REGULATION OF GLUCOSE-TRANSPORTER (GLUT-3) AND ALDOSE REDUCTASE MESSENGER-RNA IN BOVINE RETINAL ENDOTHELIAL-CELLS AND RETINAL PERICYTES IN HIGH GLUCOSE AND HIGH GALACTOSE CULTURE

The regulation of GLUT-3 and aldose reductase mRNA in retinal endothel ial cells and retinal pericytes was studied in response to variations in the extracellular concentration of hexoses. In physiological concen trations of glucose (5 mmol/l), an increase in the level of GLUT-3 mRN A was observed in cultured cells compared to the level of mRNA found i n the absence of glucose. In contrast, there was little change in the level of GLUT-3 mRNA when the cells were cultured in the presence of 5 mmol/l galactose. In high concentrations of glucose, there was a decl ine in GLUT-3 mRNA indicating that the GLUT-3 mRNA is regulated by the extracellular concentration of glucose. In contrast, at both 5 mmol/l and 25 mmol/l glucose, the level of aldose reductase mRNA was increas ed. Furthermore, there were differences in the magnitude of the increa se of aldose reductase mRNA between bovine retinal pericytes and bovin e retinal endothelial cells with a greater increase being observed in the pericytes. We propose that this demonstration of a facilitative gl ucose transporter system within retinal cells, and in particular the s pecific response to different hexoses and the known distinct kinetic p arameters of the transporter system in specific cell types, highlights the heterogeneity of hexose transport mechanisms in retinal cells. Th us, hypergalactosaemia as a model system for the study of diabetic ret inopathy should be used with caution.