In Vitro Metabolic Competence of the Frog Retina: Effects of Glucose and Oxygen Deprivation

Abstract

The metabolic competence and histological integrity of the frog retina in vitro were evaluated as a function of the presence/absence of exogenous glucose and of oxygen tension. Dark- and light-adapted frog neural retinas were incubated for 1–8 hr at 23°C in a modified Ringer's-bicarbonate medium under aerobic and anaerobic conditions, in the presence and absence of 10 mMglucose. Control retinas (+glucose, aerobic conditions) maintained ATP levels comparable to those of freshly excised tissue (ave. 17 nmol mg protein−1), produced minimal lactate (ave. 0.12 μmol mg protein−1hr−1), and exhibited normal histology. In the absence of any exogenous carbon source, retinas incubated aerobically maintained ATP levels, produced lactate, incorporated [3H]acetate into nonsaponifiable lipids, and exhibited histology comparable to controls. In the presence of 1 mMiodoacetate, aerobic ATP levels declined markedly, with or without exogenous glucose. Under anaerobic conditions with glucose present, lactate production increased ca. 8.5-fold, while ATP levels were maintained at control levels, demonstrating a marked Pasteur effect; under these conditions, retinas exhibited only moderate histopathological changes. However, in the absence of both glucose and oxygen, ATP levels declined precipitously, with concomitant massive cytological deterioration. No major differences in the biochemical measurements or histological appearance were observed as a function of light adaptation. These results demonstrate the remarkable resilience of the frog retina to anoxia and hypoglycemic stress. Aerobically, with or without exogenous glucose, ATP production and de novo lipid synthesis are maintained, apparently by recruitment of an endogenous carbohydrate substrate (e.g., glycogen).