Effect of nitric oxide donors on extracellular ATP, ADP, and AMP catabolism in rat hippocampal synaptosomes.

Extracellular adenine nucleotides acting as signaling molecules are inactivated by hydrolysis catalyzed by ectonucleotidases. Adenosine triphosphate (ATP) diphosphohydrolase (apyrase, EC 3.6.1.5) and 5'-nucleotidase (EC 3.1.3.5) are involved in an enzymatic chain for the hydrolysis of ATP to adenosine in the synaptic cleft. In this study, we investigated the in vitro effect of nitric oxide (NO) donors on extracellular ATP, adenosine diphosphate (ADP), and adenosine monophosphate (AMP) catabolism in hippocampal synaptosomes of rats. We evaluated the effect of the incubation time on ATP, ADP, and AMP hydrolysis in the absence and in the presence of 1 mM sodium nitroprusside (SNP). The inhibitory effect of SNP increased with the incubation time and the maximal inhibition was observed after 180 min for both enzyme activities. The inhibition observed attained a maximum at 1 mM SNP for ATP, ADP, and AMP hydrolysis, with the enzyme activities being markedly reduced at this concentration of SNP. However, other NO donors tested, such as S-nitroso-N-acetyl-penicillamine and isosorbide dinitrate, did not affect the enzyme activities. The effect of the NO donor, SNP, on extracellular ATP and ADP catabolism was increased by the addition of the thiol glutathione but this effect was not observed on extracellular AMP catabolism. The results suggest that the increased production of NO could have a modulatory role on the ectonucleotidase activities.