A 13C isotopomer kinetic analysis of cardiac metabolism:: influence of altered cytosolic redox and [Ca2+]o

Rat hearts were perfused with mixtures of [3-C-13]pyruvate and [3-C-13]lactate (to alter cytosolic redox) at low (0.5 mM) or high (2.5 mM) Ca2+ concentrations to alter contractility. Hearts were frozen at various times after exposure to these substrates, were extracted. and were then analyzed by C-13 NMR spectroscopy. The time-dependent multiplets observed in the C-13 NMR resonances of glutamate in all hearts and in malate and aspartate in hearts perfused with high-pyruvate/low-lactate concentrations were analyzed using a kinetic model of the tricarboxylic acid (TCA) cycle. The analysis showed that TCA cycle flux (V-TCA) and exchange flux (V-X) that involved cycle intermediates were both sensitive to cell redox and altered Ca2+ concentration, and the ratio of these fluxes (V-X/V-TCA) varied > 10-fold.