Glycolysis in the human muscle: a new approach

Glycolysis activity in flight muscles of birds according to their physiological function. An experimental model in vitro to study aerobic and anaerobic glycolysis activity separately

An experimental system in vitro is presented to assess the activity of the entire glycolysis in tissue extracts, which allows determining aerobic and anaerobic glycolysis activities separately. Glycolysis activity has been measured in pectoral and supracoracoideus muscles of the homing pigeon and the domestic fowl. These muscles support different aspects of flight in the two birds and are representative models of the two kinds of basic movements, endurance and sprint. The results obtained showed that in type I red fibers (pigeon pectoral), glucose produced a high glycolytic activity, while it was a poor substrate for type IIb white fibers (fowl pectoral and the two supracoracoideus). White fibers, however, attained its maximum glycolytic activity with phosphorylated glucose as substrate. These results demonstrated the validity of the experimental system as a method for assaying the two kinds of glycolytic activity in tissues, and supply new information about the biochemical and physiological features of these types of fibers.

Glycolytic fluxes in European silver eel, Anguilla anguilla: sex differences and temperature sensitivity

European silver eels migrate 6000 km to their supposed spawning area in the Sargasso sea. As the eel is fasting, this intense swimming activity is realised only with fat stores, involving mainly red muscle i.e. aerobic metabolism. However, eel migration is performed at depth and thus in cold water, both being known to induce changes in muscle energy metabolism. During migration, white and red muscles can operate together or separately in order to counteract the eventual effects of low temperatures and/or high pressures. We have studied the temperature sensitivity (5, 15, and 25 degrees C) of aerobic and anaerobic metabolism in both sexes. At the same temperature, migrating eels have a higher basal glycolytic flux. Moreover, there are temperature and sex effects: anaerobic glycolysis (JB) is more sensitive to cold water whereas aerobic (JA) is more affected by warm. Males, which are less sensitive to cold water, also have higher aerobic fluxes than females. As depth corresponds to low temperature, the possibility that males migrate more deeply than females is discussed. In an ecophysiological context, it is interesting to suppose that males and female eels migrate at different depths in order to optimize their energy utilization by aerobic and / or anaerobic pathways.

Effects of dichloroacetate and ubiquinone infusions on glycolysis activity and thermal sensitivity during sepsis

Energy-metabolism disturbances during sepsis are characterized by enhanced glycolytic fluxes and reduced mitochondrial respiration. However, it is not known whether these abnormalities are the result of a specific mitochondrial alteration, decreased pyruvate dehydrogenase (PDH) complex activity, depletion of ubiquinone (CoQ(10); electron donor for the mitochondrial complex III), or all 3. In this study we sought to specify metabolism disturbances in a murine model of sepsis, using either a PDH-activator infusion (dichloroacetate, DCA) or CoQ(10) supplementation. After anesthesia, Sprague-Dawley rats received intravenous saline solution (control; n = 5), DCA (n = 5; 20 mg/100 g), or CoQ(10) (n = 5; 1 mg/100 g), before the induction of sepsis. Increased plasma lactate levels and increased muscle glucose content were observed after 4 hours in the control group. In the DCA group, a decrease in the muscle content of lactate (P <.05) and an increase in muscle glucose content (P <.05) were observed at 4 hours, but no lactatemia variation was noted. In the CoQ(10) group, only increased plasma lactate levels were observed. Increased muscle glycolysis fluxes were observed after 4 hours in the control group, but to a slighter degree in both the DCA and CoQ(10) groups. Only DCA restored a normal temperature sensitivity in the hyperthermia range, but we noted no differences in survival time. In conclusion, only DCA infusion restores normal glycolysis function.

Temperature sensitivity of glycolysis during sepsis

OBJECTIVE

To investigate the temperature sensitivity of glycolysis during sepsis.

DESIGN

A prospective, randomized, controlled animal study.

SETTING

The Physiological Department of a University Hospital.

SUBJECTS

Ten male Sprague-Dawley rats, weighing 400-500 g.

INTERVENTIONS

The rats were assigned to either a septic (n = 5) or a sham-control group (n = 5). After anesthesia (H0), experimental sepsis was induced by a cecal ligation and perforation, and the left lateral gastrocnemius was sampled. Four hours later (H4), a second anesthesia was performed to sample the contralateral muscle. The sham-control group underwent the same procedures, but the cecum was neither ligated nor incised.

MEASUREMENTS AND MAIN RESULTS

Glycolytic flux (J(B), the rate at which glycogen can be used in muscle) and the transition time (t99 : the time required for the transition from aerobic to anaerobic metabolism) were measured by using spectrophotometry. The measurements were performed at seven different temperature levels, ranging from 32 to 42 degrees C. For each measured variable, the temperature sensitivity of glycolysis was assessed by computing the Q10 values, which is the variation ratio of the measured variable, attributed to a 10 degrees C temperature increase. In control rats, anesthesia and surgical procedures induced a J(B) increase (7.9 +/- 1.6 at H0 vs. 11.9 +/- 2.1 micromol x min-1 x g(tissue) at H4, p<.05) without any t99 variation. Whatever the group (control or septic), the same temperature variation induced an effect that was approximately three times higher in the hypothermia (<37 degrees C) than in the hyperthermia range (>37 degrees C; p<.05). However, a loss in thermal sensitivity was observed in septic rats in the hyperthermia range (Q10 = 1.2 +/- 0.1 for septic animals vs. 2.3 +/- 0.4 for control animals; p<.05).

CONCLUSIONS

This study demonstrates that glycolysis is more sensitive to temperature in the hypothermia range than in the hyperthermia range. The loss in thermal sensitivity at >37 degrees C in septic rats suggests that sepsis may induce a dysregulation of glycolysis. From an energetic point of view, this signifies that hyperthermia may by itself impair energy metabolism without improving energy production and thus must be treated during sepsis.

A global approach to energy metabolism in an experimental model of sepsis

Disturbances in energy metabolism during sepsis are not clearly understood. The aim of the study was to globally assess the energy drive in septic rat myocytes, studying both glycolysis rates and mitochondrial maximal activities together, using recent in vitro techniques. Measurements were assessed before (H0) and 4 h after sepsis induction (H4). Hyperlactatemia was observed in all septic animals ([lactate] = 1.2 +/- 0.3 mmol/L at H0 versus 3.3 +/- 0.6 mmol/L at H4; p < 0.001). An enhanced glycolysis rate was observed in both aerobic ( J(A) = 7.2 +/- 0.9 at H0 versus 18.2 +/- 4.1 nmol glucose/min/g at H4; p < 0.05) and anaerobic ( J(B) = 7.5 +/- 1.2 at H0 versus 15.4 +/- 3.4 micromol glucose/min/g at H4; p < 0.05) fluxes, associated with a selective significant pyruvate-malate-dependent oxygen consumption rate decrease (V O(2)-PM = 0.144 +/- 0.008 at H0 versus 0.113 +/- 0.007 micromol O(2)/h/mg at H4; p < 0.05). This oxygen consumption decrease can be interpreted either as a complex I and/or a complex I-ubiquinone relation alteration. Our results are consistent with the hypothesis that an altered mitochondrial function during sepsis is responsible, at least in part, for hyperlactatemia, which is thus a consequence of an increased glycolysis rate.