Figure 3.

Effect of β scorpion toxin CssIV on Na_v1.1 expressed in HEK 293 cells. Sodium currents due to stable expression of Na_v1.1 α subunits in HEK 293 cells were recorded by using high-sodium (120 mM) solutions. Mean normalized current–voltage relationships in the presence of 1 μM CssIV without a prepulse (open diamonds) or with a 2-ms prepulse to +50 mV preceding each depolarization (filled diamonds). All currents have been normalized to the peak of the current–voltage relationship without a prepulse. The solid line through the no-prepulse points is a fit of I_normalized = (V − V_rev)/{1 + exp[(V − V_a)/k]} to the data. The dotted line is this fit normalized to the peak of the data obtained with a prepulse to show the negative shift in activation caused by the prepulse in the presence of CssIV. A 60-ms interval at the holding potential of −100 mV separated the prepulse from the test pulse. (Inset) Sodium currents obtained in response to depolarizations to −30 mV without (dotted) and with (solid) a prepulse in the presence of 1 μ M CssIV (Bar = 100 pA, 10 ms.)