Abstract
The degradation and short-term resynthesis of adenine nucleotides have been examined in a preparation of isolated rat heart myocytes. These myocyte preparations are essentially free of vascular and endothelial cells, contain levels of adenine nucleotides quite comparable to those of intact heart tissue, and retain these components remarkably well for up to 2 h of aerobic incubation in the presence of 1 mM Ca2+. When the cells are rapidly and synchronously de-energized by addition of uncoupler, an inhibitor of respiration and iodoacetate, cellular ATP is degraded almost quantitatively to AMP. The AMP is then converted to either intracellular adenosine, which accumulates to high concentrations before release to the cell exterior, or to IMP. The relative contribution of these two pathways depends on the metabolic state of the cells just prior to de-energization, with IMP production favored when respiring cells are de-energized and adenosine formation predominant when glycolyzing myocytes are subjected to this treatment. Cells de-energized by anaerobiosis in the absence of glucose lose ATP and adenine nucleotides with the production of IMP and adenosine. Upon reoxygenation, these cells restore a high adenylate energy charge and about 60% of control levels of GTP. There is a net resynthesis of 5-7 nmol of adenine nucleotides.mg-1 protein with a corresponding decline in IMP. Added [14C]adenosine labels the adenine nucleotide pool, but little net resynthesis of adenine nucleotides via adenosine kinase can be detected. It therefore appears that a rapid regeneration of adenine nucleotides can occur via the enzymes of the purine nucleotide cycle in heart myocytes and is limited by the size of the IMP pool retained.
Highlights
From the §Department of Physiological Chemistry and the SDiuision of Cardiology, Department of Intern1 Medicine, Ohio State University Medical Center, Columbus, Ohio 43210
The degradation and short-term resynthesiosf ade- and resynthesis of adenine nucleotides in intact myocardium nine nucleotides have been examined in a preparation are cooperative processes involving contributions from vasof isolated rat heart myocytes
It is concluded that themyocytes show excellent retention of adenine nucleotides when incubated aerobically in Ca2+containing media and that rapidly de-energizedmyocytes show a clear progression of adenine nucleotide degradation from AMP to intracellular Ado, followed byexit of Ado from the cell and conversion to Ino
Summary
The degradation and short-term resynthesiosf ade- and resynthesis of adenine nucleotides in intact myocardium nine nucleotides have been examined in a preparation are cooperative processes involving contributions from vasof isolated rat heart myocytes. The relative contributionof these two pathways amounts of IMP Reaeration of these cells results in resyndepends on the metabolic state of the cells just prior to thesis of small amounts of adenine nucleotides and restoration de-energization, with IMP production favored when of the adenylate energy charge [16, 17], butalso results in the respiring cells are de-energized and adenosine forma- irreversible hypercontracture of large numbers of cells. It is concluded that themyocytes show excellent retention of adenine nucleotides when incubated aerobically in Ca2+containing media and that rapidly de-energizedmyocytes show a clear progression of adenine nucleotide degradation from AMP to intracellular Ado (and variable amounts of IMP), followed byexit of Ado from the cell and conversion to Ino. Anaerobic, substrate-depleted myocytes resynthesize considerable adenine nucleotide Retention of Adenine Nucleotides by Myoeytes Incubated Aerobically in the Presence of Cu2+-The myocyte preparations used in the present study average 72 f 3% viable cells
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