Dibutyryl cyclic adenosine monophosphate and forskolin alter the paracellular pathway in cultured corneal endothelial cells.

Purpose. This study describes the effects of the cyclic adenosine monophosphate (cAMP) pathway on the tightjunctional barrier of the corneal endothelium, which plays a critical role in maintaining the corneal stroma in an underhydrated, transparent state. Methods. Subcultured bovine corneal endothelial cells grown on filters were used to study the effects of dibutyryl-cAMP and forskolin on transendothelial electrical resistance and [ 3 H]i-nulin flux. The tight junction-associated protein ZO-1 (zonula occludens protein-1) and F-actin were visualized by indirect immunofluorescence, and the ultrastructural organization of junctional complexes was studied by freeze-fracture electron microscopy. Results. Cells formed a continuous monolayer of closely apposed hexagonal-type cells separated by a discontinuous belt of tight junctions with a transendothelial electrical resistance of 20.8 ± 0.6 Ω. cm 2 . Dibutyryl-cAMP (10 -4 M) and forskolin (10 -5 M) increased cell cAMP, significantly decreased the transendothelial resistance by 54% and 43%, respectively, and increased the flux of [ 3 H]inulin from the apical to the basal side of the cells by 56% and 40%, respectively. Both agents also induced condensation of F-actin at the cell borders without any marked changes in the immunostaining of ZO-1 that delineated cell peripheries. However, freeze-fracture studies showed that dibutyryl-cAMP and forskolin induced dispersion of the tight junction network. Conclusions. These data suggest that activation of the cAMP-dependent pathway, leading to structural changes of the tightjunctional network, may modulate the passive fluxes mediated by the paracellular pathway of the corneal endothelial barrier.