Figure 9. Effect of halothane on peak Na sup + current after removal of current inactivation by veratridine. (A) Effects of veratridine (100 micro Meter) on cardiac Na sup + current (INa). The neurotoxin was added to the external solution, and depolarizing pulses (50 ms) from a holding potential (VH) of -110 mV to -20 mV were applied at consecutive time intervals. (B, C) Time course of peak INamodified by veratridine. The INaelicited during the 50-ms pulses from a VHof -110 mV (B) or -80 mV (C) to -20 mV in the presence of veratridine (open circles), veratridine plus 1.2 mM halothane (closed circles), washout of halothane (open triangles), washout of veratridine (extracellular solution; filled triangles), 1.2 mM halothane in the absence of veratridine (open squares), and washout of halothane (filled diamonds). Left insets show tracings from the control and halothane exposure in the presence of veratridine for V sub H -110 mV (B) and -80 mV (C). Right insets show tracings after the washout of veratridine and halothane followed by a second halothane exposure. Vertical scales in insets represent 500 pA, and horizontal scales represent 5 ms.