HEXOSE-MONOPHOSPHATE SHUNT RESPONSE TO DIAMIDE IN COMPONENT LAYERS OF CORNEA

Hexose-monophosphate shunt (HMS) activity was studied in whole cornea and in each of its component layers. Activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase suggest the presence of an active HMS in epithelium and endothelium, though the presence of lower endothelial activities indicates that the HMS could be less active in this layer. Studies using selectively labelled glucose demonstrate the HMS to be the major pathway of 14CO2 generation from glucose in the epithelium, accounting for 66% of all 14CO2 evolved. While total endothelial 14CO2 generation is comparable to that of the epithelium, the HMS accounts for only 37% of this total in endothelium. Diamide increases both total labelled CO2 evolution and the percent contribution of the HMS to this total. This response is dose dependent and is seen in each of the cornea's component layers. The greatest response is seen in the endothelium where the percent contribution of the HMS rises from a control value of 37 to 87 in 0.4 mm-diamide. This reserve shunt capacity of the endothelium could provide a powerful means of handling oxidative stress. © 1978.