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.

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.

Temperature effect on ADH response of isolated perfused rabbit collecting tubules

1980 ◽  
Vol 239 (6) ◽  
pp. F595-F601 ◽  
Author(s):  
D. A. Hall ◽  
J. J. Grantham
Keyword(s):  
Water Absorption ◽  
Water Permeability ◽  
Time Course ◽  
Adenosine Monophosphate ◽  
Osmotic Gradient ◽  
Bathing Medium ◽  
Osmotic Water ◽  
Subsequent Response ◽  
Collecting Tubules ◽  
Peak Value

The time course of the water permeability response to synthetic arginine vasopressin (AVP) was examined in isolated perfused rabbit collecting tubules. When experiments were conducted at 37 degrees C, addition of AVP in a concentration of 100 microU/ml increased hydraulic water permeability (Lp) from 18 +/- 4 X 10(-7) to 153 +/- 15 X 10(-7) cm x s-1 x atm-1. However, in contrast to results obtained at 25 degrees C, the Lp immediately decreased in spite of the continued presence of AVP, reaching half the peak value in 67 +/- 6 (SE) min. A similar decline was observed at 37 degrees C when a cyclic 3',5'-adenosine monophosphate analogue was added to the bathing medium. Corticosteroids greatly enhanced the peak water absorption but did not stabilize the subsequent response to AVP at 37 degrees C. A decline in diffusional water permeability measured in the absence of a transtubule osmotic gradient excluded the possible roles of cellular hypotonicity, increased cell volume, or osmotic water absorption in the unstable response to hormone. The peritubular membrane remained highly permeable to water, independent of AVP and temperature. Duration of exposure to 37 degrees C was more important than AVP in determining the unstable response. On the basis of these studies we conclude that isolated rabbit cortical collecting tubules progressively become insensitive to AVP at 37 degrees C, possibly due to alterations in the responsiveness of the urinary plasma membrane to cAMP.

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.

Water permeability and pathways in the proximal tubule

1983 ◽  
Vol 245 (3) ◽  
pp. F279-F294 ◽  
Author(s):  
C. A. Berry
Keyword(s):  
Proximal Tubule ◽  
Water Transport ◽  
Water Permeability ◽  
Intercellular Space ◽  
Proximal Convoluted Tubule ◽  
Pressure Gradients ◽  
Solvent Drag ◽  
Lateral Intercellular Space ◽  
Volume Absorption ◽  
Osmotic Water

The route of water transport in the proximal tubule could be either transjunctional or transcellular. A transjunctional route is supported by data showing high osmotic-to-diffusive water permeability ratios, the possible correlation of junctional leakiness to ions and nonelectrolytes with water permeability, and solvent drag of nonelectrolytes and ions. These data, however, are not convincing. A transcellular route of water transport is supported by data showing that the osmotic water permeability (Pf) for apical and/or basolateral cell membranes is sufficiently high to account for the transepithelial Pf, making a tentative conclusion for a transcellular route of water transport possible. In addition, measurements of Pf have yielded insights into the mechanism of solute-solvent coupling. Pf has been reported to be mostly between 0.1 and 0.3 cm/s. In the rabbit proximal straight and the Necturus proximal convoluted tubule, in which water transport rates are low, this range of Pf will account for volume absorption with only small osmotic gradients (less than 6 mosmol). Higher osmotic gradients are required in the rat and possibly the rabbit proximal convoluted tubule, where water transport rates are higher. Solute-solvent coupling in all species is probably due to both luminal hypotonicity and lateral intercellular space hypertonicity. These two processes are directly linked. Mass balance requires that generation of luminal hypotonicity also generates a hypertonic absorbate and, thus, some degree of lateral intercellular space hypertonicity. It is likely that, in the rabbit at least, effective osmotic pressure gradients due to differences in solute reflection coefficients play little role in solute-solvent coupling.

Cytochalasin B inhibition of toad bladder apical membrane responses to ADH

1988 ◽  
Vol 255 (4) ◽  
pp. C526-C530 ◽  
Author(s):  
J. B. Wade ◽  
W. A. Kachadorian
Keyword(s):  
Water Permeability ◽  
Cytochalasin B ◽  
Apical Membrane ◽  
Freeze Fracture ◽  
Toad Urinary Bladder ◽  
Osmotic Gradient ◽  
Osmotic Water ◽  
Structural Responses ◽  
Freeze Fracture Electron Microscopy

The possible role of actin microfilaments in antidiuretic hormone (ADH)-induced increases in apical membrane water permeability was investigated in studies that evaluate inhibition by cytochalasin B of both permeability and membrane structural responses in the toad urinary bladder. Experiments were carried out in the absence of a transepithelial osmotic gradient to eliminate possible flow-induced distortions of the response. Measurements of osmotic water permeability after a brief tissue fixation with glutaraldehyde show that cytochalasin B reduces the permeability response to ADH by approximately one-third. Freeze-fracture electron microscopy indicates that the intramembrane particle aggregates, previously found to correlate closely with ADH-induced permeability, are reduced by about the same extent (28%) under these conditions. However, the frequency of apical membrane fusion events was not affected by cytochalasin B treatment. These results suggest that cytochalasin B treatment in the absence of an osmotic gradient alters the ADH-induced permeability through an effect on apical membrane aggregate frequency.

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.

Nitric oxide inhibits ADH-stimulated osmotic water permeability in cortical collecting ducts

1996 ◽  
Vol 270 (1) ◽  
pp. F206-F210 ◽  
Author(s):  
N. H. Garcia ◽  
S. I. Pomposiello ◽  
J. L. Garvin
Keyword(s):  
Nitric Oxide ◽  
Water Permeability ◽  
Collecting Duct ◽  
Sodium Reabsorption ◽  
Cortical Collecting Duct ◽  
Urinary Volume ◽  
No Donor ◽  
Osmotic Water ◽  
Spermine Nonoate

Nitric oxide (NO) reduces blood pressure in vivo by two mechanisms, vasodilation and increasing urinary volume: however, the exact mechanism by which it increases urinary volume is not clear. We hypothesized that NO inhibits antidiuretic hormone (ADH)-stimulated fluid reabsorption (J(r)) by the isolated rat cortical collecting duct (CCD) by decreasing water permeability (Pf) and sodium reabsorption (Jna). In the presence of 10(-11) MADH, Jv was 0.15 +/- 0.04 nl.min-1.mm-1; after 10(-6) M spermine nonoate (SPM) was added to the bath. Jv decreased to 0.06 +/- 0.03 nl.min-1.mm-1 (P < 0.03). To investigate whether the inhibition of Jv was the result of decreased Pf and/or Jna, we first tested the effect of SPM on ADH-stimulated Pf. Basal Pf was stimulated to 289.2 +/- 77.3 microns/s after 10(-11) M ADH was added to the bath (P < 0.01). SPM decreased Pf to 159.8 +/- 45.0 microns/s (P < 0.05). To ensure that this effect on Pf was due to NO release, we used another NO donor, nitroglycerin (NTG). Pf was initially -25.8 +/- 18.3 microns/s and increased to 133.9 +/- 30.5 microns/s after addition of 10(-11) M ADH (P < 0.002). NTG, 20 microM, lowered Pf to 92.4 +/- 18.4 microns/s (P < 0.02). In the presence of 10(-9) M ADH, NTG also decreased Pf(P < 0.04). Next we investigated the effect of SPM on ADH-stimulated JNa. In the presence of ADH, JNa was 37.8 +/- 7.3 pmol.min-1.mm-1. After SPM was added, it dropped to 24.3 +/- 5.1 pmol.min-1.mm-1 (P < 0.05). Time controls exhibited no change in ADH-stimulated Jv, Pf, or Jna. We concluded that 1) NO decreases ADH-stimulated water and sodium transport in the isolate CCD, and 2) water reabsorption is inhibited by a primary effect on Pf. A direct effect of NO on the CCD may explain its natriuretic and diuretic effects observed in vivo.

A model of osmotic and hydrostatic pressure effects on volume absorption in the proximal tubule

1987 ◽  
Vol 253 (3) ◽  
pp. F563-F575
Author(s):  
J. C. Williams ◽  
J. A. Schafer
Keyword(s):  
Hydrostatic Pressure ◽  
Proximal Tubule ◽  
Water Permeability ◽  
Solute Concentration ◽  
Pressure Effects ◽  
Good Prediction ◽  
Osmotic Water Permeability ◽  
Volume Absorption ◽  
Osmotic Water

A computer model of the proximal tubule of the rabbit is described in which the tubule is treated as a single cylindrical barrier to the flow of solute and water between lumen and bath, and volume absorption is assumed to be driven exclusively by hydrostatic and osmotic pressure differences across this barrier. The model mimics the function of the tubule in two in vitro preparations: in simulations of the isolated tubule perfused under oil, the model correctly describes the solute concentration gradients that exist between the perfusate and absorbate and predicts differences in solute concentrations among absorbate droplets on the same tubule if luminal concentration becomes limiting. This prediction was tested experimentally with glucose and found to be correct. In simulations of the tubule perfused in an aqueous bath, the role of transmural hydrostatic pressure was explored; it is predicted that, at normal rates of in vitro perfusion (approximately 10 nl/min), increases in pressure have very little effect on volume absorption but can greatly alter the osmotic differences present across the wall of the tubule, especially with high values of osmotic water permeability. At high rates of perfusion, the ability of the tubule to produce a lumen hypotonic to the bath is reduced, but the direct effects of pressure on volume absorption become more apparent, resulting in relatively little effect of perfusion rate on volume absorption if the osmotic water permeability is sufficiently high. A similar relationship was seen experimentally. In all, this simple model provides a good prediction of function in isolated perfused tubules without any assumptions of hypertonic compartments within the epithelium.

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.

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