ATP FORMATION AND ENERGY DEMAND IN ANOXIC HEART-MUSCLE OF THE RABBIT

In quiescent rabbit papillary muscle at 20-degrees-C, the formation of ATP in nitrogen, estimated from the production of lactate, is 21% of that in oxygen. Stimulating the anoxic muscles at 0.2 Hz causes a threefold increase in ATP formation. In this study we want to determine 1) whether glycolytic ATP formation can be increased to a rate that would meet the aerobic ATP demand at rest and 2) what the maximum glycolytic rate attainable through stimulation is. Glycolytic rate is estimated from the amount of lactate produced at various times over 40 min of anoxia. Nucleotides and creatine compounds are also determined. Lactate formation at the onset of anoxia is proportional to stimulus frequency. The amount of lactate formed is correlated to the breakdown of glycogen; glucose is not used. Therefore the amount of glycogen present in the muscle at the onset of anoxia is the main determinant of the amount of ATP formed when oxidative phosphorylation is inhibited. The rate of lactate formation at the onset of anoxia increases from 1.22-mu-mol.g dry wt-1.min-1 in resting muscles to 18.5-mu-mol.g dry wt-1.min-1 in 1-Hz-stimulated muscles. This implies that in anoxic myocardium, glycolysis can provide ATP at more than three times the rate found in the muscle at rest in ample oxygen.