Fig. 5. Quantitative analysis of lidocaine and bupivacaine effect on mitochondrial depolarization, determined using rhodamine 123 (R123) fluorescence at 5 min ( A ) and 60 min ( B ) after lidocaine addition. Lidocaine and its equimolar Tris controls are plotted on the lower x-axis, with bupivacaine and its equimolar Tris controls plotted on the upper x-axis. The lower and upper x-axes are scaled so that equipotent concentrations of lidocaine and bupivacaine are at equal x-coordinates assuming a 1:4 ratio of hydrochloride salts (36.9 mm = 1% lidocaine HCl equipotent to 7.7 mm = 0.25 bupivacaine HCl). P < 0.05 for (L) lidocaine versus equimolar Tris, (B) bupivacaine versus equimolar Tris, (#) lidocaine versus equipotent bupivacaine at indicated concentration. P < 0.05 for (R) effect of concentration on indicated local anesthetic or Tris control. P > 0.05 for unmarked comparisons. Four to six experiments for each condition; n > 13 neurons/experiment.