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

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Abstract

PURPOSE: This study describes the effects of the cyclic adenosine monophosphate (cAMP) pathway on the tight junctional 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 [3H]inulin 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 omega.cm2. 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 [3H]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 tight junctional network, may modulate the passive fluxes mediated by the paracellular pathway of the corneal endothelial barrier.