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 ey e. We investigated whether Dex treatment of cultured endothelial or tr abecular meshwork (TM) cells might interfere with the cell separations and retraction induced by the facility-enhancing agents ethacrynic ac id (EGA), cytochalasin B and the calcium chelator EGTA. Our hypothesis was that Dex-induced changes in the response of our model cells in vi tro might serve as a paradigm for those produced in the cells of the o utflow 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 en dothelial (CPAE) and human and porcine TM cells with Dex (1-100 mu m, 1-9 days), and then assessed monolayer and cytoskeletal integrity by i mmunofluorescence microscopy for tubulin and direct fluorescence stain ing for F-actin after exposure to the agents named above. We found tha t Dex-pretreated CPAE and TM cells gradually (over 5-7 days) became re fractory 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 f ilamentous actin staining after ECA and EGTA. Combination experiments of ECA and EGTA in Dex-treated cells suggested that the Dex effects we re due to a greater strength of cell-to-cell and cell-to-substrate att achment, possibly due to interference with the normal cellular signali ng required for coordinated cellular retraction and junctional disrupt ion. (C) 1996 Academic Press Limited