TTX-S Na⁺ channel.

<p>(A) Voltage dependence of steady state activation (<i>m</i>_∞) and inactivation (<i>h</i>_∞) of the channel. Squares (=<i>m</i>_∞) and triangles (=<i>h</i>_∞) represent the experimental data (Expt.) for bladder medium-diameter DRG neuron [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006293#pcbi.1006293.ref007" target="_blank">7</a>]. Solid (<i>m</i>_∞) and dashed (<i>h</i>_∞) lines represents simulation results (Sim.). (B) The voltage dependence of time constants of activation (<i>τ</i>_<i>m</i>, solid line) and inactivation (<i>τ</i>_<i>h</i>, dashed line). (C) Rectangular voltage clamp currents, TTX-S I_Na for different clamp levels from experiments [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006293#pcbi.1006293.ref007" target="_blank">7</a>] (symbols, squares: −15 mV, circles: −5 mV and triangles: 45 mV) and simulation (corresponding solid lines). The holding potential was kept at −70 mV and the test potentials of 25 ms were applied to −15, −5 and 45 mV. (D) Peak current-voltage (I-V) relationship obtained using experiments (squares, [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006293#pcbi.1006293.ref007" target="_blank">7</a>]) and simulations (solid line). Protocol: Rectangular voltage clamp from −80 to 40 mV in steps of 5 mV from a holding potential of −60 mV. The peak currents at each test potentials are plotted. Other parameters: , E_Na = 38 mV, RMP = −56.5 mV, soma diameter = 32.4 <i>μ</i>m [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006293#pcbi.1006293.ref007" target="_blank">7</a>] and total capacitance = 31.7 pF [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006293#pcbi.1006293.ref008" target="_blank">8</a>]. The S values for model fits and their 5% threshold values (given in brackets) are: <i>m</i>_∞ = 0.017 (0.05), <i>h</i>_∞ = 0.021 (0.05), for voltage clamp currents: at −45 mV = 0.183 nA (0.033 nA), at −15 mV = 0.189 nA (0.137 nA) & at −5 mV = 0.334 nA (0.129 nA), and I-V curve = 0.246 nA (0.276 nA).