Fig. (2).

Experimentally recorded action potential (AP) of a single human SAN pacemaker cells.

A. For cell isolation and recording procedure, see Ref 25. B. Associated net membrane current (I_net, blue line) calculated from I_net=- C_m×dV_m/dt, where C_m and V_m denote membrane capacitance and membrane potential, respectively. Note the small inward current underlying the slow diastolic depolarization. C. Computed I_f (solid red line). The time course of I_f was reconstructed using the V_m values of the recorded action potentials and a first-order Hodgkin–Huxley type kinetic scheme based on voltage clamp data from human SAN pacemaker cells. For details, see Ref 24.