Area ◽  
Water Flow ◽  
Water Permeability ◽  
Permeability Coefficient ◽  
Osmotic Water Permeability ◽  
Water Permeability Coefficient ◽  
Osmotic Water ◽  
Straight Tubules ◽  
Tubular Surface ◽  
Set Up

Proximal straight tubules were dissected and mounted in a chamber with their lumina occluded. The well-stirred bath could be 95% changed within 84 ms to set up osmotic gradients (delta Coi) across the peritubular cell aspect. Volume changes (less than or equal to 10 pl/mm) were estimated from continuous records of diameter changes (error less than 0.1 micrometers). delta Coi greater than or equal to 2-3 mosM could be discerned. delta Coi values from 10 to 44 mosM were used to evaluate Posc, the cell osmotic water permeability coefficient, and extrapolated to delta Coi = 0. Posc = 25.1 (+/- 2.3) X 10(-4) cm3.s-1.osM-1.cm2 tubular surface area-1. These values are lower than those reported for Pose, the transepithelial osmotic water permeability coefficient, and become lower if corrected for the real (infolded) peritubular cell surface area. Thus, for a given osmotic difference, transcellular water flow finds a higher resistance than paracellular water flow. Experiments were also performed with delta Coi greater than 100 mosM, but interpretation of these data is difficult because of the presence of volume regulatory phenomena and other undesirable effects.

Cell osmotic water permeability of isolated rabbit proximal convoluted tubules

1983 ◽  
Vol 244 (5) ◽  
pp. F554-F563 ◽  
Author(s):  
P. Carpi-Medina ◽  
E. Gonzalez ◽  
G. Whittembury
Keyword(s):  
Water Flow ◽  
Water Permeability ◽  
Time Course ◽  
Basal Area ◽  
Osmotic Gradient ◽  
Osmotic Water Permeability ◽  
Osmotic Water ◽  
Transcellular Osmosis ◽  
Convoluted Tubules ◽  
Paracellular Water Flow

Cell osmotic water permeability, Pcos, of the peritubular aspect of the proximal convoluted tubule (PCT) was measured from the time course of cell volume changes subsequent to the sudden imposition of an osmotic gradient, delta Cio, across the cell membrane of PCT that had been dissected and mounted in a chamber. The possibilities of artifact were minimized. The bath was vigorously stirred, the solutions could be 95% changed within 0.1 s, and small osmotic gradients (10-20 mosM) were used. Thus, the osmotically induced water flow was a linear function of delta Cio and the effect of the 70-microns-thick unstirred layers was negligible. In addition, data were extrapolated to delta Cio = 0. Pcos for PCT was 41.6 (+/- 3.5) X 10(-4) cm3 X s-1 X osM-1 per cm2 of peritubular basal area. The standing gradient osmotic theory for transcellular osmosis is incompatible with this value. Published values for Pcos of PST are 25.1 X 10(-4), and for the transepithelial permeability Peos values are 64 X 10(-4) for PCT and 94 X 10(-4) for PST, in the same units. These results indicate that there is room for paracellular water flow in both nephron segments and that the magnitude of the transcellular and paracellular water flows may vary from one segment of the proximal tubule to another.

Modulation of vasopressin action by reducing agents in Bufo marinus

1982 ◽  
Vol 243 (1) ◽  
pp. C52-C61 ◽  
Author(s):  
D. E. Butkus ◽  
J. H. Schwartz
Keyword(s):  
Adenylate Cyclase ◽  
Water Flow ◽  
Water Permeability ◽  
Regulatory Protein ◽  
Inhibitory Effect ◽  
Bufo Marinus ◽  
Inhibitory Effects ◽  
Thiol Compounds ◽  
Osmotic Water ◽  
Osmotic Water Flow

The effects of the reducing agent dithiothreitol (DTT) on vasopressin (AVP)-stimulated osmotic water flow and adenylate cyclase activity were studied in the urinary bladder of Bufo marinus. DTT produced concentration-dependent inhibition of the hydroosmotic water permeability response to 10 mU/ml AVP and 10 mM theophylline but did not inhibit the response to 10 mM adenosine 3',5'-cyclic monophosphate (cAMP). The inhibitory effects of DTT on AVP responsiveness were partially reversed by washing in DTT-free Ringer solution or by addition of oxidizing agents such as dehydroascorbic acid (DHA) or H2O2. The inhibitory effects of DTT were completely reversed by washing in DTT-free Ringer plus addition of DHA. In addition, the inhibitory effects of DTT on AVP-induced osmotic water flow were partially reversed by the GTP analogue 5'-guanylyl imidodiphosphate [Gpp(NH)p]. DTT also inhibited the adenylate cyclase response to AVP but did not alter the response to AVP plus Gpp(NH)p or the response to NaF. These observations suggest that the inhibitory effect of thiol compounds on AVP responsiveness may be modulated through alterations of a redox system distal to the hormone receptor but proximal to the catalytic subunit of adenylate cyclase. Inasmuch as Gpp(NH)p partially reversed the inhibitory effects of DTT on AVP-stimulated osmotic water permeability and prevented the inhibitory effect of DTT on AVP-stimulated adenylate cyclase, an effect on either GTPase or binding of GTP to the regulatory protein of adenylate cyclase is suggested by these observations.

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.

Hyperosmolality of absorbate from isolated rabbit proximal tubules

1984 ◽  
Vol 247 (1) ◽  
pp. F130-F139 ◽  
Author(s):  
D. W. Barfuss ◽  
J. A. Schafer
Keyword(s):  
Water Permeability ◽  
Regression Line ◽  
Complete Analysis ◽  
Rabbit Serum ◽  
Osmotic Gradient ◽  
Bathing Medium ◽  
Volume Absorption ◽  
Osmotic Water ◽  
Straight Tubules

Rabbit proximal convoluted (PCT) and proximal straight tubules (PST) were perfused under oil so that droplets of absorbate could be collected. When PCT segments were perfused with an ultrafiltrate of rabbit serum or with a similar artificial solution, the osmolality of the absorbate was higher than that of the luminal perfusate by, respectively, 18.4 +/- 1.8 (SE) (P less than 0.001) or 15.8 +/- 1.9 (P less than 0.001) mosmol/kg H2O. In the PST, the absorbate osmolality was 7.7 +/- 2.6 mosmol/kg H2O (P less than 0.012) higher than an artificial perfusate solution. In the PCT the volume absorption rate was positively correlated with the osmolality difference (r = 0.653, P less than 0.002), and the slope of the linear regression line was 0.068 +/- 0.007 nl X min-1 X mm-1 X (mosmol/kg H2O)-1. Although a complete analysis based on reflection coefficients of the several solutes could not be made, this slope indicates that the maximum osmotic water permeability of the PCT in these experiments was 800-1,000 micron/s, which is significantly less than observed previously in tubules perfused in an aqueous bathing medium. The size of the osmotic gradient in the PST also implies a lower water permeability than expected. The results show, however, that a hyperosmotic absorbate can be generated by both segments when the peritubular volume is restricted. In vivo the same process would be expected to generate luminal hypotonicity.

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.

THE SWELLING OF FROG BLADDER CELLS PRODUCED BY OXYTOCIN

1965 ◽  
Vol 33 (2) ◽  
pp. 171-177 ◽  
Author(s):  
J. V. NATOCHIN ◽  
K. JANÁČEK ◽  
R. RYBOVÁ
Keyword(s):  
Urinary Bladder ◽  
Water Flow ◽  
Osmotic Gradient ◽  
Frog Urinary Bladder ◽  
Intracellular Space ◽  
Osmotic Water ◽  
Inulin Space ◽  
Bladder Cells ◽  
Synthetic Oxytocin ◽  
Osmotic Water Flow

SUMMARY (1) Synthetic oxytocin (100 m-u./ml.) produces swelling of the isolated frog urinary bladder even in the absence of an osmotic gradient across the bladder. (2) Calculations show that the change in intracellular space does not necessarily differ significantly from that in the presence of an osmotic gradient since the inulin space is markedly affected by the osmotic water flow. (3) Part of the cellular potassium is exchanged for sodium during the swelling produced by oxytocin. (4) A possible mechanism and the significance of the swelling is discussed.

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.

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.

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