AMP-activated protein kinase (AMPK) is a serine-threonine kinase that regulates cellular metabolism and has an essential role in activating glucose transport during hypoxia and ischemia. The mechanisms responsible for AMPK stimulation of glucose transport are uncertain, but may involve interaction with other signaling pathways or direct effects on GLUT vesicular trafficking. One potential downstream mediator of AMPK signaling is the nitric oxide pathway. The aim of this study was to examine the extent to which AMPK mediates glucose transport through activation of the nitric oxide (NO)-signaling pathway in isolated heart muscles. Incubation with 1 mM 5-amino-4-imidazole-1-β-carboxamide ribofuranoside (AICAR) activated AMPK ( P < 0.01) and stimulated glucose uptake ( P < 0.05) and translocation of the cardiomyocyte glucose transporter GLUT4 to the cell surface ( P < 0.05). AICAR treatment increased phosphorylation of endothelial NO synthase (eNOS) ∼1.8-fold ( P < 0.05). eNOS, but not neuronal NOS, coimmunoprecipitated with both the α2 and α1 AMPK catalytic subunits in heart muscle. NO donors also increased glucose uptake and GLUT4 translocation ( P < 0.05). Inhibition of NOS with Nω-nitro-l-arginine and Nω-methyl-l-arginine reduced AICAR-stimulated glucose uptake by 21 ± 3% ( P < 0.05) and 25 ± 4% ( P < 0.05), respectively. Inhibition of guanylate cyclase with ODQ and LY-83583 reduced AICAR-stimulated glucose uptake by 31 ± 4% ( P < 0.05) and 22 ± 3% ( P < 0.05), respectively, as well as GLUT4 translocation to the cell surface ( P < 0.05). Taken together, these results indicate that activation of the NO-guanylate cyclase pathway contributes to, but is not the sole mediator of, AMPK stimulation of glucose uptake and GLUT4 translocation in heart muscle.
