Low-intensity contraction activates the alpha1-isoform of 5'-AMP-activated protein kinase in rat skeletal muscle.
Low-intensity contraction activates the alpha1-isoform of 5'-AMP-activated protein kinase in rat skeletal muscle.
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DOI：
10.1152/ajpendo.00395.2005
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发表时间：
2006-03
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通讯作者：
Taro Toyoda;Satsuki Tanaka;K. Ebihara;H. Masuzaki;K. Hosoda;Kenji Sato;T. Fushiki;K. Nakao;Tatsuya Hayashi
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文献类型：
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作者：
Taro Toyoda;Satsuki Tanaka;K. Ebihara;H. Masuzaki;K. Hosoda;Kenji Sato;T. Fushiki;K. Nakao;Tatsuya Hayashi
骨骼肌表达5‘-AMP激活的蛋白激酶(AMPK)的两个催化亚基，α1和α2，参与收缩刺激的葡萄糖运输和脂肪酸氧化。肌肉收缩可以激活含α2的AMPK复合体(AMPKalpha2)，但这种激活可以在含有alpha1的AMPK复合体(AMPKalpha1)激活或不激活的情况下发生，这表明AMPKalpha2是骨骼肌收缩诱导的代谢事件的主要亚型。我们首次报道，AMPKalpha1，而不是AMPKalpha2，可以在收缩骨骼肌中被激活。分离大鼠外周毛肌，孵育于含丙酮酸的Krebs-Ringer重碳酸盐缓冲液中。在孵育的最后2分钟，以1和2赫兹的频率刺激收缩的肌肉中，AMPKalpha1的活性增加了两倍，而AMPKalpha2的活性保持不变。肌肉刺激不改变肌肉AMP浓度或AMP/ATP比值。AMPK的激活与主要激活部位--α-亚基的Thr(172)磷酸化增加有关。肌肉刺激增加了AMPK下游靶标乙酰辅酶A羧基酶(ACC)的磷酸化，增加了3-O-甲基-d-葡萄糖的转运速率。相反，增加收缩的频率(或=5赫兹)或持续时间(或=5分钟)可激活AMPKalpha1和AMPKalpha2，并增加AMP浓度和AMP/ATP比率。这些结果表明：1)AMPKalpha1是低强度收缩肌中AMP非依赖性磷酸化激活的主要亚型，2)AMPKalpha2在高强度收缩肌中是由AMP依赖的机制激活的，3)各亚型的激活促进了骨骼肌中葡萄糖的转运和ACC的磷酸化。
Skeletal muscle expresses two catalytic subunits, alpha1 and alpha2, of the 5'-AMP-activated protein kinase (AMPK), which has been implicated in contraction-stimulated glucose transport and fatty acid oxidation. Muscle contraction activates the alpha2-containing AMPK complex (AMPKalpha2), but this activation may occur with or without activation of the alpha1-containing AMPK complex (AMPKalpha1), suggesting that AMPKalpha2 is the major isoform responsible for contraction-induced metabolic events in skeletal muscle. We report for the first time that AMPKalpha1, but not AMPKalpha2, can be activated in contracting skeletal muscle. Rat epitrochlearis muscles were isolated and incubated in Krebs-Ringer bicarbonate buffer containing pyruvate. In muscles stimulated to contract at a frequency of 1 and 2 Hz during the last 2 min of incubation, AMPKalpha1 activity increased twofold and AMPKalpha2 activity remained unchanged. Muscle stimulation did not change the muscle AMP concentration or the AMP-to-ATP ratio. AMPK activation was associated with increased phosphorylation of Thr(172) of the alpha-subunit, the primary activation site. Muscle stimulation increased the phosphorylation of acetyl-CoA carboxylase (ACC), a downstream target of AMPK, and the rate of 3-O-methyl-d-glucose transport. In contrast, increasing the frequency (>or=5 Hz) or duration (>or=5 min) of contraction activated AMPKalpha1 and AMPKalpha2 and increased AMP concentration and the AMP/ATP ratio. These results suggest that 1) AMPKalpha1 is the predominant isoform activated by AMP-independent phosphorylation in low-intensity contracting muscle, 2) AMPKalpha2 is activated by an AMP-dependent mechanism in high-intensity contracting muscle, and 3) activation of each isoform enhances glucose transport and ACC phosphorylation in skeletal muscle.