In vitro studies of beating heart cells in culture XII. The utilization of ATP and phosphocreatine in oligomycin and 2-deoxyglucose inhibited cells

1. The ATP concentration in the cultured rat heart cells did not change significantly when either glycolysis or oxidative phosphorylation was inhibited with 2-deoxyglucose and oligomycin, respectively. When both glycolysis and oxidative phosphorylation inhibitors were present simultaneously, the ATP level dropped significantly. The combined effect of both inhibitors exceeded the sum of the effects of the individual inhibitors. 2. The utilization of ATP in the presence of either oligomycin or 2-deoxyglucose and in the presence of both inhibitors simultaneously was reflected in a decrease in phosphocreatine concentration. 3. The rate of high energy phosphate utilization in quiescent cells was calculated to be 0.289 ± 0.040 nmole/mg protein per min. The utilization of energy for contraction was calculated to be 0.055 ± 0.010 nmole/mg protein per contraction. 4. Taking into consideration the energy requirements of beating cells and the change in ATP + phosphocreatine when the inhibitors were present singly and simultaneously, it was concluded that a control of metabolism involving glycolysis and oxydative phosphorylation is operating under normal oxidative conditions. The sum to the rates of the two pathways, when operating alone, is greater than the sum of their rates when operating simultaneously.