Dehydrogenase regulation of metabolite oxidation and efflux from mitochondria in intact hearts.
To test how alpha-ketoglutarate dehydrogenase (alpha-KGDH) activity influences the balance between oxidative flux and transmitochondrial metabolite exchange, we monitored these rates in isolated mitochondria and in perfused rabbit hearts at an altered kinetics (Km) of alpha-KGDH for alpha-ketoglutarate (alpha-KG). In isolated mitochondria, relative Km dropped from 0.23 mM at pH = 7.2 to 0.10 mM at pH 6.8 (P < 0.05), and alpha-KG efflux decreased from 126 to 95 nmol.min-1.mg-1. In intact hearts, Km was reduced with low intracellular pH, while matching control workload and respiratory rate with increased Ca2+ (pHi = 7.20, perfusate CaCl2 = 1.5 mM; pHi = 6.89, perfusate CaCl2 = 3 +/- 1 mM). Sequential 13C nuclear magnetic resonance spectra from hearts oxidizing [2-13C]acetate provided tricarboxylic acid cycle flux and the exchange rate between alpha-KG and cytosolic glutamate (F1). Tricarboxylic acid cycle flux was 10 mumol.min-1.g-1 in both groups, but F1 fell from a control of 9.3 +/- 0.6 to 2.8 +/- 0.4 mumol.min-1.g-1 at low Km. The results indicate that increased activity of alpha-KGDH occurs at the expense of alpha-KG efflux during support of normal workloads.
O'Donnell
J M
JM
Nuclear Magnetic Resonance Center, Massachusetts General Hospital, Harvard Medical School, Boston 02129, USA.
Doumen
C
C
LaNoue
K F
KF
White
L T
LT
Yu
X
X
Alpert
N M
NM
Lewandowski
E D
ED
D000085:Acetates / Q000378:metabolism; D000818:Animals; D002122:Calcium Chloride / Q000494:pharmacology; D002952:Citric Acid Cycle; D018698:Glutamic Acid / Q000378:metabolism; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism*; D007656:Ketoglutaric Acids / Q000378:metabolism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008929:Mitochondria, Heart / Q000201:enzymology*; D009206:Myocardium / Q000201:enzymology*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D010101:Oxygen Consumption; D011817:Rabbits
D000085:Acetates; D007656:Ketoglutaric Acids; D018698:Glutamic Acid; D010088:Oxidoreductases; D007655:Ketoglutarate Dehydrogenase Complex; D002122:Calcium Chloride