Organization of cell junctions in the peritoneal mesothelium

Abstract

Intercellular junctions in the mesothelium of the visceral (mesentery and omenturn), and parietal (diaphragm, pre-aortic, and iliac region) peritoneum were examined in rats and mice by using freeze-cleaved preparations. In addition to usual intercellular junctions (cell body junctions), special junctions are found between cell processes and the surface of the neighboring cell (cell process junctions). Cell body junctions are provided with tight junctions and communicating (gap) junctions. The former consist of one to two junctional strands which show a characteristic staggered arrangement, and focal discontinuities. In cell process junctions, the strands form loops or appear as short, free-ending elements; their polymorphism suggests considerable lability, probably in connection with their assembly and disassembly. The existence of free-ending strands indicates that such structures can be used as attachment devices without being concomitantly involved in the formation of occluding zonules. In both types of junctions, the strands can be resolved into bars, -80-100 nm long, frequently provided with terminal enlargements and intercalated particles which occur singly or in small clusters. These particles are morphologically similar to those present in communicating (gap) junctions. The mesothelium is also provided with isolated composite macular junctions. Throughout the mesothelium, the cleavage plane follows the outer contour of junctional strands and particles, suggesting that strand-to-strand interactions in the apposed membranes are weaker than interactions between each strand and underlying cytoplasmic structures. In their general geometry and cleavage characteristics, the mesothelial junctions resemble the junctions found in the venular endothelium.Earlier interest in the mechanisms of transport of solutes (3,5,6,8,21,9,32), particulate material (12, 10, 16), and cells across the mesothelium has been recently renewed after the success of peritoneal dialysis as a maintenance technique in chronically uremic patients (7, 23). Despite past investigations, current views concerning the structural substrate of the high permeability of the mesothelial membrane are still markedly divergent. According to a number of studies, water-soluble toolecules cross the mesothelium by passive diffusion presumably along intercellular junctions (5, 21,9, 12, 13, 10), whereas according to other investigations transport across the mesothelium is an active process (35, 32) effected primarily via vesicles (30,42,19,17). These divergent views have broader implications than are immediately apparent, since it has been postulated that the mesothelium, due to its being morphologically and functionally similar to the vascular endothelium, can

Formation of Tight and Gap Junctions in the Inner Enamel Epithelium and Preameloblasts in Human Fetal Tooth Germs

“…Perhaps, this kind of tight junction formation process is a general phenomenon in mammalian epithelial cell development. As has been noted previously by other authors [Simionescu and Simionescu, 1977;Okamoto and Ishimura. 1978;Yan cey cr al., 1979;Minutli et al.…”

A comparative study on the intercellular canalicular system and intercellular junctions in the pancreatic islets of some rodents.

“…A typical zonula occludens in the epithelium encircles the cytoplasm containing abundant felt work of cytoskeletal elements just beneath the cell apex bearing microvilli. Maculae occludentes on peritoneal mesothelial cells (SIMIoNEscu and SIMIoNEscu, 1977) and chorionic trophoblasts (BARTELS and WANG, 1983) are present on the lateral cell membrane near the microvillous free surface.…”

“…As in a previous report (KATAOKA et al, 1982), we prefer the term, macula occludens, to distinguish it from the zonula occludens, the typical belt-like tight junction in the epithelium. In addition to the pancreatic islet cells (ORCi and PERRELET, 1977;KATAOKA et al, 1982), the presence of the macula occludens has been reported on adrenocortical cells (FRIEND and GILULA, 1972), peritoneal mesothelial cells (SIMIONESCu and SIMIONESCU, 1977), renomedullary interstitial cells (MAJACK and LARSEN, 1980), neuroepithelial cells during amphibian neurulation (DECKER and FRIEND, 1974), developing thyroid cells in the chick embryo (ISHIMURA and FUJITA, 1979), chorionic trophoblasts (BARTELS and WANG, 1983) and in the pancreatic acinar cell tumor (IwANIJ et al, 1982).…”

Intersectin‐1s: An Important Regulator of Cellular and Molecular Pathways in Lung Injury

“…There will be no increase in permeability without the rearrangement of the tight junctional complex, located most apically in all endothelial cells and in some parts of the vascular tree (arteries and capillaries); in some specific vascular beds (brain, testis), tight junctional complexes can be found in more than one location along the inter-endothelial space. 53,[96][97][98] Endothelial participation and the mechanisms involved in exacerbated vascular permeability in ALI have been extensively reviewed. 84,94 In pathological conditions, dysfunctional endothelial cells show impaired caveolae and clathrincoated vesicle endocytosis and altered intracellular trafficking and signaling of cell surface receptors such as transforming growth factor beta receptor (TGFβR) and bone morphogenetic protein receptor-2 (BMPR2), both implicated in the pathogenesis of ALI/ARDS.…”