The effect of TZDs on Na_V steady-state fast inactivation. The left panels show families of Na⁺ current traces recorded using a 10-ms test pulse to 0 mV after 300-ms conditioning prepulses to potentials ranging from −130 to −10 mV (inset shows stimulation protocol) in the absence (black current traces) or presence of the drug (colored current traces). Peak I_Na was normalized to the maximum peak I_Na (elicited after a prepulse to −130 mV), plotted against the prepulse potential and fitted with a two-state Boltzmann distribution (right panels) to determine the voltage for half-maximal inactivation (V_1/2). 6 µM troglitazone (TRO, olive traces and symbols; ΔV_1/2 = −13.2 ± 4.1 mV, n = 6, and P < 0.001 vs. control by paired two-tailed Student’s t test), 200 µM rosiglitazone (ROS, pink traces and symbols; ΔV_1/2 = −5.4 ± 1.5 mV, n = 3, and P < 0.05), 10 µM pioglitazone (PIO, gray traces and symbols; ΔV_1/2 = −2.3 ± 0.4 mV, n = 4, and P < 0.05), and 6 µM ciglitazone (CIG, orange traces and symbols; ΔV_1/2 = −3.0 ± 1.9 mV, n = 4, and P < 0.05).