Acetylcholine and potassium-42 movements in right atrial muscle of the guinea pig.

The effect of acetylcholine (ACh) on potassium (K-42) movements has been studied in right atrial tissue of the guinea pig. When quiescent fibers were stimulated at 108 beats/min, potassium uptake was increased to a small but significant extent. Administration of acetylcholine (2.7 X 10(-6) M) induced an increase in potassium uptake that was greater in fibers that were quiescent than in the same fibers when stimulated. The ACh induced increase in potassium uptake was abolished by atropine (5.2 X 10(-7) M) and enhanced in the presence of nicotine (10(-5) M). In addition, ACh induced an increase in potassium efflux that was greater in fibers that were quiescent than in the same fibers when stimulated. Atropine blocked the effect of ACh on potassium efflux. It is concluded that activity of atrial tissue increases potassium uptake and modifies the action of ACh on potassium uptake and efflux. Muscarinic receptors mediate the ACh induced increase in potassium movements. Nicotinic receptors may mediate an ACh induced decrease in potassium uptake in atrial muscle.