Incomplete belts of tight junctions in cultured non-pigmented human ciliary epithelial cells.

Tight junctions of cultured human non-pigmented ciliary epithelial cells were studied with the freeze-fracture technique and related to the transepithelial electrical resistance of these monolayers. Isolated tight junctional fibrils or small groups and networks of tight junctions sometimes associated with gap junctions were revealed in freeze-fracture images of the lateral plasma membrane. The tight junctions always formed incomplete belts, so that the apical and basolateral plasma membrane domains often were in continuity without morphological evidence of interposed intercellular junctions.

Tight junctions and paracellular permeability in cultured bovine corneal endothelial cells.

Intramembrane specializations of cultured bovine corneal endothelial cells were studied with thin section and freeze-fracture electron microscopy and related to the paracellular permeability and the transendothelial resistance (Rt) of the monolayers. The following intercellular junctions were found: single and discontinuous networks of tight junctions (TJ) which girdle the apico-lateral cell perimeter incompletely, gap junctions, and membrane undulations suggesting intermediate junctions. The macromolecular tracer ruthenium red penetrated into the lateral intercellular space beyond the level of the incomplete belt of TJ.

Tight junctions of the human corneal endothelium: morphological and electrophysiological features.

The corneal endothelium controls the hydration and nutrition of the avascular corneal stroma. To analyze the role of the tight junctions (TJ) for these functions, we examined human corneal endothelium by thin-section and freeze-fracture electron microscopy and by impedance analysis. On thin sections, tannic acid was seen to mark the external leaflet of the lateral plasma membrane also beyond the location of the TJ, indicating a significant macromolecular porosity of the TJ.

Human epidermal Langerhans cells express beta 1 integrins that mediate their adhesion to laminin and fibronectin.

Members of the beta 1 or very late antigen (VLA) integrin family represent the predominant class of integrin extracellular matrix receptors. Adhesion assays were developed for the identification of the beta 1 integrins involved in the adhesive interactions between Langerhans cells (which mainly express alpha 4 beta 1, alpha 5 beta 1, and alpha 6 beta 1) and extracellular matrix proteins. For this purpose, binding assays were performed on fibronectin-, laminin-, collagen type IV-, and collagen type I-coated plates.

Identification of specific human epithelial cell integrin receptors as VLA proteins.

Cell adhesion to extracellular matrix is mediated by a set of heterodimeric cell surface receptors called integrins. We have examined the expression of the very late antigens or alpha beta 1 group of integrins in human epithelial cells. The six known members of this group share a common beta 1 subunit but have distinct alpha subunits that confer selective affinity toward collagen, fibronectin, and laminin essentially.