FIGURE 6.

Evidence for spontaneous disulfide bond formation in constitutively open channels. A, example whole cell currents recorded at +30 mV for R334C/T1122C/E1371Q, showing that inhibition by external Cd²⁺ (3 μm) is dependent on prior treatment with DTT to reduce spontaneous disulfide bonds. B, dependence of Cd²⁺ inhibition on different pretreatment conditions in different cysteine double mutants in an E1371Q background. Cadmium concentrations, chosen to give ∼50% inhibition for each mutant, are given below the name of the mutant used. Asterisks indicate a significant difference from the effect without pretreatment (p < 0.0005). The means of data from three to six cells are shown. Note that the Cd²⁺ sensitivity of the single cysteine mutants R334C/E1371Q and T338C/E1371Q was independent of DTT pretreatment (not shown), as shown in Fig. 3 for R334C and T338C. Ctrl, control.