THE EFFECTS OF ELEVATED GLUCOSE ON NA+ K+-ATPASE OF CULTURED BOVINE RETINAL-PIGMENT EPITHELIAL-CELLS MEASURED BY A NEW NONRADIOACTIVE RUBIDIUM UPTAKE ASSAY/

The effects of simulated hyperglycemia on the Na+/K+-ATPase activity o f cultured bovine retinal pigment epithelial (RPE) cells were investig ated. Total Rb+ uptake, measured by a chromatographic method, was decr eased 20-30% by 55.5 mM glucose relative to 5.55 mM glucose for cultur e periods of 2 to 28 days. An acute hyperglycemic stress (<1 week) had no effect on ouabain inhibition of Rb+ uptake or ouabain binding to R PE cells (IC50 = 55 nM for both processes) and did not alter the IC50 value (near 10 nM) for binding of strophanthidin, another selective Na +/K+-ATPase inhibitor. A small increase in the apparent K-m of Rb+ for Na+/K+-ATPase accompanied the decrease in maximal Rb+ uptake at 55.5 mM glucose. The continuous presence of AL-1576, an aldose reductase in hibitor (ARI), normalized the effect of severe hyperglycemia on Rb+ up take in the chronic (28 days) but not the acute exposure protocols. Th us, decreased efficiency of Na+/K+-ATPase caused by chronic accumulati on of intracellular sorbitol can account for previously reported funct ional and structural alterations in the RPE cell layer of diabetic rod ents. The results of the present study suggest that hyperglycemia-indu ced loss of Na+/K+-ATPase function in RPE cells, which responds to ald ose reductase inhibitor treatment, contributes to the pathogenesis of diabetic retinopathy.