Figure 8.
Disulfide bond breakage in oxidizing conditions. A, Average of 5 responses of the S729C mutant to 10 mm glutamate in reducing conditions (1 mm DTT); inset shows single exponential fit (red), kdes 287 s–1. B, In the same patch, a time-dependent relief of trapping occurred in the continuous presence of CuPhen. Four separate traces are overlaid with 1, 3, 16 and 36 s exposures to CuPhen at rest, following the application of 50 μm glutamate; DTT was present only during the test pulses of 10 mm Glu indicated by *. Relief from trapping in DTT is slow enough (0.3 s–1) that there is negligible change in the rise time and peak amplitude of the test pulse. The inset shows the final pulse, after 36 s of exposure to CuPhen at rest; single exponential fit (red) to the current during the 20 ms application of 10 mm Glu (red), kdes = 337 s–1. C, The relaxation of the trapped receptors at rest in CuPhen, normalized to the mean of prerelaxation and postrelaxation responses in DTT, was fitted with a monoexponential recovery with a lifetime of 13 ± 6 s (data from 5 patches). The steady-state level of nontrapped receptors was 21 ± 4%, similar to the level of trapped receptors at rest without pretrapping in glutamate (32 ± 2%, Fig. 4).