title: 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.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004285:Dogs; D005260:Female; D006329:Heart Conduction System / Q000378:metabolism*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011690:Purkinje Fibers / Q000378:metabolism*; D013806:Theophylline / Q000494:pharmacology*
chemical_list: D013806:Theophylline; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine