COUPLING OF ENERGY SUPPLY AND ENERGY DEMAND IN ISOLATED GOLDFISH HEPATOCYTES

The allocation of metabolic energy under fluctuating conditions of sup ply and demand was studied in isolated goldfish hepatocytes. Inhibitio n of glycolytic ATP production resulted in a decrease in the activity of one of the major ATP consuming components of cellular energy budget s, the sodium pump ((Na+, K+)ATPase), because of the removal of substr ates for the trichloroacetic acid (TCA) cycle. This was confirmed thro ugh restoration of activity to control levels by adding pyruvate and m alate to the suspension. Ouabain-sensitive oxygen consumption constitu ted a fairly constant fraction of 15% to 25% of total oxygen consumpti on, whereas the relative load exerted by the pump on anaerobic energy metabolism (on the basis of measurements of Rb+ flux and lactate produ ction) was much higher, ranging from 90% to 50% during the experimenta l period. Moreover, when pump activity was inhibited by the addition o f ouabain, oxidative energy output decreased immediately, whereas unde r the restricted conditions of glycolytic energy supply a correspondin g ouabain-sensitive component of lactate production was not observed. Such an apparent mismatch between supply and demand of ATP is interpre ted as reflecting the flexibility of energy allocation under energy-li miting conditions. When ATP production was reduced by inhibiting eithe r glycolysis or oxidative phosphorylation, the concentration of ATP in the hepatocytes dropped within 30 min from the control steady state t o a new, lower, steady state that was maintained for at least GO min.