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Abstract
The epithelial Na+ channel (ENaC) is a key regulator of the volume of airway surface liquid (ASL) and is found in the human airway epithelium. In cystic fibrosis (CF), Na+ hyperabsorption through ENaC, in the absence of cystic fibrosis transmembrane conductance regulator mediated anion secretion, results in the dehydration of respiratory secretions and the impairment of mucociliary clearance. The hypothesis of utilizing an ENaC blocking molecule to facilitate restoration of the airway surface liquid volume sufficiently to allow normal mucociliary clearance is of interest in the management of lung disease in CF patients. This review summarizes the published patent applications from 2014 to the end of 2016 that claim approaches to inhibit the function of ENaC for the treatment of CF.
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Abstract
The epithelial Na+ channel, ENaC, is a key regulator of the volume of airway surface liquid in the human airway epithelium. In cystic fibrosis (CF), Na+ hyperabsorption through ENaC in the absence of CFTR-mediated anion secretion results in the dehydration of respiratory secretions and the impairment of mucociliary clearance. The hypothesis of utilizing an ENaC-blocking molecule to facilitate restoration of the airway surface liquid volume sufficiently to allow normal mucociliary clearance is of interest in the management of lung disease in CF patients. This article summarizes the published patent applications from 2010 that claim approaches to inhibit the function of ENaC for utility in the treatment of CF. Patents were located though SciFinder®, using “ENaC” as the keyword from 2010 onwards; documents not relevant to CF were then manually removed.
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Schönberger M, Althaus M, Fronius M, Clauss W, Trauner D. Controlling epithelial sodium channels with light using photoswitchable amilorides. Nat Chem 2014; 6:712-9. [PMID: 25054942 DOI: 10.1038/nchem.2004] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Accepted: 06/12/2014] [Indexed: 11/09/2022]
Abstract
Amiloride is a widely used diuretic that blocks epithelial sodium channels (ENaCs). These heterotrimeric transmembrane proteins, assembled from β, γ and α or δ subunits, effectively control water transport across epithelia and sodium influx into non-epithelial cells. The functional role of δβγENaC in various organs, including the human brain, is still poorly understood and no pharmacological tools are available for the functional differentiation between α- and δ-containing ENaCs. Here we report several photoswitchable versions of amiloride. One compound, termed PA1, enables the optical control of ENaC channels, in particular the δβγ isoform, by switching between blue and green light, or by turning on and off blue light. PA1 was used to modify functionally δβγENaC in amphibian and mammalian cells. We also show that PA1 can be used to differentiate between δβγENaC and αβγENaC in a model for the human lung epithelium.
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Affiliation(s)
- Matthias Schönberger
- Department of Chemistry and Center for Integrated Protein Science, Ludwig Maximilians-Universität München, Butenandtstraße 5-13 (F4.086), 81377 Munich, Germany
| | - Mike Althaus
- Institute of Animal Physiology, Justus Liebig University Giessen, Heinrich-Buff-Ring 26, 35392 Giessen, Germany
| | - Martin Fronius
- 1] Institute of Animal Physiology, Justus Liebig University Giessen, Heinrich-Buff-Ring 26, 35392 Giessen, Germany [2] Department of Physiology, University of Otago, PO Box 913, Dunedin 9054, New Zealand
| | - Wolfgang Clauss
- Institute of Animal Physiology, Justus Liebig University Giessen, Heinrich-Buff-Ring 26, 35392 Giessen, Germany
| | - Dirk Trauner
- Department of Chemistry and Center for Integrated Protein Science, Ludwig Maximilians-Universität München, Butenandtstraße 5-13 (F4.086), 81377 Munich, Germany
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Discovery of a novel chemotype of potent human ENaC blockers using a bioisostere approach. Part 1: Quaternary amines. Bioorg Med Chem Lett 2012; 22:929-32. [DOI: 10.1016/j.bmcl.2011.12.016] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2011] [Revised: 12/02/2011] [Accepted: 12/03/2011] [Indexed: 11/20/2022]
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Skawinski WJ, Venanzi TJ, Venanzi CA. A Molecular Orbital Study of Tambjamine E and Analogues. J Phys Chem A 2004. [DOI: 10.1021/jp049758l] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- William J. Skawinski
- Department of Chemistry and Environmental Science, New Jersey Institute of Technology, 323 King Blvd., Newark, New Jersey 07102, and Department of Chemistry, College of New Rochelle, New Rochelle, New York 10805
| | - Thomas J. Venanzi
- Department of Chemistry and Environmental Science, New Jersey Institute of Technology, 323 King Blvd., Newark, New Jersey 07102, and Department of Chemistry, College of New Rochelle, New Rochelle, New York 10805
| | - Carol A. Venanzi
- Department of Chemistry and Environmental Science, New Jersey Institute of Technology, 323 King Blvd., Newark, New Jersey 07102, and Department of Chemistry, College of New Rochelle, New Rochelle, New York 10805
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Lemaitre V, Ali R, Kim CG, Watts A, Fischer WB. Interaction of amiloride and one of its derivatives with Vpu from HIV-1: a molecular dynamics simulation. FEBS Lett 2004; 563:75-81. [PMID: 15063726 DOI: 10.1016/s0014-5793(04)00251-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2004] [Revised: 02/26/2004] [Accepted: 03/02/2004] [Indexed: 11/24/2022]
Abstract
Vpu is an 81-residue membrane protein, with a single transmembrane segment that is encoded by HIV-1 and is involved in the enhancement of virion release via formation of an ion channel. Cyclohexamethylene amiloride (Hma) has been shown to inhibit ion channel activity. In the present 12-ns simulation study a putative binding site of Hma blockers in a pentameric model bundle built of parallel aligned helices of the first 32 residues of Vpu was found near Ser-23. Hma orientates along the channel axis with its alkyl ring pointing inside the pore, which leads to a blockage of the pore.
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Affiliation(s)
- V Lemaitre
- Biomembrane Structure Unit, Department of Biochemistry, Oxford University, South Parks Road, Oxford OX1 3QU, UK
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Giles KR, Humphries M, Abell A, Garrill A. The synthesis of NPPB and NPBB by reductive amination and the effects of these compounds on K+ channels of the alga Nitella hookeri. Bioorg Med Chem Lett 2003; 13:293-5. [PMID: 12482443 DOI: 10.1016/s0960-894x(02)00920-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
This paper communicates a new synthesis of the ion channel inhibitors NPPB and NPBB using a simple reductive amination sequence. The synthesised compounds were found to reduce channel amplitude of a K(+) channel present in cytoplasmic droplets of Nitella hookeri.
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Affiliation(s)
- Kristian R Giles
- Department of Plant and Microbial Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
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Hirsh AJ. Altering airway surface liquid volume: inhalation therapy with amiloride and hyperosmotic agents. Adv Drug Deliv Rev 2002; 54:1445-62. [PMID: 12458154 DOI: 10.1016/s0169-409x(02)00161-8] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The thin layer of liquid lining the entire respiratory tract is the first line of defense against the continuous insult of inhaled bacteria and noxious chemicals. Many chronic obstructive diseases of the airway may reflect decreased airway surface liquid, which results from imbalances in ion transport and mucus production. Reduction in the thickness of airway surface liquid leads to reduced mucociliary clearance rates, causing mucus accumulation and infection in the airway. In this chapter, two inhalation therapies to replenish airway surface liquid and enhance mucociliary clearance are discussed: (1) aerosolized hyperosmotic agents; and (2) aerosolized sodium channel blockers. The advantages and disadvantages of each therapy are discussed, as well as future directions for improving airway surface liquid volume by inhalation pharmacotherapy.
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Affiliation(s)
- Andrew J Hirsh
- Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill NC 27599, USA.
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Pena F, Neaga E, Amuzescu B, Nitu A, Flonta ML. Amitriptyline has a dual effect on the conductive properties of the epithelial Na channel. J Pharm Pharmacol 2002; 54:1393-8. [PMID: 12396302 DOI: 10.1211/002235702760345482] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
This study was undertaken with the aim of testing the action of amitriptyline on the epithelial Na channel (ENaC), which belongs to the same family (Deg/ENaC) as ASICs (acid-sensing ion channels) and many other putative members in the brain. We assumed that, having a common protein structure, characterization of the amitriptyline-ENaC interaction could help to elucidate the analgesic mechanism of this tricyclic antidepressant. Na-channel characteristics were derived from the analysis of blocker-induced lorentzian noise produced by amiloride. The effect of amitriptyline, present in the mucosal bathing solution, on the transepithelial short-circuit current (I(sc)) and conductance (G(t)), and on the blocker-induced noise of apical Na channels, was studied on isolated ventral skin of the frog Rana ridibunda. Amitriptyline exerted a dual effect on the macroscopic short-circuit current and conductance of the epithelia, increasing these two parameters in the concentration range 0.1-50 microM, while at higher concentrations (100-1000 microM) it showed an inhibitory action. The decrease in the association rate (k(01)) of amiloride to the apical Na channels from 15.6+/-4.2 microM(-1) s(-1) in control Cl-Ringer to 7.4+/-1.7 microM(-1) s(-1) at 200 microM amitriptyline in a concentration-dependent manner suggests a competitive binding of amitriptyline to the pyrazine ring binding site for amiloride.
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Affiliation(s)
- Florentina Pena
- Department of Animal Physiology and Biophysics, University of Bucharest, Faculty of Biology, Splaiul Independentei 91-95, Bucharest R-76201, Romania
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Padmanabhan S, Lavin RC, Thakker PM, Guo J, Zhang L, Moore D, Perlman ME, Kirk C, Daly D, Burke-Howie KJ, Wolcott T, Chari S, Berlove D, Fischer JB, Holt WF, Durant GJ, McBurney RN. Solution-phase, parallel synthesis and pharmacological evaluation of acylguanidine derivatives as potential sodium channel blockers. Bioorg Med Chem Lett 2001; 11:3151-5. [PMID: 11720863 DOI: 10.1016/s0960-894x(01)00644-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Solution-phase synthesis of various acylguanidine derivatives and the evaluation of a small library of compounds as potential sodium channel blockers are described.
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Affiliation(s)
- S Padmanabhan
- CeNeS Pharmaceuticals Inc., 333 Providence Highway, Norwood, MA 02062, USA.
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11
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Alvarez de la Rosa D, Canessa CM, Fyfe GK, Zhang P. Structure and regulation of amiloride-sensitive sodium channels. Annu Rev Physiol 2000; 62:573-94. [PMID: 10845103 DOI: 10.1146/annurev.physiol.62.1.573] [Citation(s) in RCA: 246] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Amiloride-sensitive Na+ channels constitute a new class of proteins known as the ENaC-Deg family of ion channels. All members in this family share a common protein structure but differ in their ion selectivity, their affinity for the blocker amiloride, and in their gating mechanisms. These channels are expressed in many tissues of invertebrate and vertebrate organisms where they serve diverse functions varying from Na+ absorption across epithelia to being the receptors for neurotransmitters in the nervous system. Here, we review progress made during the last years in the characterization, regulation, and cloning of new amiloride-sensitive Na+ channels.
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Affiliation(s)
- D Alvarez de la Rosa
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520-8026, USA
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12
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Schild L, Schneeberger E, Gautschi I, Firsov D. Identification of amino acid residues in the alpha, beta, and gamma subunits of the epithelial sodium channel (ENaC) involved in amiloride block and ion permeation. J Gen Physiol 1997; 109:15-26. [PMID: 8997662 PMCID: PMC2217053 DOI: 10.1085/jgp.109.1.15] [Citation(s) in RCA: 219] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The amiloride-sensitive epithelial Na channel (ENaC) is a heteromultimeric channel made of three alpha beta gamma subunits. The structures involved in the ion permeation pathway have only been partially identified, and the respective contributions of each subunit in the formation of the conduction pore has not yet been established. Using a site-directed mutagenesis approach, we have identified in a short segment preceding the second membrane-spanning domain (the pre-M2 segment) amino acid residues involved in ion permeation and critical for channel block by amiloride. Cys substitutions of Gly residues in beta and gamma subunits at position beta G525 and gamma G537 increased the apparent inhibitory constant (Ki) for amiloride by > 1,000-fold and decreased channel unitary current without affecting ion selectivity. The corresponding mutation S583 to C in the alpha subunit increased amiloride Ki by 20-fold, without changing channel conducting properties. Coexpression of these mutated alpha beta gamma subunits resulted in a non-conducting channel expressed at the cell surface. Finally, these Cys substitutions increased channel affinity for block by external Zn2+ ions, in particular the alpha S583C mutant showing a Ki for Zn2+ of 29 microM. Mutations of residues alpha W582L, or beta G522D also increased amiloride Ki, the later mutation generating a Ca2+ blocking site located 15% within the membrane electric field. These experiments provide strong evidence that alpha beta gamma ENaCs are pore-forming subunits involved in ion permeation through the channel. The pre-M2 segment of alpha beta gamma subunits may form a pore loop structure at the extracellular face of the channel, where amiloride binds within the channel lumen. We propose that amiloride interacts with Na+ ions at an external Na+ binding site preventing ion permeation through the channel pore.
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Affiliation(s)
- L Schild
- Institut de Pharmacologic et de Toxicologie, Université de Lausanne, Switzerland.
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14
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Andrade-L�pez N, Ariza-Castolo A, Contreras R, V�zquez-Olmos A, Barba Behrens N, Tlahuext H. Versatile behavior of 2-guanidinobenzimidazole nitrogen atoms toward protonation, coordination and methylation. HETEROATOM CHEMISTRY 1997. [DOI: 10.1002/(sici)1098-1071(1997)8:5<397::aid-hc4>3.0.co;2-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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15
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Barbry P, Lazdunski M. Structure and regulation of the amiloride-sensitive epithelial sodium channel. ION CHANNELS 1996; 4:115-167. [PMID: 8744208 DOI: 10.1007/978-1-4899-1775-1_4] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Affiliation(s)
- P Barbry
- Institute of Molecular and Cellular Pharmacology, CNRS, Valbonne, France
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16
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Canessa CM, Horisberger JD, Schild L, Rossier BC. Expression cloning of the epithelial sodium channel. Kidney Int 1995; 48:950-5. [PMID: 8569104 DOI: 10.1038/ki.1995.376] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- C M Canessa
- Department of Cellular and Molecular Physiology, Yale School of Medicine, New Haven, Connecticut, USA
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17
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Skawinski WJ, Busanic TJ, Ofsievich AD, Venanzi TJ, Luzhkov VB, Venanzi CA. The application of stereolithography to the fabrication of accurate molecular models. JOURNAL OF MOLECULAR GRAPHICS 1995; 13:126-35. [PMID: 7619788 DOI: 10.1016/0263-7855(95)00001-m] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The process of stereolithography, which automatically fabricates plastic models from designs created in certain computer-aided design programs, has been applied to the production of accurate plastic molecular models. Atomic coordinates obtained from quantum mechanical calculations and from neutron diffraction data were used to locate spheres in the I-DEAS CAD program with radii proportional to the appropriate van der Waals radii. The sterolithography apparatus was used to build the models using a photosensitive liquid resin, resulting in hard plastic models that accurately represent the computed or experimental input structures. Three examples are given to illustrate how the models can be used to interpret experimental structure-activity data for systems of biological importance or host-guest chemistry: (1) Interpretation of kinetic data for the formation of a stable blocking complex between amiloride analogs and the epithelial sodium channel, (2) interpretation of binding and neural activity data for the interaction of certain amino acids and their analogs at the L-alanine taste receptor of the channel catfish, and (3) interpretation of shape selectivity and rate acceleration in cyclodextrin catalysis using models of the neutron diffraction structure of beta-cyclodextrin and of the transition state for the cleavage of phenyl acetate by the secondary hydroxyl oxygen of beta-cyclodextrin.
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Affiliation(s)
- W J Skawinski
- Department of Chemical Engineering, Chemistry, and Environmental Science, New Jersey Institute of Technology, Newark 07102, USA
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Russ T, Ried W, Ullrich F, Mutschler E. Preparation and diuretic properties of novel amiloride analogues. Arch Pharm (Weinheim) 1992; 325:761-7. [PMID: 1489253 DOI: 10.1002/ardp.19923251204] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Fifteen novel amiloride analogues were synthesized and their diuretic properties compared to amiloride and triamterene in white wistar rats. Whereas none of the 6-substituted derivatives exhibited significant natriuretic and antikaliuretic effects, five of the compounds modified in the 2-position were found equal or better than standards. The results are discussed with respect to chemical structure and physiochemical properties.
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Affiliation(s)
- T Russ
- Institut für Organische Chemie, Universität Frankfurt am Main, Germany
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Parenti P, Ferrari P, Ferrandi M, Hanozet GM, Bianchi G. Effect of amiloride analogues on sodium transport in renal brush border membrane vesicles from Milan hypertensive rats. Biochem Biophys Res Commun 1992; 183:55-61. [PMID: 1543508 DOI: 10.1016/0006-291x(92)91608-s] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The effect of ethylisopropyl-amiloride (EIPA) and phenamil on sodium uptake in renal brush border membrane vesicles from prehypertensive rats of the Milan strain (MHS) and their normotensive controls (MNS) was investigated. In the presence of both a membrane potential and a pH gradient a differential effect of EIPA and phenamil was evidenced between the two rat strains. In the absence of a pH gradient, but in the presence of a membrane potential, EIPA was about two-fold more potent than phenamil in inhibiting sodium transport in both rat strains, excluding the presence of epithelial sodium channels in our BBMV preparations. Taken together these results support the hypothesis that a structurally different Na+/H+ exchanger located on the brush border membrane may be involved in the increased tubular sodium reabsorption observed in vivo in hypertensive rats.
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Affiliation(s)
- P Parenti
- Dipartimento di Fisiologia e Biochimica Generali, Università degli Studi di Milano, Italy
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Van Renterghem C, Lazdunski M. A new non-voltage-dependent, epithelial-like Na+ channel in vascular smooth muscle cells. Pflugers Arch 1991; 419:401-8. [PMID: 1660598 DOI: 10.1007/bf00371123] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
A new type of Na+ channel was identified in smooth muscle cells of the rat aortic cell line A7r5, and in smooth muscle cells cultured from rat aorta and rat portal vein. The channel is highly selective for Na+ (PNa/PK greater than 11). It is active in cell-attached patches, and independent of the trans-patch membrane potential. The single channel conductance is low (10.7 pS). Two substates were identified. This channel is insensitive to effectors of other types of Na+ channels, such as amiloride (100 microM) or tetrodotoxin (100 microM). It is inhibited by phenamil at high concentrations (greater than 10 microM). The mean open state probability P(O) varied from patch to patch (0.05-0.88). Kinetics analysis reveals a complex behaviour: open times separate in short (tau 1 = 84 ms) and long (tau 2 = 845 ms) openings and closed times separate into short (tau 1 = 60 ms) and long closures (tau 2 = 272-3130 ms). Short openings and long closures are preponderant at a low P(O). Long openings are absent in the presence of phenamil (50 microM) and are unaffected by amiloride (100 microM). Fluctuations of the channel activity in cell-attached patches and the fast disappearance after excision suggest that this channel is under metabolic control. This vascular smooth muscle channel appears to be a potentially important Na+ entry pathway for vascular cells and an amiloride-resistant homologue of the epithelial Na+ channel.
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Affiliation(s)
- C Van Renterghem
- Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France
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Chapter 12 Development of Epithelial Na+ Channels and Regulation by Guanine Nucleotide Regulatory (G) Proteins and Phospholipids. CURRENT TOPICS IN MEMBRANES 1991. [DOI: 10.1016/s0070-2161(08)60810-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Helman SI, Baxendale LM. Blocker-related changes of channel density. Analysis of a three-state model for apical Na channels of frog skin. J Gen Physiol 1990; 95:647-78. [PMID: 2159973 PMCID: PMC2216336 DOI: 10.1085/jgp.95.4.647] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Blocker-induced noise analysis of apical membrane Na channels of epithelia of frog skin was carried out with the electroneutral blocker (CDPC, 6-chloro-3,5-diamino-pyrazine-2-carboxamide) that permitted determination of the changes of single-channel Na currents and channel densities with minimal inhibition of the macroscopic rates of Na transport (Baxendale, L. M., and S. I. Helman. 1986. Biophys. J. 49:160a). Experiments were designed to resolve changes of channel densities due to mass law action (and hence the kinetic scheme of blocker interaction with the Na channel) and to autoregulation of Na channel densities that occur as a consequence of inhibition of Na transport. Mass law action changes of channel densities conformed to a kinetic scheme of closed, open, and blocked states where blocker interacts predominantly if not solely with open channels. Such behavior was best observed in "pulse" protocol experiments that minimized the time of exposure to blocker and thus minimized the contribution of much longer time constant autoregulatory influences on channel densities. Analysis of data derived from pulse, staircase, and other experimental protocols using both CDPC and amiloride as noise-inducing blockers and interpreted within the context of a three-state model revealed that Na channel open probability in the absence of blocker averaged near 0.5 with a wide range among tissues between 0.1 and 0.9.
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Affiliation(s)
- S I Helman
- Department of Physiology and Biophysics, University of Illinois, Urbana 61801
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Helman SI, Kizer NL. Chapter 4 Apical Sodium Ion Channels of Tight Epithelia as Viewed from the Perspective of Noise Analysis. CURRENT TOPICS IN MEMBRANES AND TRANSPORT 1990. [DOI: 10.1016/s0070-2161(08)60230-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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26
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Chapter 3 Ion Channel Fluctuations: “Noise” and Single-Channel Measurements. ACTA ACUST UNITED AC 1990. [DOI: 10.1016/s0070-2161(08)60229-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Kleyman TR, Kraehenbuhl JP, Rossier BC, Cragoe EJ, Warnock DG. Distinct epitopes on amiloride. THE AMERICAN JOURNAL OF PHYSIOLOGY 1989; 257:C1135-41. [PMID: 2481976 DOI: 10.1152/ajpcell.1989.257.6.c1135] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Most Na(+)-selective transport proteins are inhibited by the drug amiloride. Studies using amiloride analogues suggest that specific regions of amiloride might participate in binding to receptors on these transport proteins. To determine whether certain domains of this drug are recognized as distinct epitopes, amiloride was coupled to albumin through either its C-5 NH2-group on the pyrazine ring or through a terminal NH2-group of the guanidino moiety, and antibodies were raised against these amiloride-albumin conjugates. Studies of antibody binding to amiloride analogues identified the 3,5-diaminopyrazinyl, the guanidinocarbonyl, and the C-6 halo moieties as distinct epitopes, although the antibodies required the presence of both the 3,5-diaminopyrazinyl as well as the guanidinocarbonyl moiety for binding.
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Affiliation(s)
- T R Kleyman
- Department of Medicine, University of Pennsylvania, Philadelphia 19104
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Affiliation(s)
- P Avenet
- Department of Physiology, Universität des Saarlandes, Homburg, West Germany
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29
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Vigne P, Champigny G, Marsault R, Barbry P, Frelin C, Lazdunski M. A new type of amiloride-sensitive cationic channel in endothelial cells of brain microvessels. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)83285-9] [Citation(s) in RCA: 113] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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Bridges RJ, Cragoe EJ, Frizzell RA, Benos DJ. Inhibition of colonic Na+ transport by amiloride analogues. THE AMERICAN JOURNAL OF PHYSIOLOGY 1989; 256:C67-74. [PMID: 2912138 DOI: 10.1152/ajpcell.1989.256.1.c67] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The potency of several amiloride analogues to inhibit electrogenic Na+ transport in colon from dexamethasone-treated rats was compared. Short-circuit current (Isc) across the colonic mucosa and 22Na+ uptake into membrane vesicles derived from colonic enterocytes was determined in dexamethasone-treated rats. Kinetic analysis of inhibition of Isc and 22Na+ uptake revealed the presence of a high- and low-affinity amiloride pathway. One pathway had a high affinity [(Ki-Isc; Ki uptake] to benzamil (15.5 nM; 5.4 nM), phenamil (19.4 nM; 7.0 nM), 3',4'-dichlorobenzamil (29.0 nM; 25.2 nM), and amiloride (115 nM; 12.4 nM) but a much lower affinity to 5-(N-ethyl-N-isopropyl)amiloride (EIPA) (greater than 100 microM; greater than 9.9 microM) and 5-(N-propyl-N-butyl)-2'-4'-dichlorobenzamil (PBDCB) (greater than microM; greater than 32.8 microM). The high-affinity pathway accounted for 75-83% of the transport of Na+. The second pathway had nearly the same low affinity for each of the analogues (e.g., amiloride Ki-Isc 1 microM; Ki uptake 4 microM) and accounted for only 15-25% of the transport of Na+. The results demonstrate that the structure-inhibitory pattern of these amiloride analogues for the high-affinity pathway is the pattern observed in other electrogenic Na+-transporting epithelia and that this pharmacological profile is preserved in membrane vesicles derived from colonic enterocytes. In addition, the potency of EIPA and benzamil to inhibit electroneutral Na+ transport across the colon from normal rats (i.e., not treated with dexamethasone) was also investigated.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R J Bridges
- Department of Physiology and Biophysics, University of Alabama, Birmingham 35294
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Durand J, Lehmann C. Diphenylamine-2-carboxylate stimulates sodium ion transport in frog skin epithelium. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. A, COMPARATIVE PHYSIOLOGY 1989; 94:173-8. [PMID: 2571451 DOI: 10.1016/0300-9629(89)90803-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
1. Diphenylamine-2-carboxylate (DPC), added to the mucosal side of the frog skin, increased reversibly the short-circuit current (I0), even in SO2-(4) Ringer. Amiloride blocked this effect. 2. The maximal stimulation was 140% of the control value and the EC50 was 0.26 mM DPC. 3. The stimulatory effect of DPC was additive to that of oxytocin. 4. The dose-response curves for amiloride determined in the absence and in the presence of 1 mM DPC showed an IC50 of 1.0 microM and 0.8 microM amiloride, respectively. 5. Thus DPC, a blocker of Cl- channels in various Cl-transporting epithelia, exerts a stimulatory effect on the amiloride-sensitive Na+ transport in frog skin.
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Affiliation(s)
- J Durand
- Institute of Physiology, University of Fribourg, Switzerland
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Role of Na+/H+ exchange in thrombin-induced platelet-activating factor production by human endothelial cells. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(19)77653-4] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Avenet P, Lindemann B. Amiloride-blockable sodium currents in isolated taste receptor cells. J Membr Biol 1988; 105:245-55. [PMID: 2851656 DOI: 10.1007/bf01871001] [Citation(s) in RCA: 142] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Isolated taste receptor cells from the frog tongue were investigated under whole-cell patch-clamp conditions. With the cytosolic potential held at -80 mV, more than 50% of the cells had a stationary inward Na current of 10 to 700 pA in Ringer's solution. This current was in some cells partially, in others completely, blockable by low concentrations of amiloride. With 110 mM Na in the external and 10 mM Na in the internal solution, the inhibition constant of amiloride was (at -80 mV) near 0.3 microM. In some cells the amiloride-sensitive conductance was Na specific; in others it passed both Na and K. The Na/K selectivity (estimated from reversal potentials) varied between 1 and 100. The blockability by small concentrations of amiloride resembled that of channels found in some Na-absorbing epithelia, but the channels of taste cells showed a surprisingly large range of ionic specificities. Receptor cells, which in situ express these channels in their apical membrane, may be competent to detect the taste quality "salty." The same cells also express TTX-blockable voltage-gated Na channels.
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Affiliation(s)
- P Avenet
- Second Department of Physiology, University of the Saarland, Homburg, West Germany
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Frings S, Lindemann B. Odorant response of isolated olfactory receptor cells is blocked by amiloride. J Membr Biol 1988; 105:233-43. [PMID: 3265442 DOI: 10.1007/bf01871000] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Olfactory receptor cells were isolated from the nasal mucosa of Rana esculenta and patch clamped. Best results were obtained with free-floating cells showing ciliary movement. 1) On-cell mode: Current records were obtained for up to 50 min. Under control conditions they showed only occasional action potentials. The odorants cineole, amyl acetate and isobutyl methoxypyrazine were applied in saline by prolonged superfusion. At 500 nanomolar they elicited periodic bursts of current transients arising from cellular action potentials. The response was rapidly, fully and reversibly blocked by 50 microM amiloride added to the odorant solution. With 10 microM amiloride, the response to odorants was only partially abolished. 2) Whole-cell mode: Following breakage of the patch, the odorant response was lost within 5 to 15 min. Prior to this, odorants evoked a series of slow transient depolarizations (0.1/sec, 45 mV peak to peak) which reached threshold and thus elicited the periodic discharge of action potentials. These slow depolarizing waves were reversibly blocked by amiloride, which stabilized the membrane voltage between -80 and -90 mV. We conclude that amiloride inhibits chemosensory transduction of olfactory receptor cells, probably by blocking inward current pathways which open in response to odorants.
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Affiliation(s)
- S Frings
- Second Department of Physiology, University of the Saarland, Homburg/Saar, West Germany
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Abstract
Amiloride inhibits most plasma membrane Na+ transport systems. We have reviewed the pharmacology of inhibition of these transporters by amiloride and its analogs. Thorough studies of the Na+ channel, the Na+/H+ exchanger, and the Na+/Ca2+ exchanger, clearly show that appropriate modification of the structure of amiloride will generate analogs with increased affinity and specificity for a particular transport system. Introduction of hydrophobic substituents on the terminal nitrogen of the guanidino moiety enhances activity against the Na+ channel; whereas addition of hydrophobic (or hydrophilic) groups on the 5-amino moiety enhances activity against the Na+/H+ exchanger. Activity against the Na+/Ca2+ exchanger and Ca2+ channel is increased with hydrophobic substituents at either of these sites. Appropriate modification of amiloride has produced analogs that are several hundred-fold more active than amiloride against specific transporters. The availability of radioactive and photoactive amiloride analogs, anti-amiloride antibodies, and analogs coupled to support matrices should prove useful in future studies of amiloride-sensitive transport systems. The use of amiloride and its analogs in the study of ion transport requires a knowledge of the pharmacology of inhibition of transport proteins, as well as effects on enzymes, receptors, and other cellular processes, such as DNA, RNA, and protein synthesis, and cellular metabolism. One must consider whether the effects seen on various cellular processes are direct or due to a cascade of events triggered by an effect on an ion transport system.
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Affiliation(s)
- T R Kleyman
- Department of Medicine, Columbia University, New York, New York 10032
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