Figure 3

Extracellular potassium slows current decay equally in full-length Shaker and I470 mutants.

(A). Current (top) and fluorescence (bottom) traces from Shaker-FL S424C in response to a voltage pulse to +60 mV from –80 mV, in solutions containing 3 mM (black) and 99 mM (grey) extracellular K⁺. Mean fluorescence decay rates (k) calculated from τ's in 3 and 99 mM K⁺, respectively, were: 7.98 ± 0.69 s⁻¹ and 2.01 ± 0.35 s⁻¹ (n = 5). Current and fluorescence amplitudes are normalized to one another for comparison. (B). Current and fluorescence traces from oocytes expressing Shaker-FL S424C T449V. (C–F). Current and fluorescence traces from the same protocol as in A applied to Shaker-FL S424C with the indicated amino acid substitutions. Mean fluorescence rates (k) calculated from τ's in 3 and 99 mM K⁺, respectively, were: (B) for I470L, 16.34 ± 0.71 s⁻¹ and 5.19 ± 0.84 s⁻¹ (n = 6); (C) for I470V, 2.66 ± 0.54 s⁻¹ and 0.60 ± 0.04 s⁻¹ (n = 5); (D) for I470C, 0.68 ± 0.09 s⁻¹ and 0.15 ± 0.03 s⁻¹ (n = 5); (E) for I470F, 5.34 ± 0.81 s⁻¹ and 1.30 ± 0.40 s⁻¹ (n = 5). (G). Fluorescence decay rates are compared with slow current decay rates from constructs I470, I470F, I470C and I470V in 3 mM (black) and 99 mM (grey) K⁺. A slow exponential time constant was mostly obscured by the fast decaying process in I470L, so these are not shown. (H). Inactivation rates from fluorescence in (A–E) in 3 mM and 99 mM K⁺ are calculated using Equation 2 and plotted against each other and fit by linear regression analysis (slope = 0.30 ± .02, R² = 0.99). The dashed line represents the regression line fit to points in Figure 2F. Current amplitudes shown in (A–E) are normalized to the peaks of both traces and fluorescence amplitudes in (A–E) are normalized to baseline signal amplitudes at –80 mV.