EFFECT OF ELEVATED AMBIENT GLUCOSE UPON POLYPHOSPHOINOSITIDE TURNOVER IN BOVINE RETINAL ENDOTHELIAL-CELLS AND RAT ASTROCYTES

We investigated the turnover of polyphosphoinositides in bovine retinal microvascular endothelial cells and rat astrocytes cultured in the presence of high ambient concentrations of glucose in order to study the possible involvement of this pathway in the pathogenesis of diabetic retinopathy. A 35-45% decrease in the amount of 32P incorporated into phosphatidylinositol(4)phosphate (PIP) and phosphatidylinositol(4,5)biphosphate (PIP2) occurred in rat astrocytes but not bovine retinal endothelial cells grown for 14±3 days in a medium with an elevated (28 mm) glucose concentration. Incorporation of 32P into phosphatidylinositol, phosphatidylcholine, phosphatidylserine and phosphatidylethanolamine was not altered by these conditions. A 39-45% decrease in 32P incorporated into PIP PIP2 was also found in rat astrocytes grown in 28 mm glucose which were detergent solubilized and incubated with [32P]ATP. Exposure to elevated concentrations of glucose decreased the amount of PIP PIP2 cleaved by ionomycin or fluoroaluminate treatment, but did not disturb phospholipase C activity. Thus, the lower level of PIP PIP2 induced by exposure to elevated concentrations of glucose, appears due to changes in phospholipid substrate levels, or polyphosphoinositide kinase activity, rather than a decrease in ATP levels or phospholipase C activity. These result suggest that high ambient glucose levels alter second-messenger generation by astrocytes. In turn, cellular interactions dependent upon these second messengers and important for maintenance of normal microvessel function in the retina may be disrupted. © 1992.