Limit cycle oscillations in pacemaker cells

In recent decades, several mathematical models describing the pacemaker activity of the rabbit sinoatrial node have been developed. The authors observe that membrane voltage and membrane charge are treated as independent dynamic variables in some of those models, resulting in an infinite number of limit cycles. Then the authors display numerical results from a new model where membrane voltage (v) is not a dynamic variable, and observe a limit cycle oscillation that can be reached from many different initial conditions.