The purpose of this study was to examine in situ regulation of AMP deaminase in newborn piglet cardiac myocytes and to determine its role in nucleotide metabolism during ischemia. When a rapid deenergization paradigm was used to assay AMP deaminase, enzyme activity depended on the hormonal and metabolic status of cells just before deenergization. Inosine 5'-monophosphate (IMP) formation was increased 150% in deenergized myocytes pretreated with phorbol 12-myristate 13-acetate (PMA; EC₅₀ = 4.7 × 10⁸ M). This effect was 90% blocked with the protein kinase C (PKC) inhibitor staurosporine. In addition, the -adrenergic agonist isoproterenol stimulated AMP deaminase activity (EC₅₀ = 1.5 × 10⁸ M), and IMP formation was directly correlated to intracellular cAMP levels (r² = 0.9). Furthermore, adenosine increased IMP formation, whereas nonrespiring, glycolyzing piglet myocytes had reduced AMP deaminase activity. Pretreatment of perfused piglet hearts with adenosine, but not PMA, before exposure to global ischemia resulted in enhanced conversion of AMP to IMP during the ischemic period. Similar results were obtained in piglet myocytes preincubated with adenosine or PMA before exposure to simulated ischemia. These results may be relevant to the preconditioning phenomenon.

heart cells; phorbol ester; neonate; preconditioning