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  • 1
    ISSN: 1432-1424
    Keywords: Key words: Epithelia — Cell/cell junctions — Tight junctions — Apical/basolateral polarity — Transepithelial electrical resistance — Lipid composition — Occludin — Paracellular
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Tight junctions (TJs) are cell-to-cell contacts made of strands, which appear as ridges on P faces and complementary furrows on E faces on freeze fracture replicas. Evidences and opinions on whether these strands are composed of either membrane-bound proteins or lipid micelles are somewhat varied. In the present work we alter the lipid composition of Madin-Darby canine kidney monolayers using a novel approach, while studying (i) their transepithelial electrical resistance, a parameter that depends on the degree of sealing of the TJs; (ii) the apical-to-basolateral flux of 4 kD fluorescent dextran (JDEX), that reflects the permeability of the intercellular spaces; (iii) the ability of TJs to restrict apical-to-basolateral diffusion of membrane lipids; and (iv) the pattern of distribution of endogenous and transfected occludin, the sole membrane protein presently known to form part of the TJs. We show that changing the total composition of phospholipids, sphingolipids, cholesterol and the content of fatty acids, does not alter TER nor the structure of the strands. Interestingly, enrichment with linoleic acid increases the JDEX by 631%. The fact that this increase is not reflected in a decrease of TER, suggests that junctional strands do not act as simple resistive elements but may contain mobile translocating mechanisms.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1424
    Keywords: Ouabain-resistance ; Epithelia ; Ma104 cells ; MDCK cells ; Tight junctions ; Na+, K+-ATPase ; K+ content ; Metabolic cooperation ; Cell attachment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Ma104 cells (renal, epithelial) have a peculiar way of resisting ouabain: their Na+,K+-pumps bind the drug with high affinity, cellular K+ is lost and cell division arrested, but cells do not detach as most cell types do. Then, if up to 4 days later the drug is removed, Ma104 cells recover K+ and resume proliferation (Contreras et al., 1994). In the present work, we investigate whether Ma104 cells are able to protect ouabain-sensitive MDCK cells in co-culture. The main finding is that they do, but in this case protection is not elicited by the usual mechanism of maintaining the K+ content of neighboring cells through cell-cell communications. Ma104 cells treated with ouabain simply remain attached to the substrate and to their MDCK neighbors, and both cells lose K+. This attachment includes tight junctions, because the transepithelial electrical resistance of the monolayers is not abolished by ouabain. Although the β-subunit of the Na+,K+-ATPase is known to possess molecular characteristics of cell-cell attachment molecules, attachment between Ma104-MDCK cells does not seem to be mediated by this enzyme, as immunofluorescence analysis reveals that Na+,K+-ATPase is only inserted in the plasma membrane facing a neighboring cell of the same type.
    Type of Medium: Electronic Resource
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