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PubMed1989

Membrane perturbations and mediation of gap junction formation in response to taurine treatment in normal and injured alveolar epithelia.

Nitrogen dioxide is an air pollutant that causes pulmonary alterations. Employing light and transmission electron microscopy, we examined plastic sections and freeze-fracture replicas of alveolar epithelium of groups of hamsters exposed to nitrogen for 24 h to determine taurine-induced changes in intercellular junctions. Prior to exposure, one group of hamsters was given 0.5% taurine in their drinking water for 2 weeks. A second group of hamsters was given taurine-free water. The taurine-treated group was divided into three subgroups. The first subgroup was exposed to nitrogen dioxide at a concentration of 7 ppm for 24 h, the second subgroup was exposed to nitrogen dioxide at a concentration of 30 ppm for 24 h, and the third subgroup was exposed to normal room air for 24 h. The nontaurine-treated animals were similarly divided into three subgroups and treated as described above. The lungs of the hamsters exposed to nitrogen dioxide without the taurine pretreatment exhibited extensive inflammatory cell infiltration in the walls of the terminal bronchioles, alveolar ducts, and peribronchiolar alveoli. The degree of infiltration was proportional to the degree of nitrogen dioxide concentration. The taurine-treated animals exposed to nitrogen dioxide and the nontaurine-treated animals exposed to room aid did not show any inflammatory infiltrate. Freeze-fracture replicas of the tight junctional regions of the type I and type II pneumocytes revealed significant fragmentation in the nitrogen dioxide-exposed lungs. It was also observed that the tight junctions between the type I pneumocytes of the taurine-treated groups, whether exposed or not, revealed gap junction-like aggregates among the tight junction fibrils. The 30-ppm nitrogen dioxide exposed group exhibited larger and more frequent gap junctions between the pneumocytes than those observed in the 7-ppm nitrogen dioxide exposed group. The evidence suggests that taurine may have an effect on plasma membranes and intercellular communications. Changes in intercellular communication may contribute to decreased susceptibility to injury and increased pneumocyte survival.

Animals↗

PubMed2001

Prevention of organochlorine-induced inhibition of gap junctional communication by chaetoglobosin K in astrocytes.

Innumerable toxic substances present in the environment inhibit gap junctions, intercellular membrane channels that play fundamental roles in coordinated function of cells and tissues. Included are persistent organochlorine compounds, which pose health risks to humans and animals owing to their widespread use, bioaccumulation, and ability to inhibit gap junction channel-mediated intercellular communication in liver, lung, skin, heart, and brain cells. In this study, the organochlorine xenobiotics dieldrin and endosulfan, at micromolar concentrations, were found to inhibit gap junction-mediated intercellular communication and induce hypophosphorylation of connexin 43 in cultured rat astrocytes, the predominant cell type in the brain coupled through gap junctions. This inhibition of gap junctional communication was substantially reduced by preincubation with chaetoglobosin K (ChK), a bioactive natural produce previously shown to have ras tumor suppressor activity. Chaetoglobosin K also prevented dieldrin and endosulfan-induced hypophosphorylation of connexin 43 and prevented dieldrin-induced connexin 43 plaque dissolution in both astrocytes and cultured liver epithelial cells. The results suggest that stabilization of the native, phosphorylated form of connexin 43 by ChK may contribute to its ability to prevent organochlorine-induced inhibition of gap junction-mediated communication and dissolution of gap junction plaques within the plasma membrane.

Animals↗

PubMed1979

Junctions between interstitial cells of the renal medulla: a freeze-fracture study.

Cell junctions between interstitial cells of the renal medulla were studied in freeze-fracture replicas of kidneys from rat, rabbit, hamster and the tree-shrew Tupaia belangeri. In all species studied a composite type of intercellular junction was found comprising elements of tight junctions and irregular gap junctions of highly variable size and shape. The number of these junctions increased towards the tip of the papilla. Our findings suggest that the composite junctions observed play a role in the maintainance of the ladder-like arrangement of the interstitial cells in the inner zone. The existence of irregular gap junctions raises the possibility that the functions of the interstitial cells are coordinated, especially during alterations of the functional state of the kidney.

Animals↗

PubMed1994

Effects of ultraviolet radiation on intercellular communication in V79 Chinese hamster fibroblasts.

The effects of ultraviolet (UV) radiation on gap junctional intercellular communication (GJIC) in V79 Chinese hamster fibroblasts were studied by means of a dye transfer assay. Intercellular communication was shown to be altered by UVB (297/302 nm) and UVA (365 nm) radiation, the effect depending on the wavelength of exposure and time between irradiation and microinjection of the dye in the dye transfer assay. Exposure to 297/302 nm radiation induced a reduction in intercellular communication 6 min after exposure. Incubation of the cells post-irradiation reversed the inhibition of GJIC. From 2 to 24 h after exposure an increase in GJIC over the control cells was seen, with a maximum at 8 h post-irradiation. UVA (365 nm) radiation, on the other hand, induced an increase in the intercellular communication 6 min after irradiation. Incubation of the cells post-irradiation led to a decrease in the number of communicating cells, with a minimum seen 4 h after exposure. The reduction in communication observed after exposure to UVB and UVA was not correlated with similar modifications in the gap junction protein connexin43 as found when exposing the cells to the tumour promoter 12-O-tetradecanoyl-phorbol-13-acetate. For the higher fluences of UVA, a decrease in immunorecognizable connexin43 was seen, concomitant with a markedly increased background of higher mol. wt compounds. This may be due to UVA-induced crosslinking of connexin43. No correlation was found between changes in communication induced by UV radiation and levels of cyclic AMP.

Animals↗

PubMed2004

The tight junction: a multifunctional complex.

Multicellular organisms are separated from the external environment by a layer of epithelial cells whose integrity is maintained by intercellular junctional complexes composed of tight junctions, adherens junctions, and desmosomes, whereas gap junctions provide for intercellular communication. The aim of this review is to present an updated overview of recent developments in the area of tight junction biology. In a relatively short time, our knowledge of the tight junction has evolved from a relatively simple view of it being a permeability barrier in the paracellular space and a fence in the plane of the plasma membrane to one of it acting as a multicomponent, multifunctional complex that is involved in regulating numerous and diverse cell functions. A group of integral membrane proteins-occludin, claudins, and junction adhesion molecules-interact with an increasingly complex array of tight junction plaque proteins not only to regulate paracellular solute and water flux but also to integrate such diverse processes as gene transcription, tumor suppression, cell proliferation, and cell polarity.

Animals↗

PubMed1978

A freeze-fracture and lanthanum tracer study of the complex junction between Sertoli cells of the canine testis.

What appear to be true septate junctions by all techniques currently available for the cytological identification of intercellular junctions are part of a complex junction that interconnects the Sertoli cells of the canine testis. In the seminiferous epithelium, septate junctions are located basal to belts of tight junctions. In thin sections, septate junctions appear as double, parallel, transverse connections or septa spanning an approximately 90-A intercellular space between adjacent Sertoli cells. In en face sections of lanthanum-aldehyde-perfused specimens, the septa themselves exclude lanthanum and appear as electron-lucent lines arranged in a series of double, parallel rows on a background of electron-dense lanthanum. In freeze-fracture replicas this vertebrate septate junction appears as double, parallel rows of individual or fused particles which conform to the distribution of the intercellular septa. Septate junctions can be clearly distinguished from tight junctions as tight junctions prevent the movement of lanthanum tracer toward the lumen, appear as single rows of individual or fused particles in interlacing patterns within freeze-fracture replicas, and are seen as areas of close membrane apposition in thin sections. Both the septate junction and the tight junction are associated with specializations of the Sertoli cell cytoplasm. This is the first demonstration in a vertebrate tissue of a true septate junction.

Animals↗

PubMed1985

Communication compartments in mixed cell cultures.

Mixed cultures of epithelial (BRL) cells and fibroblasts (BHK), which sort themselves out into separate domains of each cell type, form communication compartments. Electrical coupling, dye coupling and metabolic coupling measurements have been used to show that small ions and molecules can move freely via intercellular junctions between all the cells in a domain, while their movement across the boundaries between domains is severely restricted. Metabolic coupling is the most sensitive method for detecting trans-boundary communication but the results obtained from all three methods are compatible. The data suggest the reduced transfer across the boundaries is due to fewer channels, resulting from a lower frequency of junction formation between heterologous cells, rather than to channels of smaller diameter. Concentration gradients of small cytoplasmic molecules can be established within these communication compartments which are similar to those predicted to explain pattern formation in developing systems. It is suggested that the cell surface features which cause this sorting out are also responsible for the reduced frequency of heterologous junction formation and hence for compartmentalization.

Animals↗

PubMed1991

[Ultrastructure of glioma vessel--morphometric study for vascular permeability].

In this study we investigated the ultrastructure of human glioma capillaries in operated sample of low grade astrocytomas and malignant gliomas. Electronmicrographs of a total of 58 vessels were analyzed with computer assisted morphometry for ultrastructural evidence of permeability routes. All of these vessels were present in the marginal area of tumors devoid of necrosis, less than 10 micron in diameter and containing one nucleus at least on axial section. We found that: (1) The number of pinocytic vesicles was significantly higher in capillaries from malignant glioma (an average of 8.1 per 1 micron (2) cytoplasm) than those from low grade astrocytoma (an average of 4.0 per 1 micron (2) cytoplasm). In capillaries from malignant glioma, most of the pinocytic vesicles were arranged in the abluminal side of endothelium and some of them were fused each other. (2) Abnormal endothelial intercellular junctions which were defined as short tight junctions (less than or equal to 0.25 microns) were equally but infrequently seen in low grade astrocytomas and malignant gliomas. (3) Fenestrations in the endothelium were not seen. Therefore we suggest that the high vascular permeability and resultant brain edema in malignant gliomas is likely to increased pinocytic vesicles and rare but abnormal inter endothelial junctions.

Adolescent↗

PubMedDate not supplied

The fine structure of exfoliated cervical and vaginal cells.

In order to understand the means by which cellular aggregates were maintained in gynecologic samples, the fine structure of samples derived from a number of women of various ages was examined with special attention paid to the intercellular junctions. Most cells in the samples were squamous cells containing numerous intercellular fibrils and glycogen granules. Parabasal or intermediate cells were also seen as well as occasional endocervical cells. All of these cell types were often found as parts of aggregates and, while other cell junctions were present, desmosomes were the most prominent. It was concluded that desmosomes were probably responsible for maintaining the aggregated state of many of the cells found in gynecologic samples.

Adult↗

PubMed1999

Role of actin stress fibres in the development of the intervertebral disc: cytoskeletal control of extracellular matrix assembly.

Orientation of collagen fibrils is a key event in the development of many tissues. In the intervertebral disc, the outer annulus fibrosus comprises lamellae of parallel collagen fibres, the direction of orientation of the long axis of which alternates in angle between lamellae. In development, this organisation is preceded by the formation of sheets of oriented fibroblasts, which then deposit the oriented lamellae. Here, using fluorescent labelling, confocal and electron microscopic techniques on developmental series, we show that the orientation of cells in lamellae is associated with the formation of adherens junctions intercellularly, involving cadherins and vinculin, and longitudinal stress fibres (label for filamentous actin and tropomyosin) intracellularly. The stress fibres direct the initial elongation of cells and control the deposition of oriented extracellular matrix via junctional complexes with the matrix involving vinculin and alpha 5 beta 1 integrins, which in turn promote the formation of oriented fibronectin at the cell surface; oriented collagen is deposited between cells at the same stages. Shortly after birth, the stress fibres disappear, probably because cells now gain orientational cues from the matrix, and are undergoing differentiation-related changes to form fibrocartilage cells. Dev Dyn 1999;215:179-189.

Actin Cytoskeleton↗

PubMed1979

Observations on closure of the neuropores in the chick embryo.

Neuropore closure was studied in chick embryos by light and electron microscopy. Surface ectoderm reflects over the crests of the neural folds at all craniocaudal levels, merging with the neural ectoderm lining the neural groove. Apices of surface ectodermal cells have an essentially identical morphology prior to approximation of folds, both within the presumptive fusion sites and more laterally. Cells of these areas have slightly convex profiles exhibiting few cellular protrusions. Each neural fold contains a superficial half, composed of neural ectoderm covered by surface ectoderm, and a deep half consisting entirely of neural ectoderm. Initial contact between folds usually occurs near the junction between these halves in cranial regions, but is restricted primarily to surface ectoderm at caudal levels. Subsequent fusion of folds at all levels involves both ectodermal layers. Cellular protrusions and small, morphologically unspecialized intercellular junctions often interconnect cells of apposed folds in areas undergoing fusion. The anterior neuropore closes at stages 10-11, but fusion of folds in this region is not completed until stages 13-14. Fusion occurs dorsoventrally in this area and is more advanced internally than externally. Numerous pleomorphic inclusions and a few apparently necrotic cells are present in areas bordering the anterior neuropore. The posterior neuropore closes at stages 12-13 and fusion is completed in this region during stages 13-14. The caudal end of the posterior neuropore closes dorsal to the developing tail bud. Several morphological features of this closure may at least partially account for the high susceptibility to myeloschisis localized specifically at caudal spinal cord levels.

Animals↗

PubMed1986

Intercellular communication of transformed and non-transformed rat liver epithelial cells. Modulation by TPA.

Gap-junctional intercellular communication of transformed and non-transformed rat liver epithelial cell lines was compared using a dye transfer method in the presence and absence of 12-O-tetradecanoylphorbol 13-acetate (TPA). Whereas non-transformed cells (IAR 20, non-tumorigenic in newborn rats and in nude mice) showed very high communication capacity throughout a culture period of 3 weeks, transformed cells (IAR 6-1, tumorigenic in newborn rats and in nude mice) were less able to communicate. Similar correlation between intercellular communication and expression of transformed phenotypes were also found in newly cloned epithelial cell lines, IAR 27E and IAR 27F. When TPA was added to culture medium at 100 ng/ml, intercellular communication in all lines tested was reduced within 60 min. However, communications recovered completely from the effect within 10 h after addition of TPA. Further addition of TPA to the cultures every 24 h for 3 weeks had no effect on intercellular communication (measured 30 min after each TPA addition), suggesting that a single application of TPA made these cells refractory to further doses. A known stimulator of gap-junctional communication, db-cAMP, also increased dye transfer in IAR 20 and IAR 6-1 cells. TPA added to db-cAMP-treated cultures of IAR 20 and IAR 6-1 cells inhibited intercellular communication, suggesting that cAMP is not an antagonist of the effect of TPA on intercellular communication in these cell lines. These results are in sharp contrast to those obtained with the fibroblast cell line BALB/c 3T3, in which db-cAMP antagonized TPA effect and inhibition by TPA of intercellular communication was transient only when administered during their growth phase, and was stable and continuous when TPA was applied at confluence, and suggest that TPA may not be an effective tumour promoter in rat liver.

Animals↗

PubMed2002

Microscopic, immunocytochemical, and ultrastructural properties of peri-implant mucosa in humans.

BACKGROUND: Microscopic and immunocytochemical studies have demonstrated both similarities and differences between the gingival mucosa and the peri-implant mucosa restored around dental implants. METHODS: This study was performed on 10 samples of peri-implant mucosa from 10 patients who had undergone implant treatment 16 to 18 months before. Microscopic, ultrastructural, and immunocytochemical investigations were performed to characterize the epithelial and connective layers of the peri-implant mucosa. RESULTS: All specimens showed the morphologic characteristics of well restored tissues. The immunocytochemical reactions used to detect cytokeratins demonstrated that the restored peri-implant mucosa had a non-keratinized epithelium. The apical part of the inner epithelium was a few cell layers thick, like the corresponding junctional epithelium, but it stained positively with the markers for the cytokeratins expressed by the stratified epithelia. Ultrastructurally the keratinocytes adjacent to the implant displayed nuclei containing a rich cytoplasm with filaments and specialized intercellular junctions right up to the more superficial strata. Immunocytochemical reactions and ultrastructural observations demonstrated the presence of non-keratinocyte cells; i.e., Langerhans cells, melanocytes, and Merkel cells. Several cells were found to be proliferating by immunoreaction with mAb anti-PCNA, while immunoreactions with mAbs to detect von Willebrand factor, CD34, and vascular endothelial growth factor marked the well-developed networks of blood and lymphatic vessels in the connective tissue. S-100 and protein gene product 9.5 positive nerve fibers were marked. Immunocytochemical reactions with mAbs anti-vimentin, anti-laminin were also performed. CONCLUSIONS: Our results demonstrated that all the epithelial and connective components of the mucosa are involved in the substantial regrowth of the peri-implant tissue and subsequently in the success of the implant.

Actin Cytoskeleton↗

PubMed1993

[The structure of bovine choriocapillaris].

The ultrastructure of bovine choriocapillaris was investigated in bovine choroid and isolated choriocapillary samples. The choriocapillaris lies in the layer just outside the Bruch's membrane. The choriocapillary endothelial cells on the side facing Bruch's membrane were found tapering their cytoplasm, with a significant number of fenestrae. The fenestrae were predominantly located in the choriocapillaris at the posterior pole, rather than at the periphery, of the eyeball. The endothelial cells on the side facing the sclera had few fenestrae, and the nuclei of endothelial cells and pericytes were located on this side. It was found that on the peripheral part of the choroid, the basement membranes of either choriocapillary endothelial cells or those of pericytes take part in composing the outer part of the Bruch's membrane. The isolated choriocapillaris revealed a typical lobular pattern of capillaries arranged in a radiating fashion. Intercellular junctions and/or cell contacts among endothelial cells and pericytes were also investigated.

Animals↗

PubMed1995

The cadmium-induced disruption of tight junctions in LLC-PK1 cells does not result from apoptosis.

Exposure of LLC-PK1 cells to low micromolar concentrations of Cd2+ for 1-4 hours causes the disruption of the adhering and occluding junctions between the cells, whereas exposure to higher concentrations of Cd2+ for longer periods of time causes more severe toxic effects and cell death. The objective of the present studies was to determine whether or not the junctional effects of Cd2+ might be a consequence of apoptotic injury. LLC-PK1 cells on cell culture inserts were exposed to either Cd2+ or tumor necrosis factor (TNF-alpha) plus cycloheximide, a treatment that has recently been shown to cause apoptosis in LLC-PK1 cells. The results showed that at the time the Cd2(+)-induced junctional changes were occurring, there was no increase in the number of apoptotic cells or evidence of DNA fragmentation. By contrast, TNF-alpha plus cycloheximide induced changes that were characteristic of apoptosis. These results indicate that the disruption of intercellular junctions by Cd2+ in the LLC-PK1 cell line occurs independently of apoptosis.

Animals↗

PubMed1998

Regulation of endothelial cell motility by complexes of tetraspan molecules CD81/TAPA-1 and CD151/PETA-3 with alpha3 beta1 integrin localized at endothelial lateral junctions.

Cell-to-cell junction structures play a key role in cell growth rate control and cell polarization. In endothelial cells (EC), these structures are also involved in regulation of vascular permeability and leukocyte extravasation. To identify novel components in EC intercellular junctions, mAbs against these cells were produced and selected using a morphological screening by immunofluorescence microscopy. Two novel mAbs, LIA1/1 and VJ1/16, specifically recognized a 25-kD protein that was selectively localized at cell-cell junctions of EC, both in the primary formation of cell monolayers and when EC reorganized in the process of wound healing. This antigen corresponded to the recently cloned platelet-endothelial tetraspan antigen CD151/PETA-3 (platelet-endothelial tetraspan antigen-3), and was consistently detected at EC cell-cell contact sites. In addition to CD151/PETA-3, two other members of the tetraspan superfamily, CD9 and CD81/ TAPA-1 (target of antiproliferative antibody-1), localized at endothelial cell-to-cell junctions. Biochemical analysis demonstrated molecular associations among tetraspan molecules themselves and those of CD151/ PETA-3 and CD9 with alpha3 beta1 integrin. Interestingly, mAbs directed to both CD151/PETA-3 and CD81/ TAPA-1 as well as mAb specific for alpha3 integrin, were able to inhibit the migration of ECs in the process of wound healing. The engagement of CD151/PETA-3 and CD81/TAPA-1 inhibited the movement of individual ECs, as determined by quantitative time-lapse video microscopy studies. Furthermore, mAbs against the CD151/PETA-3 molecule diminished the rate of EC invasion into collagen gels. In addition, these mAbs were able to increase the adhesion of EC to extracellular matrix proteins. Together these results indicate that CD81/TAPA-1 and CD151/PETA-3 tetraspan molecules are components of the endothelial lateral junctions implicated in the regulation of cell motility, either directly or by modulation of the function of the associated integrin heterodimers.

Animals↗

PubMed1980

Cytotoxicity of pivalylphenylephrine and pivalic acid to corneal endothelium.

We examined the effects of topically applied pivalylphenylephrine (PPE) and pivalic acid (PA) on the corneal endothelium of rabbits and the direct effects of PPE and PA on monolayer cultures of bovine corneal endothelium. The PPE-treated corneas without epithelium significantly increased in thickness, whereas no change in thickness was observed in corneas with epithelium intact. The PA did not alter the thickness of corneas with or without epithelium. Although 0.001% PE had no noticeable effect in two hours, 0.01% PPE caused breakdown of intercellular junctions in cultured cells in five minutes. Higher concentrations of PPE caused the cells to detach from the culture dishes within 30 minutes of treatment. Only 1% PA caused cell elongation and loss of intercellular contact after 60 to 90 minutes of exposure; lower concentrations did not effect cultured cells.

Administration, Topical↗

PubMed2005

Transepithelial migration of Toxoplasma gondii involves an interaction of intercellular adhesion molecule 1 (ICAM-1) with the parasite adhesin MIC2.

Toxoplasma gondii crosses non-permissive biological barriers such as the intestine, the blood-brain barrier and the placenta thereby gaining access to tissues where it most commonly causes severe pathology. Herein we show that in the process of migration Toxoplasma initially concentrates around intercellular junctions and probably uses a paracellular pathway to transmigrate across biological barriers. Parasite transmigration required viable and actively motile parasites. Interestingly, the integrity of host cell barriers was not altered during parasite transmigration. As intercellular adhesion molecule 1 (ICAM-1) is upregulated on cellular barriers during Toxoplasma infection, we investigated the role of this receptor in parasite transmigration. Soluble human ICAM-1 and ICAM-1 antibodies inhibited transmigration of parasites across cellular barriers implicating this receptor in the process of transmigration. Furthermore, human ICAM-1 immunoprecipitated the mature form of the parasite adhesin MIC2 present on the parasite surface, indicating that this interaction may contribute to cellular migration. These findings reveal that Toxoplasma exploits the natural cell trafficking pathways in the host to cross cellular barriers and disseminate to deep tissues.

Animals↗