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

This study has two objectives; first, to develop perfusion conditions that decrease the free energy of ATP hydrolysis, Delta GATP, in isolated hearts; and, second, to modulate the Delta GATP 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 bromo-octanoate (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 and 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 microgram/l dobutamine allowed three increasing levels of work demand to be attained. The Delta GATP values of the five groups of hearts were calculated for each workstate using the concentrations of high energy phosphate metabolites measured by 31P NMR spectroscopy. At the highest levels of workload demand, the G, GB, and GBA-Bu group hearts had Delta GATP values >/=-53 kJ/mol ATP. At the highest levels of workload demand, the GA and GBA hearts had Delta GATP values 20 min. The G, GB, and GBA-Bu hearts attained RPPs of >/=54x10(3) mmHg/min at the highest levels of workload demand. The GA and GBA hearts attained RPPs of