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.