Distribution Of Intercellular Junctions Research Articles

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.

Spatiotemporal development and distribution of intercellular junctions in adult rat cardiomyocytes in culture.

The mode of development of the intercalated disk (ID) is largely unknown, and the hypothesis was tested that the assembly of cell adhesion junctions may precede the formation of gap junctions (GJ) in developing ID in adult rat cardiomyocyte (ARC) in long-term culture. Immunostaining for connexin 43 (Cx43) and for cell adhesion junction proteins (N-cadherin, catenins, and desmoplakin) in single- and double-label techniques was analyzed and quantified by confocal and electron microscopy. All proteins investigated disappeared 48 hours after ARC isolation and reappeared parallel to redifferentiation of ARC. The newly formed ID, observed after 5 days, showed the presence of N-cadherin, catenins, and desmoplakin, low levels of Cx43, and absence of ultrastructurally discernible gap junctions. A progressive incorporation of Cx43 within ID was observed after 6 days, when cell adhesion junction proteins were already organized as zipper-like structures. Quantitative confocal analysis revealed a progressive augmentation of the fluorescence intensity of Cx43, associated with an increase in both the number and size of GJ, resulting in a substantial increase in the percentage of total GJ length per reassembled ID from 1.67% (day 6) to 15.58% (day 12). In the present study, we show that (1) the formation of the ID can be followed in ARC in culture and (2) the assembly of the adhering type of junction is the prerequisite for subsequent GJ formation within the ID. These findings may have clinical relevance in elaborating strategies for using myocardial grafts and for the potential restoration of GJ communication in cardiac diseases.

The relationship between wall tension, lamellar thickness, and intercellular junctions in the fetal and adult aorta: Its relevance to the pathology of dissecting aneurysm

It is known that the distribution of stress and strain in the vessel wall is not uniform. We believe that this explains the location of the plane of dissection in dissecting aneurysms of large elastic arteries. We have investigated the effects of non-uniformity of stress and strain on the thickness of each elastic lamella and on the distribution of intercellular junctions in the media of developing and adult rats, to seek evidence to support this hypothesis. Intercellular junctions were identified by transmission electron microscopy of whole wall sections. A morphometric study of elastic tissue distribution was made on an image analysis computer. Differences were analysed using one-way analysis of variance. There are between six and eight elastic lamellae in the aorta of rats. In the fetus, only the internal elastic lamella is complete; the others were not fully formed by term. In the adult, the inner five elastic lamellae were thicker than the remaining two or three, and smooth muscle cells in the thicker lamellar units had more cell-cell contacts of all types examined. These data support the concept of a difference in stress-resisting properties of the aortic wall on the junctions between the inner two-thirds and the outer third of the media. The findings indicate that, as proposed in theoretical models the innermost lamellae support the high tension. In the adult aorta, the structure is modified to enhance the capacity to resist stress in the internal two-thirds of the media.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution and three-dimensional structure of intercellular junctions in canine myocardium.

Electrotonic coupling of cardiac myocytes at gap junctions may influence patterns of conduction in myocardium. To delineate the three-dimensional structure and distribution of intercellular junctions, we analyzed serial ultrathin sections of canine myocardium with transmission electron microscopy and disaggregated myocytes with scanning electron microscopy. Morphometric analysis of left ventricular myocardium sectioned in three orthogonal planes revealed that 80% of total gap junctional membrane occurred in large, ribbon-like gap junctions oriented transversely at cell end processes. The remaining 20% of gap junctional membrane was contained in small gap junctions located within plicate segments (interdigitating regions of cell-to-cell adhesion) of intercalated disks. In serial ultrathin sections, all gap junctions were contiguous with plicate segments. Thus, true "lateral" gap junctions do not exist in working ventricular myocytes and would not likely be able to withstand shear forces created by laterally sliding cells. Examination of serial plastic sections with light microscopy revealed complex overlapping of myocytes such that individual myocytes were connected at intercalated disks to an average of 9.1 +/- 2.2 other myocytes. These observations provide an improved understanding of the extent and distribution of cell junctions and should facilitate experimental and model studies of conduction in myocardium.

The development of cell junction during nephrogenesis.

The differentiation and distribution of intercellular junctions especially during the early development stages of the rabbit nephron was studied by freeze-fracture electron microscopy. Metanephrogenic cells were found to be connected by sporadic focal tight junctions. During the formation of the renal vesicle similar tight junctions occurred on the periphery as well as near the developing lumen. These focal tight junction increased in size and coalesced to broad zonulae occludentes lining the vesicular lumen at a later stage. Broad occluding junctions were also observed in the different nephron segments of the S-shaped stage. Ultrastructurally, these early maculae and zonulae occludentes consisted of beaded rows of particles. As development progressed, continuous tight junctions formed, whereas the number of strands decreased with the exception of the distal tubule. In contrast to the parietal glomerular epithelium, the initial occluding zonules of the visceral glomerular cells were gradually reduced to maculae occludentes, and finally disappeared. These results suggest that zonulae occludentes appear synchronously with the establishing lumen; the ultrastructural differentiation of tight junction strands seems to be completed with the onset of glomerular filtration.

Intercellular junctions and the permeability barrier in the junctional epithelium. A study with freeze-fracture and thin sectioning.

The morphology and distribution of intercellular junctions were studied in the clinically normal junctional epithelium of dogs by freeze‐fracture and thin sectioning. Desmosomes were found in cells of the coronal and apical regions of the junctional epithelium. The occurrence values for desmosomes were low in comparison with those of other oral epithelia. Gap junctions were also observed in cells of the junctional epithelium, often in association with desmosomes. These were usually small, their diameter varying between 0.2 and 0.7 μm. Relatively large ones were found in the cells of the coronal region. Tight junctions were observed only in the intermediate cells of the coronal region, forming small, discrete maculae occludentes. Numerous dense PTA‐positive granules were observed in the peripheral cytoplasm of the intermediate and superficial cells. In freeze‐fracture replicas, hemispherical structures were also observed at the periphery of the cytoplasm. Because of similarities in their size and location, the hemispherical structures probably correspond to the dense granules. Freeze‐fracture images such as elevated membranes seem to reveal exocytosis. The hypothesis is put forward that the dense granules are related to the physiological permeability barrier in the junctional epithelium. However, it is doubtful that the epithelium provides a complete barrier function because of the vast extent of the intercellular spaces and the sparseness of desmosomes.

Intercellular junctions in salivary glands: Freeze-fracture and tracer studies of normal rat sublingual gland

Structure and distribution of intercellular junctions (tight junctions, gap junctions, and desmosomes) were studied in rat sublingual glands by freeze-fracture and tracing methods. In acinar and duct cells tight junctions were found to form continuous belts around the juxtaluminal region of plasma membrane. In the former cell type their structure was relatively simple since they were composed of one to four occasionally interrupted strands of sealing elements (average 2.4 strands and 0.28 μm in depth per junction). In contrast the junction of duct cells contained elaborate and deeper meshworks of interconnected strands. The average number of these strands was around 5, while the depth of the junctions was 0.5 μm. Gap junctions were frequently observed in acinar and myoepithelial but not in duct cells. The diameter of the gap junctions varied from 0.2 and 1.2 μm (average value of 0.47 ± 0.12 μm). Desmosomes were found in acinar, myoepithelial, and ductal cells but they were smaller and fewer than those in covering epithelia. These results may suggest that (a) the permeability barrier at the level of sublingual acini is relatively “leaky” (acinar cells can transfer electric signals and small molecules to other acinar as well as myoepithelial cells along their abundant gap junctions) and (b) no such intercellular communication exists in ducts, which are also “tight” in relation to transepithelial permeability.

Ultrastructure and distribution of intercellular junctions in corneal endothelium: by O.P. Ottersen and T. Vegge. Acta Ophthalmol 55: 69–78, 1977

Ultrastructure and distribution of intercellular junctions in corneal endothelium: by O.P. Ottersen and T. Vegge. Acta Ophthalmol 55: 69–78, 1977

The distribution of intercellular junctions in the developing myotomes of the clawed toad.

The distribution of intercellular junctions between premyotomal and myotomal cells of Xenopus embryos has been described. Intermediate junctions, gap junctions, and small desmosomes are found between unsegmented mesoderm cells. In the region of myotome formation gap junctions appear to be absent, although close appositions of cell membranes are found. Both gap and intermediate junctions are numerous between cells of the segmented myotomes; they occur within the myotomes close to the myosepts and at interdigitations between the myotomes across the myosepts. Gap junctions between the myotomes are found in embryos that have hatched and can swim. The observed distribution of gap junctions is correlated with physiological data on electrical coupling. Electrical connections via gap junctions may produce contraction of the axial musculature remote from motor innervation.

Intercellular junctions in human ependymomas.

The ultrastructure and distribution of intercellular junctions in 5 human ependymomas of the fourth ventricle are described. The most common form was the simple apposition of cells with a cleft, about 200 A wide, between their cell membranes. The zonula adhaerens was predominant in cells near microvilli which were present along a widened intercellular space. Another specialized intercellular junction, the zonula occludens, was met less frequently than the zonula adhaerens. The zonula occludens occurred mainly near the zonulae adhaerentes. Occasionally, a cytoplasmic plaque as seen in the zonula adhaerens was closely applied to the cell membrane in the zonula occludens. The zonulae adhaerens and occludens were frequent in well differentiated ependymomas but much less so in poorly differentiated ependymomas. The zonula occludens was often absent in the poorly differentiated tumour. The distribution of the zonula occludens is discussed on the physiological basis of a marked difference in function of the intercellular communicating system of normal and malignant cells.