Biomedical Engineering Reference
In-Depth Information
Figure 2
Schematic drawing of the specialized junctions of columnar epithelial
cells. The junctional complex includes the tight junction, the adherens junction,
and the desmosome. The desmosomes occur more as plaques, rather than as a band.
Gap junctions can be located elsewhere. Hemidesmosomes strengthen attachment to
the basement membrane. (Adapted from Ref. 245.)
The tight junction has several key roles in the biology of the airway.
One of its roles is to form a barrier to water and solute. One of the measures
of tight junction performance is the transepithelial electrical resistance
measurement (40). The tight junction is composed of a membrane protein,
occludin, and cytoplasmic proteins, ZO-1 and ZO-2, claudins, JAM (junc-
tion-associated membrane protein), cingulin, and others (41,42). Another
role for tight junctions may be to demarcate the boundary between the apex
of the cell and basolateral portions of polarized cells. Tight junctions thus
separate the external lipid layer of the cell membrane of the apex of the cell
from the basolateral cell membrane. This is crucial in maintaining polarized
function of epithelia. The function of tight junctions is modified by Ca2
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cAMP, and protein kinase C (PKC) (43). Alterations in claudins can affect
tight junction barrier function (44) and this has been suggested as a pathway
for fatty acid-induced edema formation in an in vivo experimental model
(45).
The adherens junction is a special structure that is somewhat ana-
logous to the focal adhesion described later in this chapter. The adherens
junction serves to anchor the cell-cell junction to the actin cytoskeleton
and contains a collection of molecules including the alpha-, beta-, and
