Reciprocal interaction between I(K1) and I(f) in biological pacemakers: A simulation study

Pacemaking dysfunction (PD) may result in heart rhythm disorders, syncope or even death. Current treatment of PD using implanted electronic pacemakers has some limitations, such as finite battery life and the risk of repeated surgery. As such, the biological pacemaker has been proposed as a potential alternative to the electronic pacemaker for PD treatment. Experimentally and computationally, it has been shown that bio-engineered pacemaker cells can be generated from non-rhythmic ventricular myocytes (VMs) by knocking out genes related to the inward rectifier potassium channel current (I(K1)) or by overexpressing hyperpolarization-activated cyclic nucleotide gated channel genes responsible for the “funny” current (I(f)). However, it is unclear if a bio-engineered pacemaker based on the modification of I(K1)- and I(f)-related channels simultaneously would enhance the ability and stability of bio-engineered pacemaking action potentials. In this study, the possible mechanism(s) responsible for VMs to generate spontaneous pacemaking activity by regulating I(K1) and I(f) density were investigated by a computational approach. Our results showed that there was a reciprocal interaction between I(K1) and I(f) in ventricular pacemaker model. The effect of I(K1) depression on generating ventricular pacemaker was mono-phasic while that of I(f) augmentation was bi-phasic. A moderate increase of I(f) promoted pacemaking activity but excessive increase of I(f) resulted in a slowdown in the pacemaking rate and even an unstable pacemaking state. The dedicated interplay between I(K1) and I(f) in generating stable pacemaking and dysrhythmias was evaluated. Finally, a theoretical analysis in the I(K1)/I(f) parameter space for generating pacemaking action potentials in different states was provided. In conclusion, to the best of our knowledge, this study provides a wide theoretical insight into understandings for generating stable and robust pacemaker cells from non-pacemaking VMs by the interplay of I(K1) and I(f), which may be helpful in designing engineered biological pacemakers for application purposes.