201
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Okada Y, Oiki S, Hazama A, Morishima S. Criteria for the molecular identification of the volume-sensitive outwardly rectifying Cl- channel. J Gen Physiol 1998; 112:365-7. [PMID: 9725895 PMCID: PMC2229417 DOI: 10.1085/jgp.112.3.365] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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202
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Affiliation(s)
- T D Bond
- Department of Anesthesiology, Vanderbilt University, Nashville, Tennessee 37232, USA
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203
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Bond TD, Ambikapathy S, Mohammad S, Valverde MA. Osmosensitive C1- currents and their relevance to regulatory volume decrease in human intestinal T84 cells: outwardly vs. inwardly rectifying currents. J Physiol 1998; 511 ( Pt 1):45-54. [PMID: 9679162 PMCID: PMC2231111 DOI: 10.1111/j.1469-7793.1998.045bi.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. The swelling-activated outwardly rectifying Cl- current (ICl(swell)) recorded in T84 human intestinal cells was completely blocked by 10 microM tamoxifen, while 300 microM Cd2+ had no effect. 2. A ClC-2-like, inwardly rectifying Cl- current was activated after strong hyperpolarization in T84 cells. This current was completely inhibited by 300 microM Cd2+, unaffected by 10 microM tamoxifen, and its magnitude increased slightly in response to cell swelling under hyposmotic conditions. However, the swelling-dependent modulation occurred only after prior activation by hyperpolarizing voltages. 3. T84 cells behaved initially close to perfect osmometers in response to changes in external osmolalities between +20 and -30 %. The cells underwent full regulatory volume decrease (RVD) within 16 min when exposed to 30 or 10 % hyposmotic shocks. 4. Pharmacological tools were used to determine the anionic pathway(s) involved in RVD in T84 cells. Tamoxifen (10 microM), 1,9-dideoxyforskolin (DDFSK; 100 microM) and 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS; 100 microM) blocked RVD while 300 microM Cd2+ had no effect upon RVD following a 30 % hyposmotic shock. The RVD response was similarly unaffected by Cd2+ when cells were exposed to a smaller (10 %) hyposmotic shock. 5. In conclusion, these data show that the anionic pathway primarily activated by cell swelling and relevant to RVD in T84 cells is the tamoxifen-, DDFSK- and DIDS-sensitive ICl(swell) and not the hyperpolarization-activated, Cd2+-sensitive Cl- current associated with the ClC-2 Cl- channel.
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Affiliation(s)
- T D Bond
- Physiology Group, Biomedical Sciences Division, King's College London, Strand, London WC2R 2LS, UK
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204
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Clayton GH, Staley KJ, Wilcox CL, Owens GC, Smith RL. Developmental expression of C1C-2 in the rat nervous system. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1998; 108:307-18. [PMID: 9693808 DOI: 10.1016/s0165-3806(98)00045-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Regulation of expression of the voltage-gated chloride channel, C1C-2, was investigated during development and adult life in rat brain. RNase protection assays demonstrated a marked increase in levels of expression of C1C-2 in brain during early postnatal development which was also detected in adult brain. In situ hybridization of E15 and E18 rat brains demonstrated C1C-2 expression in deep brain nuclei and scattered cells within the neuroepithelial layers, but not in the regions of subventricular zone that primarily give rise to glial populations. By E18 all neurons within the emerging cortical plate and its equivalent in other areas of the CNS were heavily labeled. During the first postnatal week, C1C-2 was highly expressed in most neurons. By P7 a pattern of differential expression emerged with evidence of decreased expression of C1C-2 mRNA in many neuronal populations. In adult rat brain, C1C-2 was expressed at highest levels in large neurons as found within layer V of cortex, Ammon's Horn of hippocampus, or mitral cells of the olfactory bulb and Purkinje cells within the cerebellum. Many smaller neurons within the diencephalon maintained significant levels of expression. A functional conductance was readily detected in hippocampal neurons during the first postnatal week, which had the same characteristic properties as the conductance observed in adult neurons. The observed expression and functional presence of C1C-2 suggest a widespread role in neuronal chloride homeostasis in early postnatal life, and demonstrated that cell specific shut-down resulted in the adult pattern of expression.
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Affiliation(s)
- G H Clayton
- Department of Neurology, University of Colorado Health Sciences Center, Denver 80262, USA
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205
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Schwappach B, Stobrawa S, Hechenberger M, Steinmeyer K, Jentsch TJ. Golgi localization and functionally important domains in the NH2 and COOH terminus of the yeast CLC putative chloride channel Gef1p. J Biol Chem 1998; 273:15110-8. [PMID: 9614122 DOI: 10.1074/jbc.273.24.15110] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GEF1 encodes the single CLC putative chloride channel in yeast. Its disruption leads to a defect in iron metabolism (Greene, J. R., Brown, N. H., DiDomenico, B. J., Kaplan, J., and Eide, D. (1993) Mol. Gen. Genet. 241, 542-553). Since disruption of GEF2, a subunit of the vacuolar H+-ATPase, leads to a similar phenotype, it was previously suggested that the chloride conductance provided by Gef1p is necessary for vacuolar acidification. We now show that gef1 cells indeed grow less well at less acidic pH. However, no defect in vacuolar acidification is apparent from quinacrine staining, and Gef1p co-localizes with Mnt1p in the medial Golgi. Thus, Gef1p may be important in determining Golgi pH. Systematic alanine scanning of the amino and the carboxyl terminus revealed several regions essential for Gef1p localization and function. One sequence (FVTID) in the amino terminus conforms to a class of sorting signals containing aromatic amino acids. This was further supported by point mutations. Alanine scanning of the carboxyl terminus identified a stretch of roughly 25 amino acids which coincides with the second CBS domain, a conserved protein motif recently identified. Mutations in the first CBS domain also destroyed proper function and localization. The second CBS domain can be transplanted to the amino terminus without loss of function, but could not be replaced by the corresponding domain of the homologous mammalian channel ClC-2.
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Affiliation(s)
- B Schwappach
- Zentrum für Molekulare Neurobiologie Hamburg (ZMNH), Hamburg University, Martinistrasse 52, D-20246 Hamburg, Germany
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206
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Chen S, Wan XL, Sears M. pICln can regulate swelling-induced Cl- currents in either layer of rabbit ciliary epithelium. Biochem Biophys Res Commun 1998; 246:59-63. [PMID: 9600068 DOI: 10.1006/bbrc.1998.8571] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Swelling-induced Cl- currents were investigated in freshly prepared non-pigmented epithelial (NPE) and pigmented epithelial (PE) cells of the rabbit ciliary body using the whole-cell patch clamp technique. Exposure of both NPE and PE cells to hypotonic stress induced Cl- currents that exhibited outward rectification and were insensitive to Ca+2. We found that swelling-induced Cl- currents in PE cell are observed shortly after isolation. The swelling-induced Cl- current showed little or no inactivation at positive membrane voltages and was sensitive to 100 microM NPPB and 100 microM DIDS. Injection of cRNA encoded rabbit pICln into Xenopus oocytes produced an outwardly rectifying Cl- current displaying features consistent with the swelling-induced Cl- current in epithelium. pICln is ubiquitous in the ciliary epithelium. It participates in the equilibration of short term tonicity alterations, a phenomenon underlying mechanisms with larger and slower amplitudes for aqueous secretion by these cells.
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Affiliation(s)
- S Chen
- Department of Ophthalmology and Visual Science, Yale School of Medicine, New Haven, Connecticut 06520-8061, USA
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207
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Strange K. Molecular identity of the outwardly rectifying, swelling-activated anion channel: time to reevaluate pICln. J Gen Physiol 1998; 111:617-22. [PMID: 9565399 PMCID: PMC2217135 DOI: 10.1085/jgp.111.5.617] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/1997] [Accepted: 03/16/1998] [Indexed: 11/29/2022] Open
Affiliation(s)
- K Strange
- Laboratory of Cellular and Molecular Physiology, Departments of Anesthesiology and Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
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208
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Clapham DE. The list of potential volume-sensitive chloride currents continues to swell (and shrink). J Gen Physiol 1998; 111:623-4. [PMID: 9565400 PMCID: PMC2217136 DOI: 10.1085/jgp.111.5.623] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- D E Clapham
- Howard Hughes Medical Institute, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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209
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Huber S, Schröppel B, Kretzler M, Schlöndorff D, Horster M. Single cell RT-PCR analysis of ClC-2 mRNA expression in ureteric bud tip. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:F951-7. [PMID: 9612334 DOI: 10.1152/ajprenal.1998.274.5.f951] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Embryonic epithelia at the tip of the ureteric bud (UB) face the interspace between epithelial and mesenchymal cells and are fundamentally involved in reciprocal signaling during early nephrogenesis. To characterize their membrane conductive proteins, patch-clamp and single cell RT-PCR techniques were applied to embryonic rat UBs [embryonic day 17 (day E17)] microdissected from the outer cortex. Cells at the UB tip had a high whole cell conductance (14 +/- 2 nS/10 pF, n = 8). The main fractional conductance resembled that of Ca-activated Cl channels in nonepithelial cells, with its time-dependent activation at depolarizing and inactivation at hyperpolarizing voltages. A second Cl-selective current fraction, by contrast, activated slowly during strong hyperpolarization, suggestive of a ClC-2-mediated conductance. To determine the origin of this current, cytoplasm was harvested into the patch pipette, RNA was reverse transcribed, and cDNA encoding the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) housekeeper gene or the ClC-2 Cl channel was amplified by polymerase chain reaction (PCR). GAPDH and ClC-2 PCR products were identified in 23 and 8 (out of a total of 57) single cell cDNA samples, respectively. ClC-2 PCR products with two different lengths were obtained, which might be due to two alternatively spliced ClC-2 mRNA isoforms. This first and combined approach by patch-clamp and single cell RT-PCR techniques to embryonic epithelia indicates that 1) cells at the UB tip express a phenotype remarkably different from that of postembryonic collecting duct principal cells and that 2) ClC-2 is likely to have a key role in early nephrogenesis.
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Affiliation(s)
- S Huber
- Physiologisches Institut, Universität München, Germany
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210
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Sachs F, Morris CE. Mechanosensitive ion channels in nonspecialized cells. Rev Physiol Biochem Pharmacol 1998; 132:1-77. [PMID: 9558913 DOI: 10.1007/bfb0004985] [Citation(s) in RCA: 187] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- F Sachs
- Biophysical Sciences, State University of New York, Buffalo 14214, USA
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211
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Abstract
Chloride channels are widely expressed and play important roles in cell volume regulation, transepithelial transport, intracellular pH regulation, and membrane excitability. Most chloride channels have yet to be identified at a molecular level. The ClC gene family and the cystic fibrosis transmembrane conductance regulator (CFTR) are distinct chloride channels expressed in many cell types, and mutations in their genes are the cause of several diseases including myotonias, cystic fibrosis, and kidney stones. Because of their molecular definition and roles in disease, these channels have been studied intensively over the past several years. The focus of this review is on recent studies that have provided new insights into the mechanisms governing the opening and closing, i.e. gating, of the ClC and CFTR chloride channels.
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Affiliation(s)
- J K Foskett
- Department of Physiology, University of Pennsylvania, Philadelphia 19104-6100, USA.
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212
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Fong P, Rehfeldt A, Jentsch TJ. Determinants of slow gating in ClC-0, the voltage-gated chloride channel of Torpedo marmorata. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:C966-73. [PMID: 9575793 DOI: 10.1152/ajpcell.1998.274.4.c966] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Membrane hyperpolarization normally activates the slow gate of the Torpedo voltage-gated chloride channel (ClC-0). To elucidate the structural basis of this process, carboxy terminus truncation mutants and chimeras were constructed, expressed in Xenopus oocytes, and evaluated using a two-microelectrode voltage clamp. Introduction of stop codons at several positions between transmembrane domains 12 and 13 (D12 and D13) showed no expression, whereas a truncation just after D13 yielded wild-type currents. A chimera (022) entailing the substitution of the carboxy-terminal cytoplasmic tail after Lys-520 with the corresponding region of ClC-2 lacked slow gating, whereas a more conservative construct (chimera 002), in which D13 was replaced with its ClC-2 analog, retained its capacity to slow gate. These findings suggest that important structures reside within the interdomain stretch (IDS) between D12 and D13. Unlike ClC-2, in which transplantation of "ball" structures could restore gating to constitutively open mutants, transplantation of the ClC-0 IDS to the amino terminus of chimera 022 did not restore gating. Surprisingly, replacement of the IDS by the analogous regions of either ClC-1 or ClC-2 showed slow voltage-activated gating, although the gating was altered. Our findings lead us to conclude that both the functional expression and the slow voltage gating of ClC-0 rely on structures at the carboxy terminus of the channel.
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Affiliation(s)
- P Fong
- Zentrum für Molekulare Neurobiologie Hamburg, Universität Hamburg, Germany
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213
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Schwiebert EM, Cid-Soto LP, Stafford D, Carter M, Blaisdell CJ, Zeitlin PL, Guggino WB, Cutting GR. Analysis of ClC-2 channels as an alternative pathway for chloride conduction in cystic fibrosis airway cells. Proc Natl Acad Sci U S A 1998; 95:3879-84. [PMID: 9520461 PMCID: PMC19931 DOI: 10.1073/pnas.95.7.3879] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Cystic fibrosis (CF) is a lethal inherited disease that results from abnormal chloride conduction in epithelial tissues. ClC-2 chloride channels are expressed in epithelia affected by CF and may provide a key "alternative" target for pharmacotherapy of this disease. To explore this possibility, the expression level of ClC-2 channels was genetically manipulated in airway epithelial cells derived from a cystic fibrosis patient (IB3-1). Whole-cell patch-clamp analysis of cells overexpressing ClC-2 identified hyperpolarization-activated Cl- currents (HACCs) that displayed time- and voltage-dependent activation, and an inwardly rectifying steady-state current-voltage relationship. Reduction of extracellular pH to 5.0 caused significant increases in HACCs in overexpressing cells, and the appearance of robust currents in parental IB3-1 cells. IB3-1 cells stably transfected with the antisense ClC-2 cDNA showed reduced expression of ClC-2 compared with parental cells by Western blotting, and a significant reduction in the magnitude of pH-dependent HACCs. To determine whether changes in extracellular pH alone could initiate chloride transport via ClC-2 channels, we performed 36Cl- efflux studies on overexpressing cells and cells with endogenous expression of ClC-2. Acidic extracellular pH increased 36Cl- efflux rates in both cell types, although the ClC-2 overexpressing cells had significantly greater chloride conduction and a longer duration of efflux than the parental cells. Compounds that exploit the pH mechanism of activating endogenous ClC-2 channels may provide a pharmacologic option for increasing chloride conductance in the airways of CF patients.
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Affiliation(s)
- E M Schwiebert
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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214
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Yamazaki J, Duan D, Janiak R, Kuenzli K, Horowitz B, Hume JR. Functional and molecular expression of volume-regulated chloride channels in canine vascular smooth muscle cells. J Physiol 1998; 507 ( Pt 3):729-36. [PMID: 9508834 PMCID: PMC2230812 DOI: 10.1111/j.1469-7793.1998.729bs.x] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/1997] [Accepted: 01/27/1998] [Indexed: 02/06/2023] Open
Abstract
1. We examined the possibility of functional and molecular expression of volume-regulated Cl- channels in vascular smooth muscle using the whole-cell patch-clamp technique and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) on cells from canine pulmonary and renal arteries. 2. Decreasing external osmolarity induced cell swelling, which was accompanied by activation of Cl--dependent outward-rectifying membrane currents with an anion permeability sequence of SCN- > I- > Br- > Cl- > aspartate-. These currents were sensitive to block by DIDS, extracellular ATP and the antioestrogen compound tamoxifen. 3. Experiments were performed to determine whether the molecular form of the volume-regulated chloride channel (ClC-3) is expressed in pulmonary and renal arteries. Quantitative RT-PCR confirmed expression of ClC-3 in both types of smooth muscle. ClC-3 expression was 76.4 % of beta-actin in renal artery and 48.0 % of beta-actin in pulmonary artery. 4. We conclude that volume-regulated Cl- channels are expressed in vascular smooth muscle cells and exhibit functional properties similar to those found in other types of cells, presumably contributing to the regulation of cell volume, electrical activity and, possibly, myogenic tone.
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Affiliation(s)
- J Yamazaki
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557-0046, USA
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215
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Nilius B, Eggermont J, Voets T, Buyse G, Manolopoulos V, Droogmans G. Properties of volume-regulated anion channels in mammalian cells. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1998; 68:69-119. [PMID: 9481145 DOI: 10.1016/s0079-6107(97)00021-7] [Citation(s) in RCA: 274] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- B Nilius
- KU Leuven, Laboratorium voor Fysiologie, Belgium.
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216
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Hryciw DH, Rychkov GY, Hughes BP, Bretag AH. Relevance of the D13 region to the function of the skeletal muscle chloride channel, ClC-1. J Biol Chem 1998; 273:4304-7. [PMID: 9468477 DOI: 10.1074/jbc.273.8.4304] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Although hydropathy analysis of the skeletal muscle chloride channel protein, ClC-1, initially predicted 13 potential membrane spanning domains (D1 to D13), later topological studies have suggested that domain D4 is extracellular and that D13, conserved in all eukaryotic ClC channels, is located within the extensive cytoplasmic tail that makes up the carboxyl terminus of the protein. We have examined the effect of deleting D13 (DeltaD13) and the function of the carboxyl tail by removing the final 72 (fs923X), 100 (fs895X), 125 (L869X), 398 (N596X), and 420 (Q574X) amino acids from rat ClC-1. Appropriate cDNA constructs were prepared and expressed using the baculovirus Sf9 insect cell system. Patch clamp analysis of chloride currents in Sf9 cells showed that only relatively insubstantial changes could be attributed to the expressed fs923X, fs895X, and DeltaD13 mutants compared with wild type rat ClC-1. For N596X and Q574X, however, adequate mRNA could be detected, but neither patch clamp nor polyacrylamide gel electrophoresis showed corresponding protein production. By contrast, expression of L869X was demonstrable by polyacrylamide gel electrophoresis, but no chloride conductance attributable to it could be detected. Overall, our results indicate that the domain D13 is dispensable, as are the final 100 amino acids, but not the final 125 amino acids or more, of the carboxyl tail. Some essential region of unknown significance, therefore, appears to reside in the 18 amino acids after D13, from Lys877 to Arg894.
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Affiliation(s)
- D H Hryciw
- Centre for Advanced Biomedical Studies, University of South Australia, North Terrace, Adelaide, South Australia 5000, Australia
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217
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Obermüller N, Gretz N, Kriz W, Reilly RF, Witzgall R. The swelling-activated chloride channel ClC-2, the chloride channel ClC-3, and ClC-5, a chloride channel mutated in kidney stone disease, are expressed in distinct subpopulations of renal epithelial cells. J Clin Invest 1998; 101:635-42. [PMID: 9449697 PMCID: PMC508607 DOI: 10.1172/jci1496] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The mammalian genome encodes at least nine different members of the ClC family of chloride channels. So far only two of them could be localized on a cellular level in the kidney. We now report on the precise intrarenal localization of the mRNAs coding for the chloride channels ClC-2, ClC-3 and ClC-5. Expression of ClC-2 mRNA, encoding a swelling-activated chloride channel, could be demonstrated in the S3 segment of the proximal tubule. The chloride channel ClC-3 mRNA and ClC-5 mRNA, coding for a chloride channel mutated in kidney stone disease, were both expressed in intercalated cells of the connecting tubule and collecting duct. Whereas ClC-3 mRNA expression was most prominent in the cortex of rat kidneys, ClC-5 mRNA was expressed from the cortex through the upper portion of the inner medulla. A detailed analysis revealed that ClC-3 was expressed by type B intercalated cells, whereas ClC-5 was expressed by type A intercalated cells. These findings have important implications for the pathogenesis of hereditary kidney stone disease caused by mutations in the CLCN5 gene.
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Affiliation(s)
- N Obermüller
- Medical Research Center, Klinikum Mannheim, University of Heidelberg, D-68167 Mannheim, Germany
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218
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Furukawa T, Ogura T, Katayama Y, Hiraoka M. Characteristics of rabbit ClC-2 current expressed in Xenopus oocytes and its contribution to volume regulation. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:C500-12. [PMID: 9486141 DOI: 10.1152/ajpcell.1998.274.2.c500] [Citation(s) in RCA: 178] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
In the Xenopus oocyte heterologous expression system, the electrophysiological characteristics of rabbit ClC-2 current and its contribution to volume regulation were examined. Expressed currents on oocytes were recorded with a two-electrode voltage-clamp technique. Oocyte volume was assessed by taking pictures of oocytes with a magnification of x 40. Rabbit ClC-2 currents exhibited inward rectification and had a halide anion permeability sequence of Cl- > or = Br- >> I- > or = F-. ClC-2 currents were inhibited by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), diphenylamine-2-carboxylic acid (DPC), and anthracene-9-carboxylic acid (9-AC), with a potency order of NPPB > DPC = 9-AC, but were resistant to stilbene disulfonates. These characteristics are similar to those of rat ClC-2, suggesting rabbit ClC-2 as a counterpart of rat ClC-2. During a 30-min perfusion with hyposmolar solution, current amplitude at -160 mV and oocyte diameter were compared among three groups: oocytes injected with distilled water, oocytes injected with ClC-2 cRNA, and oocytes injected with ClC-2 delta NT cRNA (an open channel mutant with NH2-terminal truncation). Maximum inward current was largest in ClC-2 delta NT-injected oocytes (-5.9 +/- 0.4 microA), followed by ClC-2-injected oocytes (-4.3 +/- 0.6 microA), and smallest in water-injected oocytes (-0.2 +/- 0.2 microA), whereas the order of increase in oocyte diameter was as follows: water-injected oocytes (9.0 +/- 0.2%) > ClC-2-injected oocytes (5.3 +/- 0.5%) > ClC-2 delta NT-injected oocytes (1.1 +/- 0.2%). The findings that oocyte swelling was smallest in oocytes with the largest expressed currents suggest that ClC-2 currents expressed in Xenopus oocytes appear to act for volume regulation when exposed to a hyposmolar environment.
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Affiliation(s)
- T Furukawa
- Department of Autonomic Physiology, Tokyo Medical and Dental University, Japan
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219
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Clark S, Jordt SE, Jentsch TJ, Mathie A. Characterization of the hyperpolarization-activated chloride current in dissociated rat sympathetic neurons. J Physiol 1998; 506 ( Pt 3):665-78. [PMID: 9503329 PMCID: PMC2230754 DOI: 10.1111/j.1469-7793.1998.665bv.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
1. Dissociated rat superior cervical ganglion (SCG) neurons have been shown to possess a hyperpolarization-activated inwardly rectifying chloride current. The current was not altered by changes in external potassium concentration, replacing external cations with NMDG (N-methyl-D-glucamine) or by addition of 10 mM caesium or barium ions. 2. The reversal potential of the current was altered by changing external anions. The anion selectivity of the current was Cl- > Br- > I- > cyclamate. All substituted permeant anions also blocked the current. 3. The current was blocked by DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid), 9AC (anthracene-9-carboxylic acid) and NPPB (5-nitro-2-(3-phenylpropylamino)benzoic acid) but was unaffected by SITS (4-acetamido-4'-isothiocyanatostilbene- 2,2'-disulphonic acid) and niflumic acid. The effective blockers were voltage dependent; DIDS and NPPB were more effective at depolarized potentials while 9AC was more effective at hyperpolarized potentials. 4. The current was enhanced by extracellular acidification and reduced by extracellular alkalinization. Reducing external osmolarity was without effect in conventional whole-cell recording but enhanced current amplitude in those perforated-patch recordings where little current was evident in control external solution. 5. The current in SCG neurons was blocked by external cadmium and zinc. ClC-2 chloride currents expressed in Xenopus oocytes were also sensitive to block by these divalent ions and by DIDS but the sensitivity of ClC-2 to block by cadmium ions was lower than that of the current in SCG neurons. 6. Reverse transcriptase-polymerase chain reaction (RT-PCR) experiments showed the presence of mRNA for ClC-2 in SCG neurons but not in rat cerebellar granule cells which do not possess a hyperpolarization-activated Cl- current. 7. The data suggest that ClC-2 may be functionally expressed in rat SCG neurons. This current may play a role in regulating the internal chloride concentration in these neurons and hence their response to activation of GABAA receptors.
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Affiliation(s)
- S Clark
- Department of Pharmacology, Royal Free Hospital School of Medicine, London, UK
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220
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Lang F, Busch GL, Ritter M, Völkl H, Waldegger S, Gulbins E, Häussinger D. Functional significance of cell volume regulatory mechanisms. Physiol Rev 1998; 78:247-306. [PMID: 9457175 DOI: 10.1152/physrev.1998.78.1.247] [Citation(s) in RCA: 1269] [Impact Index Per Article: 48.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
To survive, cells have to avoid excessive alterations of cell volume that jeopardize structural integrity and constancy of intracellular milieu. The function of cellular proteins seems specifically sensitive to dilution and concentration, determining the extent of macromolecular crowding. Even at constant extracellular osmolarity, volume constancy of any mammalian cell is permanently challenged by transport of osmotically active substances across the cell membrane and formation or disappearance of cellular osmolarity by metabolism. Thus cell volume constancy requires the continued operation of cell volume regulatory mechanisms, including ion transport across the cell membrane as well as accumulation or disposal of organic osmolytes and metabolites. The various cell volume regulatory mechanisms are triggered by a multitude of intracellular signaling events including alterations of cell membrane potential and of intracellular ion composition, various second messenger cascades, phosphorylation of diverse target proteins, and altered gene expression. Hormones and mediators have been shown to exploit the volume regulatory machinery to exert their effects. Thus cell volume may be considered a second message in the transmission of hormonal signals. Accordingly, alterations of cell volume and volume regulatory mechanisms participate in a wide variety of cellular functions including epithelial transport, metabolism, excitation, hormone release, migration, cell proliferation, and cell death.
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Affiliation(s)
- F Lang
- Institute of Physiology, University of Tübingen, Germany
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221
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Hoffmann EK. Intracellular transmission in cell volume regulation in Ehrlich ascites tumor cells. THE JOURNAL OF EXPERIMENTAL ZOOLOGY 1997; 279:398-414. [PMID: 9392861 DOI: 10.1002/(sici)1097-010x(19971201)279:5<398::aid-jez2>3.0.co;2-j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- E K Hoffmann
- Institute of Biological Chemistry, August Krogh Institute, University of Copenhagen, Denmark.
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222
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Duan D, Winter C, Cowley S, Hume JR, Horowitz B. Molecular identification of a volume-regulated chloride channel. Nature 1997; 390:417-21. [PMID: 9389484 DOI: 10.1038/37151] [Citation(s) in RCA: 348] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A volume-regulated chloride current (ICl.vol) is ubiquitously present in mammalian cells, and is required for the regulation of electrical activity, cell volume, intracellular pH, immunological responses, cell proliferation and differentiation. However, the molecule responsible for ICl.vol has yet to be determined. Although three putative chloride channel proteins expressed from cloned genes (P-glycoprotein, pICln and ClC-2 ) have been proposed to be the molecular equivalent of ICl.vol, neither P-glycoprotein nor pICln is thought to be a chloride channel or part thereof, and the properties of expressed ClC-2 channels differ from native ICl.vol. Here we report that functional expression in NIH/3T3 cells of a cardiac clone of another member of the ClC family, ClC-3, results in a large basally active chloride conductance, which is strongly modulated by cell volume and exhibits many properties identical to those of ICl.vol in native cells. A mutation of asparagine to lysine at position 579 at the end of the transmembrane domains of ClC-3 abolishes the outward rectification and changes the anion selectivity from I- > Cl- to Cl- > I- but leaves swelling activation intact. Because ClC-3 is a channel protein belonging to a large gene family of chloride channels, these results indicate that ClC-3 encodes ICl.vol in many native mammalian cells.
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Affiliation(s)
- D Duan
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno 89557-0046, USA
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223
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Wan XL, Chen S, Sears M. Cloning and functional expression of a swelling-induced chloride conductance regulatory protein, plCln, from rabbit ocular ciliary epithelium. Biochem Biophys Res Commun 1997; 239:692-6. [PMID: 9367830 DOI: 10.1006/bbrc.1997.7523] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The cDNA encoding a swelling-induced chloride conductance regulatory protein, plcln, was cloned from rabbit ciliary epithelium by using a polymerase chain reaction (PCR)-based approach. The open reading frame encoding 236 amino acids possesses high amino acid identity (93/%) with the previously cloned plcln from human ciliary epithelium. Outwardly rectifying currents were recorded in Xenopus oocytes injected with plcln cRNA, a result consistent with plcln expression in ciliary epithelium. A widespread distribution and marked expression of plcln mRNA in both nonpigmented ciliary epithelial (NPE) cells and pigmented ciliary epithelial (PE) cells was found for the first time. In situ hybridization analysis showed that plcln expression is more abundant in NPE than PE. These findings are consistent with the idea that plcln may be an important regulatory element in these secretory cells.
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Affiliation(s)
- X L Wan
- Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, Connecticut 06520-8061, USA
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224
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Chu S, Zeitlin PL. Alternative mRNA splice variants of the rat ClC-2 chloride channel gene are expressed in lung: genomic sequence and organization of ClC-2. Nucleic Acids Res 1997; 25:4153-9. [PMID: 9321672 PMCID: PMC147000 DOI: 10.1093/nar/25.20.4153] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The ClC-2 epithelial cell chloride channel is a voltage-, tonicity- and pH-regulated member of the ClC super family. We have previously shown that rat lung ClC-2 (rClC-2) is down-regulated at birth, and molecular diversity is generated by alternative splicing [Murray et al. (1995) Am. J. Respir. Cell Mol. Biol. 12, 597-604; Murray et al. (1996) Am. J. Physiol. 271, L829-L837; Chu et al . (1996) Nucleic Acids Res. 24, 3453-3457]. To investigate other possible mRNA splice variations, we sequenced the entire rClC-2 gene and found that ClC-2Sa (formerly ClC-2S) results from the deletion of exon 20. The preceding intron 19 has an unusually high CT content and a rare AAG acceptor site. Because both features were also found in intron 13, we next tested the hypothesis that intron 13 would be involved in alternative splicing. As predicted, a second splice product, ClC-2Sb, was found by RT-PCR, but only in lung. When we compared the genomic maps of rClC-2 and human ClC-1 (hClC-1), striking similarities were found in each exon except for rClC-2 exon 20, which is absent in hClC-1. These observations suggest that ClC-1 and ClC-2 may have evolved by gene duplication, mutation and DNA rearrangement.
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Affiliation(s)
- S Chu
- Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA.
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225
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Lindenthal S, Schmieder S, Ehrenfeld J, Wills NK. Cloning and functional expression of a ClC Cl- channel from the renal cell line A6. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C1176-85. [PMID: 9357761 DOI: 10.1152/ajpcell.1997.273.4.c1176] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Cl- channels are important for ion transport and cell volume regulation in A6 renal cells. In the present study, we used reverse transcriptase (RT)-polymerase chain reaction (PCR) and rapid amplification of cDNA ends (RACE) to identify proteins homologous to ClC Cl- channel proteins in A6 cells. Using degenerate primers designed on consensus sequences for members of the ClC family, we amplified an RT-PCR product that had significant homology to the ClC sequences. RACE-PCR was then used to isolate several full-length clones that had total lengths from 2,764 to 3,016 base pairs. Although the coding regions were identical, sequence differences occurred in the 5' noncoding regions. The amino acid sequences of the clones had high homologies to rat and human ClC-5 (85 and 84%, respectively, if the 5th methionine of the open reading frame represents the start codon). Three parts of the protein (53, 80, and 63 amino acids in length) were 97-100% homologous to the mammalian sequences. Ribonuclease protection assay analysis revealed mRNA for this protein in oocytes, kidney, intestine, liver, brain, and blood, with lower amounts in stomach, muscle, and skin. Expression of the clones in Xenopus laevis oocytes resulted in an outwardly rectifying Cl- current that was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and possessed an anion selectivity of I- > Cl- >> gluconate.
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Affiliation(s)
- S Lindenthal
- Department of Physiology, University of Texas Medical Branch, Galveston 77555, USA
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226
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Abstract
Phosphorylation controls the activity of ion channels in many tissues. In epithelia, the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is activated by phosphorylation of serine residues in its regulatory (R) domain and then gated by binding and hydrolysis of ATP by the nucleotide-binding domains. Current models propose that the unphosphorylated R domain serves as an inhibitory particle that occludes the pore, much like the inhibitory 'ball' in Shaker K+ channels; presumably, phosphorylation relieves this inhibition. Here we test this by adding an R-domain peptide to a CFTR variant in which much of the R domain had been deleted (CFTR-deltaR/S660A): in contrast to predictions, we found that adding an unphosphorylated R domain to CFTR-deltaR/S660A did not inhibit activity, whereas a phosphorylated R-domain peptide stimulated activity. To investigate how phosphorylation controls activity, we studied channel gating and found that phosphorylation of the R domain increases the rate of channel opening by enhancing the sensitivity to ATP. Our results indicate that CFTR is regulated by a new mechanism in which phosphorylation of one domain stimulates the interaction of ATP with another domain, thereby increasing activity.
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Affiliation(s)
- M C Winter
- Howard Hughes Medical Institute, Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242, USA
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227
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Okada Y. Volume expansion-sensing outward-rectifier Cl- channel: fresh start to the molecular identity and volume sensor. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C755-89. [PMID: 9316396 DOI: 10.1152/ajpcell.1997.273.3.c755] [Citation(s) in RCA: 514] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The maintenance of a constant volume in the face of extracellular and intracellular osmotic perturbation is essential for the normal function and survival of animal cells. Osmotically swollen cells restore their volume, exhibiting a regulatory volume decrease by releasing intracellular K+, Cl-, organic solutes, and obligated water. In many cell types, the volume regulatory effluxes of Cl- and some organic osmolytes are known to be induced by swelling-induced activation of anion channels that are characterized by their moderate outward rectification, cytosolic ATP dependency, and intermediate unitary conductance (10-100 pS). Recently, simultaneous measurements of cell size by light microscopy and whole cell Cl- current have shown that the Cl- current density is proportionally increased with an increase in the outer surface area, which is mainly achieved through unfolding of membrane invaginations by volume expansion. Thus this anion channel can somehow sense volume expansion and can be called the volume expansion-sensing outwardly rectifying (VSOR) anion channel. Its molecular identity and activation mechanism are yet to be elucidated. Three cloned proteins, ClC-2, P-glycoprotein, and pIcln, have been proposed as candidates for the VSOR anion channel. The unitary conductance, voltage dependency, anion selectivity, pH dependency, and pharmacology of the VSOR anion channel are distinct from the ClC-2 Cl- channel, which is also known to be sensitive to volume changes. Recent patch-clamp studies in combination with molecular biological techniques have shown that P-glycoprotein is not itself the channel protein but is a regulator of its volume sensitivity. Although there is still debate about another candidate protein, pIcln, the most recent study has suggested that this is likely to be a regulator of some other distinct Cl- channel. Identification of the VSOR anion channel protein per se, its volume-sensing mechanism, and its accessory/regulatory proteins at the molecular level is currently a subject of utmost physiological importance.
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Affiliation(s)
- Y Okada
- Department of Cellular and Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Japan
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228
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Voets T, Droogmans G, Nilius B. Modulation of voltage-dependent properties of a swelling-activated Cl- current. J Gen Physiol 1997; 110:313-25. [PMID: 9276756 PMCID: PMC2229363 DOI: 10.1085/jgp.110.3.313] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We used the patch-clamp technique to study the voltage-dependent properties of the swelling-activated Cl- current (ICl,swell) in BC3H1 myoblasts. This Cl- current is outwardly rectifying and exhibits time-dependent inactivation at positive potentials (potential for half-maximal inactivation of +75 mV). Single-channel Cl- currents with similar voltage-dependent characteristics could be measured in outside-out patches pulled from swollen cells. The estimated single-channel slope conductance in the region between +60 and +140 mV was 47 pS. The time course of inactivation was well described by a double exponential function, with a voltage-independent fast time constant (approximately 60 ms) and a voltage-dependent slow time constant (>200 ms). Recovery from inactivation, which occurred over the physiological voltage range, was also well described by a double exponential function, with a voltage-dependent fast time constant (10-80 ms) and a voltage-dependent slow time constant (>100 ms). The inactivation process was significantly accelerated by reducing the pH, increasing the Mg2+ concentration or reducing the Cl- concentration of the extracellular solution. Replacing extracellular Cl- by other permeant anions shifted the inactivation curve in parallel with their relative permeabilities (SCN- > I- > NO3- > Cl- >> gluconate). A leftward shift of the inactivation curve could also be induced by channel blockers. Additionally, the permeant anion and the channel blockers, but not external pH or Mg2+, modulated the recovery from inactivation. In conclusion, our results show that the voltage-dependent properties of ICl,swell are strongly influenced by external pH, external divalent cations, and by the nature of the permeant anion.
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Affiliation(s)
- T Voets
- KU Leuven, Laboratorium voor Fysiologie, Campus Gasthuisberg, B-3000 Leuven, Belgium
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229
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Adler DA, Rugarli EI, Lingenfelter PA, Tsuchiya K, Poslinski D, Liggitt HD, Chapman VM, Elliott RW, Ballabio A, Disteche CM. Evidence of evolutionary up-regulation of the single active X chromosome in mammals based on Clc4 expression levels in Mus spretus and Mus musculus. Proc Natl Acad Sci U S A 1997; 94:9244-8. [PMID: 9256467 PMCID: PMC23138 DOI: 10.1073/pnas.94.17.9244] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/1997] [Indexed: 02/05/2023] Open
Abstract
Previous studies have shown that the chloride channel gene Clc4 is X-linked and subject to X inactivation in Mus spretus, but that the same gene is autosomal in laboratory strains of mice. This exception to the conservation of linkage of the X chromosome in one of two interfertile mouse species was exploited to compare expression of Clc4 from the X chromosome to that from the autosome. Clc4 was found to be highly expressed in brain tissues of both mouse species. Quantitative analyses of species-specific expression of Clc4 in brain tissues from mice resulting from M. spretus x laboratory strain crosses, demonstrate that each autosomal locus has half the level of Clc4 expression as compared with the single active X-linked locus. In contrast expression of another chloride channel gene, Clc3, which is autosomal in both mouse species is equal between alleles in F1 animals. There is no evidence of imprinting of the Clc4 autosomal locus. These results are consistent with Ohno's hypothesis of an evolutionary requirement for a higher expression of genes on the single active X chromosome to maintain balance with autosomal gene expression [Ohno, S. (1967) Sex Chromosomes and Sex-Linked Genes (Springer, Berlin)].
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Affiliation(s)
- D A Adler
- Department of Pathology, Box 357470, University of Washington, Seattle, WA 98195-7470, USA
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230
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Schmidt-Rose T, Jentsch TJ. Reconstitution of functional voltage-gated chloride channels from complementary fragments of CLC-1. J Biol Chem 1997; 272:20515-21. [PMID: 9252364 DOI: 10.1074/jbc.272.33.20515] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We investigated the effect of truncations on the human muscle chloride channel CLC-1 and studied the functional complementation from partial proteins. Almost complete deletion of the cytoplasmic amino terminus did not affect currents, but truncating the intracellular COOH terminus after Leu720 abolished function. Currents were restored by coexpressing this membrane-embedded part with the lacking cytoplasmic fragment that contains domain D13, the second of the two conserved cystathionine beta-synthase (CBS) motifs present in all eukaryotic CLC proteins. However, if the cut was after Gln597 before the first CBS domain, no functional complementation was seen. Complementation was also obtained with channels "split" between transmembrane domains D7 and D8 or domains D8 and D9, but not when split between D10 and D11. Specificity of currents was tested by inserting point mutations in NH2-terminal (G188A and G230E) or COOH-terminal (K585E) fragments. In contrast to G188A and K585E, split channels did not tolerate the D136G mutation, suggesting that it may impede association from nonlinked fragments. Duplication, but not a lack of domain D8 was tolerated in "split" channels. Membrane domains D9-D12 can insert into the membrane without adding a preceding signal peptide to ensure the extracellular amino terminus of D9. Eventually, we succeeded in reconstituting CLC-1 channels from three separate polypeptides: the amino-terminal part up to D8, D9 through CBS1, and the remainder of the cytoplasmic carboxyl terminus. In summary, several regions of CLC channels behave autonomously regarding membrane insertion and folding and mediate protein-protein interactions strong enough to yield functional channels without a direct covalent link.
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Affiliation(s)
- T Schmidt-Rose
- Center for Molecular Neurobiology Hamburg (ZMNH), Hamburg University, Martinistrasse 52, D-20246 Hamburg, Germany
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231
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Sherry AM, Stroffekova K, Knapp LM, Kupert EY, Cuppoletti J, Malinowska DH. Characterization of the human pH- and PKA-activated ClC-2G(2 alpha) Cl- channel. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C384-93. [PMID: 9277336 DOI: 10.1152/ajpcell.1997.273.2.c384] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A ClC-2G(2 alpha) Cl- channel was identified to be present in human lung and stomach, and a partial cDNA for this Cl- channel was cloned from a human fetal lung library. A full-length expressible human ClC-2G(2 alpha) cDNA was constructed by ligation of mutagenized expressible rabbit ClC-2G(2 alpha) cDNA with the human lung ClC-2G(2 alpha) cDNA, expressed in oocytes, and characterized at the single-channel level. Adenosine 3',5'-cyclic monophosphate-dependent protein kinase (PKA) treatment increased the probability of opening of the channel (Po). After PKA activation, the channel exhibited a linear (r = 0.99) current-voltage curve with a slope conductance of 22.1 +/- 0.8 pS in symmetric 800 mM tetraethylammonium chloride (TEACl; pH 7.4). Under fivefold gradient conditions of TEACl, a reversal potential of +21.5 +/- 2.8 mV was measured demonstrating anion-to-cation discrimination. As previously demonstrated for the rabbit ClC-2G(2 alpha) Cl- channel, the human analog, hClC-2G(2 alpha), was active at pH 7.4 as well as when the pH of the extracellular face of the channel (trans side of the bilayer; pHtrans) was asymmetrically reduced to pH 3.0. The extent of PKA activation was dependent on pHtrans. With PKA treatment, Po increased fourfold with a pHtrans of 7.4 and eightfold with a pHtrans of 3.0. Effects of sequential PKA addition followed by pHtrans reduction on the same channel suggested that the PKA- and pH-dependent increases in channel Po were separable and cumulative. Northern analysis showed ClC-2G(2 alpha) mRNA to be present in human adult and fetal lung and adult stomach, and quantitative reverse transcriptase-polymerase chain reaction showed this channel to be present in the adult human lung and stomach at about one-half the level found in fetal lung. The findings of the present study suggest that the ClC-2G(2 alpha) Cl- channel may play an important role in Cl- transport in the fetal and adult human lung.
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Affiliation(s)
- A M Sherry
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Ohio 45267-0576, USA
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232
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Abstract
The Cl- channel from the Torpedo electric organ, CLC-0, is the prototype of a large gene family of Cl- channels. At the single-channel level, CLC-0 shows a "double-barreled" behavior. Recently it was shown that CLC-0 is a dimer, and it was suggested that each subunit forms a single pore. The two protopores are gated individually by a fast voltage and anion-dependent gating mechanism. A slower common gating mechanism operates on both pores simultaneously. Previously, wild-type/mutant heteromeric channels had been constructed that display a large wild-type pore and small mutant pore. Here we use patch-clamp recording of single wild-type and mutant CLC-0 channels to investigate in detail the dependence of the gating of one protopore on the physically attached neighboring pore. No difference in rate constants of opening and closing of protopores could be found comparing homomeric wild-type and heteromeric wild-type/mutant channels. In addition, detailed kinetic analysis reveals that gating of single subunits is not correlated with the gating of the neighboring subunit. The results are consistent with the view that permeation and fast gating of individual pores are fully independent of the neighboring pore. Because the two subunits are associated in a common protein complex, opening and closing transitions of individual pores are probably due to only small conformational changes in each pore. In addition to the fast and slow gating mechanisms known previously for CLC-0, in the course of this study we occasionally observed an additional gating process that led to relatively long closures of single pores.
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Affiliation(s)
- U Ludewig
- Center for Molecular Neurobiology, Hamburg University, Germany
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233
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Abstract
CLC chloride channels form a large and conserved gene family unrelated to other channel proteins. Knowledge of the transmembrane topology of these channels is important for understanding the effects of mutations found in human myotonia and inherited hypercalciuric kidney stone diseases and for the interpretation of structure-function studies. We now systematically study the topology of human ClC-1, a prototype CLC channel that is defective in human myotonia. Using a combination of in vitro glycosylation scanning and protease protection assays, we show that both N and C termini face the cytoplasm and demonstrate the presence of 10 (or less likely 12) transmembrane spans. Difficult regions were additionally tested by inserting cysteines and probing the effect of cysteine-modifying reagents on ClC-1 currents. The results show that D3 crosses the membrane and D4 does not, and that L549 between D11 and D12 is accessible from the outside. Further, since the modification of cysteines introduced between D11 and D12 and at the extracellular end of D3 strongly affect ClC-1 currents, these regions are suggested to be important for ion permeation.
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Affiliation(s)
- T Schmidt-Rose
- Center for Molecular Neurobiology Hamburg, ZMNH, Hamburg University, Martinistrasse 52, D-20246 Hamburg, Germany
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234
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Galietta LJ, Falzoni S, Di Virgilio F, Romeo G, Zegarra-Moran O. Characterization of volume-sensitive taurine- and Cl(-)-permeable channels. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C57-66. [PMID: 9252442 DOI: 10.1152/ajpcell.1997.273.1.c57] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Volume-sensitive Cl- channels [ICl(vol)] were studied using taurine efflux and patch-clamp experiments in 9HTEo- human tracheal cells. Cells were stimulated with the Ca(2+)- elevating agents ATP and ionomycin in isotonic medium or in hypotonic solutions. ATP (100 microM) or ionomycin (1 microM) and hypotonic shock produced a synergic effect. Indeed, the resulting taurine efflux was much higher than the sum of the single effects elicited by ATP, ionomycin, or hypotonic medium. The taurine release elicited by hypotonic shock and the potentiation by ATP and ionomycin were markedly inhibited by using a Ca(2+)-free extracellular medium and by incubating the cells with the membrane-permeable 1,2-bis(2-amino- phenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester chelating agent. Patch-clamp experiments confirmed the role of Ca2+ on ICl(vol) channels. Swelling-induced taurine efflux was inhibited by reactive blue 2, suramin, and pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid. Patch-clamp experiments demonstrated that these compounds shift the voltage-dependent inactivation of ICl(vol) channels toward more negative values. This study indicates that the sensitivity of ICl(vol) to cell volume changes is modulated by intracellular Ca2+ and that purinergic receptor antagonists represent a new class of CI- channel blockers.
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Affiliation(s)
- L J Galietta
- Lab di Genetica Molecolare, Istituto Giannina Gaslini, Genoa, Italy
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235
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Steinert M, Grissmer S. Novel activation stimulus of chloride channels by potassium in human osteoblasts and human leukaemic T lymphocytes. J Physiol 1997; 500 ( Pt 3):653-60. [PMID: 9161983 PMCID: PMC1159416 DOI: 10.1113/jphysiol.1997.sp022050] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
1. The whole-cell recording mode of the patch-clamp technique was used to study the effect of extracellular K+ and Rb+ on membrane currents in human osteoblasts, in a human osteoblast-like cell line, and in the Jurkat human leukaemic T cell line. 2. Increasing the extracellular concentration of K+ increased the membrane conductance of the cells in a concentration-dependent manner. This increase in membrane conductance was due to the activation of a Cl- conductance. Rb+ also induced this conductance, but conductance was less than half that seen in K+. 3. The Cl- channel blockers 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and 4-acetamido-4'-isothiocyanatostilbene 2,2'-disulphonic acid (SITS) blocked the K(+)-induced Cl- current in a voltage-dependent manner. The degree of blockade increased with membrane depolarization to a maximum level at 40 mV. At potentials above this value the block appeared to decrease. 4. Both tonicity and K+ were required for maximal activation of the Cl- conductance since the K(+)-induced Cl- conductance could be inhibited by hypertonic solutions and the activation of a volume-sensitive Cl- conductance by hypotonic solutions could be enhanced by extracellular K+. 5. We conclude that an outwardly rectifying Cl- conductance can be activated either upon osmotic swelling or by an increase in extracellular K+. Both activation pathways may be involved in cell volume regulation and seem to apply to volume-sensitive Cl- channels in general since we observe this phenomenon in two different cell types, in human osteoblasts as well as in human leukaemic T lymphocytes.
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Affiliation(s)
- M Steinert
- Department of Applied Physiology, University of Ulm, Germany
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236
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Abstract
The ClC-2 chloride channel is probably involved in the regulation of cell volume and of neuronal excitability. Site-directed mutagenesis was used to understand ClC-2 activation in response to cell swelling, hyperpolarization and acidic extracellular pH. Similar to equivalent mutations in ClC-0, neutralizing Lys566 at the end of the transmembrane domains results in outward rectification and a shift in voltage dependence, but leaves the basic gating mechanism, including swelling activation, intact. In contrast, mutations in the cytoplasmic loop between transmembrane domains D7 and D8 abolish all three modes of activation by constitutively opening the channel without changing its pore properties. These effects resemble those observed with deletions of an amino-terminal inactivation domain, and suggest that it may act as its receptor. Such a 'ball-and-chain' type mechanism may act as a final pathway in the activation of ClC-2 elicited by several stimuli.
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Affiliation(s)
- S E Jordt
- Centre for Molecular Neurobiology (ZMNH), Hamburg University, Germany
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237
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Fritsch J, Edelman A. Osmosensitivity of the hyperpolarization-activated chloride current in human intestinal T84 cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 272:C778-86. [PMID: 9124511 DOI: 10.1152/ajpcell.1997.272.3.c778] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The osmosensitivity of the hyperpolarization-activated chloride current (I(Clhyp)) in T84 cells was studied using the whole cell patch-clamp recording configuration. Hypotonicity is known to activate an outwardly rectifying chloride current (HIORC) distinct from I(Clhyp) in these cells. The differing sensitivities of HIORC and I(Clhyp) toward inhibitors (1,9-dideoxyforskolin blocked HIORC but not I(Clhyp), and Cd2+ inhibited I(Clhyp) but not HIORC) allowed us to investigate the osmoregulation of I(Clhyp). Hypotonicity induced an increase in I(Clhyp) amplitude. Protein phosphatase inhibitors prevented this effect, and hypotonic solutions became slightly inhibitory. Hypertonicity resulted in a transient increase in I(Clhyp) amplitude followed by a large decrease. The complex responses of I(Clhyp) to osmotic changes indicate that these signals affect the same channel via multiple transduction pathways. The responses of I(Clhyp) to hypotonicity have features in common with the responses of ClC-2 channels expressed in Xenopus oocytes (activation) and with hyperpolarization-activated chloride currents in other cell types, such as osteoblasts and mandibular duct cells (inhibition).
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Affiliation(s)
- J Fritsch
- Laboratoire du Calcium et Tissu Osseux dans l'Organisme en Développement, Centre National de la Recherche Scientifique Unité de Recherche Associée 583, Hôpital des Enfants Malades, Paris, France
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238
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Laich A, Gschwentner M, Krick W, Nagl UO, Fürst J, Hofer S, Susanna A, Schmarda A, Deetjen P, Burckhardt G, Paulmichl M. ICln, a chloride channel cloned from kidney cells, is activated during regulatory volume decrease. Kidney Int 1997; 51:477-8. [PMID: 9027725 DOI: 10.1038/ki.1997.65] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- A Laich
- Department of Physiology, University of Innsbruck, Austria
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239
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Ludewig U, Jentsch TJ, Pusch M. Analysis of a protein region involved in permeation and gating of the voltage-gated Torpedo chloride channel ClC-0. J Physiol 1997; 498 ( Pt 3):691-702. [PMID: 9051580 PMCID: PMC1159185 DOI: 10.1113/jphysiol.1997.sp021893] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
1. The chloride channel from the Torpedo electric organ, ClC-0, is controlled by two distinct ('fast' and 'slow') voltage-dependent gates. Here we investigate the effects of mutations in a region after putative transmembrane domain D12. A mutation in this region has previously been shown to change fast gating and permeation. 2. We used a combination of site-directed mutagenesis with two-electrode voltage-clamp and patch-clamp measurements. 3. Most conservative substitutions have minor effects, while more drastic mutations change kinetics and voltage dependence of fast gating, as well as ion selectivity and rectification. 4. While ClC-0 wild-type (WT) channels deactivate fully in two-electrode voltage clamp at negative voltages, channels do not close completely in patch-clamp experiments. Open probability is increased by intracellular chloride in a concentration- but not voltage-dependent manner. 5. In several mutants, including K519R, the minimal macroscopic open probability of fast gating is larger than in WT. Mutant channels fluctuate at negative potentials between open and closed conformations. Open probability is much more effectively increased by intracellular chloride than in WT. The observations support the idea that permeating ions inside the pore stabilize the open state. 6. Besides effects on permeation and gating of single protopores, some mutations affect 'slow' gating. In summary, the region after D12 participates in fast as well as in slow gating; mutations additionally influence permeation properties.
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Affiliation(s)
- U Ludewig
- Centre for Molecular Neurobiology (ZMNH), Hamburg University, Germany
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240
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Kajita H, Brown PD. Inhibition of the inward-rectifying Cl- channel in rat choroid plexus by a decrease in extracellular pH. J Physiol 1997; 498 ( Pt 3):703-7. [PMID: 9051581 PMCID: PMC1159186 DOI: 10.1113/jphysiol.1997.sp021894] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
1. The sensitivity of the inward-rectifying Cl- channel in choroid plexus to changes in external pH (pHo) was examined. 2. Cl- currents were recorded using whole-cell patch-clamp methods. The inward-rectifying channel was activated by 375 nM of the catalytic subunit of protein kinase A which was added to the electrode solution. 3. Reducing pHo from 7.3 to 6.5 inhibited the inward-rectifying Cl- currents, whereas an increase in current was observed when pHo was elevated to 8.5. The inhibition of the conductance exhibited a sigmoidal relationship with decreasing pH over a range of 8.5 to 5.5. A half-maximal inhibition of the current was observed at pH 7.3. 4. The inhibition of the whole-cell current by reducing pHo suggests that it is carried by channels which are distinct from other inward-rectifier Cl- channels, e.g. ClC-2, phospholemman and the channel in Xenopus oocytes.
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Affiliation(s)
- H Kajita
- Cell Physiology Group, School of Biological Sciences, University of Manchester, UK
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241
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Abstract
Chloride channels are probably found in every cell, from bacteria to mammals. Their physiological tasks range from cell volume regulation to stabilization of the membrane potential, signal transduction, transepithelial transport and acidification of intracellular organelles. These different functions require the presence of many distinct chloride channels, which are differentially expressed and regulated by various stimuli. These include various intracellular messengers (like calcium and cyclic AMP), pH, extracellular ligands and transmembrane voltage. Three major structural classes of chloride channels are known to date, but there may be others not yet identified. After an overview of the general functions of chloride channels, this review will focus on these cloned chloride channels: the CLC chloride channel family, which includes voltage-gated chloride channels, and the cystic fibrosis transmembrane regulator (CFTR), which performs other functions in addition to being a chloride channel. Finally, a short section deals with GABA and glycine receptors. Diseases resulting from chloride channel defects will be specially emphasized, together with the somewhat limited information about how these proteins work at the molecular level.
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Affiliation(s)
- T J Jentsch
- Zentrum für molekulare Neurobiologie (ZMNH), Universität Hamburg, Germany
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242
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Coca-Prados M, Sánchez-Torres J. Chapter 2 Molecular Approaches to the Study of the Na+,K+ -ATPase and Chloride Channels in the Ocular Ciliary Epithelium. CURRENT TOPICS IN MEMBRANES 1997. [DOI: 10.1016/s0070-2161(08)60242-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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243
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Abstract
The functional impact of ion channels in vascular endothelial cells (ECs) is still a matter of controversy. This review describes different types of ion channels in ECs and their role in electrogenesis, Ca2+ signaling, vessel permeability, cell-cell communication, mechano-sensor functions, and pH and volume regulation. One major function of ion channels in ECs is the control of Ca2+ influx either by a direct modulation of the Ca2+ influx pathway or by indirect modulation of K+ and Cl- channels, thereby clamping the membrane at a sufficiently negative potential to provide the necessary driving force for a sustained Ca2+ influx. We discuss various mechanisms of Ca2+ influx stimulation: those that activate nonselective, Ca(2+)-permeable cation channels or those that activate Ca(2+)-selective channels, exclusively or partially operated by the filling state of intracellular Ca2+ stores. We also describe the role of various Ca(2+)- and shear stress-activated K+ channels and different types of Cl- channels for the regulation of the membrane potential.
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Affiliation(s)
- B Nilius
- Laboratorium voor Fysiologie, KU Leuven, Belgium
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244
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Abstract
Voltage-dependent chloride (ClC) channels have not yet been identified in the cochlea. In this study, an approach utilizing the reverse transcription-polymerase chain reaction (RT-PCR) was devised to clone the cDNA of ClC channels. PCR was performed using degenerate primers corresponding to two highly conserved regions of the ClC channels. By Southern hybridization and sequencing studies, the sequences corresponding to ClC-2 and ClC-3 were found in the cochlear lateral wall, while ClC-1 was not detected. These results suggest that ClC-2 and ClC-3 might be involved in Cl- transport in the cochlear lateral wall.
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Affiliation(s)
- T Oshima
- Department of Otolaryngology, Tohoku University School of Medicine, Sendai, Japan
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245
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Chapter 1 Transport Components of Net Secretion of the Aqueous Humor and Their Integrated Regulation. CURRENT TOPICS IN MEMBRANES 1997. [DOI: 10.1016/s0070-2161(08)60241-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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246
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Hechenberger M, Schwappach B, Fischer WN, Frommer WB, Jentsch TJ, Steinmeyer K. A family of putative chloride channels from Arabidopsis and functional complementation of a yeast strain with a CLC gene disruption. J Biol Chem 1996; 271:33632-8. [PMID: 8969232 DOI: 10.1074/jbc.271.52.33632] [Citation(s) in RCA: 137] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We have cloned four novel members of the CLC family of chloride channels from Arabidopsis thaliana. The four plant genes are homologous to a recently isolated chloride channel gene from tobacco (CLC-Nt1; Lurin, C., Geelen, D., Barbier-Brygoo, H., Guern, J., and Maurel, C. (1996) Plant Cell 8, 701-711) and are about 30% identical in sequence to the most closely related CLC-6 and CLC-7 putative chloride channels from mammalia. AtCLC transcripts are broadly expressed in the plant. Similarly, antibodies against the AtCLC-d protein detected the protein in all tissues, but predominantly in the silique. AtCLC-a and AtCLC-b are highly homologous to each other ( approximately 87% identity), while being approximately 50% identical to either AtCLC-c or AtCLC-d. None of the four cDNAs elicited chloride currents when expressed in Xenopus oocytes, either singly or in combination. Among these genes, only AtCLC-d could functionally substitute for the single yeast CLC protein, restoring iron-limited growth of a strain disrupted for this gene. Introduction of disease causing mutations, identified in human CLC genes, abolished this capacity. Consistent with a similar function of both proteins, the green fluorescent protein-tagged AtCLC-d protein showed the identical localization pattern as the yeast ScCLC protein. This suggests that in Arabidopsis AtCLC-d functions as an intracellular chloride channel.
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Affiliation(s)
- M Hechenberger
- Center for Molecular Neurobiology (ZMNH), Hamburg University, Martinistr. 52, D-20246 Hamburg, Germany
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247
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Rychkov GY, Pusch M, Astill DS, Roberts ML, Jentsch TJ, Bretag AH. Concentration and pH dependence of skeletal muscle chloride channel ClC-1. J Physiol 1996; 497 ( Pt 2):423-35. [PMID: 8961185 PMCID: PMC1160994 DOI: 10.1113/jphysiol.1996.sp021778] [Citation(s) in RCA: 135] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
1. The influence of Cl- concentration and pH on gating of the skeletal muscle Cl- channel, ClC-1, has been assessed using the voltage-clamp technique and the Sf-9 insect cell and Xenopus oocyte expression systems. 2. Hyperpolarization induces deactivating inward currents comprising a steady-state component and two exponentially decaying components, of which the faster is weakly voltage dependent and the slower strongly voltage dependent. 3. Open probability (Po) and kinetics depend on external but not internal Cl- concentration. 4. A point mutation, K585E, in human ClC-1, equivalent to a previously described mutation in the Torpedo electroplaque chloride channel, ClC-0, alters the I-V relationship and kinetics, but retains external Cl- dependence. 5. When external pH is reduced, the deactivating inward currents of ClC-1 are diminished without change in time constants while the steady-state component is enhanced. 6. In contrast, reduced internal pH slows deactivating current kinetics as its most immediately obvious action and the Po curve is shifted in the hyperpolarizing direction. Addition of internal benzoate at low internal pH counteracts both these effects. 7. A current activated by hyperpolarization can be revealed at an external pH of 5.5 in ClC-1, which in some ways resembles currents due to the slow gates of ClC-0. 8. Gating appears to be controlled by a Cl(-)-binding site accessible only from the exterior and, possibly, by modification of this site by external protonation. Intracellular hydroxyl ions strongly affect gating either allosterically or by direct binding and blocking of the pore, an action mimicked by intracellular benzoate.
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Affiliation(s)
- G Y Rychkov
- Centre for Advanced Biomedical Studies, University of South Australia, Adelaide, Australia
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248
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Lorenz C, Pusch M, Jentsch TJ. Heteromultimeric CLC chloride channels with novel properties. Proc Natl Acad Sci U S A 1996; 93:13362-6. [PMID: 8917596 PMCID: PMC24098 DOI: 10.1073/pnas.93.23.13362] [Citation(s) in RCA: 209] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The skeletal muscle chloride channel CLC-1 and the ubiquitous volume-activated chloride channel CLC-2 belong to a large gene family whose members often show overlapping expression patterns. CLC-1 and CLC-2 are coexpressed in skeletal and smooth muscle and in the heart. By coexpressing CLC-1 and CLC-2 in Xenopus oocytes, we now show the formation of novel CLC-1/CLC-2 heterooligomers that yield time-independent linear chloride currents with a chloride-->bromide-->iodide selectivity sequence. Formation of heterooligomeric CLC channels increases the number and possible functions of chloride channels.
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Affiliation(s)
- C Lorenz
- Center for Molecular Neurobiology, Hamburg University, Germany
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249
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Abstract
1. An increase in cell volume activates, in most mammalian cells, a Cl- current, ICl,vol. This current is involved in a variety of cellular functions, such as the maintenance of a constant cell volume, pH regulation, and control of membrane potential. It might also play a role in the regulation of cell proliferation and in the processes that control transition from proliferation to differentiation. This review focuses on various aspects of this current, including its biophysical characterisation and its functional role for various cell processes. 2. Volume-activated Cl- channels show all outward rectification. Iodide is more permeable than chloride. In some cell types, ICl,vol inactivates at positive potentials. Single channel conductance can be divided mainly into two groups: small (< 5 pS) and medium conductance channels (around 50 pS). 3. The pharmacology and modulation of these channels are reviewed in detail, and suggest the existence of an heterogeneous family of multiple volume-activated Cl- channels. 4. Molecular candidates for this channel (i.e. ClC-2, a member of the ClC-family of voltage-dependent Cl- channels, the mdr-1 encoded P-glycoprotein, the nucleotide-sensitive pICln protein and phospholemman) will be discussed.
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Affiliation(s)
- B Nilius
- KU Leuven, Laboratorium voor Fysiologie, Belgium.
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250
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Basavappa S, Ellory JC. The role of swelling-induced anion channels during neuronal volume regulation. Mol Neurobiol 1996; 13:137-53. [PMID: 8938648 DOI: 10.1007/bf02740638] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Regulation of cell volume is an essential function of most mammalian cells. In the cells of the central nervous system, maintenance of cell osmolarity and, hence, volume, is particularly crucial because of the restrictive nature of the skull. Cell volume regulation involves a variety of pathways, with considerable differences between cell types. One common pathway activated during hypo-osmotic stress involves chloride (Cl-) channels. However, hypo-osmotically stimulated anion permeability can be regulated by a diverse array of second messengers. Although neuronal swelling can occur in a number of pathological and nonpathological conditions, our understanding of neuronal volume regulation is limited. This article summarizes our current understanding of the role of anion channels during neuronal volume regulation.
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Affiliation(s)
- S Basavappa
- University Laboratory of Physiology, University of Oxford, UK
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