Glomerulotubular balance in a mathematical model of the proximal nephron

A nonelectrolyte model of proximal tubule epithelium has been extended by the inclusion of a compliant tight junction. Here "compliance" signifies that both the junctional salt and water permeability increase and the salt reflection coefficient decreases in response to small pressure differences from lateral interspace to tubule lumen. In previous models of rat proximal tubule, there has been virtually no sensitivity of isotonic salt transport to changes in peritubular oncotic force. With the inclusion of junctional compliance, decreases in peritubular protein can open the junction and produce a secretory salt flux. Thus the model can represent the "backflux hypothesis," as it was originally put forth (J. E. Lewy and E. E. Windhager, Am. J. Physiol. 214: 943-954, 1968). Additional calculations, simulating a tight junction with negligible water permeability, reveal that the quantitative impact of peritubular protein can be realized whether or not there is substantial junctional water flux. The epithelial model of proximal tubule has also been incorporated into a model of the proximal nephron, complete with glomerulus, peritubular capillary, and interstitium. The interstitial compartment is well mixed and interstitial pressure and osmolality are determined iteratively to achieve balance between tubule reabsorption and capillary uptake. For this model, two domains of operation are identified. When interstitial pressures are low, junctions are closed, and filtration fraction has no effect on proximal reabsorption. When interstitial pressures are relatively elevated, epithelial junctions are open, and proximal salt reabsorption changes in proportion to changes in filtration fraction. In neither domain, however, does the model tubule augment salt flux with isolated increases in luminal flow rate (at constant filtration fraction). The absence of a separate effect of tubule fluid flow on salt transport precludes perfect glomerulotubular balance.

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Reflection coefficients and water permeability in rat proximal tubule

AJP Renal Physiology ◽

10.1152/ajprenal.1989.257.4.f658 ◽

1989 ◽

Vol 257 (4) ◽

pp. F658-F668 ◽

Cited By ~ 7

Author(s):

R. Green ◽

G. Giebisch

Keyword(s):

Proximal Tubule ◽

Water Permeability ◽

Significant Contribution ◽

Water Flux ◽

Reflection Coefficients ◽

Ionic Fluxes ◽

Peritubular Capillaries ◽

Solute Movement ◽

Rat Proximal Tubule ◽

Net Water Flux

Simultaneous microperfusion of proximal tubules and peritubular capillaries in kidneys of rats anesthetized with Inactin was used to measure reflection coefficients. All perfusates contained cyanide to inhibit active transport; the tubular perfusate was isotonic and the peritubular capillaries were perfused with solutions made hypertonic with NaCl, NaHCO3, L-glucose, or sodium ferrocyanide. Measurements of recollected fluid enabled a precise mean gradient and ionic fluxes to be calculated; net water flux was measured with inulin. Imposed gradients always partly dissipated. Reflection coefficients were 0.59 +/- 0.01 for NaCl, 0.87 +/- 0.04 for NaHCO3-, and 0.96 +/- 0.07 for ferrocyanide, assuming that L-glucose was 1. Water permeability of the proximal tubule was 1,030 microns/s. Ionic permeability of Cl- (21.6 +/- 1.3 X 10(-5) cm/s) was greater than that for Na+ (13.3 +/- 2.7 X 10(-5) cm/s); permeability for L-glucose was 5.4 +/- 1.3 X 10(-5), and for ferrocyanide ions 2.7 +/- 0.9 X 10(-5) cm/s. It is concluded that in rat proximal tubule both NaCl and NaHCO3 have reflection coefficients less than 1.0 and solute asymmetry across the epithelium is a significant driving force for fluid reabsorption. Furthermore the data suggest that there is a significant contribution of solvent drag to solute movement.

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A dual-pathway ultrastructural model for the tight junction of rat proximal tubule epithelium

AJP Renal Physiology ◽

10.1152/ajprenal.00331.2002 ◽

2003 ◽

Vol 285 (2) ◽

pp. F241-F257 ◽

Cited By ~ 25

Author(s):

Peng Guo ◽

Alan M. Weinstein ◽

Sheldon Weinbaum

Keyword(s):

Tight Junction ◽

Proximal Tubule ◽

Water Permeability ◽

Pore Radius ◽

Pathway Model ◽

Small Pore ◽

Order Of Magnitude ◽

Dual Pathway ◽

Ultrastructural Model ◽

Rat Proximal Tubule

A dual-pathway model is proposed for transport across the tight junction (TJ) in rat proximal tubule: large slit breaks formed by infrequent discontinuities in the TJ complex and numerous small circular pores, with spacing similar to that of claudin-2. This dual-pathway model is developed in the context of a proximal tubule model (Weinstein AM. Am J Physiol Renal Fluid Electrolyte Physiol 247: F848–F862, 1984) to provide an ultrastructural view of solute and water fluxes. Tubule model paramters (TJ reflection coefficient and water permeability), plus the measured epithelial NaCl and sucrose permeabilities, provide constraints for the dual-pathway model, which yields the small-pore radius and spacing and large slit height and area. For a small-pore spacing of 20.2 nm, comparable to the distance between adjacent particle pairs in apposing TJ strands, the small-pore radius is 0.668 nm and the large slit breaks have a height of 19.6 nm, occupying 0.04% of the total TJ length. This pore/slit geometry also satisfies the measured permeability for mannitol. The numerous small circular pores account for 91.25% of TJ NaCl permeability but only 5.0% of TJ water permeability. The infrequent large slit breaks in the TJ account for 95.0% of TJ water permeability but only 8.7% of TJ NaCl permeability. Sucrose and mannitol (4.6- and 3.6-Å radius) can pass through both the large slit breaks and the small pores. For sucrose, 78.3% of the flux is via the slits and 21.7% via the pores; for mannitol, the flux is split nearly evenly between the two pathways, 50.8 and 49.2%. In this ultrastructural model, the TJ water permeability is 21.2% of the entire transepithelial water permeability and thus an order of magnitude greater than that predicted by the single-pore/slit theory (Preisig PA and Berry CA. Am J Physiol Renal Fluid Electrolyte Physiol 249: F124–F131, 1985).

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Improving the Structural Parameter of the Membrane Sublayer for Enhanced Forward Osmosis

Membranes ◽

10.3390/membranes11060448 ◽

2021 ◽

Vol 11 (6) ◽

pp. 448

Author(s):

Jin Fei Sark ◽

Nora Jullok ◽

Woei Jye Lau

Keyword(s):

Water Permeability ◽

Elevated Temperatures ◽

Interfacial Polymerization ◽

Water Flux ◽

Forward Osmosis ◽

Salt Flux ◽

Structural Parameter ◽

Asymmetric Membrane ◽

S Parameter ◽

Phase Inversion Technique

The structural (S) parameter of a medium is used to represent the mass transport resistance of an asymmetric membrane. In this study, we aimed to fabricate a membrane sublayer using a novel composition to improve the S parameter for enhanced forward osmosis (FO). Thin film composite (TFC) membranes using polyamide (PA) as an active layer and different polysulfone:polyethersulfone (PSf:PES) supports as sublayers were prepared via the phase inversion technique, followed by interfacial polymerization. The membrane made with a PSf:PES ratio of 2:3 was observed to have the lowest contact angle (CA) with the highest overall porosity. It also had the highest water permeability (A; 3.79 ± 1.06 L m−2 h−1 bar−1) and salt permeability (B; 8.42 ± 2.34 g m−2 h−1), as well as a good NaCl rejection rate of 74%. An increase in porosity at elevated temperatures from 30 to 40 °C decreased Sint from 184 ± 4 to 159 ± 2 μm. At elevated temperatures, significant increases in the water flux from 13.81 to 42.86 L m−2 h−1 and reverse salt flux (RSF) from 12.74 to 460 g m−2 h−1 occur, reducing Seff from 152 ± 26 to 120 ± 14 μm. Sint is a temperature-dependent parameter, whereas Seff can only be reduced in a high-water- permeability membrane at elevated temperatures.

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THE ROLE OF SEASONAL SALT AND WATER FLUXES IN THE GENESIS OF SOLONETZIC B HORIZONS

Canadian Journal of Soil Science ◽

10.4141/cjss87-071 ◽

1987 ◽

Vol 67 (4) ◽

pp. 721-730 ◽

Cited By ~ 1

Author(s):

S. FULLERTON (nee Landsburg) ◽

S. PAWLUK

Keyword(s):

Water Table ◽

Water Flux ◽

Dominant Mode ◽

Salt Transport ◽

Salt Flux ◽

Water Fluxes ◽

Moisture Movement ◽

Soil Temperatures ◽

Capillary Movement

Seasonal salt and water fluxes into Black Solonetz soils were evaluated at two sites in east-central Alberta. The dominant mode of moisture movement into the soil pedon was by capillary movement of water upwards from the water table. Solonization occurred in the Bntj horizons as a consequence of salt transport; the salts responsible were NaHCO3 and Na2SO4. Seasonal salt and water fluxes were identified at both research sites. From May to November when soil temperatures were above 0 °C, capillary movement and evaporation were the major mechanisms responsible for salt transport, concentration and deposition. From December to March when soil temperatures were below 0 °C water moved upwards from the water table towards the freezing zone depositing salts upon freezing. Key words: Genesis, solonetzic; season, groundwater, salt flux, water flux

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Transport Models of Ammonium Nitrogen in Wastewater from Rare Earth Smelteries by Reverse Osmosis Membranes

Sustainability ◽

10.3390/su12156230 ◽

2020 ◽

Vol 12 (15) ◽

pp. 6230

Author(s):

Shuanglin Gui ◽

Zhaohuan Mai ◽

Jiaqi Fu ◽

Yuansong Wei ◽

Jinbao Wan

Keyword(s):

Rare Earth ◽

Reverse Osmosis ◽

Membrane Fouling ◽

Driving Force ◽

Water Flux ◽

Ammonium Nitrogen ◽

Salt Transport ◽

Salt Flux ◽

Operating Pressure ◽

Concentration Difference

Wastewater from rare earth smelteries contains large amounts of ammonium nitrogen (NH4+-N), which causes severe environmental problems. In this contribution, the desalination efficiency of reverse osmosis (RO) was investigated in the treatment of NH4Cl or NaCl solutions from 0.1 to 40 g/L under different operating pressures with a commercial RO membrane. Experimental results showed that when an operating pressure above 30 bar is applied to the 5 g/L NH4Cl solution, the permeate was found to meet the discharge standards of NH4+-N. Compared to NH4Cl, the permeate fluxes of NaCl solutions were higher due to the higher net driving force and lower propensity to membrane fouling. Theoretical models indicate a linear relationship between water flux and the net driving force for both NH4Cl and NaCl solutions. On the contrary, a power function between the salt flux and concentration difference correlated well with the experimental data for salt transport. The equations for water and salt transport obtained by this work would provide a facile and practical means for predicting the membrane performance in design and optimization of RO processes for the treatment of wastewater from the rare earth industry.

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Modeling the proximal tubule: complications of the paracellular pathway

AJP Renal Physiology ◽

10.1152/ajprenal.1988.254.3.f297 ◽

1988 ◽

Vol 254 (3) ◽

pp. F297-F305 ◽

Cited By ~ 5

Author(s):

A. M. Weinstein

Keyword(s):

Tight Junction ◽

Proximal Tubule ◽

Epithelial Transport ◽

Water Movement ◽

Water Flux ◽

Transport Equations ◽

Transport Processes ◽

Paracellular Pathway ◽

Convective Flux ◽

Solute Polarization

When the proximal tubule epithelium is represented as cellular and lateral intercellular (LIS) compartments, the presence of a paracellular pathway can render the overall phenomenologic equations quite an indirect representation of intraepithelial transport processes. 1) Active sodium transport into the LIS may create a hypertonic region that drives water movement from lumen to peritubular blood, i.e., a term for active water transport may appear in the overall transport equations. The correlate of this uphill water flux is a solute polarization effect, such that the measured epithelial water permeability is less than that of the cell membranes. 2) Basolateral uptake of potassium by the cell may lower the LIS concentration and promote diffusive entry of K across the tight junction. Even without cellular uptake of K from the lumen, the epithelial transport equations may contain a term for active K reabsorption. The solute polarization correlate is a low epithelial reflection coefficient that does not represent a convective flux of K through a specific channel. 3) When there is convective flux of Na and Cl through the tight junction but none through the cell, then a fluid circuit around junction and cell may be present, even when net epithelial volume flux is absent. In this case, part of the net epithelial Cl flux must be represented in the overall transport equations as electroneutral Na-Cl cotransport.

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Evaluating Fertilizer-Drawn Forward Osmosis Performance in Treating Anaerobic Palm Oil Mill Effluent

Membranes ◽

10.3390/membranes11080566 ◽

2021 ◽

Vol 11 (8) ◽

pp. 566

Author(s):

Ruwaida Abdul Wahid ◽

Wei Lun Ang ◽

Abdul Wahab Mohammad ◽

Daniel James Johnson ◽

Nidal Hilal

Keyword(s):

Palm Oil ◽

Pure Water ◽

Water Flux ◽

Forward Osmosis ◽

Salt Flux ◽

Palm Oil Mill Effluent ◽

Performance Ratio ◽

Water Recovery ◽

Flux Decline ◽

Palm Oil Mill

Fertilizer-drawn forward osmosis (FDFO) is a potential alternative to recover and reuse water and nutrients from agricultural wastewater, such as palm oil mill effluent that consists of 95% water and is rich in nutrients. This study investigated the potential of commercial fertilizers as draw solution (DS) in FDFO to treat anaerobic palm oil mill effluent (An-POME). The process parameters affecting FO were studied and optimized, which were then applied to fertilizer selection based on FO performance and fouling propensity. Six commonly used fertilizers were screened and assessed in terms of pure water flux (Jw) and reverse salt flux (JS). Ammonium sulfate ((NH4)2SO4), mono-ammonium phosphate (MAP), and potassium chloride (KCl) were further evaluated with An-POME. MAP showed the best performance against An-POME, with a high average water flux, low flux decline, the highest performance ratio (PR), and highest water recovery of 5.9% for a 4-h operation. In a 24-h fouling run, the average flux decline and water recovered were 84% and 15%, respectively. Both hydraulic flushing and osmotic backwashing cleaning were able to effectively restore the water flux. The results demonstrated that FDFO using commercial fertilizers has the potential for the treatment of An-POME for water recovery. Nevertheless, further investigation is needed to address challenges such as JS and the dilution factor of DS for direct use of fertigation.

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Enhancing Water Permeability with Super-hydrophilic Metal-Organic Frameworks and Hydrophobic Straight Pores

Environmental Science Water Research & Technology ◽

10.1039/d1ew00036e ◽

2021 ◽

Author(s):

Mehdi Habibollahzadeh ◽

Juran Noh ◽

Liang Feng ◽

Hong-Cai Zhou ◽

Ahmed Abdel-Wahab ◽

...

Keyword(s):

Osmotic Pressure ◽

Water Permeability ◽

Metal Organic Frameworks ◽

Water Flux ◽

Forward Osmosis ◽

High Water ◽

Metal Organic

High water flux and salt selectivity have been the most demanding goals for osmosis-based membranes. Osmotic pressure differences across membranes are particularly important in emerging forward osmosis and pressure retarded...

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Dependence of ion fluxes on fluid transport by rat proximal tubule

AJP Renal Physiology ◽

10.1152/ajprenal.1986.250.4.f680 ◽

1986 ◽

Vol 250 (4) ◽

pp. F680-F689 ◽

Cited By ~ 7

Author(s):

K. Bomsztyk ◽

F. S. Wright

Keyword(s):

Proximal Tubule ◽

Fluid Transport ◽

Rat Kidney ◽

Water Flux ◽

Fluid Secretion ◽

Proximal Convoluted Tubule ◽

Ion Fluxes ◽

Fluid Absorption ◽

Fluid Flux ◽

K Transport

The effects of changes in transepithelial water flux (Jv) on sodium, chloride, calcium, and potassium transport by the proximal convoluted tubule were examined by applying a microperfusion technique to surface segments in kidneys of anesthetized rats. Perfusion solutions were prepared with ion concentrations similar to those in fluid normally present in the later parts of the proximal tubule. Osmolality of the perfusate was adjusted with mannitol. With no mannitol in the perfusates, net fluid absorption was observed. Addition of increasing amounts of mannitol first reduced Jv to zero and then reversed net fluid flux. At the maximal rates of fluid absorption, net absorption of Na, Cl, Ca, and K was observed. When Jv was reduced to zero, Na, Cl, and Ca absorption were reduced and K entered the lumen. Na, Cl, and Ca secretion occurred in association with the highest rates of net fluid secretion. The lumen-positive transepithelial potential progressively increased as the net fluid flux was reduced to zero and then reversed. The results demonstrate that changes in net water flux can affect Na, Cl, Ca, and K transport by the proximal convoluted tubule of the rat kidney. These changes in net ion fluxes are not entirely accounted for by changes in bulk-phase transepithelial electrochemical gradients.

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