Pyruvate reverses metabolic effects produced by hypoxia in glioma and hepatoma cell cultures.

The intervention of pyruvate in glucose metabolism was investigated during hypoxic stress in tumour cell cultures having respiratory capacities under normoxic conditions. Results obtained with nuclear magnetic resonance (NMR) spectroscopy showed that, under normoxic conditions, rat glioma C6 and human hepatoma Hep G2 cell cultures metabolised [(13)C(1)]glucose into lactate, alanine, glutamate and other less abundant metabolites, as already known from the literature. In the absence of pyruvate, during hypoxia or cyanide poisoning, both cell types dramatically decreased the label into glutamate and accumulated [(13)C(3)]glycerol-3-phosphate. The compound was further identified by 31P NMR spectroscopy. The accumulation of the label in glycerol-3-phosphate, however, did not occur when the cells were incubated in the presence of pyruvate. The fate of the latter, followed under normoxic conditions by incubating cells with [(13)C(3)]pyruvate and natural glucose, showed that the label was mainly found in alanine, lactate and glutamate. Anoxic conditions increased the label in lactate and reduced that of glutamate. The data show a metabolic effect of pyruvate during mitochondrial blockade due to severe lack of oxygen in tumour cell lines.

Bax and heart mitochondria: uncoupling and inhibition of respiration without permeability transition.

The effects of Bax (full-length, FL, and C-terminal truncated, DeltaC) on respiration rate, membrane potential, MgATPase activity and kinetics of regulation of respiration were studied in isolated rat heart mitochondria and permeabilized cardiomyocytes. The results showed that while both Bax-FL and Bax-DeltaC permeabilized the outer mitochondrial membrane, released cytochrome c and reduced the respiration rate, the latter could be fully restored by exogenous cytochrome c only in the case of Bax-DeltaC, but not in presence of Bax-FL. In addition, Bax-FL but not Bax-DeltaC increased the MgATPase activity, and their effects on the mitochondrial membrane potential were quantitatively different. None of these effects was sensitive to cyclosporin A (CsA). It is concluded that Bax-FL affects both the outer and the inner mitochondrial membranes by: (1) opening large pores in the outer membrane; (2) inhibiting some segments of the respiratory chain in the inner membrane; and (3) uncoupling the inner mitochondrial membrane by increasing proton leak without opening the permeability transition pore (PTP).