Fig. 1. Effect of meperidine on the inactivating Na+current. (A ) Recordings of the tetrodotoxin-sensitive Na+current in control solution and in the presence of 10, 100, 300, and 1,000 μm meperidine. The currents were activated by a voltage step to −20 mV after a 50-ms prepulse to −120 mV. Holding potential was −80 mV. (B ) Concentration dependence of the Na+current suppression by meperidine (13 somata). The IC50value for Na+currents was 118 ± 5 μm. The currents (I) were normalized by the amplitude of the corresponding current recorded in control solution (I0).