Previous studies from this laboratory have shown that bovine and human trabecular meshwork cells (TMC) possess a highly active Na-K-Cl cotransport system that serves to regulate TMC intracellular volume. TMC v.)lume, in turn, is hypothesized to influence the resistance of the trabecular meshwork to aqueous humor outflow from the anterior chamber into the Canal of Schlemm. Dexamethasone, an agent that can induce glaucoma, has been found to induce an increase in outflow resistance through the trabecular meshwork. The present study was conducted to investigate the hypothesis that alteration of Na-K-Cl cotransport activity may play a role in steroidinduced glaucoma. To do this, the acute effects of dexamethasone (DEX) on Na-K-Cl cotransport activity and expression were evaluated. Cultured TM cell monolayers were exposed to DEX (10-8 to 10-6M) for either 24 or 48 hours, then evaluated for Na-K-Cl cotransport activity and also the amount of cotransporter protein present. Cotransport activity was assessed as bumetanide-sensitive K influx. Expression of cotransport protein was evaluated by Western blot analysis of TMC membrane preparations using a monoclonal antibody to the T84 epithelial cell Na-K-Cl cotransporter. We found that exposure of bovine and human TM cells to DEX for 24 or 48 hours increased Na-K-Cl cotransport activity approximately 1.5-fold. This effect was observed at 10 8 M DEX as well as at higher concentrations. In addition, exposure of TMC to DEX ( 10-6 to IO-8M) for 24 or 48 hours caused notable increases in the level of Na-K-Cl cotransport protein relative to control cells. Our findings suggest that DEX may exert its effect on outflow resistance, at least in part, through an increase in Na-K-Cl cotransport activity.
|Original language||English (US)|
|State||Published - 1996|
ASJC Scopus subject areas
- Agricultural and Biological Sciences (miscellaneous)
- Biochemistry, Genetics and Molecular Biology(all)
- Cell Biology