l-Lactate metabolism in HEP G2 cell mitochondria due to the l-lactate dehydrogenase determines the occurrence of the lactate/pyruvate shuttle and the appearance of oxaloacetate, malate and citrate outside mitochondria.
As part of an ongoing study of l-lactate metabolism both in normal and in cancer cells, we investigated whether and how l-lactate metabolism occurs in mitochondria of human hepatocellular carcinoma (Hep G2) cells. We found that Hep G2 cell mitochondria (Hep G2-M) possess an l-lactate dehydrogenase (ml-LDH) restricted to the inner mitochondrial compartments as shown by immunological analysis, confocal microscopy and by assaying ml-LDH activity in solubilized mitochondria. Cytosolic and mitochondrial l-LDHs were found to differ from one another in their saturation kinetics. Having shown that l-lactate itself can enter Hep G2 cells, we found that Hep G2-M swell in ammonium l-lactate, but not in ammonium pyruvate solutions, in a manner inhibited by mersalyl, this showing the occurrence of a carrier-mediated l-lactate transport in these mitochondria. Occurrence of the l-lactate/pyruvate shuttle and the appearance outside mitochondria of oxaloacetate, malate and citrate arising from l-lactate uptake and metabolism together with the low oxygen consumption and membrane potential generation are in favor of an anaplerotic role for l-LAC in Hep G2-M.
Department of Medicine and Health Sciences, University of Molise, Campobasso, Italy.
Roberto
R
Pizzuto
Gianluca
G
Paventi
Carola
C
Porcile
Daniela
D
Sarnataro
Aurora
A
Daniele
Salvatore
S
Passarella
D019343:Citric Acid / Q000378:metabolism*; D056945:Hep G2 Cells; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism*; D008293:Malates / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D062907:Oxaloacetic Acid / Q000378:metabolism*; D019289:Pyruvic Acid / Q000378:metabolism*
D008293:Malates; D019343:Citric Acid; D062907:Oxaloacetic Acid; D019344:Lactic Acid; C030298:malic acid; D019289:Pyruvic Acid; D007770:L-Lactate Dehydrogenase