Norepinephrine induces SAN discharge through ThV
. In 13.6 mM [K+]o, NE was administered during the recording of panels b-h at normal and at higher gain. In panel b, the rightward oblique arrows indicate ThVos and the leftward oblique arrow Vos. The dash lines emphasize the change in slope of DD1 past the peak of Vos, the peak being indicated by the short bars next to DD1. The traces labeled with an empty and a filled star were superimposed in inset 1. In the higher gain c-f traces, the shaded areas emphasize the progressive growth of Vos. The c-g traces have been superimposed in inset 2, the arrow pointing to the shortening of the AP. The events during the recovery from NE exposure are illustrated in inset 3. The top trace was recorded also at higher gain (see rightward oblique arrow) and the ThVos marked by an asterisk has been superimposed upon the previous AP (horizontal arrow). In panel 4, means and standard error of the mean are shown in control (empty columns) and in the presence of NE (filled columns). The parameters shown are the rate in min-1, the action potential amplitude in mV (APa), the diastolic depolarization amplitude in mV (DDa), the amplitude of Vos in mV, the depolarizing slope of Vos(Vosds) and of ThVos (ThVosds) in mV s-1, and force in mg. Asterisks indicate statistical difference with respect to control (P < 0.05).