FIGURE 5.

Concentration- and V_j-dependent spermine association and dissociation rates under symmetric [KCl] conditions. (A) Determination of the decay time constant (τ_decay) during the onset of a positive V_j step in the presence of 2 mM spermine. For this example, the steady-state open probability (P_open) was 0.11. (B) Determination of the rise-time constant (τ_rise) during the onset of a negative V_j step in the presence of 2 mM spermine. (C) The spermine on-rates (K_on), determined from the I_j decay time constants at +V_j values, were calculated using Eq. 7 for all four symmetric [KCl] conditions. The K_on values were fit by a single exponential. (D) The spermine off-rates (K_off), calculated from the decay time constants at +V_j values or rising time constants at −V_j values using Eq. 8 or 9, respectively, were fit by a single exponential function for all four symmetric [KCl] conditions. Symmetrically decreasing the [KCl] reciprocally increased and decreased the spermine on-rates and off-rates (see Supplemental Material, Fig. S3, for further details).