Relationship between 5-aminoimidazole-4-carboxamide-ribotide and AMP-activated protein kinase activity in the perfused mouse heart

• Published in: American journal of physiology. Heart and circulatory physiology 2006-03, Vol.290 (3), p.H1235-H1243
• Main Authors: Zhang, Li, Frederich, Markus, He, Huamei, Balschi, James A
• Format: Article
• Language: English
• Subjects: Adenosine Monophosphate - metabolism; Adenosine Triphosphate - metabolism; Aminoimidazole Carboxamide - administration & dosage; Aminoimidazole Carboxamide - analogs & derivatives; AMP-Activated Protein Kinases; Animals; Dose-Response Relationship, Drug; Enzyme Activation - drug effects; In Vitro Techniques; Male; Mice; Mice, Inbred C57BL; Multienzyme Complexes - metabolism; Myocardium - metabolism; Protein-Serine-Threonine Kinases - metabolism; Ribonucleosides - administration & dosage
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.00906.2005

NMR Laboratory for Physiological Chemistry, Division of Cardiovascular Medicine, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts Submitted 23 August 2005 ; accepted in final form 24 October 2005 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 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 µM. 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. signal transduction; acetyl-CoA carboxylase; 5'-aminoimidazole-4-carboxamide-1- - D -riboside Address for reprint requests and other correspondence: J. A. Balschi, 221 Longwood Ave., BLI 247, Boston, MA 02115 (e-mail: jbalschi{at}rics.bwh.harvard.edu )