title: The acetyl group deficit at the onset of contraction in ischaemic canine skeletal muscle.
abstract: Considerable debate surrounds the identity of the precise cellular site(s) of inertia that limit the contribution of mitochondrial ATP resynthesis towards a step increase in workload at the onset of muscular contraction. By detailing the relationship between canine gracilis muscle energy metabolism and contractile function during constant-flow ischaemia, in the absence (control) and presence of pyruvate dehydrogenase complex activation by dichloroacetate, the present study examined whether there is a period at the onset of contraction when acetyl-coenzyme A (acetyl-CoA) availability limits mitochondrial ATP resynthesis, i.e. whether a limitation in mitochondrial acetyl group provision exists. Secondly, assuming it does exist, we also aimed to identify the mechanism by which dichloroacetate overcomes this "acetyl group deficit". No increase in pyruvate dehydrogenase complex activation or acetyl group availability occurred during the first 20 s of contraction in the control condition, with strong trends for both acetyl-CoA and acetylcarnitine to actually decline (indicating the existence of an acetyl group deficit). Dichloroacetate increased resting pyruvate dehydrogenase complex activation, acetyl-CoA and acetylcarnitine by approximately 20-fold (P < 0.01), approximately 3-fold (P < 0.01) and approximately 4-fold (P < 0.01), respectively, and overcame the acetyl group deficit at the onset of contraction. As a consequence, the reliance upon non-oxidative ATP resynthesis was reduced by approximately 40 % (P < 0.01) and tension development was increased by approximately 20 % (P < 0.05) following 5 min of contraction. The present study has demonstrated, for the first time, the existence of an acetyl group deficit at the onset of contraction and has confirmed the metabolic and functional benefits to be gained from overcoming this inertia.
authors.affiliation: School of Biomedical Sciences, Queen's Medical Centre, University of Nottingham, Nottingham NG7 2UH, UK. p.roberts@nottingham.ac.uk
authors.forename: Paul A
authors.initials: PA
authors.lastname: Roberts
authors.forename: Susan J G
authors.initials: SJ
authors.lastname: Loxham
authors.forename: Simon M
authors.initials: SM
authors.lastname: Poucher
authors.forename: Dumitru
authors.initials: D
authors.lastname: Constantin-Teodosiu
authors.forename: Paul L
authors.initials: PL
authors.lastname: Greenhaff
mesh_terms: D000105:Acetyl Coenzyme A / Q000172:deficiency*; D000107:Acetylation; D000818:Animals; D002331:Carnitine / Q000378:metabolism; D003065:Coenzyme A / Q000378:metabolism; D004285:Dogs; D004789:Enzyme Activation; D066298:In Vitro Techniques; D007511:Ischemia / Q000503:physiopathology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000503:physiopathology*; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism; D012146:Rest / Q000502:physiology
chemical_list: D011768:Pyruvate Dehydrogenase Complex; D000105:Acetyl Coenzyme A; D002331:Carnitine; D003065:Coenzyme A