Abstract
The pacemaker activity of the S-A node cell was explained by reconstructing the pacemaker potential using a Hodgkin-Huxley type mathematical model which was based on the reported voltage clamp data. In this model four dynamic currents, the sodium current, iNa, the slow inward current, is, the potassium current, iK, and the hyperpolarizationactivated current, ih, in addition to a time-independent leak current, i1 were included. The model simulated the spontaneous action potential, the changes of activity induced by applying acetylcholine and epinephrine. It was strongly suggested that the pacemaker depolarization in the S-A node cell is mainly due to a gradual increase of is during diastole, and that the contribution of iK is much less compared to the current iK2 in the Purkinje fiber. The rising phase of the action potential was due to is and the plateau js determined by both the inactivation of is and activation of iK.
