Theoretical study of the role of the funny current (If) and the background inward current (Ib) in atrioventricular nodal conduction

The aim of the study is to theoretically explore the role of I_f in atrioventricular nodal conduction using computer simulation. The background current, I_b, is another inward current flowing during diastole and this was also investigated. We began with Inada´s model of the rabbit atrioventricular nodal action potential (N-type). There is uncertainty from experiments about the magnitude and properties of I_f. Therefore, the properties of I_f and I_b in the model were varied. Four different cases were analysed. A one-dimensional model made up of 100 elements, each 100 μM in length, was used. The diffusion coefficient, D, was set to 0.001 μS mm². One end of the string (elements 1 to 3) was stimulated at 3 Hz. The conduction velocity was calculated from the times of arrival of the action potential at the 41th and 61th elements. In Inada´s original model, blocking I_f resulted in a 0.85% slowing of conduction, whereas blocking I_f in a modified model had a greater effect (19.4% slowing in Case 4). The results show that I_f can theoretically influence the conduction velocity of the atrioventricular node.