Fig. 2. Testing the suitability of the ESI method for pharmacologic investigation. Action of the local anesthetic lidocaine on Na+currents recorded from intact neurons in the spinal cord slice and from isolated somata . (A ) Na+currents recorded in the presence of different concentrations of lidocaine. Holding potential was −80 mV. The currents in isolated somata were activated by a 50-ms voltage pulse to −20 mV after a 50-ms prepulse to −120 mV. For intact neurons, the hyperpolarizing prepulse was not applied to reduce the current amplitude. (B ) Concentration-dependent inhibition of Na+current by lidocaine in intact neurons (solid symbols, eight cells) and isolated somata (open symbols, nine somata ). The data points were fitted using with Res = 0, giving IC50 values of 112 ± 8 μm for intact neurons and 12.6 ± 1.9 μm for isolated somata . Here and in the following figures, error bars indicate ± SEM if exceeding symbol size.