A comparative study of sodium permeability in lake trout and rabbit corneas

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Abstract
The fish cornea was impermeable to Na transfer in both directions despite the presence of a gradient which favored a flux through the cornea to the solution bathing the epithelium. Permeability constantd derived for Na flux in normal and denuded corneas indicate that the endothelium offers some resistance to transfer of water and Na into or across the fish cornea; the major resistance is provided by the epithelium. The permeability constant for Na transfer across the endothelial barrier between the corneal stroma and aqueous humor in fish is 0.029 mEq/cm2-hr which is some 16% lower than that observed in rabbit corneas. Rabbit corneas had a 3-fold greater water exchange than fish corneas and they showed a sodium flux in the tears-aqueous direction. In diseased lake trout corneas, sodium ion concentration varied inversely with corneal hydration. Stage 2,3, and 4 diseased corneas were at maximal hydra-tion in situ, whereas, normal, stage 1 and 1-a corneas do imbibe water from the bathing media in vitro. Corneal hydration in fish appears to be controlled by the action of the epithelial and endothelial layers as in mammals. When studied simultaneously, HTO movement and 22Na flux appeared to occur independent of each other in both fish and rabbit corneas.

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