Properties of the fibers in the pathways along the anterior and posterior portions of the left A-V ring.

A comparison was made of the electrophysiological properties of the fibers between the previously reported conduction pathways from the left atrium to the right atrium and to the ventricle (left A-V ring pathways) and the ordinary atrial muscle, using perfused isolated rabbit hearts. Each fiber within these pathways showed action potential with a well-developed plateau phase. The plateau phase of these action potentials was distinctly shortened by an infusion of 1 x 10-6 g/ml of acetylcholine. When the heart was perfused by Tyrode solution with 15 mM KCl, the trans-membrane potential of the ordinary atrial muscle fiber showed a decrease of resting potential and of amplitude of action potential. The fibers within these pathways, however, were more resistant to the high potassium solution than the ordinary atrial fibers. A slow diastolic depolarization was observed in the fibers of the pathway when 1-isoproterenol (1 x 10-5 g/ml) was applied locally. These findings suggest that the fibers within the left A-B ring pathways possess similar electrophysiological properties to the specialized fibers in the atria.