Calcium-calmodulin/dependent protein kinase II (CaMKII), AMP-activated protein kinase (AMPK), and extracellular signal-regulated kinase (ERK1/2) have each been implicated in the regulation of substrate metabolism during exercise. The purpose of this study was to determine whether CaMKII is involved in the regulation of FA uptake and oxidation and, if it is involved, whether it does so independently of AMPK and ERK1/2. Rat hindquarters were perfused at rest with (n = 16) or without (n = 10) 3 mM caffeine, or during electrical stimulation (n = 14). For each condition, rats were subdivided and treated with 10 muM of either KN92 or KN93, inactive and active CaMKII inhibitors, respectively. Both caffeine treatment and electrical stimulation significantly increased FA uptake and oxidation. KN93 abolished caffeine-induced FA uptake, decreased contraction-induced FA uptake by 33%, and abolished both caffeine- and contraction-induced FA oxidation (P < 0.05). Caffeine had no effect on ERK1/2 phosphorylation (P > 0.05) and increased alpha(2)-AMPK activity by 68% (P < 0.05). Electrical stimulation increased ERK1/2 phosphorylation and alpha(2)-AMPK activity by 51% and 3.4-fold, respectively (P < 0.05). KN93 had no effect on caffeine-induced alpha(2)-AMPK activity, ERK1/2 phosphorylation, or contraction-induced ERK1/2 phosphorylation (P > 0.05). Alternatively, it decreased contraction-induced alpha(2)-AMPK activity by 51% (P < 0.05), suggesting that CaMKII lies upstream of AMPK. These results demonstrate that regulation of contraction-induced FA uptake and oxidation occurs in part via Ca(2+)-independent activation of ERK1/2 as well as Ca(2+)-dependent activation of CaMKII and AMPK.

These results show for the first time that the increase in FA uptake and in plasma membrane FAT/CD36 protein content is mediated, at least in part, by the ERK1/2 signalling pathway during muscle contraction.

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. AMPK activation is not critical in the regulation of muscle FA uptake and oxidation during low-intensity muscle contraction. Am J Physiol Endocrinol Metab 288: E592-E598, 2005. First published November 16, 2004; doi:10.1152/ajpendo.00301.2004.-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 U/ml insulin, 550 M 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 Ͻ 0.05) but had no effect on either variable during ES (P Ͼ 0.05). AICAR treatment significantly increased total FA oxidation (P Ͻ 0.05) during both R (0.38 Ϯ 0.11 vs., which was paralleled in both conditions by a significant increase and significant decrease in AMPK and acetyl-CoA carboxylase (ACC) activity, respectively (P Ͻ 0.05). Low-intensity muscle contraction increased glucose uptake, FA uptake, and total FA oxidation (P Ͻ 0.05) despite no change in AMPK (950.5 Ϯ 35.9 vs. 1,067.7 Ϯ 58.8 nmol ⅐ min Ϫ1 ⅐ g Ϫ1 ) or ACC (51.2 Ϯ 6.7 vs. 55.7 Ϯ 2.0 nmol ⅐ min Ϫ1 ⅐ g Ϫ1 ) activity from R to ES (P Ͼ 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 IT HAS BEEN SHOWN REPEATEDLY in isolated muscle and whole body studies that exercise and muscle contraction increase fatty acid (FA) utilization (4,5,25). In perfused muscle as well as in giant sarcolemmal vesicles isolated from muscles, it has been shown that the rate of FA uptake is higher during acute muscle contraction induced by electrical stimulation than during rest, and that this increase in FA uptake is independent of FA delivery (6,25). In perfused and isolated rat muscle and in human muscle, it has also been shown that the rate of FA oxidation is higher during acute muscle contraction induced by electrical stimulation and knee extensor exercise, respectively, than during rest (9,25,26). However, the signaling pathway(s) regulating this contraction-induced increase in FA uptake and oxidation in muscle is not well defined.

Raney, Marcella A., and Lorraine P. Turcotte. Regulation of contraction-induced FA uptake and oxidation by AMPK and ERK1/2 is intensity dependent in rodent muscle. Am J Physiol Endocrinol Metab 291: E1220 -E1227, 2006. First published July 11, 2006; doi:10.1152/ajpendo.00155.2006.-Muscle contraction activates AMP-activated protein kinase (AMPK) and extracellular signal-regulated kinase (ERK1/2), two signaling molecules involved in the regulation of muscle metabolism. The purpose of this study was to determine whether activation of AMPK and/or ERK1/2 contributes to the regulation of muscle fatty acid (FA) uptake and oxidation in contracting muscle. Rat hindquarters were perfused during rest (R) or electrical stimulation (E) of increasing intensity by manipulating train duration (E1 ϭ 25 ms, E2 ϭ 50 ms, E3 ϭ 100 ms, E4 ϭ 200 ms). For matched FA delivery, FA uptake was significantly greater than R during E1, E2, and E3 (7.8 Ϯ 0.7 vs. 14.4 Ϯ 0.3, 16.9 Ϯ 0.8, 15FA oxidation was significantly greater than R during E1 and E2 (1.5 Ϯ 0.1 vs. 2.3 Ϯ 0.2, 2.5 Ϯ 0.2 nmol ⅐ min Ϫ1 ⅐ g Ϫ1 , P Ͻ 0.05) before returning to resting levels for E3 and E4 (1.8 Ϯ 0.1 and 1.5 Ϯ 0.2 nmol ⅐ min Ϫ1 ⅐ g Ϫ1 , P Ͼ 0.05). A positive correlation was found between FA uptake and ERK1/2 phosphorylation from R to E3 (R 2 ϭ 0.55, P Ͻ 0.05) and between FA oxidation and ERK1/2 phosphorylation from R to E2 (R 2 ϭ 0.76, P Ͻ 0.05), correlations that were not maintained when the data for E4 and E3 and E4, respectively, were included in the analysis (R 2 ϭ 0.04 and R 2 ϭ 0.03, P Ͼ 0.05). A positive correlation was also found between FA uptake and FA oxidation and AMPK activity for all exercise intensities (R 2 ϭ 0.57, R 2 ϭ 0.65 respectively, P Ͻ 0.05). These results, in combination with previous data from our laboratory, suggest that ERK1/2 and AMPK are the predominant signaling molecules regulating FA uptake and oxidation during low-to moderate-intensity muscle contraction and during moderate-to high-intensity muscle contraction, respectively. adenosine monophosphate-activated protein kinase; extracellular signal-regulated kinase; fatty acid metabolism; contraction intensity; fatty acid delivery; cellular signaling; acetyl-coenzyme A carboxylase FATTY ACIDS (FA) are an important energy source for skeletal muscle at rest and, at a given FA concentration, FA utilization in muscle has been shown to be severalfold higher during muscle contraction than at rest (7,10,23,29). In incubated muscle, FA oxidation during muscle contraction has been shown to correlate positively with the stimulation frequency up to 40 tetani/min (7, 10). Similarly, in healthy subjects performing bicycle exercise, the rate of muscle FA oxidation is higher during low-and moderate-intensity muscle contraction than at rest (23,26,31,34). The increase in FA utilization during whole body exercise is associated with an increase in plasma FA concentration and, hence, FA delivery to the working muscle (18,23,25,42), leading some to hypothesize that the increase in FA delivery is the main fa...