QUANTITATIVE-ANALYSIS OF SIMILARITIES AND DIFFERENCES IN NEUROTOXICITIES CAUSED BY ADENOSINE AND 2'-DEOXYADENOSINE IN SYMPATHETIC NEURONS

These experiments characterize the nucleoside transport and quantify t he neurotoxicity of adenosine and 2'-deoxyadenosine (dAdo) in chick sy mpathetic neurons. We show that [H-3]adenosine transport was sensitive to low temperature, specific inhibitors of nucleoside transport, and an excess concentration of adenosine. However, many of these treatment s had a marginal effect on [H-3]dAdo transport. Total retention of [H- 3]dAdo over short and long periods was similar to 10 times less than t hat of [H-3]adenosine, These data suggest that adenosine and dAdo ente r sympathetic neurons by different routes. Uptake of [H-3]norepinephri ne ([H-3]NE) decreased in neurons damaged by nucleosides and increased to control levels when neurons were protected by various agents again st adenosine or dAdo toxicity. These results indicate that [H-3]NE upt ake serves as a quantitative index of toxicity by the nucleosides. Usi ng this approach we demonstrate that phosphorylation of both nucleosid es is essential for their lethal action. For example, iodotubercidin p revented nucleoside-induced neuronal death, but the effect was much mo re pronounced in the case of dAdo toxicity (IC50 of 0.83 +/- 0.4 vs. 3 0 +/- 1.6 nM). Another kinase inhibitor, 5'-amino 5'-deoxyadenosine, w as effective in protecting neurons against dAdo but had no effect agai nst adenosine toxicity. These results suggest that specific kinases ar e associated with the phosphorylation of adenosine and dAdo in sympath etic neurons to produce toxic metabolic products. Finally, neurons wer e susceptible to dAdo toxicity from the time of plating to 4 weeks in culture but were resistant to adenosine toxicity 8 h after plating. In conclusion, our results highlight major differences in the mechanism of neurotoxicity by adenosine and dAdo and provide insights for identi fication of biochemical pathways leading to neuronal death.