title: Species-independent metabolic response to an increase of [Ca(2+)](i) in quiescent cardiac muscle.
abstract: 1. The aim of the present investigation was to contrast the Ca2+ dependence of cardiac energy metabolism in two species with differential reliance on extracellular Ca2+ for excitation-contraction coupling. 2. We measured energy expenditure as the rate of oxygen consumption (Vo2) of isolated, Langendorff-perfused hearts of rats and guinea-pigs during KCl arrest. In parallel experiments, we indexed intracellular Ca2+ concentration ([Ca2+]i) of isolated right-ventricular trabeculae, using the Ca2+ fluorophore fura-2 and ratiometric spectrofluorometry. By varying extracellular Na+ concentration ([Na+]o), Vo2-[Na+]o and [Ca2+]i-[Na+]o relationships were constructed for each species. 3. Reduction of [Na+]o during K+ arrest caused pronounced species-dependent elevations of both Vo2 and [Ca2+]i. Despite the species dependence of both Vo2 and [Ca2+]i on [Na+]o, a single species-independent Vo2-[Ca2+]i relationship obtained. 4. We infer that elevation of the metabolic rate of the arrested heart above its basal value is determined primarily by [Ca2+]i and is not species dependent.
authors.affiliation: Department of Physiology, Faculty of Medicine and Health Science and Bioengineering Institute, University of Auckland, Auckland, New Zealand. ds.loiselle@auckland.ac.nz
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Ward
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Cooper
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hanley
authors.forename: Denis S
authors.initials: DS
authors.lastname: Loiselle
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D005456:Fluorescent Dyes; D016257:Fura-2; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D013045:Species Specificity
chemical_list: D005456:Fluorescent Dyes; D012964:Sodium; D002118:Calcium; D016257:Fura-2