AMP-activated kinase (AMPK) is a highly conserved heterotrimeric kinase that functions as a metabolic master switch to coordinate cellular enzymes involved in carbohydrate and fat metabolism that regulate ATP conservation and synthesis. AMPK is activated by conditions that increase AMP-to-ATP ratio, such as exercise and metabolic stress. In the present study, we probed whether AMPK was expressed in vascular smooth muscle and would be activated by metabolic stress. Endothelium-denuded porcine carotid artery segments were metabolically challenged with 2-deoxyglucose (10 mM) plus N(2) (N(2)-2DG). These vessels exhibited a rapid increase in AMPK activity by 1 min that was near maximal by 20 min. AMPK inactivation on return to normal physiological saline was approximately 50% in 1 min and fully recovered by 5 min. Immunoprecipitation of the alpha(1)- and alpha(2)-catalytic subunit followed by immunoblot analysis for [P]Thr(172)-AMPK indicates that alpha(1)-AMPK accounts for all activity. Little if any alpha(2)-AMPK was detected in carotid smooth muscle. AMPK activity was not increased by contractile agonist (endothelin-1) or by the reported AMPK activators 5-aminoimidazole-4-carboxamide ribofuranoside (2 mM), metformin (2 mM), or phenformin (0.2 mM). AMPK activation by N(2)-2DG was associated with a rapid and pronounced reduction in endothelin-induced force and reduced phosphorylation of Akt and Erk 1/2. These data demonstrate that AMPK expression differs in vascular smooth muscle compared with striated muscles and that activation and inactivation after metabolic stress occur rapidly and are associated with signaling pathways that may regulate smooth-muscle contraction.

Transgenic mice with modifications of the gamma‐2 subunit of AMPK, exhibit a hypertrophic cardiac phenotype with increased myocyte glycogen deposits. We have observed that mice in which the alpha‐1 subunit of AMP kinase (a1AMPK) gene had been knocked out (a1AMPK KO) exhibited increased cardiac dimensions and average diameter of left ventricular cardiomyocytes as compared to age‐ and gender‐matched wildtype (WT) mice (22.0 + 2.0 versus 13.8 + 0.9 microns, P < 0.05). Fractional shortening measured by echocardiography also was reduced in KO hearts (29 +/− 2) compared to WT (36 +/− 5). Immunohistochemistry demonstrated no expression of a1AMPK in cardiomyocytes of a1AMPK KO and also suggested a trend for increased percent immunoreactivity for atrial natriuretic peptide (ANP) compared to WT mice (61048.3 + 47143.3 versus 3672.7 + 4980.7). There was no difference in sections of myocardium for tingible glycogen by the periodic acid‐Schiff method, with and without diastase. However there was accumulation of oil‐red‐o‐positive lipid droplets in the myocardium of a1AMPK KO mice as compared to WT mice, suggesting that the a1AMPK KO mouse may be a potential model for cardiac lipotoxicity.