Fig. 1. Effect of continuous lidocaine exposure on neuronal death. ND7 neurons were exposed to lidocaine or Tris buffer in media at 37°C for indicated time and then analyzed by flow cytometry for cell death (necrosis and late apoptosis) using propidium iodide (PI) staining.  Filled symbols = lidocaine;  open symbols = Tris buffer;  filled with asterisk = lidocaine + 100 μm z-VAD-fmk (pan-caspase inhibitor). Note logarithmic x-axis with dual concentration scales in percent and millimolars of lidocaine HCl.  P < 0.01 for all lidocaine values  versus their equimolar Tris controls for each concentration at each time tested, except  P > 0.05 for 2.3 mm at 2 and 4 h. z-VAD-fmk did not cause a significant change for 9.2 mm lidocaine at 24 h or 36.9 mm at 2 h, whereas its effect was significant for 9.2 mm at 4 h and 18.5 mm at 2 h. Each data point is the average of three to five experiments.