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Dorothee Gunzel - One of the best experts on this subject based on the ideXlab platform.

  • claudins vital partners in transcellular and paracellular Transport coupling
    Pflügers Archiv: European Journal of Physiology, 2017
    Co-Authors: Dorothee Gunzel
    Abstract:

    Tight junction (TJ) strands between Epithelial or endothelial cells are formed by claudins, a protein family comprising up to 27 members in mammals. Although many more proteins are involved in the formation of TJ complexes, claudins are the only TJ proteins that are able to form TJ-like strands when overexpressed in cells that are normally devoid of TJs (e.g., fibroblasts). Within the paracellular cleft, the extracellular domains of claudins provide the matrix that seals the paracellular pathway. However, within this matrix, some claudins act as channels that specifically allow certain ions to cross this barrier. Barrier-forming claudins predominate in epithelia that enclose compartments containing harmful ion concentrations (e.g., H+ in the stomach, K+ in the inner ear endolymph) or high pressures (e.g., in blastocoel or brain ventricle formation during development). Here, even seemingly minor alterations in TJ composition may be detrimental to the organism. In contrast, in many Transporting epithelia, channel-forming claudins are essential for transcellular and paracellular Transport coupling. Mutation or knockout of channel-forming claudins in these tissues brings both transcellular and paracellular Transports to a standstill. The present review will present examples to illustrate the importance of single members of the claudin family in general Epithelial Transport physiology.

  • claudins and other tight junction proteins
    Comprehensive Physiology, 2012
    Co-Authors: Dorothee Gunzel, Michael Fromm
    Abstract:

    Epithelial Transport relies on the proper function and regulation of the tight junction (TJ), other-wise uncontrolled paracellular leakage of solutes and water would occur. They also act as a fence against mixing of membrane proteins of the apical and basolateral side. The proteins determining paracellular Transport consist of four transmembrane regions, intracellular N and C terminals, one intracellular and two extracellular loops (ECLs). The ECLs interact laterally and with counterparts of the neighboring cell and by this achieve a general sealing function. Two TJ protein families can be distinguished, claudins, comprising 27 members in mammals, and TJ-associated MARVEL proteins (TAMP), comprising occludin, tricellulin, and MarvelD3. They are linked to a multitude of TJ-associated regulatory and scaffolding proteins. The major TJ proteins are classified according to the physiological role they play in enabling or preventing paracellular Transport. Many TJ proteins have sealing functions (claudins 1, 3, 5, 11, 14, 19, and tricellulin). In contrast, a significant number of claudins form channels across TJs which feature selectivity for cations (claudins 2, 10b, and 15), anions (claudin-10a and -17), or are permeable to water (claudin-2). For several TJ proteins, function is yet unclear as their effects on Epithelial barriers are inconsistent (claudins 4, 7, 8, 16, and occludin). TJs undergo physiological and pathophysiological regulation by altering protein composition or abundance. Major pathophysiological conditions which involve changes in TJ protein composition are (1) effects of pathogens binding to TJ proteins, (2) altered TJ protein composition during inflammation and infection, and (3) altered TJ protein expression in cancers. © 2012 American Physiological Society. Compr Physiol 2:1819-1852, 2012.

  • claudins of intestine and nephron a correlation of molecular tight junction structure and barrier function
    Acta Physiologica, 2011
    Co-Authors: Salah Amasheh, Michael Fromm, Dorothee Gunzel
    Abstract:

    A prerequisite of Epithelial Transport is a paracellular barrier function, which seals the tissue against an uncontrolled leak flux. Moreover, selective paracellular permeability has been shown to be crucial for physiological Epithelial Transport function. Claudins are tetraspan tight junction proteins which play a major role in paracellular ion permeability across epithelia. The multigene family consists of 24 members and several splice variants which show distinct tissue-specific expression profiles. Moreover, in diseases associated with a loss of barrier function such as forms of inflammatory bowel disease, the expression of claudins is altered. Functional characterization of single claudins revealed specific contribution to barrier properties in epithelia. This review gives an overview on the exploration of molecular structure and barrier function along the intestine and nephron, which not only share mechanisms of selective restriction of the paracellular pathway but also exhibit distinct organ-specific characteristics.

  • Targeted deletion of murine Cldn16 identifies extra- and intrarenal compensatory mechanisms of Ca2+ and Mg2+ wasting
    American journal of physiology. Renal physiology, 2010
    Co-Authors: Constanze Will, Dorothee Gunzel, Tilman Breiderhoff, Iwan C. Meij, Julia Thumfart, Marchel Stuiver, Kathrin Kopplin, Kerstin Sommer, Uwe Querfeld, Qixian Shan
    Abstract:

    Claudin-16 (CLDN16) is critical for renal paracellular Epithelial Transport of Ca2+ and Mg2+ in the thick ascending loop of Henle. To gain novel insights into the role of CLDN16 in renal Ca2+ and M...

Michael Fromm - One of the best experts on this subject based on the ideXlab platform.

  • claudins and other tight junction proteins
    Comprehensive Physiology, 2012
    Co-Authors: Dorothee Gunzel, Michael Fromm
    Abstract:

    Epithelial Transport relies on the proper function and regulation of the tight junction (TJ), other-wise uncontrolled paracellular leakage of solutes and water would occur. They also act as a fence against mixing of membrane proteins of the apical and basolateral side. The proteins determining paracellular Transport consist of four transmembrane regions, intracellular N and C terminals, one intracellular and two extracellular loops (ECLs). The ECLs interact laterally and with counterparts of the neighboring cell and by this achieve a general sealing function. Two TJ protein families can be distinguished, claudins, comprising 27 members in mammals, and TJ-associated MARVEL proteins (TAMP), comprising occludin, tricellulin, and MarvelD3. They are linked to a multitude of TJ-associated regulatory and scaffolding proteins. The major TJ proteins are classified according to the physiological role they play in enabling or preventing paracellular Transport. Many TJ proteins have sealing functions (claudins 1, 3, 5, 11, 14, 19, and tricellulin). In contrast, a significant number of claudins form channels across TJs which feature selectivity for cations (claudins 2, 10b, and 15), anions (claudin-10a and -17), or are permeable to water (claudin-2). For several TJ proteins, function is yet unclear as their effects on Epithelial barriers are inconsistent (claudins 4, 7, 8, 16, and occludin). TJs undergo physiological and pathophysiological regulation by altering protein composition or abundance. Major pathophysiological conditions which involve changes in TJ protein composition are (1) effects of pathogens binding to TJ proteins, (2) altered TJ protein composition during inflammation and infection, and (3) altered TJ protein expression in cancers. © 2012 American Physiological Society. Compr Physiol 2:1819-1852, 2012.

  • claudins of intestine and nephron a correlation of molecular tight junction structure and barrier function
    Acta Physiologica, 2011
    Co-Authors: Salah Amasheh, Michael Fromm, Dorothee Gunzel
    Abstract:

    A prerequisite of Epithelial Transport is a paracellular barrier function, which seals the tissue against an uncontrolled leak flux. Moreover, selective paracellular permeability has been shown to be crucial for physiological Epithelial Transport function. Claudins are tetraspan tight junction proteins which play a major role in paracellular ion permeability across epithelia. The multigene family consists of 24 members and several splice variants which show distinct tissue-specific expression profiles. Moreover, in diseases associated with a loss of barrier function such as forms of inflammatory bowel disease, the expression of claudins is altered. Functional characterization of single claudins revealed specific contribution to barrier properties in epithelia. This review gives an overview on the exploration of molecular structure and barrier function along the intestine and nephron, which not only share mechanisms of selective restriction of the paracellular pathway but also exhibit distinct organ-specific characteristics.

  • effect of chronic giardia lamblia infection on Epithelial Transport and barrier function in human duodenum
    Gut, 2007
    Co-Authors: Hanno Troeger, Michael Fromm, H J Epple, Thomas Schneider, Ulrich Wahnschaffe, Reiner Ullrich, Gerddieter Burchard, Tomas Jelinek, M Zeitz, Jörg-dieter Schulzke
    Abstract:

    Background: Giardia lamblia causes infection of the small intestine, which leads to malabsorption and chronic diarrhoea. Aim: To characterise the inherent pathomechanisms of G lamblia infection. Methods: Duodenal biopsy specimens from 13 patients with chronic giardiasis and from controls were obtained endoscopically. Short-circuit current (I SC ) and mannitol fluxes were measured in miniaturised Ussing chambers. Epithelial and subEpithelial resistances were determined by impedance spectroscopy. Mucosal morphometry was performed and tight junction proteins were characterised by immunoblotting. Apoptotic ratio was determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labelling staining. Results: In giardiasis, mucosal surface area per unit serosa area was decreased to 75% (3%) of control, as a result of which Epithelial resistance should increase. Instead, Epithelial resistance of giardiasis biopsy specimens was decreased (19 (2) vs 25 (2) Ω cm 2 ; p 2 ). As structural correlate, reduced claudin 1 expression and increased Epithelial apoptosis were detected. Furthermore, basal I SC increased from 191 (20) in control to 261 (12) µA/h/cm 2 in giardiasis. The bumetanide-sensitive portion of I SC in giardiasis was also increased (51 (5) vs 20 (9) µA/h/cm 2 in control; p + –glucose symport was reduced in patients with giardiasis (121 (9) vs 83 (14) µA/h/cm 2 ). Conclusions: G lamblia infection causes Epithelial barrier dysfunction owing to down regulation of the tight junction protein claudin 1 and increased Epithelial apoptoses. Na + -dependent d-glucose absorption is impaired and active electrogenic anion secretion is activated. Thus, the mechanisms of diarrhoea in human chronic giardiasis comprise leak flux, malabsorptive and secretory components.

  • Epithelial Transport and barrier function in occludin deficient mice
    Biochimica et Biophysica Acta, 2005
    Co-Authors: Jörg-dieter Schulzke, Joachim Mankertz, Shoichiro Tsukita, Mitinori Saitou, Alfred H. Gitter, S. Spiegel, U. Seidler, Salah Amasheh, Michael Fromm
    Abstract:

    Abstract Background and Aims This study aimed at functional characterization of the tight junction protein occludin using the occludin-deficient mouse model. Methods Epithelial Transport and barrier functions were characterized in Ussing chambers. Impedance analysis revealed the ionic permeability of the epithelium (Re, Epithelial resistance). Conductance scanning differentiated transcellular (Gc) and tight junctional conductance (Gtj). The pH-stat technique quantified gastric acid secretion. Results In occludin+/+ mice, Re was 23±5 Ω cm2 in jejunum, 66±5 Ω cm2 in distal colon and 33±6 Ω cm2 in gastric corpus and was not altered in heterozygotic occludin+/− or homozygotic occludin−/− mice. Additionally, [3H]mannitol fluxes were unaltered. In the control colon, Gc and Gtj were 7.6±1.0 and 0.3±0.1 mS/cm2 and not different in occludin deficiency. Epithelial resistance after mechanical perturbation or EGTA exposition (low calcium switch) was not more affected in occludin−/− mice than in control. Barrier function was measured in the urinary bladder, a tight epithelium, and in the stomach. Control Rt was 5.8±0.8 kΩ cm2 in urinary bladder and 33±6 Ω cm2 in stomach and not altered in occludin−/− mice. In gastric corpus mucosa, the glandular structure exhibited a complete loss of parietal cells and mucus cell hyperplasia, as a result of which acid secretion was virtually abolished in occludin−/− mice. Conclusion Epithelial barrier characterization in occludin-deficiency points against an essential barrier function of occludin within the tight junction strands or to a substitutional redundancy of single tight junction molecules like occludin. A dramatic change in gastric morphology and secretory function indicates that occludin is involved in gastric Epithelial differentiation.

  • duodenal biopsies of hiv infected patients with diarrhoea exhibit Epithelial barrier defects but no active secretion
    AIDS, 1998
    Co-Authors: M Stockmann, Michael Fromm, Heinz Schmitz, Wolfgang Schmidt, E O Riecken, Jörg-dieter Schulzke
    Abstract:

    Objectives: To characterize diarrhoeal mechanisms in HIV-infected patients, Epithelial Transport and barrier function of the duodenal mucosa was investigated in vitro. Patients: Twenty-one HIV-seropositive patients (13 asymptomatic and eight with diarrhoea) and 12 controls from an urban referral-based tertiary care centre in Berlin who underwent duodenoscopy. Methods: A new miniaturized Ussing chamber allowed measurements on duodenal forceps biopsies. Epithelial barrier function was characterized by alternating current impedance analysis, which allows differentiation of Epithelial and subEpithelial resistance and by 3 H-lactulose and 3 H-mannitol flux measurements. Na + -glucose coTransport was quantified as phlorizin-sensitive short circuit current (I SC ) and active ion secretion by baseline and bumetanide-sensitive I SC . Results: Duodenal biopsies from asymptomatic HIV-infected patients were no different from controls, whereas biopsies from HIV-infected patients with diarrhoea showed a decrease in Epithelial resistance from 21.2±1.9 to 12.9±1.3 Ωcm 2 (P< 0.01). Concomitantly, mucosal-to-serosal lactulose flux increased from 0.29 ± 0.02 to 0.40 ± 0.03 μmol (hcm 2 ) (P < 0.01). Phlorizin-sensitive I SC indicating Na + -glucose coTransport, as well as baseline and bumetanide-sensitive I SC . indicating active electrogenic chloride secretion were not different between the three groups. Conclusions: A miniaturized Ussing device was developed for electrophysiological investigations of duodenal forceps biopsies, which allowed characterization of active ion Transport mechanisms and Epithelial barrier function. Duodenum of HIV-infected patients with diarrhoea showed no evidence for active ion secretion or Na + -glucose malabsorption, but showed an impaired Epithelial barrier function, which could contribute to diarrhoea by a leak flux mechanism.

Zhengzhu Zhang - One of the best experts on this subject based on the ideXlab platform.

  • intestinal Transport of pure theanine and theanine in green tea extract green tea components inhibit theanine absorption and promote theanine excretion
    Food Chemistry, 2011
    Co-Authors: Jinsong Zhang, Xiaochun Wan, Men Long, Pandeng Lei, Zhengzhu Zhang
    Abstract:

    Abstract Theanine, an amino acid contained in green tea, is known to possess many pharmacological functions. In this paper, we investigated the absorption of theanine in the human intestinal epithelium, using a Caco-2 monolayer model. Different concentrations of either pure theanine or green tea extracts were administered to Caco-2 cells. The theanine content in the samples was analysed by high-performance liquid chromatography, coupled with fluorescence detection. Cell permeation was also measured. The data revealed that the Transport of pure theanine occurred in a manner consistent with passive diffusion. Surprisingly, pure theanine showed good absorption, whereas theanine in the green tea extract was poorly absorbed in the Caco-2 cell model. Furthermore, the Transport of theanine in green tea extract in the basolateral (BL) to apical (AP) direction was much greater than that in the AP–BL direction, suggesting that green tea components profoundly affect the trans-Epithelial Transport of theanine in this Caco-2 cell model.

Klaus W. Beyenbach - One of the best experts on this subject based on the ideXlab platform.

  • Transport mechanisms of diuresis in malpighian tubules of insects
    The Journal of Experimental Biology, 2003
    Co-Authors: Klaus W. Beyenbach
    Abstract:

    SUMMARY We have studied Malpighian tubules of Aedes aegypti using a variety of methods: Ramsay fluid secretion assay, electron probe analysis of secreted fluid, in vitro microperfusion and two-electrode voltage clamp. Collectively, these methods have allowed us to elucidate transEpithelial Transport mechanisms under control conditions and in the presence of diuretic peptides. Mosquito natriuretic peptide (MNP), a corticotropin-releasing factor (CRF)-like diuretic peptide, selectively increases transEpithelial secretion of NaCl and water, meeting the NaCl loads of the blood meal. The intracellular messenger of MNP is cAMP, which increases the Na + conductance and activates the Na + /K + /2Cl - -coTransporter in the basolateral membrane of principal cells. Leucokinin non-selectively increases transEpithelial NaCl and KCl secretion, which may deal with hemolymph volume expansions or reduce the flight pay load upon eclosion from the aquatic habitat. The non-selective NaCl and KCl diuresis stems from the increase in septate junctional Cl - conductance activated by leucokinin using Ca 2+ as second messenger. Fundamental to diuretic mechanisms are powerful Epithelial Transport mechanisms in the distal segment of the Malpighian tubules, where transEpithelial secretion rates can exceed the capacity of mammalian glomerular kidneys in the renal turnover of the extracellular fluid compartment. In conjunction with powerful Epithelial Transport mechanisms driven by the V-type H + -ATPase, diuretic hormones enable hematophagous and probably also phytophagous insects to deal with enormous dietary loads, thereby contributing to the evolutionary success of insects.

  • the v type h atpase in malpighian tubules of aedes aegypti localization and activity
    The Journal of Experimental Biology, 2003
    Co-Authors: Xing-he Weng, Markus Huss, Helmut Wieczorek, Klaus W. Beyenbach
    Abstract:

    SUMMARY The V-type H + -ATPase is thought to provide the driving force for transEpithelial electrolyte and fluid secretion in Malpighian tubules. To confirm the presence of this proton pump in Malpighian tubules of the yellow fever mosquito Aedes aegypti , we used several antibodies raised against the V-type H + -ATPase of Manduca sexta . Western blot analysis confirmed the presence of the V-type H + -ATPase in Malpighian tubules of Aedes aegypti. In situ immunostaining identified the V-type H + -ATPase at the apical membrane of the mitochondrion-rich brush border of principal cells. The V-type H + -ATPase was not found in stellate cells. Measurements of ATPase activity revealed that bafilomycin-sensitive and NO 3 - -sensitive ATPase activity accounted for 50–60% of total ATPase activity in crude extracts of Malpighian tubules. No significant ouabain- or vanadate-sensitive Na + /K + -ATPase activity was detected. These results support the conclusion reached previously in electrophysiological studies that the mechanisms for transEpithelial electrolyte secretion in the Aedes Malpighian tubules rely on the V-type H + -ATPase as the principal energizer of Epithelial Transport. Measures of transEpithelial Na + and K + secretion and estimates of the H + flux mediated by the V-type H + -ATPase suggest a 1:1 stoichiometry for Na + /H + and K + /H + exchange Transport across the apical membrane.

  • central role of the apical membrane h atpase in electrogenesis and Epithelial Transport in malpighian tubules
    The Journal of Experimental Biology, 2000
    Co-Authors: Klaus W. Beyenbach, Thomas L Pannabecker, Wolfram Nagel
    Abstract:

    The effects of bafilomycin A(1), a blocker of V-type H(+)-ATPases, were investigated in Malpighian tubules of Aedes aegypti. Bafilomycin A(1) reduced rates of transEpithelial fluid secretion and the virtual short-circuit current (vI(sc)) with an IC(50) of approximately 5 micromol l(−)(1). As vI(sc) decreased, the electrical resistance increased across the whole epithelium and across the apical membrane, indicating effects on electroconductive pathways. Bafilomycin A(1) had no effect when applied from the tubule lumen, pointing to the relative impermeability of the apical membrane to bafilomycin A(1). Thus, bafilomycin A(1) must take a cytoplasmic route to its blocking site in the proton channel of the H(+)-ATPase located in the apical membrane of principal cells. The inhibitory effects of bafilomycin A(1) were qualitatively similar to those of dinitrophenol in that voltages across the epithelium (V(t)), the basolateral membrane (V(bl)) and the apical membrane (V(a)) depolarized towards zero in parallel. Moreover, V(bl)always tracked V(a), indicating electrical coupling between the two membranes through the shunt. Electrical coupling allows the H(+)-ATPase to energize not only the apical membrane, but also the basolateral membrane. Furthermore, electrical coupling offers a balance between electroconductive entry of cations across the basolateral membrane and extrusion across the apical membrane to support steady-state conditions during transEpithelial Transport.

Karl Kunzelmann - One of the best experts on this subject based on the ideXlab platform.

  • calmodulin dependent activation of the Epithelial calcium dependent chloride channel tmem16a
    The FASEB Journal, 2011
    Co-Authors: Yuemin Tian, Patthara Kongsuphol, Jiraporn Ousingsawat, Ralph Witzgall, Rainer Schreiber, Karl Kunzelmann
    Abstract:

    TMEM16A (anoctamin 1, Ano1), a member of a family of 10 homologous proteins, has been shown to form an essential component of Ca2+-activated Cl− channels. TMEM16A-null mice exhibit severe defects in Epithelial Transport along with tracheomalacia and death within 1 mo after birth. Despite its outstanding physiological significance, the mechanisms for activation of TMEM16A remain obscure. TMEM16A is activated on increase in intracellular Ca2+, but it is unclear whether Ca2+ binds directly to the channel or whether additional components are required. We demonstrate that TMEM16A is strictly membrane localized and requires cytoskeletal interactions to be fully activated. Despite the need for cytosolic ATP for full activation, phosphorylation by protein kinases is not required. In contrast, the Ca2+ binding protein calmodulin appears indispensable and interacts physically with TMEM16A. Openers of small- and intermediate-conductance Ca2+-activated potassium channels known to interact with calmodulin, such as 1-E...

  • calmodulin dependent activation of the Epithelial calcium dependent chloride channel tmem16a
    The FASEB Journal, 2011
    Co-Authors: Yuemin Tian, Patthara Kongsuphol, Jiraporn Ousingsawat, Ralph Witzgall, Rainer Schreiber, M J Hug, Karl Kunzelmann
    Abstract:

    TMEM16A (anoctamin 1, Ano1), a member of a family of 10 homologous proteins, has been shown to form an essential component of Ca(2+)-activated Cl(-) channels. TMEM16A-null mice exhibit severe defects in Epithelial Transport along with tracheomalacia and death within 1 mo after birth. Despite its outstanding physiological significance, the mechanisms for activation of TMEM16A remain obscure. TMEM16A is activated on increase in intracellular Ca(2+), but it is unclear whether Ca(2+) binds directly to the channel or whether additional components are required. We demonstrate that TMEM16A is strictly membrane localized and requires cytoskeletal interactions to be fully activated. Despite the need for cytosolic ATP for full activation, phosphorylation by protein kinases is not required. In contrast, the Ca(2+) binding protein calmodulin appears indispensable and interacts physically with TMEM16A. Openers of small- and intermediate-conductance Ca(2+)-activated potassium channels known to interact with calmodulin, such as 1-EBIO, DCEBIO, or riluzole, also activated TMEM16A. These results reinforce the use of these compounds for activation of electrolyte secretion in diseases such as cystic fibrosis.