Occluding junctions in a cultured transporting epithelium: Structural and functional heterogeneity

Abstract

MDCK cells (epithelioid of renal origin) form monolayers which are structurally and functionally similar to transporting epithelia. One of these similarities is the ability to form occluding junctions and act as permeability barriers. This article studies the junctions of MDCK monolayers formed on a permeable and transparent support (a disk of nylon cloth coated with collagen) by combining two different approaches: (i) Scanning of the electric field: the disk is mounted as a flat sheet between two Lucite chambers and pulses of 20--50 microA cm-2 are passed across. The apical surface of the monolayer is then scanned with a microelectrode to detect those points where the current is flowing. This shows that the occluding junctions of this preparation are not homogeneous, but contain long segments of high resistance, intercalated with sites of high conductance. (ii) Freeze fracture electron microscopy: the junctions are composed of regions of eight to ten strands intercalated with others where the strands are reduced to one or two ridges. The sites of high conductance may correspond to those segments where the number of junctional strands is reduced to 1 or 2. It is concluded that the occluding junctions of MDCK monolayers are functionally and morphologically heterogeneous, with "tight" regions intermixed with "leaky" ones.

Oxidants increase paracellular permeability in a cultured epithelial cell line.

“…Several aspects of our studies suggest that oxidants increased the permeability of this pathway. First, oxidants increased the transepithelial electrical conductance in an epithelium in which the predominant transepithelial conductive pathway is paracellular (10,12,13). Second, oxidants increased the permeability of the epithelium to mannitol, which predominately crosses the epithelium via an extracellular route (15,18).…”

“…We chose the cultured renal epithelial cell line, Madin-Darby Canine Kidney (MDCK),' for this study, because: (a) its barrier function has been extensively characterized in our and other laboratories (10)(11)(12); (b) the cultured epithelium has an intact tight junction structure with a transepithelial electrical conductance (GJ) low enough to make measurements accurate and reproducible in a given monolayer, (c) the paracellular pathway is the predominant conductive pathway (10,12,13); (d) the study of a cultured epithelium eliminates the potential problem of participation of nonepithelial cells in any response; and (e) the epithelium is widely available and easily cultured.…”

Cell Adhesion, Polarity, and Epithelia in the Dawn of Metazoans

“…This approach gave us an opportunity to study the development of the transporting epithelia phenotype. Thus we used it to study the synthesis, assembly, and sealing of tight junctions (TJs) (69,74,75,78,145,183,297), as well as the polarity of Na ϩ -K ϩ -ATPase (61,62,96,102); Enrique Rodriguez-Boulan introduced the use of viruses that bud either apically (e.g., Flu) or basolateraly (e.g., stomatitis) to track the fate of specific proteins during apical or basolateral polarity (283, 284, 379 -382), and Carlos A. Rabito analyzed the onset of polarized cotransporters (368,370,371). M. Taub perfected the approach by developing totally defined culture media (440 -442), and complementary procedures were refined to open and reseal the TJs by removing and restoring Ca 2ϩ (69,97,101,184,186), follow the cascades of phosphorylation involved (20,21,85), the role of the cytoskeleton (311, 312), the participation of protein synthesis and sorting (196,376,379,381), the polarized distribution of ion channels (317,359,360,361,421,439), the involvement of E-cadherin (199 -201), the effect of agents that induce differentiation (280), and the vectorial movement of receptors (302).…”

The interaction of Trichomonas vaginalis and Tritrichomonas foetus with epithelial cells in vitro.

“…However, in vitro these cell lines do not exhibit a behaviour similar to that observed in a true epithelium. An epithelial cell line useful for studies on the parasite-cell interaction, such as those reported for Entamoeba histolytica (28) and Giardia lamblia (7), is the Madin-Darby canine kidney cell line (MDCK), whose electrical properties (5), morphology (29), metabolic aspects (6,18) and general behaviour on culture vessels (26), are well characterized.…”