Model systems for modulating the free energy of ATP hydrolysis in normoxically perfused rat hearts

J. A. BALSCHI, H. SHEN, M. C. MADDEN, J. O. HAI, E. L. BRADLEY JR AND P. E. WOLKOWICZ. Model Systems for Modulating the Free Energy of ATP Hydrolysis in Normoxically Perfused Rat Hearts. Journal of Molecular and Cellular Cardiology (1997) 29, 3123-3133. This study has two objectives; first, to develop perfusion conditions that decrease the free energy of ATP hydrolysis, Delta G(ATP) in isolated hearts; and, second, to modulate the Delta G(ATP) in these perfused hear models. To accomplish the first goal, a series of inhibitors was employed to restrict acetyl-CoA oxidation, The second goal was accomplished by increasing work demand, Rat hearts were perfused with Krebs-Henseleit solution containing glucose and either; (i) no inhibitors (G group hearts); (ii) 0.3 mM bromooctanoate (BrO), an inhibitor of beta-oxidation (GB group); (iii) 0.4 mM amino-oxyacetate (AOA), an inhibitor of the malate-aspartate shuttle (GA group); (iv) BrO ands AOA (GBA group hearts); or (v) BrO, AOA, and 4 mM butyrate, an alternate substrate (GBA-Bu). Pacing hearts at 300 beats per min (beats/min), at 450 beats/min, and at 450 beats/min in the presence of 80 mu g/l dobutamine allowed three increasing levels of work demand to be attained. The Delta G(ATP) values of the five groups of hearts were calculated for each workstate using the concentrations of high energy phosphate metabolites measured by P-31 NMR spectroscopy. At the highest levels of workload demand, the G, GB, and GBA-Bu group hearts had Delta G(ATP) values greater than or equal to-53 kJ/mol ATP. At the highest levels of workload demand, the GA and GBA hearts had Delta G(ATP) values less than or equal to-49 kJ/mol ATP. The values of Delta G(ATP) and the heart work output during any perfusion conditions were stable for periods of >20 min. The G, GB, and GBA-Bu hearts attained RPPs of greater than or equal to 54 x 10(3) mmHg/min at the highest levels of workload demand. The GA and GBA hearts attained RPPs of less than or equal to 30 x 10(3) mmHg/min at the highest levels of workload demand. This study establishes stable, non-ischemic, isolated perfused heart preparations with which Delta G(ATP) can be easily varied across the physiological relevant range of -56 to -47 kJ/mol ATP. (C) 1997 Academic Press Limited.