title: Excess recovery heat production by isolated muscles from mice overexpressing uncoupling protein-3.
abstract: Contractile and energetic performance of bundles of muscle fibres from the soleus of mice overexpressing uncoupling protein 3 (UCP-3tg) were compared with the performance of bundles from wild-type mice. Force and heat production were measured during a series of thirty 0.2 s isometric tetani at L(o), the length optimal for force. UCP-3tg fibres were as strong as the wild-type and maintained force in the series equally well; in the first tetanus force was 116.9 +/- 15.1 and 133.3 +/- 19.7 mN x mm(-2) respectively (all values means +/- S.E.M., n = 6 for UCP-3tg and n = 5 for wild-type). Heat production was partitioned into initial heat (due to contractile ATPases and the creatine kinase reaction) and recovery heat (due to other ATP-supplying processes) and expressed relative to the first cycle total heat. Initial heat production was similar for the UCP-3tg and wild-type fibres, decreasing during the series from 0.799 +/- 0.052 to 0.661 +/- 0.061 relative units (UCP-3tg), and from 0.806 +/- 0.024 to 0.729 +/- 0.039 relative units (wild-type). In both types the recovery heat was small at the start of the series and increased as the series progressed. At the end of the series, recovery heat production by UCP-3tg fibres, 1.575 +/- 0.246 relative units, was twice that of the wild-type fibres, 0.729 +/- 0.072 relative units. The extra recovery heat represents inefficient recovery in UCP-3tg fibres. This is the first direct evidence of enhanced energy dissipation as heat when UCP-3tg is overexpressed.
authors.affiliation: Biological Structure and Function Section, Division of Biomedical Sciences, Faculty of Medicine, Sir Alexander Fleming Building, Imperial College, London SW7 2AZ, UK. n.curtin@ic.ac.uk
authors.forename: N A
authors.initials: NA
authors.lastname: Curtin
authors.forename: J C
authors.initials: JC
authors.lastname: Clapham
authors.forename: C J
authors.initials: CJ
authors.lastname: Barclay
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D066298:In Vitro Techniques; D007473:Ion Channels; D007537:Isometric Contraction / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D024101:Mitochondrial Proteins; D018482:Muscle, Skeletal / Q000502:physiology*; D000071247:Uncoupling Protein 3
chemical_list: D002352:Carrier Proteins; D007473:Ion Channels; D024101:Mitochondrial Proteins; C000604392:UCP3 protein, human; C000604393:Ucp3 protein, mouse; D000071247:Uncoupling Protein 3; D000255:Adenosine Triphosphate