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PubMed1989

[Studies on the gap junctional intercellular communication (GJIC) of human stomach carcinoma cells in comparison with normal cells and the effect of the tumor promoter, TPA].

This work was conducted by using a rapid and simple technique, scrape-loading and dye transfer (SLDT) to study GJIC of human stomach carcinoma MGC-803 cells in comparison with normal WB rat liver cells, Chinese hamster V79 cells and a primary culture of chicken embryonic myoblasts. Cells were plated and grown overnight to confluency in 35 mm plastic dishes in appropriate media. Monolayered cells, after rinsing in PBS, were immersed in the mixed 0.05% Lucifer Yellow (MW 457.2) and 0.05% Rhodamine-Dextran (MW. 10,000) in PBS. Scrape loading was performed by utilization of a sharp knife. Cells were incubated in dye solution for an additional 3 min. at room temperature before rinsing with PBS and observation under fluorescent microscope. Cells competent in GJIC showed transfer of Lucifer Yellow from the injured border to interior cells while the high MW. Rhodamine-Dextran dye stayed in situ in the loaded cells. Cells incompetent in GJIC did not show dye transfer; both Lucifer Yellow and Rhodamine-Dtranex were retained in the original loaded cells of the injured border. The background cell monolayer away from the scrape line was dark indicating that none of the dye molecules could permeate through cell membrane in the conditions described. It was found that human stomach carcinoma MGC-803 cells lack GJIC; Chinese hamster V79 cells showed modest GJIC; WB rat liver cells and chick myoblasts showed marked GJIC. The tumor promoter, TPA(1-100 ng/ml), inhibits GJIC of the normal cells efficiently. An inhibitor of calmodulin, Trifluoperazine (TFP) (5-20 microM), evidently increased the GJIC of stomach carcinoma MGC-803 cells. Noteworthy is that TFP in the dosage range used in SLDT experiments showed inhibitory effect on cell growth and DNA synthesis of MGC-803 cells documented in parallel experiments. These results indicate that the lack of GJIC in MGC-803 cells correlates with their uncontrolled cell proliferation; the improvement of GJIC correlates with the inhibition of tumor cell proliferation. TPA inhibition of GJIC in normal cells in this work confirmed previous reports. Interestingly, it was found that when V79 cells were treated with TFP and then shifted to medium containing both TFP and TPA, GJIC was blocked. It is likely that TPA overcomes the effect of TFP on GJIC of MGC-803 cells. These results provide further evidence for the role of GJIC in carcinogenesis, specially the tumor promotion phase.

Adenocarcinoma↗
PubMed1993

[Preliminary observations on junctional intercellular communication in the epidermis of the adult mammal skins].

1. Shown by the sagittal cryostat-microsections, the epidermis of the adult mouse and rabbit skins consisted of 3-4 layers of cells, occupying about 40 mu in thickness. When advancing a penetrating microelectrode from the surface of the epidermis vertically downward into its depth, the cell membrane potentials of these layers in series, being -4---8mv, -6---20mv, -12---20mv, -12---20mv, respectively, could be got. These potentials, in turn, could be used to mark the proper insertion of the electrode in cell of a desired layer. Beyond the depth of 40 mu usually no membrane potential was met. 2. Microinjection of carboxyfluorescein (CoF) into cell in the first (shallowest) epidermal layer, no matter how long the injection time was, produced restricted dye transfer-only to 1 or 2 neighbor cells. Transfer to 3-5 neighbor cells would be seen in 15 min. after 7 min. of CoF injection into cell in the 2nd layer, and this number would slowly increased if the injection time was further prolonged. Similar CoF injection into cell in the 3rd or 4th (Malpighi) layer resulted in dye transfer to 20-40 neighbor cells. Most testing injections in this work have been done to cells in the 3rd epidermal layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Intercellular junctions between macrophages in the regional lymph node of the rat after injection of large doses of steroids.

Intercellular junctions were often found between macrophages in sinuses of regional lymph nodes of the rat after injection of large doses of cholesterol, cortisone acetate, and estrone at the footpad. They were identified by subplasmalemmal densities, 20-50 nm in width, beneath the plasma membranes of apposed macrophages. No distinct filamentous structures were visible in those dense regions. Electron-dense amorphous materials are lined up at the center of the intercellular space in the junctional regions. Some macrophages form clusters with intercellular junctions. No significant difference in the effect of cholesterol, cortisone acetate, and estrone on the number of intercellular junctions between macrophages was found.

Animals↗
PubMed1982

Regional differences in the intercellular junctions of the alveolar-capillary membrane in the human lung.

There are regional differences in the human lung concerning ventilation, perfusion, and hydrostatic pressure. Structural differences corresponding to these physiologic differences have not been documented. In this study the intercellular junctions of the alveolar-capillary membrane in 3 human lungs were examined by the freeze-fracture technique. The intercellular junctions of the alveolar epithelium revealed neither qualitative nor significant quantitative differences from the upper zone to the lower zone of the lung. There were definite regional differences in the intercellular junctions of the capillary endothelium in the 3 zones of the lungs examined. The number of strands that comprise the tight junctions of the capillary endothelium increases from the upper zone (2.80) to the lower zone (4.99) of the lung.

Capillaries↗
PubMedDate not supplied

Development of intercellular junctions in the vestibular end-organ. A freeze-fracture study in the mouse.

The intercellular junctions and the tight junctions in particular are considered to be of great importance for the function of the inner ear. The two fluid compartments of the inner ear, the perilymphatic space and the endolymphatic space, need to be effectively separated from each other in order to maintain the ionic gradients between the two. The tight junctional structures have been described in mature animals of several species. In the present article the development and maturation of the intercellular junctions are described in the mouse embryo. Junctional elements are already present in the 12th gestational day otocyst. Over the next few days, the otocyst is differentiated into a cochlear portion and a vestibular portion. The tight junctions in the vestibular portion gradually attain their mature appearance. It seems as if the tight junctions of the supporting cells develop slightly faster than those of the hair cells. At the time of birth, all epithelial cells have obtained mature appearance. The tight junctions are fully developed on the supporting cells as well as the hair cells. Small gap junctions are present in the 14th gestational day specimens. Two days later the hair cells and the supporting cells are well differentiated; small to medium-sized gap junctions are present only on the supporting cells at this stage. At the time of birth larger gap junctional aggregates have developed on the supporting cells.

Animals↗
PubMed2002

Connexins, gap junctional intercellular communication and kinases.

A number of kinases and signal transduction pathways are known to affect gap junctional intercellular communication and/or phosphorylation of connexins. Most of the information is available for protein kinase A, protein kinase C, mitogen-activated protein kinase, and the tyrosine kinase Src. Much less is known for protein kinase G, Ca(2+)-calmodulin dependent protein kinase, and casein kinase. However, the present lack of knowledge is not necessarily synonymous with lack of importance in the regulation of intercellular communication and phosphorylation of connexins. Kinases and the phosphorylation of connexins may be involved in the regulation of gap junctional intercellular communication at all levels ranging from the expression of connexin genes to the degradation of the gap junction channels. The exact role of the phosphorylation depends both on the kinase and the connexin involved, as well as the cellular context.

Animals↗
PubMed1980

Intercellular junctions in the adrenal medulla: a comparative freeze-fracture study.

Observations of freeze-fractured specimens revealed that intercellular junctions in adrenal medulla are different in nature and number according to species. Only gap junctions of diverse size exhibiting characteristic loop-like configurations were found in hamster chromaffin cells. In addition to such gap junctions, polymorphic focal tight junctions occasionally combined with particle clusters or small gap junctions were found in guinea-pig. So far, no intercellular junctions were found in rat. Discussion is focused on the possible function of these junctions, in keeping with their presumably high lability.

Adrenal Medulla↗
PubMed2003

Bystander effect in suicide gene therapy is directly proportional to the degree of gap junctional intercellular communication in esophageal cancer.

Gap junctional intercellular communication (GJIC) has been shown to be involved in the bystander effect through herpes simplex virus thymidine kinase/ganciclovir (HSV-tk/GCV) gene therapy. In this study, we examined the expression of connexins, the components of gap junction, and the degree of GJIC in esophageal cancer cell lines and compared the bystander effect in cells with different capacities of GJIC. We found loss in connexin 26 expression and reduced connexin 43 in esophageal cancer. GJIC capacity varied among cell lines and was dependent on the connexin 43 expression in the cell-cell contact areas. In mixing assay, the extent of the bystander effect was tightly correlated with the degree of GJIC capacity. The effects of retinoic acid and cAMP on the bystander effect were also investigated. Treatment with retinoic acid, but not with cAMP, was associated with augmented bystander killing by increase in GJIC in some esophageal cancer cell lines. Our results indicated that the degree of GJIC was predictive to identify a tumor as suitable for gene therapy with the HSV-tk/GCV system. Also GJIC chemically-enhanced with retinoic acid might be useful to improve response in suicide gene therapy.

Blotting, Western↗
PubMed1993

Endogenous and exogenous modulation of gap junctional intercellular communication: toxicological and pharmacological implications.

During the evolution of single-celled organisms to multicellular metazoans, a family of highly conserved genes coding for proteins (connexins), which as hexameric units (connexins), has evolved to form intercellular channels (gap junctions). These gap junctions allow ions and small molecular weight molecules to flow between coupled cells, thereby facilitating synchronization of electrotonic or metabolic cooperation. Control of cell proliferation, cell differentiation and adaptive responses of differentiated cells have been speculated to be biological roles of gap junctions. The regulation of these gap junctions can occur at the transcriptional, translational and posttranslational levels. Transient downregulation by endogenous or exogenous chemicals can bring about adaptive or maladaptive consequences depending on circumstances. Stable abnormal regulation of gap junction function has been associated with the activation of several oncogenes. Several tumor suppressor genes have also been associated with the up-regulation of gap junction function. Since gap junctions exist in all organs of the multi-cellular organisms, the dysfunction of these gap junctions by various toxic chemicals which have cell type/tissue/organ specificity could bring about very distinct clinical consequences, such as embryo lethality or teratogenesis, reproductive dysfunction in the gonads, neurotoxicity of the CNS system, hyperplasia of the skin, and tumor promotion of initiated tissue. Understanding how many non-mutagenic chemicals might alter normal gap junction function should form the basis of "epigenetic" toxicology. On the other hand, restoring normal gap junction function to cells which have dysfunctional intercellular communication could be the basis for a new approach for therapeutic pharmaceuticals.

Animals↗
PubMed1997

Migration and gap junctional intercellular communication determine the metastatic phenotype of human tumor cell lines.

Gap junctional intercellular communication (GJIC) as well as cell migration play an essential role in the metastatic cascade of human tumors. We show a dependence of metastatogenic phenotypes of human tumor cells (cell lines T 24, SCC-25, MDA-MB-361 and SK-BR-3) from the GJIC and the migration activity. The GJIC was studied by microinjection of the fluorescent dye Lucifer Yellow (LY) and cell migration was studied by investigating the locomotion of the tumor cells in 3-dimensional collagen matrices. Diminished GJIC seems to be more influential for the metastatic phenotype than modulation of the locomotory behavior of the tumor cells.

Breast Neoplasms↗
PubMed1990

[Role of junctional intercellular communication in hepatic carcinogenesis in rats].

Two major alterations in gap junctional intercellular communication (GJIC) during experimental carcinogenesis have been seen: a decrease of its capacity during tumor promotion and a selective loss of intercellular communication between transformed cells and surrounding normal counterparts. These data, first discovered in our laboratory on mouse fibroblasts (BALB/c 3T3), were partly confirmed in rat liver epithelial cells. In such cells, the decreased GJIC was related to their level of transformation. Tissue-specific effect of tumor promoters is also seen in the inhibition of GJIC; administration of phenobarbital decreased the level of GJ mRNA in the liver, but not in other organs tested. Phenobarbital also inhibited GJIC among adult rat hepatocytes co-cultured with BALB/c 3T3 cells but not among the mouse fibroblasts. Moreover, our findings on the diminished level of GJ mRNA in tumors of rat liver support the importance of acquired selective GJIC in rat liver carcinogenesis.

Animals↗
PubMed1977

Intercellular junctional complexes of the rat seminiferous tubules: a freeze-fracture study.

This paper provides a description of the intercellular junctions in the rat testis, as observed using the freeze fracture technique. These intercellular junctions were categorized into four general types: Sertoli cell tight junctions, myoid cell tight junctions, gap junctions, and "heterogeneous junctions." The Sertoli cell tight junctions had a mean depth of 3.1 micron in the basal to apical direction, and contained 25 to 50 (average: 36) parallel rows of particulate sealing elements. The myoid cell tight junction was neither continuous nor extensive, but focal in nature. Interestingly the sealing elements of this junction, like those of the Sertoli cell tight junction, were quite particulate in nature. Typical gap junctions were observed between Sertoli cells where they were intercalated between the parallel rows of the Sertoli cell tight junction. The most interesting observation was the identification of gap junction-like structures, in various stages of formation, on germ cell membrane fracture faces, both in the basal and adluminal compartments. Lastly, the unusual "heterogeneous junction" was observed on large membrane fracture faces in close proximity to cells in the adluminal compartment, presumably between Sertoli cells. These junctions appeared to consist of both tight and gap junction elements.

Animals↗
PubMed1987

Contribution of solvent drag through intercellular junctions to absorption of nutrients by the small intestine of the rat.

The lumen of the small intestine in anesthetized rats was recirculated with 50 ml perfusion fluid containing normal salts, 25 mM glucose and low concentrations of hydrophilic solutes ranging in size from creatinine (mol wt 113) to Inulin (mol wt 5500). Ferrocyanide, a nontoxic, quadrupally charged anion was not absorbed; it could therefore be used as an osmotically active solute with reflection coefficient of 1.0 to adjust rates of fluid absorption, Jv, and to measure the coefficient of osmotic flow, Lp. The clearances from the perfusion fluid of all other test solutes were approximately proportional to Jv. From Lp and rates of clearances as a function of Jv and molecular size we estimate (a) the fraction of fluid absorption which passes paracellularly (approx. 50%), (b) coefficients of solvent drag of various solutes within intercellular junctions, (c) the equivalent pore radius of intercellular junctions (50 A) and their cross sectional area per unit path length (4.3 cm per cm length of intestine). Glucose absorption also varied as a function of Jv. From this relationship and the clearances of inert markers we calculate the rate of active transport of glucose, the amount of glucose carried paracellularly by solvent drag or back-diffusion at any given Jv and luminal glucose concentration and the concentration of glucose in the absorbate. The results indicate that solvent drag through paracellular channels is the principal route for intestinal transport of glucose or amino acids at physiological rates of fluid absorption and concentration. In the absence of luminal glucose the rate of fluid absorption and the clearances of all inert hydrophilic solutes were greatly reduced. It is proposed that Na-coupled transport of organic solutes from lumen to intercellular spaces provides the principal osmotic force for fluid absorption and triggers widening of intercellular junctions, thus promoting bulk absorption of nutrients by solvent drag. Further evidence for regulation of channel width is provided in accompanying papers on changes in electrical impedance and ultrastructure of junctions during Na-coupled solute transport.

Animals↗