[Effect of acetylcholine on the Na+,K+-ATPase activity of different preparations of myocardial sarcolemma].

Dose-dependent inhibition of Na+, K+-ATPase by acetylcholine was found in dog heart sarcolemma obtained after treatment with NaI. The enzyme was completely inhibited at 1 X 10(-2) M concentration of acetylcholine (Ki = 14 +/- 2 mM). Low concentrations of acetylcholine (1 X 10(-6)--1 X 10(-5) M) increased the Na+, K+-ATPase activity, the intermediate (5 X 10(-5)--5 X 10(-4) M) and high (1 X 10(-3)--1 X 10(-2) M) concentrations decreased the activity in the preparations enriched with sarcoplasmic vesicles. Sodium dodecylsulfate enhanced the activating effect but did not affect the inhibition. Atropine (1 X 10(-6)--1 X 10(-4) M) decreased the Na+, K+-ATPase activity and protected the enzyme against the inhibitory effect of acetylcholine. The data obtained suggest that interaction of acetylcholine with integral membrane proteins (Na+, K+-ATPase and/or muscarinic acetylcholine receptors) is apparently responsible for the neurotransmitter inhibitory effect.