Figure 4.

Effects of K149 mutations on the opening rate constant: initial fits to the four-state model. The voltage dependence of the opening rate constant (α) for wild type and selected K149 mutants at 110 mM external chloride were fit to the four-state model shown in Scheme 1. Fits are shown as dashed lines. Wild-type data were fit by letting all six parameters in the model vary. For mutant data, fits were derived by letting vary only α₂ ^*(0) (A), or only α₁ ^*(0) and α₂ ^*(0) (B), while holding all other parameters at their wild-type best-fit values. The fits in (B) yielded α₂ ^*(0) values for wild type, K149R, M, S, L, in s⁻¹: 501, 135, 143, 55, 39; and corresponding α₁ ^*(0) values: 0.96, 0.77, 0.74, 0.52, 0.67. For each voltage, the opening rate constant (α) was derived using data from at least five patches. These opening rate constants were averaged and the error bars show the SEM.