MICROCALORIMETRIC MEASUREMENT OF REVERSIBLE METABOLIC SUPPRESSION INDUCED BY ANOXIA IN ISOLATED HEPATOCYTES

The metabolic suppression due to anoxia in hepatocytes from the anoxia -tolerant turtle Chrysemys picta bellii was measured directly using mi crocalorimetric techniques. The normoxic heat flux from hepatocytes in suspension (25-degrees-C) was 1.08 +/- 0.08 mW/g cells and decreased by 76% to 0.26 +/- 0.03 mW/g cells in response to anoxic incubation. A fter an acute decrease in temperature (to 10-degrees-C) anoxic heat fl ux dropped by 96% relative to the normoxic control at 25-degrees-C. Th e relative decrease in heat flux at both temperatures was similar, 76% at 25-degrees-C and 68% at 10-degrees-C. From the caloric equivalent of glycogen fermentation to lactate the heat flux from lactate product ion was calculated to be -93 muW/g cells (25-degrees-C), and this acco unted for 36% of the anoxic heat flux. When the enthalpy change associ ated with the release of free glucose (from glycogen breakdown) is con sidered, an additional 6% of the anoxic heat flux can be accounted for . Therefore, a portion of the anoxic heat flux is unaccounted for (58% ), resulting in an ''exothermic gap.'' This differs from the normoxica lly incubated hepatocytes where the indirect calorimetric measurement of heat flux (hepatocyte O2 consumption) could fully account for the c alorimetrically measured heat flux. When normoxic hepatocytes were inh ibited with cyanide, a rapid suppression in heat flux was observed. Be cause rapid reequilibration to a lower, cyanide-induced steady state o ccurred in <15 min, it is also assumed that there is no short-term Pas teur effect in this tissue. There also does not appear to be a long-te rm sustained glycolytic activation; this conclusion is supported by th e similarity of normoxic and anoxic rates of glucosyl unit entry into glycolysis over a 10-h incubation period. Interestingly, the addition of 2,4-dinitrophenol to anoxic hepatocytes caused heat flux to increas e by 30%, and this is suggestive of some aspect of mitochondrial metab olism being active.