Fig. 5. Simultaneous application of meperidine and naloxone. (A ) Multiple channel Na⁺currents are recorded in control solution, 100 μM meperidine, 100 μM meperidine plus 10 nM naloxone, and 100 μM meperidine plus 1 μM naloxone (traces from bottom to top). (B ) Traces show multiple channel K^DRcurrents recorded in control, 1 mM meperidine, and 1 mM meperidine plus 100 nM naloxone (from top to bottom). (A  and B ) Pulse protocols are given above the traces; each trace represents an average of 20 recordings. (C ) Na⁺and K^DRchannel antagonism by naloxone. Voltage-dependent Na⁺and K^DRcurrents have been blocked by 100 μM and 1 mM meperidine, respectively, before different concentrations of naloxone were added (given on abscissa). Bars indicate fractional block of peak Na⁺(left ) and steady-state K^DRcurrent (right ) induced by given concentrations of meperidine and naloxone. Error bars show SEM; the number of experiments is given above each bar.