Polypeptide Neurotoxins Modify Gating and Apparent Single-Channel Conductance of Veratridine-Activated Sodium Channels in Planar Lipid Bilayers

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The effects of scorpion and sea anemone polypeptide toxins on partially purified veratridine (VER)-activated Na channels from rat brain were studied at the single-channel level in planar lipid bilayers. The probability of the VER-activated channel being open (Po ) increased with depolarization; Po was 0.5 at −40 to −50 mV. Saxitoxin (STX) blocked VER-activated channels with an apparent dissociation constant of about 1nm at −45 mV. The apparent single-channel conductance was approximately 9 pS, similar to that seen in VER-activated Na channels from skeletal muscle transverse tubules. Addition of sea anemone or scorpion polypeptide toxins to VER-activated Na channels resulted in a 19% increase in apparent single-channel conductance and a hyperpolarizing shift in the Po vs. Vm relation such that the channels were more likely to be open at potentials <40 mV. These effects of the polypeptide toxins on the single-channel properties of VER-activated Na channels may account for the previously described potentiation of VER action by polypeptide toxins.



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