IN-VITRO METABOLIC COMPETENCE OF THE FROG RETINA - EFFECTS OF GLUCOSEAND OXYGEN DEPRIVATION

The metabolic competence and histological integrity of the frog retina in vitro were evaluated as a function of the presence/absence of exog enous glucose and of oxygen tension. Dark- and light-adapted frog neur al retinas were incubated for 1-8 hr at 23 degrees C in a modified Rin ger's-bicarbonate medium under aerobic and anaerobic conditions, in th e presence and absence of 10 mM glucose. Control retinas (+ glucose, a erobic conditions) maintained ATP levels comparable to those of freshl y excised tissue (ave. 17 nmol mg protein(-1)), produced minimal lacta te (ave. 0 . 12 mu mol mg protein(-1)hr(-1)), and exhibited normal his tology. In the absence of any exogenous carbon source, retinas incubat ed aerobically maintained ATP levels, produced lactate, incorporated [ H-3]acetate into nonsaponifiable lipids, and exhibited histology compa rable to controls, In the presence of 1 mM iodoacetate, aerobic ATP le vels declined markedly, with or without exogenous glucose. Under anaer obic conditions with glucose present, lactate production increased ca. 8 . 5-fold, while ATP levels were maintained at control levels, demons trating a marked Pasteur effect; under these conditions, retinas exhib ited only moderate histopathological changes. However, in the absence of both glucose and oxygen, ATP levels declined precipitously, with co ncomitant massive cytological deterioration. No major differences in t he biochemical measurements or histological appearance were observed a s a function of light adaptation, These results demonstrate the remark able 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 e ndogenous carbohydrate substrate (e,g., glycogen). (C) 1997 Academic P ress Limited.