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Schwartz AB, Kapur A, Huang Z, Anangi R, Spear JM, Stagg S, Fardone E, Dekan Z, Rosenberg JT, Grant SC, King GF, Mattoussi H, Fadool DA. Olfactory bulb-targeted quantum dot (QD) bioconjugate and Kv1.3 blocking peptide improve metabolic health in obese male mice. J Neurochem 2020; 157:1876-1896. [PMID: 32978815 DOI: 10.1111/jnc.15200] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 09/15/2020] [Accepted: 09/16/2020] [Indexed: 01/10/2023]
Abstract
The olfactory system is a driver of feeding behavior, whereby olfactory acuity is modulated by the metabolic state of the individual. The excitability of the major output neurons of the olfactory bulb (OB) can be modulated through targeting a voltage-dependent potassium channel, Kv1.3, which responds to changes in metabolic factors such as insulin, glucose, and glucagon-like peptide-1. Because gene-targeted deletion or inhibition of Kv1.3 in the periphery has been found to increase energy metabolism and decrease body weight, we hypothesized that inhibition of Kv1.3 selectively in the OB could enhance excitability of the output neurons to evoke changes in energy homeostasis. We thereby employed metal-histidine coordination to self-assemble the Kv1.3 inhibitor margatoxin (MgTx) to fluorescent quantum dots (QDMgTx) as a means to label cells in vivo and test changes in neuronal excitability and metabolism when delivered to the OB. Using patch-clamp electrophysiology to measure Kv1.3 properties in heterologously expressed cells and native mitral cells in OB slices, we found that QDMgTx had a fast rate of inhibition, but with a reduced IC50, and increased action potential firing frequency. QDMgTx was capable of labeling cloned Kv1.3 channels but was not visible when delivered to native Kv1.3 in the OB. Diet-induced obese mice were observed to reduce body weight and clear glucose more quickly following osmotic mini-pump delivery of QDMgTx/MgTx to the OB, and following MgTx delivery, they increased the use of fats as fuels (reduced respiratory exchange ratio). These results suggest that enhanced excitability of bulbar output neurons can drive metabolic responses.
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Affiliation(s)
- Austin B Schwartz
- Institute of Molecular Biophysics, The Florida State University, Tallahassee, FL, USA
| | - Anshika Kapur
- Department of Chemistry and Biochemistry, The Florida State University, Tallahassee, FL, USA
| | - Zhenbo Huang
- Program in Neuroscience, The Florida State University, Tallahassee, FL, USA.,Department of Biological Science, The Florida State University, Tallahassee, FL, USA
| | - Raveendra Anangi
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - John M Spear
- Department of Chemistry and Biochemistry, The Florida State University, Tallahassee, FL, USA.,Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Scott Stagg
- Department of Chemistry and Biochemistry, The Florida State University, Tallahassee, FL, USA.,Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Erminia Fardone
- Program in Neuroscience, The Florida State University, Tallahassee, FL, USA
| | - Zolan Dekan
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Jens T Rosenberg
- National High Field Magnetic Laboratory, The Florida State University, Tallahassee, FL, USA
| | - Samuel C Grant
- National High Field Magnetic Laboratory, The Florida State University, Tallahassee, FL, USA.,Department of Chemical & Biomedical Engineering, FAMU-FSU College of Engineering, Florida State University, Tallahassee, FL, USA
| | - Glenn F King
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Hedi Mattoussi
- Department of Chemistry and Biochemistry, The Florida State University, Tallahassee, FL, USA
| | - Debra Ann Fadool
- Institute of Molecular Biophysics, The Florida State University, Tallahassee, FL, USA.,Program in Neuroscience, The Florida State University, Tallahassee, FL, USA.,Department of Biological Science, The Florida State University, Tallahassee, FL, USA
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2
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Barnes EA, Lee L, Barnes SL, Brenner R, Alvira CM, Cornfield DN. β1-Subunit of the calcium-sensitive potassium channel modulates the pulmonary vascular smooth muscle cell response to hypoxia. Am J Physiol Lung Cell Mol Physiol 2018; 315:L265-L275. [PMID: 29644895 PMCID: PMC6139656 DOI: 10.1152/ajplung.00060.2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Revised: 04/04/2018] [Accepted: 04/05/2018] [Indexed: 11/22/2022] Open
Abstract
Accessory subunits associated with the calcium-sensitive potassium channel (BKCa), a major determinant of vascular tone, confer functional and anatomical diversity. The β1 subunit increases Ca2+ and voltagesensitivity of the BKCa channel and is expressed exclusively in smooth muscle cells. Evidence supporting the physiological significance of the β1 subunit includes the observations that murine models with deletion of the β1 subunit are hypertensive and that humans with a gain-of-function β1 mutation are at a decreased risk of diastolic hypertension. However, whether the β1 subunit of the BKCa channel contributes to the low tone that characterizes the normal pulmonary circulation or modulates the pulmonary vascular response to hypoxia remains unknown. To determine the role of the BKCa channel β1 subunit in the regulation of pulmonary vascular tone and the response to acute and chronic hypoxia, mice with deletion of the Kcnmb1 gene that encodes for the β1 subunit ( Kcnmb1-/-) were placed in chronic hypoxia (10% O2) for 21-24 days. In normoxia, right ventricular systolic pressure (RVSP) did not differ between Kcnmb1+/+ (controls) and Kcnmb1-/- mice. After exposure to either acute or chronic hypoxia, RVSP was higher in Kcnmb1-/- mice compared with Kcnmb1+/+ mice, without increased vascular remodeling. β1 subunit expression was predominantly confined to pulmonary artery smooth muscle cells (PASMCs) from vessels ≤ 150 µm. Peripheral PASMCs contracted collagen gels irrespective of β1 expression. Focal adhesion expression and Rho kinase activity were greater in Kcnmb1-/- compared with Kcnmb1+/+ PASMCs. Compromised PASMC β1 function may contribute to the heightened microvascular vasoconstriction that characterizes pulmonary hypertension.
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MESH Headings
- Acute Disease
- Animals
- Chronic Disease
- Focal Adhesions/genetics
- Focal Adhesions/metabolism
- Focal Adhesions/pathology
- Gene Deletion
- Hypertension, Pulmonary/genetics
- Hypertension, Pulmonary/metabolism
- Hypertension, Pulmonary/pathology
- Hypoxia/genetics
- Hypoxia/metabolism
- Hypoxia/pathology
- Large-Conductance Calcium-Activated Potassium Channel beta Subunits/genetics
- Large-Conductance Calcium-Activated Potassium Channel beta Subunits/metabolism
- Lung/blood supply
- Lung/metabolism
- Lung/pathology
- Mice
- Mice, Knockout
- Muscle, Smooth, Vascular/metabolism
- Muscle, Smooth, Vascular/pathology
- Myocytes, Smooth Muscle/metabolism
- Myocytes, Smooth Muscle/pathology
- Pulmonary Artery/metabolism
- Pulmonary Artery/pathology
- Vasoconstriction
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Affiliation(s)
- Elizabeth A Barnes
- Division of Pulmonary Medicine, Department of Pediatrics, Stanford University School of Medicine , Stanford, California
| | - Lori Lee
- Division of Pulmonary Medicine, Department of Pediatrics, Stanford University School of Medicine , Stanford, California
| | - Shayna L Barnes
- Division of Pulmonary Medicine, Department of Pediatrics, Stanford University School of Medicine , Stanford, California
| | - Robert Brenner
- Department of Cellular and Integrative Physiology, School of Medicine, University of Texas Health Sciences Center , San Antonio, Texas
| | - Cristina M Alvira
- Division of Pulmonary Medicine, Department of Pediatrics, Stanford University School of Medicine , Stanford, California
- Division of Critical Care Medicine, Department of Pediatrics, Stanford University School of Medicine , Stanford, California
| | - David N Cornfield
- Division of Pulmonary Medicine, Department of Pediatrics, Stanford University School of Medicine , Stanford, California
- Division of Critical Care Medicine, Department of Pediatrics, Stanford University School of Medicine , Stanford, California
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3
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The effect of 1,25 dihydroxyvitamin D3 on HCl/Ethanol-induced gastric injury in rats. Tissue Cell 2018; 51:68-76. [DOI: 10.1016/j.tice.2018.03.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 02/12/2018] [Accepted: 03/03/2018] [Indexed: 12/11/2022]
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4
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Zou X, He Y, Qiao J, Zhang C, Cao Z. The natural scorpion peptide, BmK NT1 activates voltage-gated sodium channels and produces neurotoxicity in primary cultured cerebellar granule cells. Toxicon 2016; 109:33-41. [DOI: 10.1016/j.toxicon.2015.11.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Revised: 09/15/2015] [Accepted: 11/05/2015] [Indexed: 11/26/2022]
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5
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Kudo T, Block GD, Colwell CS. The Circadian Clock Gene Period1 Connects the Molecular Clock to Neural Activity in the Suprachiasmatic Nucleus. ASN Neuro 2015; 7:7/6/1759091415610761. [PMID: 26553726 PMCID: PMC4710129 DOI: 10.1177/1759091415610761] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The neural activity patterns of suprachiasmatic nucleus (SCN) neurons are dynamically regulated throughout the circadian cycle with highest levels of spontaneous action potentials during the day. These rhythms in electrical activity are critical for the function of the circadian timing system and yet the mechanisms by which the molecular clockwork drives changes in the membrane are not well understood. In this study, we sought to examine how the clock gene Period1 (Per1) regulates the electrical activity in the mouse SCN by transiently and selectively decreasing levels of PER1 through use of an antisense oligodeoxynucleotide. We found that this treatment effectively reduced SCN neural activity. Direct current injection to restore the normal membrane potential partially, but not completely, returned firing rate to normal levels. The antisense treatment also reduced baseline [Ca2+]i levels as measured by Fura2 imaging technique. Whole cell patch clamp recording techniques were used to examine which specific potassium currents were altered by the treatment. These recordings revealed that the large conductance [Ca2+]i-activated potassium currents were reduced in antisense-treated neurons and that blocking this current mimicked the effects of the anti-sense on SCN firing rate. These results indicate that the circadian clock gene Per1 alters firing rate in SCN neurons and raise the possibility that the large conductance [Ca2+]i-activated channel is one of the targets.
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Affiliation(s)
- Takashi Kudo
- Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, CA, USA
| | - Gene D Block
- Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, CA, USA
| | - Christopher S Colwell
- Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, CA, USA
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Gastroprotective activity of violacein isolated from Chromobacterium violaceum on indomethacin-induced gastric lesions in rats: investigation of potential mechanisms of action. ScientificWorldJournal 2014; 2014:616432. [PMID: 25162059 PMCID: PMC4138890 DOI: 10.1155/2014/616432] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Revised: 06/18/2014] [Accepted: 06/26/2014] [Indexed: 12/21/2022] Open
Abstract
Chromobacterium violaceum, Gram-negative bacteria species found in tropical regions of the world, produces a distinct deep violet-colored pigment called violacein. In the present study, we investigated whether violacein can promote a gastroprotective effect and verified the possible mechanisms involved in this action. For this study, an indomethacin-induced gastric ulcer rat model was used. The roles of biomolecules such as MPO, PGE2, pro- and anti-inflammatory cytokines, growth factors, caspase-3, NO, K+ATP channels, and α2-receptors were investigated. Violacein exhibited significant gastroprotective effect against indomethacin-induced lesions, while pretreatment with L-NAME and glibenclamide (but not with NEM or yohimbine) was able to reverse this action. Pretreatment with violacein also restored cNOS level to normal and led to attenuation of enhanced apoptosis and gastric microvascular permeability. Our results suggest that violacein provides a significant gastroprotective effect in an indomethacin-induced ulcer model through the maintenance of some vital protein molecules, and this effect appears to be mediated, at least in part, by endogenous prostaglandins, NOS, K+ATP channel opening, and inhibition of apoptosis and gastric microvascular permeability.
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Kalia J, Milescu M, Salvatierra J, Wagner J, Klint JK, King GF, Olivera BM, Bosmans F. From foe to friend: using animal toxins to investigate ion channel function. J Mol Biol 2014; 427:158-175. [PMID: 25088688 DOI: 10.1016/j.jmb.2014.07.027] [Citation(s) in RCA: 125] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Revised: 07/18/2014] [Accepted: 07/18/2014] [Indexed: 12/19/2022]
Abstract
Ion channels are vital contributors to cellular communication in a wide range of organisms, a distinct feature that renders this ubiquitous family of membrane-spanning proteins a prime target for toxins found in animal venom. For many years, the unique properties of these naturally occurring molecules have enabled researchers to probe the structural and functional features of ion channels and to define their physiological roles in normal and diseased tissues. To illustrate their considerable impact on the ion channel field, this review will highlight fundamental insights into toxin-channel interactions and recently developed toxin screening methods and practical applications of engineered toxins.
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Affiliation(s)
- Jeet Kalia
- Indian Institute of Science Education and Research Pune; Pune, Maharashtra 411 008 India
| | - Mirela Milescu
- Division of Biological Sciences; University of Missouri, Columbia, MO 65211 USA
| | - Juan Salvatierra
- Department of Physiology; Johns Hopkins University, School of Medicine, Baltimore, MD 21205 USA
| | - Jordan Wagner
- Department of Physiology; Johns Hopkins University, School of Medicine, Baltimore, MD 21205 USA
| | - Julie K Klint
- Institute for Molecular Bioscience; The University of Queensland, St. Lucia, QLD 4072 Australia
| | - Glenn F King
- Institute for Molecular Bioscience; The University of Queensland, St. Lucia, QLD 4072 Australia
| | | | - Frank Bosmans
- Department of Physiology; Johns Hopkins University, School of Medicine, Baltimore, MD 21205 USA.,Solomon H. Snyder Department of Neuroscience; Johns Hopkins University, School of Medicine, Baltimore, MD 21205 USA
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8
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Banerjee A, Lee A, Campbell E, Mackinnon R. Structure of a pore-blocking toxin in complex with a eukaryotic voltage-dependent K(+) channel. eLife 2013; 2:e00594. [PMID: 23705070 PMCID: PMC3660741 DOI: 10.7554/elife.00594] [Citation(s) in RCA: 161] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Accepted: 04/12/2013] [Indexed: 11/26/2022] Open
Abstract
Pore-blocking toxins inhibit voltage-dependent K+ channels (Kv channels) by plugging the ion-conduction pathway. We have solved the crystal structure of paddle chimera, a Kv channel in complex with charybdotoxin (CTX), a pore-blocking toxin. The toxin binds to the extracellular pore entryway without producing discernable alteration of the selectivity filter structure and is oriented to project its Lys27 into the pore. The most extracellular K+ binding site (S1) is devoid of K+ electron-density when wild-type CTX is bound, but K+ density is present to some extent in a Lys27Met mutant. In crystals with Cs+ replacing K+, S1 electron-density is present even in the presence of Lys27, a finding compatible with the differential effects of Cs+ vs K+ on CTX affinity for the channel. Together, these results show that CTX binds to a K+ channel in a lock and key manner and interacts directly with conducting ions inside the selectivity filter. DOI:http://dx.doi.org/10.7554/eLife.00594.001 The deadly toxins produced by many creatures, including spiders, snakes, and scorpions, work by blocking the ion channels that are essential for the normal operation of many different types of cells. Ion channels are proteins and, as their name suggests, they allow ions—usually sodium, potassium, or calcium ions—to move in and out of cells. They are especially important for cells that generate or respond to electrical signals, such as neurons and the cells in heart muscle. Ion channels are located in the lipid membranes that surround all cells, and the ions enter or leave the cell via a pore that runs through the channel protein. They can be opened and closed (or ‘gated’) in different ways: some ion channels open and close in response to voltages, whereas others are gated by biomolecules, such as neurotransmitters, that bind to them. Now, Banerjee et al. have used x-ray crystallography to study the structure of the complex that is formed when charybdotoxin (CTX), a toxin that is found in scorpion venom, blocks a voltage-gated potassium channel. Previous studies have shown that CTX binds to the channel on the extracellular side of the pore. Banerjee et al. show that the toxin fits into the entrance to the channel like a key into a lock, which means the toxin is preformed to fit the shape of the channel. The potassium ion channel is made up of four subunits, and the pore contains four ion-binding sites that form a ‘selectivity filter’: it is this filter that ensures that only potassium ions can pass through the channel when it is open. When CTX binds to the channel, a lysine residue poised at a critical position on the toxin is so close to the outermost ion-binding site that it prevents potassium ions binding to the site. The structure determined by Banerjee et al. explains many previous findings, including the fact that ions entering the pore from inside the cell can disrupt the binding between the toxin and the ion channel protein. It remains to be seen if the toxins that target the pore of other types of ion channels work in the same way. DOI:http://dx.doi.org/10.7554/eLife.00594.002
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Affiliation(s)
- Anirban Banerjee
- Laboratory of Molecular Neurobiology and Biophysics , Rockefeller University , New York , United States ; Howard Hughes Medical Institute, Rockefeller University , New York , United States
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9
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Lozos VA, Toumpoulis IK, Agrogiannis G, Giamarellos-Bourboulis EJ, Chamogeorgakis TP, Rizos IK, Patsouris ES, Anagnostopoulos CE, Rokkas CK. Aprikalim a potassium adenosine triphosphate channel opener reduces neurologic injury in a rabbit model of spinal cord ischemia. Int J Surg 2013; 11:354-9. [PMID: 23473993 DOI: 10.1016/j.ijsu.2013.02.025] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2012] [Revised: 01/30/2013] [Accepted: 02/23/2013] [Indexed: 11/28/2022]
Abstract
BACKGROUND Potassium adenosine triphosphate (KATP) channel openers have been involved in the enhancement of ischemic tolerance in various tissues. The purpose of the present study is to evaluate the effects of aprikalim, a specific KATP channel opener, on spinal cord ischemic injury. METHODS Fifty-four rabbits were randomly assigned to three groups: group 1 (n = 18, sham operation), group 2 (n = 18, 30 min of normothermic aortic cross-clamping) and group 3 (n = 18, aprikalim 100 μg/kg was administered 15 min before 30 min of normothermic aortic cross-clamping). Neurologic evaluation was performed according to the modified Tarlov scale. Six animals from each group were sacrificed at 24, 48 and 168 h postoperatively. The lumbar spinal cords were harvested and examined histologically. The motor neurons were counted and the histologic lesions were scored (0-3, 3: normal). RESULTS Group 3 (aprikalim group) had better Tarlov scores compared to group 2 at all-time points (P < 0.025). The histologic changes were proportional to the Tarlov scores and group 3 had better functional outcome as compared to group 2 at 168 h (number of neurons: 21.2 ± 4.9 vs. 8.0 ± 2.7, P < 0.001 and histologic score: 1.67 ± 1.03 vs. 0.50 ± 0.55, P = 0.03). Although aprikalim exhibited improved effect on clinical and histologic neurologic outcome when compared to normothermic spinal cord ischemia, animals in group 3 had worse Tarlov score, reduced number of motor neurons and worse histologic score when compared to group 1 (sham operation) at 168 h (P = 0.003, P = 0.001 and P = 0.019 respectively). CONCLUSION Aprikalim reduces the severity of spinal cord ischemic injury in a rabbit model of spinal cord ischemia.
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Affiliation(s)
- Vasileios A Lozos
- Department of Cardiothoracic Surgery, National and Kapodistrian University of Athens Medical School, Attikon University Hospital Center, Rimini 1, Chaidari, Athens, Greece
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10
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Bergeron ZL, Bingham JP. Scorpion toxins specific for potassium (K+) channels: a historical overview of peptide bioengineering. Toxins (Basel) 2012. [PMID: 23202307 PMCID: PMC3509699 DOI: 10.3390/toxins4111082] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Scorpion toxins have been central to the investigation and understanding of the physiological role of potassium (K+) channels and their expansive function in membrane biophysics. As highly specific probes, toxins have revealed a great deal about channel structure and the correlation between mutations, altered regulation and a number of human pathologies. Radio- and fluorescently-labeled toxin isoforms have contributed to localization studies of channel subtypes in expressing cells, and have been further used in competitive displacement assays for the identification of additional novel ligands for use in research and medicine. Chimeric toxins have been designed from multiple peptide scaffolds to probe channel isoform specificity, while advanced epitope chimerization has aided in the development of novel molecular therapeutics. Peptide backbone cyclization has been utilized to enhance therapeutic efficiency by augmenting serum stability and toxin half-life in vivo as a number of K+-channel isoforms have been identified with essential roles in disease states ranging from HIV, T-cell mediated autoimmune disease and hypertension to various cardiac arrhythmias and Malaria. Bioengineered scorpion toxins have been monumental to the evolution of channel science, and are now serving as templates for the development of invaluable experimental molecular therapeutics.
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Affiliation(s)
- Zachary L Bergeron
- Department of Molecular Biosciences and Bioengineering, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa, Honolulu, HI 96822, USA.
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11
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Gastroprotective activity of carvacrol on experimentally induced gastric lesions in rodents. Naunyn Schmiedebergs Arch Pharmacol 2012; 385:899-908. [DOI: 10.1007/s00210-012-0771-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Accepted: 06/12/2012] [Indexed: 10/27/2022]
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12
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Santos Cerqueira G, dos Santos e Silva G, Rios Vasconcelos E, Fragoso de Freitas AP, Arcanjo Moura B, Silveira Macedo D, Lopes Souto A, Barbosa Filho JM, de Almeida Leal LK, de Castro Brito GA, Souccar C, de Barros Viana GS. Effects of hecogenin and its possible mechanism of action on experimental models of gastric ulcer in mice. Eur J Pharmacol 2012; 683:260-9. [DOI: 10.1016/j.ejphar.2012.02.043] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Revised: 02/18/2012] [Accepted: 02/26/2012] [Indexed: 10/28/2022]
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13
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Zhu L, Gao B, Luo L, Zhu S. Two dyad-free Shaker-type K⁺ channel blockers from scorpion venom. Toxicon 2012; 59:402-7. [PMID: 22239942 DOI: 10.1016/j.toxicon.2011.11.016] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Revised: 11/14/2011] [Accepted: 11/15/2011] [Indexed: 11/27/2022]
Abstract
Most of scorpion toxins affecting voltage-gated K⁺ channels (KTxs) contain a functional dyad composed of a lysine and an aromatic amino acid separated by a suitable distance. By means of two-electrode voltage clamp technique, we describe functional characterization of two Mesobuthus martensii KTxs (BmP02 and BmP03) without the dyad. These two toxins differ by only one single residue at site 16 (K16N) but they display differential affinities on insect and mammalian Shaker-type K⁺ channels expressed in Xenopus oocytes. At 1 μM concentration, BmP02 and BmP03 inhibited currents of rK(v)1.1, rK(v)1.2, rK(v)1.3, and Shaker IR, but lacked detectable activity on rK(v)1.4. The half-inhibitory concentrations (IC₅₀) of BmP02 for rK(v)1.1, rK(v)1.2, rK(v)1.3 and Shaker IR channels are 1.95 μM, 4.40 μM, 7 nM and 20.44 μM, respectively. For BmP03, the corresponding IC₅₀ values for these channels are 5.48 μM, 530 nM, 85.4 nM, and 4.64 μM, respectively. Affinity variation (more than 10-fold) between BmP02 and BmP03 on rK(v)1.3 indicates functional importance of a cationic side chain at site 16. A pH-dependent experiment and a double mutant cycle analysis suggest that the residue K16 resides on the channel-facing surface of the toxin and within 5 Å of rK(v)1.3 position 401. These two toxins block rK(v)1.3 in a weak voltage-dependent manner and both slightly shift the current activation curve to positive potentials. Our work is thus crucial to further understanding structure-function relationship of KTxs without a functional dyad.
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Affiliation(s)
- Limei Zhu
- Group of Animal Innate Immunity, State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, 1 Beichen West Road, Chaoyang District, Beijing 100101, China
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Bhagawati S, Sanjay S. Investigations on gastroprotective effect of citalopram, an antidepressant drug against stress and pyloric ligation induced ulcers. Pharmacol Rep 2011; 63:1413-26. [DOI: 10.1016/s1734-1140(11)70705-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2010] [Revised: 06/28/2011] [Indexed: 10/25/2022]
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Girasole AE, Palmer CP, Corrado SL, Marie Southerland E, Ardell JL, Hardwick JC. Angiotensin II potentiates adrenergic and muscarinic modulation of guinea pig intracardiac neurons. Am J Physiol Regul Integr Comp Physiol 2011; 301:R1391-9. [PMID: 21865545 DOI: 10.1152/ajpregu.00145.2011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The intrinsic cardiac plexus represents a major peripheral integration site for neuronal, hormonal, and locally produced neuromodulators controlling efferent neuronal output to the heart. This study examined the interdependence of norepinephrine, muscarinic agonists, and ANG II, to modulate intrinsic cardiac neuronal activity. Intracellular voltage recordings from whole-mount preparations of the guinea pig cardiac plexus were used to determine changes in active and passive electrical properties of individual intrinsic cardiac neurons. Application of either adrenergic or muscarinic agonists induced changes in neuronal resting membrane potentials, decreased afterhyperpolarization duration of single action potentials, and increased neuronal excitability. Adrenergic responses were inhibited by removal of extracellular calcium ions, while muscarinic responses were inhibited by application of TEA. The adrenergic responses were heterogeneous, responding to a variety of receptor-specific agonists (phenylephrine, clonidine, dobutamine, and terbutaline), although α-receptor agonists produced the most frequent responses. Application of ANG II alone produced a significant increase in excitability, while application of ANG II in combination with either adrenergic or muscarinic agonists produced a much larger potentiation of excitability. The ANG II-induced modulation of firing was blocked by the angiotensin type 2 (AT(2)) receptor inhibitor PD 123319 and was mimicked by the AT(2) receptor agonist CGP-42112A. AT(1) receptor blockade with telmasartin did not alter neuronal responses to ANG II. These data demonstrate that ANG II potentiates both muscarinically and adrenergically mediated activation of intrinsic cardiac neurons, doing so primarily via AT(2) receptor-dependent mechanisms. These neurohumoral interactions may be fundamental to regulation of neuronal excitability within the intrinsic cardiac nervous system.
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Saxena B, Krishnamurthy S, Singh S. Gastroprotective potential of risperidone, an atypical antipsychotic, against stress and pyloric ligation induced gastric lesions. Chem Biol Interact 2011; 190:155-64. [DOI: 10.1016/j.cbi.2011.02.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Revised: 02/01/2011] [Accepted: 02/04/2011] [Indexed: 12/29/2022]
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17
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Jimenez-Vargas JM, Restano-Cassulini R, Quintero-Hernández V, Gurrola GB, Possani LD. Recombinant expression of the toxic peptide ErgTx1 and role of Met35 on its stability and function. Peptides 2011; 32:560-7. [PMID: 20600425 DOI: 10.1016/j.peptides.2010.06.018] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2010] [Revised: 06/22/2010] [Accepted: 06/22/2010] [Indexed: 01/05/2023]
Abstract
Ergtoxin 1 (ErgTx1) is a 42 amino acid peptide purified from the venom of the Mexican scorpion Centruroides noxius Hoffmann, capable of blocking specifically human potassium channels of the ether-á-go-go-related gene family (hERG). This peptide binds to a partially overlapping site on the channel outer mouth, in which residues of the S5-P linker are critically involved. Here we describe results of site directed mutagenesis of the ErgTx1 gene and its heterologous expression in Escherichia coli. The recombinant products show the fundamental role played by methionine in position 35 (Met35) of the primary structure. Naturally oxidized Met35 decreases by three orders of magnitude the affinity of the peptide for the hERG1 channels. This result is quite relevant, because it shows two possible situations: either Met35 is involved in the proper folding of the molecule or it plays a direct role in the interaction with the channel, i.e., constitutes part of the interacting surfaces. These two situations were evaluated by preparing heterologously expressed ErgTx1 gene and a mutant containing alanine in position 35. Additionally circular dichroism measurements of both native and recombinant peptides were performed. The electrophysiological recordings and the structural values obtained by optical measurements, strongly support the idea that Met35 is indeed a key residue on the interacting surfaces of the toxin with the channels.
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Affiliation(s)
- J M Jimenez-Vargas
- Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, National Autonomous University of Mexico, Av. Universidad, 2001, P. O. Box 501-3, Cuernavaca 62210, Mexico.
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18
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Gastroprotective activity of isopulegol on experimentally induced gastric lesions in mice: investigation of possible mechanisms of action. Naunyn Schmiedebergs Arch Pharmacol 2009; 380:233-45. [PMID: 19479241 DOI: 10.1007/s00210-009-0429-5] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2008] [Accepted: 05/12/2009] [Indexed: 12/27/2022]
Abstract
The present study investigated whether isopulegol, a monoterpene present in essential oils of several aromatic plants, would be able to promote some gastroprotective effect and also verified the possible mechanisms involved in this action. For this study, ethanol- and indomethacin-induced gastric ulcer models in mice and histopathological assessment were used. The roles of NO, sulfhydryls (glutathione, GSH), ATP-sensitive K(+) channels (K(ATP) channels), and prostaglandins were also investigated. Isopulegol exhibited a dose-related gastroprotective effect against ethanol-induced lesions, while the pretreatment with glibenclamide and indomethacin [but not with N(G)-nitro-L-arginine methyl ester] were able to reverse this action. The pretreatment with isopulegol also restored GSH levels to normal levels and exhibited dose-related gastroprotective effect against indomethacin-induced ulcer. The results suggested that isopulegol presents significant gastroprotective effects in both ethanol- and indomethacin-induced ulcer models, which appear to be mediated, at least in part, by endogenous prostaglandins, K(ATP) channel opening, and antioxidant properties.
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Hu P, Sun L, Zhu ZQ, Hou XW, Wang S, Yu SS, Wang HL, Zhang P, Wang M, Niu LW, Teng MK, Ruan DY. Crystal structure of Natratoxin, a novel snake secreted phospholipaseA2 neurotoxin from Naja atra venom inhibiting A-type K+ currents. Proteins 2008; 72:673-83. [PMID: 18247353 DOI: 10.1002/prot.21964] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Snake secreted phospholipasesA2 (sPLA2s) are widely used as pharmacological tools to investigate their role in diverse pathophysiological processes. Some members of snake venom sPLA2s have been found to block voltage-activated K(+) channels (K(v) channels). However, most studies involved in their effects on ion channels were indirectly performed on motor nerve terminals while few studies were directly done on native neurons. Here, a novel snake sPLA2 peptide neurotoxin, Natratoxin, composed of 119 amino acid residues and purified from Naja atra venom was reported. It was characterized using whole-cell patch-clamp in acutely dissociated rat dorsal root ganglion (DRG) neurons. It was found to effectively inhibit A-type K(+) currents and cause alterations of channel gating characters, such as the shifts of steady-state activation and inactivation curves to hyperpolarization direction and changes of V(1/2) and slope factor. Therefore, Natratoxin was suggested to be a gating modifier of K(v) channel. In addition, this inhibitory effect was found to be independent of its enzymatic activity. These results suggested that the toxin enacted its inhibitory effect by binding to K(v) channel. To further elucidate the structural basis for this electrophysiological phenomenon, we determined the crystal structure of Natratoxin at 2.2 A resolution by molecular replacement method and refined to an R-factor of 0.190. The observed overall fold has a different structural organization from other K(+) channel inhibitors in animal toxins. Compared with other K(v) channel inhibitors, a similar putative functional surface in its C-terminal was revealed to contribute to protein-protein interaction in such a blocking effect. Our results demonstrated that the spatial distribution of key amino acid residues matters most in the recognition of this toxin towards its channel target rather than its type of fold.
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Affiliation(s)
- Pu Hu
- Department of Neurobiology and Biophysics, School of Life Sciences, University of Science and Technology of China, HeFei, Anhui, 230027, People's Republic of China
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20
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Burrell BD, Crisp KM. Serotonergic Modulation of Afterhyperpolarization in a Neuron That Contributes to Learning in the Leech. J Neurophysiol 2008; 99:605-16. [DOI: 10.1152/jn.00989.2007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Modulation of afterhyperpolarization (AHP) represents an important mechanism by which excitability of a neuron can be regulated. In the leech brain, sensitization enhances excitability of the S-cell, an interneuron thought to play an important role in this form of nonassociative learning. This increase in excitability is serotonin (5-HT) dependent, but it is not known whether changes in AHP contribute to 5-HT–mediated enhancement of excitability. Therefore electrophysiological recordings and computational modeling were used to determine whether 5-HT enhances excitability via modulation of AHP. 5-HT reduced S-cell AHP and this decrease in the AHP corresponded with an increase in excitability. Little or no AHP is observed in the presence of Ca2+-free saline, suggesting the involvement of Ca2+-dependent K+channels. Furthermore, AHP amplitude decreased following treatment with drugs (tubocurare and charybdotoxin) that block Ca2+-dependent K+channel activity. The S-cell also exhibits an afterdepolarization (ADP), which is usually masked by the AHP, and was inhibited by the Na+channel blocker saxitoxin. A model of the S-cell AHP was constructed using two Ca2+-dependent K+currents and a Na+-driven ADP current. Reduction of the model conductances underlying the AHP to mimic the effects of 5-HT was sufficient to enhance excitability. These findings were confirmed in occlusion experiments in which pretreatment with tubocurare was able to block 5-HT–mediated decreases in mAHP levels and increases in excitability. These data show that modulation of S-cell AHP can contribute to 5-HT–mediated increases in excitability and that the S-cell afterpotential is due to the combined effects of AHP- and ADP-producing currents.
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21
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Hiraizumi Y, Nishimura I, Ishii H, Tanaka N, Takeshita T, Sakuma Y, Kato M. Rat GnRH neurons exhibit large conductance voltage- and Ca2+-Activated K+ (BK) currents and express BK channel mRNAs. J Physiol Sci 2008; 58:21-9. [PMID: 18177544 DOI: 10.2170/physiolsci.rp013207] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2007] [Accepted: 01/05/2008] [Indexed: 11/05/2022]
Abstract
Gonadotropin-releasing hormone (GnRH) neurons form the final common pathway for the central regulation of reproduction. As in other neurons, the discharge pattern of action potentials is important for these neurons to function properly. Therefore it is important to elucidate the expression patterns of various types of ion channels in these neurons because they determine cell excitability. To date, voltage-gated Ca2+ channels and SK channels have been reported to be expressed in rat GnRH neurons. In this study, we focused on K+ channels and analyzed their expression in primary cultured GnRH neurons, prepared from GnRH-EGFP transgenic rats, by means of perforated patch-clamp recordings. GnRH neurons exhibited delayed-rectifier K+ currents and large conductance voltage- and Ca2+-activated K+ (BK) currents. Moreover, multicell RT-PCR (reverse transcriptase-polymerase chain reaction) experiments revealed the expression of BK channel mRNAs (alpha, beta1, beta2, and beta4). The results show the presence of delayed-rectifier K+ currents and BK currents besides previously reported slow afterhyperpolarization currents. These currents control the action potential repolarization and probably also the firing pattern, thereby regulating the cell excitability of GnRH neurons.
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22
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Stehling EG, da Silveira WD, Campos TA, Brocchi M, Pertinhez TA, Spisni A. Development of a bacterial cloning vector for expression of scorpion toxins for biotechnological studies. Protein Expr Purif 2007; 57:88-94. [PMID: 17904381 DOI: 10.1016/j.pep.2007.08.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2007] [Revised: 08/08/2007] [Accepted: 08/13/2007] [Indexed: 11/20/2022]
Abstract
Scorpion venoms contain toxic peptides that recognize K(+) channels of excitable and non-excitable cells. These toxins comprise three structurally distinct groups designated alpha-KTx, beta-KTx, and gamma-KTx. It is highly desirable to develop systems for the expression of these toxins for further physiological and structural studies. In this work, an expression vector (pTEV3) was constructed by inserting protein D (major capsid of phage lambda) and TEV protease recognition site into plasmid pET21d DNA sequences. Three alpha-KTx toxins (OsK2, PbTx1, and BmKK3) were cloned into vector pTEV3 and expressed as soluble fusion proteins. The fractions containing the purified fusion proteins (protein D-toxin) were treated with TEV protease to remove protein D. The resulting toxins were analyzed by MALDI-TOF Mass Spectrometry. The results showed that the vector is appropriate for the expression of the target toxins in soluble form and that ion exchange purification of these toxins by flow-through recovery is possible. Analysis by MALDI-TOF Mass Spectrometry of Osk2 demonstrated that this toxin was expressed in its native form, as suggested by the values expected for the presence of two disulfide bridges.
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Affiliation(s)
- Eliana Guedes Stehling
- Department of Microbiology and Immunology, Biology Institute, Campinas University, Campinas, SP, Brazil.
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23
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Sarantopoulos CD, McCallum JB, Rigaud M, Fuchs A, Kwok WM, Hogan QH. Opposing effects of spinal nerve ligation on calcium-activated potassium currents in axotomized and adjacent mammalian primary afferent neurons. Brain Res 2007; 1132:84-99. [PMID: 17184741 PMCID: PMC2692681 DOI: 10.1016/j.brainres.2006.11.055] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2006] [Revised: 11/09/2006] [Accepted: 11/09/2006] [Indexed: 10/23/2022]
Abstract
UNLABELLED Calcium-activated potassium channels regulate AHP and excitability in neurons. Since we have previously shown that axotomy decreases I(Ca) in DRG neurons, we investigated the association between I(Ca) and K((Ca)) currents in control medium-sized (30-39 microM) neurons, as well as axotomized L5 or adjacent L4 DRG neurons from hyperalgesic rats following L5 SNL. Currents in response to AP waveform voltage commands were recorded first in Tyrode's solution and sequentially after: 1) blocking Na(+) current with NMDG and TTX; 2) addition of K((Ca)) blockers with a combination of apamin 1 microM, iberiotoxin 200 nM, and clotrimazole 500 nM; 3) blocking remaining K(+) current with the addition of 4-AP, TEA-Cl, and glibenclamide; and 4) blocking I(Ca) with cadmium. In separate experiments, currents were evoked (HP -60 mV, 200 ms square command pulses from -100 to +50 mV) while ensuring high levels of activation of I(K(Ca)) by clamping cytosolic Ca(2+) concentration with pipette solution in which Ca(2+) was buffered to 1 microM. This revealed I(K(Ca)) with components sensitive to apamin, clotrimazole and iberiotoxin. SNL decreases total I(K(Ca)) in axotomized (L5) neurons, but increases total I(K(Ca)) in adjacent (L4) DRG neurons. All I(K(Ca)) subtypes are decreased by axotomy, but iberiotoxin-sensitive and clotrimazole-sensitive current densities are increased in adjacent L4 neurons after SNL. In an additional set of experiments we found that small-sized control DRG neurons also expressed iberiotoxin-sensitive currents, which are reduced in both axotomized (L5) and adjacent (L4) neurons. CONCLUSIONS Axotomy decreases I(K(Ca)) due to a direct effect on K((Ca)) channels. Axotomy-induced loss of I(Ca) may further potentiate current reduction. This reduction in I(K(Ca)) may contribute to elevated excitability after axotomy. Adjacent neurons (L4 after SNL) exhibit increased I(K(Ca)) current.
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MESH Headings
- Animals
- Axotomy
- Calcium/metabolism
- Calcium Signaling/drug effects
- Calcium Signaling/physiology
- Cell Size/drug effects
- Cells, Cultured
- Ganglia, Spinal/cytology
- Ganglia, Spinal/metabolism
- Ganglia, Spinal/physiopathology
- Hyperalgesia/metabolism
- Hyperalgesia/physiopathology
- Ligation
- Male
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Neurons, Afferent/cytology
- Neurons, Afferent/drug effects
- Neurons, Afferent/metabolism
- Organ Culture Techniques
- Patch-Clamp Techniques
- Peripheral Nervous System Diseases/metabolism
- Peripheral Nervous System Diseases/physiopathology
- Potassium Channel Blockers/pharmacology
- Potassium Channels, Calcium-Activated/drug effects
- Potassium Channels, Calcium-Activated/metabolism
- Rats
- Rats, Sprague-Dawley
- Sciatic Neuropathy/metabolism
- Sciatic Neuropathy/physiopathology
- Sodium Channel Blockers/pharmacology
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Affiliation(s)
- Constantine D Sarantopoulos
- Department of Anesthesiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
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Tirosh R, Resnik ER, Herron J, Sukovich DJ, Hong Z, Weir EK, Cornfield DN. Acute normoxia increases fetal pulmonary artery endothelial cell cytosolic Ca2+ via Ca2+-induced Ca2+ release. Pediatr Res 2006; 60:258-63. [PMID: 16857761 DOI: 10.1203/01.pdr.0000233077.29866.f0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
To test the hypothesis that an acute increase in O(2) tension increases cytosolic calcium ([Ca(2+)](i)) in fetal pulmonary artery endothelial cells (PAECs) via entry of extracellular calcium and subsequent calcium-induced calcium release (CICR) and nitric oxide release, low-passage PAECs (<10 passages) were isolated from the intralobar pulmonary artery (PA) of fetal sheep and maintained under hypoxic conditions (Po(2), 25 Torr). Using the calcium-sensitive dye fura-2, we demonstrated that acute normoxia (Po(2) = 120 Torr) increased PAECs [Ca(2+)](i) by increasing the rate of entry of extracellular calcium. In the presence of either ryanodine or 2-aminoethoxy-diphenylborate (2APB), normoxia did not lead to a sustained increase in PAECs [Ca(2+)](i) Whole-cell patch clamp studies demonstrated that acute normoxia causes PAEC membrane depolarization. When loaded with the nitric oxide (NO)-sensitive dye, DAF - FM, acute normoxia increased PAEC fluorescence. In PAECs derived from fetal lambs with pulmonary hypertension, an acute increase in O(2) tension had no effect on either [Ca(2+)](i) or NO production. Hypoxia increases loading of acetylcholine-sensitive calcium stores, as hypoxia potentiated the response to acetylcholine We conclude that acute normoxia increases [Ca(2+)](i) and NO production in normotensive but not hypertensive fetal PAECs via extracellular calcium entry and calcium release from calcium-sensitive intracellular stores.
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Affiliation(s)
- Raz Tirosh
- Department of Pediatrics, Division of Pediatric Pulmonary and Critical Care Medicine, University of Minnesota, Minneapolis, MN 55455, USA
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25
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Jakab M, Grundbichler M, Benicky J, Ravasio A, Chwatal S, Schmidt S, Strbak V, Fürst J, Paulmichl M, Ritter M. Glucose induces anion conductance and cytosol-to-membrane transposition of ICln in INS-1E rat insulinoma cells. Cell Physiol Biochem 2006; 18:21-34. [PMID: 16914887 DOI: 10.1159/000095131] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The metabolic coupling of insulin secretion by pancreatic beta cells is mediated by membrane depolarization due to increased glucose-driven ATP production and closure of K(ATP) channels. Alternative pathways may involve the activation of anion channels by cell swelling upon glucose uptake. In INS-1E insulinoma cells superfusion with an isotonic solution containing 20 mM glucose or a 30% hypotonic solution leads to the activation of a chloride conductance with biophysical and pharmacological properties of anion currents activated in many other cell types during regulatory volume decrease (RVD), i.e. outward rectification, inactivation at positive membrane potentials and block by anion channel inhibitors like NPPB, DIDS, 4-hydroxytamoxifen and extracellular ATP. The current is not inhibited by tolbutamide and remains activated for at least 10 min when reducing the extracellular glucose concentration from 20 mM to 5 mM, but inactivates back to control levels when cells are exposed to a 20% hypertonic extracellular solution containing 20 mM glucose. This chloride current can likewise be induced by 20 mM 3-Omethylglucose, which is taken up but not metabolized by the cells, suggesting that cellular sugar uptake is involved in current activation. Fluorescence resonance energy transfer (FRET) experiments show that chloride current activation by 20 mM glucose and glucose-induced cell swelling are accompanied by a significant, transient redistribution of the membrane associated fraction of ICln, a multifunctional 'connector hub' protein involved in cell volume regulation and generation of RVD currents.
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Affiliation(s)
- Martin Jakab
- Institute of Physiology and Pathophysiology, Paracelsus Private Medical University, Salzburg
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26
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Sharma M, Ethayathulla AS, Jabeen T, Singh N, Sarvanan K, Yadav S, Sharma S, Srinivasan A, Singh TP. Crystal structure of a highly acidic neurotoxin from scorpion Buthus tamulus at 2.2Ǻ resolution reveals novel structural features. J Struct Biol 2006; 155:52-62. [PMID: 16677826 DOI: 10.1016/j.jsb.2005.12.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2005] [Revised: 12/02/2005] [Accepted: 12/06/2005] [Indexed: 10/25/2022]
Abstract
The crystal structure of a highly acidic neurotoxin from the scorpion Buthus tamulus has been determined at 2.2A resolution. The amino acid sequence determination shows that the polypeptide chain has 64 amino acid residues. The pI measurement gave a value of 4.3 which is one of the lowest pI values reported so far for a scorpion toxin. As observed in other alpha-toxins, it contains four disulphide bridges, Cys12-Cys63, Cys16-Cys36, Cys22-Cys46, and Cys26-Cys48. The crystal structure reveals the presence of two crystallographically independent molecules in the asymmetric unit. The conformations of two molecules are identical with an r.m.s. value of 0.3A for their C(alpha) tracings. The overall fold of the toxin is very similar to other scorpion alpha-toxins. It is a betaalphabetabeta protein. The beta-sheet involves residues Glu2-Ile6 (strand beta1), Asp32-Trp39 (strand beta3) and Val45-Val55 (strand beta4). The single alpha-helix formed is by residues Asn19-Asp28 (alpha2). The structure shows a trans peptide bond between residues 9 and 10 in the five-membered reverse turn Asp8-Cys12. This suggests that this toxin belongs to classical alpha-toxin subfamily. The surface features of the present toxin are highly characteristic, the first (A-site) has residues, Phe18, Trp38 and Trp39 that protrude outwardly presumably to interact with its receptor. There is another novel face (N-site) of this neurotoxin that contains several negatively charged residues such as, Glu2, Asp3, Asp32, Glu49 and Asp50 which are clustered in a small region of the toxin structure. On yet another face (P-site) in a triangular arrangement, with respect to the above two faces there are several positively charged residues, Arg58, Lys62 and Arg64 that also protrude outwardly for a potentially potent interaction with other molecules. This toxin with three strong features appears to be one of the most toxic molecules reported so far. In this sense, it may be a new subclass of neurotoxins with the largest number of hot spots.
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Affiliation(s)
- Madhu Sharma
- Department of Biophysics, All India Institute of Medical Sciences, New Delhi 110029, India
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27
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Forti L, Cesana E, Mapelli J, D'Angelo E. Ionic mechanisms of autorhythmic firing in rat cerebellar Golgi cells. J Physiol 2006; 574:711-29. [PMID: 16690702 PMCID: PMC1817727 DOI: 10.1113/jphysiol.2006.110858] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Although Golgi cells (GoCs), the main type of inhibitory interneuron in the cerebellar granular layer (GL), are thought to play a central role in cerebellar network function, their excitable properties have remained unexplored. GoCs fire rhythmically in vivo and in slices, but it was unclear whether this activity originated from pacemaker ionic mechanisms. We explored this issue in acute cerebellar slices from 3-week-old rats by combining loose cell-attached (LCA) and whole-cell (WC) recordings. GoCs displayed spontaneous firing at 1-10 Hz (room temperature) and 2-20 Hz (35-37 degrees C), which persisted in the presence of blockers of fast synaptic receptors and mGluR and GABAB receptors, thus behaving, in our conditions, as pacemaker neurons. ZD 7288 (20 microM), a potent hyperpolarization-activated current (Ih) blocker, slowed down pacemaker frequency. The role of subthreshold Na+ currents (INa,sub) could not be tested directly, but we observed a robust TTX-sensitive, non-inactivating Na+ current in the subthreshold voltage range. When studying repolarizing currents, we found that retigabine (5 microM), an activator of KCNQ K+ channels generating neuronal M-type K+ (IM) currents, reduced GoC excitability in the threshold region. The KCNQ channel antagonist XE991 (5 microM) did not modify firing, suggesting that GoC IM has low XE991 sensitivity. Spike repolarization was followed by an after-hyperpolarization (AHP) supported by apamin-sensitive Ca2+-dependent K+ currents (I(apa)). Block of I(apa) decreased pacemaker precision without altering average frequency. We propose that feed-forward depolarization is sustained by Ih and INa,sub, and that delayed repolarizing feedback involves an IM-like current whose properties remain to be characterized. The multiple ionic mechanisms shown here to contribute to GoC pacemaking should provide the substrate for fine regulation of firing frequency and precision, thus influencing the cyclic inhibition exerted by GoCs onto the cerebellar GL.
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Affiliation(s)
- Lia Forti
- Dipartimento di Scienze Fisiologiche e Farmacologiche, Università di Pavia, Via Forlanini 6, 27100 Pavia, Italy.
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28
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Schmachtenberg O. Histological and electrophysiological properties of crypt cells from the olfactory epithelium of the marine teleost Trachurus symmetricus. J Comp Neurol 2006; 495:113-21. [PMID: 16432906 DOI: 10.1002/cne.20847] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Crypt cells from the olfactory epithelium of the Pacific jack mackerel Trachurus symmetricus were characterized by light and electron microscopy and analyzed in dissociation with the patch-clamp technique in its cell-attached, perforated patch and normal whole-cell mode. Isolated crypt cells remained united with their supporting cells, and both were electrically coupled through gap junctions. Under voltage-clamp, depolarizing voltage steps triggered a transient sodium current, a sustained calcium current, and two types of potassium currents with fast and slow inactivation kinetics. No calcium-dependent potassium current could be observed. The sodium current was blocked by saxitoxin, the calcium current by cobalt and furnidipine, and the potassium currents by tetraethylammonium chloride. In the cell-attached configuration, crypt cells displayed spontaneous spike activity and responded to amino acid solutions with dose-dependent excitation, followed by a period of spike inhibition. These first recordings of individual crypt cells provide the basis for future studies of their odorant specificity, transduction mechanism, and overall function in the fish olfactory epithelium.
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Affiliation(s)
- Oliver Schmachtenberg
- Centro de Neurociencias de Valparaiso CNV, Facultad de Ciencias, Universidad de Valparaiso, Valparaiso, Chile.
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29
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Kato M, Tanaka N, Usui S, Sakuma Y. The SK channel blocker apamin inhibits slow afterhyperpolarization currents in rat gonadotropin-releasing hormone neurones. J Physiol 2006; 574:431-42. [PMID: 16627563 PMCID: PMC1817775 DOI: 10.1113/jphysiol.2006.110155] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Gonadotropin-releasing hormone (GnRH) neurones play an essential role in the hypothalamo-pituitary-gonadal axis. As for other neurones, the discharge pattern of action potentials is important for GnRH neurones to properly function. In the case of a luteinizing hormone (LH) surge, for example, GnRH neurones are likely to continuously fire for more than an hour. For this type of firing, GnRH neurones must have a certain intrinsic property. To address this issue, we investigated the voltage-gated Ca(2+) currents and Ca(2+)-activated voltage-independent K(+) currents underlying afterhyperpolarization, because they affect cell excitability. Dispersed GnRH neurones from adult GnRH-EGFP (enhanced green fluorescent protein) transgenic rats were cultured overnight and then used for an electrophysiological experiment involving the perforated patch-clamp configuration. The GnRH neurones showed five subtypes of voltage-gated Ca(2+) currents, i.e. the T-, L-, N-, P/Q- and R-types. The GnRH neurones also showed a slow afterhyperpolarization current (I(sAHP)), but not a medium one. It is reported that the SK channel blocker apamin (10 pm-100 nm) blocks a medium afterhyperpolarization current but not an I(sAHP). In contrast to previous reports, the I(sAHP) observed in rat GnRH neurones was potently blocked by apamin. In addition, the GnRH neurones expressed transcripts for SK1-3 channels. The results indicate that rat GnRH neurones express all five subtypes of voltage-gated Ca(2+) channels and exhibit an apamin-sensitive I(sAHP), which may allow continuous firing in response to a relatively strong depolarizing input.
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Affiliation(s)
- Masakatsu Kato
- Department of Physiology, Nippon Medical School, Sendagi 1, Bunkyo-ku, Tokyo 113-8602, Japan.
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30
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Fordyce CB, Jagasia R, Zhu X, Schlichter LC. Microglia Kv1.3 channels contribute to their ability to kill neurons. J Neurosci 2006; 25:7139-49. [PMID: 16079396 PMCID: PMC6725234 DOI: 10.1523/jneurosci.1251-05.2005] [Citation(s) in RCA: 157] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Many CNS disorders involve an inflammatory response that is orchestrated by cells of the innate immune system: macrophages, neutrophils, and microglia (the endogenous CNS immune cell). Hence, there is considerable interest in anti-inflammatory strategies that target these cells. Microglia express Kv1.3 (KCNA3) channels, which we showed previously are important for their proliferation and the NADPH-mediated respiratory burst. Here, we demonstrate the potential for targeting Kv1.3 channels to control CNS inflammation. Rat microglia express Kv1.2, Kv1.3, and Kv1.5 transcripts and protein, but only a Kv1.3 current was detected. When microglia were activated with lipopolysaccharide or a phorbol ester, only the Kv1.3 transcript (but not protein) expression changed. Using a Transwell cell-culture system that allows separate drug treatment of microglia or neurons, we found that activated microglia killed postnatal hippocampal neurons through a process that requires Kv1.3 channel activity in microglia but not in neurons. A major neurotoxic molecule in this model was peroxynitrite, which is formed from superoxide and nitric oxide; thus, it is significant that Kv1.3 channel blockers reduced the respiratory burst, but not nitric oxide production, by the activated microglia. In addressing the biochemical pathway affected by Kv1.3 channel activity, we found that Kv1.3 acts via a different cellular mechanism from the broad-spectrum drug minocycline, which is often used in animal models of neuroinflammation. That is, the dose-dependent reduction in neuron killing by minocycline corresponded with a reduction in p38 mitogen-activated protein kinase activation in microglia; however, none of the Kv1.3 blockers affected p38 activation.
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Affiliation(s)
- Christopher B Fordyce
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, M5T 2S8, Canada
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Pitts GR, Ohta H, McMahon DG. Daily rhythmicity of large-conductance Ca2+ -activated K+ currents in suprachiasmatic nucleus neurons. Brain Res 2006; 1071:54-62. [PMID: 16412396 DOI: 10.1016/j.brainres.2005.11.078] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2005] [Revised: 11/20/2005] [Accepted: 11/22/2005] [Indexed: 11/28/2022]
Abstract
Neurons within the suprachiasmatic nucleus (SCN) comprise the master circadian pacemaker in mammals. These neurons exhibit circadian rhythms in spontaneous action potential frequency and in the transcription of core circadian clock genes, including Period1 (Per1). Targeted electrophysiological recordings from SCN neurons marked with a green fluorescent protein (GFP) reporter of Per1 gene transcription have previously indicated that K(+) currents are critically involved in the expression of neurophysiological rhythmicity. The present study examined the role of large conductance, Ca(2+)-activated K(+) channels (BK) in the daily rhythmicity of mouse SCN neurons. BK-mediated currents were examined in Per1::GFP neurons under voltage clamp using iberiotoxin, a specific BK channel blocker. BK current was a greater proportion of whole-cell outward currents during the night than during the day. Analysis of iberiotoxin difference currents also demonstrated that BK current amplitude and density were greater during the night and that the day/night difference in steady state amplitude was not due to altered inactivation. Single cell RT-PCR demonstrated the presence of the BK channel transcript, KCNMA1, in Per1-expressing neurons. In situ hybridization analysis further showed that KCNMA1 mRNA was rhythmically expressed in the SCN under light:dark (LD) conditions, peaking during the middle of the night phase. Acute inhibition of BK currents blunted the circadian rhythm SCN neuron spike frequency. These results establish that BK channel function is elevated at night, thus altering SCN neuron activity.
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Affiliation(s)
- Gilbert R Pitts
- Department of Biological Sciences, Vanderbilt University, VU Station B, Box 35-1634, Nashville, TN 37235-1634, USA
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32
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Newell EW, Schlichter LC. Integration of K+ and Cl- currents regulate steady-state and dynamic membrane potentials in cultured rat microglia. J Physiol 2005; 567:869-90. [PMID: 16020460 PMCID: PMC1474215 DOI: 10.1113/jphysiol.2005.092056] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The role of ion channels and membrane potential (V(m)) in non-excitable cells has recently come under increased scrutiny. Microglia, the brain's resident immune cells, express voltage-gated Kv1.3 channels, a Kir2.1-like inward rectifier, a swelling-activated Cl(-) current and several other channels. We previously showed that Kv1.3 and Cl(-) currents are needed for microglial cell proliferation and that Kv1.3 is important for the respiratory burst. Although their mechanisms of action are unknown, one general role for these channels is to maintain a negative V(m). An impediment to measuring V(m) in non-excitable cells is that many have a very high electrical resistance, which makes them extremely susceptible to leak-induced depolarization. Using non-invasive V(m)-sensitive dyes, we show for the first time that the membrane resistance of microglial cells is several gigaohms; much higher than the seal resistance during patch-clamp recordings. Surprisingly, we observed that small current injections can evoke large V(m) oscillations in some microglial cells, and that injection of sinusoidal currents of varying frequency exposes a strong intrinsic electrical resonance in the 5- to 20-Hz frequency range in all microglial cells tested. Using a dynamic current clamp that we developed to actively compensate for the damage done by the patch-clamp electrode, we found that the V(m) oscillations and resonance were more prevalent and larger. Both types of electrical behaviour required Kv1.3 channels, as they were eliminated by the Kv1.3 blocker, agitoxin-2. To further determine how the ion currents integrate in these cells, voltage-clamp recordings from microglial cells displaying these behaviours were used to analyse the biophysical properties of the Kv1.3, Kir and Cl(-) currents. A mathematical model that incorporated only these three currents reproduced the observed V(m) oscillations and electrical resonance. Thus, the electrical behaviour of this 'non-excitable' cell type is much more complex than previously suspected, and might reflect a more common oversight in high resistance cells.
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Affiliation(s)
- Evan W Newell
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, Ontario, Canada
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Caliendo G, Perissutti E, Santagada V, Fiorino F, Severino B, Cirillo D, di Villa Bianca RD, Lippolis L, Pinto A, Sorrentino R. Synthesis by microwave irradiation of a substituted benzoxazine parallel library with preferential relaxant activity for guinea pig trachealis. Eur J Med Chem 2005; 39:815-26. [PMID: 15464615 DOI: 10.1016/j.ejmech.2004.05.003] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2003] [Revised: 05/10/2004] [Accepted: 05/10/2004] [Indexed: 11/23/2022]
Abstract
An efficient, facile, and practical parallel combinatorial synthesis of substituted-benzoxazines under microwave irradiation was described. The procedure involved the use of a microwave oven especially designed for organic synthesis suitable for parallel synthesis of solution libraries. A demonstration 19-membered library of substituted N,N-dimethyl- and N-methyl-benzoxazine amide derivatives, structurally related to the potassium channel opener cromakalim, was generated by both conventional and microwave procedures, achieving a reduction from 7 h to 30-36 min in library generation time for the microwave approach. All the synthesized compounds were tested using the in vitro models of rat aorta and guinea pig trachea rings pre-contracted with phenylephrine and carbachol, respectively. All N,N-dimethyl amide derivatives showed a relaxant activity higher on guinea pig trachea rings than on rat aorta rings.
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Affiliation(s)
- Giuseppe Caliendo
- Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli Federico II, Via D. Montesano 49, 80131 Naples, Italy.
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Amarante LH, Alves DP, Duarte IDG. Study of the involvement of K+ channels in the peripheral antinociception of the kappa-opioid receptor agonist bremazocine. Eur J Pharmacol 2005; 494:155-60. [PMID: 15212969 DOI: 10.1016/j.ejphar.2004.05.009] [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: 12/22/2003] [Revised: 04/19/2004] [Accepted: 05/10/2004] [Indexed: 11/18/2022]
Abstract
The involvement of the nitric oxide (NO)/cyclic GMP pathway in the molecular mechanisms of antinociceptive drugs like morphine has been previously shown by our group. Additionally, it is known that the desensitisation of nociceptors by K(+) channel opening should be the final target for several analgesic drugs including nitric oxide donors and exogenous micro-opioid receptor agonists. In our previous study, we demonstrated that bremazocine, a kappa-opioid receptor agonist, induces peripheral antinociception by activating nitric oxide/cyclic GMP pathway. In the current study, we assessed whether bremazocine is capable to activate K(+) channels eliciting antinociception. Bremazocine (20, 40 and 50 microg) dose-dependently reversed the hyperalgesia induced in the rat paw by local injection of carrageenan (250 microg) or prostaglandin E(2) (2 microg), measured by the paw pressure test. Using the selective kappa-opioid receptor antagonist nor-binaltorphimine (Nor-BNI, 200 microg/paw), it was confirmed that bremazocine (50 microg/paw) acts specifically on the kappa-opioid receptors present at peripheral sites. Prior treatment with the ATP-sensitive K(+) channel blockers glibenclamide (40, 80 and 160 microg) and tolbutamide (40, 80 and 160 microg) did not antagonise the antinociceptive effect of bremazocine (50 microg). The same results were obtained when we used prostaglandin E(2) (2 microg) as the hyperalgesic stimulus. The supposed participation of other types of K(+) channels was tested using the Ca(2+)-activated K(+) channel blockers dequalinium (12.5, 25 and 50 microg) and charybdotoxin (0.5, 1 and 2 microg) and different types of the non-selective K(+) channel blockers tetraethylammonium (25, 50 and 100 microg) and 4-aminopyridine (10, 25 and 50 microg). None of the K(+) channel blockers reversed the antinociceptive effect of bremazocine. On the basis of these results, we suggest that K(+) channels are not involved in the peripheral antinociceptive effect of bremazocine, although this opioid receptor agonist induces nitric oxide/cGMP pathway activation.
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Affiliation(s)
- Luiz H Amarante
- Department of Pharmacology, Institute of Biological Sciences, Universidade Federal de Minas Gerais (UFMG), Av. Antônio Carlos 6627, Belo Horizonte MG, 31.270-100, Brazil
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Valdez-Cruz NA, Dávila S, Licea A, Corona M, Zamudio FZ, García-Valdes J, Boyer L, Possani LD. Biochemical, genetic and physiological characterization of venom components from two species of scorpions: Centruroides exilicauda Wood and Centruroides sculpturatus Ewing. Biochimie 2005; 86:387-96. [PMID: 15358055 DOI: 10.1016/j.biochi.2004.05.005] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2003] [Accepted: 05/14/2004] [Indexed: 11/17/2022]
Abstract
Current literature concerning the taxonomic names of two possibly distinct species of scorpions from the genus Centruroides (sculpturatus and/or exilicauda) is controversial. This communication reports the results of biochemical, genetic and electrophysiological experiments conducted with C. exilicauda Wood of Baja California (Mexico) and C. sculpturatus Ewing of Arizona (USA). The chromatographic profile fractionation of the soluble venom from both species of scorpions is different. The N-terminal amino acid sequence for nine toxins of C. exilicauda was determined and compared with those from C. sculpturatus. Lethality tests conducted in mice support the idea that C. exilicauda venom should be expected to be medically less important than C. sculpturatus. Thirteen genes from the venomous glands of the scorpion C. exilicauda were obtained and compared with previously published sequences from genes of the species C. sculpturatus. Genes coding for cytochrome oxidase I and II of both species were also sequenced. A phylogenetic tree was generated with this information showing important differences between them. Additionally, the results of electrophysiological assays conducted with the venom from both species on the Ca(2+)-dependent K(+)-channels, showed significant differences. These results strongly support the conclusion that C. exilicauda and C. sculpturatus are in fact two distinct species of scorpions.
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Affiliation(s)
- Norma A Valdez-Cruz
- Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, National Autonomous University of Mexico, Avenida Universidad 2001, Apartado Postal 510-3, Cuernavaca 62210, Mexico
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36
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Keck M, Resnik E, Linden B, Anderson F, Sukovich DJ, Herron J, Cornfield DN. Oxygen increases ductus arteriosus smooth muscle cytosolic calcium via release of calcium from inositol triphosphate-sensitive stores. Am J Physiol Lung Cell Mol Physiol 2005; 288:L917-23. [PMID: 15695541 DOI: 10.1152/ajplung.00403.2004] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In utero, blood shunts away from the lungs via the ductus arteriosus (DA) and the foramen ovale. After birth, the DA closes concomitant with increased oxygen tension. The present experimental series tests the hypothesis that oxygen directly increases DA smooth muscle cell (SMC) cytosolic calcium ([Ca(2+)](i)) through inactivation of a K(+) channel, membrane depolarization, and entry of extracellular calcium. To test the hypothesis, DA SMC were isolated from late-gestation fetal lambs and grown to subconfluence in primary culture in low oxygen tension (25 Torr). DA SMC were loaded with the calcium-sensitive fluorophore fura-2 under low oxygen tension conditions and studied using microfluorimetry while oxygen tension was acutely increased (120 Torr). An acute increase in oxygen tension progressively increased DA SMC [Ca(2+)](i) by 11.7 +/- 1.4% over 40 min. The effect of acute normoxia on DA SMC [Ca(2+)](i) was mimicked by pharmacological blockade of the voltage-sensitive K(+) channel. Neither removal of extracellular calcium nor voltage-operated calcium channel blockade prevented the initial increase in DA SMC [Ca(2+)](i). Manganese quenching experiments demonstrated that acute normoxia initially decreases the rate of extracellular calcium entry. Pharmacological blockade of inositol triphosphate-sensitive, but not ryanodine-sensitive, intracellular calcium stores prevented the oxygen-induced increase in [Ca(2+)](i). Endothelin increased [Ca(2+)](i) in acutely normoxic, but not hypoxic, DA SMC. Thus acute normoxia 1) increases DA SMC [Ca(2+)](i) via release of calcium from intracellular calcium stores, and subsequent entry of extracellular calcium, and 2) potentiates the effect of contractile agonists. Prolonged patency of the DA may result from disordered intracellular calcium homeostasis.
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Affiliation(s)
- Maggie Keck
- Div. of Pediatric Pulmonary and Critical Care Medicine, University of Minnesota Medical School, Minneapolis, MN 55455, USA
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37
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Rodrigues ARA, Castro MSA, Francischi JN, Perez AC, Duarte IDG. Participation of ATP-sensitive K+ channels in the peripheral antinociceptive effect of fentanyl in rats. Braz J Med Biol Res 2005; 38:91-7. [PMID: 15665994 DOI: 10.1590/s0100-879x2005000100014] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We examined the effect of several K+ channel blockers such as glibenclamide, tolbutamide, charybdotoxin (ChTX), apamin, tetraethylammonium chloride (TEA), 4-aminopyridine (4-AP), and cesium on the ability of fentanyl, a clinically used selective micro-opioid receptor agonist, to promote peripheral antinociception. Antinociception was measured by the paw pressure test in male Wistar rats weighing 180-250 g (N = 5 animals per group). Carrageenan (250 microg/paw) decreased the threshold of responsiveness to noxious pressure (delta = 188.1 +/- 5.3 g). This mechanical hyperalgesia was reduced by fentanyl (0.5, 1.5 and 3 microg/paw) in a peripherally mediated and dose-dependent fashion (17.3, 45.3 and 62.6%, respectively). The selective blockers of ATP-sensitive K+ channels glibenclamide (40, 80 and 160 microg/paw) and tolbutamide (80, 160 and 240 microg/paw) dose dependently antagonized the antinociception induced by fentanyl (1.5 microg/paw). In contrast, the effect of fentanyl was unaffected by the large conductance Ca2+-activated K+ channel blocker ChTX (2 microg/paw), the small conductance Ca2+-activated K+ channel blocker apamin (10 microg/paw), or the non-specific K+ channel blocker TEA (150 microg/paw), 4-AP (50 microg/paw), and cesium (250 microg/paw). These results extend previously reported data on the peripheral analgesic effect of morphine and fentanyl, suggesting for the first time that the peripheral micro-opioid receptor-mediated antinociceptive effect of fentanyl depends on activation of ATP-sensitive, but not other, K+ channels.
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Affiliation(s)
- A R A Rodrigues
- Departamento de Farmacologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
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Szyk A, Lu W, Xu C, Lubkowski J. Structure of the scorpion toxin BmBKTtx1 solved from single wavelength anomalous scattering of sulfur. J Struct Biol 2004; 145:289-94. [PMID: 14960379 DOI: 10.1016/j.jsb.2003.11.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2003] [Revised: 10/21/2003] [Indexed: 11/26/2022]
Abstract
This report describes the crystal structure of the K(+) channel-blocking toxin, BmBKTx1, isolated recently from the venom of the scorpion Buthus martensi Karsch. This is only the second structure of the short-chain K(+) channel-blocking toxin from scorpion solved by means of X-ray crystallography. Additionally, reductive dimethylation of folded BmBKTx1 employed to induce its crystallization and solution of the structure based on the anomalous signal from the sulfur atoms make this example quite unique. The monomer of BmBKTx1 is formed by 31 amino acid residues, including 6 cysteines connected in 3 disulfide bridges. Crystals of this toxin belong to the space group P2(1) with two molecules present in the asymmetric unit. The unit cell parameters are a = 21.40 A, b=39.70 A, c=29.37 A, and beta-94.13 grades. Based on the high-quality dataset (anomalous signal) collected to the resolution 1.72A using the conventional X-radiation generator (lambda Cu, K alpha = 1.5478 A), the positions of sulfur atoms contributed by 12 cysteine residues have been identified, and subsequent improvement of the experimental phases have allowed structure solution. The final model was refined to the crystallographic R-factor of 0.166. The methyl groups on several lysine residues could be easily modeled into the electron density.
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Affiliation(s)
- Agnieszka Szyk
- Macromolecular Crystallography Laboratory, National Cancer Institute at Frederick, Frederick, MD 21702, USA
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Abstract
Much of our knowledge on K+-channels was elucidated using specific peptide ligands isolated from a number of venomous organisms. Recently, this field received a strong support and increased interest due to the solution of the three-dimensional structure of a couple of K+-channels. At the same time, several new subfamilies of specific toxins for K+-channels were isolated from scorpion venoms, enhancing the availability and diversity of such useful molecular tools. It opened new lines of research for the better understanding of K+-channel biophysics and pharmacology. In this review, we listed 120 amino acid sequences of peptides isolated from scorpion venoms. They were demonstrated or assumed to be specific for K+-channels. These sequences were aligned and used to generate a rooted phylogenetic tree. The evolutionary tree indicates that several clusters of divergent peptides show preference for specific subtypes of channels. The three-dimensional structures of representative examples of these peptides were drawn and analysed concerning the molecular fitness of their interactions with the channel targets. Four different interacting modes were identified to exist between scorpion toxins and the various subtypes of K+-channels.
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Affiliation(s)
- Ricardo C Rodríguez de la Vega
- Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, National Autonomous University of Mexico, Avenida Universidad, 2001, Apartado Postal 510-3, Cuernavaca 62210, Mexico
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40
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Zhang N, Li M, Chen X, Wang Y, Wu G, Hu G, Wu H. Solution structure of BmKK2, a new potassium channel blocker from the venom of chinese scorpion Buthus martensi Karsch. Proteins 2004; 55:835-45. [PMID: 15146482 DOI: 10.1002/prot.20117] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A natural K+ channel blocker, BmKK2 (a member of scorpion toxin subfamily alpha-KTx 14), which is composed of 31 amino acid residues and purified from the venom of the Chinese scorpion Buthus martensi Karsch, was characterized using whole-cell patch-clamp recording in rat hippocampal neurons. The three dimensional structure of BmKK2 was determined with two-dimensional NMR spectroscopy and molecular modelling techniques. In solution this toxin adopted a common alpha/beta-motif, but showed distinct local conformation in the loop between alpha-helix and beta-sheet in comparison with typical short-chain scorpion toxins (e.g., CTX and NTX). Also, the alpha helix is shorter and the beta-sheet element is smaller (each strand consisted only two residues). The unusual structural feature of BmKK2 was attributed to the shorter loop between the alpha-helix and beta-sheet and the presence of two consecutive Pro residues at position 21 and 22 in the loop. Moreover, two models of BmKK2/hKv1.3 channel and BmKK2/rSK2 channel complexes were simulated with docking calculations. The results demonstrated the existence of a alpha-mode binding between the toxin and the channels. The model of BmKK2/rSK2 channel complex exhibited favorable contacts both in electrostatic and hydrophobic, including a network of five hydrogen bonds and bigger interface containing seven pairs of inter-residue interactions. In contrast, the model of BmKK2/hKv1.3 channel complex, containing only three pairs of inter-residue interactions, exhibited poor contacts and smaller interface. The results well explained its lower activity towards Kv channel, and predicted that it may prefer a type of SK channel with a narrower entryway as its specific receptor.
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Affiliation(s)
- Naixia Zhang
- State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, People's Republic of China
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Zhang N, Wu G, Wu H, Chalmers MJ, Gaskell SJ. Purification, characterization and sequence determination of BmKK4, a novel potassium channel blocker from Chinese scorpion Buthus martensi Karsch. Peptides 2004; 25:951-7. [PMID: 15203241 DOI: 10.1016/j.peptides.2004.03.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/12/2003] [Revised: 03/26/2004] [Accepted: 03/29/2004] [Indexed: 10/26/2022]
Abstract
The scorpion neurotoxin BmKK4 was purified from the venom of the Chinese scorpion Buthus martensi Karsch by a combination of gel-filtration, ion exchange and reversed phase chromatography. The primary sequence of BmKK4 was determined using the tandem MS/MS technique and the cDNA database searching as followings: ZTQCQ SVRDC QQYCL TPDRC SYGTC YCKTT (NH(2)). BmKK4 is the first isolated member of a new subfamily alpha-KTx17 of scorpion K(+) toxins.
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Affiliation(s)
- Naixia Zhang
- State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, PR China
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Giangiacomo KM, Ceralde Y, Mullmann TJ. Molecular basis of α-KTx specificity. Toxicon 2004; 43:877-86. [PMID: 15208020 DOI: 10.1016/j.toxicon.2003.11.029] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2003] [Accepted: 11/05/2003] [Indexed: 11/18/2022]
Abstract
Potassium channel inhibitor peptides from scorpion venom, alpha-KTx, have greatly advanced our understanding of potassium channel structure and function, Because of their high affinity interaction with the outer pore, alpha-KTx's have aided, in identification of amino acids lining the pore and of proteins constituting functional channels. The alpha-KTx's display a large range of affinities for different potassium channels with differences in binding free energy exceeding approximately 8 kcal/mol. These differences in affinities are the foundation of alpha-KTx specificity and have aided in revealing the physiological and patho-physiological roles of potassium channels. The alpha-KTx subfamilies 1-3, display gross differences in specificity for maxi-K vs. KV channels. However, many potassium channels are largely untouched by alpha-KTx's. Differences in toxin binding free energy provide a quantitative framework for defining specificity. As a practical criterion for specificity a minimum binding free energy difference of 2.72 kcal/mol is proposed. Binding free energy differences for wild-type and mutant toxins and channels can point to amino acids underlying specificity and to unique features of potassium channel outer pores. Known 3D structures of potassium channels in combination with CLUSTALW sequence alignment of over 60 potassium channels reveal significant variation in alpha-KTx binding domains. Structure-based homology models of potassium channels complexed with alpha-KTxs, in combination with measurements of toxin binding free energy, will further our understanding of the molecular basis of alpha-KTx specificity.
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Affiliation(s)
- Kathleen M Giangiacomo
- Department of Biochemistry, Temple University School of Medicine, 3420 N. Broad Street, Philadelphia, PA 19140, USA.
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del Río-Portilla F, Hernández-Marín E, Pimienta G, Coronas FV, Zamudio FZ, Rodríguez de la Vega RC, Wanke E, Possani LD. NMR solution structure of Cn12, a novel peptide from the Mexican scorpion Centruroides noxius with a typical beta-toxin sequence but with alpha-like physiological activity. ACTA ACUST UNITED AC 2004; 271:2504-16. [PMID: 15182366 DOI: 10.1111/j.1432-1033.2004.04181.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Cn12 isolated from the venom of the scorpion Centruroides noxius has 67 amino-acid residues, closely packed with four disulfide bridges. Its primary structure and disulfide bridges were determined. Cn12 is not lethal to mammals and arthropods in vivo at doses up to 100 microg per animal. Its 3D structure was determined by proton NMR using 850 distance constraints, 36 phi angles derived from 36 coupling constants obtained by two different methods, and 22 hydrogen bonds. The overall structure has a two and half turn alpha-helix (residues 24-32), three strands of antiparallel beta-sheet (residues 2-4, 37-40 and 45-48), and a type II turn (residues 41-44). The amino-acid sequence of Cn12 resembles the beta scorpion toxin class, although patch-clamp experiments showed the induction of supplementary slow inactivation of Na(+) channels in F-11 cells (mouse neuroblastoma N18TG-2 x rat DRG2), which means that it behaves more like an alpha scorpion toxin. This behaviour prompted us to analyse Na(+) channel binding sites using information from 112 Na(+) channel gene clones available in the literature, focusing on the extracytoplasmic loops of the S5-S6 transmembrane segments of domain I and the S3-S4 segments of domain IV, sites considered to be responsible for binding alpha scorpion toxins.
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Rahgozar M, Willgoss DA, Gobé GC, Endre ZH. ATP-dependent K+ channels in renal ischemia reperfusion injury. Ren Fail 2004; 25:885-96. [PMID: 14669848 DOI: 10.1081/jdi-120026024] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
ATP-dependent K+ channels (KATP) account for most of the recycling of K+ which enters the proximal tubules cell via Na, K-ATPase. In the mitochondrial membrane, opening of these channels preserves mitochondrial viability and matrix volume during ischemia. We examined KATP channel modulation in renal ischemia-reperfusion injury (IRI), using an isolated perfused rat kidney (IPRK) model, in control, IRI, IRI+200 microM diazoxide (a KATP opener), IRI + 10 microM glibenclamide (a KATP blocker) and IRI + 200 microM diazoxide + 10 microM glibenclamide groups. IRI was induced by 2 periods of warm ischemia, followed by 45 min of reperfusion. IRI significantly decreased glomerular filtration rate (GFR) and increased fractional excretion of sodium (FENa) (p < 0.01). Neither diazoxide nor glibenclamide had an effect on control kidney function other than an increase in renal vascular resistance produced by glibenclamide. Pretreatment with 200 microM diazoxide reduced the postischemic increase in FENa (p < 0.05). Adding 10 microM glibenclamide inhibited the diazoxide effect on postischemic FENa (p < 0.01). Histology showed that kidneys pretreated with glibenclamide demonstrated an increase in injury in the thick ascending limb of outer medulla (p < 0.05). Glibenclamide significantly decreased post ischemic renal vascular resistance (p < 0.05), but had no significant effect on other renal function parameters. Our results suggest that sodium reabsorption is improved by KATP activation and blockade of KATP channels during IRI has an injury enhancing effect on renal epithelial function and histology. This may be mediated through KATP modulation in cell and/or mitochondrial inner membrane.
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Affiliation(s)
- Majid Rahgozar
- Department of Medicine, Central Clinical Division, School of Medicine, University of Queensland, Brisbane, Australia
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Nakamura K, Okada S, Yamaguchi N, Shimizu T, Yokotani K, Yokotani K. Role of K+ Channels in M2 Muscarinic Receptor-Mediated Inhibition of Noradrenaline Release From the Rat Stomach. J Pharmacol Sci 2004; 96:286-92. [PMID: 15528842 DOI: 10.1254/jphs.fpj04036x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
Previously we reported the cholinergic M2 muscarinic receptor-mediated inhibition of noradrenaline release from the rat stomach (K. Yokotani, Y. Osumi. J Pharmacol Exp Ther. 1993;264:54-60). In the present study, we investigated the role of K+ channels in oxotremorine (a muscarinic receptor agonist)-induced inhibition of noradrenaline release using isolated, vascularly perfused rat stomach. The gastric postganglionic sympathetic nerves were electrically stimulated twice at 2.5 Hz for 1 min and test reagents were added during the second stimulation. The electrically evoked release of noradrenaline was augmented by tetraethylammonium and 4-aminopyridine (non-selective K+ channel blockers) and also by charybdotoxin (a blocker of big conductance Ca2+-activated K+ channel). On the other hand, apamin (a selective blocker of small conductance Ca2+-activated K+ channels) and glibenclamide (an ATP-activated K+ channel blocker) had no effect on the evoked noradrenaline release. Oxotremorine-induced inhibition of noradrenaline release was attenuated by tetraethylammonium and 4-aminopyridine, while the inhibition was not influenced by charybdotoxin, apamin, and glibenclamide. These results suggest that tetraethylammonium- and 4-aminopyridine-sensitive K+ channels (probably voltage-activated K+ channels) are involved in the muscarinic receptor-mediated inhibition of noradrenaline release from the rat stomach.
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Affiliation(s)
- Kumiko Nakamura
- Department of Neuropharmacology, Program of Neural Integration, Graduate School of Medicine, Kochi University, Nankoku, Japan
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46
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Huys I, Olamendi-Portugal T, Garcia-Gómez BI, Vandenberghe I, Van Beeumen J, Dyason K, Clynen E, Zhu S, van der Walt J, Possani LD, Tytgat J. A Subfamily of Acidic α-K+ Toxins. J Biol Chem 2004; 279:2781-9. [PMID: 14561751 DOI: 10.1074/jbc.m311029200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Three homologous acidic peptides have been isolated from the venom of three different Parabuthus scorpion species, P. transvaalicus, P. villosus, and P. granulatus. Analysis of the primary sequences reveals that they structurally belong to subfamily 11 of short chain alpha-K(+)-blocking peptides (Tytgat, J., Chandy, K. G., Garcia, M. L., Gutman, G. A., Martin-Eauclaire, M. F., van der Walt, J. J., and Possani, L. D. (1999) Trends Pharmacol. Sci. 20, 444-447). These toxins are 36-37 amino acids in length and have six aligned cysteine residues, but they differ substantially from the other alpha-K(+) toxins because of the absence of the critical Lys(27) and their total overall negative charge. Parabutoxin 1 (PBTx1), which has been expressed by recombinant methods, has been submitted to functional characterization. Despite the lack of the Lys(27), this toxin blocks several Kv1-type channels heterologously expressed in Xenopus oocytes but with low affinities (micromolar range). Because a relationship between the biological activity and the acidic residue substitutions may exist, we set out to elucidate the relative impact of the acidic character of the toxin and the lack of the critical Lys(27) on the weak activity of PBTx1 toward Kv1 channels. To achieve this, a specific mutant named rPBTx1 T24F/V26K was made recombinantly and fully characterized on Kv1-type channels heterologously expressed in Xenopus oocytes. Analysis of rPBTx1 T24F/V26K displaying an affinity toward Kv1.2 and Kv1.3 channels in the nanomolar range shows the importance of the functional dyad above the acidic character of this toxin.
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Affiliation(s)
- Isabelle Huys
- Laboratory of Toxicology, University of Leuven, E Van Evenstraat 4, 3000 Leuven, Belgium
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Liu H, Li Y, Song M, Tan X, Cheng F, Zheng S, Shen J, Luo X, Ji R, Yue J, Hu G, Jiang H, Chen K. Structure-Based Discovery of Potassium Channel Blockers from Natural Products. ACTA ACUST UNITED AC 2003; 10:1103-13. [PMID: 14652078 DOI: 10.1016/j.chembiol.2003.10.011] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Potassium ion (K(+)) channels are attractive targets for rational drug design. Based upon a three-dimensional model of the eukaryotic K(+) channels, the docking virtual screening approach was employed to search the China Natural Products Database. Compounds were ranked according to the relative binding energy, favorable shape complementarity, and potential of forming hydrogen bonds with the K(+) channel. Four candidate compounds found by virtual screening were investigated by using the whole-cell voltage-clamp recording in rat dissociated hippocampal neurons. When applied extracellularly, compound 1 markedly depressed the delayed rectifier K(+) current (I(K)) and fast transient K(+) current (I(A)), whereas compounds 2, 3, and 4 exerted a more potent and selective inhibitory effect on I(K). Intracellular application of the four compounds had no effect on both the K(+) currents.
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Affiliation(s)
- Hong Liu
- Center for Drug Discovery and Design, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 201203, Shanghai, People's Republic of China
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48
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Koni PA, Khanna R, Chang MC, Tang MD, Kaczmarek LK, Schlichter LC, Flavella RA. Compensatory anion currents in Kv1.3 channel-deficient thymocytes. J Biol Chem 2003; 278:39443-51. [PMID: 12878608 DOI: 10.1074/jbc.m304879200] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Kv1.3 is a voltage-gated potassium channel with roles in human T cell activation/proliferation, cell-mediated cytotoxicity, and volume regulation and is thus a target for therapeutic control of T cell responses. Kv1.3 is also present in some mouse thymocyte subsets and splenocytes, but its role in the mouse is less well understood. We report the generation and characterization of Kv1.3-deficient (Kv1.3-/-) mice. In contrast to wild-type cells, the majority of Kv1.3-/- thymocytes had no detectable voltage-dependent potassium current, although RNA and protein for several potassium channel subunits were found in the thymocyte population. Surprisingly, the level of chloride current in the Kv1.3-/- thymocytes was increased approximately 50-fold over that in wild-type cells. There were no abnormalities in lymphocyte types or absolute numbers in thymus, spleen, and lymph nodes and no obvious defect in thymocyte apoptosis or T cell proliferation in the Kv1.3-/- animals. The compensatory effects of the enhanced chloride current may account for the apparent lack of immune system defects in Kv1.3-/-mice.
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Affiliation(s)
- Pandelakis A Koni
- Section of Immunobiology,, Yale University School of Medicine, New Haven, Connecticut 06520, USA
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Wang DD, Krueger DD, Bordey A. Biophysical properties and ionic signature of neuronal progenitors of the postnatal subventricular zone in situ. J Neurophysiol 2003; 90:2291-302. [PMID: 12801891 DOI: 10.1152/jn.01116.2002] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Previous studies have reported the presence of neuronal progenitors in the subventricular zone (SVZ) and rostral migratory stream (RMS) of the postnatal mammalian brain. Although many studies have examined the survival and migration of progenitors after transplantation and the factors influencing their proliferation or differentiation, no information is available on the electrophysiological properties of these progenitors in a near-intact environment. Thus we performed whole cell and cell-attached patch-clamp recordings of progenitors in brain slices containing either the SVZ or the RMS from postnatal day 15 to day 25 mice. Both regions displayed strong immunoreactivity for nestin and neuron-specific class III beta-tubulin, and recorded cells displayed a morphology typical of the neuronal progenitors known to migrate throughout the SVZ and RMS to the olfactory bulb. Recorded progenitors had depolarized zero-current resting potentials (mean more depolarized than -28 mV), very high input resistances (about 4 GOmega), and lacked action potentials. Using the reversal potential of K+ currents through a cell-attached patch a mean resting potential of -59 mV was estimated. Recorded progenitors displayed Ca2+-dependent K+ currents and TEA-sensitive-delayed rectifying K+ (KDR) currents, but lacked inward K+ currents and transient outward K+ currents. KDR currents displayed classical kinetics and were also sensitive to 4-aminopyridine and alpha-dendrotoxin, a blocker of Kv1 channels. Na+ currents were found in about 60% of the SVZ neuronal progenitors. No developmental changes were observed in the passive membrane properties and current profile of neuronal progenitors. Together these data suggest that SVZ neuronal progenitors display passive membrane properties and an ionic signature distinct from that of cultured SVZ neuronal progenitors and mature neurons.
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Affiliation(s)
- D D Wang
- Department of Neurosurgery and Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520-8082, USA
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50
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Gao YD, Garcia ML. Interaction of agitoxin2, charybdotoxin, and iberiotoxin with potassium channels: selectivity between voltage-gated and Maxi-K channels. Proteins 2003; 52:146-54. [PMID: 12833539 DOI: 10.1002/prot.10341] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
To gain insight into the molecular determinants that define the specificity of interaction of pore-blocking peptides, such as agitoxin 2 (AgTX2), charybdotoxin (ChTX), and iberiotoxin (IbTX) with the Shaker-type voltage-gated potassium channel Kv1.3, or the large-conductance Ca(2+)-activated K(+) (Maxi-K) channel, homology models of these channels were generated based on the crystal structure of the bacterial, KcsA, potassium channel. Peptide-channel complexes were analyzed to evaluate the predicted interaction interfaces between the peptides and the channels' outer vestibules. The docking model, for either AgTX2 or ChTX with the Kv1.3 channel, predicts a novel hydrogen bonding interaction between the Asn30 side-chain of the peptide and the Asp381 side-chain of the channel. This interaction is consistent with the >500-fold decreased potency of both AgTX2 and ChTX mutants at position 30 for the Shaker channel [(Ranganathan et al., Neuron 1996;16:131-139); (Goldstein et al., Neuron 1994;12:1377-1388)]. This hydrogen bonding interaction also suggests that Gly30 in IbTX may be the critical determinant for its lack of activity against Shaker Kv channels. The model of the Maxi-K channel reveals a narrower and more structurally restrained outer vestibule in which the aromatic residues Phe266 and Tyr294 may stabilize binding of IbTX and ChTX by pi-pi stacking with the aromatic residues Trp14 and Tyr36 of the peptides. This study also suggests that the extra net negative charge of IbTX is not related to the selectivity of this peptide for the Maxi-K channel.
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Affiliation(s)
- Ying-Duo Gao
- Molecular Systems, Merck Research Laboratories, Rahway, New Jersey 07065, USA.
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