Larger fraction of KV current is sensitive to 4-AP in KChIP2-/- myocytes. A, Current traces normalized to cell capacitance recorded using 400-ms pulses from VH=-70 mV to Vstep=+40 mV from a WT and a KChIP2-/- cell, before and after addition of 50 μM 4-AP to the superfusate. Arrowheads indicate 0 pA. Note the prominent inactivation of the 4-AP resistant current in WT. B, The current fraction sensitive to 50 μM 4-AP obtained by digital offline subtraction of the current traces shown in A. C, 4-AP-sensitive current relative to the full IP in WT and KChIP2-/- cells. *, P<0.05.