Submitted on October 5, 2005
Revised on November 7, 2005
Accepted on November 21, 2005
Regulation of AMP-activated protein kinase and acetyl-CoA carboxylase phosphorylation by palmitate in skeletal muscle cells
Sergiu Fediuc, Mandeep P. Gaidhu, and Rolando B. Ceddia
Kinesiology and Health Science, York University, Toronto, Ontario M3J 1P3
Corresponding Author: roceddia{at}yorku.ca
The purpose of this study was to investigate the effects of long-chain fatty acids (LCFAs) on AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) phosphorylation, and 
-oxidation in skeletal muscle. L6 rat skeletal muscle cells were exposed to various concentrations of palmitate (1 to 800
M). Subsequently, ACC and AMPK phosphorylation, and fatty acid oxidation were measured. A 2-fold increase in both AMPK and ACC phosphorylation was observed in the presence of palmitate concentrations as low as 10 M, which was also accompanied by a significant increase in fatty acid oxidation. The effect of palmitate on AMPK and ACC phosphorylation was dose-dependent, reaching maximum increases of 3.5-fold and 4.5-fold, respectively. Interestingly, ACC phosphorylation was coupled with AMPK activation at palmitate concentrations ranging from 10 to 100M; however, at concentrations above 200M, ACC phosphorylation and fatty acid oxidation remained elevated even after AMPK phosphorylation was completely prevented by the utilization of a selective AMPK inhibitor. This indicates that LCFAs regulate ACC activity by AMPK-dependent and independent mechanisms, based on their abundance in skeletal muscle cells. Here, we provide novel evidence that the AMPK/ACC pathway may operate as a mechanism to sense and respond to the lipid energy charge of skeletal muscle cells.
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