scholarly journals The eag domain regulates hERG channel inactivation gating via a direct interaction

2013 ◽  
Vol 141 (2) ◽  
pp. 229-241 ◽  
Author(s):  
Ahleah S. Gustina ◽  
Matthew C. Trudeau
Keyword(s):  
Amino Acids ◽  
Steady State ◽  
Direct Interaction ◽  
Terminal Region ◽  
Herg Channel ◽  
Channel Inactivation ◽  
Large N ◽  
Recovery From Inactivation ◽  
Steady State Inactivation ◽  
Resurgent Current

Human ether-á-go-go (eag)-related gene (hERG) potassium channel kinetics are characterized by rapid inactivation upon depolarization, along with rapid recovery from inactivation and very slow closing (deactivation) upon repolarization. These factors combine to create a resurgent hERG current, where the current amplitude is paradoxically larger with repolarization than with depolarization. Previous data showed that the hERG N-terminal eag domain regulated deactivation kinetics by making a direct interaction with the C-terminal region of the channel. A primary mechanism for fast inactivation depends on residues in the channel pore; however, inactivation was also shown to be slower after deletion of a large N-terminal region. The mechanism for N-terminal region regulation of inactivation is unclear. Here, we investigated the contributions of the large N-terminal domains (amino acids 1–354), including the eag domain (amino acids 1–135), to hERG channel inactivation kinetics and steady-state inactivation properties. We found that N-deleted channels lacking just the eag domain (Δ2–135) or both the eag domain and the adjacent proximal domain (Δ2–354) had less rectifying current–voltage (I-V) relationships, slower inactivation, faster recovery from inactivation, and lessened steady-state inactivation. We coexpressed genetically encoded N-terminal fragments for the eag domain (N1–135) or the eag domain plus the proximal domain (N1–354) with N-deleted hERG Δ2–135 or hERG Δ2–354 channels and found that the resulting channels had more rectifying I-V relationships, faster inactivation, slower recovery from inactivation, and increased steady-state inactivation, similar to those properties measured for wild-type (WT) hERG. We also found that the eag domain–containing fragments regulated the time to peak and the voltage at the peak of a resurgent current elicited with a ramp voltage protocol. The eag domain–containing fragments effectively converted N-deleted channels into WT-like channels. Neither the addition of the proximal domain to the eag domain in N1–354 fragments nor the presence of the proximal domain in hERG Δ2–135 channels measurably affected inactivation properties; in contrast, the proximal region regulated steady-state activation in hERG Δ2–135 channels. The results show that N-terminal region-dependent regulation of channel inactivation and resurgent current properties are caused by a direct interaction of the eag domain with the rest of the hERG channel.

The TTX metabolite 4,9-anhydro-TTX is a highly specific blocker of the Nav1.6 voltage-dependent sodium channel

2007 ◽  
Vol 293 (2) ◽  
pp. C783-C789 ◽  
Author(s):  
Christian Rosker ◽  
Birgit Lohberger ◽  
Doris Hofer ◽  
Bibiane Steinecker ◽  
Stefan Quasthoff ◽  
...  
Keyword(s):  
Steady State ◽  
Sodium Channels ◽  
Therapeutic Intervention ◽  
Time Course ◽  
Specific Interaction ◽  
Xenopus Laevis Oocytes ◽  
Recovery From Inactivation ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Invaluable Tool

The blocking efficacy of 4,9-anhydro-TTX (4,9-ah-TTX) and TTX on several isoforms of voltage-dependent sodium channels, expressed in Xenopus laevis oocytes, was tested (Nav1.2, Nav1.3, Nav1.4, Nav1.5, Nav1.6, Nav1.7, and Nav1.8). Generally, TTX was 40–231 times more effective, when compared with 4,9-ah-TTX, on a given isoform. An exception was Nav1.6, where 4,9-ah-TTX in nanomole per liter concentrations sufficed to result in substantial block, indicating that 4,9-ah-TTX acts specifically at this peculiar isoform. The IC50 values for TTX/4,9-ah-TTX were as follows (in nmol/l): 7.8 ± 1.3/1,260 ± 121 (Nav1.2), 2.8 ± 2.3/341 ± 36 (Nav1.3), 4.5 ± 1.0/988 ± 62 (Nav1.4), 1,970 ± 565/78,500 ± 11,600 (Nav1.5), 3.8 ± 1.5/7.8 ± 2.3 (Nav1.6), 5.5 ± 1.4/1,270 ± 251 (Nav1.7), and 1,330 ± 459/>30,000 (Nav1.8). Analysis of approximal half-maximal doses of both compounds revealed minor effects on voltage-dependent activation only, whereas steady-state inactivation was shifted to more negative potentials by both TTX and 4,9-ah-TTX in the case of the Nav1.6 subunit, but not in the case of other TTX-sensitive ones. TTX shifted steady-state inactivation also to more negative potentials in case of the TTX-insensitive Nav1.5 subunit, where it also exerted profound effects on the time course of recovery from inactivation. Isoform-specific interaction of toxins with ion channels is frequently observed in the case of proteinaceous toxins. Although the sensitivity of Nav1.1 to 4,9-ah-TTX is not known, here we report evidence on a highly isoform-specific TTX analog that may well turn out to be an invaluable tool in research for the identification of Nav1.6-mediated function, but also for therapeutic intervention.

Electrophysiological characteristics of cloned skeletal and cardiac muscle sodium channels

1996 ◽  
Vol 271 (2) ◽  
pp. H498-H506 ◽  
Author(s):  
M. Chahine ◽  
I. Deschene ◽  
L. Q. Chen ◽  
R. G. Kallen
Keyword(s):  
Steady State ◽  
Sodium Channels ◽  
H Infinity ◽  
Hek 293 ◽  
Human Embryonic Kidney Cells ◽  
Current Decay ◽  
Voltage Gated Sodium Channels ◽  
Recovery From Inactivation ◽  
Steady State Inactivation ◽  
Kinetics Of

The alpha-subunit encoding for voltage-gated sodium channels rSkM1 (rat skeletal muscle subtype 1) and hH1 (human heart subtype 1) has been cloned and expressed by various groups under various conditions in Xenopus oocytes and the tsA201 (HEK 293) mammalian cell line derived from human embryonic kidney cells. In this study, we have expressed hH1 and rSkM1 in tsA201 cells for comparison under the same conditions using patch-clamp methods. Our results show significant differences in the current-voltage (I-V) relationship, kinetics of current decay, voltage dependence of steady-state inactivation, and the time constant for recovery from inactivation. We studied several rSkM1/hH1 chimeric sodium channels to identify the structural regions responsible for the different biophysical behavior of the two channel subtypes. Exchanging the interdomain (ID3-4) loops, thought to contain the inactivation particle, between rSkM1 and hH1 had no effect on the electrophysiological behaviors, including inactivation, indicating that the differences in channel subtype characteristics are determined by parts of the channel other than the ID3-4 segment. The data on a chimeric channel in which D1 and D4 are derived from hH1 while D2 and D3 and the ID1-2, ID2-3, and ID3-4 loops are from rSkM1 show that D1 and/or D4 seem to be responsible for the slower kinetics of inactivation of hH1 while D2 and/or D3 appear to contain the determinants for the differences in the I-V relationship, steady-state inactivation (h infinity) curve, and the kinetics of the recovery from inactivation.

Modification of Synaptic Transmission and Sodium Channel Inactivation by the Insect-Selective Scorpion Toxin LqhαIT

2000 ◽  
Vol 83 (3) ◽  
pp. 1181-1187 ◽  
Author(s):  
Daewoo Lee ◽  
Michael Gurevitz ◽  
Michael E. Adams
Keyword(s):  
Steady State ◽  
Sodium Channel ◽  
Transmitter Release ◽  
House Fly ◽  
The Body ◽  
Scorpion Toxin ◽  
Nerve Endings ◽  
Channel Inactivation ◽  
Sodium Channel Inactivation ◽  
Steady State Inactivation

The peptide LqhαIT is an α-scorpion toxin that shows significant selectivity for insect sodium channels over mammalian channels. We examined the symptoms of LqhαIT-induced paralysis and its neurophysiological correlates in the house fly ( Musca domestica). Injection of LqhαIT into fly larvae produced hyperactivity characterized by continuous, irregular muscle twitching throughout the body. These symptoms were correlated with elevated excitability in motor units caused by two physiological effects of the toxin: 1) increased transmitter release and 2) repetitive action potentials in motor nerves. Increased transmitter release was evident as augmentation of neurally evoked synaptic current, and this was correlated with an increased duration of action potential–associated current (APAC) in loose patch recordings from nerve terminals. Repetitive APACs were observed to invade nerve endings. The toxin produced marked inhibition of sodium current inactivation in fly central neurons, which can account for increased duration of the APAC and elevated neurotransmitter release at the neuromuscular junction. Steady-state inactivation was shifted significantly to more positive potentials, whereas voltage-dependent activation of the channels was not affected. The shift in steady-state inactivation provides a mechanism for inducing repetitive activity in motoneurons. The effects of LqhαIT on sodium channel inactivation in motor nerve endings can account both for increased transmitter release and repetitive activity leading to hyperactivity in affected insects.

DPP10 is an inactivation modulatory protein of Kv4.3 and Kv1.4

2006 ◽  
Vol 291 (5) ◽  
pp. C966-C976 ◽  
Author(s):  
Hong-Ling Li ◽  
Yu-Jie Qu ◽  
Yi Chun Lu ◽  
Vladimir E. Bondarenko ◽  
Shimin Wang ◽  
...  
Keyword(s):  
Steady State ◽  
Interacting Protein ◽  
Voltage Gated ◽  
Time To Peak ◽  
Kv Channel ◽  
Closed State ◽  
Channel Inactivation ◽  
Recovery From Inactivation

Voltage-gated K+ channels exist in vivo as multiprotein complexes made up of pore-forming and ancillary subunits. To further our understanding of the role of a dipeptidyl peptidase-related ancillary subunit, DPP10, we expressed it with Kv4.3 and Kv1.4, two channels responsible for fast-inactivating K+ currents. Previously, DPP10 has been shown to effect Kv4 channels. However, Kv1.4, when expressed with DPP10, showed many of the same effects as Kv4.3, such as faster time to peak current and negative shifts in the half-inactivation potential of steady-state activation and inactivation. The exception was recovery from inactivation, which is slowed by DPP10. DPP10 expressed with Kv4.3 caused negative shifts in both steady-state activation and inactivation of Kv4.3, but no significant shifts were detected when DPP10 was expressed with Kv4.3 + KChIP2b (Kv channel interacting protein). DPP10 and KChIP2b had different effects on closed-state inactivation. At −60 mV, KChIP2b nearly abolishes closed-state inactivation in Kv4.3, whereas it developed to a much greater extent in the presence of DPP10. Finally, expression of a DPP10 mutant consisting of its transmembrane and cytoplasmic 58 amino acids resulted in effects on Kv4.3 gating that were nearly identical to those of wild-type DPP10. These data show that DPP10 and KChIP2b both modulate Kv4.3 inactivation but that their primary effects are on different inactivation states. Thus DPP10 may be a general modulator of voltage-gated K+ channel inactivation; understanding its mechanism of action may lead to deeper understanding of the inactivation of a broad range of K+ channels.

scholarly journals p.L1612P, a Novel Voltage-gated Sodium Channel Nav1.7 Mutation Inducing a Cold Sensitive Paroxysmal Extreme Pain Disorder

2015 ◽  
Vol 122 (2) ◽  
pp. 414-423 ◽  
Author(s):  
Marc R. Suter ◽  
Zahurul A. Bhuiyan ◽  
Cédric J. Laedermann ◽  
Thierry Kuntzer ◽  
Muriel Schaller ◽  
...  
Keyword(s):  
Steady State ◽  
Sodium Channel ◽  
Cold Exposure ◽  
Pain Disorder ◽  
Clinical Genetic ◽  
Voltage Gated Sodium Channel ◽  
Voltage Gated ◽  
Recovery From Inactivation ◽  
Steady State Inactivation ◽  
Extreme Pain

Abstract Background: Mutations in the SCN9A gene cause chronic pain and pain insensitivity syndromes. We aimed to study clinical, genetic, and electrophysiological features of paroxysmal extreme pain disorder (PEPD) caused by a novel SCN9A mutation. Methods: Description of a 4-generation family suffering from PEPD with clinical, genetic and electrophysiological studies including patch clamp experiments assessing response to drug and temperature. Results: The family was clinically comparable to those reported previously with the exception of a favorable effect of cold exposure and a lack of drug efficacy including with carbamazepine, a proposed treatment for PEPD. A novel p.L1612P mutation in the Nav1.7 voltage-gated sodium channel was found in the four affected family members tested. Electrophysiologically the mutation substantially depolarized the steady–state inactivation curve (V1/2 from −61.8 ± 4.5 mV to −30.9 ± 2.2 mV, n = 4 and 7, P < 0.001), significantly increased ramp current (from 1.8% to 3.4%, n = 10 and 12) and shortened recovery from inactivation (from 7.2 ± 5.6 ms to 2.2 ± 1.5 ms, n = 11 and 10). However, there was no persistent current. Cold exposure reduced peak current and prolonged recovery from inactivation in wild-type and mutated channels. Amitriptyline only slightly corrected the steady–state inactivation shift of the mutated channel, which is consistent with the lack of clinical benefit. Conclusions: The novel p.L1612P Nav1.7 mutation expands the PEPD spectrum with a unique combination of clinical symptoms and electrophysiological properties. Symptoms are partially responsive to temperature but not to drug therapy. In vitro trials of sodium channel blockers or temperature dependence might help predict treatment efficacy in PEPD.

scholarly journals Paramyotonia congenita mutations reveal different roles for segments S3 and S4 of domain D4 in hSkM1 sodium channel gating.

1996 ◽  
Vol 107 (2) ◽  
pp. 183-194 ◽  
Author(s):  
S Ji ◽  
A L George ◽  
R Horn ◽  
R L Barchi
Keyword(s):  
Steady State ◽  
Sodium Channel ◽  
Molecular Mechanisms ◽  
Dominant Role ◽  
Channel Gating ◽  
Paramyotonia Congenita ◽  
Double Mutation ◽  
Recovery From Inactivation ◽  
Steady State Inactivation ◽  
Kinetics Of

Mutations in the gene encoding the voltage-gated sodium channel of skeletal muscle (SkMl) have been identified in a group of autosomal dominant diseases, characterized by abnormalities of the sarcolemmal excitability, that include paramyotonia congenita (PC) and hyperkalemic periodic paralysis (HYPP). We previously reported that PC mutations cause in common a slowing of inactivation in the human SkMl sodium channel. In this investigation, we examined the molecular mechanisms responsible for the effects of L1433R, located in D4/S3, on channel gating by creating a series of additional mutations at the 1433 site. Unlike the R1448C mutation, found in D4/S4, which produces its effects largely due to the loss of the positive charge, change of the hydropathy of the side chain rather than charge is the primary factor mediating the effects of L1433R. These two mutations also differ in their effects on recovery from inactivation, conditioned inactivation, and steady state inactivation of the hSkMl channels. We constructed a double mutation containing both L1433R and R1448C. The double mutation closely resembled R1448C with respect to alterations in the kinetics of inactivation during depolarization and voltage dependence, but was indistinguishable from L1433R in the kinetics of recovery from inactivation and steady state inactivation. No additive effects were seen, suggesting that these two segments interact during gating. In addition, we found that these mutations have different effects on the delay of recovery from inactivation and the kinetics of the tail currents, raising a question whether this delay is a reflection of the deactivation process. These results suggest that the S3 and S4 segments play distinct roles in different processes of hSkM1 channel gating: D4/S4 is critical for the deactivation and inactivation of the open channel while D4/S3 has a dominant role in the recovery of inactivated channels. However, these two segments interact during the entry to, and exit from, inactivation states.

scholarly journals K(+) currents in cultured neurones from a polyclad flatworm

2000 ◽  
Vol 203 (20) ◽  
pp. 3189-3198
Author(s):  
S.D. Buckingham ◽  
A.N. Spencer
Keyword(s):  
Steady State ◽  
Patch Clamp ◽  
K Channels ◽  
Type K ◽  
Whole Cell Patch Clamp ◽  
Recovery From Inactivation ◽  
Steady State Inactivation ◽  
The Brain ◽  
K Currents ◽  
Cultured Neurones

Cells from the brain of the polyclad flatworm Notoplana atomata were dispersed and maintained in primary culture for up to 3 weeks. Whole-cell patch-clamp of presumed neurones revealed outwardly directed K(+) currents that comprised, in varying proportions, a rapidly activating (time constant tau =0.94+/−0.79 ms; N=15) and inactivating (tau =26.1+/−1.9 ms; N=22) current and a second current that also activated rapidly (tau =1.1+/−0.2 ms; N=9) (means +/− s.e.m.) but did not inactivate within 100 ms. Both current types activated over similar voltage ranges. Activation and steady-state inactivation overlap and are markedly rightward-shifted compared with most Shaker-like currents (half-activation of 16.9+/−1. 9 mV, N=7, half-inactivation of −35.4+/−3.0 mV, N=5). Recovery from inactivation was rapid (50+/−2.5 ms at −90 mV). Both currents were unaffected by tetraethylammonium (25 mmol l(−1)), whereas 4-aminopyridine (10 mmol l(−1)) selectively blocked the inactivating current. The rapidly inactivating current, like cloned K(+) channels from cnidarians and certain cloned K(+) channels from molluscs and the Kv3 family of vertebrate channels, differed from most A-type K(+) currents reported to date. These findings suggest that K(+) currents in Notoplana atomata play novel roles in shaping excitability properties.

scholarly journals Influence of l-Leucine and l-Alanine on Lrp Regulation of foo, Coding for F1651, a Pap Homologue

2004 ◽  
Vol 186 (24) ◽  
pp. 8537-8541 ◽  
Author(s):  
Frédéric Berthiaume ◽  
Cécile Crost ◽  
Vincent Labrie ◽  
Christine Martin ◽  
Elaine B. Newman ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Amino Acids ◽  
Steady State ◽  
Phase Variation ◽  
Terminal Region ◽  
Repressive Effect ◽  
Pbad Promoter

ABSTRACT The foo operon encodes F1651 fimbriae that belong to the P-regulatory family and are synthesized by septicemic Escherichia coli. Using an Lrp-deficient host and the lrp gene cloned under the arabinose pBAD promoter, we demonstrated that foo was transcribed proportionally to the amount of Lrp synthesized. l-Leucine and l-alanine decreased drastically the steady-state transcription of foo and modified phase variation, independently of the presence of FooI. Specific mutations in the C-terminal region of Lrp reduced or abolished the repressive effect of these amino acids, indicating that they modulate F1651 by affecting Lrp.

Characterization of the isoform-specific differences in the gating of neuronal and muscle sodium channels

1998 ◽  
Vol 76 (10-11) ◽  
pp. 1041-1050 ◽  
Author(s):  
Michael E O'Leary
Keyword(s):  
Skeletal Muscle ◽  
Steady State ◽  
Cultured Cells ◽  
Na Channel ◽  
Na Channels ◽  
Patch Clamp Technique ◽  
Recovery From Inactivation ◽  
Na Currents ◽  
Steady State Inactivation ◽  
Rate Of Recovery

Human heart (hH1), human skeletal muscle (hSkM1), and rat brain (rIIA) Na channels were expressed in cultured cells and the activation and inactivation of the whole-cell Na currents measured using the patch clamp technique. hH1 Na channels were found to activate and inactivate at more hyperpolarized voltages than hSkM1 and rIIA. The conductance versus voltage and steady state inactivation relationships have midpoints of -48 and -92 mV (hH1), -28 and -72 mV (hSkM1), and -22 and -61 mV (rIIA). At depolarized voltages, where Na channels predominately inactivate from the open state, the inactivation of hH1 is 2-fold slower than that of hSkM1 and rIIA. The recovery from fast inactivation of all three isoforms is well described by a single rapid component with time constants at -100 mV of 44 ms (hH1), 4.7 ms (hSkM1), and 7.6 ms (rIIA). After accounting for differences in voltage dependence, the kinetics of activation, inactivation, and recovery of hH1 were found to be generally slower than those of hSkM1 and rIIA. Modeling of Na channel gating at hyperpolarized voltages where the channel does not open suggests that the slow rate of recovery from inactivation of hH1 accounts for most of the differences in the steady-state inactivation of these Na channels.Key words: cardiac, neuronal, skeletal muscle, sodium channel.

scholarly journals The activation gate controls steady-state inactivation and recovery from inactivation in Shaker

2020 ◽  
Vol 152 (8) ◽  
Author(s):  
Tibor G. Szanto ◽  
Florina Zakany ◽  
Ferenc Papp ◽  
Zoltan Varga ◽  
Carol J. Deutsch ◽  
...  
Keyword(s):  
Steady State ◽  
Membrane Potentials ◽  
Tight Coupling ◽  
Shaker Channels ◽  
Recovery From Inactivation ◽  
Activation Gate ◽  
The Status ◽  
Steady State Inactivation

Despite major advances in the structure determination of ion channels, the sequence of molecular rearrangements at negative membrane potentials in voltage-gated potassium channels of the Shaker family remains unknown. Four major composite gating states are documented during the gating process: closed (C), open (O), open-inactivated (OI), and closed-inactivated (CI). Although many steps in the gating cycle have been clarified experimentally, the development of steady-state inactivation at negative membrane potentials and mandatory gating transitions for recovery from inactivation have not been elucidated. In this study, we exploit the biophysical properties of Shaker-IR mutants T449A/V474C and T449A/V476C to evaluate the status of the activation and inactivation gates during steady-state inactivation and upon locking the channel open with intracellular Cd2+. We conclude that at negative membrane potentials, the gating scheme of Shaker channels can be refined in two aspects. First, the most likely pathway for the development of steady-state inactivation is C→O→OI⇌CI. Second, the OI→CI transition is a prerequisite for recovery from inactivation. These findings are in accordance with the widely accepted view that tight coupling is present between the activation and C-type inactivation gates in Shaker and underscore the role of steady-state inactivation and recovery from inactivation as determinants of excitability.

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