FIGURE 4.
Modulation of the effects of gating modifiers at DmNav1 by DRS. Oocytes expressing DmNav1/TipE were clamped at −80 mV, and currents were elicited by step depolarizations of 50 ms to −10 mV. A, increasing concentrations of the toxin and toxin mixture with DRS were applied, and their relative effects on the current inactivation (sustained current) at −10 mV were determined after 50 ms. Activity of LqhαIT (empty symbols; EC50 = 2.6 ± 0.2 nm; n = 4) and LqhαIT in a mixture with DRS (filled symbols; 1:50 molar ratio) on DmNav1 provided an EC50 value of 0.9 ± 0.2 nm, n = 3. Inset, representative current traces from a single cell. a, control; b, 0.5 nm LqhαIT; c, 25 nm DRS + 0.5 nm LqhαIT. B, dose-response curve for the enhancement of LqhαIT effect induced by increasing concentrations of DRS with an EC50 value of 56 ± 11 nm (n = 4). LqhαIT at 0.5 nm induces 8% inhibition of channel steady-state fast inactivation (see inset and the ●*). Inset, traces from a single cell used for the analysis of the dose response shown in Fig. 2B. C, inhibition of PbTx-2 effect by DRS. Alteration in conductance-voltage relations of DmNav1/TipE by PbTx-2 in the presence and absence of DRS. Toxin concentrations and the activation parameters (V½ in mV and k value, respectively) are: control, −15.9 ± 0.2 and 5.1 ± 0.2; PbTx-g (0.5 μm) −27.7 ± 0.3 and 7.3 ± 0.9; Drs (5 μm), −14.9 ± 0.6 and 5.3 ± 0.4; PbTx-2 + DRS (0.5 + 1 μm, respectively), −14.9 ± 0.9 and 5.5 ± 0.3. The data represent the mean ± S.E. of at least three independent experiments. Inset, DmNav1 currents from a single cell induced by a test pulse to −25 mV in the presence of control (a); 0.5 μm PbTx-2 + 1 μm DRS (b); 0.5 μm PbTx-2 (c).