Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan.
Acta Physiol (Oxf). 2011 Feb;201(2):227-38. doi: 10.1111/j.1748-1716.2010.02169.x.
Caffeine activates 5'AMP-activated protein kinase (AMPK), a signalling intermediary implicated in the regulation of glucose, lipid and energy metabolism in skeletal muscle. Skeletal muscle expresses two catalytic α subunits of AMPK, α1 and α2, but the isoform specificity of caffeine-induced AMPK activation is unclear. The aim of this study was to determine which α isoform is preferentially activated by caffeine in vitro and in vivo using rat skeletal muscle.
Rat epitrochlearis muscle was isolated and incubated in vitro in the absence or presence of caffeine. In another experiment, the muscle was dissected after intravenous injection of caffeine. Isoform-specific AMPK activity, the phosphorylation status of AMPKα Thr(172) and acetyl-CoA carboxylase (ACC) Ser(79) , the concentrations of ATP, phosphocreatine (PCr) and glycogen, and 3-O-methyl-d-glucose (3MG) transport activity were estimated.
Incubation of isolated epitrochlearis muscle with 1 mm of caffeine for 15 min increased AMPKα1 activity, but not AMPKα2 activity; concentrations of ATP, PCr and glycogen were not affected. Incubation with 3 mm of caffeine activated AMPKα2 and reduced PCr and glycogen concentrations. Incubation with 1 mm of caffeine increased the phosphorylation of AMPK and ACC and enhanced 3MG transport. Intravenous injection of caffeine (5 mg kg(-1) ) predominantly activated AMPKα1 and increased 3MG transport without affecting energy status.
Our results suggest that of the two α isoforms of AMPK, AMPKα1 is predominantly activated by caffeine via an energy-independent mechanism and that the activation of AMPKα1 increases glucose transport and ACC phosphorylation in skeletal muscle.
咖啡因激活 5'AMP 激活的蛋白激酶（AMPK），这是一种信号中介物，参与调节骨骼肌中的葡萄糖、脂质和能量代谢。骨骼肌表达 AMPK 的两种催化α亚基，α1 和α2，但咖啡因诱导的 AMPK 激活的同工型特异性尚不清楚。本研究的目的是使用大鼠骨骼肌在体外和体内确定哪种α同工型优先被咖啡因激活。
分离大鼠比目鱼肌并在不存在或存在咖啡因的情况下进行体外孵育。在另一个实验中，在静脉注射咖啡因后解剖肌肉。估计同工型特异性 AMPK 活性、AMPKα Thr(172)和乙酰辅酶 A 羧化酶 (ACC) Ser(79)的磷酸化状态、ATP、磷酸肌酸 (PCr)和糖原的浓度以及 3-O-甲基-d-葡萄糖 (3MG) 转运活性。
用 1mM 咖啡因孵育分离的比目鱼肌 15 分钟可增加 AMPKα1 活性，但不增加 AMPKα2 活性；ATP、PCr 和糖原的浓度不受影响。用 3mM 咖啡因孵育可激活 AMPKα2 并降低 PCr 和糖原浓度。用 1mM 咖啡因孵育可增加 AMPK 和 ACC 的磷酸化并增强 3MG 转运。静脉注射咖啡因（5mgkg(-1)）主要激活 AMPKα1 并增加 3MG 转运，而不影响能量状态。
我们的结果表明，在 AMPK 的两种α同工型中，AMPKα1 主要通过能量独立机制被咖啡因激活，并且 AMPKα1 的激活增加了骨骼肌中的葡萄糖转运和 ACC 磷酸化。
