The alteration in energy metabolic products was analyzed in cultured retinal cells submitted to oxidative stress, hypoxia, glucopenia, or ischemia-like conditions. Ischemia highly reduced cellular ATP and increased AMP formation, without significant changes in ADP. Ischemia induced a significant increase in extracellular adenosine (ADO) and hypoxanthine (HYP), and to a lesser extent inosine (INO). Glucopenia reduced cellular ATP by about two- to threefold, which was not compensated for by AMP formation. Under glucopenia, extracellular ADO and HYP were significantly increased, although a major increase in extracellular INO was observed. 5-(4-Nitrobenzyl)-6-thioinosine (10 microM) reduced extracellular ADO during glucopenia or ischemia by approximately 80%, indicating that ADO accumulation occurs mainly via the transporter. Intracellular ATP, ADP, or AMP and extracellular ADO, INO, or HYP were not apparently changed after oxidative stress or hypoxia. Nevertheless, in the presence of 10 microM erythro-9-(2-hydroxy-3-nonyl)adenosine, oxidative stress was shown to increase significantly the accumulation of ADO, which was reduced in the presence of 200 microM alpha,beta-methyleneadenosine 5'-diphosphate, suggesting that ADO accumulation after oxidative stress may result from extracellular degradation of adenine nucleotides. The increase in ADO accumulation resulting from the depletion of cellular ATP was directly related to the release of endogenous glutamate occurring through a Ca2+-independent pathway after ischemia. Increased metabolic products derived from ATP are suggested to exert a modulating effect against excitotoxic neuronal death.
Adenine Adenosine