Effects of acetylcholine on automaticity and conduction in the proximal portion of the His-Purkinje specialized conduction system of the dog.

Conventional intracellular recordings from the bundle of His and right bundle branch of the canine heart demonstrated that the slope of diastolic depolarization is markedly depressed by superfusion with relatively small concentrations (4—8 jug/ml) of acetylcholine. As the cells become less automatic, take-off potential increases, rise time of phase 0 is reduced, action potential amplitude increases, and conduction proceeds more rapidly.