Effect of Anticholinesterases on the Membrane Potential of the Rabbit Heart

Abstract

We have already reported on the action of drugs such as acetylcholine, epinephrine, reserpine, cardiac glycosides, antiarrhythmic agents, veratrine and chelating agents on the intracellular action potentials recorded from the ventricular muscle, sinoatrial node and the non-pacemaker atrial fibers of the isolated rabbit heart using the ultramicro electrode method (1-3).The present experiments were undertaken to determine the influences of anticholin esterases on the membrane potentials of the isolated rabbit atrial muscle exhibiting spon taneous beating. Observations on the antagonisms between the action of anticholinesterases and of cholinesterase reactivators on the membrane potentials were also designed . METHODSAs described previously (1-3), the experiments were carried out on the right incised atrium of rabbits. The endocardial surface of the dissected right incised atrium was pinned on a cork block mounted in a lucite chamber containing about 10 ml of oxygen saturated Tyrode solution at approximately 30°C. The drugs were added directly to Tyrode solution in the chamber and their concentrations were expressed in terms of w/v (g/ml). Recordings of the transmembrane potentials from non-pacemaker and pacemaker areas were taken by the intracellular microelectrode. The recording electrode , less than 1 µ in diameter, drawn from special glass capillary tubing and filled with 3 M-KCI , having low resistance (8-20 MQ), was selected and fixed on the arm of a micromanipulator . A chloride silver wire was pushed into the shaft of the electrode and was soldered onto flexible strand thereby connected to a d.c. amplifier with an input cathode follower of low grid current and reduced grid-earth capacity. The output of the amplifier was led to a cathode-ray oscilloscope and ink-writing recorder (Sanei's Type MPA-204) .

The Antagonizing Mechanism of Acetylcholine on the Atrial Non-Pacemaker Potentials Depressed by Adrenolytics

“…However, the pretreatment of the atrial preparation with atro pine lessened the restarting effect of acetylcholine on the arrested atria by dibenamine. Takaori et al (14) have shown that high concentration of atropine causes marked irre gularities of the atrial action potentials accompanied with reduction of the rate and amplitude but the followed addition of acetylcholine restores the almost normal poten tials. It has been reported that the reduction of the rate and the shortening of the total duration caused by acetylcholine are blocked by atropine (15).…”