Studies on Aconitine-induced Atrial Fibrillation of the Young Rabbit by the Microelectrode Technique

The aconitine-induced fibrillation of the right atrium of the young rabbit was studied by the simultaneous recording of the transmembrane potentials of two myocardial cells with intracellular microelectrodes. The results obtained were as follows : 1. After aconitine application, the ordinary spontaneous contraction of the atrium was inhibited, and then atrial fibrillation gradually developed. At the beginning of the fibrillation, coordination and synchronism of the electrical activities between two cells were fairly well maintained with relatively regular rhythm and amplitude of the action potential. Irregularity of the single cell activity, however, increaced with time, though the grade and temporal process of appearance of fibrillation varied with aconitine concentration. 2. When fibrillation was extinguished, regular rhythm and amplitude of action potentials usually recovered. But the amplitude of the action potentials appeared still decaying with time, and irregularities of the potentials were maintained. The action of aconitine on the atrium was therefore not completely reversible. 3. Coordination or synchronism between the electrical activities of the two fibers of the fibrillating atrial muscle was found to depend not only on the direction (transverse or longitudinal) of those fibers, but also on the distance between two microelectrodes. 4. Two types of "slow" or "small" depolarizations were recorded from the fibrillating atrial muscle. The first type was a oscillatory slow potential in the ectopic pace-maker, and the second type was a "junctional potential", which appeared to be produced by an electrotonic spread of the action potential of the adjoining fiber through the intercellular junction. 5. It was discussed that the behaviour of the fibrillating atrial muscle is determined by the degree of decrease of the safety factor of the intercellular junction, in other words by the "junctional potential".