TY - JOUR T1 - Gating Pore Currents Demonstrate Selective and Specific Modulation of Individual Sodium Channel Voltage Sensors by Biological Toxins JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.114.092338 SP - mol.114.092338 AU - Yucheng Xiao AU - Kenneth M. Blumenthal AU - Theodore R. Cummins Y1 - 2014/06/04 UR - http://molpharm.aspetjournals.org/content/early/2014/06/04/mol.114.092338.abstract N2 - Voltage gated sodium channels are critical determinants of nerve and muscle excitability. While numerous toxins and small molecules target sodium channels, identifying the mechanisms of action is challenging. Here we used gating pore currents selectively generated in each of the voltage-sensors from the four alpha-subunit domains (DI-DIV) to monitor the activity of individual voltage-sensors and to investigate the molecular determinants of sodium channel pharmacology. The tarantula toxin HWTX-IV, which inhibits sodium channel current, exclusively enhanced inward gating pore currents through the DII voltage-sensor. By contrast, the tarantula toxin ProTx-II, which also inhibits sodium channel currents, altered the gating pore currents in multiple voltage-sensors in a complex manner. Thus while HWTX-IV inhibits central pore currents by selectively trapping the DII voltage-sensor in the resting configuration, ProTx-II seems to inhibit central pore currents by differentially altering the configuration of multiple voltage-sensors. The sea anemone toxin anthopleurin B, which impairs open-channel inactivation, exclusively enhanced inward gating pore currents through the DIV voltage-sensor. This indicates that trapping the DIV voltage-sensor in the resting configuration selectively impairs open-channel inactivation. Furthermore, these data indicate that while activation of all four voltage-sensors is not required for central pore current generation, activation of the DII voltage-sensor is crucial. Overall, our data demonstrate that gating pore currents can determine the mechanism of action for sodium channel gating modifiers with high precision. We propose this approach could be adapted to identify the molecular mechanisms of action for gating modifiers of various voltage gated ion channels. ER -