Effect of TTX on sodium current in ventricular myocytes in the presence of 1 μM β scorpion toxin CssIV. Sodium currents were evoked with a 30-ms test pulse to −60 mV, without and with a 2-ms prepulse to +50 mV in high sodium (120 mM) saline. Mean traces obtained in the absence of a prepulse or CssIV (control, n = 5), with a prepulse in the presence of 1 μM CssIV (CssIV, n = 6), or with a prepulse in the presence of CssIV and 181 nM TTX (CssIV + TTX, n = 8). The dotted lines flanking each trace represent ± SEM.