An Engineering-Optimized Cardiac Pacemaker by Manipulating Na+/Ca+ Exchange and Na+/K+ Pumping

Yacong Li1, Kuanquan Wang1, Qince Li1, Cunjin Luo2, Henggui Zhang3
1Harbin Institute of Technology, 2Southwest Medical University, 3University of Manchester


Aims: Biological pacemaker is an innovative therapy for heart failure but there are several shortcomings when creating single pacemaker cells based on ventricular myocytes by inhibiting inward rectifier current (IK1) and combining hyperpolarization-activated funny channel current (If), such as unbalanced intracellular concentration and unsatisfied pacing frequency. Na+-Ca2+ exchange current (INaCa) plays an essential role in depolarization and INaCa-related gene increased 4-fold than control in cardiac pacemaker cells. In addition, the accumulation of intracellular sodium concentration ([Na+]i) was observed due to the combination of If and Na+/K+ pumping (INaK) may contribute to pump out extra Na+ in pacemaker cells. Thus, overexpressing INaCa and INaK is hoped to improve the pacemaking ability of original biological pacemaker. Methods: A pacemaker model is constructed based on TP06 model by suppressing IK1 and incorporating If. INaCa and INaK is overexpressed to optimize the original pacemaker model by manipulating the conductance of these two currents systematically. Results: Compared with overexpressing INaCa or INaK alone, the cooperation between INaCa and INaK witnessed a greatest equilibrium of intracellular concentration and the shortest cycle length. Under the action of INaCa and INaK, the intracellular calcium concentration ([Ca2+]i) became balanced at the original level, which promoted the activation of L-type calcium current (ICaL). Also, the flux of extra [Na+]i encouraged If, which accumulated the depolarization of action potential. Surprisingly, the overexpression of INaCa and INaK changed the action of If in pacemaker. With the increase of If, the cycle length (CL) became shorter in optimized model while CL was prolonged with If increasing in original model. Conclusion: The overexpression of INaCa and INaK balances the equilibrium of intracellular ionic concentration thus intensifies the pacemaking activity of IK1-If-induced pacemaker dramatically.