Possible functional significance of a novel type of cardiac Ca channel.

Pacemaker activity of sino-atrial (SA) node cells is explained by reconstructing the pacemaker potentials using a Hodgkin-Huxley type model which based on voltage clamp data. The new point of the reconstruction is the consideration of kinetic data of a novel "transient" (T-type) Ca current. It is demonstrated that the diastolic depolarization is closely correlated to the activation of the T-type Ca current. Overshooting SA node action potentials, however, are evoked by activation of the conventional L-type Ca current triggered by a depolarization induced by the T-type Ca current.