Figure 7.

Cd²⁺ can be trapped in closed TC/TC channels. Current from an inside-out patch containing TC/TC channels, which contain cysteines at 464 in two of four subunits (see results and Fig. 4 A). In the top trace, channels were held open at −90 mV and blocked with Cd²⁺ (20 μM, horizontal bar). Cd²⁺ was removed, and the current recovered over the next 30 s. A subsequent test pulse (500 ms at −90 mV) shows activation of the recovered channels. In the bottom trace, channels were held open at −90 mV and blocked with the same concentration of Cd²⁺. After allowing for a fast component of recovery (results), a brief test pulse (500 ms at −90 mV) was given to measure the initial level of block. We attempted to hold the channels closed at +10 mV for 30 s. A subsequent test pulse showed that almost no recovery occurred after the initial test pulse, indicating that Cd²⁺ had been trapped.