Cardiac responses to induced lactate oxidation: NMR analysis of metabolic equilibria.
The role of lactate as a source of pyruvate oxidation in supporting cardiac work, energetics, and formation of oxidative metabolites was examined in normal myocardium. 13C- and 31P-nuclear magnetic resonance (NMR) spectra were acquired from isolated rabbit hearts supplied 2.5 mM [3-13C]lactate or [3-13C]pyruvate with or without stimulation of pyruvate dehydrogenase (PDH) by dichloroacetate (DCA). Similar workloads determined by rate-pressure products were noted with pyruvate (21,700 +/- 2,400; mean +/- SE) and lactate (18,970 +/- 1,510). Oxygen consumption was similar in all four groups with means between 19.0 and 22.2 mumol.min-1.g dry weight-1 (SE = 1.6-2.0) as was the ratio of phosphocreatine to ATP with means between 1.8 and 2.1 (SE = 0.1-0.6). Intracellular pH, determined from 31P-NMR spectra, was essentially the same with pyruvate (7.06 +/- 0.02) and lactate (7.05 +/- 0.04). 13C enrichment of glutamate was higher with lactate (92%) than with pyruvate (70%). Pyruvate plus DCA induced no change in glutamate content at 9-10 mumol/g, but 13C enrichment increased to 83%, while lactate plus DCA maintained enrichment at 90%. Levels of alpha-ketoglutarate were lower with lactate (1.81 mumol/g) than with pyruvate (2.36 mumol/g). Lactate plus DCA elevated glutamate by 60% with a proportional increase in alpha-ketoglutarate. Thus the balance between glutamate and alpha-ketoglutarate was affected by substrate supply only and not by PDH activation. The results suggest that the equilibrium between alpha-ketoglutarate and glutamate is sensitive to cytosolic redox state, an important consideration for 13C-NMR analyses that rely on glutamate.(ABSTRACT TRUNCATED AT 250 WORDS)
Lewandowski
E D
ED
Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown 02129, USA.
Damico
L A
LA
White
L T
LT
Yu
X
X
D000818:Animals; D002244:Carbon / Q000378:metabolism; D002247:Carbon Isotopes; D004734:Energy Metabolism; D006321:Heart / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D007773:Lactates / Q000378:metabolism*; D019344:Lactic Acid; D009682:Magnetic Resonance Spectroscopy; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D010084:Oxidation-Reduction; D011773:Pyruvates / Q000378:metabolism; D019289:Pyruvic Acid; D011817:Rabbits
D002247:Carbon Isotopes; D007773:Lactates; D011773:Pyruvates; D019344:Lactic Acid; D002244:Carbon; D019289:Pyruvic Acid