1
|
Huang CW, Lai HJ, Huang PY, Lee MJ, Kuo CC. Anomalous enhancement of resurgent Na + currents at high temperatures by SCN9A mutations underlies the episodic heat-enhanced pain in inherited erythromelalgia. Sci Rep 2019; 9:12251. [PMID: 31439884 PMCID: PMC6706385 DOI: 10.1038/s41598-019-48672-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Accepted: 08/09/2019] [Indexed: 01/12/2023] Open
Abstract
Inherited erythromelalgia (IEM), caused by mutations in Nav1.7 channel is characterized by episodic neuropathic pain triggered especially by warm temperature. However, the mechanism underlying the temperature–dependent episodic attacks of IEM remains elusive. We investigated the electrophysiological effect of temperature changes on Nav1.7 channels with three different mutations, p.I136V, p. I848T, and p.V1316A, both in vitro and in vivo. In vitro biophysical studies of the mutant channels show consistent temperature-dependent enhancement of the relative resurgent currents if normalized to the transient currents, as well as temperature-dependent changes in the time to peak and the kinetics of decay of the resurgent currents, but no congruent temperature–dependent changes in steady–state parameters such as shift of activation/inactivation curves and changes of the absolute size of the window or resurgent currents. In vivo nerve excitability tests (NET) in IEM patients reveal the essentially normal indices of NET at a single stimulus. However, there are evident abnormalities if assessed with preconditioning pulses, such as the decrease of threshold elevation in hyperpolarizing threshold electrotonus (50–100 ms), the increase of inward rectification in current–voltage curve, and the increase of refractoriness at the interpulse interval of 2–6 ms in recovery cycle, probably also implicating derangements in temperature dependence of inactivation and of recovery from inactivation in the mutant channels. The pathogenesis of heat–enhanced pain in IEM could be attributed to deranged temperature dependence of Nav1.7 channels responsible for the genesis of resurgent currents.
Collapse
Affiliation(s)
- Chiung-Wei Huang
- Department of Physiology, Kaohsiung Medical University, Kaohsiung, Taiwan
| | - Hsing-Jung Lai
- Department of Physiology, National Taiwan University College of Medicine, Taipei, Taiwan.,Department of Neurology, National Taiwan University Hospital Jinshan Branch, New Taipei City, Taiwan.,Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan
| | - Po-Yuan Huang
- Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan
| | - Ming-Jen Lee
- Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan. .,Department of Medical Genetics, National Taiwan University Hospital, Taipei, Taiwan.
| | - Chung-Chin Kuo
- Department of Physiology, National Taiwan University College of Medicine, Taipei, Taiwan. .,Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan.
| |
Collapse
|
2
|
Huang CW, Lai HJ, Huang PY, Lee MJ, Kuo CC. The Biophysical Basis Underlying Gating Changes in the p.V1316A Mutant Nav1.7 Channel and the Molecular Pathogenesis of Inherited Erythromelalgia. PLoS Biol 2016; 14:e1002561. [PMID: 27653502 PMCID: PMC5031448 DOI: 10.1371/journal.pbio.1002561] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Accepted: 08/24/2016] [Indexed: 12/16/2022] Open
Abstract
The Nav1.7 channel critically contributes to the excitability of sensory neurons, and gain-of-function mutations of this channel have been shown to cause inherited erythromelalgia (IEM) with neuropathic pain. In this study, we report a case of a severe phenotype of IEM caused by p.V1316A mutation in the Nav1.7 channel. Mechanistically, we first demonstrate that the Navβ4 peptide acts as a gating modifier rather than an open channel blocker competing with the inactivating peptide to give rise to resurgent currents in the Nav1.7 channel. Moreover, there are two distinct open and two corresponding fast inactivated states in the genesis of resurgent Na+ currents. One is responsible for the resurgent route and practically existent only in the presence of Navβ4 peptide, whereas the other is responsible for the “silent” route of recovery from inactivation. In this regard, the p.V1316A mutation makes hyperpolarization shift in the activation curve, and depolarization shift in the inactivation curve, vividly uncoupling inactivation from activation. In terms of molecular gating operation, the most important changes caused by the p.V1316A mutation are both acceleration of the transition from the inactivated states to the activated states and deceleration of the reverse transition, resulting in much larger sustained as well as resurgent Na+ currents. In summary, the genesis of the resurgent currents in the Nav1.7 channel is ascribable to the transient existence of a distinct and novel open state promoted by the Navβ4 peptide. In addition, S4–5 linker in domain III where V1316 is located seems to play a critical role in activation–inactivation coupling, chiefly via direct modulation of the transitional kinetics between the open and the inactivated states. The sustained and resurgent Na+ currents may therefore be correlatively enhanced by specific mutations involving this linker and relevant regions, and thus marked hyperexcitability in corresponding neural tissues as well as IEM symptomatology. Mutations in the Nav1.7 sodium channel cause idiopathic erythromelalgia. This study shows that the pathogenic resurgent sodium currents arise via modification of gating behavior rather than via competing pore block by the Navβ4 peptide. The gain-of-function mutation (p.V1316A) of the Nav1.7 channel causes inherited erythromelalgia (IEM), a disease characterized by extremely enhanced activity in relevant neural tissues that results in neuropathic pain. We found that the p.V1316A mutation alters the basic gating properties of the channel, leading to increased sustained currents during membrane depolarization and resurgent currents during repolarization. Neurons expressing these mutant channels are more difficult to maintain in a hyperpolarized state and are thus more excitable. We demonstrate that there is very likely a distinct set of open/inactivated (O/I) states responsible for the genesis of resurgent currents. We show that the p.V1316A mutation chiefly accelerates the I to O transition in this set, but also decelerates the transitions between different sets of O/I states, to cause the channel gating and cellular excitability changes. Contrary to the conventional view, we find that the Navβ4 peptide, a key element responsible for sizable resurgent currents, does not seem to act as a pore blocker that competes with the inactivation peptide. Instead, we show that it acts as a gating modifier of the Nav1.7 channel. Thus, the DIII/S4–5 linker, where V1316 is located, may play a critical role not only in O/I coupling but also in the couplings between different sets of O/I in the Nav1.7 channel.
Collapse
Affiliation(s)
- Chiung-Wei Huang
- Department of Physiology, National Taiwan University College of Medicine, Taipei, Taiwan
| | - Hsing-Jung Lai
- Department of Neurology, National Taiwan University Hospital Jinshan Branch, New Taipei City, Taiwan
| | - Po-Yuan Huang
- Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan
| | - Ming-Jen Lee
- Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan
- * E-mail: (MJL); (CCK)
| | - Chung-Chin Kuo
- Department of Physiology, National Taiwan University College of Medicine, Taipei, Taiwan
- Department of Neurology, National Taiwan University Hospital, Taipei, Taiwan
- * E-mail: (MJL); (CCK)
| |
Collapse
|
3
|
A synergistic blocking effect of Mg²⁺ and spermine on the inward rectifier K⁺ (Kir2.1) channel pore. Sci Rep 2016; 6:21493. [PMID: 26869275 PMCID: PMC4751470 DOI: 10.1038/srep21493] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Accepted: 01/25/2016] [Indexed: 11/23/2022] Open
Abstract
Inward rectifier K+ channels (Kir2.1) exhibit an extraordinary rectifying feature in the current–voltage relationship. We have previously showed that the bundle–crossing region of the transmembrane domain constitutes the crucial segment responsible for the polyamine block. In this study, we demonstrated that the major blocking effect of intracellular Mg2+ on Kir2.1 channels is also closely correlated with K+ current flow, and the coupled movements of Mg2+ and K+ seem to happen in the same flux–coupling segment of the pore as polyamines. With a preponderant outward K+ flow, intracellular Mg2+ would also be pushed to and thus stay at the outermost site of a flux–coupling segment in the bundle–crossing region of Kir2.1 channels to block the pore, although with a much lower apparent affinity than spermine (SPM). However, in contrast to the evident possibilities of outward exit of SPM through the channel pore especially during strong membrane depolarization, intracellular Mg2+ does not seem to traverse the Kir2.1 channel pore in any case. Intracellular Mg2+ and SPM therefore may have a synergistic action on the pore–blocking effect, presumably via prohibition of the outward exit of the higher–affinity blocking SPM by the lower–affinity Mg2+.
Collapse
|
4
|
Chang HK, Iwamoto M, Oiki S, Shieh RC. Mechanism for attenuated outward conductance induced by mutations in the cytoplasmic pore of Kir2.1 channels. Sci Rep 2015; 5:18404. [PMID: 26678093 PMCID: PMC4683409 DOI: 10.1038/srep18404] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 11/18/2015] [Indexed: 01/12/2023] Open
Abstract
Outward currents through Kir2.1 channels regulate the electrical properties of excitable cells. These currents are subject to voltage-dependent attenuation by the binding of polyamines to high- and low-affinity sites, which leads to inward rectification, thereby controlling cell excitability. To examine the effects of positive charges at the low-affinity site in the cytoplasmic pore on inward rectification, we studied a mutant Kir channel (E224K/H226E) and measured single-channel currents and streaming potentials (Vstream), the latter provide the ratio of water to ions queued in a single-file permeation process in the selectivity filter. The water-ion coupling ratio was near one at a high K+ concentration ([K+]) for the wild-type channel and increased substantially as [K+] decreased. On the other hand, fewer ions occupied the selectivity filter in the mutant at all [K+]. A model for the Kir channel involving a K+ binding site in the wide pore was introduced. Model analyses revealed that the rate constants associated with the binding and release to and from the wide-pore K+ binding site was modified in the mutant. These effects lead to the reduced contribution of a conventional two-ion permeation mode to total conductance, especially at positive potentials, thereby inward rectification.
Collapse
Affiliation(s)
- Hsueh-Kai Chang
- Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan, ROC
| | - Masayuki Iwamoto
- Department of Molecular Physiology and Biophysics, University of Fukui Faculty of Medical Sciences, Eiheiji-cho, Yoshida-gun, Fukui 910-1193, Japan
| | - Shigetoshi Oiki
- Department of Molecular Physiology and Biophysics, University of Fukui Faculty of Medical Sciences, Eiheiji-cho, Yoshida-gun, Fukui 910-1193, Japan
| | - Ru-Chi Shieh
- Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan, ROC
| |
Collapse
|
5
|
Kim J, Moon SH, Shin YC, Jeon JH, Park KJ, Lee KP, So I. Intracellular spermine blocks TRPC4 channel via electrostatic interaction with C-terminal negative amino acids. Pflugers Arch 2015; 468:551-61. [PMID: 26631167 DOI: 10.1007/s00424-015-1753-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Revised: 10/27/2015] [Accepted: 10/29/2015] [Indexed: 01/09/2023]
Abstract
Transient receptor potential canonical (TRPC) 4 channels are calcium-permeable, nonselective cation channels and are widely expressed in mammalian tissue, especially in the GI tract and brain. TRPC4 channels are known to be involved in neurogenic contraction of ileal smooth muscle cells via generating cationic current after muscarinic stimulation (muscarinic cationic current (mIcat)). Polyamines exist in numerous tissues and are believed to be involved in cell proliferation, differentiation, scar formation, wound healing, and carcinogenesis. Besides, physiological polyamines are essential to maintain inward rectification of cardiac potassium channels (Kir2.1). At membrane potentials more positive than equilibrium potential, intracellular polyamines plug the cytosolic surface of the Kir2.1 so that potassium ions cannot pass through the pore. Recently, it was reported that polyamines inhibit not only cardiac potassium channels but also nonselective cation channels that mediate the generation of mIcat. Here, we report that TRPC4, a definite mIcat mediator, is inhibited by intracellular spermine with great extent. The inhibition was specific to TRPC4 and TRPC5 channels but was not effective to TRPC1/4, TRPC1/5, and TRPC3 channels. For this inhibition to occur, we found that glutamates at 728th and 729th position of TRPC4 channels are essential whereby we conclude that spermine blocks the TRPC4 channel with electrostatic interaction between negative amino acids at the C-terminus of the channel.
Collapse
Affiliation(s)
- Jinsung Kim
- College of Medicine, Catholic University of Korea, Seoul, 137-701, Republic of Korea.,Department of Physiology, College of Medicine, Seoul National University, Seoul, 110-799, Republic of Korea
| | - Sang Hui Moon
- Department of Surgery, College of Medicine, Seoul National University, Seoul, 110-799, Republic of Korea
| | - Young-Cheul Shin
- Department of Physiology, College of Medicine, Seoul National University, Seoul, 110-799, Republic of Korea
| | - Ju-Hong Jeon
- Department of Physiology, College of Medicine, Seoul National University, Seoul, 110-799, Republic of Korea
| | - Kyu Joo Park
- Department of Surgery, College of Medicine, Seoul National University, Seoul, 110-799, Republic of Korea
| | - Kyu Pil Lee
- Department of Physiology, College of Veterinary Medicine, Chungnam National University, Daejeon, 305-764, Republic of Korea.
| | - Insuk So
- Department of Physiology, College of Medicine, Seoul National University, Seoul, 110-799, Republic of Korea.
| |
Collapse
|
6
|
Huang CW, Kuo CC. Gating of the kir2.1 channel at the bundle crossing region by intracellular spermine and other cations. J Cell Physiol 2014; 229:1703-21. [PMID: 24633623 DOI: 10.1002/jcp.24616] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Accepted: 03/12/2014] [Indexed: 11/06/2022]
Abstract
In the Kir2.1 channel, the flow-dependent blocking effect of intracellular spermine (SPM) strongly indicates coupled movement of ions in a segment of the pore. We have shown that the bundle crossing region of M2 constitutes this critical segment of the pore. Moreover, this segment may undergo opening/closing conformational changes mimicking channel gating. In this study, we further investigate these "gating" conformational changes and relevant controlling mechanisms at this critical segment. We demonstrate that A184R mutation in the inner end of the bundle crossing region not only abolishes the inward rectifying features of SPM block but also tends to close the channel pore, which can then only be opened by intracellular (e.g., Na(+) , or equally effectively, K(+) ) but not extracellular cations. We also found that the exit (back to the intracellular milieu) of the blocking in the deep site is facilitated rather than deterred by the presence of the other SPM in the superficial site. We conclude that intracellular SPM may bind to a deep site in the pore and serve as a flow-dependent blocker. The SPM in the superficial site, on the other hand, serves both as a docking form ready for permeation to the deep site, and as a gating particle capable of opening the bundle crossing region. This inner end of the bundle crossing region of the Kir2.1 channel pore thus constitutes a pivotal segment, which, in collaboration with intracellular SPM and K(+) ions, closely couple channel gating to (inward rectifying) ion permeation.
Collapse
Affiliation(s)
- Chiung-Wei Huang
- Department of Physiology, National Taiwan University College of Medicine, Taipei, Taiwan
| | | |
Collapse
|
7
|
Flow- and voltage-dependent blocking effect of ethosuximide on the inward rectifier K⁺ (Kir2.1) channel. Pflugers Arch 2014; 467:1733-46. [PMID: 25220134 DOI: 10.1007/s00424-014-1611-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Revised: 08/21/2014] [Accepted: 09/05/2014] [Indexed: 12/31/2022]
Abstract
Absence seizures are manifestations of abnormal thalamocortical oscillations characterized by spike-and-wave complexes in EEG. Ethosuximide (ETX) is one of the principal medications against absence seizures. We investigate the effect of ETX on the Kir2.1 channel, a prototypical inward rectifier K(+) channel possibly playing an important role in the setting of neuronal membrane potential. We demonstrate that the outward currents of Kir2.1 channels are significantly inhibited by intracellular ETX. We further show that the movement of neutral molecule ETX in the Kir2.1 channel is accompanied by ∼1.2 K(+), giving rise to the vivid voltage dependence of ETX unbinding rate. Moreover, the apparent affinity (K d ) of ETX in the channels are decreased by single-point mutations involving M183, E224, and S165, and especially by double mutations involving T141/S165, which always also disrupt the flux-coupling feature of ETX block. Molecular dynamics simulation demonstrates narrowing of the pore at ∼D172 by binding of ETX to S165 or T141. ETX block of the Kir2.1 channels may cause a modest but critical depolarization of the relevant neurons, decreasing available T-type Ca(2+) channels and consequently lessening pathological thalamocortical burst discharges.
Collapse
|