Altered retinal metabolism in diabetes. II. Measurement of sodium-potassium ATPase and total sodium and potassium in individual retinal layers.

Pathological changes in retinas of diabetics include specific morphological, biochemical, and functional abnormalities. As biochemical manifestations of the disease, increased sorbitol and decreased myo-inositol were found in retinas of experimentally diabetic animals. Similar alterations in polyol metabolism have been associated in nerves of diabetics with a reduction of Na+-K+-ATPase activity. To determine whether this association extends to the retinas of diabetic animals, we applied quantitative histochemical techniques to measure ATPase activities and the amounts of sodium and potassium in samples from nine individual layers of cryostat sections of rabbit retina. ATPase activities were determined fluorimetrically, and the ions were measured by atomic absorption with a carbon rod atomizer. The activity of Na+-K+-ATPase was reduced in the retinal pigmented epithelium (retinal pigment epithelium) and in selected layers of the neural retina, and total sodium in the retinal pigment epithelium layer was elevated in diabetes. The retinal pigment epithelium forms the outer component of the blood-retinal barrier and partly determines the composition of the retinal interstitial fluid. Changes in retinal pigment epithelium biochemistry and function might alter the intraretinal environment, predisposing neural retina or retinal blood vessels to disease. The morphologically and functionally well defined retinal pigment epithelium may provide a useful model for studying the pathogenesis of diabetic complications.