Figure 7. Summary of the effects of holding potential (V^H), stimulation frequency, and halothane on cardiac Na sup + current (I^Na). (A) Data from at least six cells represent the last pulse of the train (P⁵⁰) of the normalized peak Na sup + current during control and 4 min after addition of halothane (1.2 mM). Stimulation frequencies of 2 and 11 Hz (V^H=-80 mV) and 11 and 20 Hz (V^H=-110 mV) were applied as described in Figure 5. *Significantly different versus control (P < 0.05). (B) To demonstrate the relation between V^Hand stimulation frequency, the normalized difference [(control -halothane)/control] is plotted versus stimulation frequency. Data are shown for V^H=-80 mV (filled square) at 2 and 11 Hz and V^H=-110 mV (open triangle) at 11 and 20 Hz. (dagger)Significantly different versus 2 Hz (P < 0.05).