title: Skeletal muscle mitochondrial respiration in AMPKα2 kinase-dead mice.
abstract: OBJECTIVE
  To study whether the phenotypical characteristics (exercise intolerance; reduced spontaneous activity) of the AMPKα2 kinase-dead (KD) mice can be explained by a reduced mitochondrial respiratory flux rates (JO(2) ) in skeletal muscle. Secondly, the effect of the maturation process on JO(2)  was studied.
  
  
  METHODS
  In tibialis anterior (almost exclusively type 2 fibres) muscle from young (12-17 weeks, n = 7) and mature (25-27 weeks, n = 12) KD and wild-type (WT) (12-17 weeks, n = 9; 25-27 weeks, n = 11) littermates, JO(2)  was quantified in permeabilized fibres ex vivo by respirometry, using a substrate-uncoupler-inhibitor-titration (SUIT) protocol: malate, octanoyl carnitine, ADP and glutamate (GMO(3) ), + succinate (GMOS(3) ), + uncoupler (U) and inhibitor (rotenone) of complex I respiration. Citrate synthase (CS) activity was measured as an index of mitochondrial content.
  
  
  RESULTS
  Citrate synthase activity was highest in young WT animals and lower in KD animals compared with age-matched WT. JO(2)  per mg tissue was lower (P < 0.05) in KD animals (state GMOS(3) ). No uncoupling effect was seen in any of the animals. Normalized oxygen flux (JO(2) /CS) revealed a uniform pattern across the SUIT protocol with no effect of KD. However, JO(2) /CS was higher [GMO(3) , GMOS(3) , U and rotenone (only WT)] in the mature compared with the young mice - irrespective of the genotype (P < 0.05).
  
  
  CONCLUSIONS
  Exercise intolerance and reduced activity level seen in KD mice may be explained by reduced JO(2)  in the maximally coupled respiratory state. Furthermore, an enhancement of oxidative phosphorylation capacity per mitochondrion is seen with the maturation process.
authors.affiliation: Xlab - Center for Healthy Aging, Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: S
authors.initials: S
authors.lastname: Larsen
authors.forename: J M
authors.initials: JM
authors.lastname: Kristensen
authors.forename: N
authors.initials: N
authors.lastname: Stride
authors.forename: J F P
authors.initials: JF
authors.lastname: Wojtaszewski
authors.forename: J W
authors.initials: JW
authors.lastname: Helge
authors.forename: F
authors.initials: F
authors.lastname: Dela
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002950:Citrate (si)-Synthase / Q000378:metabolism; D051379:Mice; D008931:Mitochondria, Muscle / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010805:Physical Conditioning, Animal / Q000502:physiology
chemical_list: D002950:Citrate (si)-Synthase; C534978:Prkaa2 protein, mouse; D055372:AMP-Activated Protein Kinases