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At least 127 records · Page 7Linked to original sources
PubMed1986

Acetylcholine modulation of the conductance of intercellular junctions between rat lacrimal cells.

The conductance of intercellular junctions between rat lacrimal cells was studied with the double whole-cell tight-seal recording technique. This conductance decreases spontaneously with time as a result of the double-cell dialysis. The rate of this 'spontaneous' uncoupling is unaffected by changing the internal Ca concentration, [Ca]i, between 10(-8) M and 10(-6) M. This rate of uncoupling is greatly increased when [Ca]i is approximately 10(-5) M, and this effect does not involve changes in the internal proton concentration. When [Ca]i is weakly buffered in one of the two cells, 1-2 microM-acetylcholine (ACh) both activates Ca-dependent channels in that cell (Marty, Tan & Trautmann, 1984) and uncouples the two cells. The uncoupling is not synchronous with the increase in [Ca]i as reflected by the Ca-dependent currents. When [Ca]i is strongly buffered in both cells, ACh fails to activate Ca-dependent currents, but it can still uncouple the cells. This ACh-induced uncoupling is often preceded by a transient enhancing of the coupling. In conclusion, ACh has several distinct effects on lacrimal cells: activation of Ca-dependent channels in the plasma membrane, closure of junctional channels involving a Ca-independent mechanism, and sometimes, an increase in the junctional coupling by a Ca-independent mechanism.

Acetylcholine↗
PubMed2006

Intercellular junctions in rabbit eye ora serrata.

Summary The aim of this study was to describe and localize the intercellular junctions in the ora serrata region of albino and pigmented rabbit eyes. Eyes of albino and pigmented rabbits were fixed and processed for transmission electron microscopy. Light and electron microscope examination was carried out on semithin and ultrathin sections. The ora serrata region showed adherens, gap and tight junctions in the retinal and ciliary margins of albino and pigmented rabbit eyes. In the retinal margin, zonulae adherens between Müller cells and photoreceptors are associated with tight junctions. In the ciliary margin, epithelial cells are joined by adherens, gap and tight junctions localized between apical and apicolateral cell membranes. Tight junctions appear as zonulae occludens in the non-pigmented apicolateral cell membranes and as tight focal junctions between pigmented and non-pigmented apical cell membranes. Between the ciliary and retinal margins there are adherens and tight focal junctions which attach pigmented apical cell membranes to adjacent cells. There were no differences in the distribution of intercellular junctions between albino and pigmented rabbits.

Animals↗
PubMed2004

Connexin 26-mediated gap junctional intercellular communication suppresses paracellular permeability of human intestinal epithelial cell monolayers.

In some cell types, gap junctional intercellular communication (GJIC) is associated with tight junctions. The present study was performed to determine the roles of GJIC in regulation of the barrier function of tight junctions. Caco-2 human colonic cells were used as a monolayer model, and barrier function was monitored by measuring mannitol permeability and transepithelial electrical resistance (TER). The monolayers were chemically disrupted by treatment with oleic acid and taurocholic acid. Western blotting analyses were performed to evaluate the protein levels of connexins, which are components of gap junctional intercellular channels. Cx26 expression was detected in preconfluent Caco-2 cells, and its level increased gradually after the monolayer reached confluency. These results prompted us to examine whether overexpression of Cx26 affects barrier function. Monolayers of Caco-2 cells stably expressing Cx26 showed significantly lower mannitol permeability and higher TER than mock transfectants when the monolayers were chemically disrupted. The levels of claudin-4, an important component of tight junctions, were significantly increased in the stable Cx26 transfectant. These results suggest that Cx26-mediated GJIC may play a crucial role in enhancing the barrier function of Caco-2 cell monolayers.

Caco-2 Cells↗
PubMed2005

Staphylococcus aureus-derived peptidoglycan induces Cx43 expression and functional gap junction intercellular communication in microglia.

Gap junctions serve as intercellular conduits that allow the exchange of small molecular weight molecules (up to 1 kDa) including ions, metabolic precursors and second messengers. Microglia are capable of recognizing peptidoglycan (PGN) derived from the outer cell wall of Staphylococcus aureus, a prevalent CNS pathogen, and respond with the robust elaboration of numerous pro-inflammatory mediators. Based on recent reports demonstrating the ability of tumor necrosis factor-alpha and interferon-gamma to induce gap junction coupling in macrophages and microglia, it is possible that pro-inflammatory mediators released from PGN-activated microglia are capable of inducing microglial gap junction communication. In this study, we examined the effects of S. aureus-derived PGN on Cx43, the major connexin in microglial gap junction channels, and functional gap junction communication using single-cell microinjections of Lucifer yellow (LY). Exposure of primary mouse microglia to PGN led to a significant increase in Cx43 mRNA and protein expression. LY microinjection studies revealed that PGN-treated microglia were functionally coupled via gap junctions, the specificity of which was confirmed by the reversal of activation-induced dye coupling by the gap junction blocker 18-alpha-glycyrrhetinic acid. In contrast to PGN-activated microglia, unstimulated cells consistently failed to exhibit LY dye coupling. These results indicate that PGN stimulation can induce the formation of a functional microglial syncytium, suggesting that these cells may be capable of influencing neuro-inflammatory responses in the context of CNS bacterial infections through gap junction intercellular communication.

Animals↗
PubMed1995

Delayed inhibition of gap-junctional intercellular communication in the acinar cells of rat submandibular glands induced by parasympathectomy and cholinergic agonists.

In this study, the effects of parasympathectomy and cholinergic agonists on gap-junctional intercellular communication and salivary secretion were investigated to clarify the involvement of salivary secretion in delayed uncoupling between acinar cells of rat submandibular glands. Gap-junctional intercellular communication was monitored as dye-coupling in the acinar cells of isolated acini by the transfer of Lucifer Yellow CH. Parasympathectomy induced dye-uncoupling in the acinar cells isolated from denervated salivary glands 12 hr after parasympathectomy-induced salivary secretion. Intraperitoneal application of carbachol (CCh), acetylcholine, pilocarpine, but not isoproterenol, stimulated salivary secretion, and then induced dye-uncoupling in the acinar cells 12 hr later. Atropine suppressed both the salivary secretion and delayed dye-uncoupling induced by parasympathectomy and CCh, when atropine was applied intraperitoneally before the induction of salivary secretion. However, atropine did not suppress the delayed dye-uncoupling by intraperitoneal application of CCh, when atropine was injected after the cessation of CCh-induced secretion. These results suggest that delayed inhibition of gap-junctional intercellular communication by parasympathectomy and cholinergic agonists in rat submandibular glands might be related to the change of secretory function after salivary secretion.

Animals↗
PubMed2003

Nectin and afadin: novel organizers of intercellular junctions.

The cadherin superfamily plays key roles in intercellular adhesion. An emerging intercellular adhesion system, consisting of nectin and afadin, also has roles in organization of a variety of intercellular junctions either in cooperation with, or independently of, cadherin. Nectin is a Ca(2+)-independent immunoglobulin-like intercellular adhesion molecule, and afadin is a nectin- and actin-filament-binding protein that connects nectin to the actin cytoskeleton. This novel intercellular adhesion system has roles in the organization of E-cadherin-based adherens junctions and claudin-based tight junctions in epithelial cells. The adhesion system is furthermore involved in the formation of synapses in neurons and the organization of heterotypic junctions between Sertoli cells and spermatids in the testis.

Animals↗
PubMed1980

A freeze-fracture study of intercellular junctions between various kinds of epithelial cells surrounding common endolymphatic space in the hearing organ of the chick.

Intercellular junctions between various epithelial cells in the hearing organ (basilar papilla) of the chick were studied with the freeze-fracture technique. The effects of hypertonic solutions on the intercellular junctions were also examined. The basilar papilla of the chick is primarily composed of hair cells and supporting cells in the neuroepithelium, specialized columnar cells (TMC) which attach to the tectorial membrane, and light cells (LC) and dark cells (DC) in the tegmentum vasculosum. All of these epithelial cells surround a common endolymphatic space. The tight junctions between hair and supporting cells, and those between adjacent supporting cells in the neuroepithelium are 0.1--0.3 micrometer in depth and display the usual network of branching and anastomosing strands of shared intramembrane proteins. The tight junctions in the tegmentum vasculosum have the same structure as in the neuroepithelium. In contrast, the tight junctions between the TMCs are extremely well developed. They are 1--2 micrometer in depth. In freeze-fracture replicas, they appear as a fingerprint pattern of unbranched parallel particulate strands, running both parallel and perpendicular to the cell surface. After exposure to hypertonic solutions, all the epithelial cells are shrunken and intercellular spaces are expanded; all tight junctions, however, are intact. Thus, tight junctions in the basilar papillae are resistant to dissociation by hypertonic solutions. The usual zonulae occuludentes in the neuroepithelium and tegmentum vasculosum are thought to prevent diffusion of endolymph through the intercellular spaces of epithelial cells. However, the tight junctions on the TMCs may function not only as a diffusion barrier, but also provide structural support to the cells anchoring the tectorial membrane which receives mechanical forces induced by the vibration of the basilar membrane. Extensive gap junctions are found between all the supporting cells (supporting cells in the neuroepithelium, TMCs, and LCs in the tegmentum vasculosum) surrounding the endolymphatic space.

Animals↗
PubMed1996

Structure of gap junction intercellular channels.

Gap junctions are formed by a multigene family of polytopic membrane channel proteins, connexins, that have four hydrophobic transmembrane domains and their N and C termini located on the cytoplasmic membrane face. The C-terminal tail plays important roles in channel regulation by pH and phosphorylation. Conserved cysteine residues stabilize the conformation of the extracellular loops that mediate the 'docking' between connexons in the intercellular channel. Over the past year, electron cryocrystallography of two-dimensional crystals of a truncated recombinant alpha 1 (Cx43) has revealed that the transmembrane boundary of the intercellular channel is lined with alpha helices. Furthermore, a ring of alpha helices resides at the interface with the membrane lipids. A three-dimensional analysis based on images recorded from tilted crystals should reveal the location and secondary structure of additional transmembrane domains, as well as provide important structural details about the interactions between connexins within a hemi-channel and connexon-connexon interactions in the extracellular gap.

Amino Acid Sequence↗
PubMed1982

Intercellular junctions in the rat vomeronasal neuroepithelium: a freeze-fracture study.

The intercellular junctions (tight junctions, desmosomes and gasp junctions) of the vomeronasal neuroepithelium of male Wistar rats were investigated by freeze-fracture. Tight junctions were localized apically sealing the intercellular clefts. Tight junctions were composed of 6 to 12 junctional strands arranged in a meshwork. the distance between the most apical and the most basal junctional strand was 430 +/- 90 nm. No proper distinction could be made between receptor-supporting and supporting-supporting cell tight junctions. Besides tight junctions, numerous desmosomes and ga junctions were found. Desmosomes were present on the supporting and receptor cell membranes below the level of the tight junctions. Gap junctions could be seen at the level of the perikarya of the supporting and receptor cells. They were only found on supporting cell membranes.

Animals↗
PubMed1982

Cell surface specializations and intercellular junctions in human amniotic epithelium: an electron microscopic and freeze-fracture study.

Cell surface specializations and intercellular junctions of human term amniotic epithelium were examined by conventional thin-section electron microscopy, after staining with the cationic probes ruthenium red and cationic ferritin, and by freeze-fracture methods. Desmosomes were the predominant type of intercellular junction and often the most apical of the junctional types. In freeze-fracture replicas, desmosomes were characterized by roughly circular areas of large, often irregular, P-face intramembranous particles. Gap junctions were identified in the laterobasal regions between cells. In thin sections they were characterized by a narrow intercellular space, and in freeze-fracture replicas had a typical plaquelike arrangement of P-face intramembranous particles and E-face depressions. Hemidesmosomes at the basal cell surface were characterized by occasional large particles and clusters of particles on both the E and P fracture faces. No evidence of tight junctions was found. The apical cell surface was heavily stained by both ruthenium red and cationic ferritin, indicating the negatively charged nature of this surface. Ruthenium red penetrated between the epithelial cells and bound to anionic materials on the lateral cell surfaces, especially at the location of desmosomes. Below the base of the intercellular cleft, large ruthenium red-positive granules were present in the extracellular matrix. The possibility that the anionic substances in the intercellular region may contribute to the control of permeability in the amniotic epithelium is discussed.

Amnion↗
PubMed2000

Effect of glucose on intercellular junctions of cultured human peritoneal mesothelial cells.

During continuous ambulatory peritoneal dialysis, the peritoneum is directly and continuously exposed to unphysiologic peritoneal dialysis fluid; the resulting mesothelial damage has been suggested to cause loss of ultrafiltration and dialysis efficacy. The present study investigated the effect of a high glucose concentration on cultured human peritoneal mesothelial cells to clarify the cause of decreased dialysis efficacy during prolonged peritoneal dialysis. High glucose caused a concentration-dependent decrease in cell proliferation, damage to the intercellular junctions, and excess production of transforming growth factor-beta (TGF-beta). The levels of intercellular junctional proteins (ZO-1, E-cadherin, and beta-catenin) were decreased, and immuno-staining by anti-ZO-1 and anti- beta-catenin antibodies became weaker and often discontinuous along the cell contour. Mannitol had similar but weaker effects at the same osmolality, and an anti-TGF-beta neutralizing antibody reduced the effects of high glucose. Therefore, these effects were induced not only by glucose itself but also by hyperosmolality and by a glucose-induced increase of TGF-beta. These findings suggest that the peritoneal mesothelium is damaged by prolonged peritoneal dialysis using high glucose dialysate and that impairment of the intercellular junctions of peritoneal mesothelial cells by high glucose dialysate induces peritoneal hyperpermeability and a progressive reduction in dialysis efficacy.

Antibodies↗
PubMed2002

The focal adhesion kinase amino-terminal domain localises to nuclei and intercellular junctions in HEK 293 and MDCK cells independently of tyrosine 397 and the carboxy-terminal domain.

The function and intracellular localisation of the non-catalytic NH(2)-terminal region of focal adhesion kinase (FAK) are unclear. We investigated the targetting of the FAK NH(2)-terminal domain in HEK 293 and epithelial MDCK cells. Exogenous expression of a variety of GFP-fused and epitope-tagged NH(2) terminal domain constructs either including or lacking the major Tyr 397 autophosphorylation and Src-binding site targeted to nuclei and cell-cell junctions in HEK 293 cells and co-localised at junctions with occludin, and beta1 integrin subunits at junctions. Mutation of Tyr 397 also had no effect on localisation of the NH(2)-terminal domain. In contrast, constructs encoding either the kinase or focal adhesion targeting (FAT) domains but lacking the NH(2)-terminal region failed to localise to intercellular junctions or nuclei. The NH(2)-terminal domain was not associated with beta1 integrin subunits as indicated by co-immunoprecipitation experiments, but did co-localise with cortical actin filaments. The NH(2)-terminal domain also targetted to nuclei and intercellular junctions in MDCK cells, whereas full-length FAK localised only to focal adhesions in these cells. These results indicate that the FAK NH(2)-terminal domain targets to epithelial intercellular junctions and nuclei and suggest novel functions for FAK NH(2)-terminal domain fragments independent of Y397, kinase, and FAT domains.

Actins↗
PubMed1989

Close relationship between modulation of serum-induced stimulation of DNA synthesis and changes in gap-junctional intercellular communication in quiescent 3T3-L1 cells caused by cyclic AMP and the tumor-promoting phorbol ester TPA.

Involvement of gap-junctional intercellular communication in the stimulation of growth was investigated in quiescent 3T3-L1 cells. When the cells in monolayer were growth-arrested by culture in a low concentration of calf serum, addition of dibutyryl cyclic AMP enhanced dye-coupling and suppressed the enhancement of DNA synthesis, induced by calf serum, in quiescent cells. 12-O-Tetradecanoylphorbol-13-acetate (TPA) suppressed dye-coupling in quiescent cells and enhanced DNA synthesis in both quiescent and serum-treated cells. When about 5000 cells were cultured in contact to form a colony, growth arrest of the cells was observed in the central region of such colonies rather than in the peripheral region, but addition of calf serum induced DNA synthesis in the cells in both the peripheral and central regions of the colonies. Addition of TPA enhanced serum-induced DNA synthesis in the cells in the central region of colonies rather than in the peripheral region. These results suggest that the ability of quiescent cells to escape from growth arrest is inversely correlated to the extent of gap-junctional intercellular communication.

Animals↗
PubMed1998

Synthesis, assembly and structure of gap junction intercellular channels.

Gap junction membrane channels assemble as dodecameric complexes, in which a hexameric hemichannel (connexon) in one plasma membrane docks end to end with a connexon in the membrane of a closely apposed cell. Steps in the synthesis, assembly and turnover of gap junction channels appear to follow the general secretory pathway for membrane proteins. In addition to homo-oligomeric connexons, different connexin polypeptide subunits can also assemble as hetero-oligomers. The ability to form homotypic and heterotypic channels that consist of two identical or two different connexons, respectively, adds even greater versatility to the functional modulation of gap junction channels. Electron cryocrystallography of recombinant gap junction channels has recently provided direct evidence for alpha-helical folding of at least two of the transmembrane domains within each connexin subunit. The potential to correlate the structure and biochemistry of gap junction channels with recently identified human diseases involving connexin mutations makes this a particularly exciting area of research.

Animals↗
PubMed1985

Organization of the intercellular junctions in the endothelium of cardiac valves.

The intramembranous organization of valvular endothelial cells and the structure of their intercellular junctions were studied using both thin section and freeze fracture electron microscopy. Using the double replica method, large areas of fractured endothelial cell plasma membrane are exposed. On both faces, the intramembranous particles are randomly distributed, but they are 2-3 times more frequent on the P face than on the E face: on the former, their number varies from 340 to 1700 particles/micron 2. The density of vesicular openings seems to be slightly higher on the tissue front (29-43 openings/micron 2) than on the blood front (24-34 openings/micron 2). The vesicular stomata are absent in parajunctional areas. The intercellular junction structure appears as a variation to that described for arteries. The occluding junctions appear as a network of 1-6 (most frequently 3-4) interconnected ridges on P faces or grooves on E faces. Occasionally, the presence of strands formed by association of short bars can be observed on the P face ridge. In addition, there are a small number of occluding junctions with low profile ridges, free or marked by few particles, similar to those described for the venules. These junctions are probably involved in the inflammatory reaction occurring during clinically manifested valvular disease. The communicating (gap) junctions, small or large, are free, partially or completely associated. In all valves examined we observed a special kind of communicating junction the particles of which are disposed in 1-4 rows, forming branched or circular patterns. Intracellular injection of 6-carboxyfluorescein shows transfer of the dye to the neighboring cell, suggesting that the cells are coupled. In both atrioventricular and sigmoid valves, the endothelial junctions have a similar pattern with some differences in the degree of complexity. The ventricular aspect of the valves contains junctions with a larger number of junctional strands than the atrial or arterial aspect. This suggests a possible relationship between the number of strands and the stress factors (i.e. blood hydrostatic pressure). The presence of functionally communicating junctions of various dimensions and shapes suggests that the endothelial cells of valvular endocardium are metabolically coupled. At short exposure times (5-10 min), filipin-incubated valves exhibit characteristic filipin-sterol complexes (FSC) around the vesicular stomata of the endothelium. After a longer exposure (30-90 min) FSC labeled randomly the rest of plasma membrane except for coated pits, gap junction regions and area boundering tight junctional strands.

Animals↗
PubMed1979

Intercellular junctions in FANFT-induced carcinomas of rat urinary bladder in tissue culture: in situ thin-section, freeze-fracture, and scanning electron microscopy studies.

This paper describes a set of simple methods for comparative light and electron microscopy studies on tissue cultured tumour cells derived from both noninvasive and invasive carcinogen-induced rat urinary bladder carcinomas. Cells are grown on Thermanox plastic coverslips and fixed in situ. Each plastic coverslip is then divided with scissors into four parts: the first is processed for light microscopy, the second for thin-section electron microscopy, the third for freeze-fracture electron microscopy, and the fourth for scanning electron microscopy. In some experiments, portions of the culture which have first been examined by light microscopy are subsequently prepared for electron microscopy. In this way, the culture conditions are kept constant and comparison of structural features (i.e. intercellular junctions) by several preparative techniques is possible. Noninvasive and invasive rat bladder tumour cells, characterized by numerous pleomorphic microvilli, have normal zonulae occludentes at the apices of lateral surfaces of tumour cells in all cultures. In some areas of invasive tumour cells, occludens junctions are focally attenuated, consisting of only one or two strands, and occasionally the strands are discontinuous. Gap junctions, type PF-1, as well as numerous demosomes are present in all cell lines. Thus, intercellular junctions in noninvasive and invasive rate bladder epithelial cell lines bear a striking resemblance to those previously described in the comparable solid primary tumours. These culture systems may be useful for studying factors which influence the formation of intercellular junctions during malignant transformation.

Animals↗
PubMed2005

Localization of alkaline phosphatase and proteins related to intercellular junctions in primary cultures of fetal rat hepatocytes.

The localization of alkaline phosphatase (ALP) and four proteins related to intercellular junctions in primary cultures of fetal rat hepatocytes was immunocytochemically investigated using fluorescence-labeled antibodies and confocal laser microscopy in order to determine whether the formation of intercellular junctions at the borders between adjacent rat hepatocytes becomes the trigger of translocation of ALP from the cytoplasm to the plasma membrane. Dexamethasone (DEX) which was supplemented in the base medium promoted the translocation of ALP from the cytoplasm to the plasma membrane surrounding bile canaliculus-like intercellular spaces and the appearance of connexin-32 at cell borders between adjacent fetal hepatocytes. E-cadherin, occludin and ZO-1 were localized at the cell borders between adjacent fetal hepatocytes irrespective of the presence of DEX. Occludin and ZO-1 were further localized along the plasma membrane surrounding bile canaliculus-like intercellular spaces formed by DEX. The present study indicates that the formation of adherens and tight junctions between adjacent rat hepatocytes does not become the trigger of ALP translocation from the cytoplasm to the plasma membrane, although we cannot be certain of whether the formation of gap junctions between adjacent rat hepatocytes triggers ALP translocation.

Alkaline Phosphatase↗
PubMed1979

Junctional intercellular communication pattern of cultured human breast cancer cells.

Junctional intercellular communication between several established human breast cancer cell lines and a variety of mammalian cells has been examined. All the cancer cell lines were found to be either noncommunicators or nonselective communicators. This contrasts with normal human mammary epithelium which shows selectivity in junctional communication. Loss of selectivity in junctional communication appears to be a general feature of cultured human breast cancer cells.

Animals↗