Regulation of Cytosolic and Mitochondrial Oxidation via Malate-Aspartate Shuttle: An Observation Using Dynamic ¹³C NMR Spectroscopy

Abstract

The malate-aspartate (M-A) shuttle provides an important mechanism of metabolic communication between the cytosol and the mitochondria. In this study, dynamic ¹³C NMR spectroscopy was combined with a multi-domain model of cardiacmetabolism for direct quantification ofmetabolic fluxes through the tricarboxylic acid (TCA) cycle (VTCA) and the M-Ashuttle (VM−A) in intact heart. The sensitivity of this approach to altered M-A shuttle activity was examined at different cytosolic redox states. Dynamic ¹³C NMR spectra were acquired from isolated rat hearts perfused with ¹³C labeled fatty acid at either low (fatty acid only) or high cytosolic redox state induced by exogenous glucose and lactate. VTCA and VM−A were determined by least-square fitting of the model to NMR data. Our results showed that while VTCA was similar, VM−A increased by 75% at high cytosolic redox state. Therefore, our proposed method provides the opportunity for direct quantification of metabolic communication between subcellular compartments via the M-A shuttle.