Low 4-AP–sensitive potassium current density is reduced in myocytes from LC15 mice. (A) Representative outward potassium current traces in ventricular myocytes from WT (left; black) and LC15 (right; red) mice. Following recording in control solution, the bath solution was exchanged for one containing a low concentration (50 µM) of 4-AP and then a high concentration (500 µM) of 4-AP. (B) The low 4-AP–sensitive current component (4-AP Diff.) was determined by subtracting current traces recorded in the presence of 500 µM 4-AP from that obtained in the presence of 50 µM 4-AP. (C) Average voltage dependence of peak 4-AP Diff. current density in myocytes from WT (n = 8; closed circles) and LC15 (n = 6; open circles) mice. (D) Average voltage dependence of the integral of the 4-AP Diff. current density. Error bars represent SEM. *, P < 0.05.