Dexamethasone inhibits trabecular cell retraction.

Glucocorticosteroids such as dexamethasone (Dex) are known to cause an increased resistance to aqueous outflow in the intact and cultured eye. We investigated whether Dex treatment of cultured endothelial or trabecular meshwork (TM) cells might interfere with the cell separations and retraction induced by the facility-enhancing agents ethacrynic acid (ECA), cytochalasin B and the calcium chelator EGTA. Our hypothesis was that Dex-induced changes in the response of our model cells in vitro might serve as a paradigm for those produced in the cells of the outflow pathway, perhaps through influencing the changing dimensions of the pathway for aqueous humor through the juxtacanalicular tissue and/or inner wall of Schlemm's canal. We treated calf pulmonary artery endothelial (CPAE) and human and porcine TM cells with Dex (1-100 microns, 1-9 days), and then assessed monolayer and cytoskeletal integrity by immunofluorescence microscopy for tubulin and direct fluorescence staining for F-actin after exposure to the agents named above. We found that Dex-pretreated CPAE and TM cells gradually (over 5-7 days) became refractory to the effects of both ECA and EGTA, but not to cytochalasin B. Despite the preservation of general cell shape and attachment after ECA in Dex-treated cells, microtubule disruption still took place as in controls. Dex-treated cells also demonstrated a reorganization of filamentous actin staining after ECA and EGTA. Combination experiments of ECA and EGTA in Dex-treated cells suggested that the Dex effects were due to a greater strength of cell-to-cell and cell-to-substrate attachment, possibly due to interference with the normal cellular signaling required for coordinated cellular retraction and junctional disruption.