Probing the link between citrate and malonyl-CoA in perfused rat hearts

• Published in: American journal of physiology. Heart and circulatory physiology Vol. 283; no. 4; p. H1379
• Main Authors: Poirier, Myriame, Vincent, Geneviève, Reszko, Aneta E, Bouchard, Bertrand, Kelleher, Joanne K, Brunengraber, Henri, Des Rosiers, Christine
• Format: Journal Article
• Language: English
• Published: United States 01-10-2002
• Subjects: Acetyl Coenzyme A - metabolism; Animals; ATP Citrate (pro-S)-Lyase - metabolism; Carbon Isotopes; Citrates - metabolism; Citric Acid - metabolism; Citric Acid Cycle - physiology; Gas Chromatography-Mass Spectrometry; In Vitro Techniques; Male; Malonyl Coenzyme A - metabolism; Myocardial Contraction - physiology; Myocardium - metabolism; Perfusion; Pyruvic Acid - pharmacokinetics; Rats; Rats, Sprague-Dawley
• ISSN: 0363-6135
• DOI: 10.1152/ajpheart.00244.2002

Little is known about the sources of cytosolic acetyl-CoA used for the synthesis of malonyl-CoA, a key regulator of fatty acid oxidation in the heart. We tested the hypothesis that citrate provides acetyl-CoA for malonyl-CoA synthesis after its mitochondrial efflux and cleavage by cytosolic ATP-citrate lyase. We expanded on a previous study where we characterized citrate release from perfused rat hearts (Vincent G, Comte B, Poirier M, and Des Rosiers C. Citrate release by perfused rat hearts: a window on mitochondrial cataplerosis. Am J Physiol Endocrinol Metab 278: E846-E856, 2000). In the present study, we show that citrate release rates, ranging from 6 to 22 nmol/min, can support a net increase in malonyl-CoA concentrations induced by changes in substrate supply, at most 0.7 nmol/min. In experiments with [U-(13)C](lactate + pyruvate) and [1-(13)C]oleate, we show that the acetyl moiety of malonyl-CoA is derived from both pyruvate and long-chain fatty acids. This (13)C-labeling of malonyl-CoA occurred without any changes in its concentration. Hydroxycitrate, an inhibitor of ATP-citrate lyase, prevents increases in malonyl-CoA concentrations and decreases its labeling from [U-(13)C](lactate + pyruvate). Our data support at least a partial role of citrate in the transfer from the mitochondria to cytosol of acetyl units for malonyl-CoA synthesis. In addition, they provide a dynamic picture of malonyl-CoA metabolism: even when the malonyl-CoA concentration remains constant, there appears to be a constant need to supply acetyl-CoA from various carbon sources, both carbohydrates and lipids, for malonyl-CoA synthesis.