Changes in lens amino acid transport and protein metabolism during osmotic cataract produced by ouabain

Osmotic (cortical) cataract was induced in bovine lenses during long-term organ culture by adding the cardiac glycoside, ouabain, to the incubation medium. This insult produces a much more rapid effect on protein synthesis than it does on amino acid influx, efflux or net protein loss. The kinetics of amino acid transport and protein synthesis were studied in detail using 14C-tyrosine in the incubation medium and a simple mathematical model was developed to help interpret the data. During efflux experiments, loss of radioactivity could be explained in terms of a single exponential process and ouabain was found to reduce the rate constant of loss after a delay of 50 hours. There was no delay, however, on the effect of ouabain on protein synthesis which was significantly reduced compared to control values. There was no effect of ouabain on net protein loss from the lens until after 120 hours, when significant amounts of 14-C labelled protein began to appear in the washing medium. This initiation of protein loss was accompanied by an increase in the amount of light scattered from the lens. Further studies are underway to determine which of the protein fractions are lost from the lens during osmotic insult.