title: Frequency dependent myocardial potassium fluxes during beta adrenergic stimulation of intact pig hearts.
abstract: OBJECTIVE
  The aim was to determine the frequency dependent myocardial potassium fluxes of intact pig hearts at control inotropy and during beta adrenergic stimulation. DESIGN - Atrial pacing rate was suddenly raised and decreased by 50 beats.min-1 at control inotropy and during infusion of isoprenaline, 2.5 nmol.min-1, into the left coronary artery.
  
  
  METHODS
  Nine anaesthetised pigs (21-33 kg) were instrumented for electric pacing of the right atrium and metabolic and haemodynamic recordings.
  
  
  RESULTS
  Myocardial potassium balance was measured by PVC-valinomycin electrodes in the left atrial cavity and in a shunt (with flow meter) diverting blood from the coronary sinus to the right atrium. Isoprenaline raised net myocardial potassium flux following the change in pacing rate from 19(14-23) to 38(32-46) mumol.100 g-1.min-1 (median, 95% confidence interval, difference: p = 0.03). The corresponding myocardial potassium flux per beat increased from 0.38(0.29-0.45) to 0.80(0.63-0.97) mumol.100 g-1 (p = 0.03). Accumulated potassium flux increased from 9(8-11) to 17(11-27) mumol.100 g-1, respectively (p = 0.03).
  
  
  CONCLUSIONS
  In intact hearts beta adrenergic stimulation doubles the frequency dependent myocardial potassium flux. This component constitutes 22-25% of the ouabain inhibitable potassium flux at both levels of inotropy.
authors.affiliation: University of Oslo, Institute for Experimental Medical Research, Ullevål Hospital, Norway.
authors.forename: O
authors.initials: O
authors.lastname: Ellingsen
authors.forename: O M
authors.initials: OM
authors.lastname: Sejersted
authors.forename: O A
authors.initials: OA
authors.lastname: Vengen
authors.forename: A
authors.initials: A
authors.lastname: Ilebekk
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002304:Cardiac Pacing, Artificial; D006321:Heart / Q000187:drug effects; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000502:physiology; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects; D011188:Potassium / Q000097:blood*; D013552:Swine
chemical_list: D007545:Isoproterenol; D011188:Potassium