Induction of sudden fast rhythm by V
on lowering high [K+]
. In panels A and B, [K+]o was decreased while the same SAN was driven. The bars mark the peak of Vos. The downward arrows mark the ThVos that initiated an AP followed by the fast rhythm. The horizontal arrow points to the stimulus artifact of the last driven AP. The traces labeled with a dot and a rhombus are shown at higher gain in inset 1. In inset 2, the circle labels a ThVos that missed the threshold during the subsiding of the fast rhythm. In panel C, the upward oblique arrows indicate driven APs that initiated runs of fast discharge. The downward oblique arrows indicate ThVos that initiated an AP followed by runs of fast discharge.