title: Relationship between 5-aminoimidazole-4-carboxamide-ribotide and AMP-activated protein kinase activity in the perfused mouse heart.
abstract: AMP-activated protein kinase (AMPK) is a cellular energy sensor whose activity responds to AMP concentration ([AMP]). An agent that activates AMPK in cells is 5-aminoimidazole-4-carboxamide-1-riboside (AICA-riboside). Phosphorylated AICA-riboside or AICA-ribotide (ZMP) is an AMP analog. It is generally assumed that ZMP accumulation does not alter [AMP]. Additionally, the effect of AICA-riboside on AMPK activity of the heart is uncertain. Two hypotheses were tested in the isolated mouse heart: 1) sufficient ZMP concentration ([ZMP]) forms to increase AMPK activity, and 2) [ZMP] accumulation increases [AMP]. Perfusion of isolated mouse hearts with Krebs-Henseleit buffer containing 0.15-2 mM AICA-riboside concentration resulted in [ZMP] of 2-8 mM. ZMP accumulation reduced phosphocreatine concentration, which increased cytosolic [AMP]. In hearts with [ZMP] less than approximately 3 mM, in vivo AMPK allosteric activity effects of ZMP were observed; AMPK phosphorylation and [AMP] were not increased. With [ZMP] between 3 and 5 mM, in vitro AMPK activity and phosphorylation increased with unchanged [AMP]. This occurred in hearts perfused with 0.25 mM AICA-riboside for 48 min and 0.5 mM AICA-riboside for 24 min. The [ZMP] resulting in 50% AMPK activity (covalent phosphorylation of AMPK) was 4.1 +/- 0.6 mM. Hearts with [ZMP] >5 mM displayed increased [AMP] and AMPK activity that was not different from hearts with similar [AMP] with no [ZMP]; the half-maximal activity of AMP was 5.6 +/- 1.6 microM. Thus, in mouse hearts, AICA-riboside was metabolized to [ZMP] adequately to increase AMPK activity. Higher [ZMP] also increased cytosolic [AMP], which affects AMPK activity.
authors.affiliation: NMR Laboratory for Physiological Chemistry, Division of Cardiovascular Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA. jbalschi@rics.bwh.harvard.edu
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Markus
authors.initials: M
authors.lastname: Frederich
authors.forename: Huamei
authors.initials: H
authors.lastname: He
authors.forename: James A
authors.initials: JA
authors.lastname: Balschi
mesh_terms: D055372:AMP-Activated Protein Kinases; D000249:Adenosine Monophosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000620:Aminoimidazole Carboxamide / Q000008:administration & dosage / Q000031:analogs & derivatives*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009097:Multienzyme Complexes / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012263:Ribonucleosides / Q000008:administration & dosage*
chemical_list: D009097:Multienzyme Complexes; D012263:Ribonucleosides; D000620:Aminoimidazole Carboxamide; D000249:Adenosine Monophosphate; C011651:acadesine; D000255:Adenosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases