Effect of troglitazone on Na_V. (A) Macroscopic Na⁺ current traces elicited with a pulse to 0 mV in control (left panel, black traces) or in the presence of 6 µM troglitazone (TRO, right panel, olive traces) after a 300-ms prepulse to either −130 mV (V₀) or to a voltage at which approximately half of the channels are in the fast-inactivated state (V_1/2 of ≈68 mV). (B) Time course of wash-in and washout of 6 µM troglitazone (TRO) during an alternating pulse protocol applied every 5 s in which the prepulse potential was either V₀ or V_1/2 (see inset for pulse protocol). The currents are normalized to the peak I_Na in control. Troglitazone inhibits peak I_Na, and the inhibition is larger after a prepulse to V_1/2. The inhibition was fully reversible after washout (2 min) when tested after a prepulse to V₀ mV; the inhibition was only partially reversible when tested after a prepulse to V_1/2 (n = 4).