FIGURE 8.

Voltage-dependence of the inactivation time constants of Rb⁺ currents under bi-ionic conditions. (A) and (B) Kv4.1 currents evoked as described in Fig. 6 legend under the bi-ionic conditions indicated in the corresponding panels. Note that the currents mediated by Rb⁺ exhibit slower inactivation. (C) Voltage-dependence of the slow time constants of inactivation. Symbols are color coded to represent three ionic conditions: red, Rb_out/Rb_in; black, Rb_out/K_in; and blue, K_out/Rb_in. Note the marked voltage-dependence that is only apparent under bi-ionic conditions. Solid lines across the symbols are the best-fit exponentials that describe the voltage-dependence of the time constants (Materials and Methods). The derived apparent charges (q) were 0.73 and 0.66 from the inward and outward currents mediated by Rb⁺, respectively. The dashed line is the K_out/K_in average of the slow time constants measured across the indicated voltage range as demonstrated in Fig. 7.