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PubMed1988

The epithelial tight junction: structure, function and preliminary biochemical characterization.

The tight junction, or zonula occludens (ZO), forms a semi-permeable barrier in the paracellular pathway in most vertebrate epithelia. The ZO is the apical-most member of a series of intercellular junctions, collectively known as the junctional complex, found at the interface of the apical and lateral cell surface. This structure not only restricts movement of substances around the cells, but may also serve as a 'fence' acting to maintain the cell surface compositional polarity characteristic of epithelial cells. The morphology and physiology of the ZO have been well documented and are briefly reviewed here. The biochemistry of this important intercellular junction remains largely unknown, although a tight junction-specific polypeptide called 'ZO-1' has recently been identified. Preliminary observations regarding the role of this peripheral phosphoprotein in the biology of the ZO are presented.

Animals↗
PubMed1980

Cell junctions in the excitable epithelium of bioluminescent scales on a polynoid worm: a freeze-fracture and electrophysiological study.

The bioluminescent scales of the polynoid worm Acholoe are covered by a dorsal and ventral monolayer of epithelium. The luminous activity is intracellular and arises from the ventral epithelial cells, which are modified as photocytes. Photogenic and non-photogenic epithelial cells have been examined with regard to intercellular junctions and electrophysiological properties. Desmosomes, septate and gap junctions are described between all the epithelial cells. Lanthanum impregnation and freeze-fracture reveal that the septate junctions belong to the pleated-type found in molluscs, arthropods and other annelid tissues. Freeze-fractured gap junctions show polygonal arrays of membrane particles on the P face and complementary pits on the E face. Gap junctions are of the P type as reported in vertebrate, mollusc and some annelid tissues. Intracellular current passage also induces propagated non-overshooting action potentials in all the epithelial cells; in photocytes, an increase of injected current elicits another response which is a propagated 2-component overshooting action potential correlated with luminous activity. This study shows the coexistence of septate and gap junctions in a conducting and excitable invertebrate epithelium. The results are discussed in relation to the functional roles of intercellular junctions in invertebrate epithelia. It is concluded that the gap junctions found in this excitable epithelium represent the structural sites of the cell-to-cell propagation of action potentials.

Action Potentials↗
PubMed1976

Freeze-fracture replica of the rat cornea.

The fine structures of the rat cornea, with special reference to their intercellular junctions, were studied using the freeze-fracture technique. At the corneal epithelium, gap junctions could be observed between the adjacent cells. At the stroma, crater-shaped depressions (between 300 and 500 A diameter) with pipe-like appearing structures connecting the lamellae were found. Intercellular junctions existing between the endothelial cells at the area near the anterior chamber are postulated to be the fascia (macula) occludens.

Animals↗
PubMed1985

Effect of 16,16-dimethyl prostaglandin E2 on gastric epithelial cell membrane potentials and resistances.

Intracellular microelectrode techniques were employed to examine the effects of 16,16-dimethyl prostaglandin E2 (dmPGE2) on Necturus antral mucosa epithelial cell membrane potentials and resistances. Necturus antral mucosa was mounted in a modified Ussing chamber and stable intracellular impalements were obtained. Addition of 0.01 microgram/ml dmPGE2 to the mucosal solution produced an increase of the apical cell membrane potential (Vmc) from -44.3 +/- 3.1 to -53.5 +/- 3.8 mV (p less than 0.001) and of the basolateral cell membrane potential (Vcs) from -48.8 +/- 2.8 to -57.7 +/- 3.2 mV (p less than 0.001). This reversible, dose-dependent hyperpolarization of both cell membranes was accompanied by a decrease in the electrical resistance of the apical membranes (Ra) from 2550 +/- 250 omega/cm2 to 1870 +/- 210 omega/cm2 (p less than 0.05) and a decrease in the resistance of the basolateral membrane (Rb) from 1020 +/- 250 omega/cm2 to 630 +/- 80 omega/cm2 (p less than 0.05). In addition, there was an increase in the resistance of the shunt (intercellular junction, Rs), the major route of transepithelial ion flow, from 710 +/- 60 omega/cm2 to 750 +/- 80 omega/cm2 (p less than 0.05). Thus dmPGE2 increased the cell membrane potentials and reduced the ionic permeability of the intercellular junction.

16,16-Dimethylprostaglandin E2↗
PubMed1996

The involvement of PKC in N-cadherin-mediated adherens junction assembly in cultured cardiomyocytes.

Activation of PKC by PMA was shown to promote the separation of chicken cardiomyocytes from each other in culture. Immunofluorescence staining for N-cadherin indicated that PMA, but not its inactive isoform 4 alpha PMA, induces the separation of cardiomyocytes and of co-cultured fibroblasts at intercellular junctional regions. The PMA-induced separation of cardiomyocytes and of co-cultured fibroblasts was inhibited by the PKC inhibitor, H-7. Immunoblot analysis further demonstrated that both PKC iota and PKC lambda were expressed in the cardiomyocyte cultures. While PKC lambda was localized to the cell-cell contact areas between cardiomyocytes, PKC iota was only detectable in the perinuclear cytoplasm of the co-cultured fibroblasts. The present findings suggest the involvement of PKC in regulating N-cadherin-mediated adherens junction formation in chicken cardiomyocytes. The differential distribution of PKC lambda and PKC iota in the cardiomyocytes and in the co-cultured fibroblasts suggests that different PKC isozymes are involved in regulating the assembly of intercellular junctions in these two cell types.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1978

Focal "spontaneous" alterations and loss of endothelial cells in rabbit aorta.

Rabbit aortas were examined by light, scanning, and transmission electron microscopy to observe the morphological steps in focal endothelial cell desquamation. The aortas were not subjected to any instrumentation prior to fixation by either immersion alone or combined perfusion and immersion. In areas where boundary layers separation of flow with eddy formation is known to occur, many elongated protruding cells were observed, some obviously partly loosened from the basement membrane. Some of the latter cells appeared to be attached by two ends and to be twisted longitudinally. Single cells, or even sheets of cells, were completely detached. The breaks seemed to have taken place close to, and parallel with, intercellular junctions, but not within these structures. Platelets had reacted both with injured cells and the denuded intimal surface. Thus, the sequence appears to be protrusion of cell body, partial loosening of cells from the basement membrane, breaks near the intercellular junctions, twisting of cells, and complete detachment.

Animals↗
PubMed2006

Increased expression of CD146, a new marker of the endothelial junction in active inflammatory bowel disease.

BACKGROUND: Crohn's disease (CD) and ulcerative colitis (UC), the 2 major forms of inflammatory bowel diseases (IBD), have been associated with disturbances in vascular physiology, including permeability and angiogenesis, that are in part regulated by the endothelial intercellular junctions. These junctions are composed of several adhesion molecules including the platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) and the more recently described CD146 (S-Endo1 Ag, MUC18). AIM: To study the expression of tissue and soluble form of CD146 in patients with CD or UC in relation to disease activity and location. This study was made in comparison with the soluble form of CD31 (sCD31). RESULTS: In active disease, a high expression of CD146 was observed on endothelial cells in intestinal biopsies from both CD and UC. In addition, we observed a decrease of sCD146 in relation to active disease and extensive location of CD and UC. Lower levels of sCD31 were also detected in active and extensive location of UC, but no difference could be observed in CD. CONCLUSION: sCD146 is a novel marker of the endothelial intercellular junction that reflects endothelial remodeling more effectively than soluble CD31. Further studies are warranted to determine whether sCD146 will provide a serological assay reflecting alterations in vascular permeability and vessel proliferation in the inflamed IBD intestine.

Adolescent↗
PubMed1994

Platelet aggregation on the endothelium of Schlemm's canal.

By using monkey eyes and light microscopy, transmission electron microscopy and scanning electron microscopy we have studied the role of platelets in Schlemm's canal. In eyes connected to a reservoir and subjected to an elevated intraocular pressure, there was break-down of the cell membranes facing the invaginations into the endothelial cells, resulting in local protrusions from the invaginations and ruptures. Other unphysiological openings in the inner wall were due to separation of the intercellular junctions. Aggregates of platelets were observed at both these types of openings. Small aggregates were observed also in massaged eyes and in eyes which had not been touched before fixation. It seems likely that the intercellular junctions are fragile, tending to disrupt even under normal conditions and that platelets play a role in their repair. It is also suggested that platelets tend to restrict the size of the physiological pores.

Animals↗
PubMed1970

Transitional cardiac cells of the conductive system of the dog heart. Distinguishing morphological and electrophysiological features.

Cardiac cells with distinctive electrophysiological and morphological features were found at the junctional region between Purkinje and ventricular cells of the dog heart. The electrophysiological exploration of these "transitional" cells revealed action potentials markedly different in configuration from those generated by Purkinje or by ventricular cells. The impaled cardiac cells which generated transitional action potentials were identified in serial sections and studied with the light and the electron microscopes. The transitional cells were found to be characterized cytologically by: (a) their subendocardial location, (b) their small diameter, (c) the absence of T system and sarcoplasmic reticulum, and (d) the lack of intercalated discs under the light microscope and the sparsity of specialized intercellular junctions under the electron microscope. Purkinje, transitional, and ventricular cells were found to be joined by gap junctions permeable to lanthanum. A quantitative difference in the extent and distribution of specialized intercellular junctions may be one of the factors responsible for the slow velocity of conduction characteristic of the Purkinje-ventricular junctional region.

Action Potentials↗
PubMed1996

Effect of cell polarization and differentiation on entry of Listeria monocytogenes into the enterocyte-like Caco-2 cell line.

The entry of Listeria monocytogenes into the enterocyte-like Caco-2 cell line was studied as a function of cell polarization and differentiation. L. monocytogenes entered through the entire surface of nonpolarized cells and, predominantly, through the basolateral surface of polarized cells based on the following observations: (i) sites of L. monocytogenes invasion paralleled the distribution of the transferrin receptor, a well-known basolateral marker of polarization; (ii) numbers of internalized bacteria decreased dramatically when Caco-2 monolayers cultured beyond confluency were used (about 0.1% of the inoculated bacteria versus 1 to 2% with nonconfluent monolayers); and (iii) L. monocytogenes entry into postconfluent monolayers was greatly enhanced by treating cells with Ca(2)+ -free medium, a procedure that disrupts intercellular junctions and thus exposes the basolateral surface to bacteria. Ethylene glycol-bis (beta-aminoethyl ether)-N, N, N',N' -tetraacetic acid (EGTA) had contradictory effects on L. monocytogenes entry as this reagent opened intercellular junctions but inhibited binding and internalization of bacteria. Finally, the role of the inlAB locus in L. monocytogenes entry was confirmed because and inlAB mutant was 50- to 100-fold less invasive than the parental strain regardless of the monolayer's age. However, the inlAB mutant was still able to enter cells and to induce intracellular actin polymerization. Entry of inlAB bacteria into Caco-2 cells was not inhibited by EGTA.

Bacterial Adhesion↗
PubMedDate not supplied

[Electron microscopic study of the corneal endothelium in 2 cases of keratitis. Herpetic disciform keratitis. Neuroparalystic keratitis with dry keratitis].

Study of corneal endothelium by scanning and transmission electron microscopy in two cases of corneal disease. In one case of herpetic keratitis with stromal oedema, there is no cellular reaction. The endothelium is damaged with cellular necrosis and nucleus irregularity. Intercellular junctions are abnormal. With TEM it is possible to say that there are two layers of cells on some places with cellular necrosis. In one case of corneal dryness with lesions of corneal anaesthesia the cells are very damaged and a retrocorneal membrane if formed by many layers of cells. The intercellular junctions are almost normal.

Cornea↗
PubMed1995

IFN-gamma and TNF-alpha induce redistribution of PECAM-1 (CD31) on human endothelial cells.

Platelet endothelial adhesion molecule-1 (PECAM-1/CD31) is a glycoprotein adhesion molecule of the Ig superfamily that is constitutively expressed on leukocytes, platelets, and endothelial cells where it concentrates at the intercellular borders of adjacent cells. Recent studies have confirmed that endothelial PECAM-1 is involved in the recruitment of neutrophils into inflammatory sites. However, the effects of inflammatory cytokines such as TNF-alpha and IFN-gamma on endothelial PECAM-1 expression are not known. We studied the effect of several inflammatory cytokines on human umbilical vein endothelial cell PECAM-1 expression. We found that TNF-alpha and IFN-gamma produced dose-dependent changes in the surface distribution of PECAM-1, with a loss of the typical staining of PECAM-1 at intercellular junctions. Because TNF-alpha and IFN-gamma did not alter PECAM-1 transcription or total surface PECAM-1, these changes in PECAM-1 localization are most consistent with a redistribution of the protein away from intercellular junctions. This cytokine-induced surface redistribution of PECAM-1 was associated with changes in PECAM-1 cytoskeletal association but did not involve the expression of different alternatively spliced variants of the molecule. Given the involvement of endothelial PECAM-1 in neutrophil recruitment, redistribution of PECAM-1 may serve as a mechanism for regulating the transmigration of leukocytes across the vascular endothelium.

Alternative Splicing↗
PubMed1985

Rapid formation of gap-junction-like structures induced by glycerol.

Intercellular junctions, identified in freeze-fracture by narrowing of the intercellular gap and codistribution of P-face membrane particles, proliferate during incubation of excised rat prostate tissue in 30% glycerol solution. These junctions fulfill the criteria used to identify gap junctions in freeze-fracture replicas with respect to the size and uniformity of their component particles, the codistribution of the particle aggregates on P-faces of adjacent membranes, and the narrowing of the extracellular cleft at the junction. These gap-junction-like structures form on the lateral surfaces of epithelial cells, where they are normally scarce, within minutes after exposure to glycerol. Glycerol-induced junction formation is not blocked by DNP, a metabolic uncoupler, or by cycloheximide, a protein synthesis inhibitor. Newly formed junctions occur initially in clusters and the number per cluster decreases as individual junctions become larger with longer periods of incubation, suggesting that the clusters coalesce. The structural changes that precede and accompany the formation of these junctions at early times of incubation are comparable to the changes reported to precede the formation of gap junctions accompanying hormonal treatment, development, and other means of natural induction.

Animals↗
PubMed1982

Tissue connections in a transplantable virus-producing sebaceous adenoma of the mouse. II. A freeze-fracture study in conjunction with filipin.

The distribution, size, and configuration of intercellular junctions in the sebaceous tumor of mice were examined using the freeze-fracture technique. Three types of junctions were observed: desmosomes, gap, and tight junctions. Tight junctions in general consisted of short linear unbranched fibrils, and macular or complex tight junctional patterns were present only occasionally. Gap junctions ranged from small sports of 0.9 x 10(-3) micrometer2 to areas of approximately 0.46 micrometers2. Desmosomes were the most frequent junctional specializations, and it is concluded that they are at least partially responsible for this tumor not being metastatic. Filipin in conjunction with freeze-fracture showed filipin-sterol complexes on the plasma membrane, the nuclear envelope, and the membranes of the endoplasmic reticulum and mitochondria. The intercellular junctions were devoid of these complexes indicating that these regions are low in cholesterol.

Adenoma↗