[Effect of iontophoretic application of acetylcholine on the discharge rate and action potential shape of pacemaker cells].

A study was made of the action of iontophoretic application of acetylcholine to the limited number of pacemaker cells with a simultaneous recording of the activity of one of them. It was shown that both generalized and strictly localized action of acetylcholine is capable of exerting different chronotropic effects. Acceleration of the rhythm was normally accompanied by an increase in the rate of accretion of slow diastolic depolarization (SDD) and by a decrease in the action potential. The same pacemaker cell was demonstrated to modulate the direction of the chronotropic reaction for an opposite one depending on acetyl-choline concentration. Low concentration of the mediator induced rhythm acceleration and an increase in the accretion rate of SDD whereas high concentration led to rhythm deceleration and SDD lowering.