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Results for “Tight junctions”

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PubMed1978

A freeze-fracture study of tight junctions in the pars convoluta and pars recta of the renal proximal tubule.

The morphology of tight junctions of the renal proximal tubule was studied comparing the pars convoluta and pars recta of rat, golden hamster, rabbit, cat, dog and tupaia. Though some interspecies variations were observed, the convoluted portions of the proximal tubules revealed quite uniformly very leaky tight junctions with mainly 1-2 strands. Along the whole proximal tubule of the rabbit kidney including the pars recta only minor differences of the zonulae occludentes were found. By contrast, the tight junctions of the pars recta in other species were much more elaborate, especially in cat and tupaia, having up to 6 strands and an overall depth of more than 150 nm. The implications of these findings are discussed with special regard to the functional differences between the pars convoluta and pars recta of the proximal tubule.

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PubMed1979

Changes in tight junctions of rat intestinal crypt cells associated with changes in their mitotic activity.

The freeze-fracture appearance of tight junctions between rat duodenal crypt cells was studied in normal, mitotically suppressed, and mitotically enhanced animals. In normal animals crypt cell tight junctions present a pleomorphic appearance. The population includes junctions resembling postmitotic junctions of the intestinal villus, junctions composed largely or completely of particle chains, and regions at the cell apex in which junctions are absent for 3-4 micron distances laterally. Mitotic suppression by inhibition of DNA synthesis with cytosine arabinoside results in the disappearance of pleomorphism and crypt tight junctions progressively come to resemble those of the intestinal villus. With recovery from the drug and further synchronization with Colcemid, the crypt cells undergo a mitotic burst, and all varieties of unusual junctional configurations are observed with increased frequency.

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PubMed1979

Gap and tight junctions in tunicates. Study in conventional and freeze-fracture techniques.

Intercellular junctions have been investigated in epidermis and pharyngeal epithelium of larvae and adults of various species of tunicates with conventional and freeze-fracture techniques. Gap and tight junctions were found, similar to those observed in vertebrate tissues. Gap junctions were frequent in glandular epithelia and in larval tissues. They were interpreted as ways of intercellular communication in these developing tissues. They were also particularly numerous in Phallusia pharyngeal cells. Tight junctions were found preferentially in adult pharyngeal and epidermal epithelia, where they were arranged in strands of distinct particles forming a belt-like network at the apical part of cells. These junctions were interpreted as providing a tight barrier between the internal medium and the external environment. In larvae, tight junctions were found only between epidermal cells of the tail. These junctions thus characterized completely differentiated tissues, where they might play, in tunicates and in vertebrates, the same role as septate junctions do in invertebrates.

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PubMed2026

Phytolacca acinosa Roxb. induces intestinal toxicity through the histamine-MLCK-tight junction axis: Integrated evidence from proteomics, metabolomics, intestinal organoids and epithelial barrier validation.

Phytolacca acinosa Roxb. (PR) is a saponin-rich medicinal plant associated with gastrointestinal toxicity, but the mechanisms underlying PR-induced intestinal barrier injury remain unclear. In this study, raw PR extract was analytically characterized by UPLC-ZenoTOF-MS/MS, confirming triterpenoid saponins as the predominant constituents. C57BL/6 J mice were orally exposed to characterized PR extract (1.20 or 12.0 g/kg for 5 h), and Caco-2 cells and mouse intestinal organoids were used to assess epithelial toxicity and barrier disruption. Histopathology, ELISA, FITC-dextran permeability assays, immunofluorescence, CCK-8, LDH release, western blotting, DIA-based proteomics and untargeted metabolomics were integrated to define toxicological mechanisms. PR induced dose-dependent intestinal inflammation and barrier dysfunction, with the ileum as the most sensitive target. PR increased serum DAO and D-lactate and intestinal TNF-α and IL-1β, disrupted organoid morphology, enhanced epithelial permeability, and reduced ZO-1 expression. Proteomics revealed changes in inflammatory, lipid-metabolic, cytoskeletal and tight-junction pathways, including upregulation of MLCK3 and phospholipase-related proteins and downregulation of ZO-1 and ZO-2. Metabolomics identified histidine metabolism disturbance and histamine accumulation. Integrated multi-omics and pharmacological validation indicated that histamine activated the PLC/IP₃/Ca²⁺/CaM/MLCK cascade, promoting MLC phosphorylation, tight-junction disassembly and epithelial leakiness. MLCK inhibition partially restored ZO-1/ZO-2 expression and attenuated PR-induced epithelial injury. These findings identify the histamine-MLCK-tight junction axis as a key mechanism of PR-induced intestinal toxicity and support hazard identification of saponin-rich PR exposure.

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PubMed1979

Tight junctions in the choroid plexus epithelium. A freeze-fracture study including complementary replicas.

The tight junctions of the choroid plexus epithelium of rats were studied by freeze-fracture. In glutaraldehyde-fixed material, the junctions exhibited rows of aligned particles and short bars on P-faces, the E-faces showing grooves bearing relatively many particles. A particulate nature of the junctional strands could be established by using unfixed material. The mean values of junctional strands from the lateral, third, and fourth ventricles of Lewis rats were 7.5 +/- 2.6, 7.4 +/- 2.2, and 7.5 +/- 2.4; and of Sprague-Dawley rats 7.7 +/- 3.4, 7.4 +/- 2.3, and 7.3 +/- 1.6. Examination of complementary replicas (of fixed tissue) showed that discomtinuities are present in the junctional strands: 42.2 +/- 4.6% of the length of measured P-face ridges were discontinuities, and the total amount of complementary particles in E-face grooves constituted 17.8 +/- 4.4% of the total length of the grooves, thus approximately 25% of the junctional strands can be considered to be discontinuous. The average width of the discontinuities, when corrected for complementary particles in E-face grooves, was 7.7 +/- 4.5 nm. In control experiments with a "tighter" tight junction (small intestine), complementary replicas revealed that the junctional fibrils are rather continuous and that the very few particles in E-face grooves mostly filled out discontinuities in the P-face ridges. Approximately 5% of the strands were found to be discontinuous. These data support the notion that the presence of pores in the junctional strands of the choroid plexus epithelium may explain the high transepithelial conductance in a "leaky" epithelium having a high number of junctional strands. However, loss of junctional material during fracturing is also considered as an alternative explanation of the present results.

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PubMed1979

Tight junctions in a fluid-transporting epithelium of an insect.

Occluding junctions have been found between the lateral cell borders at the base of the rectum of Periplaneta americana. They appear as punctate membrane appositions in thin sections, and after incubation in physiological solutions containing lanthanum before fixation the inward penetration of tracer is impeded in this same basal area. Moreover, freeze-fracture studies of this region reveal simple linear ridges on fracture face P and grooves on fracture face E, which are similar to the less complex vertebrate tight junctions. The luminal clefts, which permit free inward diffusion of tracers, present no tight junctions, but do have septate junctions. These results support the contention that, contrary to earlier speculation, arthropods do possess tight junctions; these, rather than septate junctions, appear to form the morphological basis of at least some of the permeability barriers observed in invertebrates.

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PubMed1979

The formation of gap and tight junctions between retinal pigment cells in cell cultures.

The reformation of the junctional complex of retinal pigment cells was studied after trypsin disaggregation and in vitro reaggregation. Control specimens show a zonula occludens (tight junction) with integrated gap junctions and very large macular gap junctions. Isolation after trypsination results in disaggregation of the large gap junctions and fragmentation of the tight junctions with disaggregation of their integrated gap junctions. After two to four days of incubation the restoration of the zonula occludens is complete. After approximately five days of incubation, large gap junctions are found with a patchy arrangement of particles similar to that seen in vivo.

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PubMed1977

"Tight" junctions in the sheath of normal and regenerating motor nerves of the crayfish, Orconectes virilis.

"Tight" or occluding intercellular junctions occur between adjacent glial processes in normal and regenerating crayfish motor nerve sheaths. Although infrequent, these junctions possess the ridge and groove configuration characteristics of freeze-cleaved occluding junctions. When present, nerve sheath tight junctions consist of a single, or at most a few, parallel intramembrane ridges situated on the EF membrane face of the glial plasma membrane. Consequently, such contacts are rarely recognized in thin sections of plastic-embedded nerve sheaths. Crayfish nerve sheath tight junctions are of the fascia occludens type and, therefore, do not impede solute flow across the nerve sheath. Fasciae occludentes of regenerating nerve sheaths occur in close proximity to discoid plaque-like aggregates of particles assumed to represent maculae adhaerentes. This relationship, which was not observed in normal nerve sheaths, suggests a functional association between the two types of junctions, perhaps developmental transformation of one junction type into the other. Although ridges and grooves of tight junctions occur next to cross-fractured trans-glial channels, no functional significance is proposed for this relationship. This study is the first report of tight intercellular junctions in crustacean glial nerve sheaths.

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PubMed1979

Double replica technique applied to choroid plexus from early foetal sheep: completeness and complexity of tight junctions.

Choroid plexuses from early and late sheep foetuses were examined by an improved freeze-fracture technique and the use of double-replicas to define the structure of the tight junction network of the epithelial cells. 'Complex' strands which consist of two normal parallel strands separated by a single row of pits or particles are defined and demonstrated in complementary faces. Since this strand variety was encountered in the same proportion in the different development stages investigated, it could not be correlated with changes in permeability. It is more likely that the 'complex' strands are associated with the transfer of gap junction particles within the membrane. The question of the significance of discontinuities in P face ridges was also resolved by the double replica technique: the few discontinuities which were observed could be accounted for by particles in the complementary E faces. Furthermore, approximately the same number of such junction displacements was found in early and late stages which makes it unlikely that this phenomenon could contribute to changes in permeability. Thus it has not been possible so far to relate any structural feature of the tight junction network in developing choroid plexus epithelial cells with the reported changes in permeability of the blood-C.S.F. barrier.

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PubMed1979

Freeze-fracture observations on the visceral yolk sac placenta of rats, mice and hamsters. With special reference to endodermal cell tight junctions.

Freeze-fracture replicas of visceral yolk sac from rats, mice and hamsters in late stages of gestation were studied by electron microscopy. Special attention was directed toward determining the types of junctional specializations that exist between the columnar endoderm cells of this placental membrane. In all three species, well-developed, zonular tight (occluding) junctions were found on the contiguous lateral surfaces of the endoderm cells. The tight junctional network, located in an immediate subluminal position, was from 0.2--0.5 micrometers in depth and consisted at any point of 2--5, interconnecting, approximately 9 eta wide, strands (P-face) or shallow furrows (E-face). Patch-like aggregations of irregular intramembrane particles, characteristic of desmosomes (maculae adherentes), also were observed at scattered sites below the tight junctions. However, no evidence of gap (communicating) junctions was encountered. The endoderm cells of the rodent visceral yolk sac have been shown to play a central role in the selective transport of macromolecular substances from the maternal to the fetal system. Tight junctions may be vital to this endodermal cell function by preventing random paracellular fluxes of macromolecules.

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PubMed1975

Establishment of tight junctions between epithelial cells.

Epithelia serve as barriers to the diffusion of solutes between body compartments, and must do so despite the frequent loss of cells. When single cells are experimentally removed from the Necturus gallbladder epithelium, contiguous cells migrate to fill the defect within 30 min. Electrophysiological measurements show that the local electrical resistance across the epithelium in the region of a wound returns to normal in the same period of time; electron microscopy demonstrates that tight junctions are formed concurrently. Physiologically functional and morphologically recognizable tight junctions can thus be established within 30 min, demonstrating a mechanism for the rapid restoration of epithelial integrity after cell loss.

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PubMed1979

Development of tight junctions in rat tracheal epithelium during the early hours after mechanical injury.

Mild abrasion of rat tracheal epithelium results in the death of superficial cells and flattening of basal cells to cover the exposed areas of basal lamina. Six hours after injury, colloidal tracers were shown in previous studies to be excluded from the spaces between cells and from the underlying lamina propria. The structural basis for this restoration of barrier function was investigated in the present experiments using transmission electron microscopy of thin sections and freeze fracture replicas. For each of 4 elapsed times after injury, 12 healing lesions in the epithelium were studied extensively. In specimens obtaine 2 and 4 hours after wounding, apical junctions between epithelium cells could not be identified in either thin sections or freeze fracture replicas. Six hours after injury, point contact could be recognized between epithelial cells in thin sections, whereas freeze fracture replicas revealed rudimentary tight junctions consisting of fragmented strands and linearly organized particles. Twelve hours after injury, highly developed tight junctions similar in complexity to those in normal uninjured tracheal epithelium were observed between the relatively undifferentiated basal cells comprising the regenerating epithelium. The focal membrane modification that appears 6 hours after injury is thus an early step in the process of regeneration and restoration of cytologic specialization.

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PubMed1979

Reformation of gap and tight junctions in regenerating liver after cholestasis.

Morphometric analysis of the alterations in interhepatocyte junctions induced by bile duct ligation revealed that after 48 h, during which time the serum bilirubin increased 6 to 8 fold, the membrane area occupied by gap junctions on the apico-lateral and medio-lateral sides decreased from 3.6% in controls to 0.02% in the ligated group. The strands of the zonulae occludentes were reduced in number and showed increased discontinuities. Within 45 min of recanalization of the common bile duct, clusters of particles appeared within and adjacent to the tight junctional areas or in the lateral hepatocyte membrane. Subsequently, the particle aggregations localized in the apico-lateral membrane areas increased in number and size becoming finally indistinguishable from those of controls within 96 h after the onset of recanalization. The zonulae occludentes also rearranged and reestablished their original structure during this period. The serum bilirubin fell to normal within 24 h of recanalization. It is concluded that metabolic and ultrastructural restitution associated with the recanalization of the ligated bile duct have no strict temporal correlation to one another. These studies provide further evidence that alterations in gap and tight junctions induced by pathological processes, e.g. during bile duct ligation, are completely reversible when regeneration occurs.

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PubMed1976

In vivo induction of tight junction proliferation in rat liver.

The chronic administration of phalloidin induces an extensive development of tight junctions between rat hepatocytes. The junctional strands lose their predominantly parallel orientation with respect to the canalicular lumen and extend abluminally in irregular patterns which cover large membrane areas at considerable distance from the bile canaliculi. These changes indicate both proliferation and provide further evidence that these junctions are not permanent differentiations of the cell membrane.

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PubMed1979

On the cross-reactivity of amiloride and 2,4,6 triaminopyrimidine (TAP) for the cellular entry and tight junctional cation permeation pathways in epithelia.

2,4,6 Triaminopyrimidine (TAP) has been previously shown to inhibit the passive tight junctional cation permeation pathway in various "leaky" epithelia. Amiloride has been shown to be an effective inhibitor of the cation cellular entry pathway in "tight" epithelia. In this paper we demonstrate that TAP and amiloride at appropriate concentrations are able to block either of these epithelial cation permeation pathways. TAP was found to block the Na entry pathway in frog skin with the following characteristics: it (1) inhibits from the external solution only, (2) is completely reversible, (3) increases the transepithelial resistance, (4) is active in the monoprotonated form, (5) is noncompetitive with Na, (6) displays saturation kinetics which obey a simple kinetic model (KI = 1 X 10(-3) M), (7) is independent of external calcium, (8) is dependent on external buffering capacity, and (9) is competitive with amiloride. Amiloride inhibition of the junctional permeation in gallbladder had the following characteristics: it (1) increases the transepithelial resistance, (2) decreases cation conductance without affecting the anion conductance, (3) displays saturation kinetics which obey a simple kinetic model (KI = 1 X 10(-3) M), and (4) possesses inhibitory activity in both its protonated and unprotonated form. These results not only indicate that a similar inhibitory site may exist in both of these cation permeation pathways, but also provide information on the chemical nature and possible location of these inhibitory sites.

Amiloride↗

PubMed1978

Fine structure of tight junctions between rat choroidal cells after osmotic opening induced by urea and sucrose.

After ventriculo-cisternal perfusion of hypertonic urea or sucrose, both the choroid plexus permeability to horseradish peroxidase and the structure of tight junctions between choroidal cells are modified. Intercellular spaces are swollen, continuous ridges are fragmented and intrajunctional spaces are invested by many membranous particles. These morphological alterations appear to be reversible. These ultrastructural data are related to an osmotic maladjustment induced by the introduction of hypertonic solutions into the cerebro-spinal fluid.

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PubMed1979

Tight junctions in choroid plexus papillomas.

Four cases of choroid plexus papilloma (CPP) obtained at the time of surgical excision were examined by electron microscopy and compared with normal choroid plexus (CP) of mouse and chick. In apical tight junctions fusion of the two outer leaflets of the adjacent cytoplasmic membrane was verified as in CP. This fact suggests that there is a blood-CSF barrier not only in CP but also in CPP.

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PubMed1979

Absence of tight junctions in endothelium of marrow sinuses: possible significance for marrow cell egress.

The nature of contact between endothelial cells in rat marrow sinuses was studied. Colloidal lanthanum permeated freely into the interendothelial space. Moreover, using freeze-fracture technique, we failed to show junctional structures where these endothelial cells came into contact. With thin sectioning electron microscopy, we observed occasional submembranous densities but the interendothelial distance measured 20 nm and no membrane fusion was seen. Absence of tight junctions between endothelial cells of marrow sinuses may serve a function in marrow cell egress by permitting these cells to slide over each other, thereby changing the luminal size. Within the fixed volume of marrow, an increase in luminal size results in displacement of haemopoietic cells into the lumen.

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