Figure 3. Blockade of Na sup + currents in dorsal horn neurons by bupivacaine, lidocaine, and mepivacaine. (A) Whole-cell Na sup + currents activated by voltage steps from a holding potential of -80 to -30 mV in the presence of different concentrations of bupivacaine (indicated near the corresponding traces). (B) Comparison of potencies of channel block produced by 100-micro Meter mepivacaine, lidocaine, and bupivacaine. Na sup + currents were activated by voltage steps from -80 to -30 mV. (C) Concentration dependence of Na sup + current block by bupivacaine (squares), lidocaine (triangles), and mepivacaine (circles). Data points were fitted using a nonlinear least-squares method with the equation: f(C)= 1 - C/(C + IC50), where C is the blocker concentration and IC50is the constant of dissociation. IC50values (mean +/- SEM) were 26 +/- 3 micro Meter for bupivacaine (n = 7), 112 +/- 8 micro Meter for lidocaine (n = 8), and 324 +/- 4 micro Meter for mepivacaine (n = 5). Error bars indicate +/- SEM if exceeding symbol size.