Relationship between the ΔV_1/2 of F-V curves and maximal use-dependent block by lidocaine. ΔV_1/2 of F-V curves upon lidocaine addition and the maximal use-dependent block of ionic currents by lidocaine were obtained as described in the Results. The mutants whose ΔV_1/2 shifts linearly correlate with use-dependent block are represented as open squares. The mutants that show the most reduction in ΔV_1/2 without much change in use-dependent block are represented by filled circles, and the remaining mutants that show intermediate levels of reduction in the ΔV_1/2 are represented by open symbols.