Automatic activity of the pacemaker cells of the atrioventricular valves under the action of parasympathetic and sympathetic mediators

: Effects of neorpinephrine, epinephrine, and acetylcholine 4.5.10(-7) M--2.9.10(-6)M on the automatic activity of the pace-maker cells of the rabbit atrioventricular valves were studied. The sympathetic mediators accelerated spontaneous beating by increasing the rate of slow diastolic depolarization or by the inducing additional subthreshold potentials converted in action potentials. Acetylcholine (1.1.10(-6)M) reduced the rate of the spontaneous beating and in concentrations 2.7.10(-6)M eliminated automatic activity either by suppression of AP when subthreshold potentials gradually disappeared or by gradual decrement of AP rate and amplitude. Simultaneous application of equal doses of acetylcholine and sympathetic mediators revealed a predominant effect of acetylcholine as well as intensification of the acetylcholine effect under the influence of sympathetic mediators. Sympathetic-parasympathetic interactions can be explained by their influence on permeability of membrane of the pace-maker cells through the slow Na-Ca channel.