INCOMPLETE BELTS OF TIGHT JUNCTIONS IN CULTURED NONPIGMENTED HUMAN CILIARY EPITHELIAL-CELLS

Tight junctions of cultured human non-pigmented ciliary epithelial cel ls were studied with the freeze-fracture technique and related to the transepithelial electrical resistance of these monolayers. Isolated ti ght junctional fibrils or small groups and networks of tight junctions sometimes associated with gap junctions were revealed in freeze-fract ure images of the lateral plasma membrane. The tight junctions always formed incomplete belts, so that the apical and basolateral plasma mem brane domains often were in continuity without morphological evidence of interposed intercellular junctions. The monolayers revealed a trans epithelial resistance of 19.7 +/- .2.1 Ohm.cm(2). Protamine induced a reversible increase of the transepithelial resistance of the cultures by 91 +/- 12%, but still the tight junctions formed incomplete belts. We conclude that contrary to complete networks of tight junctions in n ative non-pigmented ciliary epithelium, cultured monolayers only expre ss incomplete belts of tight junctions which may be the morphological correlate of the relatively low transepithelial resistance of these mo nolayers. Interpretations on transepithelial transport and permeabilit y characteristics of these cultures have to take into account the diff erences in junctional morphology from their native epithelium.