Subcellular distribution of malate-aspartate cycle intermediates during normoxia and anoxia in the heart.
The subcellular distribution of adenine nucleotides, phosphocreatine and intermediates of the malate-aspartate cycle was investigated in adult rat heart myocytes under normoxia and anoxia. Cytosolic and mitochondrial concentrations of metabolites were determined by a fractionation method using digitonin. Under normoxia, cytosolic/mitochondrial gradients were found for ATP (c/m = 4), AMP (c/m less than 0.01), citrate (c/m = 0.5), aspartate (c/m = 3), glutamate (c/m = 2), while phosphocreatine and glutamine were confined to the cytosolic space. No gradients were found for malate and 2-oxoglutarate. The results show that the transport of electrons from the cytosol into the mitochondria is supported by the glutamate gradient and by a high glutamate/aspartate ratio inside the mitochondria (Glu/Asp = 15) which is maintained by the energy-dependent Glu-Asp exchange across the mitochondrial membrane. Under anoxia, cytosolic glutamate is transaminated with pyruvate, yielding alanine and 2-oxoglutarate, which is oxidized to succinate inside the mitochondria and leaves the cell. The data indicate that stimulation of transamination is caused by a mass action effect following a decrease in cytosolic 2-oxoglutarate which may be due to succinate-2-oxoglutarate exchange across the mitochondrial membrane. Inhibition of the energy-dependent inward transport of glutamate may support this process.
D000227:Adenine Nucleotides / Q000378:metabolism; D000693:Anaerobiosis; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism*; D002951:Citrates / Q000378:metabolism; D019343:Citric Acid; D002952:Citric Acid Cycle; D003600:Cytosol / Q000378:metabolism; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D005973:Glutamine / Q000378:metabolism; D007656:Ketoglutaric Acids / Q000378:metabolism; D007773:Lactates / Q000378:metabolism; D019344:Lactic Acid; D008293:Malates / Q000378:metabolism*; D008297:Male; D008929:Mitochondria, Heart / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism / Q000648:ultrastructure*; D010100:Oxygen / Q000494:pharmacology*; D010725:Phosphocreatine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000378:metabolism*
D000227:Adenine Nucleotides; D002951:Citrates; D005971:Glutamates; D007656:Ketoglutaric Acids; D007773:Lactates; D008293:Malates; D010725:Phosphocreatine; D005973:Glutamine; D019343:Citric Acid; D001224:Aspartic Acid; D019344:Lactic Acid; D018698:Glutamic Acid; C030298:malic acid; D010100:Oxygen