Correspondence to: Michael F. Sheets, CVRTI, Bldg. 500, 95 South 2000 East, University of Utah, Salt Lake City, UT 84112. Fax:801-581-3128 E-mail:michael{at}cvrti.utah.edu.
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Abstract |
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We investigated the contribution of the putative inactivation lid in voltage-gated sodium channels to gating charge immobilization (i.e., the slow return of gating charge during repolarization) by studying a lid-modified mutant of the human heart sodium channel (hH1a) that had the phenylalanine at position 1485 in the isoleucine, phenylalanine, and methionine (IFM) region of the domain IIIIV linker mutated to a cysteine (ICM-hH1a). Residual fast inactivation of ICM-hH1a in fused tsA201 cells was abolished by intracellular perfusion with 2.5 mM 2-(trimethylammonium)ethyl methanethiosulfonate (MTSET). The time constants of gating current relaxations in response to step depolarizations and gating chargevoltage relationships were not different between wild-type hH1a and ICM-hH1aMTSET. The time constant of the development of charge immobilization assayed at -180 mV after depolarization to 0 mV was similar to the time constant of inactivation of INa at 0 mV for hH1a. By 44 ms, 53% of the gating charge during repolarization returned slowly; i.e., became immobilized. In ICM-hH1aMTSET, immobilization occurred with a similar time course, although only 31% of gating charge upon repolarization (OFF charge) immobilized. After modification of hH1a and ICM-hH1aMTSET with Anthopleurin-A toxin, a site-3 peptide toxin that inhibits movement of the domain IV-S4, charge immobilization did not occur for conditioning durations up to 44 ms. OFF charge for both hH1a and ICM-hH1aMTSET modified with Anthopleurin-A toxin were similar in time course and in magnitude to the fast component of OFF charge in ICM-hH1aMTSET in control. We conclude that movement of domain IV-S4 is the rate-limiting step during repolarization, and it contributes to charge immobilization regardless of whether the inactivation lid is bound. Taken together with previous reports, these data also suggest that S4 in domain III contributes to charge immobilization only after binding of the inactivation lid.
Key Words: sodium channel, gating charge, inactivation, site-3 toxin, immobilization
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INTRODUCTION |
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The primary process by which voltage-gated sodium channels become nonconductive after opening in response to a strong step depolarization is called inactivation.
Since the first cloning of a voltage-gated sodium channel by subunit. Part of the fast inactivation process was localized to the intracellular region formed by the linker between domains III and IV by
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To investigate the role of the inactivation lid in charge immobilization, we studied the human cardiac sodium channel that had the phenylalanine at amino acid position 1485 in the IFM motif mutated to a cysteine (ICM-hH1a). The mutant sodium channel was transiently expressed in fused mammalian cells (
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METHODS |
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cDNA Clones
In hH1a (kindly provided by H. Hartmann and A. Brown (see
Cell Preparation
Multiple tsA201 cells (SV40-transformed HEK293 cells) or multiple HEK293 cells were fused together using polyethylene glycol, as previously described (
Recording Technique, Solutions, and Experimental Protocols
Recordings were made using a large bore, double-barreled glass suction pipette for both voltage clamp and internal perfusion, as previously described ( feedback resistor. Voltage protocols were imposed from a 16-bit DA converter (Masscomp 5450; Concurrent Computer) over a 30/1 voltage divider. Data were filtered by the inherent response of the voltage-clamp circuit (corner frequency near 125 kHz) and recorded with a 16-bit AD converter on a Masscomp 5450 at 200 kHz. A fraction of the current was fed back to compensate for series resistance. Temperature was controlled using a Sensortek thermoelectric stage (TS-4; Physiotemp Instruments, Inc.) mounted beneath the bath chambers and it typically varied <0.5°C during an experimental set. Cells were usually studied at 12°13°C.
A cell was placed in the aperture of the pipette and, after a high resistance seal formed, the cell membrane inside the pipette was disrupted with a manipulator-controlled platinum wire. Voltage control was assessed by evaluating the time course of the capacitive current and the steepness of the negative slope region of the peak currentvoltage relationship as per criteria previously established (
The control extracellular solution for INa measurements contained (mM): 15 Na+, 185 TMA+, 2 Ca2+, 200 MES-, and 10 HEPES, pH 7.2; and the intracellular solution contained: 200 TMA+, 200 F-, 10 EGTA, and 10 HEPES, pH 7.2. For measurement of Ig, the intracellular solution contained (mM): 200 TMA+, 50 mM F-, 150 mM MES-, 1 mM BAPTA (1,2-bis 2-aminophenoxy-ethane-N,N,N ',N-tetraacetic acid; Sigma Chemical Co.), 10 HEPES, and 10 EGTA, pH 7.2, 10 µM saxitoxin (Calbiochem Corp.), and the extracellular solution had Na+ replaced with TMA+. Reduction of intracellular F- and inclusion of BAPTA reduced the magnitude of endogenous ionic currents that occasionally interfered with recordings. Anthopleurin A toxin (Sigma Chemical Co.) was used at a concentration of 1 µM, which is three orders of magnitude greater than the Kd (
Data Analysis
Leak resistance was calculated as the reciprocal of the linear conductance between -190 and -110 mV, and cell capacitance was measured from the integral of the current responses to voltage steps between -150 and -190 mV. Peak INa was taken as the mean of four data samples clustered around the maximal value of data digitally filtered at 5 kHz and leak corrected by the amount of the calculated time-independent linear leak. Data were capacity corrected using 416 scaled current responses recorded from voltage steps between -150 and -190 mV. All Ig were leak corrected by the mean of 24 ms of data, beginning at least 8 ms after the change in potential. For ON-Ig, this was typically at 8 ms, and 10 ms for OFF-Ig.
To determine time constants of Ig decay, current traces were trimmed until the decay phase was clearly apparent, and then fit by a sum of exponentials with DISCRETE (
Charge-voltage relationships were fit with a simple Boltzmann distribution as follows:
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(1) |
where Q is the charge during depolarizing step, Qmax is the maximum charge, Vt is the test potential, V1/2 is the half point of the relationship, and s is the slope factor in millivolts. For comparison between cells, fractional Q was calculated as Q/Qmax for each cell.
Data were analyzed and graphed on a SUN Sparcstation using SAS (Statistical Analysis System). Unless otherwise specified, summary statistics are expressed as means ± 1 SD. Regression parameters are reported as the estimate and the standard error of the estimate (S.E.E.), and figures show means ± SEM.
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RESULTS |
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Intracellular MTSET Modification of ICM-hH1a
Similar to previous reports (
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ON-Gating Current Studies
If the putative inactivation lid were outside the voltage field and all voltage sensors had completed their translocation before the binding of the inactivation lid to its receptor, then Ig measured during step depolarizations should be insensitive to whether the inactivation lid can become bound to its receptor. Fig 3 shows capacity and leak-corrected Ig traces and their corresponding integrals for typical cells expressing hH1a and ICM-hH1aMTSET. Ig decays were fit by a sum of up to two exponentials, and a two-time-constant fit was accepted when it produced a statistically significant F statistic (
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Development of Ionic Current Inactivation of hH1a-ICM Sodium Channels after Intracellular MTSET
A standard two-step development of inactivation protocol was used to assess the time course of fast inactivation of INa (Fig 4). Fig 4 A (insert) illustrates the voltage-clamp protocol, which included a short voltage clamp-back step to -120 for 2 ms, which allowed any open sodium channels to close, but did not allow for recovery of inactivated channels. Over the 44-ms conditioning time, wild-type hH1a almost completely inactivated, while ICM-hH1aMTSET demonstrated little inactivation. Data for development times up to 1 s were fitted with the sum of two exponentials:
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(2) |
where the parameters determined by the fit were: f, the faster time constant, Af, the amplitude contribution of
f,
s, the slower time constant, As, the amplitude contribution of
s, and k (1 - Af - As), the noninactivating fraction, which was set to 0 for hH1a. Table 1 shows the values from fits to data from wild-type hH1a, ICM-hH1aMTSET, and unmodified ICM-hH1a. For wild-type hH1a, the faster time constant was short (2.1 ± 0.3 ms) and accounted for most of the inactivation (83 ± 2%). In contrast, inactivation was almost completely abolished for ICM-hH1aMTSET, with only 18% ± 2% (n = 4) of the current inactivated by 44 ms, and the faster time constant (6.9 ± 3.0 ms) was more than three times longer than that for hH1a. Similar results were found when cells were perfused with 10 mM MTSETi; only 16% ± 6% (n = 4) of the current inactivated by 44 ms (data not shown). The residual "fast" inactivation in ICM-hH1aMTSET was unlikely to reflect residual ICM-hH1a unmodified by MTSETi because the fast time constant of unmodified ICM-hH1a was much shorter (1.4 ± 0.3 ms). In addition, although a second time constant was present for each channel isoform, the slow time constant for ICM-hH1aMTSET would contribute little to the small reduction in INa at 44 ms because it was nearly 80-fold longer than the fast time constant.
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OFF-gating Current Studies
To investigate the contribution of the putative inactivation lid to gating charge immobilization (i.e., the slow return of gating charge during repolarization), Ig was recorded during repolarization steps to -180 mV after conditioning to 0 mV for up to 44 ms in cells expressing wild-type hH1a and ICM-hH1aMTSET. The potential of -180 mV was selected for recording of Ig during repolarization (OFF-Ig) because the slow component became fast enough such that all of the OFF charge could be measured over 1015 ms (i.e., the OFF charge measurement equaled the ON charge measurement), but it was still long enough that the slow and fast time constants of OFF-Ig were different by about an order of magnitude and could be clearly separated using two exponential fits. Examples of OFF-Ig and their integrals are shown for hH1a and ICM-hH1aMTSET in Fig 5. The presence of a slow component is more apparent by inspection of the integrals of OFF-Ig (bottom).
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OFF-Ig were fit by a sum of up to two exponentials, and the time constants sorted by speed. Fig 6 shows the results of this analysis for both hH1a and ICM-hH1aMTSET. For this and subsequent experiments, results from five cells expressing hH1a were compared with those from four cells expressing ICM-hH1aMTSET. The values for both f and
s were very similar for the two groups with a faster time constant of <0.4 ms and a slower time constant of ~2 ms. Note that no slow time constant was detectable until the duration of the conditioning step was at least 0.7 ms for either channel type.
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Even though the time constants of relaxations of OFF-Ig traces for hH1a and ICM-hH1aMTSET were similar, the contributions to OFF charge were very different between the two channels (Fig 7). Data are graphed in a manner similar to those presented by
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For hH1a, the fraction of OFF charge contributed by the fast-time constant decreased with a time constant of 2.8 ± 2.3 ms, which was similar to the time course of the development of INa inactivation at 0 mV (2.1 ms, Table 1). It reached a steady state value of 47 ± 10%, where the slow component accounted for the remainder (53%) of the total OFF charge. Surprisingly, in the absence of a normally functioning inactivation gate (i.e., in ICM-hH1aMTSET), there still remained two time constants in OFF-Ig. The time course of the decrease in the fraction of OFF charge accounted by the fast-time constant had a similar value (2.5 ± 1.4 ms) to that for hH1a, although the fraction of OFF charge that was accounted for by the fast-time constant after longer conditioning durations was 69 ± 9%, while the fraction of OFF charge accounted for by the slow component decreased to 31% (P < 0.01 compared with wild-type hH1a by nonpaired t test). Analysis of the time course of the appearance of the slow component in the OFF charge gave nearly equivalent values; time constants and amplitudes were 2.1 ± 1.9 ms and 52 ± 10% (wild-type hH1a) and 3.6 ± 3.0 ms and 33 ± 3% (ICM-hH1aMTSET). In one cell, we confirmed that wild-type hH1a perfused with intracellular MTSET showed no changes in OFF-Ig.
While it is possible that the slow-time constant in ICM-hH1aMTSET was related to residual inactivation of unmodified channels, this seems unlikely for the following reasons. First, the fast-time constant of INa inactivation in ICM-hH1aMTSET was more than threefold longer than that in unmodified ICM-hH1a channels (6.9 vs. 1.4 ms, see Table 1). Second, if inactivation of residual, nonMTSET-modified ICM-hH1a channels were responsible for the fast-time constant that remained in the OFF charge, then the amount of OFF charge accounting for the slow component should have been much smaller than the measured 31%. After all wild-type hH1a channels have been fast inactivated, ~47% of the OFF charge returned rapidly and 53% returned slowly. Applying a similar ratio to OFF charge of ICM-hH1aMTSET, where <20% of INa became inactivated by 44 ms (Fig 4), it would be expected that <10% of the charge should have become immobilized. Instead, >30% of the charge was contained in the slow-time constant. Lastly, the time constant of INa inactivation at 0 mV for ICM-hH1aMTSET (6.9 ms) did not correspond to its time constant of development of immobilization (2.5 ms). Consequently, it is more likely that one or more of the four putative voltage sensors of ICM-hH1aMTSET return to their repolarized conformation with a slow-time constant even in the absence of an intact inactivation lid.
The Effect of Inhibition of Movement of the Domain IVS4 on Charge Immobilization
We have shown that Ap-A toxin slows inactivation of INa by inhibiting movement of the voltage sensor formed by the S4 of domain IV (
Because fast inactivation had already been modified in ICM-hH1aMTSET cells, the application of Ap-A toxin had little additional effect on INa decay (data not shown). However, because Ap-A toxin also reduces Qmax by about one-third (
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The role of the domain IVS4 in charge immobilization was then investigated by recording OFF-Ig for both hH1a and ICM-hH1aMTSET after modification by Ap-A toxin. The same voltage protocol was used as previously; cells were depolarized to 0 mV for durations up to 44 ms before repolarization to -180 mV. OFF-Ig were fit by a sum of up to two exponentials and sorted by speed. In contrast to the findings in control solutions (Fig 6), OFF-Ig for both hH1a and ICM-hH1aMTSET were best fit by a single exponential at all conditioning durations (Fig 9). The time constants clustered around 0.3 ms, and they were similar to the fast-time constants recorded for both hH1a and ICM-hH1aMTSET cells in control solutions (Fig 6 A). A decrease in the amount of charge immobilization has been previously reported in frog myelinated nerve after exposure to site-3 toxins (
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To compare the magnitude of OFF charge for the two channels after toxin modification, the fraction of OFF charge in Ap-A toxin was normalized to the maximal OFF charge (i.e., Qmax) measured for each cell in the absence of toxin and plotted as a function of the duration of the conditioning pulse at 0 mV. These data are shown in Fig 10 A for both wild-type hH1a and ICM-hH1aMTSET. The time course of the increase in OFF charge was nearly identical for both sodium channels with a time constant of ~0.7 ms. Note that the largest fraction of OFF charge was almost 70%, consistent with the reduction in gating charge by Ap-A toxin (Fig 9). Both the absence of a slow component in the OFF charge of ICM-hH1aMTSET after toxin modification and the ~30% reduction in OFF charge suggest that the slow component of OFF charge for ICM-hH1aMTSET in control solutions (Fig 7) may result from the slow return of charge associated with the S4 in domain IV.
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If this were the case, then one would expect the OFF charge associated with the fast-time constant in ICM-hH1aMTSET to be similar to the OFF charge of both toxin-modified ICM-hH1aMTSET and toxin-modified wild-type hH1a. Fig 10 B shows the time course of the appearance of OFF charge contributed by the fast time constant in control solutions for both wild-type hH1a and ICM-hH1aMTSET normalized to maximal OFF charge (i.e., Qmax). Note that the fraction and time course of OFF charge contributed by the fast-time constant in ICM-hH1aMTSET recorded in control solutions was nearly identical to that for toxin-modified ICM-hH1aMTSET. Also shown in Fig 10 B is the time course and magnitude of the fraction of OFF charge accounted for by the fast component for wild-type hH1a recorded in control solutions.
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DISCUSSION |
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To study the role of putative inactivation lid on charge immobilization, we investigated hH1a that had the phenylalanine at position 1485 in the IFM region of the domain IIIIV linker mutated to a cysteine (F1485C). Although the mutation itself has been shown to only moderately disrupt INa inactivation in three different mammalian sodium channel isoforms (rat brain IIa, skeletal muscle, and heart), fast inactivation is almost completely eliminated by exposure of the mutated cysteine to intracellular MTSET (
We found that the Q-V relationships of wild-type hH1a and ICM-hH1aMTSET were similar, as were the time courses of ON-Ig relaxations, demonstrating that an intact inactivation lid had little effect on movement of the channel's voltage sensors during step depolarizations. However, comparison of the OFF-charge measurements between the two sodium channels showed that 53% of the charge became immobilized in wild-type hH1a, while only 31% of the charge became immobilized in ICM-hH1aMTSET. After the application of Ap-A toxin, a site-3 peptide toxin that has been shown to modify inactivation of INa by inhibiting movement of the S4 segment of domain IV (
The Role of the Inactivation Lid in Charge Immobilization
In the absence of binding of the inactivation lid, what then is the origin of the gating charge that can become immobilized in ICM-hH1aMTSET? Fig 10 suggests that the S4 in domain IV is responsible for charge immobilization in ICM-hH1aMTSET. Previous studies have shown that site-3 toxins such as Ap-A toxin bind extracellularly to regions in domain IV (
These data also suggest that charge movement from the S4 in domain IV occurs on a slower time scale than activation. In the presence of Ap-A toxin, all OFF charge is contained in the fast component with a time course of appearance of ~0.7 ms (Fig 10), and represents the return of gating charge associated only with channel activation because fast inactivation has been inhibited by the toxin. Similarly, because the fast component of OFF charge in ICM-hH1aMTSET is nearly identical to the OFF charge in Ap-A toxin, it also is likely to represent gating charge associated with channel activation resulting from movement of the S4s in domains IIII. The time course of appearance of the slow component of OFF charge in ICM-hH1aMTSET is much longer (~2.5 vs. 0.7 ms), suggesting that the S4 in domain IV moved after the other S4s had moved. This conclusion is consistent with previous ON charge studies showing that the S4 in domain IV moved after sodium channel activation had occurred (
As shown in Fig 7, there was an additional 22% of OFF charge in control solutions that returned slowly in wild-type hH1a (53%) compared with the amount that returned slowly in ICM-hH1aMTSET (31%). The data with Ap-A toxin suggest that this voltage sensor is not the S4 in domain IV, but they do not directly address what additional voltages sensors may be responsible for the slow return of OFF charge in wild-type hH1a. Recently,
Implications for a Structurally Based Model
The experiments reported here expand upon the model recently proposed by
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Footnotes |
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Portions of this work were previously published in abstract form (Sheets, M.F., J.W. Kyle, and D.A. Hanck. 2000. Biophys. J. 76:A193).
1 Abbreviations used in this paper: Ap-A, Anthopleurin-A; hH1a, human heart sodium channel; ICM-hH1a, human heart sodium channel with F1485C mutation; IFM, isoleucine, phenylalanine, and methionine; MTSET, 2-(trimethylammonium)ethyl methanethiosulfonate; OFF charge, gating charge upon repolarization; ON charge, gating charge upon depolarization.
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Acknowledgements |
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We thank WenQing Yu for her excellent technical assistance.
This research was supported by National Heart, Lung and Blood Institute grants HL-PO1-20592 (D.A. Hanck and J.W. Kyle) and HL-R01-44630 (M.F. Sheets).
Submitted: 29 November 1999
Revised: 7 March 2000
Accepted: 10 March 2000
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References |
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---|
Bennett, P.B., Valenzuela, C., Chen, L.Q., Kallen, R.G. 1995. On the molecular nature of the lidocaine receptor of cardiac Na+ channels. Modification of block by alterations in the alpha-subunit IIIIV interdomain. Circ. Res. 77:584-592
Benzinger, G.R., Drum, C.L., Chen, L.Q., Kallen, R.G., Hanck, D.A., Hanck, D. 1997. Differences in the binding sites of two site-3 sodium channel toxins. Pflügers Arch 434:742-749.
Benzinger, G.R., Kyle, J.W., Blumenthal, K.M., Hanck, D.A. 1998. A specific interaction between the cardiac sodium channel and site-3 toxin anthopleurin B. J. Biol.Chem. 273:80-84
Cha, A., Ruben, P.C., George, A.L., Jr., Fujimoto, E., Bezanilla, F. 1999. Voltage sensors in domains III and IV, but not I and II, are immobilized by Na+ channel fast inactivation. Neuron. 22:73-87[Medline].
Chahine, M., George, A.L., Jr., Zhou, M., Ji, S., Sun, W., Barchi, R.L., Horn, R. 1994. Sodium channel mutations in paramyotonia congenita uncouple inactivation from activation. Neuron 12:281-294[Medline].
Chahine, M., Deschenes, I., Trottier, E., Chen, L.Q., Kallen, R.G. 1997. Restoration of fast inactivation in an inactivation-defective human heart sodium channel by the cysteine modifying reagent benzyl-MTS: analysis of IFM-ICM mutation. Biochem. Biophys. Res. Commun. 233:606-610[Medline].
Chen, L.Q., Santarelli, V., Horn, R., Kallen, R.G. 1996. A unique role for the S4 segment of domain 4 in the inactivation of sodium channels. J. Gen. Physiol. 108:549-556[Abstract].
Clarkson, C. 1990. Modification of Na channel inactivation by alpha-chymotrypsin in single cardiac myocytes. Pflügers Arch. 417:48-57.
Featherstone, D.E., Richmond, J.E., Ruben, P.C. 1996. Interaction between fast and slow inactivation in Skm1 sodium channels. Biophys. J. 71:3098-3109[Abstract].
Greeff, N.G., Keynes, R.D., VanHelden, D.F. 1982. Fractionation of the asymmetry current in the squid giant axon into inactivating and non-inactivating components. Proc. R. Soc. Lond. B Biol. Sci. 215:375-389[Medline].
Hanck, D.A., Sheets, M.F., Fozzard, H.A. 1990. Gating currents associated with Na channels in canine cardiac Purkinje cells. J. Gen. Physiol. 95:439-457[Abstract].
Hanck, D.A., Sheets, M.F. 1992. Time-dependent changes in kinetics of Na current in single canine cardiac Purkinje cells. Am. J. Physiol. Heart Circ. Physiol. 262:H1197-H1207
Hanck, D.A., Sheets, M.F. 1995. Modification of inactivation in cardiac sodium channels: ionic current studies with Anthopleurin-A toxin. J. Gen. Physiol. 106:601-616[Abstract].
Hartmann, H.A., Tiedeman, A.A., Chen, S.F., Brown, A.M., Kirsch, G.E. 1994. Effects of IIIIV linker mutations on human heart Na+ channel inactivation gating. Circ. Res. 75:114-122[Abstract].
Higuchi, R., Krummel, B., Saiki, R.K. 1988. A general method of in vitro preparation and specific mutagenesis of DNA fragments: study of protein and DNA interactions. Nucleic Acids Res 16:7351-7367[Abstract].
Ho, S.N., Hunt, H.D., Horton, R.M., Pullen, J.K., Pease, L.R. 1989. Site-directed mutagenesis by overlap extension using the polymerase chain reaction. Gene 77:51-59[Medline].
Kellenberger, S., Scheuer, T., Catterall, W.A. 1996. Movement of the Na+ channel inactivation gate during inactivation. J. Biol. Chem. 271:30971-30979
Khera, P.K., Benzinger, G.R., Lipkind, G., Drum, C.L., Hanck, D.A., Blumenthal, K.M. 1995. Multiple cationic residues of Anthopleurin B that determine high affinity and channel isoform discrimination. Biochemistry 34:8533-8541[Medline].
Khodakhah, K., Melishchuk, A., Armstrong, C.M. 1998. Charge immobilization caused by modification of internal cysteines in squid Na channels. Biophys. J 75:2821-2829
Kontis, K.J., Rounaghi, A., Goldin, A.L. 1997. Sodium channel activation gating is affected by substitutions of voltage sensor positive charges in all four domains [published erratum appears in J. Gen. Physiol. 1997. 110:763]. J. Gen. Physiol 110:391-401
Kuhn, F.J., Greeff, N.G. 1999. Movement of voltage sensor S4 in domain 4 is tightly coupled to sodium channel fast inactivation and gating charge immobilization. J. Gen. Physiol 114:167-183
Meves, H., Vogel, W. 1977. Inactivation of the asymmetrical displacement current in giant axons of Loligo forbesi. J. Physiol. 267:377-393[Abstract].
Neumcke, B., Schwarz, W., Stampfli, R. 1985. Comparison of the effects of Anemonia toxin II on sodium and gating currents in frog myelinated nerve. Biochim. Biophys. Acta 814:111-119[Medline].
Noda, M., Shimizu, S., Tanabe, T., Takai, T., Kayano, T., Ikeda, T., Takahashi, H., Nakayama, H., Kanaoka, Y., Minamino, N. et al. 1984. Primary structure of Electrophorus electricus sodium channel deduced from cDNA sequence. Nature 312:121-127[Medline].
Nonner, W. 1980. Relations between the inactivation of sodium channels and the immobilization of gating charge in frog myelinated nerve. J. Physiol. 299:573-603[Medline].
Provencher, S.W. 1976. A Fourier method for the analysis of exponential decay curves. Biophys. J. 16:27-41[Abstract].
Rogers, J.C., Qu, Y., Tanada, T.N., Scheuer, T., Catterall, W.A. 1996. Molecular determinants of high affinity binding of alpha-scorpion toxin and sea anemone toxin in the S3S4 extracellular loop in domain IV of the Na+ channel alpha subunit. J. Biol.Chem 271:15950-15962
Satin, J., Limberis, J.T., Kyle, J.W., Rogart, R.B., Fozzard, H.A. 1994. The saxitoxin/tetrodoxin binding site on cloned rat brain IIa Na channel is in the electric field. Biophys. J. 67:1007-1014[Abstract].
Sheets, M.F., Hanck, D.A. 1995. Voltage-dependent open-state inactivation of cardiac sodium channels: gating currents studies with Anthopleurin-A toxin. J. Gen. Physiol. 106:617-640[Abstract].
Sheets, M.F., Kyle, J.W., Krueger, S., Hanck, D.A. 1996. Optimization of a mammalian expression system for the measurement of sodium channel gating currents. Am. J. Physiol. Cell Physiol. 271:C1001-C1006
Sheets, M.F., Hanck, D.A. 1999. Gating of skeletal and cardiac muscle sodium channels in mammalian cells. J. Physiol. 514:425-436
Sheets, M.F., Kyle, J.W., Kallen, R.G., Hanck, D.A. 1999. The Na channel voltage sensor associated with inactivation is localized to the external charged residues of domain IV, S4. Biophys. J 77:747-757
Smith, M.R., Goldin, A.L. 1997. Interaction between the sodium channel inactivation linker and domain III S4S5. Biophys. J 73:1885-1895[Abstract].
Starkus, J.G., Fellmeth, B.D., Raynor, M.D. 1981. Gating currents in the intact crayfish giant axon. Biophys. J. 35:521-533[Abstract].
Stühmer, W., Conti, F., Suzuki, H., Wang, X.D., Noda, M., Yahagi, N., Kubo, H., Numa, S. 1989. Structural parts involved in activation and inactivation of the sodium channel. Nature 339:597-603[Medline].
Thomsen, W.J., Catterall, W.A. 1989. Localization of the receptor site for alpha-scorpion toxins by antibody mapping: implications for sodium channel topology. Proc. Natl. Acad. Sci. USA 86:10161-10165[Abstract].
Vassilev, P.M., Scheuer, T., Catterall, W.A. 1988. Identification of an intracellular peptide segment involved in sodium channel inactivation. Science 241:1658-1661[Medline].
Vedantham, V., Cannon, S.C. 1998. Slow inactivation does not affect movement of the fast inactivation gate in voltage-gated Na+ channels. J. Gen. Physiol 111:83-93
West, J.W., Patton, D.E., Scheuer, T., Wang, Y., Goldin, A.L., Catterall, W.A. 1992. A cluster of hydrophobic amino acid residues required for fast Na{++}-channel inactivation. Proc. Natl. Acad. Sci. USA 89:10910-10914[Abstract].
Yang, N., Horn, R. 1995. Evidence for voltage-dependent S4 movement in sodium channels. Neuron 15:213-218[Medline].
Yang, N.B., George, A.L., Jr., Horn, R. 1996. Molecular basis of charge movement in voltage-gated sodium channels. Neuron 16:113-122[Medline].