Kanevsky M , Aldrich RW .

GM07365 NIGMS NIH HHS , NS23294 NINDS NIH HHS , T32 GM007365 NIGMS NIH HHS

	Figure 1. Steady state voltage dependence of the wild-type ShBΔ6-46 K channel and the F401I mutant. (A) Activation families were elicited from the holding potential of −100 mV with steps in 10-mV increments between −80 to +50 mV, and tail currents were recorded at −65 mV, as indicated schematically above the traces. Patch-clamp records were obtained in the inside-out excised configuration (Hamill et al. 1981), digitized at 20 kHz, and low-pass filtered at 8 (wt) or 3 (F401I) kHz. (B) Relative conductance is plotted versus voltage. Conductances were normalized to the maximal value in each family and the results from different patches were averaged to obtain the means and standard errors shown (wt: n = 5; F401I: n = 6). Averaged G(V) curves were fit with the fourth power of a Boltzmann function (see methods). The apparent gating valence per subunit from these fits is reduced from 4.18 e0 for the wild type to 2.40 e0 for F401I. V1/2 parameters from the fits are −56.3 mV for wt and −57.6 mV for F401I. (C) The amino acid sequence difference between wild-type Shaker and the neomorphic Sh5 allele is localized to a single substitution in the S5 region: phenylalanine is mutated to isoleucine at position 401 (Gautam and Tanouye 1990; Lichtinghagen et al. 1990). The sequence is shown using the standard single-letter amino acid code; dashes in the Sh5 sequence indicate amino acid identity with wt. Asterisks mark the residues that were mutated in this study.
	Figure 7. Substitutions at position 401 affect deactivation. (A) Deactivation time constants for the F401L, F401V, and F401A mutant channels were obtained from single exponential fits to currents during channel closing. The time constants, τ, are plotted as a function of tail potential and fitted with an exponential. For F401L and F401V, results are shown as the mean ± SEM of 8 and 10 experiments, respectively. Due to the bandwidth limitations on our ability to fully resolve closing kinetics in the F401A mutant, results from the two best patches are shown at selected voltages. For comparison, fits to wild-type and F401I deactivation curves from Fig. 3 are also included. The voltage dependence of deactivation τ yielded apparent zr values of 1.15 e0 for F401L, 0.74 e0 for F401V, and <0.5 e0 for F401A. (B) Differences of deactivation kinetics are illustrated with the tail families of the F401A and F401L mutants, shown on the same time scale. The F401A family (left) was recorded under standard ionic conditions (see methods) from an inside-out patch, sampled at 100 kHz and low-pass filtered at 9.5 kHz. Tail voltage ranged between −20 and −170 mV in 10-mV increments. The F401L currents (right) were recorded from an outside-out patch with symmetrical 140 mM K+ as the permeant cation. Increasing external K+ from 2 to 140 mM does not significantly affect tail kinetics of this channel (data not shown, but see Zagotta et al. 1994a. Tail voltage was stepped to between −80 and −180 mV in 10-mV increments. For both families, a 10-ms pulse to +50 mV preceded the steps to the tail potentials.
	Figure 2. Kinetics and voltage dependence of forward transitions in the wild-type Shaker channel and the F401I mutant. (A) The time course of activation was compared in current traces obtained as in Fig. 1, with pulse voltages indicated on the right. Currents from wild-type and mutant channels were scaled to match maximal amplitudes at each of three voltage levels and fit with a single exponential function beginning at the time point corresponding to half-maximal current amplitude (see methods). Fits are superimposed on the traces as dotted curves. (B) Voltage dependence of the activation time constant. Values of the time constant, τ, derived from single-exponential fits from a number of patches (wt: n = 7; F401I: n = 5) were averaged and plotted against pulse voltage on semilogarithmic axes. Error bars represent the standard error of the mean. The time constant versus voltage relation was fit with a decaying exponential function above −10 mV, shown as solid (F401I) and dashed (wt) lines. The apparent charge associated with forward transitions late in activation, zf, was calculated from the slope of the fitted line, and found to be 0.36 e0 for the wt and 0.31 e0 for F401I. (C) Difference in activation delay between wt and mutant currents. Sets of representative traces recorded from two patches different from those in A are shown, with pulse voltage to the right of the traces. Current amplitudes for the +20-mV traces in each family were set to unity. Arrows indicate the time points at which current amplitudes are half-maximal. (D) As a way to quantify the absolute activation delay, the mean time to reach half-maximum is displayed against pulse voltage for wt (n = 8) and F401I (n = 5) currents. The standard error of the mean is shown as error bars when it exceeds the size of a symbol.
	Figure 3. Alterations in the kinetics and voltage dependence of the closing transitions associated with the F401I mutation. (A and B) Deactivation families from wt (A) and F401I (B) patches were obtained with brief (8–10 ms) depolarizations to +50 mV, followed by steps to voltages between −60 and −160 mV in 10-mV increments, as indicated schematically above the traces. (C) Relaxations of the tail currents were fitted with a single exponential function (see methods). Means and standard errors of deactivation time constants, τ, from the fits are plotted against tail potential for patches containing wt (n = 8) and F401I (n = 6) channels. Average τ vs. voltage curves were computed and fitted with an exponential over the voltage range below −60 mV. Fits are shown as solid (F401I) and broken (wt) lines. The apparent charge associated with reverse transitions, zr, was calculated from the steepness of the exponential voltage dependence of τ. zr for the wt is 1.30 e0 whereas zr for F401I is 0.68 e0. (Inset) Shown are superimposed wt and mutant tail currents recorded at −60 (left) and −160 (right) mV. The currents were scaled to match their peak amplitudes during the +50-mV prepulse. Note that the time scales are different so as to enable comparison of kinetic detail for the two species at both voltage extremes.
	Figure 4. Alanine replacements in the S5 region and the steady state activation in Shaker. On the left are representative families recorded from inside-out patches containing the mutant channels indicated. Test steps were given in the voltage ranges shown under the traces in 10-mV increments. Tail voltage was −65 mV for all families. On the right, corresponding G(V) relations are shown for each mutant; curves fitted to the wt G(V) are included for comparison (shown as broken lines). For the F416A mutant, the mean of 12 experiments with its standard error is displayed. For the other mutants, combined data from three (F404A), two (L403A), two (S411A), and three (S412A) patches are shown. Thin lines through the data represent fits of the Boltzmann function raised to the fourth power (see methods), yielding the following estimates of apparent gating valence and midpoint of voltage-dependent transition: z = 3.81 e0 and V1/2 = −55.5 mV (F404A); z = 3.97 e0 and V1/2 = −51.1 mV (F416A); z = 3.86 e0 and V1/2 = −49.1 mV (L403A); z = 4.16 e0 and V1/2 = −50.4 mV (S411A); z = 4.10 e0 and V1/2 = −49.6 mV (S412A).
	Figure 5. Aliphatic side-chain substitutions at position 401 affect the steady state voltage dependence of activation. (A) Families of macroscopic currents from patches expressing (left to right) F401L, F401V, and F401A channels were recorded as in Fig. 1. The voltage ranges for the three families were as follows (step increment in parentheses): −85 to +25 mV (10 mV) for F401L, −80 to +60 mV (10 mV) for F401V, and −80 to +160 mV (20 mV) for F401A. Note the faster time scale for the F401A family used to resolve its kinetic features. (B) Relative conductance versus voltage relationships for the three mutants are shown. For comparison, fits to G(V) curves for the wt and F401I channels are reproduced from Fig. 1. F401L and F401V data are plotted as means ± SEM of eight and nine families, respectively. Averaged G(V) data were fitted with the fourth power of a Boltzmann function, as previously described, giving apparent z of 4.25 and 2.52 e0, and V1/2 of −69.7 and −53.1 mV for F401L and F401V, respectively. For the F401A experiment shown (representative of 11 patches), G(V) was measured either as the chord conductance assuming the reversal potential of −80 mV (denoted “pulse”), or as the isochronal tail current amplitude (denoted “tail”). The characteristic failure of the steady state conductance to reach a maximum within the attainable voltage range prevented meaningful normalization of the F401A G(V).
	Figure 6. Effects of replacing phenylalanine 401 with aliphatic residues on the activation kinetics and voltage dependence. (A) Representative current traces from wt, F401I, F401V, F401A, and F401L patches were superimposed and scaled to match at their peaks. Pulse voltages are indicated on the left. (B) A semilogarithmic plot of the activation time constants (mean ± SEM), determined from fitting an exponential function to the activation time course (see methods), is shown for the F401L (n = 12), F401V (n = 12), and F401A (n = 11) mutants. From the steepness of the exponential fit to the τ versus voltage relation, apparent valence associated with the forward transitions, zf, was found to be 0.41 e0 for F401L, 0.42 e0 for F401V, and 0.32 e0 for F401A. Fits are shown as thin solid and broken lines; for comparison, a fit to the wt activation τ is reproduced from Fig. 2 as a thick broken line.
	Figure 8. Gating charge movement in the wild type and channels containing F401L and F401A mutations. Gating currents were recorded from nonconducting channels containing the indicated mutations using a cut-open oocyte voltage clamp, digitized at 20 kHz (42 kHz for wfF401A) and low-pass filtered at 10 kHz. Traces elicited by steps to the voltages indicated on the left, beginning from and returning to the holding potential of −100 mV, are shown staggered to facilitate the kinetic comparison. Chloride-free standard solutions were used (see methods).
	Figure 9. F401 substitutions affect the steady state charge transfer and kinetics of the forward transitions. (A) Relative charge versus voltage relations were computed for the wf, wfF401L, and wfF401A channels by integrating the gating current during the −100-mV post-pulse (IgOFF). Normalized Q(V) relations from a number of experiments were averaged and plotted as a function of test voltage as mean ± SEM (wf: n = 17; wfF401L: n = 10; wfF401A: n = 12). The fitted lines through the data are the Boltzmann function predictions for channels with independent and identical subunit transitions with the following values of voltage midpoint (V1/2) and associated charge displacement (z): −43 mV and 3.73 e0, −61.6 mV and 4.14 e0, and −52.3 mV and 2.76 e0, for wf, wfF401L, and wfF401A, respectively. (B) The decay phase of the IgON was fitted with a single exponential and the time constants are plotted against pulse voltage for the wf (n = 11), wfF401L (n = 8), and wfF401A (n = 8) channels. From the exponential fits of the voltage dependence, beginning at −10, −25, and −20 mV, the estimate zf of the charge associated with the forward transitions is 0.57, 0.61, and 0.63 e0, for wf, wfF401L, and wfF401A, respectively.
	Figure 10. Mutations of F401 and cooperative gating: sigmoidicity. (A) Activation families of wt currents taken at voltages between −65 and 25 mV, F401L (−80 to +30 mV), and F401A (-70 mV to +90 mV) in 10-mV increments. (B) Data transformed to normalize the current amplitude and overall speed of activation for the voltages shown. Sigmoidicity is defined as the amount of initial delay relative to the overall rate of activation. Its voltage dependence can be visualized by following transformation (Zagotta et al. 1994a). The currents from different voltage steps are first scaled to match at their peaks. Then the time derivative of the current waveform is determined at the time when current amplitude is half maximal. In general, it is at that point that the slope is the steepest. All the records in the family are then expanded or compressed along the time axis so that their derivatives at half-maximum match. This transformation results in parallel curves whose relative displacement along the x axis is the measure of sigmoidicity. The noisier traces correspond to lower voltages. Data were filtered at between 8 and 10 kHz and sampled every 20–50 μs.
	Figure 11. Mutations of F401 and cooperative gating: Cole-Moore analysis. (A) Families of currents from the wt, F401L, and F401A channels were obtained as follows: pulses to 0 mV were preceded by 1-s-long prepulses to voltages between −140 and −40 mV (wt, left), −170 and −50 mV (F401L, center), or between −130 and −20 mV (F401A, right). A few of the most depolarizing prepulses are in the activation range of the channels, as evident from the steady current recorded during the prepulse. The most negative prepulses induce greatest delay at the onset of activation. (B) The voltage families above were scaled in amplitude to match at the peak to compensate for steady state C-type inactivation incurred at the more depolarized prepulses. Scaled traces were then shifted along the time axis to obtain the best superposition. Note that, whereas in wt and F401L (left, center) traces in which the prepulse opens channels with detectable probability are not superimposable on the rest of the family, in F401A such behavior is not seen. At the onset of current during the main pulse, gating currents can be seen as bumps in the F401A family.
	Figure 20. The model accounts for the sigmoidicity in wt and F401 mutants. The activation families for the three models, with the relevant transitions shown in the box, were scaled in time and amplitude as described in the text to assess the dependence of sigmoidal delay on pulse voltage. Current families were simulated at voltages shown. Compare these results with the experimental data in Fig. 10.
	Figure 13. Predictions of the ZHA model at different levels of cooperativity. (A) Connectivity of the ZHA model is shown in the collapsed format (for expanded version showing all nondegenerate states, see Fig. 7 of Zagotta et al. 1994b). Note that the rate of the first backward transition for leaving the open state is slowed by the cooperative factor θ. Simulations were performed on the versions of the ZHA model that varied the value of the factor θ as indicated. Simulated currents were then analyzed in the manner identical to the experimental data. Shown are the simulations for the normalized steady state G(V) relationship (B), ionic tail currents at −65 mV (C), normalized steady state Q(V) relation (D), and pulse-length dependence of the OFF gating current at −30 mV (E).
	Figure 14. A kinetic model for Shaker and the F401 mutants. Note that, compared with the ZHA model, independent transitions within each of the four subunits are completely symmetrical and that a concerted transition precedes channel opening. A closed state in which all four subunits are in the C2 state is implicit in the model; is it referred to as the Cn state in the text. (Bottom) The model estimates of the zero-voltage rate constants (k0, in s−1) and associated quantities of charge movement (zk, in e0) for each of the rates for the wt, F401L, and F401A channels are shown. The initial closing transition parameters are enclosed in a box to highlight the differences among the models.
	Figure 15. (A) Model description of the steady state gating charge movement. The averaged Q(V) curves for the wf, wfF401L, and wfF401A channels are replotted from Fig. 9. Fits of the model in Fig. 14 are shown superimposed as solid lines. These were obtained by integrating the simulated OFF gating currents at −100 mV, low-pass filtered at 10 kHz, following steps to the test potentials shown on the x axis in 2-mV increments and normalizing by the charge obtained at the most positive voltages. This analysis follows the normal procedure we use for the experimental data. (B) Comparison of gating current kinetics with the model predictions. Representative families of gating currents from oocytes containing wf (top, from −80 to +40 mV), wfF401L (middle, −80 to +40 mV), and wfF401A (bottom, −95 to +25 mV) channels are shown. Voltage increment is 20 mV in each case. Simulated gating currents are superimposed (thin lines). Models shown in Fig. 14 were used for the three channels, with the following modifications to obtain better fits to these experimental families: in the wf model, λ0 = 101 s−1; in the F401L model, λ0 = 39 s−1; and in the F401A model, κ0 = 3,500 s−1, λ0 = 8,000 s−1, and zγ = 0.8 e0.
	Figure 16. Model predictions for the pulse duration dependence of the OFF gating charge movement. Experimental records of wf (left), wfF401L (center), and wfF401A (right) gating currents obtained at −50 and 0 mV are shown as in Fig. 12. The fits of the corresponding models are shown overlaid (thin lines). Modifications of the models needed for these simulations were as follows (s−1): for wf, β0 = 153, δ0 = 14, and λ0 = 113 at 0 mV; for wfF401L, α0 = 1,150, δ0 = 11.5, and λ0 = 39 at −50 mV and β0 = 136 and δ0 = 11.5 at 0 mV; and for wfF401A, α0 = 1,200 and λ0 = 8,000 at both −50 and 0 mV.
	Figure 17. (A) Model predictions for the activation of ionic currents. On the left, representative families of currents recorded at between −90 and +50 mV (wt), −95 to +25 mV (F401L), and −80 to +140 mV (F401A) are displayed. Voltage increments were 10 mV (20 mV for F401A). Corresponding simulated ionic currents are shown on the right. Model parameters were not altered from those in Fig. 14B and Fig. C. Comparison of the model with measured ionic current activation kinetics. Activation time constants (B) and time-to-half-maximum (C), obtained as described in the text, are plotted as a function of test voltage for wt, F401L, and F401A channels. Predictions of the models are shown as solid and dashed lines. These were obtained by the same analysis procedures applied to the simulated currents as to the experimental records.
	Figure 18. Model description of the conductance–voltage relationships. Experimental data for wt, F401L, and F401A are shown plotted as in Fig. 1 and Fig. 5. Simulated G(V) relations were generated from current families taken every 2 mV. The resultant curves were then shifted negatively by 6 (wt and F401L) or 7 (F401A) mV and shown superimposed as lines. The predicted G(V) curves from pulse and tail (see methods) for F401A were normalized to match the maximum relative conductance of the data.
	Figure 19. Models predict the deactivation kinetics in Shaker and F401 mutants. Ionic tail currents that arise during channel deactivation at negative voltages are shown as relative open probability as the function of time by scaling to match the instantaneous amplitudes after the end of the +50-mV test pulse (top). The current families for the tail voltages of −60 to −160 mV (wt, left), −60 to −180 mV (F401L, center), and −30 to −90 mV (F401A, right) are shown. Records at −100 mV are omitted because the current amplitudes are very low near the reversal potential. Note the inward current at the start of the tail at −90 mV in F401A, which is largely due to the OFF gating current component. Model predictions for the time course of the open probability decay are superimposed as thin lines. (Bottom) The data and model traces for the wt and F401L are replotted on a logarithmic time axis to enable closer comparison of the model to the data at the lowest voltages. For these simulations, λ0 was 50 and 29 s−1 for the wt and F401L models, respectively.
	Figure 12. Mutations of F401 and cooperative gating: return of the gating charge before and after channel opening. (A) Families of gating currents recorded in the cut-open oocyte clamp are shown. In all families, steps were given from the holding voltage of −100 mV. For the wf (left) and wfF401L (center) channels, pulse voltages were (top to bottom) −50, −30, and 0 mV. For wfF401A (right), pulse voltages were −50, 0, and +100 mV. Voltage electrode traces are included above each family to indicate the voltage protocol used. In each family, gating currents resulting from different durations of the pulse are overlaid such that the changes with the pulse length can be observed as the envelope of OFF gating currents. Data were filtered at 8–10 kHz. (B) Voltage and pulse-length dependence of charge return kinetics. For the wf (left), wfF401L (center), and wfF401A (right) channels, records obtained as in Fig. 8 were fitted with an exponential function to describe the time course of IgOFF decay. The time constants from the fits for the different levels of pulse voltage are plotted as a function of duration of the pulse.

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