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Mesirca P, Chemin J, Barrère C, Torre E, Gallot L, Monteil A, Bidaud I, Diochot S, Lazdunski M, Soong TW, Barrère-Lemaire S, Mangoni ME, Nargeot J. Selective blockade of Ca v1.2 (α1C) versus Ca v1.3 (α1D) L-type calcium channels by the black mamba toxin calciseptine. Nat Commun 2024; 15:54. [PMID: 38167790 PMCID: PMC10762068 DOI: 10.1038/s41467-023-43502-w] [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: 04/21/2023] [Accepted: 11/10/2023] [Indexed: 01/05/2024] Open
Abstract
L-type voltage-gated calcium channels are involved in multiple physiological functions. Currently available antagonists do not discriminate between L-type channel isoforms. Importantly, no selective blocker is available to dissect the role of L-type isoforms Cav1.2 and Cav1.3 that are concomitantly co-expressed in the heart, neuroendocrine and neuronal cells. Here we show that calciseptine, a snake toxin purified from mamba venom, selectively blocks Cav1.2 -mediated L-type calcium currents (ICaL) at concentrations leaving Cav1.3-mediated ICaL unaffected in both native cardiac myocytes and HEK-293T cells expressing recombinant Cav1.2 and Cav1.3 channels. Functionally, calciseptine potently inhibits cardiac contraction without altering the pacemaker activity in sino-atrial node cells, underscoring differential roles of Cav1.2- and Cav1.3 in cardiac contractility and automaticity. In summary, calciseptine is a selective L-type Cav1.2 Ca2+ channel blocker and should be a valuable tool to dissect the role of these L-channel isoforms.
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Affiliation(s)
- Pietro Mesirca
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, 34094, Montpellier, France.
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France.
| | - Jean Chemin
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, 34094, Montpellier, France
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
| | - Christian Barrère
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, 34094, Montpellier, France
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
| | - Eleonora Torre
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, 34094, Montpellier, France
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
| | - Laura Gallot
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, 34094, Montpellier, France
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
| | - Arnaud Monteil
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, 34094, Montpellier, France
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
- Department of Physiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - Isabelle Bidaud
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, 34094, Montpellier, France
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
| | - Sylvie Diochot
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
- Université Côte d'Azur, CNRS, IPMC (Institut de Pharmacologie Moléculaire et Cellulaire), FHU InovPain (Fédération Hospitalo-Universitaire "Innovative Solutions in Refractory Chronic Pain"), F-06560, Valbonne, France
| | - Michel Lazdunski
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
- Université Côte d'Azur, CNRS, IPMC (Institut de Pharmacologie Moléculaire et Cellulaire), FHU InovPain (Fédération Hospitalo-Universitaire "Innovative Solutions in Refractory Chronic Pain"), F-06560, Valbonne, France
| | - Tuck Wah Soong
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Stéphanie Barrère-Lemaire
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, 34094, Montpellier, France
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
| | - Matteo E Mangoni
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, 34094, Montpellier, France
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France
| | - Joël Nargeot
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, 34094, Montpellier, France.
- Laboratory of Excellence Ion Channels, Science & Therapeutics, F-06560, Valbonne, France.
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Dupuy M, Gueguinou M, Potier-Cartereau M, Lézot F, Papin M, Chantôme A, Rédini F, Vandier C, Verrecchia F. SK Ca- and Kv1-type potassium channels and cancer: Promising therapeutic targets? Biochem Pharmacol 2023; 216:115774. [PMID: 37678626 DOI: 10.1016/j.bcp.2023.115774] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Revised: 08/29/2023] [Accepted: 08/30/2023] [Indexed: 09/09/2023]
Abstract
Ion channels are transmembrane structures that allow the passage of ions across cell membranes such as the plasma membrane or the membranes of various organelles like the nucleus, endoplasmic reticulum, Golgi apparatus or mitochondria. Aberrant expression of various ion channels has been demonstrated in several tumor cells, leading to the promotion of key functions in tumor development, such as cell proliferation, resistance to apoptosis, angiogenesis, invasion and metastasis. The link between ion channels and these key biological functions that promote tumor development has led to the classification of cancers as oncochannelopathies. Among all ion channels, the most varied and numerous, forming the largest family, are the potassium channels, with over 70 genes encoding them in humans. In this context, this review will provide a non-exhaustive overview of the role of plasma membrane potassium channels in cancer, describing 1) the nomenclature and structure of potassium channels, 2) the role of these channels in the control of biological functions that promotes tumor development such as proliferation, migration and cell death, and 3) the role of two particular classes of potassium channels, the SKCa- and Kv1- type potassium channels in cancer progression.
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Affiliation(s)
- Maryne Dupuy
- Nantes Université, Inserm UMR 1307, CNRS UMR 6075, Université d'Angers, CRCI2NA, F-44000 Nantes, France.
| | | | | | - Frédéric Lézot
- Sorbonne University, INSERM UMR933, Hôpital Trousseau (AP-HP), Paris F-75012, France
| | - Marion Papin
- N2C UMR 1069, University of Tours, INSERM, Tours, France
| | | | - Françoise Rédini
- Nantes Université, Inserm UMR 1307, CNRS UMR 6075, Université d'Angers, CRCI2NA, F-44000 Nantes, France
| | | | - Franck Verrecchia
- Nantes Université, Inserm UMR 1307, CNRS UMR 6075, Université d'Angers, CRCI2NA, F-44000 Nantes, France.
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3
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Zahra A, Liu R, Han W, Meng H, Wang Q, Wang Y, Campbell SL, Wu J. K Ca-Related Neurological Disorders: Phenotypic Spectrum and Therapeutic Indications. Curr Neuropharmacol 2023; 21:1504-1518. [PMID: 36503451 PMCID: PMC10472807 DOI: 10.2174/1570159x21666221208091805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2022] [Revised: 07/21/2022] [Accepted: 07/23/2022] [Indexed: 12/14/2022] Open
Abstract
Although potassium channelopathies have been linked to a wide range of neurological conditions, the underlying pathogenic mechanism is not always clear, and a systematic summary of clinical manifestation is absent. Several neurological disorders have been associated with alterations of calcium-activated potassium channels (KCa channels), such as loss- or gain-of-function mutations, post-transcriptional modification, etc. Here, we outlined the current understanding of the molecular and cellular properties of three subtypes of KCa channels, including big conductance KCa channels (BK), small conductance KCa channels (SK), and the intermediate conductance KCa channels (IK). Next, we comprehensively reviewed the loss- or gain-of-function mutations of each KCa channel and described the corresponding mutation sites in specific diseases to broaden the phenotypic-genotypic spectrum of KCa-related neurological disorders. Moreover, we reviewed the current pharmaceutical strategies targeting KCa channels in KCa-related neurological disorders to provide new directions for drug discovery in anti-seizure medication.
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Affiliation(s)
- Aqeela Zahra
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China
- Department of Zoology, University of Sialkot, Sialkot 51310, Pakistan
| | - Ru Liu
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China
- Advanced Innovation Center for Human Brain Protection, Capital Medical University, Beijing 100070, China
- National Clinical Research Center for Neurological Diseases, Beijing 100070, China
| | - Wenzhe Han
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China
| | - Hui Meng
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China
| | - Qun Wang
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China
- National Clinical Research Center for Neurological Diseases, Beijing 100070, China
| | - YunFu Wang
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China
| | - Susan L. Campbell
- Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States
| | - Jianping Wu
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China
- Advanced Innovation Center for Human Brain Protection, Capital Medical University, Beijing 100070, China
- National Clinical Research Center for Neurological Diseases, Beijing 100070, China
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Halling DB, Philpo AE, Aldrich RW. Calcium dependence of both lobes of calmodulin is involved in binding to a cytoplasmic domain of SK channels. eLife 2022; 11:e81303. [PMID: 36583726 PMCID: PMC9803350 DOI: 10.7554/elife.81303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Accepted: 12/15/2022] [Indexed: 12/31/2022] Open
Abstract
KCa2.1-3 Ca2+-activated K+-channels (SK) require calmodulin to gate in response to cellular Ca2+. A model for SK gating proposes that the N-terminal domain (N-lobe) of calmodulin is required for activation, but an immobile C-terminal domain (C-lobe) has constitutive, Ca2+-independent binding. Although structures support a domain-driven hypothesis of SK gate activation by calmodulin, only a partial understanding is possible without measuring both channel activity and protein binding. We measured SK2 (KCa2.2) activity using inside-out patch recordings. Currents from calmodulin-disrupted SK2 channels can be restored with exogenously applied calmodulin. We find that SK2 activity only approaches full activation with full-length calmodulin with both an N- and a C-lobe. We measured calmodulin binding to a C-terminal SK peptide (SKp) using both composition-gradient multi-angle light-scattering and tryptophan emission spectra. Isolated lobes bind to SKp with high affinity, but isolated lobes do not rescue SK2 activity. Consistent with earlier models, N-lobe binding to SKp is stronger in Ca2+, and C-lobe-binding affinity is strong independent of Ca2+. However, a native tryptophan in SKp is sensitive to Ca2+ binding to both the N- and C-lobes of calmodulin at Ca2+ concentrations that activate SK2, demonstrating that the C-lobe interaction with SKp changes with Ca2+. Our peptide-binding data and electrophysiology show that SK gating models need deeper scrutiny. We suggest that the Ca2+-dependent associations of both lobes of calmodulin to SKp are crucial events during gating. Additional investigations are necessary to complete a mechanistic gating model consistent with binding, physiology, and structure.
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Affiliation(s)
- David B Halling
- Department of Neuroscience, The University of Texas at AustinAustinUnited States
| | - Ashley E Philpo
- Department of Neuroscience, The University of Texas at AustinAustinUnited States
| | - Richard W Aldrich
- Department of Neuroscience, The University of Texas at AustinAustinUnited States
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5
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Gholami S, Mirian M, Eftekhari SM, Aliomrani M. Apamin administration impact on miR-219 and miR-155-3p expression in cuprizone induced multiple sclerosis model. Mol Biol Rep 2020; 47:9013-9019. [PMID: 33174081 DOI: 10.1007/s11033-020-05959-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2020] [Accepted: 10/29/2020] [Indexed: 02/07/2023]
Abstract
Multiple sclerosis (MS) is a chronic debilitating disease that attacks the central nervous system. This study aims to investigate miR-219 and miR-155-3p expression levels involved in the myelination process following the administration of apamin peptide in the model of multiple sclerosis disease. Forty-four 8 week C57BL/6 male mice (22 ± 5 g) randomly divided into six groups. Apamin (100 µg/kg/BW) was administered intraperitoneally as a co-treatment during phase I (demyelination) or post-treatment phase II (remyelination) twice a week in cuprizone induced MS model. At the end of study myelin content and microRNA expression levels were measured with LFB staining and quantitative Real-Time PCR method, respectively. It was observed that the intended microRNAs were dysregulated during the different phases of disease induction. After 6 weeks of cuprizone exposure, miR-219 downregulated in phase I in comparison with the negative control. On the other hand, the apamin co-treatment significantly inhibit the miR-155-3p upregulation during the phase I as compared with the cuprizone group (p < 0.0001). Apamin has more impact on the miR155-3p reduction in phase I than miR-219 elevation in phase II. It could be considered as a therapeutic option for decreasing plaque formation during the exacerbation phase of the MS disease. Apamin has more impact on the miR155-3p reduction in phase I than miR-219 elevation in phase II. It could be considered as a therapeutic option for decreasing plaque formation during the exacerbation phase of the MS disease.
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Affiliation(s)
- Samira Gholami
- School of Pharmacy and Pharmaceutical Sciences, Isfahan University of Medical Sciences and Health Services, Isfahan, Iran
| | - Mina Mirian
- Department of Biotechnology, School of Pharmacy and Pharmaceutical Sciences, Isfahan University of Medical Sciences and Health Services, Isfahan, Iran
| | | | - Mehdi Aliomrani
- Department of Toxicology and Pharmacology, Faculty of Pharmacy, Isfahan Pharmaceutical Science Research Center, School of Pharmacy and Pharmaceutical Sciences, Isfahan University of Medical Sciences, Room 117, Isfahan, Islamic Republic of Iran.
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6
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Kouba S, Braire J, Félix R, Chantôme A, Jaffrès PA, Lebreton J, Dubreuil D, Pipelier M, Zhang X, Trebak M, Vandier C, Mathé-Allainmat M, Potier-Cartereau M. Lipidic synthetic alkaloids as SK3 channel modulators. Synthesis and biological evaluation of 2-substituted tetrahydropyridine derivatives with potential anti-metastatic activity. Eur J Med Chem 2020; 186:111854. [PMID: 31753515 DOI: 10.1016/j.ejmech.2019.111854] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Accepted: 11/04/2019] [Indexed: 11/18/2022]
Abstract
Small Conductance Calcium (Ca2+)-activated potassium (K+) channels (SKCa) are now proved to be involved in many cancer cell behaviors such as proliferation or migration. The SK3 channel isoform was particularly described in breast cancer where it can be associated with the Orai1 Ca2+ channel to form a complex that regulates the Ca2+ homeostasis during tumor development and acts as a potent mediator of bone metastases development in vivo. Until now, very few specific blockers of Orai1 and/or SK3 have been developed as potential anti-metastatic compounds. In this study, we illustrated the synthesis of new families of lipophilic pyridine and tetrahydropyridine derivatives designed as potential modulators of SK3 channel. The toxicity of the newly synthesized compounds and their migration effects were evaluated on the breast cancer cell line MDA-MB-435s. Two molecules (7a and 10c) demonstrated a significant decrease in the SK3 channel-dependent migration as well as the SK3/Orai1-related Ca2+ entry. Current measurements showed that these compounds are more likely SK3-selective. Taken all together these results suggest that such molecules could be considered as promising anti-metastatic drugs in breast cancer.
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Affiliation(s)
- Sana Kouba
- University of Tours, Inserm U1069 Nutrition, Croissance et Cancer (N2C), Faculty of Medicine, 10 Boulevard Tonnellé, 37032, Tours Cedex, France
| | - Julien Braire
- University of Nantes, CNRS, Faculty of Sciences, Chimie et Interdisciplinarité: Synthèse, Analyse, Modélisation (CEISAM), UMR CNRS 6230, 2, Rue de La Houssinière, 44322, Nantes Cedex 3, France
| | - Romain Félix
- University of Tours, Inserm U1069 Nutrition, Croissance et Cancer (N2C), Faculty of Medicine, 10 Boulevard Tonnellé, 37032, Tours Cedex, France
| | - Aurélie Chantôme
- University of Tours, Inserm U1069 Nutrition, Croissance et Cancer (N2C), Faculty of Medicine, 10 Boulevard Tonnellé, 37032, Tours Cedex, France
| | - Paul-Alain Jaffrès
- University of Brest, CNRS, CEMCA, UMR 6521, 6 Avenue Victor Le Gorgeu, 29238, Brest, France
| | - Jacques Lebreton
- University of Nantes, CNRS, Faculty of Sciences, Chimie et Interdisciplinarité: Synthèse, Analyse, Modélisation (CEISAM), UMR CNRS 6230, 2, Rue de La Houssinière, 44322, Nantes Cedex 3, France
| | - Didier Dubreuil
- University of Nantes, CNRS, Faculty of Sciences, Chimie et Interdisciplinarité: Synthèse, Analyse, Modélisation (CEISAM), UMR CNRS 6230, 2, Rue de La Houssinière, 44322, Nantes Cedex 3, France
| | - Muriel Pipelier
- University of Nantes, CNRS, Faculty of Sciences, Chimie et Interdisciplinarité: Synthèse, Analyse, Modélisation (CEISAM), UMR CNRS 6230, 2, Rue de La Houssinière, 44322, Nantes Cedex 3, France
| | - Xuexin Zhang
- Pennylvania State University College of Medicine, Department of Cellular and Molecular Physiology, 700 HMC Crescent Road, Hershey, PA, 17033, USA
| | - Mohamed Trebak
- Pennylvania State University College of Medicine, Department of Cellular and Molecular Physiology, 700 HMC Crescent Road, Hershey, PA, 17033, USA
| | - Christophe Vandier
- University of Tours, Inserm U1069 Nutrition, Croissance et Cancer (N2C), Faculty of Medicine, 10 Boulevard Tonnellé, 37032, Tours Cedex, France
| | - Monique Mathé-Allainmat
- University of Nantes, CNRS, Faculty of Sciences, Chimie et Interdisciplinarité: Synthèse, Analyse, Modélisation (CEISAM), UMR CNRS 6230, 2, Rue de La Houssinière, 44322, Nantes Cedex 3, France.
| | - Marie Potier-Cartereau
- University of Tours, Inserm U1069 Nutrition, Croissance et Cancer (N2C), Faculty of Medicine, 10 Boulevard Tonnellé, 37032, Tours Cedex, France.
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de Oliveira Amaral H, Monge-Fuentes V, Biolchi Mayer A, Alves Campos GA, Soares Lopes K, Camargo LC, Ferroni Schwartz M, Galante P, Mortari MR. Animal venoms: therapeutic tools for tackling Parkinson's disease. Drug Discov Today 2019; 24:2202-2211. [PMID: 31539640 DOI: 10.1016/j.drudis.2019.09.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Revised: 08/02/2019] [Accepted: 09/10/2019] [Indexed: 12/16/2022]
Abstract
Parkinson's disease (PD) is a neurodegenerative pathology of the central nervous system, mainly involving the selective and progressive loss of dopaminergic neurons from the substantia nigra, resulting in motor and non-motor symptoms. PD remains an incurable ailment; thus, treatments are limited to symptom alleviation. With long-term use, conventional treatments can become inefficient, often triggering possible side effects. Considering these drawbacks, drug discovery constantly turns to nature as a source of efficient therapeutics. Thus, this review explores animal venoms as a rich source of bioactive compounds with potent neuropharmacological profiles for the development of effective adjuvant treatments with fewer side effects, ultimately aiming for the neuroprotection of dopaminergic neurons and the symptomatic relief of PD.
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Affiliation(s)
- Henrique de Oliveira Amaral
- Laboratory of Neuropharmacology, Department of Physiological Sciences, Institute of Biological Sciences, University of Brasilia, Brasilia, Brazil
| | - Victoria Monge-Fuentes
- Laboratory of Neuropharmacology, Department of Physiological Sciences, Institute of Biological Sciences, University of Brasilia, Brasilia, Brazil.
| | - Andréia Biolchi Mayer
- Laboratory of Neuropharmacology, Department of Physiological Sciences, Institute of Biological Sciences, University of Brasilia, Brasilia, Brazil
| | - Gabriel Avohay Alves Campos
- Laboratory of Neuropharmacology, Department of Physiological Sciences, Institute of Biological Sciences, University of Brasilia, Brasilia, Brazil
| | - Kamila Soares Lopes
- Laboratory of Neuropharmacology, Department of Physiological Sciences, Institute of Biological Sciences, University of Brasilia, Brasilia, Brazil
| | - Luana C Camargo
- Laboratory of Neuropharmacology, Department of Physiological Sciences, Institute of Biological Sciences, University of Brasilia, Brasilia, Brazil
| | - Matheus Ferroni Schwartz
- Laboratory of Neuropharmacology, Department of Physiological Sciences, Institute of Biological Sciences, University of Brasilia, Brasilia, Brazil
| | - Priscilla Galante
- Laboratory of Neuropharmacology, Department of Physiological Sciences, Institute of Biological Sciences, University of Brasilia, Brasilia, Brazil
| | - Márcia R Mortari
- Laboratory of Neuropharmacology, Department of Physiological Sciences, Institute of Biological Sciences, University of Brasilia, Brasilia, Brazil
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Brown BM, Shim H, Christophersen P, Wulff H. Pharmacology of Small- and Intermediate-Conductance Calcium-Activated Potassium Channels. Annu Rev Pharmacol Toxicol 2019; 60:219-240. [PMID: 31337271 DOI: 10.1146/annurev-pharmtox-010919-023420] [Citation(s) in RCA: 65] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The three small-conductance calcium-activated potassium (KCa2) channels and the related intermediate-conductance KCa3.1 channel are voltage-independent K+ channels that mediate calcium-induced membrane hyperpolarization. When intracellular calcium increases in the channel vicinity, it calcifies the flexible N lobe of the channel-bound calmodulin, which then swings over to the S4-S5 linker and opens the channel. KCa2 and KCa3.1 channels are highly druggable and offer multiple binding sites for venom peptides and small-molecule blockers as well as for positive- and negative-gating modulators. In this review, we briefly summarize the physiological role of KCa channels and then discuss the pharmacophores and the mechanism of action of the most commonly used peptidic and small-molecule KCa2 and KCa3.1 modulators. Finally, we describe the progress that has been made in advancing KCa3.1 blockers and KCa2.2 negative- and positive-gating modulators toward the clinic for neurological and cardiovascular diseases and discuss the remaining challenges.
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Affiliation(s)
- Brandon M Brown
- Department of Pharmacology, University of California, Davis, California 95616, USA;
| | - Heesung Shim
- Department of Pharmacology, University of California, Davis, California 95616, USA;
| | | | - Heike Wulff
- Department of Pharmacology, University of California, Davis, California 95616, USA;
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9
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Bajaj S, Han J. Venom-Derived Peptide Modulators of Cation-Selective Channels: Friend, Foe or Frenemy. Front Pharmacol 2019; 10:58. [PMID: 30863305 PMCID: PMC6399158 DOI: 10.3389/fphar.2019.00058] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2018] [Accepted: 01/18/2019] [Indexed: 01/31/2023] Open
Abstract
Ion channels play a key role in our body to regulate homeostasis and conduct electrical signals. With the help of advances in structural biology, as well as the discovery of numerous channel modulators derived from animal toxins, we are moving toward a better understanding of the function and mode of action of ion channels. Their ubiquitous tissue distribution and the physiological relevancies of their opening and closing suggest that cation channels are particularly attractive drug targets, and years of research has revealed a variety of natural toxins that bind to these channels and alter their function. In this review, we provide an introductory overview of the major cation ion channels: potassium channels, sodium channels and calcium channels, describe their venom-derived peptide modulators, and how these peptides provide great research and therapeutic value to both basic and translational medical research.
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Affiliation(s)
- Saumya Bajaj
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Singapore
| | - Jingyao Han
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Singapore
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10
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dos Santos-Pinto JRA, Perez-Riverol A, Lasa AM, Palma MS. Diversity of peptidic and proteinaceous toxins from social Hymenoptera venoms. Toxicon 2018; 148:172-196. [DOI: 10.1016/j.toxicon.2018.04.029] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Revised: 04/24/2018] [Accepted: 04/25/2018] [Indexed: 12/20/2022]
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Chung BYT, Bailey CDC. Similar nicotinic excitability responses across the developing hippocampal formation are regulated by small-conductance calcium-activated potassium channels. J Neurophysiol 2018; 119:1707-1722. [PMID: 29384449 DOI: 10.1152/jn.00426.2017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The hippocampal formation forms a cognitive circuit that is critical for learning and memory. Cholinergic input to nicotinic acetylcholine receptors plays an important role in the normal development of principal neurons within the hippocampal formation. However, the ability of nicotinic receptors to stimulate principal neurons across all regions of the developing hippocampal formation has not been determined. We show in this study that heteromeric nicotinic receptors mediate direct inward current and depolarization responses in principal neurons across the hippocampal formation of the young postnatal mouse. These responses were found in principal neurons of the CA1, CA3, dentate gyrus, subiculum, and entorhinal cortex layer VI, and they varied in magnitude across regions with the greatest responses occurring in the subiculum and entorhinal cortex. Despite this regional variation in the magnitude of passive responses, heteromeric nicotinic receptor stimulation increased the excitability of active principal neurons by a similar amount in all regions. Pharmacological experiments found this similar excitability response to be regulated by small-conductance calcium-activated potassium (SK) channels, which exhibited regional differences in their influence on neuron activity that offset the observed regional differences in passive nicotinic responses. These findings demonstrate that SK channels play a role to coordinate the magnitude of heteromeric nicotinic excitability responses across the hippocampal formation at a time when nicotinic signaling drives the development of this cognitive brain region. This coordinated input may contribute to the normal development, synchrony, and maturation of the hippocampal formation learning and memory network. NEW & NOTEWORTHY This study demonstrates that small-conductance calcium-activated potassium channels regulate similar-magnitude excitability responses to heteromeric nicotinic acetylcholine receptor stimulation in active principal neurons across multiple regions of the developing mouse hippocampal formation. Given the importance of nicotinic neurotransmission for the development of principal neurons within the hippocampal formation, this coordinated excitability response is positioned to influence the normal development, synchrony, and maturation of the hippocampal formation learning and memory network.
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Affiliation(s)
- Beryl Y T Chung
- Department of Biomedical Sciences, University of Guelph , Guelph, Ontario , Canada
| | - Craig D C Bailey
- Department of Biomedical Sciences, University of Guelph , Guelph, Ontario , Canada
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12
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Calcium-activated SK potassium channels are key modulators of the pacemaker frequency in locus coeruleus neurons. Mol Cell Neurosci 2018. [DOI: 10.1016/j.mcn.2018.03.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
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Venom-derived peptides inhibiting Kir channels: Past, present, and future. Neuropharmacology 2017; 127:161-172. [PMID: 28716449 DOI: 10.1016/j.neuropharm.2017.07.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 07/05/2017] [Accepted: 07/13/2017] [Indexed: 12/17/2022]
Abstract
Inwardly rectifying K+ (Kir) channels play a significant role in vertebrate and invertebrate biology by regulating the movement of K+ ions involved in membrane transport and excitability. Yet unlike other ion channels including their ancestral K+-selective homologs, there are very few venom toxins known to target and inhibit Kir channels with the potency and selectivity found for the Ca2+-activated and voltage-gated K+ channel families. It is unclear whether this is simply due to a lack of discovery, or instead a consequence of the evolutionary processes that drive the development of venom components towards their targets based on a collective efficacy to 1) elicit pain for defensive purposes, 2) promote paralysis for prey capture, or 3) facilitate delivery of venom components into the circulation. The past two decades of venom screening has yielded three venom peptides with inhibitory activity towards mammalian Kir channels, including the discovery of tertiapin, a high-affinity pore blocker from the venom of the European honey bee Apis mellifera. Venomics and structure-based computational approaches represent exciting new frontiers for venom peptide development, where re-engineering peptide 'scaffolds' such as tertiapin may aid in the quest to expand the palette of potent and selective Kir channel blockers for future research and potentially new therapeutics. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'
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Abstract
Atrial fibrillation (AF) is associated with increased morbidity and mortality. Atrial-selective potassium (K(+)) channel blockers may represent a novel therapeutic target. The best validated atrial-specific ion currents are the acetylcholine-activated inward-rectifier K(+) current IK,ACh and ultrarapidly activating delayed-rectifier K(+) current IKur. Two-pore domain and small-conductance Ca(2+)-activated K(+) channels and Kv1.1 channels may also contribute to the atrial repolarization. We review the molecular and electrophysiologic characteristics of atrial-selective K(+) channels and their potential pathophysiologic role in AF. We summarize currently available K(+) channel blockers focusing on the most important compounds.
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Affiliation(s)
- Niels Voigt
- Institute of Pharmacology, West German Heart and Vascular Center, University Duisburg-Essen, Hufelandstr. 55, Essen 45122, Germany
| | - Dobromir Dobrev
- Institute of Pharmacology, West German Heart and Vascular Center, University Duisburg-Essen, Hufelandstr. 55, Essen 45122, Germany.
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15
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Bragança B, Oliveira-Monteiro N, Ferreirinha F, Lima PA, Faria M, Fontes-Sousa AP, Correia-de-Sá P. Ion Fluxes through KCa2 (SK) and Cav1 (L-type) Channels Contribute to Chronoselectivity of Adenosine A1 Receptor-Mediated Actions in Spontaneously Beating Rat Atria. Front Pharmacol 2016; 7:45. [PMID: 27014060 PMCID: PMC4780064 DOI: 10.3389/fphar.2016.00045] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Accepted: 02/18/2016] [Indexed: 11/24/2022] Open
Abstract
Impulse generation in supraventricular tissue is inhibited by adenosine and acetylcholine via the activation of A1 and M2 receptors coupled to inwardly rectifying GIRK/KIR3.1/3.4 channels, respectively. Unlike M2 receptors, bradycardia produced by A1 receptors activation predominates over negative inotropy. Such difference suggests that other ion currents may contribute to adenosine chronoselectivity. In isolated spontaneously beating rat atria, blockade of KCa2/SK channels with apamin and Cav1 (L-type) channels with nifedipine or verapamil, sensitized atria to the negative inotropic action of the A1 agonist, R-PIA, without affecting the nucleoside negative chronotropy. Patch-clamp experiments in the whole-cell configuration mode demonstrate that adenosine, via A1 receptors, activates the inwardly-rectifying GIRK/KIR3.1/KIR3.4 current resulting in hyperpolarization of atrial cardiomyocytes, which may slow down heart rate. Conversely, the nucleoside inactivates a small conductance Ca2+-activated KCa2/SK outward current, which eventually reduces the repolarizing force and thereby prolong action potentials duration and Ca2+ influx into cardiomyocytes. Immunolocalization studies showed that differences in A1 receptors distribution between the sinoatrial node and surrounding cardiomyocytes do not afford a rationale for adenosine chronoselectivity. Immunolabelling of KIR3.1, KCa2.2, KCa2.3, and Cav1 was also observed throughout the right atrium. Functional data indicate that while both A1 and M2 receptors favor the opening of GIRK/KIR3.1/3.4 channels modulating atrial chronotropy, A1 receptors may additionally restrain KCa2/SK activation thereby compensating atrial inotropic depression by increasing the time available for Ca2+ influx through Cav1 (L-type) channels.
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Affiliation(s)
- Bruno Bragança
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Nádia Oliveira-Monteiro
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Fátima Ferreirinha
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Pedro A Lima
- Departamento de Química e Bioquímica, Faculdade de Ciências, Centro de Química e Bioquímica, Universidade de Lisboa Lisboa, Portugal
| | - Miguel Faria
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Ana P Fontes-Sousa
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Paulo Correia-de-Sá
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
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Zhan C, Li C, Wei X, Lu W, Lu W. Toxins and derivatives in molecular pharmaceutics: Drug delivery and targeted therapy. Adv Drug Deliv Rev 2015; 90:101-18. [PMID: 25959429 DOI: 10.1016/j.addr.2015.04.025] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Revised: 04/20/2015] [Accepted: 04/29/2015] [Indexed: 01/13/2023]
Abstract
Protein and peptide toxins offer an invaluable source for the development of actively targeted drug delivery systems. They avidly bind to a variety of cognate receptors, some of which are expressed or even up-regulated in diseased tissues and biological barriers. Protein and peptide toxins or their derivatives can act as ligands to facilitate tissue- or organ-specific accumulation of therapeutics. Some toxins have evolved from a relatively small number of structural frameworks that are particularly suitable for addressing the crucial issues of potency and stability, making them an instrumental source of leads and templates for targeted therapy. The focus of this review is on protein and peptide toxins for the development of targeted drug delivery systems and molecular therapies. We summarize disease- and biological barrier-related toxin receptors, as well as targeted drug delivery strategies inspired by those receptors. The design of new therapeutics based on protein and peptide toxins is also discussed.
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Affiliation(s)
- Changyou Zhan
- Department of Pharmaceutics, School of Pharmacy, Fudan University & Key Laboratory of Smart Drug Delivery (Fudan University), Ministry of Education, Shanghai 201203, PR China
| | - Chong Li
- College of Pharmaceutical Sciences, Southwest University & Chongqing Engineering Research Center for Pharmaceutical Process and Quality Control, Chongqing 400716, PR China
| | - Xiaoli Wei
- Department of Pharmaceutics, School of Pharmacy, Fudan University & Key Laboratory of Smart Drug Delivery (Fudan University), Ministry of Education, Shanghai 201203, PR China; State Key Laboratory of Medical Neurobiology and the Collaborative Innovation Center for Brain Science, Fudan University, Shanghai 200032, PR China
| | - Wuyuan Lu
- Institute of Human Virology and Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Weiyue Lu
- Department of Pharmaceutics, School of Pharmacy, Fudan University & Key Laboratory of Smart Drug Delivery (Fudan University), Ministry of Education, Shanghai 201203, PR China; State Key Laboratory of Medical Neurobiology and the Collaborative Innovation Center for Brain Science, Fudan University, Shanghai 200032, PR China; State Key Laboratory of Molecular Engineering of Polymers, Fudan University, Shanghai 200433, PR China.
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17
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From naturally-occurring neurotoxic agents to CNS shuttles for drug delivery. Eur J Pharm Sci 2015; 74:63-76. [DOI: 10.1016/j.ejps.2015.04.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Revised: 03/19/2015] [Accepted: 04/08/2015] [Indexed: 12/20/2022]
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18
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Toxins Targeting the Kv1.3 Channel: Potential Immunomodulators for Autoimmune Diseases. Toxins (Basel) 2015; 7:1749-64. [PMID: 25996605 PMCID: PMC4448172 DOI: 10.3390/toxins7051749] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 05/05/2015] [Accepted: 05/05/2015] [Indexed: 12/23/2022] Open
Abstract
Autoimmune diseases are usually accompanied by tissue injury caused by autoantigen-specific T-cells. KV1.3 channels participate in modulating calcium signaling to induce T-cell proliferation, immune activation and cytokine production. Effector memory T (TEM)-cells, which play major roles in many autoimmune diseases, are controlled by blocking KV1.3 channels on the membrane. Toxins derived from animal venoms have been found to selectively target a variety of ion channels, including KV1.3. By blocking the KV1.3 channel, these toxins are able to suppress the activation and proliferation of TEM cells and may improve TEM cell-mediated autoimmune diseases, such as multiple sclerosis and type I diabetes mellitus.
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Apamin inhibits PDGF-BB-induced vascular smooth muscle cell proliferation and migration through suppressions of activated Akt and Erk signaling pathway. Vascul Pharmacol 2015; 70:8-14. [PMID: 25737404 DOI: 10.1016/j.vph.2014.12.004] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Revised: 11/13/2014] [Accepted: 12/28/2014] [Indexed: 11/21/2022]
Abstract
The increased proliferation and migration of vascular smooth muscle cells (VSMC) are key process in the development of atherosclerosis lesions. Platelet-derived growth factor (PDGF) initiates a multitude of biological effects that contribute to VSMC proliferation and migration. Apamin, a component of bee venom, has been known to block the Ca(2+)-activated K(+) channels. However, the effects of apamin in the regulation PDGF-BB-induced VSMC proliferation and migration has not been identified. In this study, we investigate the inhibitory effect of apamin on PDGF-BB-induced VSMC proliferation and migration. Apamin suppressed the PDGF-BB-induced VSMC proliferation and migration with no apparent cytotoxic effect. In accordance with these findings, apamin induced the arrest of cell cycle progression at G0/G1 phase. Apamin also decreased the expressions of G0/G1 specific regulatory proteins including proliferating cell nuclear antigen (PCNA), cyclin D1, cyclin-dependent kinases (CDK) 4, cyclin E and CDK2, as well as increased the expression of p21(Cip1) in PDGF-BB-induced VSMC. Moreover, apamin inhibited PDGF-BB-induced phosphorylation of Akt and Erk1/2. These results suggest that apamin plays an important role in prevention of vascular proliferation and migration through the G0/G1 cell cycle arrest by PDGF signaling pathway. Thus, apamin may be a promising candidate for the therapy of atherosclerosis.
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20
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Donato F, Borges Filho C, Giacomeli R, Alvater EET, Del Fabbro L, Antunes MDS, de Gomes MG, Goes ATR, Souza LC, Boeira SP, Jesse CR. Evidence for the Involvement of Potassium Channel Inhibition in the Antidepressant-Like Effects of Hesperidin in the Tail Suspension Test in Mice. J Med Food 2015; 18:818-23. [PMID: 25647144 DOI: 10.1089/jmf.2014.0074] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The administration of hesperidin elicits an antidepressant-like effect in mice by a mechanism dependent on an interaction with the L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway, whose stimulation is associated with the activation of potassium (K(+)) channels. Thus, this study investigated the involvement of different types of K(+) channels in the antidepressant-like effect of hesperidin in the mice tail suspension test (TST). The intracerebroventricular administration of tetraethylammonium (TEA, a nonspecific blocker of K(+) channels), glibenclamide (an ATP-sensitive K(+) channel blocker), charybdotoxin (a large- and intermediate-conductance calcium-activated K(+) channel blocker) or apamin (a small-conductance calcium-activated K(+) channel blocker) combined with a subeffective dose of hesperidin (0.01 mg/kg, intraperitoneally [i.p.]) was able to produce a synergistic antidepressant-like effect in the mice TST. Moreover, the antidepressant-like effect elicited by an effective dose of hesperidin (0.3 mg/kg, i.p.) in TST was abolished by the treatment of mice with pharmacological compounds K(+) channel openers (cromakalim and minoxidil). Results showed that the antidepressant-like effect of hesperidin in TST may involve, at least in part, the modulation of neuronal excitability through inhibition of K(+) channels and may act through a mechanism dependent on the inhibition of L-arginine-NO pathway.
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Affiliation(s)
- Franciele Donato
- Laboratory of Pharmacological and Toxicological Assessments Applied to Bioactive Molecules, LaftamBio Pampa, Federal University of Pampa , Itaqui, Rio Grande do Sul, Brazil
| | - Carlos Borges Filho
- Laboratory of Pharmacological and Toxicological Assessments Applied to Bioactive Molecules, LaftamBio Pampa, Federal University of Pampa , Itaqui, Rio Grande do Sul, Brazil
| | - Renata Giacomeli
- Laboratory of Pharmacological and Toxicological Assessments Applied to Bioactive Molecules, LaftamBio Pampa, Federal University of Pampa , Itaqui, Rio Grande do Sul, Brazil
| | - Elza Eliza Tenório Alvater
- Laboratory of Pharmacological and Toxicological Assessments Applied to Bioactive Molecules, LaftamBio Pampa, Federal University of Pampa , Itaqui, Rio Grande do Sul, Brazil
| | - Lucian Del Fabbro
- Laboratory of Pharmacological and Toxicological Assessments Applied to Bioactive Molecules, LaftamBio Pampa, Federal University of Pampa , Itaqui, Rio Grande do Sul, Brazil
| | - Michele da Silva Antunes
- Laboratory of Pharmacological and Toxicological Assessments Applied to Bioactive Molecules, LaftamBio Pampa, Federal University of Pampa , Itaqui, Rio Grande do Sul, Brazil
| | - Marcelo Gomes de Gomes
- Laboratory of Pharmacological and Toxicological Assessments Applied to Bioactive Molecules, LaftamBio Pampa, Federal University of Pampa , Itaqui, Rio Grande do Sul, Brazil
| | - André Tiago Rossito Goes
- Laboratory of Pharmacological and Toxicological Assessments Applied to Bioactive Molecules, LaftamBio Pampa, Federal University of Pampa , Itaqui, Rio Grande do Sul, Brazil
| | - Leandro Cattelan Souza
- Laboratory of Pharmacological and Toxicological Assessments Applied to Bioactive Molecules, LaftamBio Pampa, Federal University of Pampa , Itaqui, Rio Grande do Sul, Brazil
| | - Silvana Peterini Boeira
- Laboratory of Pharmacological and Toxicological Assessments Applied to Bioactive Molecules, LaftamBio Pampa, Federal University of Pampa , Itaqui, Rio Grande do Sul, Brazil
| | - Cristiano Ricardo Jesse
- Laboratory of Pharmacological and Toxicological Assessments Applied to Bioactive Molecules, LaftamBio Pampa, Federal University of Pampa , Itaqui, Rio Grande do Sul, Brazil
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21
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Benton DCH, Garbarg M, Moss GWJ. The relationship between functional inhibition and binding for K(Ca)2 channel blockers. PLoS One 2013; 8:e73328. [PMID: 24039913 PMCID: PMC3769273 DOI: 10.1371/journal.pone.0073328] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2013] [Accepted: 07/30/2013] [Indexed: 11/25/2022] Open
Abstract
Small conductance calcium-activated potassium channels (KCa2.1,2.2,2.3) are blocked with high affinity by both peptide toxins (e.g. apamin) and small molecule blockers (e.g. UCL 1848). In electrophysiological experiments, apamin shows subtype selectivity with IC50s of ∼100 pM and ∼1 nM for block KCa2.2 and KCa2.3 respectively. In binding studies, however, apamin appears not to discriminate between KCa2.2 and 2.3 and is reported to have a significantly higher (∼20–200-fold) affinity (∼5 pM). This discrepancy between binding and block has been suggested to reflect an unusual mode of action of apamin. However, these binding and electrophysiological block experiments have not been conducted in the same ionic conditions, so it is also possible that the discrepancy arises simply because of differences in experimental conditions. We have now examined this latter possibility. Thus, we measured 125I-apamin binding to intact HEK 293 cells expressing KCa2 channels under the same ionic conditions (i.e. normal physiological conditions) that we also used for current block measurements. We find that binding and block experiments agree well if the same ionic conditions are used. Further, the binding of apamin and other blockers showed subtype selectivity when measured in normal physiological solutions (e.g.125I-apamin bound to KCa2.2 with KL 91±40 pM and to KCa2.3 with KL 711±126 pM, while inhibiting KCa2.2 current at IC50 103±2 pM). We also examined KCa2 channel block in Ca2+ and Mg2+ free solutions that mimic conditions reported in the literature for binding experiments. Under these (non-physiological) conditions the IC50 for apamin block of KCa2.2 was reduced to 20±3 pM. Our results therefore suggest that the apparent discrepancy between blocking and binding reported in the literature can be largely accounted for by the use of non-physiological ionic conditions in binding experiments.
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Affiliation(s)
- David Charles Hammond Benton
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom
- * E-mail:
| | - Monique Garbarg
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom
| | - Guy William John Moss
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom
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22
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Gur S, Sikka SC, Abdel-Mageed AB, Abd Elmageed ZY, Rezk B, Pankey E, Kadowitz PJ, Hellstrom WJ. Imatinib Mesylate (Gleevec) Induces Human Corpus Cavernosum Relaxation by Inhibiting Receptor Tyrosine Kinases (RTKs): Identification of New RTK Targets. Urology 2013; 82:745.e11-6. [DOI: 10.1016/j.urology.2013.04.030] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 04/10/2013] [Accepted: 04/19/2013] [Indexed: 12/23/2022]
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Kuiper EFE, Nelemans A, Luiten P, Nijholt I, Dolga A, Eisel U. K(Ca)2 and k(ca)3 channels in learning and memory processes, and neurodegeneration. Front Pharmacol 2012; 3:107. [PMID: 22701424 PMCID: PMC3372087 DOI: 10.3389/fphar.2012.00107] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Accepted: 05/19/2012] [Indexed: 11/13/2022] Open
Abstract
Calcium-activated potassium (KCa) channels are present throughout the central nervous system as well as many peripheral tissues. Activation of KCa channels contribute to maintenance of the neuronal membrane potential and was shown to underlie the afterhyperpolarization (AHP) that regulates action potential firing and limits the firing frequency of repetitive action potentials. Different subtypes of KCa channels were anticipated on the basis of their physiological and pharmacological profiles, and cloning revealed two well defined but phylogenetic distantly related groups of channels. The group subject of this review includes both the small conductance KCa2 channels (KCa2.1, KCa2.2, and KCa2.3) and the intermediate-conductance (KCa3.1) channel. These channels are activated by submicromolar intracellular Ca2+ concentrations and are voltage independent. Of all KCa channels only the KCa2 channels can be potently but differentially blocked by the bee-venom apamin. In the past few years modulation of KCa channel activation revealed new roles for KCa2 channels in controlling dendritic excitability, synaptic functioning, and synaptic plasticity. Furthermore, KCa2 channels appeared to be involved in neurodegeneration, and learning and memory processes. In this review, we focus on the role of KCa2 and KCa3 channels in these latter mechanisms with emphasis on learning and memory, Alzheimer’s disease and on the interplay between neuroinflammation and different neurotransmitters/neuromodulators, their signaling components and KCa channel activation.
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Affiliation(s)
- Els F E Kuiper
- Molecular Neurobiology, University of Groningen Groningen, Netherlands
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24
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Moretti M, Budni J, Ribeiro CM, Rodrigues ALS. Involvement of different types of potassium channels in the antidepressant-like effect of ascorbic acid in the mouse tail suspension test. Eur J Pharmacol 2012; 687:21-7. [PMID: 22575518 DOI: 10.1016/j.ejphar.2012.04.041] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Revised: 04/19/2012] [Accepted: 04/21/2012] [Indexed: 12/18/2022]
Abstract
Considering that the administration of ascorbic acid elicits an antidepressant-effect in mice by a mechanism which involves an interaction with N-methyl-D-aspartate receptors and the l-arginine-nitric oxide-cGMP pathway and taking into account that the stimulation of this pathway is associated with the activation of potassium (K⁺) channels, this study investigated the involvement of different types of K⁺ channels on the effect of ascorbic acid in the mouse tail suspension test (TST). Intracerebroventricular administration of tetraethylammonium (TEA, a non-specific blocker of K⁺ channels, 25 pg/site), glibenclamide (an ATP-sensitive K⁺ channel blocker, 0.5 pg/site), charybdotoxin (a large- and intermediate conductance calcium-activated K⁺ channel blocker, 25 pg/site) or apamin (a small-conductance calcium-activated K⁺ channel blocker, 10 pg/site) was able to produce a synergistic effect with a sub-effective dose of ascorbic acid (0.1 mg/kg) given orally (p.o.). The antidepressant-like effect of ascorbic acid (1 mg/kg, p.o.) in the TST was prevented by the pre-treatment of mice with cromakalim (a K⁺ channel opener, 10 μg/site, i.c.v.) and minoxidil (10 μg/site, i.c.v.). Moreover, cromakalim abolished the synergistic effect elicited by the combined treatment with sub-effective doses of ascorbic acid and 7-nitroindazole. The administration of the K⁺ channel modulators alone or in combination with ascorbic acid did not affect the locomotion of mice. Together, our results show that the antidepressant-like effect of ascorbic acid in the TST may involve, at least in part, the modulation of neuronal excitability, via inhibition of K⁺ channels.
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Affiliation(s)
- Morgana Moretti
- Departamento de Bioquímica, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Florianópolis, 88040-900 SC, Brazil
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25
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Dilly S, Poncin S, Lamy C, Liégeois JF, Seutin V. Physiologie, pharmacologie et modélisation de canaux potassiques. Med Sci (Paris) 2012; 28:395-402. [DOI: 10.1051/medsci/2012284017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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26
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Budni J, E. Freitas A, W. Binfaré R, S. Rodrigues AL. Role of potassium channels in the antidepressant-like effect of folic acid in the forced swimming test in mice. Pharmacol Biochem Behav 2012; 101:148-54. [DOI: 10.1016/j.pbb.2011.12.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2011] [Revised: 12/01/2011] [Accepted: 12/12/2011] [Indexed: 11/29/2022]
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27
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Eleventh international symposium on radiopharmaceutical chemistry: Abstracts. J Labelled Comp Radiopharm 2012. [DOI: 10.1002/jlcr.2580370601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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28
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Nishikawa H, Kitani S. Gangliosides inhibit bee venom melittin cytotoxicity but not phospholipase A(2)-induced degranulation in mast cells. Toxicol Appl Pharmacol 2011; 252:228-36. [PMID: 21334356 DOI: 10.1016/j.taap.2011.02.011] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2010] [Revised: 02/09/2011] [Accepted: 02/10/2011] [Indexed: 12/25/2022]
Abstract
Sting accident by honeybee causes severe pain, inflammation and allergic reaction through IgE-mediated anaphylaxis. In addition to this hypersensitivity, an anaphylactoid reaction occurs by toxic effects even in a non-allergic person via cytolysis followed by similar clinical manifestations. Auto-injectable epinephrine might be effective for bee stings, but cannot inhibit mast cell lysis and degranulation by venom toxins. We used connective tissue type canine mast cell line (CM-MC) for finding an effective measure that might inhibit bee venom toxicity. We evaluated degranulation and cytotoxicity by measurement of β-hexosaminidase release and MTT assay. Melittin and crude bee venom induced the degranulation and cytotoxicity, which were strongly inhibited by mono-sialoganglioside (G(M1)), di-sialoganglioside (G(D1a)) and tri-sialoganglioside (G(T1b)). In contrast, honeybee venom-derived phospholipase A(2) induced the net degranulation directly without cytotoxicity, which was not inhibited by G(M1), G(D1a) and G(T1b). For analysis of distribution of Gα(q) and Gα(i) protein by western blotting, lipid rafts were isolated by using discontinuous sucrose gradient centrifuge. Melittin disrupted the localization of Gα(q) and Gα(i) at lipid raft, but gangliosides stabilized the rafts. As a result from this cell-based study, bee venom-induced anaphylactoid reaction can be explained with melittin cytotoxicity and phospholipase A(2)-induced degranulation. Taken together, gangliosides inhibit the effect of melittin such as degranulation, cytotoxicity and lipid raft disruption but not phospholipase A(2)-induced degranulation in mast cells. Our study shows a potential of gangliosides as a therapeutic tool for anaphylactoid reaction by honeybee sting.
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Affiliation(s)
- Hirofumi Nishikawa
- Health Service Center, Tokyo University of Marine Science and Technology, Konan 4-5-7, Minato-ku, Tokyo 108-8477, Japan
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The sigma agonist 1,3-di-o-tolyl-guanidine directly blocks SK channels in dopaminergic neurons and in cell lines. Eur J Pharmacol 2010; 641:23-8. [DOI: 10.1016/j.ejphar.2010.05.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Revised: 04/27/2010] [Accepted: 05/06/2010] [Indexed: 11/18/2022]
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Weatherall KL, Goodchild SJ, Jane DE, Marrion NV. Small conductance calcium-activated potassium channels: From structure to function. Prog Neurobiol 2010; 91:242-55. [DOI: 10.1016/j.pneurobio.2010.03.002] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Revised: 03/05/2010] [Accepted: 03/24/2010] [Indexed: 10/19/2022]
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31
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Chen J, Lariviere WR. The nociceptive and anti-nociceptive effects of bee venom injection and therapy: a double-edged sword. Prog Neurobiol 2010; 92:151-83. [PMID: 20558236 DOI: 10.1016/j.pneurobio.2010.06.006] [Citation(s) in RCA: 115] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2009] [Revised: 03/31/2010] [Accepted: 06/08/2010] [Indexed: 12/23/2022]
Abstract
Bee venom injection as a therapy, like many other complementary and alternative medicine approaches, has been used for thousands of years to attempt to alleviate a range of diseases including arthritis. More recently, additional theraupeutic goals have been added to the list of diseases making this a critical time to evaluate the evidence for the beneficial and adverse effects of bee venom injection. Although reports of pain reduction (analgesic and antinociceptive) and anti-inflammatory effects of bee venom injection are accumulating in the literature, it is common knowledge that bee venom stings are painful and produce inflammation. In addition, a significant number of studies have been performed in the past decade highlighting that injection of bee venom and components of bee venom produce significant signs of pain or nociception, inflammation and many effects at multiple levels of immediate, acute and prolonged pain processes. This report reviews the extensive new data regarding the deleterious effects of bee venom injection in people and animals, our current understanding of the responsible underlying mechanisms and critical venom components, and provides a critical evaluation of reports of the beneficial effects of bee venom injection in people and animals and the proposed underlying mechanisms. Although further studies are required to make firm conclusions, therapeutic bee venom injection may be beneficial for some patients, but may also be harmful. This report highlights key patterns of results, critical shortcomings, and essential areas requiring further study.
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Affiliation(s)
- Jun Chen
- Institute for Biomedical Sciences of Pain and Institute for Functional Brain Disorders, Tangdu Hospital, The Fourth Military Medical University, 1 Xinsi Road, Baqiao District, Xi'an 710038, PR China.
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SK channel blocker apamin attenuates the effect of SSRI fluoxetine upon cell firing in dorsal raphe nucleus: A concomitant electrophysiological and electrochemical in vivo study reveals implications for modulating extracellular 5-HT. Brain Res 2010; 1334:1-11. [DOI: 10.1016/j.brainres.2010.03.081] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2009] [Revised: 03/22/2010] [Accepted: 03/23/2010] [Indexed: 11/23/2022]
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Escoffier J, Couvet M, de Pomyers H, Ray PF, Sève M, Lambeau G, De Waard M, Arnoult C. Snake venoms as a source of compounds modulating sperm physiology: Secreted phospholipases A2 from Oxyuranus scutellatus scutellatus impact sperm motility, acrosome reaction and in vitro fertilization in mice. Biochimie 2010; 92:826-36. [PMID: 20226834 DOI: 10.1016/j.biochi.2010.03.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2010] [Accepted: 03/05/2010] [Indexed: 11/19/2022]
Abstract
The goal of this study was to identify new compounds from venoms able to modulate sperm physiology and more particularly sperm motility. For this purpose, we screened the effects of 16 snake venoms cleared of molecules higher than 15 kDa on sperm motility. Venoms rich in neurotoxins like those from Oxyuranus scutellatus scutellatus or Daboia russelii, were highly potent inhibitors of sperm motility. In contrast, venoms rich in myotoxins like those from Echis carinatus, Bothrops alternatus and Macrovipera lebetina, were inactive. From the main pharmacologically-active fraction of the Taipan snake O. scutellatus s., a proteomic approach allowed us to identify 16 different proteins, among which OS1 and OS2, two secreted phospholipases A2 (sPLA(2)). Purified OS1 and OS2 mimicked the inhibitory effect on sperm motility and were likely responsible for the inhibitory effect of the active fraction. OS1 and OS2 triggered sperm acrosome reaction and induced lipid rearrangements of the plasma membrane. The catalytic activity of OS2 was required to modulate sperm physiology since catalytically inactive mutants had no effect. Finally, sperm treated with OS2 were less competent than control sperm to initiate in vitro normal embryo development. This is the first report characterizing sPLA(2) toxins that modulate in vitro sperm physiology.
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Zhang Y, Lomax AE, Paterson WG. P2Y1 receptors mediate apamin-sensitive and -insensitive inhibitory junction potentials in murine colonic circular smooth muscle. J Pharmacol Exp Ther 2010; 333:602-11. [PMID: 20103587 DOI: 10.1124/jpet.109.160978] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Purinergic inhibitory neuromuscular transmission plays an important role in the control of intestinal motility. In most tissues this neurotransmission is apamin-sensitive, but recent studies in human colonic circular smooth muscle (CSM) suggest the presence of apamin-insensitive purinergic inhibitory junction potentials (IJPs). The current studies used conventional intracellular recordings on colonic CSM strips to characterize the purinergic IJPs in murine colonic CSM. P2Y1 receptor expression was examined by using reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. The IJP induced by nerve stimulation (NS) of one and four pulses in neuronal nitric-oxide synthase knockout mice consists of an apamin-sensitive and a dominant apamin-resistant component. These are identical to the IJPs in wild-type and CD1 mice in the presence of N(omega)-nitro-l-arginine methyl ester (200 microM) and were significantly inhibited by alpha,beta-methylene ATP (50 microM), an analog of ATP. IJPs were not affected by the P2X receptor antagonist 2',3'-o-(2,4,6-trinitrophenyl)-ATP (10 microM). Furthermore, apamin-resistant IJPs induced by single-pulse NS were abolished by pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (100 microM), a P2 receptor antagonist; 2'-deoxy-N6-methyl adenosine 3,5-diphosphate (MRS-2179; 10 microM), a selective P2Y1 receptor antagonist; and tetrodotoxin (1 microM). Aboral NS induced apamin-sensitive purinergic IJPs, whereas oral and circumferential NS produced apamin-sensitive and -resistant IJPs, with the latter predominating. RT-PCR and immunohistochemistry confirmed the presence of P2Y1 receptors on smooth muscle and in the myenteric plexus. These data suggest that, depending on stimulus location, activation of P2Y1 receptors produces both apamin-sensitive and apamin-resistant IJPs in murine colonic CSM.
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Affiliation(s)
- Yong Zhang
- Gastrointestinal Diseases Research Unit, Queen's University, Kingston, Ontario, Canada
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Crespi F. Apamin increases 5-HT cell firing in raphe dorsalis and extracellular 5-HT levels in amygdala: A concomitant in vivo study in anesthetized rats. Brain Res 2009; 1281:35-46. [DOI: 10.1016/j.brainres.2009.05.021] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2009] [Revised: 05/07/2009] [Accepted: 05/08/2009] [Indexed: 10/20/2022]
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Rouchet N, Waroux O, Lamy C, Massotte L, Scuvée-Moreau J, Liégeois JF, Seutin V. SK channel blockade promotes burst firing in dorsal raphe serotonergic neurons. Eur J Neurosci 2008; 28:1108-15. [DOI: 10.1111/j.1460-9568.2008.06430.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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37
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Preliminary SAR studies on non-apamin-displacing 4-(aminomethylaryl)pyrrazolopyrimidine K(Ca) channel blockers. Bioorg Med Chem Lett 2008; 18:5694-7. [PMID: 18824351 DOI: 10.1016/j.bmcl.2008.08.026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2008] [Revised: 08/07/2008] [Accepted: 08/08/2008] [Indexed: 11/22/2022]
Abstract
An exploratory SAR study on a series of potent, non-apamin-displacing 4-(aminomethylaryl)pyrazolopyrimidine K(Ca) channel blockers is described and their selectivity against K(Ca) channel subtypes is reported. The most potent analog, 5-chloro-N-(thiophen-2-ylmethyl)pyrazolo[1,5-a]pyrimidin-7-amine (24) displayed sub-micromolar activity in both a thallium flux and whole-cell electrophysiology assay and did not displace apamin in a competitive binding study.
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Favero M, Jiang DJ, Chiamulera C, Cangiano A, Fumagalli GF. Expression of small-conductance calcium-activated potassium channels (SK3) in skeletal muscle: regulation by muscle activity. J Physiol 2008; 586:4763-74. [PMID: 18703580 DOI: 10.1113/jphysiol.2008.156588] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The type 3 small conductance calcium-activated potassium channel (SK3) is expressed in embryonic and adult denervated skeletal muscles where it contributes to hyperexcitability. This study aimed at determining the role of muscle activity in regulating SK3 channels. Soleus muscles of adult rats were denervated by cutting the sciatic nerve. In reinnervation studies, the soleus nerve was crushed: in one group, muscles were reinnervated with electrically silent axons, by chronic sciatic nerve perfusion with tetrodotoxin. Several groups of denervated muscles were subjected to chronic direct electrical stimulation, using either fast (100 Hz) or slower patterns (20 or 30 Hz). The SK3 mRNA and protein levels in soleus muscle were determined by reverse transcriptional-PCR, Western blot and immunofluorescence. Both denervated and reinnervated-paralysed soleus muscles displayed similar up-regulation of SK3 mRNA and protein. Reinnervation with electrically active axons instead inhibited SK3 up-regulation. Chronic muscle direct stimulation in vivo, irrespective of the pattern used, reversed the denervation-induced up-regulation of SK3 expression or prevented it when initiated at the time of denervation. Chronic electrical stimulation of denervated muscles also completely prevented the development of the after-hyperpolarization (AHP) following the action potential, normally induced in the muscle fibres by denervation. We conclude that action potential activity evoked by motor neurones in muscle fibres is both necessary and sufficient to account for the physiological down-regulation of SK3 channels in the non-junctional membrane of skeletal muscle.
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Affiliation(s)
- Morgana Favero
- Department of Neurological and Visual Sciences, Section of Physiology, University of Verona, Strada Le Grazie 8, 37134 Verona, Italy
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Wulff H, Zhorov BS. K+ channel modulators for the treatment of neurological disorders and autoimmune diseases. Chem Rev 2008; 108:1744-73. [PMID: 18476673 PMCID: PMC2714671 DOI: 10.1021/cr078234p] [Citation(s) in RCA: 168] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Heike Wulff
- Department of Pharmacology, University of California, Davis, California 95616, USA.
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Ji H, Shepard PD. Lateral habenula stimulation inhibits rat midbrain dopamine neurons through a GABA(A) receptor-mediated mechanism. J Neurosci 2007; 27:6923-30. [PMID: 17596440 PMCID: PMC6672239 DOI: 10.1523/jneurosci.0958-07.2007] [Citation(s) in RCA: 299] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Transient changes in the activity of midbrain dopamine neurons encode an error signal that contributes to associative learning. Although considerable attention has been devoted to the mechanisms contributing to phasic increases in dopamine activity, less is known about the origin of the transient cessation in firing accompanying the unexpected loss of a predicted reward. Recent studies suggesting that the lateral habenula (LHb) may contribute to this type of signaling in humans prompted us to evaluate the effects of LHb stimulation on the activity of dopamine and non-dopamine neurons of the anesthetized rat. Single-pulse stimulation of the LHb (0.5 mA, 100 micros) transiently suppressed the activity of 97% of the dopamine neurons recorded in the substantia nigra and ventral tegmental area. The duration of the cessation averaged approximately 85 ms and did not differ between the two regions. Identical stimuli transiently excited 52% of the non-dopamine neurons in the ventral midbrain. Electrolytic lesions of the fasciculus retroflexus blocked the effects of LHb stimulation on dopamine neurons. Local application of bicuculline but not the SK-channel blocker apamin attenuated the effects of LHb stimulation on dopamine cells, indicating that the response is mediated by GABA(A) receptors. These data suggest that LHb-induced suppression of dopamine cell activity is mediated indirectly by orthodromic activation of putative GABAergic neurons in the ventral midbrain. The habenulomesencephalic pathway, which is capable of transiently suppressing the activity of dopamine neurons at a population level, may represent an important component of the circuitry involved in encoding reward expectancy.
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Affiliation(s)
- Huifang Ji
- Maryland Psychiatric Research Center and Department of Psychiatry, University of Maryland School of Medicine, Baltimore, Maryland 21228
| | - Paul D. Shepard
- Maryland Psychiatric Research Center and Department of Psychiatry, University of Maryland School of Medicine, Baltimore, Maryland 21228
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41
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Ozgen N, Dun W, Sosunov EA, Anyukhovsky EP, Hirose M, Duffy HS, Boyden PA, Rosen MR. Early electrical remodeling in rabbit pulmonary vein results from trafficking of intracellular SK2 channels to membrane sites. Cardiovasc Res 2007; 75:758-69. [PMID: 17588552 PMCID: PMC2034441 DOI: 10.1016/j.cardiores.2007.05.008] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2007] [Revised: 05/01/2007] [Accepted: 05/02/2007] [Indexed: 01/19/2023] Open
Abstract
OBJECTIVE Atrial fibrillation is often initiated by bursts of ectopic activity arising in the pulmonary veins. We have previously shown that a 3-h intermittent burst pacing protocol (BPP), mimicking ectopic pulmonary vein foci, shortens action potential duration (APD) locally at the pulmonary vein-atrial interface (PV) while having no effect elsewhere in rabbit atrium. This shortening is Ca(2+) dependent and is prevented by apamin, which blocks small conductance Ca(2+)-activated K(+) channels (SK(Ca)). The present study investigates the ionic and molecular mechanisms whereby two apamin-sensitive SK(Ca) channels, SK2 and SK3, might contribute to the regional APD changes. METHODS Microelectrode and patch clamp techniques were used to record APDs and apamin-sensitive currents in isolated rabbit left atria and cells dispersed from PV and Bachmann's bundle (BB) regions. SK2 and SK3 mRNA and protein levels were quantified, and immunofluorescence was used to observe channel protein distribution. RESULTS There was a direct relationship between APD shortening and apamin-sensitive current in burst-paced but not sham-paced PV. Moreover, apamin-sensitive current density increased in PV but not BB after BPP. SK2 mRNA, protein, and current were increased in PV after BPP, while SK2 immunostaining shifted from a perinuclear pattern in sham atria to predominance at sites near or at the PV membrane. CONCLUSIONS BPP-induced acceleration of repolarization in PV results from SK2 channel trafficking to the membrane, leading to increased apamin-sensitive outward current. This is the first indication of involvement of Ca(2+)-activated K(+) currents in atrial remodeling and provides a possible basis for evolution of an arrhythmogenic substrate.
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Affiliation(s)
- Nazira Ozgen
- Center for Molecular Therapeutics, Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York, New York 10032, USA
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Kaplan N, Morpurgo N, Linial M. Novel families of toxin-like peptides in insects and mammals: a computational approach. J Mol Biol 2007; 369:553-66. [PMID: 17433819 DOI: 10.1016/j.jmb.2007.02.106] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2006] [Revised: 02/14/2007] [Accepted: 02/21/2007] [Indexed: 11/19/2022]
Abstract
Most animal toxins are short proteins that appear in venom and vary in sequence, structure and function. A common characteristic of many such toxins is their apparent structural stability. Sporadic instances of endogenous toxin-like proteins that function in non-venom context have been reported. We have utilized machine learning methodology, based on sequence-derived features and guided by the notion of structural stability, in order to conduct a large-scale search for toxin and toxin-like proteins. Application of the method to insect and mammalian sequences revealed novel families of toxin-like proteins. One of these proteins shows significant similarity to ion channel inhibitors that are expressed in cone snail and assassin bug venom, and is surprisingly expressed in the bee brain. A toxicity assay in which the protein was injected to fish induced a strong yet reversible paralytic effect. We suggest that the protein may function as an endogenous modulator of voltage-gated Ca(2+) channels. Additionally, we have identified a novel mammalian cluster of toxin-like proteins that are expressed in the testis. We suggest that these proteins might be involved in regulation of nicotinic acetylcholine receptors that affect the acrosome reaction and sperm motility. Finally, we highlight a possible evolutionary link between venom toxins and antibacterial proteins. We expect our methodology to enhance the discovery of additional novel protein families.
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Affiliation(s)
- Noam Kaplan
- Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University, Jerusalem, Israel.
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Chen YN, Li KC, Li Z, Shang GW, Liu DN, Lu ZM, Zhang JW, Ji YH, Gao GD, Chen J. Effects of bee venom peptidergic components on rat pain-related behaviors and inflammation. Neuroscience 2006; 138:631-40. [PMID: 16446039 DOI: 10.1016/j.neuroscience.2005.11.022] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2005] [Revised: 11/11/2005] [Accepted: 11/17/2005] [Indexed: 11/25/2022]
Abstract
To identify the active components of honeybee venom in production of inflammation and pain-related behaviors, five major peptidergic subfractions were separated, purified and identified from the whole honeybee venom. Among them, four active peptidergic components were characterized as apamin, mast-cell degranulating peptide (MCDP), phospholipase A(2) (PLA(2))-related peptide and melittin, respectively. All five subfractions were effective in production of local inflammatory responses (paw edema) in rats although the efficacies were different. Among the five identified subfractions, only MCDP, PLA(2)-related peptide and melittin were able to produce ongoing pain-related behaviors shown as paw flinches, while only apamin and melittin were potent to produce both thermal and mechanical hypersensitivity. As shown in our previous report, melittin was the most potent polypeptide in production of local inflammation as well as ongoing pain and hypersensitivity. To further explore the peripheral mechanisms underlying melittin-induced nociception and hypersensitivity, a single dose of capsazepine, a blocker of thermal nociceptor transient receptor potential vanilloid receptor 1, was treated s.c. prior to or after melittin administration. The results showed that both pre- and post-treatment of capsazepine could significantly prevent and suppress the melittin-induced ongoing nociceptive responses and thermal hypersensitivity, but were without influencing mechanical hypersensitivity. The present results suggest that the naturally occurring peptidergic substances of the whole honeybee venom have various pharmacological potencies to produce local inflammation, nociception and pain hypersensitivity in mammals, and among the five identified reverse-phase high pressure liquid chromatography subfractions (four polypeptides), melittin, a polypeptide occupying over 50% of the whole honeybee venom, plays a central role in production of local inflammation, nociception and hyperalgesia or allodynia following the experimental honeybee's sting. Peripheral transient receptor potential vanilloid receptor 1 is likely to be involved in melittin-produced ongoing pain and heat hyperalgesia, but not mechanical hyperalgesia, in rats.
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Affiliation(s)
- Y-N Chen
- Institute for Functional Brain Disorders and Institute for Biomedical Sciences of Pain, Tangdu Hospital, Fourth Military Medical University, #1 Xinsi Road, Baqiao, Xi'an 710038, PR China
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Mpari B, Regaya I, Escoffier G, Mourre C. Differential effects of two blockers of small conductance Ca2+-activated K+ channels, apamin and lei-Dab7, on learning and memory in rats. J Integr Neurosci 2006; 4:381-96. [PMID: 16178064 DOI: 10.1142/s0219635205000884] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2004] [Accepted: 08/08/2005] [Indexed: 11/18/2022] Open
Abstract
SK channels are responsible for long-lasting hyperpolarization following action potential and contribute to the neuronal integration signal. This study evaluates the involvement of SK channels on learning and memory in rats, by comparing the effects of two SK channel blockers, i.e., apamin which recognizes SK2 and SK3 channels, and lei-Dab7 which binds SK2 channels only. lei-Dab7 totally competes and contests apamin binding on whole brain sections (IC(50): 11.4 nM). Using an olfactory associative task, intracerebroventricular blocker injections were tested on reference memory. Once the task was mastered with one odor pair, it was then tested with a new odor pair. Apamin (0.3 ng), injected before or after the acquisition session, improved new odor pair learning in a retention session 24 hours later, whereas lei-Dab7 (3 ng) did not significantly affect the mnesic processes. These results indicated that the blockage of SK channels by apamin facilitates consolidation on new odor associations; lei-Dab7, containing only SK2 subunits, remains without effect suggesting an involvement of SK3 channels in the modulation of the mnesic processes.
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Affiliation(s)
- Bedel Mpari
- Laboratoire de Neurobiologie Intégrative et Adaptative, Neurobiologie des Processus Mnésiques, UMR 6149, CNRS-Université de Provence, Marseille, France
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Zalat S, Elbana S, Rizzoli S, Schmidt JO, Mellor IR. Modulation of nicotinic acetylcholine and N-methyl-d-aspartate receptors by some Hymenopteran venoms. Toxicon 2005; 46:282-90. [PMID: 15970304 DOI: 10.1016/j.toxicon.2005.04.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2005] [Accepted: 04/14/2005] [Indexed: 11/28/2022]
Abstract
The effect of 19 venoms from solitary wasps, solitary bees, social wasps and ants were investigated for their effects on nicotinic acetylcholine receptors (nAChR) and ionotropic glutamate receptors (IGRs) of both the N-methyl-d-aspartate (NMDAR) and non-NMDAR type. Whole-cell patch clamp of human muscle TE671 cells was used to study nAChR, and of rat cortical and cerebellar granule cells for IGRs. Solitary wasp venoms caused significant voltage-dependent antagonism of nAChR responses to 10 microM ACh and NMDAR responses to 100 microM NMDA (+10 microM glycine) when co-applied at 1 microg/ml with the agonists. At positive holding potentials (V(H)) potentiation of these receptors was observed with some venoms. Solitary bee venoms only affected nAChR by causing either voltage-independent antagonism or potentiation of their responses to 10 microM ACh. Of four social wasp venoms, one acted on nAChR by potentiating responses to 10 ACh, while another generated an ACh-like response when applied alone. They had no effect on IGRs. Of the two ant venoms, one caused voltage-independent inhibition of nAChR. Neither affected IGRs. The data indicate the presence of nAChR agonists and antagonists and NMDAR antagonists in Hymenopteran venoms and warrant further investigation to separate and identify these venom components.
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Affiliation(s)
- Samy Zalat
- Department of Zoology, Suez Canal University, Ismailia, Egypt; School of Biology, University of Nottingham, University Park, Nottingham NG7 2RD, UK
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46
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Limón A, Pérez C, Vega R, Soto E. Ca2+-activated K+-current density is correlated with soma size in rat vestibular-afferent neurons in culture. J Neurophysiol 2005; 94:3751-61. [PMID: 16107534 DOI: 10.1152/jn.00177.2005] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Vestibular-afferent neurons (VANs) transmit information about linear and angular accelerations during head movements from vestibular end organs to vestibular nuclei. In situ, these neurons show heterogeneous discharge patterns that may be produced by differences in their intrinsic properties. However, little is known about the ionic currents underlying their different firing patterns. Using the whole cell patch-clamp technique, we analyzed the expression of Ca(2+) and Ca(2+)-activated K(+) currents (I(KCa)) in primary cultured neurons isolated from young rats (p7-p10). We found two overlapping subpopulations of VANs classified according to low-threshold Ca(2+)-current [low-voltage-activated (LVA)] expression; LVA (-) neurons, formed by small cells, and LVA (+) neurons composed of medium to large cells. The I(KCa) in both cell-groups was carried through channels of high (BK), intermediate (IK), and low conductance (SK), besides a resistant channel to classical blockers (IR). BK was expressed preferentially in LVA (+) cells, whereas IR expression was preferentially in LVA (-) cells. No correlation between SK and IK expression with the soma size was found. Current-clamp experiments showed that BK participates in the adaptation of discharge and in the duration of the action potential, whereas SK and IK did not show a significant contribution to electrical discharge of cultured VANs. However, because of the low number of VANs in culture with repetitive firing it is difficult to interpret our results in terms of discharge patterns. Our results demonstrate that vestibular-afferent neurons possess different Ca(2+)-activated K(+) (K(Ca)) channels and that their expression, heterogeneous among the cells, would contribute to explain some of the differences in the electrical-firing properties of these neurons.
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MESH Headings
- 4-Aminopyridine/pharmacology
- Action Potentials/drug effects
- Action Potentials/physiology
- Action Potentials/radiation effects
- Animals
- Animals, Newborn
- Apamin/pharmacology
- Calcium/metabolism
- Cell Size
- Cells, Cultured
- Charybdotoxin/pharmacology
- Clotrimazole/pharmacology
- Dose-Response Relationship, Radiation
- Drug Interactions
- Electric Capacitance
- Electric Stimulation/methods
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Membrane Potentials/radiation effects
- Neurons, Afferent/cytology
- Neurons, Afferent/drug effects
- Neurons, Afferent/physiology
- Neurons, Afferent/radiation effects
- Neurotoxins/pharmacology
- Patch-Clamp Techniques/methods
- Peptides/pharmacology
- Potassium Channel Blockers/pharmacology
- Potassium Channels, Calcium-Activated/physiology
- Rats
- Rats, Wistar
- Tetraethylammonium/pharmacology
- Tetrodotoxin/pharmacology
- Vestibule, Labyrinth/cytology
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Affiliation(s)
- Agenor Limón
- Institute of Physiology, Autonomous University of Puebla, Mexico.
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47
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Smith GT. Pharmacological characterization of ionic currents that regulate high-frequency spontaneous activity of electromotor neurons in the weakly electric fish,Apteronotus leptorhynchus. ACTA ACUST UNITED AC 2005; 66:1-18. [PMID: 16187302 DOI: 10.1002/neu.20202] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The neural circuit that controls the electric organ discharge (EOD) of the brown ghost knifefish (Apteronotus leptorhynchus) contains two spontaneous oscillators. Both pacemaker neurons in the medulla and electromotor neurons (EMNs) in the spinal cord fire spontaneously at frequencies of 500-1,000 Hz to control the EOD. These neurons continue to fire in vitro at frequencies that are highly correlated with in vivo EOD frequency. Previous studies used channel blocking drugs to pharmacologically characterize ionic currents that control high-frequency firing in pacemaker neurons. The goal of the present study was to use similar techniques to investigate ionic currents in EMNs, the other type of spontaneously active neuron in the electromotor circuit. As in pacemaker neurons, high-frequency firing of EMNs was regulated primarily by tetrodotoxin-sensitive sodium currents and by potassium currents that were sensitive to 4-aminopyridine and kappaA-conotoxin SIVA, but resistant to tetraethylammonium. EMNs, however, differed from pacemaker neurons in their sensitivity to some channel blocking drugs. Alpha-dendrotoxin, which blocks a subset of Kv1 potassium channels, increased firing rates in EMNs, but not pacemaker neurons; and the sodium channel blocker muO-conotoxin MrVIA, which reduced firing rates of pacemaker neurons, had no effect on EMNs. These results suggest that similar, but not identical, ionic currents regulate high-frequency firing in EMNs and pacemaker neurons. The differences in the ionic currents expressed in pacemaker neurons and EMNs might be related to differences in the morphology, connectivity, or function of these two cell types.
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Affiliation(s)
- G Troy Smith
- Department of Biology, Center for the Integrative Study of Animal Behavior, and Program in Neuroscience, Indiana University, Bloomington, 47405, USA.
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48
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Lee SY, MacKinnon R. A membrane-access mechanism of ion channel inhibition by voltage sensor toxins from spider venom. Nature 2004; 430:232-5. [PMID: 15241419 DOI: 10.1038/nature02632] [Citation(s) in RCA: 222] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2004] [Accepted: 05/05/2004] [Indexed: 11/08/2022]
Abstract
Venomous animals produce small protein toxins that inhibit ion channels with high affinity. In several well-studied cases the inhibitory proteins are water-soluble and bind at a channel's aqueous-exposed extracellular surface. Here we show that a voltage-sensor toxin (VSTX1) from the Chilean Rose Tarantula (Grammostola spatulata) reaches its target by partitioning into the lipid membrane. Lipid membrane partitioning serves two purposes: to localize the toxin in the membrane where the voltage sensor resides and to exploit the free energy of partitioning to achieve apparent high-affinity inhibition. VSTX1, small hydrophobic poisons and anaesthetic molecules reveal a common theme of voltage sensor inhibition through lipid membrane access. The apparent requirement for such access is consistent with the recent proposal that the sensor in voltage-dependent K+ channels is located at the membrane-protein interface.
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Affiliation(s)
- Seok-Yong Lee
- The Howard Hughes Medical Institute and Rockefeller University, 1230 York Avenue, New York, New York 10021, USA
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Diochot S, Baron A, Rash LD, Deval E, Escoubas P, Scarzello S, Salinas M, Lazdunski M. A new sea anemone peptide, APETx2, inhibits ASIC3, a major acid-sensitive channel in sensory neurons. EMBO J 2004; 23:1516-25. [PMID: 15044953 PMCID: PMC391081 DOI: 10.1038/sj.emboj.7600177] [Citation(s) in RCA: 289] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2003] [Accepted: 02/25/2004] [Indexed: 01/23/2023] Open
Abstract
From a systematic screening of animal venoms, we isolated a new toxin (APETx2) from the sea anemone Anthopleura elegantissima, which inhibits ASIC3 homomeric channels and ASIC3-containing heteromeric channels both in heterologous expression systems and in primary cultures of rat sensory neurons. APETx2 is a 42 amino-acid peptide crosslinked by three disulfide bridges, with a structural organization similar to that of other sea anemone toxins that inhibit voltage-sensitive Na+ and K+ channels. APETx2 reversibly inhibits rat ASIC3 (IC50=63 nM), without any effect on ASIC1a, ASIC1b, and ASIC2a. APETx2 directly inhibits the ASIC3 channel by acting at its external side, and it does not modify the channel unitary conductance. APETx2 also inhibits heteromeric ASIC2b+3 current (IC50=117 nM), while it has less affinity for ASIC1b+3 (IC50=0.9 microM), ASIC1a+3 (IC50=2 microM), and no effect on the ASIC2a+3 current. The ASIC3-like current in primary cultured sensory neurons is partly and reversibly inhibited by APETx2 with an IC50 of 216 nM, probably due to the mixed inhibitions of various co-expressed ASIC3-containing channels.
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Affiliation(s)
- Sylvie Diochot
- Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Anne Baron
- Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Lachlan D Rash
- Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Emmanuel Deval
- Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Pierre Escoubas
- Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Sabine Scarzello
- Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Miguel Salinas
- Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Michel Lazdunski
- Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
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50
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Presynaptic capacitance measurements and Ca2+ uncaging reveal submillisecond exocytosis kinetics and characterize the Ca2+ sensitivity of vesicle pool depletion at a fast CNS synapse. J Neurosci 2003. [PMID: 12904466 DOI: 10.1523/jneurosci.23-18-07059.2003] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The intracellular Ca2+ sensitivity of synaptic vesicle fusion is an important determinant of transmitter release probability, but it is unknown for most CNS synapses. We combined whole-cell membrane capacitance measurements and Ca2+ uncaging at the large calyx of Held nerve terminals to determine the Ca2+ sensitivity of synaptic vesicle fusion at a glutamatergic CNS synapse, independent of recording EPSCs. Capacitance increases measured 30-50 msec after elevating the intracellular Ca2+ concentration ([Ca2+]i) by Ca2+ uncaging were half-maximal at approximately 5 microm [Ca2+]i. At 10 microm [Ca2+]i, capacitance increases reached maximal values (256 +/- 125 fF; mean +/- SD), indicating the depletion of an average pool of approximately 4000 readily releasable vesicles. Vesicle pool depletion was confirmed in cross-depletion experiments, in which capacitance responses were measured after Ca2+ uncaging, or after combined stimuli of prolonged presynaptic depolarizations and Ca2+ uncaging. To analyze the Ca2+-dependent rates of vesicle pool depletion, the capacitance rise after Ca2+ uncaging was fitted with single- or double-exponential functions. The fast time constants of double-exponential fits, and the time constants of single-exponential fits were 2-3 msec at 10-15 microm [Ca2+]i and reached submillisecond values at 30 microm [Ca2+]i. These results suggest that three to five readily releasable vesicles can fuse within <1 msec at each active zone of a calyx of Held, given that [Ca2+]i rises sufficiently high. Submillisecond kinetics of exocytosis are reached at significantly lower [Ca2+]i than at ribbon-type sensory synapses previously investigated by capacitance measurements.
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