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Kuschke S, Thon S, Sattler C, Schwabe T, Benndorf K, Schmauder R. cAMP binding to closed pacemaker ion channels is cooperative. Proc Natl Acad Sci U S A 2024; 121:e2315132121. [PMID: 38377199 PMCID: PMC10907242 DOI: 10.1073/pnas.2315132121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Accepted: 01/04/2024] [Indexed: 02/22/2024] Open
Abstract
The cooperative action of the subunits in oligomeric receptors enables fine-tuning of receptor activation, as demonstrated for the regulation of voltage-activated HCN pacemaker ion channels by relating cAMP binding to channel activation in ensemble signals. HCN channels generate electric rhythmicity in specialized brain neurons and cardiomyocytes. There is conflicting evidence on whether binding cooperativity does exist independent of channel activation or not, as recently reported for detergent-solubilized receptors positioned in zero-mode waveguides. Here, we show positive cooperativity in ligand binding to closed HCN2 channels in native cell membranes by following the binding of individual fluorescence-labeled cAMP molecules. Kinetic modeling reveals that the affinity of the still empty binding sites rises with increased degree of occupation and that the transition of the channel to a flip state is promoted accordingly. We conclude that ligand binding to the subunits in closed HCN2 channels not pre-activated by voltage is already cooperative. Hence, cooperativity is not causally linked to channel activation by voltage. Our analysis also shows that single-molecule binding measurements at equilibrium can quantify cooperativity in ligand binding to receptors in native membranes.
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Affiliation(s)
- Stefan Kuschke
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University, Jena07743, Germany
| | - Susanne Thon
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University, Jena07743, Germany
| | - Christian Sattler
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University, Jena07743, Germany
| | - Tina Schwabe
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University, Jena07743, Germany
| | - Klaus Benndorf
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University, Jena07743, Germany
| | - Ralf Schmauder
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University, Jena07743, Germany
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2
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Guan F, Li T, Dong W, Guo R, Chai H, Chen Z, Ren Z, Li Y, Ye S. Novel insights into the allosteric gating mechanism of MthK channel. Natl Sci Rev 2022; 9:nwac072. [PMID: 36072506 PMCID: PMC9440719 DOI: 10.1093/nsr/nwac072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 02/28/2022] [Accepted: 03/29/2022] [Indexed: 11/29/2022] Open
Abstract
Allostery is a fundamental element during channel gating in response to an appropriate stimulus by which events occurring at one site are transmitted to distal sites to regulate activity. To address how binding of the first Ca2+ ion at one of the eight chemically identical subunits facilitates the other Ca2+-binding events in MthK, a Ca2+-gated K+ channel containing a conserved ligand-binding RCK domain, we analysed a large collection of MthK structures and performed the corresponding thermodynamic and electrophysiological measurements. These structural and functional studies led us to conclude that the conformations of the Ca2+-binding sites alternate between two quaternary states and exhibit significant differences in Ca2+ affinity. We further propose an allosteric model of the MthK-gating mechanism by which a cascade of structural events connect the initial Ca2+-binding to the final changes of the ring structure that open the ion-conduction pore. This mechanical model reveals the exquisite design that achieves the allosteric gating and could be of general relevance for the action of other ligand-gated ion channels containing the RCK domain.
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Affiliation(s)
- Fenghui Guan
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin Key Laboratory of Function and Application of Biological Macromolecular Structures, School of Life Sciences, Tianjin University, 92 Weijin Road, Nankai District, Tianjin300072, China
- The Cancer Hospital of the University of Chinese Academy of Sciences, Institute of Basic Medicine and Cancer (IBMC), Chinese Academy of Sciences, Hangzhou, Zhejiang310022, China
| | - Tianyu Li
- State Key Laboratory of Drug Research and Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai201203, China
- University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing100049, China
| | - Wei Dong
- Life Sciences Institute, Zhejiang University, Hangzhou, 310058Zhejiang, China
| | - Rui Guo
- Department of Logistics, Tianjin University, 92 Weijin Road, Nankai District, Tianjin300072, China
| | - Hao Chai
- State Key Laboratory of Drug Research and Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai201203, China
- University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing100049, China
| | - Zhiqiu Chen
- University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing100049, China
| | - Zhong Ren
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL60607, USA
- Renz Research Inc., Westmont, IL60559, USA
| | - Yang Li
- State Key Laboratory of Drug Research and Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai201203, China
- University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing100049, China
- National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, China
| | - Sheng Ye
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin Key Laboratory of Function and Application of Biological Macromolecular Structures, School of Life Sciences, Tianjin University, 92 Weijin Road, Nankai District, Tianjin300072, China
- Life Sciences Institute, Zhejiang University, Hangzhou, 310058Zhejiang, China
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3
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Thermodynamic profile of mutual subunit control in a heteromeric receptor. Proc Natl Acad Sci U S A 2021; 118:2100469118. [PMID: 34301910 PMCID: PMC8325370 DOI: 10.1073/pnas.2100469118] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cyclic nucleotide-gated (CNG) ion channels of olfactory neurons are tetrameric membrane receptors that are composed of two A2 subunits, one A4 subunit, and one B1b subunit. Each subunit carries a cyclic nucleotide-binding domain in the carboxyl terminus, and the channels are activated by the binding of cyclic nucleotides. The mechanism of cooperative channel activation is still elusive. Using a complete set of engineered concatenated olfactory CNG channels, with all combinations of disabled binding sites and fit analyses with systems of allosteric models, the thermodynamics of microscopic cooperativity for ligand binding was subunit- and state-specifically quantified. We show, for the closed channel, that preoccupation of each of the single subunits increases the affinity of each other subunit with a Gibbs free energy (ΔΔG) of ∼-3.5 to ∼-5.5 kJ ⋅ mol-1, depending on the subunit type, with the only exception that a preoccupied opposite A2 subunit has no effect on the other A2 subunit. Preoccupation of two neighbor subunits of a given subunit causes the maximum affinity increase with ΔΔG of ∼-9.6 to ∼-9.9 kJ ⋅ mol-1 Surprisingly, triple preoccupation leads to fewer negative ΔΔG values for a given subunit as compared to double preoccupation. Channel opening increases the affinity of all subunits. The equilibrium constants of closed-open isomerizations systematically increase with progressive liganding. This work demonstrates, on the example of the heterotetrameric olfactory CNG channel, a strategy to derive detailed insights into the specific mutual control of the individual subunits in a multisubunit membrane receptor.
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4
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Sunkara MR, Schwabe T, Ehrlich G, Kusch J, Benndorf K. All four subunits of HCN2 channels contribute to the activation gating in an additive but intricate manner. J Gen Physiol 2018; 150:1261-1271. [PMID: 29959170 PMCID: PMC6122924 DOI: 10.1085/jgp.201711935] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Revised: 04/25/2018] [Accepted: 06/14/2018] [Indexed: 01/25/2023] Open
Abstract
HCN pacemaker channels are dually gated by hyperpolarizing voltages and cyclic nucleotide binding. Sunkara et al. show that each of the four binding sites promotes channel opening, most likely by exerting a turning momentum on the tetrameric intracellular gating ring. Hyperpolarization-activated cyclic nucleotide–modulated (HCN) channels are tetramers that elicit electrical rhythmicity in specialized brain neurons and cardiomyocytes. The channels are dually activated by voltage and binding of cyclic adenosine monophosphate (cAMP) to their four cyclic nucleotide-binding domains (CNBDs). Here we analyze the effects of cAMP binding to different concatemers of HCN2 channel subunits, each having a defined number of functional CNBDs. We show that each liganded CNBD promotes channel activation in an additive manner and that, in the special case of two functional CNBDs, functionality does not depend on the arrangement of the subunits. Correspondingly, the reverse process of deactivation is slowed by progressive liganding, but only if four and three ligands as well as two ligands in trans position (opposite to each other) are bound. In contrast, two ligands bound in cis positions (adjacent to each other) and a single bound ligand do not affect channel deactivation. These results support an activation mechanism in which each single liganded CNBD causes a turning momentum on the tetrameric ring-like structure formed by all four CNBDs and that at least two liganded subunits in trans positions are required to maintain activation.
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Affiliation(s)
- Mallikarjuna Rao Sunkara
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Tina Schwabe
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Gunter Ehrlich
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Jana Kusch
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Klaus Benndorf
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
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5
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Hummert S, Thon S, Eick T, Schmauder R, Schulz E, Benndorf K. Activation gating in HCN2 channels. PLoS Comput Biol 2018; 14:e1006045. [PMID: 29565972 PMCID: PMC5863937 DOI: 10.1371/journal.pcbi.1006045] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Accepted: 02/19/2018] [Indexed: 12/12/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels control electrical rhythmicity in specialized brain and heart cells. We quantitatively analysed voltage-dependent activation of homotetrameric HCN2 channels and its modulation by the second messenger cAMP using global fits of hidden Markovian models to complex experimental data. We show that voltage-dependent activation is essentially governed by two separable voltage-dependent steps followed by voltage-independent opening of the pore. According to this model analysis, the binding of cAMP to the channels exerts multiple effects on the voltage-dependent gating: It stabilizes the open pore, reduces the total gating charge from ~8 to ~5, makes an additional closed state outside the activation pathway accessible and strongly accelerates the ON-gating but not the OFF-gating. Furthermore, the open channel has a much slower computed OFF-gating current than the closed channel, in both the absence and presence of cAMP. Together, these results provide detailed new insight into the voltage- and cAMP-induced activation gating of HCN channels. Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are tetrameric voltage-controlled ion channels in the cell membrane of specialized nerve and heart cells. Their main function is to generate a so-called pacemaker current which plays a key role in the generation of electrical rhythmicity. A special messenger molecule, cAMP, synthesized within these cells at sympathetic stimulation, can bind to these channels, thereby enhancing channel opening evoked by voltage. The mechanism of this dual activation is still poorly understood. Here we quantified this duality of activation for HCN2 channels by globally fitting hidden Markovian state models to extensive sets of data. We propose that activation of this tetrameric channel requires for a full description only two voltage-dependent steps that are followed by a voltage-independent opening step of the channel pore. According to this model analysis cAMP exerts multiple effects on channel activation: It notably accelerates the charge movement of the voltage-dependent steps and reduces the number of the involved electrical charges. Furthermore, it introduces an additional closed state and stabilizes the open pore. Together, our results provide new insight into the duality of voltage- and cAMP-induced activation of HCN channels.
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Affiliation(s)
- Sabine Hummert
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Susanne Thon
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Thomas Eick
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Ralf Schmauder
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Eckhard Schulz
- Fachhochschule Schmalkalden, Fakultät Elektrotechnik, Blechhammer, Schmalkalden, Germany
| | - Klaus Benndorf
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Jena, Germany
- * E-mail:
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6
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Liu C, Xie C, Grant K, Su Z, Gao W, Liu Q, Zhou L. Patch-clamp fluorometry-based channel counting to determine HCN channel conductance. J Gen Physiol 2017; 148:65-76. [PMID: 27353446 PMCID: PMC4924933 DOI: 10.1085/jgp.201511559] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 05/23/2016] [Indexed: 11/20/2022] Open
Abstract
Counting ion channels on cell membranes is of fundamental importance for the study of channel biophysics. Channel counting has thus far been tackled by classical approaches, such as radioactive labeling of ion channels with blockers, gating current measurements, and nonstationary noise analysis. Here, we develop a counting method based on patch-clamp fluorometry (PCF), which enables simultaneous electrical and optical recordings, and apply it to EGFP-tagged, hyperpolarization-activated and cyclic nucleotide-regulated (HCN) channels. We use a well-characterized and homologous cyclic nucleotide-gated (CNG) channel to establish the relationship between macroscopic fluorescence intensity and the total number of channels. Subsequently, based on our estimate of the total number of HCN channels, we determine the single-channel conductance of HCN1 and HCN2 to be 0.46 and 1.71 pS, respectively. Such a small conductance would present a technical challenge for traditional electrophysiology. This PCF-based technique provides an alternative method for counting particles on cell membranes, which could be applied to biophysical studies of other membrane proteins.
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Affiliation(s)
- Chang Liu
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA 23298 School of Medicine, Nankai University, Tianjin 300071, China
| | - Changan Xie
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA 23298
| | - Khade Grant
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA 23298
| | - Zhuocheng Su
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA 23298
| | - Weihua Gao
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA 23298
| | - Qinglian Liu
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA 23298
| | - Lei Zhou
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA 23298
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7
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Thon S, Schulz E, Kusch J, Benndorf K. Conformational Flip of Nonactivated HCN2 Channel Subunits Evoked by Cyclic Nucleotides. Biophys J 2016; 109:2268-76. [PMID: 26636938 PMCID: PMC4675818 DOI: 10.1016/j.bpj.2015.08.054] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Revised: 08/21/2015] [Accepted: 08/24/2015] [Indexed: 12/11/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are tetrameric proteins that evoke electrical rhythmicity in specialized neurons and cardiomyocytes. The channels are activated by hyperpolarizing voltage but are also receptors for the intracellular ligand adenosine-3',5'-cyclic monophosphate (cAMP) that enhances activation but is unable to activate the channels alone. Using fcAMP, a fluorescent derivative of cAMP, we analyzed the effect of ligand binding on HCN2 channels not preactivated by voltage. We identified a conformational flip of the channel as an intermediate state following the ligand binding and quantified it kinetically. Globally fitting the time courses of ligand binding and unbinding revealed modest cooperativity among the subunits in the conformational flip. The intensity of this cooperativity, however, was only moderate compared to channels preactivated by hyperpolarizing voltage. These data provide kinetic information about conformational changes proceeding in nonactivated HCN2 channels when cAMP binds. Moreover, our approach bears potential for analyzing the function of any other membrane receptor if a potent fluorescent ligand is available.
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Affiliation(s)
- Susanne Thon
- Institut für Physiologie II, Universitätsklinikum Jena, Jena, Germany
| | - Eckhard Schulz
- Fachhochschule Schmalkalden, Fakultät Elektrotechnik, Blechhammer, Schmalkalden, Germany
| | - Jana Kusch
- Institut für Physiologie II, Universitätsklinikum Jena, Jena, Germany
| | - Klaus Benndorf
- Institut für Physiologie II, Universitätsklinikum Jena, Jena, Germany.
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8
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Goldschen-Ohm MP, Klenchin VA, White DS, Cowgill JB, Cui Q, Goldsmith RH, Chanda B. Structure and dynamics underlying elementary ligand binding events in human pacemaking channels. eLife 2016; 5:e20797. [PMID: 27858593 PMCID: PMC5115869 DOI: 10.7554/elife.20797] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Accepted: 11/01/2016] [Indexed: 01/07/2023] Open
Abstract
Although molecular recognition is crucial for cellular signaling, mechanistic studies have relied primarily on ensemble measures that average over and thereby obscure underlying steps. Single-molecule observations that resolve these steps are lacking due to diffraction-limited resolution of single fluorophores at relevant concentrations. Here, we combined zero-mode waveguides with fluorescence resonance energy transfer (FRET) to directly observe binding at individual cyclic nucleotide-binding domains (CNBDs) from human pacemaker ion channels critical for heart and brain function. Our observations resolve the dynamics of multiple distinct steps underlying cyclic nucleotide regulation: a slow initial binding step that must select a 'receptive' conformation followed by a ligand-induced isomerization of the CNBD. X-ray structure of the apo CNBD and atomistic simulations reveal that the isomerization involves both local and global transitions. Our approach reveals fundamental mechanisms underpinning ligand regulation of pacemaker channels, and is generally applicable to weak-binding interactions governing a broad spectrum of signaling processes.
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Affiliation(s)
| | - Vadim A Klenchin
- Department of Neuroscience, University of Wisconsin-Madison, Madison, United States
| | - David S White
- Department of Neuroscience, University of Wisconsin-Madison, Madison, United States,Department of Chemistry, University of Wisconsin-Madison, Madison, United States
| | - John B Cowgill
- Department of Neuroscience, University of Wisconsin-Madison, Madison, United States
| | - Qiang Cui
- Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin-Madison, Madison, United States
| | - Randall H Goldsmith
- Department of Chemistry, University of Wisconsin-Madison, Madison, United States
| | - Baron Chanda
- Department of Neuroscience, University of Wisconsin-Madison, Madison, United States,Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, United States,
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9
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Zhou M, Luo P, Lu Y, Li CJ, Wang DS, Lu Q, Xu XL, He Z, Guo LJ. Imbalance of HCN1 and HCN2 expression in hippocampal CA1 area impairs spatial learning and memory in rats with chronic morphine exposure. Prog Neuropsychopharmacol Biol Psychiatry 2015; 56:207-14. [PMID: 25301101 DOI: 10.1016/j.pnpbp.2014.09.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 09/13/2014] [Accepted: 09/29/2014] [Indexed: 12/12/2022]
Abstract
The hyperpolarization-activated cyclic-nucleotide-gated non-selective cation (HCN) channels play a vital role in the neurological basis underlying nervous system diseases. However, the role of HCN channels in drug addiction is not fully understood. In the present study, we investigated the expression of HCN1 and HCN2 subunits in hippocampal CA1 and the potential molecular mechanisms underlying the modulation of HCN channels in rats with chronic morphine exposure with approaches of electrophysiology, water maze, and Western blotting. We found that chronic morphine exposure (5 mg/kg, sc, for 7 days) caused an inhibition of long-term potentiation (LTP) and impairment of spatial learning and memory, which is associated with a decrease in HCN1, and an increase in HCN2 on cell membrane of hippocampal CA1 area. Additional experiments showed that the imbalance of cell membrane HCN1 and HCN2 expression under chronic morphine exposure was related to an increase in expression of TPR containing Rab8b interacting protein (TRIP8b) (1a-4) and TRIP8b (1b-2), and phosphorylation of protein kinase A (PKA) and adaptor protein 2 μ2 (AP2 μ2). Our results demonstrate the novel information that drug addiction-induced impairment of learning and memory is involved in the imbalance of HCN1 and HCN2 subunits, which is mediated by activation of TRIP8b (1a-4), TRIP8b (1b-2), PKA and AP2 μ2.
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Affiliation(s)
- Mei Zhou
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Pan Luo
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Yun Lu
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Chang-jun Li
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Dian-shi Wang
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Qing Lu
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China; Institute of Brain Research, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Xu-lin Xu
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China; Institute of Brain Research, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Zhi He
- Department of Neuropsychopharmacology, Medical School of China Three Gorges University, Yichang, 443002, China.
| | - Lian-jun Guo
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China; Institute of Brain Research, Huazhong University of Science and Technology, Wuhan 430030, China.
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10
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Kusch J, Zifarelli G. Patch-clamp fluorometry: electrophysiology meets fluorescence. Biophys J 2014; 106:1250-7. [PMID: 24655500 DOI: 10.1016/j.bpj.2014.02.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Revised: 12/23/2013] [Accepted: 02/06/2014] [Indexed: 12/26/2022] Open
Abstract
Ion channels and transporters are membrane proteins whose functions are driven by conformational changes. Classical biophysical techniques provide insight into either the structure or the function of these proteins, but a full understanding of their behavior requires a correlation of both these aspects in time. Patch-clamp and voltage-clamp fluorometry combine spectroscopic and electrophysiological techniques to simultaneously detect conformational changes and ionic currents across the membrane. Since its introduction, patch-clamp fluorometry has been responsible for invaluable advances in our knowledge of ion channel biophysics. Over the years, the technique has been applied to many different ion channel families to address several biophysical questions with a variety of spectroscopic approaches and electrophysiological configurations. This review illustrates the strength and the flexibility of patch-clamp fluorometry, demonstrating its potential as a tool for future research.
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Affiliation(s)
- Jana Kusch
- Universitätsklinikum Jena, Institut für Physiologie II, Jena, Germany.
| | - Giovanni Zifarelli
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy.
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11
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Nache V, Eick T, Schulz E, Schmauder R, Benndorf K. Hysteresis of ligand binding in CNGA2 ion channels. Nat Commun 2014; 4:2866. [PMID: 24287615 PMCID: PMC3868267 DOI: 10.1038/ncomms3866] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Accepted: 11/04/2013] [Indexed: 01/19/2023] Open
Abstract
Tetrameric cyclic nucleotide-gated (CNG) channels mediate receptor potentials in olfaction and vision. The channels are activated by the binding of cyclic nucleotides to a binding domain embedded in the C terminus of each subunit. Here using a fluorescent cGMP derivative (fcGMP), we show for homotetrameric CNGA2 channels that ligand unbinding is ~50 times faster at saturating than at subsaturating fcGMP. Analysis with complex Markovian models reveals two pathways for ligand unbinding; the partially liganded open channel unbinds its ligands from closed states only, whereas the fully liganded channel reaches a different open state from which it unbinds all four ligands rapidly. Consequently, the transition pathways for ligand binding and activation of a fully liganded CNGA2 channel differ from that of ligand unbinding and deactivation, resulting in pronounced hysteresis of the gating mechanism. This concentration-dependent gating mechanism allows the channels to respond to changes in the cyclic nucleotide concentration with different kinetics. Cyclic nucleotide-gated channels mediate olfactory and visual responses. Using a fluorescent cGMP derivative, Nache et al. show that the rate of cyclic nucleotide release from CNGA2 depends on the extent to which this tetrameric receptor is liganded, revealing hysteresis in the gating mechanism.
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Affiliation(s)
- Vasilica Nache
- Institut für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, 07743 Jena, Germany
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12
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Campos FO, Davenport MH, dos Santos RW, Nygren A, Giles WR. High heart rate in pregnancy is modulated by augmented expression of an ion channel, HCN-2, in pacemaker tissue. Circulation 2013; 127:2003-5. [PMID: 23609808 DOI: 10.1161/circulationaha.113.002760] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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