148 PATHWAYS OF ATP CATABOLISM IN PRIMARY RAT CARDIOMYOCYTE CULTURES

Abstract

The pathways of ATP catabolism were investigated in cultured beating cardiomyocytes. The activity of the enzymes involved in AMP degradation was assayed in cell extracts, whereas fluxes of label from ATP to the various purine derivatives were measured in intact cells. Under physiological conditions, in accord with a 7 fold higher activity of AMP deaminase than that of AMP 5′-Nucleotidase, cells degraded AMP through deamination to IMP. Mild ATP degradation, induced by inhibition of glycolysis by iodoacetate, caused no alterations in the degradation pathways (more than 85% through deamination to IMP). However, fast ATP degradation (83% of adenine nucleotides/10 min), induced by simultaneous inhibition of glycolysis and electron transport (by antimycin A), caused increased dephosphorylation of AMP to adenosine (50% of total AMP-degradation). IMP was rapidly degraded to inosine, hypoxanthine, xanthine and uric acid, which were effluxed from the cells. The cardiomyocyte extracts were found to contain a significant activity of PNP. Despite the presence of HGPRT, salvage of hypoxanthine to IMP, both at physiological as well as at conditions associated with ATP degradation, was slow. The salvage of adenosine appeared to be efficient at physiological conditions, but not at fast rates of ATP degradation.