Figure 5.

Effect of 100 nM Mb1a on the voltage-dependence of activation of P. americana DUM neuron Na_V channels. (a) Families of Na_V channel currents were elicited by depolarizing test pulses to +40 mV from a holding potential of −90 mV in 10-mV steps. Representative superimposed families of I_Na are shown prior to (b), and 5 min after (c), application of 100 nM Mb1a. Currents were generated using the test pulse protocol shown in panel a. (d) Normalised I_Na-V relationships before (open circles), and after (red circles and shaded), application of 100 nM Mb1a. Data were fitted using Equation (1) (see Materials and Methods). Currents recorded in the presence of toxin were normalised against maximum peak I_Na in controls (red solid curve) and maximum peak I_Na in the presence of toxin (red dashed curve). (e) Linear regression analysis of the data using Equation (2) (see Materials and Methods) revealed that inhibition of I_Na was voltage-independent over the range −40 to 0 mV in the presence of 100 nM Mb1a. Data points are the mean ± S.E.M of 3 experiments.