Figure 3: rDc1a promotes opening of BgNa_v1 channels.

(a) Comparison of the gating properties of BgNa_v1 before (black), and after (red), addition of 1 μM rDc1a. Shown are the normalized deduced conductance (G)–voltage (filled circles) (G/G_max) and steady-state inactivation (open circles; I/I_max) relationships. Currents were elicited by 5-mV step depolarizations from a holding voltage of −90 mV or −100 mV, respectively. n=3–5, and error bars represent s.e.m. Descriptive values resulting from Boltzmann fits can be found in the Results section. (b) Recovery from fast inactivation of WT BgNa_v1 before (black), and after (red), addition of 1 μM rDc1a (red) determined by a double-pulse protocol to −30 mV with a varying time between pulses (0–50 ms). Values are reported in the Results section. Data represents n=4 experiments, and error bars represent the s.e.m. (c) On addition of 1 μM rDc1a to channels depolarized to −60 mV every 5 s (red open circles) or 50 s (green open circles; holding voltage was −100 mV), BgNa_v1-mediated sodium currents become rapidly visible. Channels completely recover after toxin washout. Inset shows current trace before (black), and after (red), addition of 1 μM rDc1a at −60 mV (5 s pulses). Noticeable is the persistent current that appears at this voltage, even in control experiments. Abscissa scale is 10 ms, ordinate scale is 0.3 μA. (d) Concentration dependence of rDc1a-induced current potentiation determined from shifts in the midpoint of channel activation (V_1/2). Line represents a fit of the data with the Hill equation resulting in a half-maximal concentration (EC₅₀) of 65±1 nM and a slope factor of 1.19±0.02; n=5 and error bars represent s.e.m.