Figure 2. Characterization of E403C, E758C, D1241C and D1532C mutant channels.

A, voltage-dependent fast-inactivation channel availability using the pulse protocol shown in the inset was fitted with Boltzmann distributions for wild type (WT) (n = 5), E403C (n = 14), E758C (n = 6), D1241C (n = 5) and D1532C (n = 8). The midpoints and slope factors were −53.03 ± 1.77 and 5.95 ± 0.26 for WT, −55.03 ± 0.98 and 6.81 ± 0.45 for E403C, −53.89 ± 1.32 and 5.42 ± 0.30 for E758C, −54.58 ± 1.14 and 5.91 ± 0.38 for D1241C, −53.60 ± 0.50 and 5.31 ± 0.21 for D1532C. B, recovery from fast inactivation was determined using the two-pulse protocol shown in the inset. The data were fitted with a single exponential with time constants as follows: 2.89 ± 0.30 WT, 2.47 ± 0.29 E403C, 2.70 ± 0.04 E758C, 2.60 ± 0.25 D1241C and 2.54 ± 0.35 D1532C; n = 4. C, development of slow inactivation using the two-pulse protocol shown in the inset. The interval between each episode is 60 s with a holding potential of −100 mV. The time constants (τ) and fractional amplitudes (in parentheses) were as follows: WT, τ = 15612 ± 910 ms (0.85 ± 0.02); E403C, τ = 6846 ± 2286 ms** (0.79 ± 0.06); E758C, τ = 6587 ± 1632 ms** (0.76 ± 0.07); D1241C, τ = 9623 ± 878 ms** (0.72 ± 0.07); D1532C, τ = 3970 ± 971 ms** (0.84 ± 0.02); n = 4–5. D, time course of recovery from slow inactivation using the two-pulse protocol shown in the inset. The interval between each episode is 30 s with a holding potential of −100 mV. Time constants and fractional amplitudes (in parentheses) were as follows: WT (n = 5), τ₁ = 48.28 ± 37.10 ms (0.34 ± 0.09), τ₂ = 406.87 ± 87.52 ms (0.67 ± 0.11); E403C (n = 5), τ₁ = 45.46 ± 36.87 ms (0.32 ± 0.04), τ₂ = 2204.03 ± 698.01 ms* (0.64 ± 0.03); E758C (n = 4), τ₁ = 34.29 ± 19.44 ms (0.32 ± 0.06), τ₂ = 1345.04 ± 407.00 ms* (0.58 ± 0.05); D1241C (n = 5), τ₁ = 11.25 ± 3.41 ms (0.41 ± 0.04), τ₂ = 1741.49* ± 497.12 ms (0.63 ± 0.03); D1532C (n = 6), τ₁ = 114.52 ± 43.41 ms (0.42 ± 0.04), τ₂ = 1707.04* ± 387.64 ms (0.52 ± 0.05). *P < 0.05; **P < 0.01.