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

The aim of the study is to theoretically explore the role of If 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.