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PubMed2000

[Ultrastructure of the lymph capillaries in human dental pulp].

OBJECTIVE: The purpose of this article is to observe the ultrastructures of the lymph capillaries in the human dental pulps. METHODS: Investigations have been performed on dental pulps from 8 human permanent teeth, including 4 mandibular first premolars and 4 maxillary first premolars, which were extracted for orthodontic reason. As soon as possible, we cleaved the teeth longitudinally and immersed in the fixative solution at 4 degrees C for 1 hour, then kindly removed the pulps and immersed in the same fixative solution for 3 hours, then routinely postfixed, dehydrated, embedded, and prepared the ultrathin sections (50-70 nm) without semithin section localization. The lymph vessels were distinguished from blood vessels on ultrathin sections by their morphological features. RESULTS: We have observed three fundamental kinds of intercellular junctions, overlapping(51%), end to end(36.1%), and interdigistating (10.6%). A few complex junctions also could be seen, but we failed to find the open junction. The Weibel-Palade bodies were occasionally present in the lymphatic vessels endothelial cells of young dental pulps. And we even found the lipofuscins in the cytoplasm of the endothelium. Some inclusion bodies, such as paracrystalline inclusions and myeloid bodies, also could be seen. There were many micropinocytotic vesicles in the cytoplasm of the lymphatic endothelium, the diameter of the most vesicles was about 50-80 nm, some was about 100-500 nm. Some vesicles appeared to lie free within the cytoplasm, and some were seen to touch or open onto the luminal or abluminal surfaces of the endothelia, which suggested that many vesicles were not simple discrete units but rather from parts of chains that reached either luminal or abluminal surfaces. It was reported that micropinocytotic vesicles, open junctions and intraparietal channels provided fluid transport. CONCLUSION: Dental pulp is a special organ, and the lymph capillaries in it have their own ultrastructural features.

Adolescent↗

PubMed2003

On the mechanism of fluid transport across corneal endothelium and epithelia in general.

The mechanism by which fluid is transported across epithelial layers is still unclear. The prevalent idea is that fluid traverses these layers transcellularly, driven by local osmotic gradients secondary to electrolyte transport and utilizing the high osmotic permeability of aquaporins. However, recent findings that some aquaporin knockout mice epithelia transport fluid sow doubts on local osmosis. This review discusses recent evidence in corneal endothelium that points instead to electro-osmosis as the mechanism underlying fluid transport. In this concept, a local recirculating electrical current would result in electro-osmotic coupling at the level of the intercellular junctions, dragging fluid via the paracellular route. The text also mentions possible mechanisms for apical bicarbonate exit from endothelial cells, and discusses whether electro-osmosis could be a general mechanism.

Animals↗

PubMed2002

Flow conditions modulate homocysteine induced changes in the expression of endothelial cell genes associated with cell-cell interaction and cytoskeletal rearrangement.

In the present study we analyzed changes in the pattern of gene expression in endothelial cells (HUVEC) exposed to elevated homocysteine levels under flow conditions. RNA samples of untreated and homocysteine treated EC were analyzed using a human cDNA array containing 588 cDNAs relevant to the cardiovascular system. Exposure to homocysteine under flow resulted in altered expression of 8 genes, the alterations of 3 of which were further confirmed by RT-PCR analysis: upregulation of MCP-1 and of profilin-I, and downregulation of alpha-catenin. The increased expression of profilin-I and the decreased expression of alpha-catenin were also confirmed at the protein level by Western blot analysis. Furthermore, immunostaining for alpha-catenin demonstrated complete loss of the protein from intercellular junctions following exposure to homocysteine under flow. All these changes were not observed in cells exposed to homocysteine under static conditions. We show that under flow conditions, homocysteine modulates the expression of genes/proteins involved in actin cytoskeleton reorganization, as well as in the formation and/or maintenance of cell-cell junction, thus contributing to the morphological changes (e.g. cell retraction) reflecting endothelial cell injury.

Base Sequence↗

PubMed1980

[Ultrastructure of specialized intercellular contacts].

The review contains some literary evidence and the authors' own data on the ultrastructure and molecular organization of specialized intercellular junctions (tight, septate, intermediate, gap junctions and desmosomes). The analysis of structural organization of junctions was carried out using data obtained by various electron microscopic techniques (ultrathin sections, freeze-cleaving, negative contrasting, optical diffraction of electron microscopic images), low-angle X-ray diffraction and biochemical methods. Some aspects of structural organization of specialized junctions providing for their functioning are concerned. Among other things, recent findings on the molecular structure of connexons and on their conformational changes promoting permeability regulation of their hydrophilic channels are reviewed. Available data on the lability of specialized junctions, both in the process of the organism's viability and during pathological states and after certain experimental treatment, are emphasized. Facts testifying to the lability of separate components of a junction including its perimembraneous cytoplasmic regions, are in a good agreement with a widespread liquid-mosaic model of the structural organization of cell membranes.

Animals↗

PubMed1982

Endothelium and "silver lines". An electron microscopic study.

The significance of endothelial "silver lines" was studied by TEM in rat aortas after perfusion with glutaraldehyde followed by silver nitrate. Standard TEM technique proved unsatisfactory (coarse silver granules, imprecise localization, artefacts). Exposure of the silver-treated aortas to photographic fixer markedly improved the image of the deposits leaving fine, stable, uniform "residual granules" about 100 A in diameter. Most of these granules were localized along the intercellular junctions; they also tended to pool in the basement membrane beneath each junction. This image suggests that the Ag+ ions pass through the junction, and react with its contents as well as with the basement membrane beyond it. A scheme is proposed to explain the reaction of Ag+ ions with anions and negatively charged radicals within the junction. It is concluded that the "silver lines" represent not only a histochemical effect, but also the visualization of a transendothelial electrolyte pathway.

Animals↗

PubMed1980

Intercellular communication patterns are involved in cell determination in early molluscan development.

The formation of specialized intercellular junctions, allowing the passage of low-molecular weight regulatory molecules, has been considered as a possible mechanism for regulating embryonic development. No direct evidence for this concept has been found in early development. In the mollusc Pattella vulgata it was demonstrated that cell positioning and specific cellular interactions are key factors in the control of early development. We have now investigated the pattern of intercellular communication during early development of this embryo by intracellular iontophoresis of the fluorescent dye Lucifer Yellow CH. We demonstrate that the formation of regional- and temporal-specific cell-to-cell coupling is correlated with the determination of the mesentoblast--the stem cell of the mesoderm--and the establishment of dorso-ventral polarity.

Animals↗

PubMed1997

Alteration of interendothelial adherens junctions following tumor cell-endothelial cell interaction in vitro.

The integrity of the vascular endothelium is mainly dependent upon the organization of interendothelial adherens junctions (AJ). These junctions are formed by the homotypic interaction of a transmembrane protein, vascular endothelial cadherin (VE-cadherin), which is complexed to an intracellular protein network including alpha-, beta-, and gamma-catenin. Additional proteins such as vinculin and alpha-actinin have been suggested to link the VE-cadherin/catenin complex to the actin-based cytoskeleton. During the process of hematogenous metastasis, circulating tumor cells must disrupt these intercellular junctions in order to extravasate. In the present study, we have investigated the influence of tumor cell-endothelial cell interaction upon interendothelial AJ. We show that human breast adenocarcinoma cells (MCF-7), but not normal human mammary epithelial cells, induce a rapid endothelial cell (EC) dissociation which correlates with the loss of VE-cadherin expression at the site of tumor cell-EC contact and with profound changes in vinculin distribution and organization. This process could not be inhibited by metalloproteinase nor serine protease inhibitors. Immunoprecipitations and Western blot analysis demonstrate that the overall expression of VE-cadherin and vinculin as well as the composition of the VE-cadherin/catenins complex are not affected by tumor cells while the tyrosine phosphorylation status of proteins within the complex is significantly altered. Our data suggest that tumor cells modulate AJ protein distribution and phosphorylation in EC and may, thereby, facilitate EC dissociation.

Adenocarcinoma↗

PubMed1989

The ultrastructure of human abdominal mesothelium.

Fresh specimens of human peritoneum collected from heart-beating cadaver organ donors have been examined by transmission electron microscopy. Samples were taken from the anterior abdominal wall and from the surfaces of the liver, stomach and diaphragm. The mesothelium consisted of a single layer of flattened cells generally 2.5 microns to 3 microns thick. These were joined by tight junctions and desmosomes to form a continuous sheet. The cells rested on a prominent basement membrane deep to which was a layer of fibrous connective tissue. This layer was more compact under the mesothelium from the abdominal wall and liver than elsewhere. Long microvilli projected from apical surface of the cells. In many cases these covered the entire surface but sometimes they were more profuse at the edges of the cells near the intercellular junctions. The cells possessed a well-developed cytoskeleton of intermediate filaments which coursed through the cytoplasm in thick bundles. The cells also had a well-developed rough endoplasmic reticulum and Golgi apparatus. Numerous smooth-surfaced and coated vesicles could be seen adjacent to the plasmalemma at all surfaces, providing evidence of considerable pinocytotic activity. There was little regional variation in the structure of the mesothelium. We found no evidence of pores passing through the layer although, on the liver, cisternae were present between the cells and these were often occupied by lymphocytes.

Adolescent↗

PubMed1995

Endothelial cells injured by oxidized low density lipoprotein.

Cultured endothelial cells from bovine aorta were exposed to oxidized low density lipoprotein and examined by electron microscopy. The endothelial cells contracted slightly and the intercellular junctions became unclear. Some osmiophilic material increased in the cytoplasm. The oxidized low density lipoprotein appears to injure endothelial cells and thereby plays a causative role in atherogenesis and thrombogenesis.

Animals↗

PubMed1990

Glucose transporters are abundant in cells with "occluding" junctions at the blood-eye barriers.

We studied the distribution of the "erythroid/brain" glucose transporter protein in the human and rat eye by immunocytochemistry with monoclonal and polyclonal antibodies to the C terminus of the human erythrocyte glucose transporter. We found intense immunocytochemical staining in the endothelium of microvessels of the retina, optic nerve, and iris but not in microvessels of the choroid, ciliary body, sclera, and other retro-orbital tissues. In addition, we found marked immunocytochemical staining of retinal pigment epithelium, ciliary body epithelium, and posterior epithelium of the iris. The common feature of all those endothelial and epithelial cells that stained intensely for the glucose transporter is the presence of "occluding" intercellular junctions, which constitute the anatomical bases of the blood-eye barriers. We propose that a high density of the glucose transporter is a biochemical concomitant of epithelial and endothelial cells with barrier characteristics, at least in tissues that have a high metabolic requirement for glucose.

Animals↗

PubMed1975

Ultrastructural changes of the capillaries of the cat iris in experimental neuroparalytic keratitis.

In order to study the morphological basis of the increased permeability of the capillaries of the iris in neuroparalytic keratitis the ophthalmic division of the trigeminal nerve in the cat was denervated using a stereotactic method. The homolateral iris was studied by electron microscopy three days after denervation. Abnormally large pinocytotic vacuoles were observed in the endothelial cells of the iris capillaries and the intercellular junctions of the endothelial cells showed widened inter-cellular space and macula occludens. These ultrastructural changes may explain the protein leakage into the anterior chamber in neuroparalytic keratitis.

Animals↗

PubMed1987

Physiological regulation of transepithelial impedance in the intestinal mucosa of rats and hamsters.

Isolated intestinal segments from rats or hamsters were recirculated with balanced salt solutions containing fluorocarbon emulsion to provide 6 vpc oxygen. The lumen contained an axial Ag-AgCl electrode, and the serosal surface was surrounded by a cylindrical shell of Ag-AgCl. Transmural impedances were measured at frequencies from 0.01-30 kHz before and after removal of the mucosal epithelium. The resistance of intercellular junctions, RJ, the distributed resistance of the lateral spaces, RL, and the distributed membrane capacitance, CM, were computed from the relations between frequency and impedance. Activation of Na-coupled solute transport by addition of glucose, 3-0-methyl glucose, alanine or leucine caused two- to threefold decreases of transepithelial impedance. Typical changes induced by glucose in hamster small intestine were RJ 30----13 omega, RL 23----10 omega, and CM 8----20 microF (per cm length of segment). Half maximal response occurred at a glucose concentration of 2-3 mM. The area per unit path length of the junctions (Ap/delta chi = specific resistance divided by RJ) in glucose activated epithelium was 3.7 cm in hamster midgut and 6.8 cm in rat. These values are close to the 4.3 cm estimated independently from coefficients of solvent drag and hydrodynamic conductance in glucose-activated rat intestine in vivo. The transepithelial impedance response to Na-coupled solute transport was reversibly dependent upon oxygen tension. It is proposed that activation of Na-coupled solute transport triggers contraction of circumferential actomyosin fibers in the terminal web of the microvillar cytoskeletal system, thereby pulling apart junctions and allowing paracellular absorption of nutrients by solvent drag as described in the previous accompanying paper. Anatomical evidence in support of this hypothesis is presented in the following second accompanying paper.

Animals↗

PubMed1992

Light- and electron microscopic study of oligodendrocytes in the lateral line area of the medulla in Chelon labrosus (Teleostei).

The oligodendrocytes of the medullary lateral line area of the teleost Chelon labrosus were studied with light and electron microscopy. Oligodendrocytes are sharply differentiated from neurons or other class of glia cells from their ultrastructural characteristics. The three subtypes of oligodendrocytes (light, medium and dark) that have been recognized are not homogeneously distributed but have preferential locations related to the size of nearby myelinated fibres. No perineuronal oligodendrocytes are present in this medullary center. Oligodendrocytes show a variety of dense bodies, sometimes of bizarre shapes, in addition to characteristic mitochondria and endoplasmic reticulum. Three types of intercellular junctions were observed in these cells: gap junctions, tight junctions and puncta adhaerentia. Gap junctions and puncta adhaerentia link oligodendrocyte somata and astrocytic processes. Tight junctions were observed both between oligodendrocytes and between oligodendrocytes and astrocytic processes. The significance of these results is discussed in relation to the maturation and function of oligodendrocytes and the characteristics of fish brains.

Animals↗

PubMed1981

Ultrastructural alterations in the mouse liver following vincristine administration.

The damage pattern in mouse liver was investigated following a single administration of 0.15 mg vincristine sulfate using the conventional thin-section technique and freeze-fracture. Numerous cytoplasmic changes were observed. Foremost of these was the increase in autophagosomes and vacuoles with very-low-density-lipoprotein (VLDL)-like vesicles. The rough endoplasmic reticulum exhibited a vesicular structure. The mitochondria also exhibited alterations such as enlargement and polymorphism. Both the interstitium and bile canaliculi were dilated. Lanthanum penetrated into the lumen of the canaliculi, i.e. the sinusoid/canaliculus compartmentalization did not remain intact, thus permitting bile to pass into the blood. Of particular significance are the alterations in the intercellular junctions. In contrast to the controls, the tight junctions were reduced and irregularly arranged. The gap junctions exhibited hypertrophy as well as a very irregular contour. The alterations may either be attributed to non-specific toxic effects of vincristine and/or the destructive properties of the agent on microtubules.

Animals↗

PubMed1994

Effect of polycations on permeability of glomerular epithelial cell monolayers to albumin.

Polycations can interact with the surface negative charges of the glomerular epithelial cells in the kidney and give rise to metabolic alterations. This study examined whether charge neutralization can affect intercellular junctions and increase macromolecular permeability across epithelial monolayers. We examined this question by studying the effect of polycations on the leakage of albumin across monolayers of glomerular epithelial cells. Cells were grown to confluency on filter-lined cups. They were treated apically with cationic bovine gamma globulin or protamine (100 micrograms/ml) for 2 hours at 37 degrees C. After washing the cells, the monolayers were tested for leakage of albumin by the addition of radioactive bovine serum albumin on the apical side and determining the time course of its appearance on the basal side. Polycation treatment caused significant leakage of albumin in the absence of any toxic effect on viability or lactate dehydrogenase release. The leakage was shown to be through the tight junctions of the monolayer. Permeability alterations were compared at 4 degrees C and 37 degrees C to determine whether impairment was due to the membrane ruffling effect of charge neutralization or due to intracellular metabolic changes. Despite equal bindings of polycations at 4 degrees C and 37 degrees C, significant leak occurred only at 37 degrees C, suggesting the role of active processes in the maintenance of permselectivity. This was consistent with the rapid interiorization of the polycation at 37 degrees C after membrane binding. Further substantiation of this point was obtained by studying the protective effect of removing bound polycation with heparin. Removal of polycation after initial binding failed to protect the monolayer from albumin leakage. The conclusion was that neutralization of glomerular epithelial cell surface charges results in subtle impairment of tight junction control of permeability to macromolecules across the monolayer. The impairment was due to active intracellular processes that ensue after polycation binding to cell surface charges and their subsequent internalization.

Animals↗

PubMed1996

Cell culture dosimetry for low-frequency magnetic fields.

Calculations of the current density and electric field distributions induced in cell cultures by an applied low-frequency magnetic field have assumed that the medium is uniform. This paper calculates these distributions for a more realistic, inhomogeneous, anisotropic model in which the cells are regarded as conducting squares surrounded by insulating membranes. Separate parameters are used to specify the resistivities of the cell interior, the cell membrane parallel to its surface, the cell membrane perpendicular to its surface, and the intercellular junction parallel to the membrane. The presence of gap junctions connecting the interiors of adjacent cells is also considered. For vertical applied magnetic fields, the induced currents and field distributions may deviate considerably from the homogeneous medium model if there is sufficiently tight binding of the cells to each other. The presence of gap junctions can produce relatively large transmembrane electric fields or intracellular current densities. These considerations are generally less important for horizontal applied fields. A simple microscopic model of the cell surface is also discussed.

Animals↗

PubMed1975

Lymphocytes and cells in malignant transformation: similarities and possible relationship between the two cell types.

This paper points out some similarities between the behaviour and characteristics of lymphocytes and their transformation to lymphoblasts on one hand and malignant cells on the other. The areas of similarity are (1) anomalous communicating junction formation; (2) recruitment of neighbouring cells; (3) random antigen expression; (4) Fc synthesis; (5) stimulation by immune attack; (6) relation to a plasminogen activator, and (7) inhibition of stimulation by trypsin inhibitors. It is argued that, considering the anomalous membrane characteristics shown by lymphocytes and malignant cells and the list of similarities, carcinogenesis could represent a normal cell line infected with lymphocytic information. Two incidental ideas are presented based on the main idea. These concern lymphocytes but are related to malignant cells and their characteristics too. They are (1) a mechanism whereby generation of randomness in the variable region of Ig molecules could take place, and (2) a mechanism whereby the lymphocyte, in order to kill its target, could use the normal cell's propensity to form communicating intercellular junctions.

Animals↗

PubMed2003

Junctional complex revisited by high-resolution scanning electron microscopy.

The present study correlates the ultrastructural morphology of junctional complexes as revealed by transmission electron microscopy (TEM) with that observed by high-resolution scanning electron microscopy (HRSEM), thanks to a new modification of the osmium tetroxide maceration technique. The removal of all cytoplasmic organelles by this technique allows the inspection of the inner side of the plasmalemma. With this treatment, a continuous band of tightly packed particles is observed at the most apical portion of lateral membranes. Just below this band, irregular clusters of apparently identical particles are placed all around the cellular contour. The topographical correspondence among these clusters and spot desmosomes seen by TEM identifies them as desmosomes. The continuous band seems to represent the combination of both zonulae, occludens and adherens. Regarding the nature of the particles, we suppose that they probably consist of peripheral membrane proteins clustered at the cytoplasmic surface of intercellular junctions and involved in the linkage between cytoskeleton and plasmalemma.

Adolescent↗