Freeze-fracture examination of cultured human trabecular meshwork cells: effect of dexamethasone

Glucocorticoids can alter the trabecular meshwork in the aqueous outflow pathway of the eye leading to the development of ocular hypertension and glaucoma. Previous studies have shown biochemical and ultrastructural changes in cultured human trabecular meshwork (TM) cells treated with dexamethasone (DEX). In order to assess how the membranes of these treated cells were responding to this glucocorticoid, we compared DEX-treated and control TM cells using the freeze-fracture technique. Human TM cells were grown to confluence on either Millipore HA filter inserts or glass coverslips and then treated for 14 days with or without 0.1 microM dexamethasone. The cell cultures were then aldehyde fixed and prepared for electron microscopy and freeze-fracture. Junctional complexes in control and DEX-treated cells consisted of gap junctions of various shapes and sizes. No tight junctional complexes were apparent in either control or DEX-treated cells. The majority of vesicle fusion sites on the control cells appeared to be randomly distributed and were few in number. In contrast, DEX-treated cells had a significantly greater density of fusion sites, and the majority of the vesicles were aligned into linear arrays. These findings support our previous findings of increased secretory activity in DEX-treated cultured human TM cells. These in vitro model system data appear to correlate with previous in vivo biochemical, ultrastructural and freeze-fracture data.