Metabolic and morphologic changes in the corneal endothelium: The effects of potassium cyanide, iodoacetamide, and ouabain

The metabolic pathways of glycolysis and mitochondrial respiration in the corneal endothelial cell are the primary sources of the adenosine triphosphate (ATP) necessary to maintain endothelial structure and pump fluid to maintain the corneal stroma in its normally dehydrated and transparent state. The correlation between endothelial metabolism and morphology in rabbits was studied for 7 days after the application of three different agents: (1) iodoacetamide, used to inhibit ATP synthesis from both glycolysis and respiration; (2) potassium cyanide (KCN), used to inhibit ATP synthesis from respiration only; and (3) ouabain, used to inhibit fluid pumping but not ATP synthesis. After application of each of these three drugs to the corneal endothelium, changes in endothelial morphology were measured. The greatest change resulted from the use of iodoacetamide. Specular microscopic examination of the endothelium after the application of iodoacetamide showed progressive degradation of the integrity of the cellular structure; after 6 hr, there were no discernible cell borders. In those corneas treated with either KCN or ouabain, only minor changes in the endothelium were seen during the full 7 days of the investigation. Computer-assisted morphometric analysis showed an increase in the coefficient of variation of both cell area and perimeter in all cases. This increase was greater in the corneas treated with ouabain than those treated with either iodoacetamide or KCN. Redox fluorometry showed that the metabolic ratio (autofluorescence of reduced pyridine nucleotides divided by that of oxidized flavoproteins) decreased significantly in the iodoacetamide-treated corneas, increased significantly in the KCN group, and showed no significant change in the corneas in the ouabain group, all compared with a control group. The results showed that (1) when ATP produced by both glycolysis and respiration was inhibited by 0.1 mmol/l iodoacetamide, the endothelial cells could not survive, but (2) when ATP synthesis produced by respiration alone was inhibited by 1.0 mmol/l KCN, the cells could survive for at least 1 wk on the ATP produced by anaerobic glycolysis. Furthermore, the polymegathism seen after application of ouabain, a drug that is not believed to affect ATP synthesis but inhibits the endothelial pump function, is greater than that seen as a result of reduced pump function caused by inhibited respiration produced by 1.0 mmol/l KCN. Combining specular microscopy, computer-assisted morphometric analysis, redox fluorometry, and corneal pachymetry allowed correlations between corneal endothelial metabolism, pump function, and morphology to be studied.