title: Respiration rate of hepatocytes varies with body mass in birds.
abstract: Hepatocytes were isolated from eight species of birds ranging from 13 g zebra finches to 35 kg emus. This represents a 2800-fold range of body mass (Mb). Liver mass (g) was allometrically related to species body mass by the equation: liver mass=19.6 x Mb(0.91). There was a significant allometric decline in hepatocyte respiration rate (HRR; nmol O2 mg(-1) dry mass min(-1)) with species body mass (kg) described by the relationship: HRR=5.27 x Mb(-0.10). The proportions of hepatocyte oxygen consumption devoted to (i) mitochondrial ATP production, (ii) mitochondrial proton leak and (iii) non-mitochondrial processes were estimated by using excess amounts of appropriate inhibitors. It was found that although hepatocyte respiration rate varied with body mass in birds, these processes constitute a relatively constant proportion of hepatocyte metabolic rate irrespective of the size of the bird species. The respective percentages were 54%, 21% and 25%. The portion of hepatocyte respiration devoted to ATP production for use by the sodium pump was estimated and found to be a relatively constant 24% of hepatocyte respiration and 45% of mitochondrial ATP production in different-sized bird species. These results are discussed in the context of competing theories to explain the metabolism-body size allometry, and are found to support the 'allometric cascade' model.
authors.affiliation: Department of Biomedical Science, Metabolic Research Centre, University of Wollongong, Wollongong, NSW 2522, Australia. pelse@uow.edu.au
authors.forename: Paul L
authors.initials: PL
authors.lastname: Else
authors.forename: M D
authors.initials: MD
authors.lastname: Brand
authors.forename: N
authors.initials: N
authors.lastname: Turner
authors.forename: A J
authors.initials: AJ
authors.lastname: Hulbert
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D001481:Basal Metabolism / Q000502:physiology; D001717:Birds / Q000502:physiology*; D001835:Body Weight / Q000502:physiology*; D002452:Cell Count; D022781:Hepatocytes / Q000502:physiology*; D008099:Liver / Q000502:physiology; D008928:Mitochondria / Q000502:physiology; D008954:Models, Biological; D009840:Oligomycins; D009929:Organ Size / Q000502:physiology; D010042:Ouabain; D010101:Oxygen Consumption / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism / Q000502:physiology
chemical_list: D009840:Oligomycins; D010042:Ouabain; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase