title: Energy for myocardial Ca2+ handling per beat increases with heart rate in excised cross-circulated canine heart.
abstract: OBJECTIVE
  Although tachycardia is well known to increase cardiac oxygen consumption (Vo2) per min, the relationship between Vo2 for excitation-contraction (E-C) coupling per beat and heart rate change over its full working range still remains controversial.
  
  
  METHODS
  To elucidate this relationship, we varied heart rate over a reasonably wide range (60-180 beat/min) and studied the relationship between left ventricular (LV) Emax (load-independent contractility index), PVA (pressure-volume area)-independent Vo2, and basal metabolic Vo2 in nine excised, cross-circulated canine hearts.
  
  
  RESULTS
  PVA-independent Vo2 per min significantly increased linearly with increasing heart rate while Emax remained unchanged. Basal metabolic Vo2 per min was measured under KCl arrest. E-C coupling Vo2 per min obtained by subtracting the constant basal metabolic Vo2 from the PVA-independent Vo2 also significantly increased linearly with increasing heart rate. However, PVA-independent Vo2 per beat significantly decreased with increasing heart rate. In contrast, E-C coupling Vo2 per beat, as well as that normalized to Emax, slightly but significantly increased with increasing heart rate.
  
  
  CONCLUSIONS
  The E-C coupling energy for myocardial Ca2+ handling increases with heart rate despite constant contractility in the left ventricle of the excised cross-circulated canine heart.
authors.affiliation: Division of Cardiology, Tokai University Oiso Hospital, 21-1 Gakkyo, Oisomachi, Nakagun, Kanagawa 259-0198, Japan. tkiyooka@oiso.u-tokai.ac.jp.
authors.forename: Takahiko
authors.initials: T
authors.lastname: Kiyooka
authors.forename: Yu
authors.initials: Y
authors.lastname: Oshima
authors.forename: Waso
authors.initials: W
authors.lastname: Fujinaka
authors.forename: Gentaro
authors.initials: G
authors.lastname: Iribe
authors.forename: Satoshi
authors.initials: S
authors.lastname: Mohri
authors.forename: Juichiro
authors.initials: J
authors.lastname: Shimizu
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003427:Cross Circulation / Q000379:methods*; D004285:Dogs; D004734:Energy Metabolism / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000502:physiology; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption; D016276:Ventricular Function / Q000502:physiology
chemical_list: D002118:Calcium