Submitted on October 14, 2003
Accepted on March 18, 2004
A 13C Isotopomer Kinetic Analysis of Cardiac Metabolism:Influence of Altered Cytosolic Redox and Extracellular [Ca2+]
Rui A. Carvalho1, Tiago B. Rodrigues1, Piyu Zhao2, F. Mark H. Jeffrey3, Craig R. Malloy4, and A. Dean Sherry5*
1 Department of Biochemistry and Center Neurosciences and Cell Biology, University of Coimbra, Coimbra, Portugal
2 Department of Chemistry, University of Texas at Dallas, Richardson, Texas, USA
3 Department of Radiology, Mary Nell and Ralph B. Rogers Magnetic Resonance Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA
4 Department of Radiology, Mary Nell and Ralph B. Rogers Magnetic Resonance Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA; Department of Internal Medicine, UT Southwestern Medical Center and Department of Veternas Affairs Medical Center, Dallas, Texas, USA
5 Department of Chemistry, University of Texas at Dallas, Richardson, Texas, USA; Department of Radiology, Mary Nell and Ralph B. Rogers Magnetic Resonance Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA
* To whom correspondence should be addressed. E-mail: dean.sherry{at}utsouthwestern.
Rat hearts were perfused with mixtures of [3-13C]pyruvate and [3-13C]lactate (to alter cytosolic redox) at low Ca2+ (0.5 mM) or high Ca2+ (2.5 mM) to alter contractility. Hearts were
frozen at various times after exposure to these substrates, extracted and analyzed by 13C NMR spectroscopy. The time-dependent multiplets observed in the 13C NMR resonances of glutamate in all hearts and in malate and aspartate in hearts perfused with high pyruvate/low lactate were analyzed using a kinetic model of the tricarboxylic acid (TCA) cycle. The analysis showed that
TCA cycle flux (VTCA) and exchange flux (VX) involving cycle intermediates were both sensitive to cell redox and altered [Ca2+], with the ratio of these fluxes, VX/VTCA, varying over 10-fold.
