Intercellular junctions

Classical and desmosomal cadherins are constituents of different types of intercellular junctions. E-cadherin, the classical cadherin of epithelial cells, is part of the adherens junction (zonula adherens), which is attached to a belt of actin via the catenins. As the name says, desmosomal cadherins are part of the desmosomes, which are rivet-like structures that make focal connections between cells. Desmosomes are characterized by a... 

Fig. 10. Intercellular junction zones of carrot cells grown in suspension have been observed in electron microscopy after immunogold labeling with the 2F4 antibody, (a) no treatment of the sections prior to labeling the gold particles are restricted to the center of the junction zones (b) enzymatic (pectin methyl esterase) deesterification of the E.M. grids before labeling the deesterified pectins present in the primary walls now bind the probe. Scale bars = 1 pm.

The structure of the blood capillary wall is complex and varies in different organs and tissues. It consists of a single layer of endothelial cells joined together by intercellular junctions. Each endothelial cell, on an average, is 20-40 pm long, 10-15 pm wide, and 0.1-0.5 pm thick, and contains 10,000-15,000 uniform, spherical vesicles called plasmalemmal vesicles. These vesicles range in size between 60 and 80 nm in diameter. About 70% of these vesicles open on the luminal side of the endothelial surface, and the remaining open within the cytoplasm. Plasmalemmal vesicles are believed to be involved in the pinocytic transport of substances across the endothelium. The transition time of pinocytic vesicles across the cell is... 

Similar to blood capillaries, the lymphatic capillaries consist of a single layer of endothelial cells joined together by intercellular junctions. The diameter of small pores is 12 nm, whereas large pores range between 50 and 70 nm. The rate of formation of lymph depends on the hydrostatic pressure of blood and the... 

Figure 6 An electron micrograph of intercellular junctions between two human colon Caco-2 cells in culture. D, desmosome LS, lateral space mv, microvilli ZA, zonula adherens ZO, zonula occludens (i.e., tight junction). Bar equals 200 nm.

Figure 7 (A) Spatial orientation of intercellular junctions within an epithelial cell mono-...

Human tears contain 0.5-1.1 mM Ca2+ [215], which may be the source of extracellular calcium for maintaining the integrity of the corneal and conjunctival intercellular junctions. Indeed, chelation of extracellular Ca2+ with 0.5% EDTA reduced transcorneal and transconjunctival resistance by 80 and 65%, respectively (Kompella, Kim, and Lee, unpublished observation). In 1991, Rojanasakul... 

Skeletal and cardiac muscles also have important differences. Skeletal muscle cells are elongated and run the length of the entire muscle furthermore, these cells have no electrical communication between them. Cardiac muscle cells, on the other hand, branch and interconnect with each other. Intercellular junctions found where adjoining cells meet end-to-end are referred to as intercalated discs. Two types of cell-to-cell junctions exist within these discs. Desmosomes hold the muscle cells together and provide the structural support needed when the heart beats and exerts a mechanical... 

Pappenheimer, J. R., Reiss, K. Z., Contribution of solvent drag through intercellular junctions to absorption of nutrients by the small intestine of the rat,/. Membr. Biol. 1987, 300, 123-136. 

Schnittler HJ. Structural and functional aspects of intercellular junctions in vascular endothelium. Basic Res Cardiol 1998 93 30-39. 

Hirakawa, H., Okajima, S., Nagaoka, T., Takamatsu, T. and Oyamada, M. Loss and recovery of the blood-nerve barrier in the rat sciatic nerve after crush injury are associated with expression of intercellular junctional proteins. Exp. Cell Res. 284 196-210,2003. 

Ehrhardt C, Kneuer C, Fiegel J, Hanes J, Schaefer UF, Kim KJ, Lehr CM (2002) Influence of apical fluid volume on the development of functional intercellular junctions in the human epithelial cell line 16HBE14o- Implications for the use of this cell line as an in vitro model for bronchial drug absorption studies. Cell Tissue Res 308(3) 391-400. 

Martin-Padura I, Lostaglio S, Schneemann M, Williams L, Romano M, Fruscella P, Panzeri C, Stoppacciaro A, Ruco L, Villa A, Simmons D, and Dejana E [1998] Junctional adhesion molecule, a novel member of the immunoglobulin superfamily that distributes at intercellular junctions and modulates monocyte transmigration. J Cell Biol 142 117-127... 

Stuart RO, Sun A, Bush KT, and Nigam SK [1996] Dependence of epithelial intercellular junction biogenesis on thapsigargin-sensitive intracellular calcium stores. J Biol Chem 271 13636-13641... 

Caco-2 cells cultured on filters achieve a monolayer density, and exhibit morphological characteristics similar to enterocytes such as tight intercellular junctions and highly developed microvilli.13-15,42 Transport of drugs across Caco-2 monolayers is limited by the action of biochemical and physical barriers (Figure 9.2). The biochemical component comprises drug-metabolizing enzymes, uptake transporters, and efflux transporters.17,19-23,28,30 The... 

This permeability barrier shows selectivity in that small hydrophobic molecules can partition into and diffuse across the lipid bilayer of the cell membrane, whereas small hydrophilic molecules can only diffuse between cells (i.e., through the intercellular junctions). In addition, the presence of uptake and efflux transporters complicates our ability to predict intestinal permeability based on physicochemical properties alone because transporters may increase or decrease absorptive flux. The complexity of the permeability process makes it difficult to elucidate permeability pathways in complex biological model systems such as animals and tissues. For this reason, cultured cells in general, and Caco-2 cells in particular, have been used extensively to investigate the role of specific permeability pathways in drug absorption. 

Exposure to histamine [10 pM for 30-45 minutes recovery (in the presence of histamine) after 90 minutes] specifically blocks the uptake of 5-methyltetra-hydrofolate, a substance that is used to study potocytosis/caveolae uptake (48,64). Histamine might also be used to increase the permeability of the endothelium binding of histamine to its receptor leads to the contraction of the cytoskeleton and to the opening of intercellular junctions (65). 

Paracellular, in which the passage of drug occurs through intercellular junctions of the mucosa. The paracellular flux of drug molecules usually does not depend on the partition coefficient. 

The existence of tissues implies that some cohesive force or stracture holds the constituent cells together. In some cases, this also provides communication between cells to achieve coordination within the tissue. There are three classes of such intercellular junctions ... 

The arteriolar dilation produced by kinins causes an increase in pressure and flow in the capillary bed, thus favoring efflux of fluid from blood to tissues. This effect may be facilitated by increased capillary permeability resulting from contraction of endothelial cells and widening of intercellular junctions, and by increased venous pressure secondary to constriction of veins. As a result of these changes, water and solutes pass from the blood to the extracellular fluid, lymph flow increases, and edema may result. 

Hoyt RH, Cohen ML, Corr PB, Saffitz JE Alterations of intercellular junctions induced by hypoxia in canine myocardium. Am J Physiol 1990 258 H1439-H1448. 

Hoyt RH, Cohen ML, Saffitz JE Distribution and three-dimensional structure of intercellular junctions in canine myocardium. Circ Res 1989 64 563-574. 

Mazet F, Wittenberg BA, Spray DC Fate of intercellular junctions in isolated adult rat cardiac cells. Circ Res 1985 56 195-204. 

Neyton J, Trautmann A Single channel curents of an intercellular junction. Nature 1985 317 331-335. Neyton J, Trautmann A Acetylcholine modulation of the conductance of intercellular junctions between... 

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