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Ågren R, Zeberg H. Low-Resistance silver bromide electrodes for recording fast ion channel kinetics under voltage clamp conditions. J Neurosci Methods 2020; 348:108984. [PMID: 33164817 DOI: 10.1016/j.jneumeth.2020.108984] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2020] [Revised: 10/14/2020] [Accepted: 10/20/2020] [Indexed: 10/23/2022]
Abstract
BACKGROUND Two-electrode voltage clamp is a widely used technique for studying ionic currents. However, fast activation kinetics of ion channels are disguised by the capacitive transient during voltage clamp of Xenopus oocytes. The limiting factors of clamp performance include, but are not limited to, amplifier gain, membrane capacitance, and micropipette resistance. Previous work has focused on increasing amplifier gain (e.g.; high performing two-electrode amplifiers) or reducing the membrane capacitance (e.g.; the cut-open technique). NEW METHOD The use of an Ag-AgBr electrode with saturated KBr solution to reduce micropipette resistance. RESULTS The conductivity of 4 M KBr was 37 % higher compared to 3 M KCl and the micropipette resistance was reduced by 19 % when 4 M KBr was used, compared to the standard 3 M KCl solution. Micropipette resistances correlated positively with capacitive transient durations. Neither the current-voltage relationship of the voltage-gated sodium channel, Nav1.7, nor Xenopus oocyte stability were affected by bromide ions. COMPARISON WITH EXISTING METHODS The de facto standard for two-electrode voltage clamp is 3 M KCl and Ag-AgCl electrodes, which are associated an unnecessarily high micropipette resistance. Elsewise, cut-open voltage clamp techniques are technically demanding and require manipulation of the intracellular environment. CONCLUSIONS The use of an Ag-AgBr electrode with saturated KBr as micropipette solution reduces the capacitive transient in two-electrode voltage clamp recordings. Moreover, the exchange of chloride against bromide ions does not seem to affect oocyte physiology and ion channel kinetics.
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Affiliation(s)
- Richard Ågren
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.
| | - Hugo Zeberg
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
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Cheng L, Fu H, Wang X, Ye L, Lakhani I, Tse G, Zhang Z, Liu T, Li G. Effects of ticagrelor pretreatment on electrophysiological properties of stellate ganglion neurons following myocardial infarction. Clin Exp Pharmacol Physiol 2020; 47:1932-1942. [PMID: 33459403 DOI: 10.1111/1440-1681.13385] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2019] [Revised: 06/21/2020] [Accepted: 07/15/2020] [Indexed: 12/26/2022]
Abstract
Higher sympathetic activity predisposes to malignant ventricular arrhythmias in the context of myocardial infarction (MI). This is, in part, mediated by the electrical activity of the stellate ganglion (SG). The aim of this study is to examine the effects of ticagrelor pretreatment on the electrophysiological properties of SG neurons following MI in rabbits. MI was induced by isoproterenol (ISO) of 150 mg kg-1 d-1 (twice at an interval of 24 hours). Ticagrelor pretreatment was administered at low- (10 mg kg-1 d-1) or high-dose (20 mg kg-1 d-1). Protein and RNA expression were determined by immunohistochemical analysis and real-time PCR, respectively. The activity of sodium channel current (INa), delayed rectifier potassium current (IKDR), M-type potassium current (IKM) as well as action potentials (APs) from SG neurons were measured by whole-cell patch-clamp. Intracellular calcium concentrations were measured by confocal microscopy. Compared with the control group, the MI group exhibited a greater amplitude of INa, IKDR and IKM, significantly altered activation and inactivation characteristics of INa, no significant alterations in protein or mRNA expression of sodium and M-type potassium channels, along with higher AP amplitude and frequency and intracellular calcium concentrations. Most of these abnormalities were prevented by pretreatment with low- or high-dose ticagrelor. Our data suggest that ticagrelor exerts cardioprotective effects, potentially through modulating the activity of different ion channels in SG neurons.
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Affiliation(s)
- Lijun Cheng
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, the Second Hospital of Tianjin Medical University, Tianjin, China
| | - Huaying Fu
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, the Second Hospital of Tianjin Medical University, Tianjin, China
| | - Xinghua Wang
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, the Second Hospital of Tianjin Medical University, Tianjin, China
| | - Lan Ye
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, the Second Hospital of Tianjin Medical University, Tianjin, China
| | - Ishan Lakhani
- Laboratory of Cardiovascular Physiology, Li Ka Shing Institute of Health Sciences, Hong Kong, China
| | - Gary Tse
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, the Second Hospital of Tianjin Medical University, Tianjin, China
| | - Zhiwei Zhang
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, the Second Hospital of Tianjin Medical University, Tianjin, China
| | - Tong Liu
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, the Second Hospital of Tianjin Medical University, Tianjin, China
| | - Guangping Li
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, the Second Hospital of Tianjin Medical University, Tianjin, China
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Effraim PR, Huang J, Lampert A, Stamboulian S, Zhao P, Black JA, Dib-Hajj SD, Waxman SG. Fibroblast growth factor homologous factor 2 (FGF-13) associates with Nav1.7 in DRG neurons and alters its current properties in an isoform-dependent manner. NEUROBIOLOGY OF PAIN (CAMBRIDGE, MASS.) 2019; 6:100029. [PMID: 31223136 PMCID: PMC6565799 DOI: 10.1016/j.ynpai.2019.100029] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Revised: 03/22/2019] [Accepted: 03/22/2019] [Indexed: 11/29/2022]
Abstract
Fibroblast Growth Factor Homologous Factors (FHF) constitute a subfamily of FGF proteins with four prototypes (FHF1-4; also known as FGF11-14). FHF proteins have been shown to bind directly to the membrane-proximal segment of the C-terminus in voltage-gated sodium channels (Nav), and regulate current density, availability, and frequency-dependent inhibition of sodium currents. Members of the FHF2 subfamily, FHF2A and FHF2B, differ in the length and sequence of their N-termini, and, importantly, differentially regulate Nav1.6 gating properties. Using immunohistochemistry, we show that FHF2 isoforms are expressed in adult dorsal root ganglion (DRG) neurons where they co-localize with Nav1.6 and Nav1.7. FHF2A and FHF2B show differential localization in neuronal compartments in DRG neurons, and levels of expression of FHF2 factors are down-regulated following sciatic nerve axotomy. Because Nav1.7 in nociceptors plays a critical role in pain, we reasoned that its interaction with FHF2 isoforms might regulate its current properties. Using whole-cell patch clamp in heterologous expression systems, we show that the expression of FHF2A in HEK293 cell line stably expressing Nav1.7 channels causes no change in activation, whereas FHF2B depolarizes activation. Both FHF2 isoforms depolarize fast-inactivation. Additionally, FHF2A causes an accumulation of inactivated channels at all frequencies tested due to a slowing of recovery from inactivation, whereas FHF2B has little effect on these properties of Nav1.7. Measurements of the Nav1.7 current in DRG neurons in which FHF2 levels are knocked down confirmed the effects of FHF2A on repriming, and FHF2B on activation, however FHF2A and B did not have an effect on fast inactivation. Our data demonstrates that FHF2 does indeed regulate the current properties of Nav1.7 and does so in an isoform and cell-specific manner.
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Affiliation(s)
- Philip R. Effraim
- Department of Anesthesiology, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Jianying Huang
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Angelika Lampert
- Institute of Physiology, Uniklinik RWTH Aachen University, Aachen, Germany
| | - Severine Stamboulian
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Peng Zhao
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Joel A. Black
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Sulayman D. Dib-Hajj
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Stephen G. Waxman
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA
- Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT 06516, USA
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Takkala P, Prescott SA. Using dynamic clamp to quantify pathological changes in the excitability of primary somatosensory neurons. J Physiol 2018; 596:2209-2227. [PMID: 29601637 PMCID: PMC5983269 DOI: 10.1113/jp275580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Accepted: 03/21/2018] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Primary somatosensory neurons normally respond to somatic depolarization with transient spiking but can switch to repetitive spiking under pathological conditions. This switch in spiking pattern reflects a qualitative change in spike initiation dynamics and contributes to the hyperexcitability associated with chronic pain. Neurons can be converted to repetitive spiking by adding a virtual conductance using dynamic clamp. By titrating the conductance to determine how much must be added to cause repetitive spiking, we found that small cells are more susceptible to switching (i.e. required less added conductance) than medium-large cells. By measuring how much less conductance is required to cause repetitive spiking when dynamic clamp was combined with other pathomimetic manipulations (e.g. application of inflammatory mediators), we measured how much each manipulation facilitated repetitive spiking. Our results suggest that many pathological factors facilitate repetitive spiking but that the switch to repetitive spiking requires the cumulative effect of many co-occurring factors. ABSTRACT Primary somatosensory neurons become hyperexcitable in many chronic pain conditions. Hyperexcitability can include a switch from transient to repetitive spiking during sustained somatic depolarization. This switch results from diverse pathological processes that impact ion channel expression or function. Because multiple pathological processes co-occur, isolating how much each contributes to switching the spiking pattern is difficult. Our approach to this challenge involves adding a virtual sodium conductance via dynamic clamp. The magnitude of that conductance was titrated to determine the minimum required to enable rheobasic stimulation to evoke repetitive spiking. The minimum required conductance, termed g¯ Na ∗, was re-measured before and during manipulations designed to model various pathological processes in vitro. The reduction in g¯ Na ∗ caused by each pathomimetic manipulation reflects how much the modelled process contributes to switching the spiking pattern. We found that elevating extracellular potassium or applying inflammatory mediators reduced g¯ Na ∗ whereas direct hyperpolarization had no effect. Inflammatory mediators reduced g¯ Na ∗ more in medium-large (>30 μm diameter) neurons than in small (⩽30 μm diameter) neurons, but had equivalent effects in cutaneous and muscle afferents. The repetitive spiking induced by dynamic clamp was also found to differ between small and medium-large neurons, thus revealing latent differences in adaptation. Our study demonstrates a novel way to determine to what extent individual pathological factors facilitate repetitive spiking. Our results suggest that most factors facilitate but do not cause repetitive spiking on their own, and, therefore, that a switch to repetitive spiking results from the cumulative effect of many co-occurring factors.
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Affiliation(s)
- Petri Takkala
- Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario, Canada, M5G 0A4.,Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada, M5S 1A8
| | - Steven A Prescott
- Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario, Canada, M5G 0A4.,Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada, M5S 1A8.,Department of Physiology and Institute of Biomaterials and Biomedical Engineering, University of Toronto, Ontario, Canada, M5S 1A8
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Huang J, Mis MA, Tanaka B, Adi T, Estacion M, Liu S, Walker S, Dib-Hajj SD, Waxman SG. Atypical changes in DRG neuron excitability and complex pain phenotype associated with a Na v1.7 mutation that massively hyperpolarizes activation. Sci Rep 2018; 8:1811. [PMID: 29379075 PMCID: PMC5788866 DOI: 10.1038/s41598-018-20221-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Accepted: 01/16/2018] [Indexed: 02/06/2023] Open
Abstract
Sodium channel Nav1.7 plays a central role in pain-signaling: gain-of-function Nav1.7 mutations usually cause severe pain and loss-of-function mutations produce insensitivity to pain. The Nav1.7 I234T gain-of-function mutation, however, is linked to a dual clinical presentation of episodic pain, together with absence of pain following fractures, and corneal anesthesia. How a Nav1.7 mutation that produces gain-of-function at the channel level causes clinical loss-of-function has remained enigmatic. We show by current-clamp that expression of I234T in dorsal root ganglion (DRG) neurons produces a range of membrane depolarizations including a massive shift to >−40 mV that reduces excitability in a small number of neurons. Dynamic-clamp permitted us to mimic the heterozygous condition via replacement of 50% endogenous wild-type Nav1.7 channels by I234T, and confirmed that the I234T conductance could drastically depolarize DRG neurons, resulting in loss of excitability. We conclude that attenuation of pain sensation by I234T is caused by massively depolarized membrane potential of some DRG neurons which is partly due to enhanced overlap between activation and fast-inactivation, impairing their ability to fire. Our results demonstrate how a Nav1.7 mutation that produces channel gain-of-function can contribute to a dual clinical presentation that includes loss of pain sensation at the clinical level.
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Affiliation(s)
- Jianying Huang
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT, USA, 06510.,Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT, USA, 06516
| | - Malgorzata A Mis
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT, USA, 06510.,Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT, USA, 06516
| | - Brian Tanaka
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT, USA, 06510.,Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT, USA, 06516
| | - Talia Adi
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT, USA, 06510.,Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT, USA, 06516
| | - Mark Estacion
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT, USA, 06510.,Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT, USA, 06516
| | - Shujun Liu
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT, USA, 06510.,Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT, USA, 06516
| | - Suellen Walker
- Developmental Neurosciences Program, Department of Anaesthesia and Pain Medicine, UCL Great Ormond Street Hospital, London, WC1N 1EH, UK
| | - Sulayman D Dib-Hajj
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT, USA, 06510.,Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT, USA, 06516
| | - Stephen G Waxman
- Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT, USA, 06510. .,Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT, USA, 06516.
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Abstract
Erythromelalgia is a rare syndrome characterized by the intermittent or, less commonly, by the permanent occurrence of extremely painful hyperperfused skin areas mainly located in the distal extremities. Primary erythromelalgia is nowadays considered to be a genetically determined neuropathic disorder affecting SCN9A, SCN10A, and SCN11A coding for NaV1.7, NaV1.8, and NaV1.9 neuronal sodium channels. Secondary forms might be associated with myeloproliferative disorders, connective tissue disease, cancer, infections, and poisoning. Between the pain episodes, the affected skin areas are usually asymptomatic, but there are patients with typical features of acrocyanosis and/or Raynaud's phenomenon preceding or occurring in between the episodes of erythromelalgia. Diagnosis is made by ascertaining the typical clinical features. Thereafter, the differentiation between primary and secondary forms should be made. Genetic testing is recommended, especially in premature cases and in cases of family clustering in specialized genetic institutions after genetic counselling. Multimodal therapeutic intervention aims toward attenuation of pain and improvement of the patient's quality of life. For this purpose, a wide variety of nonpharmacological approaches and pharmacological substances for topical and systemic use have been proposed, which are usually applied individually in a step-by-step approach. Prognosis mainly depends on the underlying condition and the ability of the patients and their relatives to cope with the disease.
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Affiliation(s)
| | | | - Jutta Gisela Richter
- 2 Poliklinik, Funktionsbereich und Hiller Forschungszentrum für Rheumatologie, Medizinische Fakultät, Universitätsklinikum Düsseldorf, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany
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