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AMP-Activated Protein Kinase Activation by Adrenoceptors in L6 Skeletal Muscle Cells

Mediation by ₁-Adrenoceptors Causing Glucose Uptake

From the Department of Physiology, The Wenner-Gren Institute, Arrhenius Laboratory F3, Stockholm University, Stockholm, Sweden

Address correspondence and reprint requests to Tore Bengtsson, Department of Physiology, The Wenner-Gren Institute, Arrhenius Laboratory F3, Stockholm University, SE 10691 Stockholm, Sweden. E-mail: tore.bengtsson{at}zoofys.su.se

Abbreviations: ACC, acetyl-CoA carboxylase; AICAR, 5-aminoimidazole-4-carboxamide 1-ß-D-ribonucleoside; AMPK, AMP-activated protein kinase; PKC, protein kinase C; TPA, 12-O-tetradecanoylphorbol-13-acetate

AMP-activated protein kinase (AMPK), which functions as a sensor of cellular energy homeostasis, was phosphorylated after norepinephrine stimulation in L6 skeletal muscle cells. This effect was mediated by ₁-adrenoceptors, with no stimulatory effects due to interactions at ₂- or ß-adrenoceptors. ₁-Adrenoceptors are Gq-coupled receptors, and calcium but not phorbol esters could mimic the effect of ₁-adrenergic stimulation; and we show that protein kinase C is not involved as an upstream signal to AMPK by ₁-adrenergic stimulation and that the AMP-to-ATP ratio is unaltered after ₁-adrenergic stimulation. We further show that glucose uptake mediated by ₁- but not by ß-adrenoceptors can be inhibited by AMPK inhibition. Acetyl-CoA carboxylase (ACC) is phosphorylated at Ser218 by AMPK, and ₁- but not ß-adrenoceptor stimulation results in phosphorylation of ACC at this residue. These results suggest a novel pathway where ₁-adrenoceptor activation, independent of protein kinase C, leads to activation of AMPK in skeletal muscle, which contributes to ₁-adrenoceptor–mediated increases in glucose uptake.

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