Voltage dependency of the binding/unbinding kinetics. (A). Family of TEVC current traces, from an oocyte expressing Shaker K427E, elicited by 500-ms voltage pulses ranging from −70 to 90 mV (top panel). The oocyte was under continuous superfusion with the Hi-Na⁺ recording solution (see Materials and methods). (B) Same as A, but plus 4 nM CTX. The trace coloring corresponds to the same voltage pulses in A. (C). Point-by-point quotients between the trace with the toxin divided by it corresponding control trace in the interval 0–90 mV. The trace coloring is as in A and B. The blue line on top of each current-ratio trace are single-exponential fits with time constant, τ, and an equilibrium fractional inhibition, ss. (D) Plot of τ versus pulse voltage. (E) Plot of ss versus voltage. (F) The association and dissociation rates, k_on and k_off, for each voltage, calculated by solving the equation system 1, are plotted as a function of the voltage. The continuous lines were drawn with Eq. 4, where k_V0 is the rate constant (k_on or k_off) at Vm = 0 mV and zδ is the effective valence of the voltage dependency. The solid lines were traced with Eq. 4 with parameters k_off0 = 0.32 s⁻¹, zδ = +0.61 and k_on0 = 0.093 nM⁻¹·s⁻¹, zδ = −0.06. See also Data S2 for underlying data.