Passive electrical properties of the atrio-ventricular node

Summary The passive electrical properties of the atrioventricular node and of the atrial muscle of the rabbit heart were determined. To polarize the cells, a small suction electrode was used. The space constant of the atrio-ventricular node was found to be small (430 ) compared to other cardiac fibers. The small value of in nodal cells is due to a high intracellular resistance (r_a, 40.9 ± 9 M/cm) which is higher than in atrial muscle (9.6 ± 2.2 M/cm). The input resistance of cells of the N layer was found equals to 880 K while in the right atrium was 320 K. The time constant of nodal cells in the AN layer was 3.4 ms, in the N layer 9 ms and in the atrium 5 ms. Assuming a specific membrane capacity (C_m) of nodal and atrial fibers of 1 F/cm²,R_m was found equals to 9.000 cm² in N layer, 3.400 cm² in AN layer and 3.800 cm² in the right atrium.Acetylcholine (5 g/ml) reduced the space constant of the atrio-ventricular node by 38% and the time constant of nodal cells by 33%.The delay of impulse conduction in the A-V node semms then related to a high intracellular resistance along the pathway of conduction.This work was supported by Grant # HL-10897 from the NHI, Bethesda, Maryland and in part by a Grant from the P. R. Heart Association