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-1 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) 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.