Figure 5

V _os , ThV _os and sudden fast discharge during recovery from high [K⁺] _o to Tyrode solution. V_os, ThV_os and sudden fast discharge during recovery from high [K⁺]_o to Tyrode solution. The SAN was quiescent in 19.2 mM [K⁺]_o and recovery in the Tyrode solution started at the downward arrow and continued for the rest of the figure. In panel A, subthreshold stimuli (15 V, 3 ms; leftward oblique arrows) were applied at 6 min^-1. Subthreshold ThV_os is shown at higher gain in inset 1. In panel B, the star indicates ThV_os leading to spontaneous discharge and the rightward oblique arrow points to the depolarising slope of a ThV_os that initiated an AP and fast rhythm. In the inset 2, the arrow points to the peak of V_os. The trace indicated by a horizontal line ending with two dots is shown at higher gain in inst 3, where the dots and the shaded areas emphasize the growth of V_os. In the inset 4, the subthreshold stimuli initiated ThV_os at the resting potential (upward arrow), but not during early DD₁ (leftward oblique arrow). The dots show ThV_os that began prior to the electrical stimulus.