Figure 2.
Permeability of guanidinium ion through the R666G gating pore. (A) Representative gating pore currents through the wild-type NaV1.4 and R666G channels in an external solution containing 80 mM NMDG + 40 mM guanidinium as permeant cations. (B) Conductance-voltage relationship of gating pore conductance for 120 mM Na+ (open squares, n = 20), 40 mM guanidinium (closed circles, n = 7), and 40 mM ethylguanidinium (open triangles, n = 5). (inset) Voltage protocol and representative record of gating charge movement used for normalization of gating pore currents to gating charge. −P/10 subtraction from a holding potential of 0 mV was used to subtract capacity transients. A 20-ms voltage step to −150 mV was followed by repolarization to 0 mV. Gating charge was calculated by integrating the current transient evoked by this repolarization step (area between the arrows). (C) Dependence of normalized guanidinium conductance on concentration. Currents were first recorded in 120 mM NMDG solution and then after addition of increasing concentrations of guanidinium (open circles, individual experiments; closed circles, mean, n ≥ 5). Error bars represent SEM.