A Specific Inhibitor of Heart Cytosolic 5′-Nucleotidase I Attenuates Hydrolysis of Adenosine 5′-Monophosphate in Primary Rat Myocytes

ATP breakdown was triggered in primary rat myocytes in the presence of coformycin to force the catabolism of AMP through hydrolysis to adenosine. Selective inhibitors of the cytosolic 5′-nucleotidase I (c-N-I) from myocardium were used to measure the intracellular contribution of this enzyme to AMP hydrolysis under these conditions. The selective inhibitor 5-ethynyl-2′,3′-dideoxyuridine inhibited the hydrolysis of AMP to adenosine in a concentration-dependent manner with an IC50value of 20 μM. Maximal inhibition prevented 76% of the conversion of AMP to adenosine, indicating that under these conditions the majority of AMP hydrolysis in rat myocytes occurs through this enzyme. When ATP breakdown was triggered in the presence of thymidine 5′-phosphonate, a more potent inhibitor of the purified cytosolic 5′-nucleotidase, less inhibition of AMP hydrolysis occurred and only after prolonged preincubation of the myocytes with the inhibitor. These data demonstrate that the selectivenucleosideinhibitors of c-N-I can effectively block the hydrolysis of AMP inside myocytes. Thus, these inhibitors may be useful tools in identifying the role of c-N-I during ATP catabolism in whole tissue and animal experiments.