The Relationship between AMP-activated Protein Kinase Activity and AMP Concentration in the Isolated Perfused Rat Heart

• Published in: The Journal of biological chemistry 2002-01, Vol.277 (3), p.1928-1932
• Main Authors: Frederich, Markus, Balschi, James A.
• Format: Article
• Language: English
• Subjects: Acetyl-CoA Carboxylase - metabolism; Adenosine Monophosphate - metabolism; Amino Acid Sequence; AMP-Activated Protein Kinases; Animals; Caprylates - pharmacology; Enzyme Inhibitors - pharmacology; In Vitro Techniques; Molecular Sequence Data; Multienzyme Complexes - antagonists & inhibitors; Multienzyme Complexes - metabolism; Myocardium - enzymology; Myocardium - metabolism; Nuclear Magnetic Resonance, Biomolecular; Protein-Serine-Threonine Kinases - antagonists & inhibitors; Protein-Serine-Threonine Kinases - metabolism; Rats; Rats, Sprague-Dawley
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M107128200

The objective of this study was to define the relationship among AMP-activated protein kinase (AMPK) activity, AMP concentration ([AMP]), and [ATP] in perfused rat hearts. Bromo-octanoate, an inhibitor of β-oxidation, and amino-oxyacetate, an inhibitor of the malate-aspartate shuttle, were used to modify substrate flux and thus increase cytosolic [AMP]. Cytosolic [AMP] was calculated using metabolites measured by 31P NMR spectroscopy. Rat hearts were perfused with Krebs-Henseleit solution containing glucose and either no inhibitor, the inhibitors, or the inhibitors plus butyrate, a substrate that bypasses the metabolic blocks. In this way, [AMP] changed from 0.2 to 27.9 μm, and [ATP] varied between 11.7 and 6.8 mm. AMPK activity ranged from 7 to 60 pmol·min−1·μg of protein−1. The half-maximal AMPK activation (A0.5) was 1.8 ± 0.3 μmAMP. Measurements in vitro have reported similar AMPKA0.5 at 0.2 mm ATP, but found thatA0.5 increased 10–20-fold at 4 mmATP. The low A0.5 of this study despite a high [ATP] suggests that in vivo the ATP antagonism of AMPK activation is reduced, and/or other factors besides AMP activate AMPK in the heart.