S209F increases I_Ks during simulated cardiac APs. Protocol as for Fig. 7. 2-Hz currents from cells expressing WT I_Ks (B) or S209F I_Ks (C) during simulated AP clamps (A). (D) Normalized charge during the AP protocol for WT and S209F I_Ks (P < 0.001). 4-Hz AP clamp currents in WT (E) or S209F (F) cells. (G) Charge movement at 4 Hz was not significantly different between WT and S209F (P > 0.05).