Covalent activation of heart AMP-activated protein kinase in response to physiological concentrations of long-chain fatty acids.
Rat hearts were perfused for 1 h with 5 mm glucose with or without palmitate or oleate at concentrations characteristic of the fasting state. The inclusion of fatty acids resulted in increased activities of the alpha-1 or the alpha-2 isoforms of AMP-activated protein kinase (AMPK), increased phosphorylation of acetyl-CoA carboxylase and a decrease in the tissue content of malonyl-CoA. Activation of AMPK was not accompanied by any changes in the tissue contents of ATP, ADP, AMP, phosphocreatine or creatine. Palmitate increased phosphorylation of Thr172 within AMPK alpha-subunits and the activation by palmitate of both AMPK isoforms was abolished by protein phosphatase 2C leading to the conclusion that exposure to fatty acid caused activation of an AMPK kinase or inhibition of an AMPK phosphatase. In vivo, 24 h of starvation also increased heart AMPK activity and Thr172 phosphorylation of AMPK alpha-subunits. Perfusion with insulin decreased both alpha-1 and alpha-2 AMPK activities and increased malonyl-CoA content. Palmitate prevented both of these effects. Perfusion with epinephrine decreased malonyl-CoA content without an effect on AMPK activity but prevented the activation of AMPK by palmitate. The concept is discussed that activation of AMPK by an unknown fatty acid-driven signalling process provides a mechanism for a 'feed-forward' activation of fatty acid oxidation.
Clark
Hilary
H
Department of Biochemistry and Molecular Biology, University College London, Gower Street, London WC1E 6BT, UK.
Carling
David
D
Saggerson
David
D
D055372:AMP-Activated Protein Kinases; D000227:Adenine Nucleotides / Q000378:metabolism; D000322:Adrenergic Agonists / Q000494:pharmacology; D000818:Animals; D004789:Enzyme Activation; D005215:Fasting; D005227:Fatty Acids / Q000737:chemistry / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D009097:Multienzyme Complexes / Q000378:metabolism*; D009206:Myocardium / Q000201:enzymology*; D009924:Organ Culture Techniques; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
D000227:Adenine Nucleotides; D000322:Adrenergic Agonists; D005227:Fatty Acids; D007328:Insulin; D009097:Multienzyme Complexes; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases