Fig. 3. Effect of holding potential on lidocaine block. (A ) Traces of tetrodotoxin-resistant Na⁺currents. Dashed lines represent the current trace elicited by the first pulse in control, and solid lines are 10 successive traces at 2-Hz stimulation in 100 μm lidocaine. Holding potential was set either to −90 mV (left ) or −60 mV (right ). (B ) Tonic block of the current as elicited by the first pulse of the stimulus train at different holding potentials is plotted against lidocaine concentration. Data points are mean values, and error bars represent SEM. IC⁵⁰values obtained by fitting e quation 1 to all data points at each holding potential are listed in table 1.