Coupling of energy supply and energy demand in isolated goldfish hepatocytes

KRUMSCHNABEL G, SCHWARZBAUM PJ, WIESER W.

PHYSIOLOGICAL ZOOLOGY

The University of Chicago

Año: 1994 p. 438 - 448

0031-935X

The allocation of metabolic energy under fluctuating conditions of supply and demand was studied in isolated goldfish hepatocytes. Inhibition ofglycolytic ATP production resulted in a decrease in the activity of one of the major ATP consum- ing components of cellular energy budgets, the sodium pump ((Na K+)- ATPase), because of the removal of substrates for the trichloroacetic acid (TCA) cycle. This was confirmed through restoration of activity to control levels by add- ingpyruvate and malate to the suspension. Ouabain-sensitive oxygen consump- tion constituted a fairly constant fraction of 15% to 25% of total oxygen con- sumption, whereas the relative load exerted by the pump on anaerobic energy metabolism (on the basis of measurements of Rb+ flux and lactate production) was much higher, ranging from 90% to 50% during the experimental period. Moreover, when pump activity was inhibited by the addition of ouabain, oxida- tive energy output decreased immediately, whereas under the restricted condi- tions of glycolytic energy supply a corresponding ouabain-sensitive component of lactate production was not observed. Such an apparent mismatch between sup- ply and demand ofATP is interpreted as reflecting the flexibility of energy alloca- tion under energy-limiting conditions. When ATPproduction was reduced by in- hibiting either glycolysis or oxidative phosphorylation, the concentration ofATP in the hepatocytes dropped within 30 min from the control steady state to a new, lower, steady state that was maintained for at least 60 min.