The demonstration of intercellular coupling between cells of the canine distal AV bundle using lucifer yellow-CH and...

To determine whether iontophoresed lucifer yellow and histological paraffin sections could be utilized to evaluate electrical coupling in the canine heart, the negatively charged vital dye was injected into cells of the distal AV bundle (DAVB) in superfused atrial preparations by applying a hyperpolarizing 35 to 100 nA current. Dye injection periods ranged from minutes to over an hour in some cells. Following diffusion periods of 1 to 19 h, fluorescence was found to be restricted to fascicular compartments over a distance of 0.06 to 3.0 mm. Since the fascicles contained eight to nine fibers, and the cells have an estimated length of 0.1 mm, dye had diffused into as many as 200 cells. The results produced novel findings concerning the apparent electrical isolation of fascicles within the DAVB and it is suggested that the method may possibly be useful in tracing intercellularly coupled pathways.