EFFECTS OF NO-GENERATING COMPOUNDS ON SYNAPTOSOMAL ENERGY-METABOLISM

The effects of nitroprusside and S-nitrosocysteine, compounds that gen erate nitric oxide (NO), on synaptosomal energy-producing pathways and energy level were investigated. The decrease in respiration was much faster and more pronounced with S-nitrosocysteine than with nitropruss ide, S-Nitrosocysteine, at 10 mu M, inhibited by 80% respiration with glucose and succinate (plus rotenone) in intact synaptosomes and with ascorbate/cytochrome c in broken preparations, Oxygenated hemoglobin r eversed and/or prevented the inhibition, whereas glutathione (GSH) pro longed it. Under aerobic conditions, the synaptosomal energy level (cr eatine phosphate/creatine and ATP/ADP ratios) was reduced by the prese nce of S-nitrosocysteine, whereas lactate generation was enhanced. The effects on energy parameters were greater at 5 min than at 15 min of incubation and were more pronounced in the presence of GSH. Under stri ctly anaerobic conditions, lactate production was reduced by the NO-ge nerating compounds in a concentration-dependent manner. It is conclude d that (a) inhibition of oxidative phosphorylation by NO leads to a fa ll in the synaptosomal energy level, which in turn stimulates glycolys is; (b) glycolysis can be inhibited by higher concentrations of the ra dical; and (c) inhibitory effects on the energy-generating pathway and ATP level could contribute to NO toxicity under some in vivo situatio ns.