Coupling of Mitochondrial Fatty Acid Uptake to Oxidative Flux in the Intact Heart |
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Authors: | J Michael O’DonnellNathaniel M Alpert Lawrence T WhiteE Douglas Lewandowski |
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Institution: | * Program in Integrative Cardiac Metabolism, Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois 60612-7342 † Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02129-2060 USA |
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Abstract: | The coordination of long chain fatty acid (LCFA) transport across the mitochondrial membrane (VPAL) with subsequent oxidation rate through β-oxidation and the tricarboxylic acid (TCA) cycle (Vtca) has been difficult to characterize in the intact heart. Kinetic analysis of dynamic 13C-NMR distinguished these flux rates in isolated rabbit hearts. Hearts were perfused in a 9.4 T magnet with either 0.5 mM 2,4,6,8,10,12,14,16-13C8] palmitate (n = 4), or 0.5 mM 13C-labeled palmitate plus 0.08 mM unlabeled butyrate (n = 4). Butyrate is a short chain fatty acid (SCFA) that bypasses the LCFA transporters of mitochondria. In hearts oxidizing palmitate alone, the ratio of VTCA to VPAL was 8:1. This is consistent with one molecule of palmitate yielding eight molecules of acetyl-CoA for the subsequent oxidation through the TCA cycle. Addition of butyrate elevated this ratio; VTCA/VPAL = 12:1 due to an SCFA-induced increase in VTCA of 43% (p < 0.05). However, SCFA oxidation did not significantly reduce palmitate transport into the mitochondria: VPAL = 1.0 ± 0.2 μmol/min/g dw with palmitate alone versus 0.9 ± 0.1 with palmitate plus butyrate. Thus, the products of β-oxidation are preferentially channeled to the TCA cycle, away from mitochondrial efflux via carnitine acetyltransferase. |
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