General Comments: Ionic Currents Underlying Spontaneous Rhythm of the Cardiac Primary Pacemaker Cells

Abstract

To understand the ionic mechanism underlying the pacemaker potential one has to know the kinetic properties of the current system and which ions are involved in these currents. This information will only become available if the voltage clamp technique is used and this was not possible in the sinus node until very recently (Irisawa, 1972; Noma and Irisawa, 1976a,b; Seyama, 1976; Brown et al., 1976). In very small isolated specimen of the area of the sinus node there is a fairly equal potential distribution within the specimen (see Figure 1); therefore electrotonic spread can be ignored. There are two other advantages of the small sized preparation: firstly, because of the removal of the connective tissue from the epicardial surface the diffusion is favored and secondly, a stable impalement with a microelectrode during a couple of hours is possible. Therefore the small preparations of the sinus node turned out to be useful for voltage clamp experiments using the double microelectrode technique.