FIGURE 7.

Cd²⁺ has no effect on the development of I_US but selectively hastens the time course of recovery. To examine which phase of the inactivation process was modulated by Cd²⁺, the application of Cd²⁺ was restricted to either the development or the recovery process. (A) Selective application of Cd²⁺ during development of I_US. Time course of peak inward sodium currents during a typical experiment (voltage clamp protocol as in Fig. 2 C). Superfusion with Cd²⁺ was started 100 s before the conditioning prepulse to allow for steady-state Cd²⁺ concentrations to be established at the beginning of the conditioning prepulse. Exposure to Cd²⁺ was terminated 180 s before the end of the conditioning prepulse to allow for complete washout of Cd²⁺ before initiation of recovery. (B) Normalized time course of recovery. Four experiments as described in A. Data points were fitted by Eq. 5, yielding the following parameters: I_US (drug free: A₂ = 0.58 ± 0.02, τ₂ = 163 ± 6, n = 6; Cd²⁺: A₂ = 0.59 ± 0.03, τ₂ = 158 ± 4 (n.s.), n = 4). (C) Selective application of Cd²⁺ during recovery from I_US. Time course of peak inward sodium currents during a typical experiment (voltage clamp protocol as in Fig. 2 C). Superfusion with Cd²⁺ was started 120 s before the end of the conditioning prepulse to allow the bath concentration of Cd²⁺ to reach steady state at the time of the start of the recovery period. (D) Normalized time course of recovery. Four experiments as described in C. Data points were fitted to Eq. 5, yielding the following parameters: drug free: A₂ = 0.68 ± 0.04, τ₂ = 120.0 ± 5.9; Cd²⁺: A₂ = 0.64 ± 0.03 (P < 0.05), τ₂ = 64.2 ± 3.8 s, (P < 0.05).