Evidence for water channels in renal proximal tubule cell membranes

Meyer, Mary M.; Verkman, A. S.

doi:10.1007/bf01869237

“…This is also the first report on the measurement of the Pf in the EVs. The value obtained (4.75 × 10 −4 cm s −1 ) was much smaller than the values reported for kidney proximal tubule brush border membrane vesicles and erythrocytes (~ 100 × 10 −4 cm s −1 ) [17,21]. The reasons for this discrepancy can be multifold.…”

Section: Discussioncontrasting

confidence: 71%

AQP2 in human urine is predominantly localized to exosomes with preserved water channel activities

Miyazawa

¹

,

Mikami

²

,

Yamamoto

³

et al. 2018

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Background AQP2 water channel is critical for urinary concentration in the kidney. Interestingly, AQP2 is abundantly excreted in the urine as extracellular vesicles (EVs), which is known to be a useful biomarker for water-balance disorders although the character of AQP2-enriched EVs is poorly understood including water channel function. Methods Human urine EVs were obtained by a differential centrifugation method. AQP2-bearing EVs were isolated by immunoprecipitation with an AQP2-specific antibody, and the proteins in the EVs were analyzed by LC-MS/MS proteomic analysis. Osmotic water permeability (Pf) of the AQP2-rich EVs was measured by a stopped-flow method monitoring scattered light intensity in response to outwardly directed osmotic gradient. Results Sequential centrifugation of human urine showed that AQP2 was present predominantly (80%) in low-density EVs (160,000 g), whereas negligible amount in high-density EVs (17,000 g). Proteomic analysis of the AQP2-bearing EVs identified 137 proteins, mostly in the endosome pathway, including the components of ESCRT (endosomal sorting complex required transporter)-I, II, III. Pf value of the 160,000 g EVs was 4.75 ± 0.38 × 10 −4 cm s −1 (mean ± SE) with the activation energy of 3.51 kcal mol −1 which was inhibited with 0.3 mM HgCl 2 by 63%, suggesting a channel-mediated water transport. Moreover, Pf value showed a significant correlation with the abundance of AQP2 protein in EVs. Conclusion Taken together, AQP2 is localized predominantly to urinary exosomes with preserved water channel activities.

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“…A low E a (Ͻ6 kcal mol Ϫ1 ) for water transport is among the typical features of membranes with water-transporting pores (Chrispeels and Agre, 1994;Verkman et al, 1996;Maurel et al, 1997;Niemietz and Tyerman, 1997), while transport through the membrane lipid bilayer is associated with high Arrhenius E a values. Mercurials can increase the E a of water permeation facilitated by water channels (Macey, 1984;Meyer and Verkman, 1987;van Hoek et al, 1990). However, in our study, HgCl 2 significantly reduced E a values for Q v in roots and more studies will be required for a proper explanation of these results.…”

Section: Discussionmentioning

confidence: 51%

“…At the present time, we cannot conclude with any certainty that the water channels in aspen are sensitive to temperature; nevertheless, the results suggest that the mercury-sensitive processes are also temperature sensitive. If the effect of HgCl 2 is mainly on water channels, as reported for individual cells and isolated membrane vesicles (Macey, 1984;Meyer and Verkman, 1987;Pratz et al, 1986;Maurel et al, 1997;Niemietz and Tyerman, 1997), then the channels may indeed be temperature sensitive. However, we cannot exclude the possibility that other, temperature-sensitive processes involved in root water transport are affected by mercury resulting in this effect.…”

Section: Discussionmentioning

confidence: 86%

“…Mercury reversibly inhibits the bulk water transport across membranes in animal cells (Pratz et al, 1986;Meyer and Verkman, 1987) and plant cells (Maggio and Joly, 1995;Carvajal et al, 1996;Maurel et al, 1997;Niemietz and Tyerman, 1997). This reversible inhibition is used to demonstrate the existence of proteinaceous water channels (Chrispeels and Maurel, 1994).…”

Section: Discussionmentioning

confidence: 99%

“…E a depends on the nature of the rate-limiting barrier for water movement and on the energetics of the waterpore interactions (Verkman et al, 1996). Moreover, Arrhenius plots of water movement in soybean (Markhart et al, 1979a) and in renal proximal tubule cell membranes (Meyer and Verkman, 1987) were found to be nonlinear. In our experiment, when the temperature was decreased from 25°C to 4°C and then increased back to 25°C, control roots did not yield a linear Arrhenius plot (Fig.…”

Section: Discussionmentioning

confidence: 99%

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Mercuric Chloride Effects on Root Water Transport in Aspen Seedlings

Wan

¹

,

Zwiazek

²

1999

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HgCl 2 (0.1 mM) reduced pressure-induced water flux and root hydraulic conductivity in the roots of 1-year-old aspen (Populus tremuloides Michx.) seedlings by about 50%. The inhibition was reversed with 50 mM mercaptoethanol. Mercurial treatment reduced the activation energy of water transport in the roots from 10.82 ؎ 0.700 kcal mol ؊1 to 6.67 ؎ 0.193 kcal mol ؊1 when measured over the 4°C to 25°C temperature range. An increase in rhodamine B concentration in the xylem sap of mercury-treated roots suggested a decrease in the symplastic transport of water. However, the apoplastic pathway in both control and mercurytreated roots constituted only a small fraction of the total root water transport. Electrical conductivity and osmotic potentials of the expressed xylem sap suggested that 0.1 mM HgCl 2 and temperature changes over the 4°C to 25°C range did not induce cell membrane leakage. The 0.1 mM HgCl 2 solution applied as a root drench severely reduced stomatal conductance in intact plants, and this reduction was partly reversed by 50 mM mercaptoethanol. In excised shoots, 0.1 mM HgCl 2 did not affect stomatal conductance, suggesting that the signal that triggered stomatal closure originated in the roots. We suggest that mercury-sensitive processes in aspen roots play a significant role in regulating plant water balance by their effects on root hydraulic conductivity.Several criteria have been used to infer the presence of water-transporting channels in cell membranes. These include a high ratio of osmotic to diffusional water permeability (P f /P d Ͼ1), low Arrhenius activation energy (E a Ͻ 6 kcal mol Ϫ1 ) for water transport, and its reversible inhibition by mercury sulfhydryl reagents (for reviews, see Chrispeels and Agre, 1994;Verkman et al., 1996;Maurel, 1997). The transport of water through the lipid bilayer has a high E a , usually above 10 kcal mol Ϫ1 (Macey, 1984). Water transport can also be via water channel proteins (aquaporins), which have been found in the tonoplasts (Maurel et al., 1993) and plasma membranes (Kammerloher et al., 1994) of plants. It is generally acknowledged that the transport of water via channels is less temperature dependent and has a lower E a (Ͻ 6 kcal mol Ϫ1 ) than transport via the lipid pathway (Finkelstein, 1987;Chrispeels and Agre, 1994). Water transport via aquaporins is characteristically inhibited by mercurial reagents, which react with sulfhydryl groups in the channel proteins and result in closure of the channels. This closure inhibits water transport and increases E a to the level of that for transport through the lipid pathway (Macey, 1984). An inhibition of water transport by mercury was reported in cell membranes isolated from higher plants Niemietz and Tyerman, 1997) and in whole root systems (Maggio and Joly, 1995;Carvajal et al., 1996). However, the effects of mercury reagents on E a have not been investigated in intact higher plants.Based on the composite transport model (Steudle and Frensch, 1996), water transport is via three parallel pathways, apoplastic, ...

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Mechanisms of Fluid Transport Across Renal Tubules

Schafer

¹

,

Reeves²,

Andreoli³

1992

Comprehensive Physiology

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The sections in this article are: Theoretical Foundations of Water Transport in Epithelia Volume Absorption in the Proximal Tubule Water Permeability of the Proximal Tubule Measurement of Water Permeability Importance of the Osmotic Water Permeability Location of the Osmotic Gradient Luminal Hypotonicity Produced by Solute Absorption Absorbate Hypertonicity “Passive” Driving Forces for Volume Absorption NaCl Diffusion in Volume Absorption Reflection Coefficient Differences Models of Solute‐Solvent Coupling in Proximal Volume Absorption Routes of Volume Movement in the Proximal Nephron Measurement of Cell Membrane Osmotic Water Permeabilities Consequences of Transcellular Volume Flow The ADH ‐Sensitive Distal Nephron Measurement of Permeability Changes Produced by ADH Wafer Permeability of ADH ‐Sensitive Nephron Segments in Vivo and in Vitro Site of the Change in Water Permeability with ADH Evaluation of the P f / P Dw Ratio Large Pore Hypothesis Unstirred Layer Effects The Narrow Channel Hypothesis: Single‐File Diffusion Through Small Aqueous Channels ADH Increases the Number of Narrow Aqueous Channels in Apical Plasma Membranes The Apparent E A for Water Transport in Cortical Collecting Tubules The Raw Data Correction for Diffusion Constraints in Series with Apical Membranes The “True” E A for Water Transport Pseudo‐“Breaks” in E A Measurements Comparison of ADH ‐Dependent Apical Membrane Water Channels with Gramicidin A Channels Parallel Paths for Water and Solute Permeation Morphologic Studies Intracellular Mediators of ADH Action Modulation of ADH Action—α‐Adrenergic Agents Atrial Natriuretic Peptide Prostaglandins Calcium Protein Kinase C Summary

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Evidence for water channels in renal proximal tubule cell membranes

Cited by 64 publications

References 47 publications

AQP2 in human urine is predominantly localized to exosomes with preserved water channel activities

AQP2 in human urine is predominantly localized to exosomes with preserved water channel activities

Mercuric Chloride Effects on Root Water Transport in Aspen Seedlings

Mechanisms of Fluid Transport Across Renal Tubules

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