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Rubashkin AA, Iserovich P, Vorotyntsev MA. A Theory of Charge Selectivity Reversal in Cation- or Anion-Selective Tight Junctions between Epithelial Cells: A Nonlocal Electrostatic Approach. Biophysics (Nagoya-shi) 2021. [DOI: 10.1134/s0006350921010127] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Physical origin of Na+/Cl− selectivity of tight junctions between epithelial cells. Nonlocal electrostatic approach. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.113884] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Mosaliganti KR, Swinburne IA, Chan CU, Obholzer ND, Green AA, Tanksale S, Mahadevan L, Megason SG. Size control of the inner ear via hydraulic feedback. eLife 2019; 8:39596. [PMID: 31571582 PMCID: PMC6773445 DOI: 10.7554/elife.39596] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Accepted: 08/26/2019] [Indexed: 01/05/2023] Open
Abstract
Animals make organs of precise size, shape, and symmetry but how developing embryos do this is largely unknown. Here, we combine quantitative imaging, physical theory, and physiological measurement of hydrostatic pressure and fluid transport in zebrafish to study size control of the developing inner ear. We find that fluid accumulation creates hydrostatic pressure in the lumen leading to stress in the epithelium and expansion of the otic vesicle. Pressure, in turn, inhibits fluid transport into the lumen. This negative feedback loop between pressure and transport allows the otic vesicle to change growth rate to control natural or experimentally-induced size variation. Spatiotemporal patterning of contractility modulates pressure-driven strain for regional tissue thinning. Our work connects molecular-driven mechanisms, such as osmotic pressure driven strain and actomyosin tension, to the regulation of tissue morphogenesis via hydraulic feedback to ensure robust control of organ size. Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).
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Affiliation(s)
| | - Ian A Swinburne
- Department of Systems Biology, Harvard Medical School, Boston, United States
| | - Chon U Chan
- School of Engineering and Applied Sciences, Harvard University, Cambridge, United States
| | - Nikolaus D Obholzer
- Department of Systems Biology, Harvard Medical School, Boston, United States
| | - Amelia A Green
- Department of Systems Biology, Harvard Medical School, Boston, United States
| | - Shreyas Tanksale
- Department of Systems Biology, Harvard Medical School, Boston, United States
| | - L Mahadevan
- School of Engineering and Applied Sciences, Harvard University, Cambridge, United States.,Department of Organismal and Evolutionary Biology, Harvard University, Cambridge, United States.,Department of Physics, Harvard University, Cambridge, United States.,Kavli Institute for NanoBio Science and Technology, Harvard University, Cambridge, United States
| | - Sean G Megason
- Department of Systems Biology, Harvard Medical School, Boston, United States
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Dvoriashyna M, Foss AJ, Gaffney EA, Jensen OE, Repetto R. Osmotic and electroosmotic fluid transport across the retinal pigment epithelium: A mathematical model. J Theor Biol 2018; 456:233-248. [DOI: 10.1016/j.jtbi.2018.08.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Revised: 08/03/2018] [Accepted: 08/06/2018] [Indexed: 01/26/2023]
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Net Fluorescein Flux Across Corneal Endothelium Strongly Suggests Fluid Transport is due to Electro-osmosis. J Membr Biol 2016; 249:469-73. [PMID: 26989056 PMCID: PMC4942490 DOI: 10.1007/s00232-016-9887-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Accepted: 03/09/2016] [Indexed: 11/04/2022]
Abstract
We have presented prior evidence suggesting that fluid transport results from electro-osmosis at the intercellular junctions of the corneal endothelium. Such phenomenon ought to drag other extracellular solutes. We have investigated this using fluorescein-Na2 as an extracellular marker. We measured unidirectional fluxes across layers of cultured human corneal endothelial (HCE) cells. SV-40-transformed HCE layers were grown to confluence on permeable membrane inserts. The medium was DMEM with high glucose and no phenol red. Fluorescein-labeled medium was placed either on the basolateral or the apical side of the inserts; the other side carried unlabeled medium. The inserts were held in a CO2 incubator for 1 h (at 37 °C), after which the entire volume of the unlabeled side was collected. After that, label was placed on the opposite side, and the corresponding paired sample was collected after another hour. Fluorescein counts were determined with a (Photon Technology) DeltaScan fluorometer (excitation 380 nm; emission 550 nm; 2 nm bwth). Samples were read for 60 s. The cells utilized are known to transport fluid from the basolateral to the apical side, just as they do in vivo in several species. We used 4 inserts for influx and efflux (total: 20 1-h periods). We found a net flux of fluorescein from the basolateral to the apical side. The flux ratio was 1.104 ± 0.056. That difference was statistically significant (p = 0.00006, t test, paired samples). The endothelium has a definite restriction at the junctions. Hence, an asymmetry in unidirectional fluxes cannot arise from osmosis, and can only point instead to paracellular solvent drag. We suggest, once more, that such drag is due to electro-osmotic coupling at the paracellular junctions.
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Avetisov SE, Trufanov SV, Novikov IA, Subbot AM, Fedorov AA. [SEM visualization of corneal epithelium through lanthanoid staining based on Ca/Nd isomorphous substitution in Ca-dependent molecular systems]. Vestn Oftalmol 2016; 132:11-19. [PMID: 28121294 DOI: 10.17116/oftalma2016132611-19] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
UNLABELLED Cumulative biomicroscopic evidence is usually sufficient for the diagnosis of recurrent corneal erosion or bullous keratopathy, however, exploration of the disease pathogenesis requires subcellular-level visualization of corneal structure. In the current study, lanthanoid staining and scanning electron microscopy were employed to visualize quite a number of structures responsible for epithelium organization. In particular, the study proves possible the use of Ca/Nd isomorphous substitution at Ca2+ sites of cytoadherence proteins for visualization of corresponding cellular structures. AIM To assess the value of information provided by scanning electron microscopy of corneal epithelium that involves lanthanoid staining based on the Ca/Nd isomorphous substitution in Ca-dependent molecular systems. MATERIAL AND METHODS Anterior corneal epithelial scrapes were obtained from patients with recurrent corneal erosion or bullous keratopathy and cadaver eyes with no signs of any ophthalmic disease. Samples were then studied under a scanning electron microscope (Zeiss EVO LS10, BSE, EP - 79 Pa, 20-28 kV, Ln-staining with the BioREE assay kit). RESULTS In all cases, lanthanoid staining of biopsy material provided high-contrast SEM images with well-recognizable structural and ultrastructural elements associated with Ca2+ sites of cytoadherence proteins. CONCLUSION Lanthanoid staining of biopsy material and subsequent SEM enabled detailed visualization of structural features of the corneal epithelium in various pathologies. Due to the Ca/Nd isomorphism we were able to evaluate structural position of the majority of protein molecules engaged in Ca-dependant processes and, consequently, in cytoadherence. Basing on the neodymium distribution within the basal membrane, we have described local effects of different substances on the lamina densa in the projection of basal layer cell borders that occur after unidirectional ultrafiltration. The results confirm the failure of the junctional adhesion complex in recurrent corneal erosion.
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Affiliation(s)
- S E Avetisov
- Research Institute of Eye Diseases, 11 A, B Rossolimo St., Moscow, 119021, Russian Federation; The First Sechenov The Moscow State Medical University under Ministry of Health of the Russian Federation, 8-2 Trubetskaya St., Moscow, 119991, Russian Federation
| | - S V Trufanov
- Research Institute of Eye Diseases, 11 A, B Rossolimo St., Moscow, 119021, Russian Federation
| | - I A Novikov
- Research Institute of Eye Diseases, 11 A, B Rossolimo St., Moscow, 119021, Russian Federation
| | - A M Subbot
- Research Institute of Eye Diseases, 11 A, B Rossolimo St., Moscow, 119021, Russian Federation
| | - A A Fedorov
- Research Institute of Eye Diseases, 11 A, B Rossolimo St., Moscow, 119021, Russian Federation
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Cacace V, Kusnier CF, Fischbarg J. RETRACTED ARTICLE: Net Fluorescein Flux Across Corneal Endothelium Suggests Fluid Transport is Driven by Electroosmosis. J Membr Biol 2015; 249:197. [PMID: 26423751 PMCID: PMC4851691 DOI: 10.1007/s00232-015-9849-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Accepted: 09/18/2015] [Indexed: 11/30/2022]
Affiliation(s)
- V Cacace
- ININCA, Conicet, Marcelo T. de Alvear 2270, CP 1122AAJ, Buenos Aires, Argentina
| | - C F Kusnier
- ININCA, Conicet, Marcelo T. de Alvear 2270, CP 1122AAJ, Buenos Aires, Argentina
| | - J Fischbarg
- ININCA, Conicet, Marcelo T. de Alvear 2270, CP 1122AAJ, Buenos Aires, Argentina.
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Larsen EH, Deaton LE, Onken H, O'Donnell M, Grosell M, Dantzler WH, Weihrauch D. Osmoregulation and Excretion. Compr Physiol 2014; 4:405-573. [DOI: 10.1002/cphy.c130004] [Citation(s) in RCA: 127] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Tasoglu S, Rohan LC, Katz DF, Szeri AJ. Transient swelling, spreading, and drug delivery by a dissolved anti-HIV microbicide-bearing film. PHYSICS OF FLUIDS (WOODBURY, N.Y. : 1994) 2013; 25:31901. [PMID: 23554549 PMCID: PMC3606300 DOI: 10.1063/1.4793598] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2012] [Accepted: 02/05/2013] [Indexed: 05/15/2023]
Abstract
There is a widespread agreement that more effective drug delivery vehicles with more alternatives, as well as better active pharmaceutical ingredients (APIs), must be developed to improve the efficacy of microbicide products. For instance, in tropical regions, films are more appropriate than gels due to better stability of drugs at extremes of moisture and temperature. Here, we apply fundamental fluid mechanical and physicochemical transport theory to help better understand how successful microbicide API delivery depends upon properties of a film and the human reproductive tract environment. Several critical components of successful drug delivery are addressed. Among these are: elastohydrodynamic flow of a dissolved non-Newtonian film; mass transfer due to inhomogeneous dilution of the film by vaginal fluid contacting it along a moving boundary (the locally deforming vaginal epithelial surface); and drug absorption by the epithelium. Local rheological properties of the film are dependent on local volume fraction of the vaginal fluid. We evaluated this experimentally, delineating the way that constitutive parameters of a shear-thinning dissolved film are modified by dilution. To develop the mathematical model, we integrate the Reynolds lubrication equation with a mass conservation equation to model diluting fluid movement across the moving vaginal epithelial surface and into the film. This is a complex physicochemical phenomenon that is not well understood. We explore time- and space-varying boundary flux model based upon osmotic gradients. Results show that the model produces fluxes that are comparable to experimental data. Further experimental characterization of the vaginal wall is required for a more precise set of parameters and a more sophisticated theoretical treatment of epithelium.
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Affiliation(s)
- Savas Tasoglu
- Department of Mechanical Engineering, University of California, Berkeley, California 94720-1740, USA
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Aqueous salt transport through soft contact lenses: An osmotic-withdrawal mechanism for prevention of adherence. Cont Lens Anterior Eye 2012; 35:260-5. [DOI: 10.1016/j.clae.2012.07.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2012] [Revised: 06/04/2012] [Accepted: 07/03/2012] [Indexed: 11/22/2022]
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Fischbarg J. Water channels and their roles in some ocular tissues. Mol Aspects Med 2012; 33:638-41. [PMID: 22819922 DOI: 10.1016/j.mam.2012.07.016] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2011] [Revised: 07/06/2012] [Accepted: 07/09/2012] [Indexed: 01/23/2023]
Abstract
Water is a major component of the eye, and water channels (aquaporins) are ubiquitous in ocular tissues, and quite abundant at their different locations. AQP1 is expressed in corneal endothelium, lens epithelium, ciliary epithelium, and retinal pigment epithelium. AQP3 is expressed in corneal epithelium, and in conjunctival epithelium. AQP4 is expressed in ciliary epithelium and retinal Muller cells. AQP5 is expressed in corneal epithelium, and conjunctival epithelium. AQP0 is expressed in lens fiber cells. It is known that five ocular tissues transport fluid, namely: (1) Corneal endothelium; (2) Conjunctival epithelium; (3) Lens epithelium; (4) Ciliary epithelium; (5) Retinal pigment epithelium. For the corneal endothelium, aquaporins are not the main route for trans-tissue water movement, which is paracellular. Instead, we propose that aquaporins allow fast osmotic equilibration of the cell, which is necessary to maintain optimal rates of fluid movement since the cyclic paracellular water transfer mechanism operates separately and tends to create periodic osmotic imbalances (τ∼5 s).
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Affiliation(s)
- Jorge Fischbarg
- Institute for Cardiological Investigations A.C. Taquini, University of Buenos Aires and CONICET, Marcelo T. de Alvear 2270, Buenos Aires, Argentina.
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Osmoregulation and epithelial water transport: lessons from the intestine of marine teleost fish. J Comp Physiol B 2011; 182:1-39. [DOI: 10.1007/s00360-011-0601-3] [Citation(s) in RCA: 97] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2011] [Revised: 06/08/2011] [Accepted: 06/15/2011] [Indexed: 12/15/2022]
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Comparative Permeabilities of the Paracellular and Transcellular Pathways of Corneal Endothelial Layers. J Membr Biol 2011; 242:41-51. [DOI: 10.1007/s00232-011-9375-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Accepted: 06/13/2011] [Indexed: 10/18/2022]
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Fischbarg J. Fluid Transport Across Leaky Epithelia: Central Role of the Tight Junction and Supporting Role of Aquaporins. Physiol Rev 2010; 90:1271-90. [DOI: 10.1152/physrev.00025.2009] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The mechanism of epithelial fluid transport remains unsolved, which is partly due to inherent experimental difficulties. However, a preparation with which our laboratory works, the corneal endothelium, is a simple leaky secretory epithelium in which we have made some experimental and theoretical headway. As we have reported, transendothelial fluid movements can be generated by electrical currents as long as there is tight junction integrity. The direction of the fluid movement can be reversed by current reversal or by changing junctional electrical charges by polylysine. Residual endothelial fluid transport persists even when no anions (hence no salt) are being transported by the tissue and is only eliminated when all local recirculating electrical currents are. Aquaporin (AQP) 1 is the only AQP present in these cells, and its deletion in AQP1 null mice significantly affects cell osmotic permeability (by ∼40%) but fluid transport much less (∼20%), which militates against the presence of sizable water movements across the cell. In contrast, AQP1 null mice cells have reduced regulatory volume decrease (only 60% of control), which suggests a possible involvement of AQP1 in either the function or the expression of volume-sensitive membrane channels/transporters. A mathematical model of corneal endothelium we have developed correctly predicts experimental results only when paracellular electro-osmosis is assumed rather than transcellular local osmosis. Our evidence therefore suggests that the fluid is transported across this layer via the paracellular route by a mechanism that we attribute to electro-osmotic coupling at the junctions. From our findings we have developed a novel paradigm for this preparation that includes 1) paracellular fluid flow; 2) a crucial role for the junctions; 3) hypotonicity of the primary secretion; and 4) an AQP role in regulation rather than as a significant water pathway. These elements are remarkably similar to those proposed by the laboratory of Adrian Hill for fluid transport across other leaky epithelia.
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Affiliation(s)
- Jorge Fischbarg
- Institute of Cardiology Research “A. C. Taquini,” University of Buenos Aires and National Council for Scientific and Technical Investigations, Buenos Aires, Argentina
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Montalbetti N, Fischbarg J. Frequency spectrum of transepithelial potential difference reveals transport-related oscillations. Biophys J 2009; 97:1530-7. [PMID: 19751657 PMCID: PMC2741586 DOI: 10.1016/j.bpj.2009.05.063] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Revised: 05/18/2009] [Accepted: 05/28/2009] [Indexed: 11/24/2022] Open
Abstract
How epithelia transport fluid is a fundamental issue that is unresolved. Explanations offered include molecular engines, local transcellular osmosis, local paracellular osmosis, and paracellular fluid transport. On the basis of experimental and theoretical work done on corneal endothelium, a fluid transporting epithelium, we suggest electroosmotic coupling at the level of the intercellular junctions driven by the transendothelial electrical potential difference as an explanation of paracellular fluid transport. We collect frequency spectra of that potential difference in real-time. For what we believe is the first time for any epithelium, we report that, unexpectedly, the potential difference displays oscillations at many characteristic frequencies. We also show that on both stimulating cell activity and inhibiting ion transport mechanisms, there are corresponding changes in the oscillations amplitudes that mirror changes known previously in rates of fluid transport. We believe these findings provide a novel tool to study the kinetics of electrogenic elements such as channels and transporters, which from this evidence would give rise to current oscillations with characteristic periods going from 150 ms to 8 s.
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Affiliation(s)
| | - Jorge Fischbarg
- Institute of Cardiology Research, University of Buenos Aires, and CONICET, Buenos Aires, Argentina
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Abstract
PURPOSE Quantitative understanding of tear dynamics may help in developing better ophthalmic drug delivery vehicles and dry eye treatments. This paper attempts to develop a comprehensive model that can predict the effect of physiological parameters on various issues related to tear dynamics. METHODS The model is based on mass balances of water and solutes such as glucose, sodium, potassium, and chloride. The mass balances require models for the drainage of fluid through the canaliculi and the transport of tears and solutes through the conjunctiva. The model parameters are obtained by simulating Ussing-chamber experiments. The differential equations for the unsteady balances are solved numerically. RESULTS The model predicts that under normal conditions, the tear volume, tear osmolarity and potential are 7.1 microl, 297.6 mM, and -15.1 mV, respectively. The model also predicts that the conjunctiva is secretory and contributes about 25% of the total tear production. We also predict the effect of evaporation on tear physiology and show that an increase in evaporation increases osmolarity, reduces tear volume, and increases conjuctival secretion. Additionally, the new tear dynamics model helps assess the effect of osmolarity of the instilled drops, insertion of punctum plugs and use of moisture chamber as treatments for dry eyes. Furthermore, the model is used to predict the effect of modulation of specific transport pathways, which is proposed as a potential remedy for dry eyes, on conjuctival secretion and total tear volume. CONCLUSIONS Most of the predicted results agree with the reported experimental results, at least qualitatively. However, some predictions disagree with experiments suggesting that further improvements in the model are needed. The model developed in this paper can improve our understanding of tear dynamics and also serve as a tool to evaluate the efficacy of various modalities at treating dry eyes.
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Affiliation(s)
- Heng Zhu
- Chemical Engineering Department, University of Florida, Gainesville, Florida 32611-6005, USA
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Guy Y, Sandberg M, Weber SG. Determination of zeta-potential in rat organotypic hippocampal cultures. Biophys J 2008; 94:4561-9. [PMID: 18263658 PMCID: PMC2480665 DOI: 10.1529/biophysj.107.112722] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2007] [Accepted: 12/27/2007] [Indexed: 11/18/2022] Open
Abstract
zeta-potentials of entities such as cells and synaptosomes have been determined, but zeta of brain tissue has never been measured. Electroosmotic flow, and the resulting transport of neuroactive substances, would result from naturally occurring and experimentally or clinically induced electric fields if zeta is significant. We have developed a simple method for determining zeta in tissue. An electric field applied across a rat organotypic hippocampal slice culture (OHSC) drives fluorescent molecules through the tissue by both electroosmotic flow and electrophoresis. Fluorescence microscopy is used to determine each molecule's velocity. Independently, capillary electrophoresis is used to measure the molecules' electrophoretic mobilities. The experiment yields zeta-potential and average tissue tortuosity. The zeta-potential of OHSCs is -22 +/- 2 mV, and the average tortuosity is 1.83 +/- 0.06. In a refined experiment, zeta-potential is measured in various subregions. The zeta-potentials of the CA1 stratum pyramidale, CA3 stratum pyramidal, and dentate gyrus are -25.1 +/- 1.6 mV, -20.3 +/- 1.7 mV, and -25.4 +/- 1.0 mV, respectively. Simple dimensional arguments show that electroosmotic flow is potentially as important as diffusion in molecular transport.
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Affiliation(s)
- Yifat Guy
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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Hill AE. Fluid Transport: A Guide for the Perplexed. J Membr Biol 2008; 223:1-11. [DOI: 10.1007/s00232-007-9085-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2007] [Accepted: 11/12/2007] [Indexed: 11/28/2022]
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Larsen EH, Møbjerg N, Nielsen R. Application of the Na+ recirculation theory to ion coupled water transport in low- and high resistance osmoregulatory epithelia. Comp Biochem Physiol A Mol Integr Physiol 2007; 148:101-16. [PMID: 17303459 DOI: 10.1016/j.cbpa.2006.12.039] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2006] [Revised: 12/18/2006] [Accepted: 12/20/2006] [Indexed: 11/28/2022]
Abstract
The theory of Na+ recirculation for isosmotic fluid absorption follows logically from Hertz's convection-diffusion equation applied to the exit of water and solutes from the lateral intercellular space. Experimental evidence is discussed indicating Na+ recirculation based upon the following approaches: (i) An isotope tracer method in small intestine. Simultaneous measurement of water flow and ion transport in toad skin epithelium demonstrating, (ii) occasional hyposmotic absorbates, and (iii) reduced fluid absorption in the presence of serosal bumetanide. (iv) Studies of the metabolic cost of net Na+ absorption demonstrating an efficiency that is lower than the 18 Na+ per O2 consumed given by the stoichiometry of the Na+/K+-pump. Mathematical modeling predicts a significant range of observations such as isosmotic transport, hyposmotic transport, solvent drag, anomalous solvent drag, the residual hydraulic permeability in proximal tubule of AQP1(-/-) mice, the adverse relationship between hydraulic permeability and the concentration difference needed to reverse transepithelial water flow, and in a non-contradictory way the wide range of metabolic efficiencies from above to below 18 Na+/O2. Certain types of observations are poorly or not at all reproduced by the model. It is discussed that such lack of agreement between model and experiment is due to cellular regulations of ion permeabilities that are not incorporated in the modeling. Clarification of these problems requires further experimental studies.
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Affiliation(s)
- Erik Hviid Larsen
- Institute of Molecular Biology and Physiology, University of Copenhagen, August Krogh Building, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark.
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Ma L, Kuang K, Smith RW, Rittenband D, Iserovich P, Diecke F, Fischbarg J. Modulation of tight junction properties relevant to fluid transport across rabbit corneal endothelium. Exp Eye Res 2007; 84:790-8. [PMID: 17320078 PMCID: PMC1993899 DOI: 10.1016/j.exer.2006.12.018] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2006] [Revised: 11/30/2006] [Accepted: 12/15/2006] [Indexed: 11/20/2022]
Abstract
Paracellular junctions could play an important role in corneal endothelial fluid transport. In this study we explored the effects of different reagents on the tight junctional barrier by assessing the translayer specific electrical resistance (TER) across rabbit corneal endothelial preparations and cultured rabbit corneal endothelial cells' (CRCEC) monolayers, the paracellular permeability (Papp) for fluorescein isothiocyanate (FITC) dextrans across CRCEC, and fluid transport across de-epithelialized rabbit corneal endothelial preparations. Palmitoyl carnitine (PC), poly-L-lysine (PLL), adenosine triphosphate (ATP), and dibutyryl adenosine 3',5'-cyclic monophosphate (dB-cAMP) were used to modulate corneal endothelial fluid transport and tight junctions (TJs). After seeding, the TER across CRCEC reached maximal values (29.2+/-1.0 Omega cm2) only after the 10th day. PC (0.1 mM) caused decreases both in TER (by 40%) and fluid transport (swelling rate: 18.5+/-0.3 microm/h), and an increase in Papp. PLL resulted in increased TER rose and Papp but decreased fluid transport (swelling rate: 10+/-0.3 microm/h). dB-cAMP (0.1 mM) and ATP (0.1 mM) decreased TER by 16% and 6%, increased Papp slightly, and stimulated fluid transport; the rates of de-swelling (in microm/h) were -5.4+/-0.3 and -12.1+/-0.4, respectively. PC might cause the junctions to open up unspecifically and thus increase passive leak. PLL is a known junctional charge modifier that may be adding steric hindrance to the tight junctions. The results with dB-cAMP and ATP are consistent with fluid transport via the paracellular route.
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Affiliation(s)
- Li Ma
- Department of Ophthalmology, College of Physicians and Surgeons, Columbia University
| | - Kunyan Kuang
- Department of Ophthalmology, College of Physicians and Surgeons, Columbia University
| | | | | | - Pavel Iserovich
- Department of Ophthalmology, College of Physicians and Surgeons, Columbia University
| | - F.P.J. Diecke
- Dept. of Pharmacology and Physiology, UMDNJ-New Jersey Medical School, Newark, NJ
| | - Jorge Fischbarg
- Department of Ophthalmology, College of Physicians and Surgeons, Columbia University
- Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University
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Larsen EH, Møbjerg N. Na+ Recirculation and Isosmotic Transport. J Membr Biol 2007; 212:1-15. [PMID: 17206513 DOI: 10.1007/s00232-006-0864-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2006] [Revised: 09/05/2006] [Indexed: 10/23/2022]
Abstract
The Na(+) recirculation theory for solute-coupled fluid absorption is an expansion of the local osmosis concept introduced by Curran and analyzed by Diamond & Bossert. Based on studies on small intestine the theory assumes that the observed recirculation of Na(+) serves regulation of the osmolarity of the absorbate. Mathematical modeling reproducing bioelectric and hydrosmotic properties of small intestine and proximal tubule, respectively, predicts a significant range of observations such as isosmotic transport, hyposmotic transport, solvent drag, anomalous solvent drag, the residual hydraulic permeability in proximal tubule of AQP1 (-/-) mice, and the inverse relationship between hydraulic permeability and the concentration difference needed to reverse transepithelial water flow. The model reproduces the volume responses of cells and lateral intercellular space (lis) following replacement of luminal NaCl by sucrose as well as the linear dependence of volume absorption on luminal NaCl concentration. Analysis of solvent drag on Na(+) in tight junctions provides explanation for the surprisingly high metabolic efficiency of Na(+) reabsorption. The model predicts and explains low metabolic efficiency in diluted external baths. Hyperosmolarity of lis is governed by the hydraulic permeability of the apical plasma membrane and tight junction with 6-7 mOsm in small intestine and < or = 1 mOsm in proximal tubule. Truly isosmotic transport demands a Na(+) recirculation of 50-70% in small intestine but might be barely measurable in proximal tubule. The model fails to reproduce a certain type of observations: The reduced volume absorption at transepithelial osmotic equilibrium in AQP1 knockout mice, and the stimulated water absorption by gallbladder in diluted external solutions. Thus, it indicates cellular regulation of apical Na(+) uptake, which is not included in the mathematical treatment.
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Affiliation(s)
- E H Larsen
- Department of Molecular Biology, University of Copenhagen, August Krogh Building, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark.
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Fischbarg J, Diecke FPJ, Iserovich P, Rubashkin A. The Role of the Tight Junction in Paracellular Fluid Transport across Corneal Endothelium. Electro-osmosis as a Driving Force. J Membr Biol 2006; 210:117-30. [PMID: 16868674 DOI: 10.1007/s00232-005-0850-8] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2006] [Indexed: 11/29/2022]
Abstract
The mechanism of epithelial fluid transport is controversial and remains unsolved. Experimental difficulties pose obstacles for work on a complex phenomenon in delicate tissues. However, the corneal endothelium is a relatively simple system to which powerful experimental tools can be applied. In recent years our laboratory has developed experimental evidence and theoretical insights that illuminate the mechanism of fluid transport across this leaky epithelium. Our evidence points to fluid being transported via the paracellular route by a mechanism requiring junctional integrity, which we attribute to electro-osmotic coupling at the junctions. Fluid movements can be produced by electrical currents. The direction of the movement can be reversed by current reversal or by changing junctional electrical charges by polylysine. Aquaporin 1 (AQP1) is the only AQP present in these cells, and its deletion in AQP1 null mice significantly affects cell osmotic permeability but not fluid transport, which militates against the presence of sizable water movements across the cell. By contrast, AQP1 null mice cells have reduced regulatory volume decrease (only 60% of control), which suggests a possible involvement of AQP1 in either the function or the expression of volume-sensitive membrane channels/transporters. A mathematical model of corneal endothelium predicts experimental results only when based on paracellular electro-osmosis, and not when transcellular local osmosis is assumed instead. Our experimental findings in corneal endothelium have allowed us to develop a novel paradigm for this preparation that includes: (1) paracellular fluid flow; (2) a crucial role for the junctions; (3) hypotonicity of the primary secretion; (4) an AQP role in regulation and not as a significant water pathway. These elements are remarkably similar to those proposed by the Hill laboratory for leaky epithelia.
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Affiliation(s)
- J Fischbarg
- Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, 630 W 168th St, New York, NY 10032, USA.
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