AMPK activation is not critical in the regulation of muscle FA uptake and oxidation during low-intensity muscle contraction

To determine the role of AMP-activated protein kinase (AMPK) activation on the regulation of fatty acid (FA) uptake and oxidation, we perfused rat hindquarters with 6 mM glucose, 10 muU/ml insulin, 550 muM palmitate, and [C-14] palmitate during rest (R) or electrical stimulation (ES), inducing low-intensity (0.1 Hz) muscle contraction either with or without 2 mM 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR). AICAR treatment significantly increased glucose and FA uptake during R (P<0.05) but had no effect on either variable during ES (P>0.05). AICAR treatment significantly increased total FA oxidation (P<0.05) during both R (0.38 +/- 0.11 vs. 0.89 +/- 0.1 nmol.min(-1).g(-1)) and ES (0.73 +/- 0.11 vs. 2.01 +/- 0.1 nmol.min(-1).g(-1)), which was paralleled in both conditions by a significant increase and significant decrease in AMPK and acetyl-CoA carboxylase (ACC) activity, respectively (P<0.05). Low-intensity muscle contraction increased glucose uptake, FA uptake, and total FA oxidation (P<0.05) despite no change in AMPK (950.5 +/- 35.9 vs. 1,067.7 +/- 58.8 nmol.min(-1).g(-1)) or ACC (51.2 +/- 6.7 vs. 55.7 +/- 2.0 nmol.min(-1).g(-1)) activity from R to ES (P>0.05). When contraction and AICAR treatment were combined, the AICAR-induced increase in AMPK activity (34%) did not account for the synergistic increase in FA oxidation (175%) observed under similar conditions. These results suggest that while AMPK-dependent mechanisms may regulate FA uptake and FA oxidation at rest, AMPK-independent mechanisms predominate during low-intensity muscle contraction.