Glucose metabolism in the cornea and lens in elasmobranchs, teleosts and mammals: response to thiol-oxidation.

Various structural and metabolic adaptations that have occurred in elasmobranchs, in salt and fresh water teleosts, and in mammals have enabled these species to adapt to varied environments. In all cases the corneas of these species remain transparent and expend metabolic energy to maintain this transparency. The studies reported in this paper describe the structural and the metabolic adaptations that have occurred in these corneas. Included are measurements of corneal oxygen consumption, Q10 and corneal hydration. Thiol-oxidation of the intracellular glutathione with diamide has been shown to produce marked stimulation of the hexose-monophosphate shunt in the component layers of the cornea and the lens of rabbit, dogfish, and sculpin. Activities of glycolytic, citric acid cycle, and pentose phosphate shunt enzymes in the corneal and muscle tissue were also studied. Species variations were found between elasmobranchs, marine teleosts, and rabbits. In each of these species, the corneal endothelium was distinguished from the epithelium by much lower enzyme activities. It can be concluded that the enzyme activities and metabolic differences represent functional adaptations that have occurred to insure transparency under these extremely varied osmotic conditions.