Reconstruction of sino-atrial node pacemaker potential based on the voltage clamp experiments.

Abstract

The pacemaker activity of the S-A [sino-atrial] node cell was explained by reconstructing the pacemaker potential using a Hodgkin-Huxley type mathematical model based on the reported voltage clamp data. In this model 4 dynamic currents, the Na current, iNa, the slow inward current, is, the K current, iK, and the hyperpolarization-activated current, ih, in addition to a time-independent leak current, il, were included. The model simulated the spontaneous action potential, the current voltage relationship and the voltage clamp experiment in normal Tyrode solution of the rabbit S-A node. The changes of activity induced by the K current blocker Ba2+, by applying constant current, acetylcholine, and epinephrine, were also reconstructed. The pacemaker depolarization in the S-A node cell apparently is mainly due to a gradual increase of is during diastole, and the contribution of iK is much less than the K current iK2 in the Purkinje fiber pacemaker depolarization. The rising phase of the action potential was due to is and the plateau phase is determined by both the inactivation is and activation of iK.