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PubMed1980

[Effect of Novocaine on the stimulation by lanthanum of intercellular exchange].

Some influences on intercellular junctions permeable to Fluorescein Na were studied with the aid of intracellular glass microelectrodes in the cultures of transformed mouse--embryo kidney cells (MTR) and fibroblast--like cells (L). 1 mM of lanthanum increased the degree of coupling by 2 or 3 times. The preceeding incubation of cells with a 0.02% procaine solution protected them from the influence of lanthanum. A possible mechanism of concurrence between lanthanum and procaine on intercellular junctions is discussed.

Animals↗
PubMed1995

Epidermal growth factor induces tyrosine phosphorylation and reorganization of the tight junction protein ZO-1 in A431 cells.

Addition of epidermal growth factor (EGF) to A431 human epidermal carcinoma cells results in actin reorganization and phosphorylation of several cytoskeletal proteins. In the present study, we found that EGF treatment of this cell line also results in the redistribution and tyrosine phosphorylation of ZO-1. In normal polarized epithelial cells, ZO-1 is restricted to the cytoplasmic surface of the most apical of the intercellular junctions, the tight junction. In contrast, ZO-1 in the majority of unstimulated A431 cells in small subconfluent islands colocalizes with actin along the lateral cell membranes and in rare microspikes and membrane ruffles. Exposure to EGF results in a transient redistribution of actin into an apically positioned ring. ZO-1 becomes highly focused at apical sites of cell contact and co-localizes with the newly formed band of perijunctional actin. Coincidently, ZO-1 and another tight junction protein, ZO-2, become transiently phosphorylated on tyrosine residues, as determined by anti-phosphotyrosine immunoblotting. Pre-treatment of A431 cells with cytochalasin D, which disrupts normal microfilament organization, does not affect EGF-dependent phosphorylation of the EGF receptor. However, cytochalasin D pretreatment blocks both the EGF-induced ZO-1 rearrangement and tyrosine phosphorylation, suggesting that these responses are dependent on an intact actin microfilament system. We speculate that the transient tyrosine phosphorylation of ZO-1 in response to EGF treatment may be involved in remodeling of intercellular junctions in A431 cells.

Actins↗
PubMed1980

Lymphatic removal of fluids and particles in the mammalian lung.

The structure and distribution of pulmonary lymphatics and their permeability to fluids and particulate materials have been investigated in the lungs of rats following fixation by combined intratracheal and vascular perfusion. In such preparations, the lymphatics remain in a distended state, and a close relationship to other structural components of the pulmonary interstitium is maintained. They were identified in regions with an abundant amount of connective tissue, forming an eleborate plexus within the pleura, the interlobular septum, peribronchial and perivascular areas. Recent data have shown that water-soluble molecules and particulate matter are removed from the interstitium along the lymphatic capillary (initial lymphatics) segment. It is distinguished by attenuated endothelial cells with extensively overlapping cell margins which are easily separated. We have studied this segment of the lymphatic vascular system following intratracheal injections of colloidal particles (ferritin and carbon) to determine the structural features responsible for the transport of large molecules and particulate materials across the lymphatic endothelial wall in the lung. The results showed that the tracer particles cross the lymphatic endothelial wall via the clefts of intercellular junctions. While the tracer particles were observed within vesicles, the question of transport across the lymphatic endothelium via plasmalemmal vesicles is still not settled since the number and size of vesicles containing tracer particles also increased with time. Intravascular injected dextran was also localized within the clefts of intercellular junctions and plasmalemmal vesicles. The results obtained with intratracheal and intravascular injected tracer substances are consistent with those observed in lymphatic capillaries for other tissues.

Animals↗
PubMed2000

Junctional complexes in the early mammalian embryo.

Preimplantation embryos generate intercellular junctions during differentiation of the trophectoderm epithelium and the formation of the blastocyst. These membrane complexes comprise gap junctions, adherens junctions, tight junctions, and desmosomes, each performing fundamental roles in cellular communication, adhesion, and differentiation. The mouse embryo has been used as a model for the biogenesis of cell junctions. Their construction is achieved by temporally regulated gene expression programs. Mechanisms of junction membrane assembly include the timing of transcription, translation, and post-translational modifications of specific junctional proteins. Human embryos exhibit similar expression programs, and defects in these programs may contribute to reduced embryo viability.

Adherens Junctions↗
PubMed1997

Binding of neuroligins to PSD-95.

PSD-95 is a component of postsynaptic densities in central synapses. It contains three PDZ domains that localize N-methyl-D-aspartate receptor subunit 2 (NMDA2 receptor) and K+ channels to synapses. In mouse forebrain, PSD-95 bound to the cytoplasmic COOH-termini of neuroligins, which are neuronal cell adhesion molecules that interact with beta-neurexins and form intercellular junctions. Neuroligins bind to the third PDZ domain of PSD-95, whereas NMDA2 receptors and K+ channels interact with the first and second PDZ domains. Thus different PDZ domains of PSD-95 are specialized for distinct functions. PSD-95 may recruit ion channels and neurotransmitter receptors to intercellular junctions formed between neurons by neuroligins and beta-neurexins.

Amino Acid Sequence↗
PubMed2002

Evidence for a central role for electro-osmosis in fluid transport by corneal endothelium.

The mechanism of transepithelial fluid transport remains unclear. The prevailing explanation is that transport of electrolytes across cell membranes results in local concentration gradients and transcellular osmosis. However, when transporting fluid, the corneal endothelium spontaneously generates a locally circulating current of approximately 25 microA cm(-2), and we report here that electrical currents (0 to +/-15 microA cm(-2)) imposed across this layer induce fluid movements linear with the currents. As the imposed currents must be approximately 98% paracellular, the direction of induced fluid movements and the rapidity with which they follow current imposition (rise time < or =3 sec) is consistent with electro-osmosis driven by sodium movement across the paracellular pathway. The value of the coupling coefficient between current and fluid movements found here (2.37 +/- 0.11 microm cm(2) hr(-1) microA (-1), suggests that: 1) the local endothelial current accounts for spontaneous transendothelial fluid transport; 2) the fluid transported becomes isotonically equilibrated. Ca(++)-free solutions or endothelial damage eliminate the coupling, pointing to the cells and particularly their intercellular junctions as a main site of electro-osmosis. The polycation polylysine, which is expected to affect surface charges, reverses the direction of current-induced fluid movements. Fluid transport is proportional to the electrical resistance of the ambient medium. Taken together, the results suggest that electro-osmosis through the intercellular junctions is the primary process in a sequence of events that results in fluid transport across this preparation.

Animals↗
PubMed2000

Truncation mutants of the tight junction protein ZO-1 disrupt corneal epithelial cell morphology.

The tight junction is the most apical intercellular junction of epithelial cells and regulates transepithelial permeability through the paracellular pathway. To examine possible functions for the tight junction-associated protein ZO-1, C-terminally truncated mutants and a deletion mutant of ZO-1 were epitope tagged and stably expressed in corneal epithelial cell lines. Only full-length ZO-1 and one N-terminal truncation mutant targeted to cell borders; other mutants showed variable cytoplasmic distributions. None of the mutants initially disrupted the localization of endogenous ZO-1. However, long-term stable expression of two of the N-terminal mutants resulted in a dramatic change in cell shape and patterns of gene expression. An elongated fibroblast-like shape replaced characteristic epithelial cobblestone morphology. In addition, vimentin and smooth muscle actin expression were up-regulated, although variable cytokeratin expression remained, suggesting a partial transformation to a mesenchymal cell type. Concomitant with the morphological change, the expression of the integral membrane tight junction protein occludin was significantly down-regulated. The localizations of endogenous ZO-1 and another family member, ZO-2, were disrupted. These findings suggest that ZO-1 may participate in regulation of cellular differentiation.

Animals↗
PubMed1995

Inhibition by anandamide of gap junctions and intercellular calcium signalling in striatal astrocytes.

Anandamide, an endogenous arachidonic acid derivative that is released from neurons and activates cannabinoid receptors, may act as a transcellular cannabimimetic messenger in the central nervous system. The biological actions of anandamide and the identity of its target cells are, however, still poorly documented. Here we show that anandamide is a potent inhibitor of gap-junction conductance and dye permeability in striatal astrocytes. This inhibitory effect is specific for anandamide as compared to co-released congeners or structural analogues, is sensitive to pertussis toxin and to protein-alkylating agents, and is neither mimicked by cannabinoid-receptor agonists nor prevented by a cannabinoid-receptor antagonist. Glutamate released from neurons evokes calcium waves in astrocytes that propagate via gap junctions, and may, in turn, activate neurons distant from their initiation sites in astrocytes. We find that anandamide blocks the propagation of astrocyte calcium waves generated by either mechanical stimulation or local glutamate application. Thus, by regulating gap-junction permeability, anandamide may control intercellular communication in astrocytes and therefore neuron-glial interactions.

Animals↗
PubMed2001

Group A Streptococcus tissue invasion by CD44-mediated cell signalling.

Streptococcus pyogenes (also known as group A Streptococcus, GAS), the agent of streptococcal sore throat and invasive soft-tissue infections, attaches to human pharyngeal or skin epithelial cells through specific recognition of its hyaluronic acid capsular polysaccharide by the hyaluronic-acid-binding protein CD44 (refs 1, 2). Because ligation of CD44 by hyaluronic acid can induce epithelial cell movement on extracellular matrix, we investigated whether molecular mimicry by the GAS hyaluronic acid capsule might induce similar cellular responses. Here we show that CD44-dependent GAS binding to polarized monolayers of human keratinocytes induced marked cytoskeletal rearrangements manifested by membrane ruffling and disruption of intercellular junctions. Transduction of the signal induced by GAS binding to CD44 on the keratinocyte surface involved Rac1 and the cytoskeleton linker protein ezrin, as well as tyrosine phosphorylation of cellular proteins. Studies of bacterial translocation in two models of human skin indicated that cell signalling triggered by interaction of the GAS capsule with CD44 opened intercellular junctions and promoted tissue penetration by GAS through a paracellular route. These results support a model of host cytoskeleton manipulation and tissue invasion by an extracellular bacterial pathogen.

Bacterial Adhesion↗
PubMed2001

Junctional proteins and Ca2+ transport in the rat odontoblast-like cell line MRPC-1.

A transcellular bulk flow of Ca2+ ions through the odontoblast layer is of central importance during dentinogenesis. For this, specialized mechanisms may exist, which by a concerted action, gate Ca2+ into the proximal end of the cells and extrude the ions towards the mineralization front. To elucidate these mechanisms, an in vitro model would be useful. Mature odontoblasts are, however, post-mitotic cells and cannot be propagated in cell culture. The aim of the present study was, therefore, to characterize the odontoblast-like rat cell line MRPC-1(1) with regard to transcellular Ca2+ transport, barrier function, and intercellular junctions when cultured on membranes in Transwell chambers. The MRPC-1 cells grew as epithelial-like cells in a continuous bilayer separated by a thin collagenous matrix and with intercellular junctional complexes. They exhibited properties of a low-resistance epithelium, maintained a Ca(2+)-dependent diffusion barrier, and exhibited a functional diversity between the two cell layers. MRPC-1 cells expressed ZO-1, occludin, E-, and N-cadherins in addition to alpha-, beta-, gamma- and p120cat catenins, thereby demonstrating some traits in common with, but also differences from, epithelial cells and major differences from fibroblasts. The transcellular Ca2+ flux was inhibitable by nifedipine unidirectionally, giving evidence for an active intracellular Ca2+ transport through voltage-gated channels of the L-type. Similarities with native odontoblasts indicate that MRPC-1 cells may be useful for in vitro studies of transcellular Ca2+ transport mechanisms of importance for the calcification process.

Animals↗
PubMed1982

Function-related structural characters and their modifications in the hindgut epithelium of two terrestrial isopods, Armadillidium vulgare and Oniscus asellus.

Intercellular junctions of the hindgut epithelial cells of two terrestrial isopods, Armadillidium vulgare and Oniscus asellus, are described. Long septate desmosomes occupy the subluminal region while gap junctions, zonulae adherens and intercellular spaces characterize the remainder of the convoluted lateral cell borders. The specialized junctional complexes and the ultrastructural morphology of the cells indicate that the terrestrial isopod hindgut epithelium functions in transport. Using mitochondrial morphometry as an indicator of cell transport activity, it appears that the posterior hindgut of A. vulgare also participates in osmoregulation, which is not the case with O. asellus. With increased desiccation there develops a significant difference between the mitochondrial structure of the two species. The mitochondria of the former retain the active structural condition (intermediate condensed conformation) while those of the latter become swollen and damaged.

Animals↗
PubMedDate not supplied

Anemone cell tumor with neuroendocrine differentiation (presumed Merkel cell carcinoma).

A neuroendocrine tumor with ultrastructural "anemone cell" features in lymph nodes is reported. A primary tumor was not identified, but clinical and morphologic features suggested a metastatic Merkel cell carcinoma. The anemone cells were dissociated, lacked intercellular junctions, and contained cytoplasmic intermediate filament aggregates that immunohistochemically reacted with keratins, but they had only sparse neurosecretory granules. Where the tumor cells had infiltrated beyond the lymph nodes, however, they formed a trabecular pattern. A fine-needle aspirate from a later recurrence of the tumor lacked anemone cell features and was ultrastructurally typical of a Merkel cell carcinoma, with neurosecretory granules and intercellular junctions both being evident. The concept of anemone cell tumors and the morphologic variations determined by site are discussed.

Carcinoma, Merkel Cell↗
PubMed1980

Morphogenetic movements during the early development of the chick eye. An ultrastructural and spatial reconstructive study. A. Invagination of the lens placode.

An electron microscopic study of the invagination of the chick lens placode led to the following observations: In addition to the cyclic movement of the dividing lens placode cells there is a continuous apical extrusion of delaminated lumps of cytoplasm and membranous material, which has been collected in vesicles. Beneath the level of the apical terminal network (junctional complexes and microfilaments) new intercellular junctions are formed. During the invagination the average length of the cells and consequently the thickness of the lens placode remains constant. By combining data from literature as well as from our own observations, we arrived at the following conception: The lens placode cells are in continual movement, and shift their external boundaries as a result of apical shrinkage by extrusion of cellular material and a shift of the apical terminal network on one side and presumably by an outgrowth of cells in the basal direction on the other. This may be the explanation to the change in shape of the entire ectodermal placode, described as invagination. A gradient in this process could account for the final asymmetry in the formation of the lens pit.

Animals↗
PubMed1985

The significance of endothelial stomata and stigmata in the rat aorta. An electron microscopic study.

Perfusion of arteries with dilute silver nitrate produces in the endothelium (a) a pattern of pericellular black lines, which we earlier interpreted as a marker of the physiological electrolyte pathway (Zand et al. 1982), and (b) focal black deposits on or between the cells, either ring-shaped (stomata) or solid (stigmata). The purpose of this study was to clarify the nature and significance of these controversial structures. A glutaraldehyde-fixed normal rat aorta was perfused with silver nitrate; 17 typical stomata and stigmata were photographed en face, then studied on ultrathin serial sections. When seen en face, they fell into three groups: (I) 4 stomata in endothelial cells; (II) 6 stigmata in endothelial cells; (III) 7 stigmata on intercellular junctions. By electron microscopy, (I) all the stomata in endothelial cells corresponded to myoendothelial herniae. (II) Of the 6 stigmata in endothelial cells, 4 corresponded again to myoendothelial herniae, 2 corresponded to blebs (it seemed likely that these blebs had existed in vivo, but the possibility of a fixation artefact could not be excluded). (III) Of the 7 stigmata on intercellular junctions, one corresponded to the diapedesis of a mononuclear cell; the other 6 did not correspond to visible endothelial changes and are best interpreted as points of normally higher permeability. We conclude that stomata and stigmata (under the conditions of our experiments) can be explained in at least 4 different ways, depending in part on their location (in cells, on junctions). These ancient terms therefore remain useful for descriptive purposes, as long as it is realized that their significance in any given case must be determined by electron microscopic study.

Animals↗
PubMed1991

Cytochalasin D treatment induces meiotic resumption in follicular sheep oocytes.

Ovine cumulus-enclosed oocytes collected from antral follicles (3-5 mm in diameter) were cultured in vitro with 2 x 10(6) granulosa cells/ml in the presence or absence of gonadotropins or in the presence of cytochalasin D (CD). The maturation rate was assessed after 24 h of culture. In the control group, in the presence of gonadotropins (follicle-stimulating hormone-luteinizing hormone (FSH-LH; -10 micrograms/ml) 100% of the oocytes reached metaphase II. Whereas intercellular junctions were no longer present after 6-7 h of culture, germinal vesicle breakdown (GVBD) occurred by the same time. In contrast, in the absence of gonadotropin, the majority of the oocytes (59%) remained blocked in GV stage. The inhibition exerted by the granulosa cells on meiotic resumption was overcome when the cumulus-oocyte complexes (COCs) were incubated in CD (5 micrograms/ml) for 6 h at the beginning of the culture. Under these conditions, 85% of the oocytes matured with extrusion of the first polar body. Cytological analysis by cytofluorescence (NBD phallacidin) and electron microscopy showed that, after 6 h of treatment, CD provoked a redistribution of the microfilaments, mainly in the cumulus cells and to a lesser extent in the oocyte cortex. Intercellular junctions disappeared concomitantly with a significant decrease of the intercellular transport of tritiated uridine. The initiation of GVBD occurred at the same time. These results indicate that the resumption of meiosis was correlated with a loss of both junctional complexes (intermediate and gap junctions) between the cumulus cells and the oocyte.

Animals↗
PubMed1975

The effects of topoinhibition and cytochalasin B on metabolic cooperation.

Metabolic cooperation was used to investigate the ability of 3T3 cells to form intercellular junctions under conditions of topoinhibition and topostimulation, respectively. A transformed BHK cell lacking hypoxanthine guanosine phosphoribosyl tranferase, which was used an an indicator, was found to incorporate 3H-hypoxanthine when in prolonged (20 hr) or brief (1 hr) contact with donor 3T3 cells, whether the latter were in a quiescent layer of in the region of stimulation at the edge of a wound. Cytochalasin B (1 mug/ml) prevented the development of metabolic cooperation and abolished most preexisting cooperation between donor 3T3 cells and recipient BHK cells. Cooperation was reestablished by removal of the drug. Cytochalasin B inhibited cooperation by the donor 3T3 cells in both the layer and wound edges, irrespective of topoinhibition and topostimulation. This provides further evidence that alteration in capacity to form stable intercellular junctions is not a necessary feature of the topoinhibition phenomenon.

Cell Division↗
PubMed1982

A freeze-fracture study of the guinea pig yolk sac epithelium.

The yolk sac epithelium functions in endocytic absorption of macromolecules from the uterine lumen and in maintaining permeability barriers between the maternal (uterine) compartment and underlying fetal compartments. In this study, cell membranes and intercellular junctions of the guinea pig yolk sac were examined using the freeze-fracture technique. Intramembranous particle (IMP) distribution and size were examined in microvilli, intermicrovillous membrane, and endocytic pits. IMPs on the P-fracture face were not evenly distributed within these membrane domains and the IMPs were of several sizes. In addition, short filamentous strands sometimes bridged between the cytoplasm and the E-face of endocytic pit membranes. These results indicated that the regions of yolk sac cell membrane involved in endocytosis did not have unusual numbers or distributions of IMPs compared to other membrane regions. The intercellular junctions between endoderm cells consisted of zonulae occludentes, gap junctions, and desmosomes. The zonula occludens usually consisted of four or five interconnected strands or ridges, and were elaborately developed where three cells abutted one another. Gap junctions were infrequent, small, and often associated with the zonula occludens. Desmosomes were observed both as typical macular structures and as more extensive, elongated structures. These results confirm previous thin-section studies of yolk sac indicating the presence of tight junctions. However, the extent of development of tight junctions does not correlate with the regard absence of a potential difference across yolk sac epithelium. The presence of gap junctions does not confirm results of previous freeze-fracture studies of other yolk sacs.

Animals↗
PubMed1986

Campylobacter pyloridis and gastritis: association with intercellular spaces and adaptation to an environment of mucus as important factors in colonization of the gastric epithelium.

Stomach biopsy specimens from greater than 40 individuals with Campylobacter pyloridis-associated gastritis were examined by light and electron microscopy. The bacteria were consistently seen in two locations: within the gastric mucus and associated with intercellular junctions of gastric epithelial cells. C. pyloridis is suggested to be one of a broad group of spiral bacteria that are adapted to the peculiar niche provided by intestinal mucus. The spiral morphology and the form of motility of these organisms give them a selective advantage in a viscous environment. This point has been demonstrated in vitro by measurement of the velocity of clinical isolates in solutions of methyl cellulose of varying viscosity. The localization of C. pyloridis close to intercellular junctions is proposed to be due to the presence of preferred metabolites or growth factors, e.g., urea and hemin. All isolates show an extremely high urease activity and require hemin for growth.

Campylobacter↗