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Groome JR, Bayless-Edwards L. Roles for Countercharge in the Voltage Sensor Domain of Ion Channels. Front Pharmacol 2020; 11:160. [PMID: 32180723 PMCID: PMC7059764 DOI: 10.3389/fphar.2020.00160] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Accepted: 02/07/2020] [Indexed: 12/19/2022] Open
Abstract
Voltage-gated ion channels share a common structure typified by peripheral, voltage sensor domains. Their S4 segments respond to alteration in membrane potential with translocation coupled to ion permeation through a central pore domain. The mechanisms of gating in these channels have been intensely studied using pioneering methods such as measurement of charge displacement across a membrane, sequencing of genes coding for voltage-gated ion channels, and the development of all-atom molecular dynamics simulations using structural information from prokaryotic and eukaryotic channel proteins. One aspect of this work has been the description of the role of conserved negative countercharges in S1, S2, and S3 transmembrane segments to promote sequential salt-bridge formation with positively charged residues in S4 segments. These interactions facilitate S4 translocation through the lipid bilayer. In this review, we describe functional and computational work investigating the role of these countercharges in S4 translocation, voltage sensor domain hydration, and in diseases resulting from countercharge mutations.
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Affiliation(s)
- James R. Groome
- Department of Biological Sciences, Idaho State University, Pocatello, ID, United States
| | - Landon Bayless-Edwards
- Department of Biological Sciences, Idaho State University, Pocatello, ID, United States
- Oregon Health and Sciences University School of Medicine, Portland, OR, United States
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de Souza JG, Fonseca FGD, Martins-Filho OA, Teixeira-Carvalho A, Martins CPS, Carvalho LD, Coelho-Dos-Reis JGA, Barbosa-Stancioli EF. Diagnostic tool based on an HTLV-1-Tax expression system in eukaryotic cells using a poxvirus vector. J Virol Methods 2010; 166:65-71. [PMID: 20219542 DOI: 10.1016/j.jviromet.2010.02.021] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2009] [Revised: 02/11/2010] [Accepted: 02/18/2010] [Indexed: 10/19/2022]
Abstract
Human T-lymphotropic virus 1 (HTLV-1) induces an immune-mediated inflammatory disease affecting the nervous system that eventually is accompanied by ocular, rheumatic and dermatologic manifestations (HTLV-1 associated myelopathy/tropical spastic paraparesis, or HAM/TSP). Proviral load and HTLV-1 protein expression, mainly of Tax, is correlated with disease progression and induction of host-virus equilibrium breakdown that, reportedly, involves the presence of Tax-specific cytotoxic T lymphocytes (CTL), T regulatory cells and anti-Tax antibodies. Based on knowledge of anti-Tax antibodies as markers of disease progression, the objectives of this study were both to design an infection/transfection system using the Vaccinia virus and a tax-encoding plasmid for the expression of Tax protein as well as to use this cell support to evaluate anti-Tax IgG by flow cytometry. The flow cytometry assay was standardized using pooled sera from each test group (negative, asymptomatic and HAM/TSP patients). The HAM/TSP group presented higher IgG anti-Tax reactivity (above 70%) than the asymptomatic group (nearly 40% reactivity). The data indicate that the infection/transfection system is useful for assessing Tax expression. This is a promising assay for use as a diagnostic tool to detect IgG anti-Tax and monitor HTLV-1 infected individuals.
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Affiliation(s)
- Jaqueline Gontijo de Souza
- Departamento de Microbiologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais - UFMG, Belo Horizonte, Brazil
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Johnson D, Bennett ES. Gating of the shaker potassium channel is modulated differentially by N-glycosylation and sialic acids. Pflugers Arch 2007; 456:393-405. [PMID: 18043943 DOI: 10.1007/s00424-007-0378-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2007] [Revised: 10/09/2007] [Accepted: 10/23/2007] [Indexed: 12/19/2022]
Abstract
N-linked glycans, including sialic acids, are integral components of ion channel complexes. To determine if N-linked sugars can modulate a rapidly inactivating K+ channel, the glycosylated Drosophila melanogaster Shaker K+ channel (ShB) and the N-glycosylation-deficient mutant (ShNQ), were studied under conditions of full and reduced sialylation. Through an apparent electrostatic mechanism, full sialylation induced uniform and significant hyperpolarizing shifts in all measured voltage-dependent ShB gating parameters compared to those measured under conditions of reduced sialylation. Steady-state gating of ShNQ was unaffected by changes in sialylation and was nearly identical to that observed for ShB under conditions of reduced sialylation, indicating that N-linked sialic acids were wholly responsible for the observed effects of sialic acid on ShB gating. Interestingly, the rates of transition among channel states and the voltage-independent rates of activation and inactivation were significantly slower for ShNQ compared to ShB. Both effects were independent of sialylation, indicating that N-linked sugars other than sialic acids alter ShB gating kinetics but have little to no effect on the steady-state distribution of channels among states. The effect of sialic acids on channel gating, particularly inactivation gating, and the impact of other N-linked sugars on channel gating kinetics are unique to the ShB isoform. Thus, ShB gating is modulated by two complementary but distinct sugar-dependent mechanisms, (1) an N-linked sialic acid-dependent surface charge effect and (2) a sialic acid-independent effect that is consistent with N-linked sugars affecting the stability of ShB among its functional states.
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Affiliation(s)
- Daniel Johnson
- Department of Molecular Pharmacology and Physiology and Programs in Neuroscience and Cardiovascular Sciences, University of South Florida College of Medicine, Tampa, FL 33612, USA
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Affiliation(s)
- D C Johns
- Section of Molecular and Cellular Cardiology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Moss B. Genetically engineered poxviruses for recombinant gene expression, vaccination, and safety. Proc Natl Acad Sci U S A 1996; 93:11341-8. [PMID: 8876137 PMCID: PMC38059 DOI: 10.1073/pnas.93.21.11341] [Citation(s) in RCA: 383] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Vaccinia virus, no longer required for immunization against smallpox, now serves as a unique vector for expressing genes within the cytoplasm of mammalian cells. As a research tool, recombinant vaccinia viruses are used to synthesize and analyze the structure-function relationships of proteins, determine the targets of humoral and cell-mediated immunity, and investigate the types of immune response needed for protection against specific infectious diseases and cancer. The vaccine potential of recombinant vaccinia virus has been realized in the form of an effective oral wild-life rabies vaccine, although no product for humans has been licensed. A genetically altered vaccinia virus that is unable to replicate in mammalian cells and produces diminished cytopathic effects retains the capacity for high-level gene expression and immunogenicity while promising exceptional safety for laboratory workers and potential vaccine recipients.
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Affiliation(s)
- B Moss
- Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892-0445, USA
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Sun T, Naini AA, Miller C. High-level expression and functional reconstitution of Shaker K+ channels. Biochemistry 1994; 33:9992-9. [PMID: 7520281 DOI: 10.1021/bi00199a024] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Voltage-gated K+ channels were expressed in COS cells transiently transfected with a plasmid carrying a cDNA for an inactivation-removed Shaker K+ channel driven by an adenovirus promoter. Channel expression was followed by immunological detection, binding of radioactive charybdotoxin (CTX), and functional reconstitution into planar lipid bilayers. About 10(7) channels per transfected cell are expressed on the plasma membrane. The expressed channels are glycosylated and competent to bind CTX with the expected characteristics. Channels observed after insertion into planar lipid bilayers displayed the voltage-dependent gating, conduction, and ion selectivity behavior expected for this channel. Channels were solubilized in several detergents without loss of CTX binding activity. The results make plausible a systematic attack on the purification of milligram-level amounts of functional K+ channels from a heterologous expression system.
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Affiliation(s)
- T Sun
- Howard Hughes Medical Institute, Graduate Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02254-9110
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Santacruz-Toloza L, Huang Y, John SA, Papazian DM. Glycosylation of shaker potassium channel protein in insect cell culture and in Xenopus oocytes. Biochemistry 1994; 33:5607-13. [PMID: 8180185 DOI: 10.1021/bi00184a033] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We have studied the glycosylation of Shaker K+ channel protein made in two expression systems: an insect cell culture line and amphibian oocytes. In both systems, two potential sites for N-linked glycosylation were modified. The modified sites were located between the first and second putative transmembrane segments, S1 and S2. Although the same sites appeared to be glycosylated in both systems, the fraction of protein glycosylated and the size, structure, or composition of the oligosaccharide chains added were quite different. The results indicate that the S1-S2 loop is extracellular, consistent with a cytoplasmic location for the N-terminus and a transmembrane disposition for hydrophobic segment S1. We have also shown that glycosylation occurs in two stages in oocytes, generating an immature and a mature form of Shaker protein. However, glycosylation is not required either for the assembly of functional channels or for their transport to the cell surface.
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Affiliation(s)
- L Santacruz-Toloza
- Department of Physiology, School of Medicine, University of California, Los Angeles 90024-1751
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Quick MW, Lester HA. Methods for Expression of Excitability Proteins in Xenopus Oocytes. METHODS IN NEUROSCIENCES 1994. [DOI: 10.1016/b978-0-12-185287-0.50020-x] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Hsu H, Huang E, Yang XC, Karschin A, Labarca C, Figl A, Ho B, Davidson N, Lester HA. Slow and incomplete inactivations of voltage-gated channels dominate encoding in synthetic neurons. Biophys J 1993; 65:1196-206. [PMID: 8241400 PMCID: PMC1225839 DOI: 10.1016/s0006-3495(93)81153-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Electrically excitable channels were expressed in Chinese hamster ovary cells using a vaccinia virus vector system. In cells expressing rat brain IIA Na+ channels only, brief pulses (< 1 ms) of depolarizing current resulted in action potentials with a prolonged (0.5-3 s) depolarizing plateau; this plateau was caused by slow and incomplete Na+ channel inactivation. In cells expressing both Na+ and Drosophila Shaker H4 transient K+ channels, there were neuron-like action potentials. In cells with appropriate Na+/K+ current ratios, maintaining stimulation produced repetitive firing over a 10-fold range of frequencies but eventually led to "lock-up" of the potential at a positive value after several seconds of stimulation. The latter effect was due primarily to slow inactivation of the K+ currents. Numerical simulations of modified Hodgkin-Huxley equations describing these currents, using parameters from voltage-clamp kinetics studied in the same cells, accounted for most features of the voltage trajectories. The present study shows that insights into the mechanisms for generating action potentials and trains of action potentials in real excitable cells can be obtained from the analysis of synthetic excitable cells that express a controlled repertoire of ion channels.
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Affiliation(s)
- H Hsu
- Division of Biology 156-29, California Institute of Technology, Pasadena 91125
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Karschin A. Heterologous expression of the membrane proteins that control cellular excitability. EXS 1993; 63:31-47. [PMID: 7678529 DOI: 10.1007/978-3-0348-7265-2_2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Versatile and potent expression systems are needed to decipher the structure and functions of the many excitability proteins that have been identified through molecular cloning. This article reviews the use of recombinant vaccinia viruses (VV), which have been recently explored for the heterologous expression of eukaryotic proteins. Vaccinia viruses feature a series of favourable properties, most of all a broad host range and high efficiency of infection, that make them uniquely suited as flexible expression vectors. In one type of experiment, the recombinant virus simply harbors the cDNA for the foreign protein; in a second type the virus harbors the cDNA for the specific and efficient RNA polymerase of bacteriophage T7, which in turn generates RNA from a separate introduced plasmid or virus. Both variations have been successfully applied to the expression and analysis of voltage-dependent ion channels, neurotransmitter receptors and other excitability proteins in many cell lines and postmitotic cells in culture. VV vectors promise to be particularly useful to study membrane proteins that require posttranslational processing, association with cell-specific subunits or coupling to endogenous second messengers pathways.
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Affiliation(s)
- A Karschin
- Division of Biology, California Institute of Technology, Pasadena 91125
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Abstract
MinK is a novel protein which induces an extremely slowly activating potassium channel when expressed in Xenopus oocytes. We discuss the properties and regulation of the current and localization and possible physiological roles of the MinK protein.
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Affiliation(s)
- E M Blumenthal
- Interdepartmental Neuroscience Program, Yale University Medical School, New Haven, CT 06510
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Ferroni S, Planells-Cases R, Ahmed CM, Montal M. Expression of a genomic clone encoding a brain potassium channel in mammalian cells using lipofection. EUROPEAN BIOPHYSICS JOURNAL : EBJ 1992; 21:185-91. [PMID: 1425474 DOI: 10.1007/bf00196762] [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: 12/27/2022]
Abstract
A genomic clone encoding a mouse brain K+ channel (MBK1) was isolated, characterized and expressed in COS cells using the lipofection technique. Transfected COS cells expressed voltage-dependent K+ currents that activated within 20 ms at 0 mV and showed less than 10% inactivation during 250 ms depolarizing pulses at 60 mV. Expressed K+ currents were reversibly blocked by 4-aminopyridine and tetraethylammonium, and were moderately sensitive to dendrotoxin, but insensitive to charybdotoxin. Thus MBK1, expressed transiently in a mammalian cell line, exhibits features characteristic of non-inactivating K+ channels with a conspicuous insensitivity to charybdotoxin. Lipofection is, therefore, a valuable strategy for expression of channel proteins in mammalian cells.
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Affiliation(s)
- S Ferroni
- Department of Biology, University of California San Diego, La Jolla 92093-0319
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Garcia ML, Galvez A, Garcia-Calvo M, King VF, Vazquez J, Kaczorowski GJ. Use of toxins to study potassium channels. J Bioenerg Biomembr 1991; 23:615-46. [PMID: 1917911 DOI: 10.1007/bf00785814] [Citation(s) in RCA: 159] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Potassium channels comprise groups of diverse proteins which can be distinguished according to each member's biophysical properties. Some types of K+ channels are blocked with high affinity by specific peptidyl toxins. Three toxins, charybdotoxin, iberiotoxin, and noxiustoxin, which display a high degree of homology in their primary amino acid sequences, have been purified to homogeneity from scorpion venom. While charybdotoxin and noxiustoxin are known to inhibit more than one class of channel (i.e., several Ca(2+)-activated and voltage-dependent K+ channels), iberiotoxin appears to be a selective blocker of the high-conductance, Ca(2+)-activated K+ channel that is present in muscle and neuroendocrine tissue. A distinct class of small-conductance Ca(2+)-activated K+ channel is blocked by two other toxins, apamin and leiurotoxin-1, that share no sequence homology with each other. A family of homologous toxins, the dendrotoxins, have been purified from venom of various related species of snakes. These toxins inhibit several inactivating voltage-dependent K+ channels. Although molecular biology approaches have been employed to identify and characterize several species of voltage-gated K+ channels, toxins directed against a particular channel can still be useful in defining the physiological role of that channel in a particular tissue. In addition, for those K+ channels which are not yet successfully probed by molecular biology techniques, toxins can be used as biochemical tools with which to purify the target protein of interest.
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Affiliation(s)
- M L Garcia
- Department of Membrane Biochemistry and Biophysics, Merck Institute for Therapeutic Research, Rahway, New Jersey 07065
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Abstract
Voltage-gated potassium channels make up a large molecular family of integral membrane proteins that are fundamentally involved in the generation of bioelectric signals such as nerve impulses. These proteins span the cell membrane, forming potassium-selective pores that are rapidly switched open or closed by changes in membrane voltage. After the cloning of the first potassium channel over 3 years ago, recombinant DNA manipulation of potassium channel genes is now leading to a molecular understanding of potassium channel behavior. During the past year, functional domains responsible for channel gating and potassium selectivity have been identified, and detailed structural pictures underlying these functions are beginning to emerge.
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Affiliation(s)
- C Miller
- Howard Hughes Medical Institute, Graduate Department of Biochemistry, Brandeis University, Waltham, MA 02254
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Anderson MP, Rich DP, Gregory RJ, Smith AE, Welsh MJ. Generation of cAMP-activated chloride currents by expression of CFTR. Science 1991; 251:679-82. [PMID: 1704151 DOI: 10.1126/science.1704151] [Citation(s) in RCA: 419] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis. In order to evaluate its function, CFTR was expressed in HeLa, Chinese hamster ovary (CHO), and NIH 3T3 fibroblast cells, and anion permeability was assessed with a fluorescence microscopic assay and the whole-cell patch-clamp technique. Adenosine 3',5'-monophosphate (cAMP) increased anion permeability and chloride currents in cells expressing CFTR, but not in cells expressing a mutant CFTR (delta F508) or in nontransfected cells. The simplest interpretation of these observations is that CFTR is itself a cAMP-activated chloride channel. The alternative interpretation, that CFTR directly or indirectly regulates chloride channels, requires that these cells have endogenous cryptic, chloride channels that are stimulated by cAMP only in the presence of CFTR.
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Affiliation(s)
- M P Anderson
- Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242
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Karschin A, Aiyar J, Gouin A, Davidson N, Lester HA. K+ channel expression in primary cell cultures mediated by vaccinia virus. FEBS Lett 1991; 278:229-33. [PMID: 1899389 DOI: 10.1016/0014-5793(91)80123-k] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
A recombinant vaccinia virus (VV) was used to express functional Drosophila Shaker H4 K+ channels in primary cell cultures from rat heart (atrial and ventricular myocytes, fibroblasts), autonomic ganglia (SCG neurons) and CNS (hippocampal neurons, cerebral astroglia). In most cells the expressed currents possessed the typical characteristics of the native Drosophila muscle A currents; a few cells showed evidence of hetero-oligomers with new properties. The maximum current density corresponded to a channel density of 2-3/microns 2. Voltage recordings in heart cells showed altered action potential waveforms after successful infection. VV vectors thus are useful for studying altered excitability and cell-specific processing of ion channel proteins.
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Affiliation(s)
- A Karschin
- Division of Biology 156-29, California Institute of Technology, Pasadena 91125
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Rich DP, Anderson MP, Gregory RJ, Cheng SH, Paul S, Jefferson DM, McCann JD, Klinger KW, Smith AE, Welsh MJ. Expression of cystic fibrosis transmembrane conductance regulator corrects defective chloride channel regulation in cystic fibrosis airway epithelial cells. Nature 1990; 347:358-63. [PMID: 1699126 DOI: 10.1038/347358a0] [Citation(s) in RCA: 455] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) was expressed in cultured cystic fibrosis airway epithelial cells and Cl- channel activation assessed in single cells using a fluorescence microscopic assay and the patch-clamp technique. Expression of CFTR, but not of a mutant form of CFTR (delta F508), corrected the Cl- channel defect. Correction of the phenotypic defect demonstrates a causal relationship between mutations in the CFTR gene and defective Cl- transport which is the hallmark of the disease.
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Affiliation(s)
- D P Rich
- Howard Hughes Medical Institute, Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242
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