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

Departments of Kinesiology and Biological Sciences, Diabetes Research Center, University of Southern California, Los Angeles, California Submitted 8 July 2004 ; accepted in final form 11 November 2004 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 µU/ml insulin, 550 µM palmitate, and [ 14 C]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- - 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. electrical stimulation; perfused hindquarter; acetyl-coenzyme A carboxylase; malonyl-coenzyme A; cellular signaling; 5-aminoimidazole-4-carboxamide-1- - D -ribofuranoside; fatty acids Address for reprint requests and other correspondence: L. P. Turcotte, Dept. of Kinesiology and Biological Sciences, Univ. of Southern California, 3560 Watt Way, PED 107, Los Angeles, CA 90089-0652 (E-mail: turcotte{at}usc.edu )