The Action of Theophylline on Potassium Uptake in Cardiac Purkinje Fibers

Abstract

The effect of theophylline on potassium uptake of cardiac Purkinje fibers was studied under different conditions. The following results were obtained: (1) theophylline decreases K uptake and enhances Purkinje fiber automaticity; (2) norepinephrine and high [Ca]₀ counteract the decrease in K uptake induced by theophylline; (3) adrenergic receptor blockers do not modify the effect of theophylline on K uptake; (4) norepinephrine increases K uptake and this effect is potentiated by theophylline and is little affected by imidazole and acetylcholine. It is concluded that theophylline may depress K uptake by releasing intracellular calcium and thereby inhibiting the sodium-potassium pump. However, theophylline potentiates the effect of norepinephrine on K uptake probably by enhancing the intracellular levels of cyclic AMP.