FREQUENCY-DEPENDENT MYOCARDIAL POTASSIUM FLUXES DURING BETA-ADRENERGIC STIMULATION OF INTACT PIG HEARTS

Study 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 at control inotropy and during infusion of isoprenaline, 2.5 nmol.min-1, into the left coronary artery. Experimental material - Nine anaesthetised pigs (21-33 kg) were instrumented for electric pacing of the right atrium and metabolic and haemodynamic recordings. Measurements and main 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) mu-mol.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)-mu-mol.100 g-1 (p = 0.03). Accumulated potassium flux increased from 9(8-11) to 17(11-27)-mu-mol.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.