Action potential transfer at the Purkinje - Ventricular junction: Role of transitional cells

At the Purkinje (P) - ventricular (V) junction a zone of "transitional (T)" cells is found. In the present study we investigated the role of these T cells in P-to-V conduction. Using the "model clamp" technique, an experimentally recorded rabbit P cell was coupled to a phase-2 Luo and Rudy (LR) model cell, which in turn was coupled to a strand of phase-2 LR model cells. In our experiments, the single LR model represents the T cell, while the strand of LR models represents subendocardial V cells. This approach enabled us to change selectively coupling conductance (G_c) between cells, presence of T cell, and relative size of cells. We demonstrated that: 1) a decrease of G_c between P-T and T-V increases the delay of V activation, 2) the delay of V activation is importantly due to conduction between T and V cells, 3) there is a critical G_c for successful conduction at the P-V junction, 4) the critical value of G_c for conduction at the P-V junction is lower in presence (11.0±0.7 nS) than in absence (13.7±0.8 nS) of the T cell, and 5) enlargement of the T zone size hampers successful P-to-V conduction.