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Marunaka Y. Physiological roles of chloride ions in bodily and cellular functions. J Physiol Sci 2023; 73:31. [PMID: 37968609 PMCID: PMC10717538 DOI: 10.1186/s12576-023-00889-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Accepted: 10/31/2023] [Indexed: 11/17/2023]
Abstract
Physiological roles of Cl-, a major anion in the body, are not well known compared with those of cations. This review article introduces: (1) roles of Cl- in bodily and cellular functions; (2) the range of cytosolic Cl- concentration ([Cl-]c); (3) whether [Cl-]c could change with cell volume change under an isosmotic condition; (4) whether [Cl-]c could change under conditions where multiple Cl- transporters and channels contribute to Cl- influx and efflux in an isosmotic state; (5) whether the change in [Cl-]c could be large enough to act as signals; (6) effects of Cl- on cytoskeletal tubulin polymerization through inhibition of GTPase activity and tubulin polymerization-dependent biological activity; (7) roles of cytosolic Cl- in cell proliferation; (8) Cl--regulatory mechanisms of ciliary motility; (9) roles of Cl- in sweet/umami taste receptors; (10) Cl--regulatory mechanisms of with-no-lysine kinase (WNK); (11) roles of Cl- in regulation of epithelial Na+ transport; (12) relationship between roles of Cl- and H+ in body functions.
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Affiliation(s)
- Yoshinori Marunaka
- Medical Research Institute, Kyoto Industrial Health Association, General Incorporated Foundation, 67 Kitatsuboi-Cho, Nishinokyo, Nakagyo-Ku, Kyoto, 604-8472, Japan.
- Research Organization of Science and Technology, Ritsumeikan University, Kusatsu, 525-8577, Japan.
- Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kamigyo-Ku, Kyoto, 602-8566, Japan.
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Murtazina AR, Nikishina YO, Bondarenko NS, Dil'mukhametova LK, Sapronova AY, Ugrumov MV. Developing brain as a source of circulating norepinephrine in rats during the critical period of morphogenesis. Brain Struct Funct 2019; 224:3059-3073. [PMID: 31493024 DOI: 10.1007/s00429-019-01950-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Accepted: 08/28/2019] [Indexed: 11/29/2022]
Abstract
The development of individual organs and the whole organism is under the control by morphogenetic factors over the critical period of morphogenesis. This study was aimed to test our hypothesis that the developing brain operates as an endocrine organ during morphogenesis, in rats during the perinatal period (Ugrumov in Neuro Chem 35:837-850, 2010). Norepinephrine, which is a morphogenetic factor, was used as a marker of the endocrine activity of the developing brain, although it is also secreted by peripheral organs. In this study, it was first shown that the concentration of norepinephrine in the peripheral blood of neonatal rats is sufficient to ensure the morphogenetic effect on the peripheral organs and the brain itself. Using pharmacological suppression of norepinephrine production in the brain, but not in peripheral organs, it was shown that norepinephrine is delivered from the brain to the general circulation in neonatal rats, that is, during morphogenesis. In fact, even partial suppression of norepinephrine production in the brain of neonatal rats led to a significant decrease of norepinephrine concentration in plasma, suggesting that at this time the brain is an important source of circulating norepinephrine. Conversely, the suppression of the production of norepinephrine in the brain of prepubertal rats did not cause a change in its concentration in plasma, showing no secretion of brain-derived norepinephrine to the bloodstream after morphogenesis. The above data support our hypothesis that morphogenetic factors, including norepinephrine, are delivered from the developing brain to the bloodstream, which occurs only during the critical period of morphogenesis.
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Affiliation(s)
- Aliia R Murtazina
- Laboratory of Neural and Neuroendocrine Regulations, Institute of Developmental Biology, Russian Academy of Sciences, 26 Vavilov str., 119334, Moscow, Russia
| | - Yulia O Nikishina
- Laboratory of Neural and Neuroendocrine Regulations, Institute of Developmental Biology, Russian Academy of Sciences, 26 Vavilov str., 119334, Moscow, Russia
| | - Nadezhda S Bondarenko
- Laboratory of Neural and Neuroendocrine Regulations, Institute of Developmental Biology, Russian Academy of Sciences, 26 Vavilov str., 119334, Moscow, Russia
| | - Liliya K Dil'mukhametova
- Laboratory of Neural and Neuroendocrine Regulations, Institute of Developmental Biology, Russian Academy of Sciences, 26 Vavilov str., 119334, Moscow, Russia
| | - Anna Ya Sapronova
- Laboratory of Neural and Neuroendocrine Regulations, Institute of Developmental Biology, Russian Academy of Sciences, 26 Vavilov str., 119334, Moscow, Russia
| | - Michael V Ugrumov
- Laboratory of Neural and Neuroendocrine Regulations, Institute of Developmental Biology, Russian Academy of Sciences, 26 Vavilov str., 119334, Moscow, Russia.
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Nomura T, Taruno A, Shiraishi M, Nakahari T, Inui T, Sokabe M, Eaton DC, Marunaka Y. Current-direction/amplitude-dependent single channel gating kinetics of mouse pannexin 1 channel: a new concept for gating kinetics. Sci Rep 2017; 7:10512. [PMID: 28874774 PMCID: PMC5585217 DOI: 10.1038/s41598-017-10921-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 08/16/2017] [Indexed: 11/25/2022] Open
Abstract
The detailed single-channel gating kinetics of mouse pannexin 1 (mPanx1) remains unknown, although mPanx1 is reported to be a voltage-activated anion-selective channel. We investigated characteristics of single-channel conductances and opening and closing rates of mPanx1 using patch-clamp techniques. The unitary current of mPanx1 shows outward rectification with single-channel conductances of ~20 pS for inward currents and ~80 pS for outward currents. The channel open time for outward currents (Cl- influx) increases linearly as the amplitude of single channel currents increases, while the open time for inward currents (Cl- efflux) is constant irrespective of changes in the current amplitude, as if the direction and amplitude of the unitary current regulates the open time. This is supported by further observations that replacement of extracellular Cl- with gluconate- diminishes the inward tail current (Cl- efflux) at a membrane potential of -100 mV due to the lowered outward current (gluconate- influx) at membrane potential of 100 mV. These results suggest that the direction and rate of charge-carrier movement regulate the open time of mPanx1, and that the previously reported voltage-dependence of Panx1 channel gating is not directly mediated by the membrane potential but rather by the direction and amplitude of currents through the channel.
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Affiliation(s)
- Takeshi Nomura
- Department of Molecular Cell Physiology, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, 602-8566, Japan
- Department of Bio-Ionomics, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, 602-8566, Japan
- Department of Physical Therapy, Faculty of Rehabilitation, Kyushu Nutrition Welfare University, Kitakyushu, 800-0298, Japan
| | - Akiyuki Taruno
- Department of Molecular Cell Physiology, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, 602-8566, Japan
| | - Makoto Shiraishi
- Department of Molecular Cell Physiology, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, 602-8566, Japan
| | - Takashi Nakahari
- Department of Molecular Cell Physiology, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, 602-8566, Japan
- Department of Bio-Ionomics, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, 602-8566, Japan
- Japan Institute for Food Education and Health, St. Agnes' University, Kyoto, 602-8013, Japan
| | - Toshio Inui
- Department of Molecular Cell Physiology, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, 602-8566, Japan
- Department of Bio-Ionomics, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, 602-8566, Japan
- Saisei Mirai Clinics, Moriguchi, 570-0012, Japan
| | - Masahiro Sokabe
- Mechanobiology Laboratory, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Douglas C Eaton
- Center for Cell & Molecular Signaling, Department of Physiology, Emory University School of Medicine, Atlanta, Georgia, 30322, USA
| | - Yoshinori Marunaka
- Department of Molecular Cell Physiology, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, 602-8566, Japan.
- Department of Bio-Ionomics, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, 602-8566, Japan.
- Japan Institute for Food Education and Health, St. Agnes' University, Kyoto, 602-8013, Japan.
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Sasamoto K, Niisato N, Taruno A, Marunaka Y. Simulation of Cl(-) Secretion in Epithelial Tissues: New Methodology Estimating Activity of Electro-Neutral Cl(-) Transporter. Front Physiol 2015; 6:370. [PMID: 26779025 PMCID: PMC4688368 DOI: 10.3389/fphys.2015.00370] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2015] [Accepted: 11/20/2015] [Indexed: 12/21/2022] Open
Abstract
Transcellular Cl− secretion is, in general, mediated by two steps; (1) the entry step of Cl− into the cytosolic space from the basolateral space across the basolateral membrane by Cl− transporters, such as Na+-K+-2Cl− cotransporter (NKCC1, an isoform of NKCC), and (2) the releasing step of Cl− from the cytosolic space into the luminal (air) space across the apical membrane via Cl− channels, such as cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel. Transcellular Cl− secretion has been characterized by using various experimental techniques. For example, measurements of short-circuit currents in the Ussing chamber and patch clamp techniques provide us information on transepithelial ion movements via transcellular pathway, transepithelial conductance, activity (open probability) of single channel, and whole cell currents. Although many investigators have tried to clarify roles of Cl− channels and transporters located at the apical and basolateral membranes in transcellular Cl− secretion, it is still unclear how Cl− channels/transporters contribute to transcellular Cl− secretion and are regulated by various stimuli such as Ca2+ and cAMP. In the present study, we simulate transcellular Cl− secretion using mathematical models combined with electrophysiological measurements, providing information on contribution of Cl− channels/transporters to transcellular Cl− secretion, activity of electro-neutral ion transporters and how Cl− channels/transporters are regulated.
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Affiliation(s)
- Kouhei Sasamoto
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine Kyoto, Japan
| | - Naomi Niisato
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of MedicineKyoto, Japan; Department of Health and Sports Sciences, Faculty of Health and Medical Sciences, Kyoto Gakuen UniversityKameoka, Japan; Japan Institute for Food Education and Health, St. Agnes' UniversityKyoto, Japan
| | - Akiyuki Taruno
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine Kyoto, Japan
| | - Yoshinori Marunaka
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of MedicineKyoto, Japan; Japan Institute for Food Education and Health, St. Agnes' UniversityKyoto, Japan; Department of Bio-Ionomics, Graduate School of Medical Science, Kyoto Prefectural University of MedicineKyoto, Japan
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Hosogi S, Kusuzaki K, Inui T, Wang X, Marunaka Y. Cytosolic chloride ion is a key factor in lysosomal acidification and function of autophagy in human gastric cancer cell. J Cell Mol Med 2014; 18:1124-33. [PMID: 24725767 PMCID: PMC4508152 DOI: 10.1111/jcmm.12257] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Accepted: 01/22/2014] [Indexed: 12/21/2022] Open
Abstract
The purpose of the present study was to clarify roles of cytosolic chloride ion (Cl(-) ) in regulation of lysosomal acidification [intra-lysosomal pH (pHlys )] and autophagy function in human gastric cancer cell line (MKN28). The MKN28 cells cultured under a low Cl(-) condition elevated pHlys and reduced the intra-lysosomal Cl(-) concentration ([Cl(-) ]lys ) via reduction of cytosolic Cl(-) concentration ([Cl(-) ]c ), showing abnormal accumulation of LC3II and p62 participating in autophagy function (dysfunction of autophagy) accompanied by inhibition of cell proliferation via G0 /G1 arrest without induction of apoptosis. We also studied effects of direct modification of H(+) transport on lysosomal acidification and autophagy. Application of bafilomycin A1 (an inhibitor of V-type H(+) -ATPase) or ethyl isopropyl amiloride [EIPA; an inhibitor of Na(+) /H(+) exchanger (NHE)] elevated pHlys and decreased [Cl(-) ]lys associated with inhibition of cell proliferation via induction of G0 /G1 arrest similar to the culture under a low Cl(-) condition. However, unlike low Cl(-) condition, application of the compound, bafilomycin A1 or EIPA, induced apoptosis associated with increases in caspase 3 and 9 without large reduction in [Cl(-) ]c compared with low Cl(-) condition. These observations suggest that the lowered [Cl(-) ]c primarily causes dysfunction of autophagy without apoptosis via dysfunction of lysosome induced by disturbance of intra-lysosomal acidification. This is the first study showing that cytosolic Cl(-) is a key factor of lysosome acidification and autophagy.
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Affiliation(s)
- Shigekuni Hosogi
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of MedicineKyoto, Japan
- Japan Institute for Food Education and Health, Heian Jogakuin (St. Agnes') UniversityKyoto, Japan
- * Correspondence to: Dr. Shigekuni HOSOGI, M.D., Ph.D. and Prof. Yoshinori MARUNAKA, M.D., Ph.D., Department of Molecular Cell Physiology, Kyoto Prefectural University of Medicine, 465 Kajii-cho, Kamigyo-ku, Kyoto 602-8566, Japan., Tel.: +81-75-251-5311, Fax: +81-75-251-0295, E-mails: for Shigekuni Hosogi; for Yoshinori Marunaka
| | - Katsuyuki Kusuzaki
- Japan Institute for Food Education and Health, Heian Jogakuin (St. Agnes') UniversityKyoto, Japan
- Department of Orthopaedic Surgery, Kyoto Kujo HospitalKyoto, Japan
| | - Toshio Inui
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of MedicineKyoto, Japan
- Department of Bio-Ionomics, Graduate School of Medical Science, Kyoto Prefectural University of MedicineKyoto, Japan
- Saisei Mirai ClinicsMoriguchi, Japan
| | - Xiangdong Wang
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of MedicineKyoto, Japan
- Department of Respiratory Medicine, Shanghai Respiratory Research Institute, Fudan University Zhongshan HospitalShanghai, China
| | - Yoshinori Marunaka
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of MedicineKyoto, Japan
- Japan Institute for Food Education and Health, Heian Jogakuin (St. Agnes') UniversityKyoto, Japan
- Department of Bio-Ionomics, Graduate School of Medical Science, Kyoto Prefectural University of MedicineKyoto, Japan
- Department of Respiratory Medicine, Shanghai Respiratory Research Institute, Fudan University Zhongshan HospitalShanghai, China
- * Correspondence to: Dr. Shigekuni HOSOGI, M.D., Ph.D. and Prof. Yoshinori MARUNAKA, M.D., Ph.D., Department of Molecular Cell Physiology, Kyoto Prefectural University of Medicine, 465 Kajii-cho, Kamigyo-ku, Kyoto 602-8566, Japan., Tel.: +81-75-251-5311, Fax: +81-75-251-0295, E-mails: for Shigekuni Hosogi; for Yoshinori Marunaka
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Uhlig C, Silva PL, Ornellas D, Santos RS, Miranda PJ, Spieth PM, Kiss T, Kasper M, Wiedemann B, Koch T, Morales MM, Pelosi P, de Abreu MG, Rocco PR. The effects of salbutamol on epithelial ion channels depend on the etiology of acute respiratory distress syndrome but not the route of administration. Respir Res 2014; 15:56. [PMID: 24886221 PMCID: PMC4026154 DOI: 10.1186/1465-9921-15-56] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Accepted: 04/24/2014] [Indexed: 02/06/2023] Open
Abstract
Introduction We investigated the effects of intravenous and intratracheal administration of salbutamol on lung morphology and function, expression of ion channels, aquaporin, and markers of inflammation, apoptosis, and alveolar epithelial/endothelial cell damage in experimental pulmonary (p) and extrapulmonary (exp) mild acute respiratory distress syndrome (ARDS). Methods In this prospective randomized controlled experimental study, 56 male Wistar rats were randomly assigned to mild ARDS induced by either intratracheal (n = 28, ARDSp) or intraperitoneal (n = 28, ARDSexp) administration of E. coli lipopolysaccharide. Four animals with no lung injury served as controls (NI). After 24 hours, animals were anesthetized, mechanically ventilated in pressure-controlled mode with low tidal volume (6 mL/kg), and randomly assigned to receive salbutamol (SALB) or saline 0.9% (CTRL), intravenously (i.v., 10 μg/kg/h) or intratracheally (bolus, 25 μg). Salbutamol doses were targeted at an increase of ≈ 20% in heart rate. Hemodynamics, lung mechanics, and arterial blood gases were measured before and after (at 30 and 60 min) salbutamol administration. At the end of the experiment, lungs were extracted for analysis of lung histology and molecular biology analysis. Values are expressed as mean ± standard deviation, and fold changes relative to NI, CTRL vs. SALB. Results The gene expression of ion channels and aquaporin was increased in mild ARDSp, but not ARDSexp. In ARDSp, intravenous salbutamol resulted in higher gene expression of alveolar epithelial sodium channel (0.20 ± 0.07 vs. 0.68 ± 0.24, p < 0.001), aquaporin-1 (0.44 ± 0.09 vs. 0.96 ± 0.12, p < 0.001) aquaporin-3 (0.31 ± 0.12 vs. 0.93 ± 0.20, p < 0.001), and Na-K-ATPase-α (0.39 ± 0.08 vs. 0.92 ± 0.12, p < 0.001), whereas intratracheal salbutamol increased the gene expression of aquaporin-1 (0.46 ± 0.11 vs. 0.92 ± 0.06, p < 0.001) and Na-K-ATPase-α (0.32 ± 0.07 vs. 0.58 ± 0.15, p < 0.001). In ARDSexp, the gene expression of ion channels and aquaporin was not influenced by salbutamol. Morphological and functional variables and edema formation were not affected by salbutamol in any of the ARDS groups, regardless of the route of administration. Conclusion Salbutamol administration increased the expression of alveolar epithelial ion channels and aquaporin in mild ARDSp, but not ARDSexp, with no effects on lung morphology and function or edema formation. These results may contribute to explain the negative effects of β2-agonists on clinical outcome in ARDS.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | | | - Marcelo Gama de Abreu
- Laboratory of Pulmonary Investigation, Carlos Chagas Filho Biophysics Institute, Federal University of Rio de Janeiro, Av, Carlos Chagas Filho s/n, Bloco G-014, Rio de Janeiro, RJ 21941-902, Brazil.
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Marunaka Y. Characteristics and Pharmacological Regulation of Epithelial Na+ Channel (ENaC) and Epithelial Na+ Transport. J Pharmacol Sci 2014. [DOI: 10.1254/jphs.14r01sr] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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Guo LJ, Alli AA, Eaton DC, Bao HF. ENaC is regulated by natriuretic peptide receptor-dependent cGMP signaling. Am J Physiol Renal Physiol 2013; 304:F930-7. [PMID: 23324181 DOI: 10.1152/ajprenal.00638.2012] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Epithelial sodium channels (ENaCs) located at the apical membrane of polarized epithelial cells are regulated by the second messenger guanosine 3',5'-cyclic monophosphate (cGMP). The mechanism for this regulation has not been completely characterized. Guanylyl cyclases synthesize cGMP in response to various intracellular and extracellular signals. We investigated the regulation of ENaC activity by natriuretic peptide-dependent activation of guanylyl cyclases in Xenopus 2F3 cells. Confocal microscopy studies show natriuretic peptide receptors (NPRs), including those coupled to guanylyl cyclases, are expressed at the apical membrane of 2F3 cells. Single-channel patch-clamp studies using 2F3 cells revealed that atrial natriuretic peptide (ANP) or 8-(4-chlorophenylthio)-cGMP, but not C-type natriuretic peptide or cANP, decreased the open probability of ENaC. This suggests that NPR-A, but not NPR-B or NPR-C, is involved in the natriuretic peptide-mediated regulation of ENaC activity. Also, it is likely that a signaling pathway involving cGMP and nitric oxide (NO) are involved in this mechanism, since inhibitors of soluble guanylyl cyclase, protein kinase G, inducible NO synthase, or an NO scavenger blocked or reduced the effect of ANP on ENaC activity.
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Affiliation(s)
- Lai-Jing Guo
- Department of Physiology, Emory University School of Medicine and the Center for Cell and Molecular Signaling, Atlanta, GA 30322, USA
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9
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Regulation of epithelial sodium transport via epithelial Na+ channel. J Biomed Biotechnol 2011; 2011:978196. [PMID: 22028593 PMCID: PMC3196915 DOI: 10.1155/2011/978196] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2011] [Revised: 07/09/2011] [Accepted: 08/03/2011] [Indexed: 12/02/2022] Open
Abstract
Renal epithelial Na+ transport plays an important role in homeostasis of our body fluid content and blood pressure. Further, the Na+ transport in alveolar epithelial cells essentially controls the amount of alveolar fluid that should be kept at an appropriate level for normal gas exchange. The epithelial Na+ transport is generally mediated through two steps: (1) the entry step of Na+ via epithelial Na+ channel (ENaC) at the apical membrane and (2) the extrusion step of Na+ via the Na+, K+-ATPase at the basolateral membrane. In general, the Na+ entry via ENaC is the rate-limiting step. Therefore, the regulation of ENaC plays an essential role in control of blood pressure and normal gas exchange. In this paper, we discuss two major factors in ENaC regulation: (1) activity of individual ENaC and (2) number of ENaC located at the apical membrane.
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Mac Sweeney R, Fischer H, McAuley DF. Nasal potential difference to detect Na+ channel dysfunction in acute lung injury. Am J Physiol Lung Cell Mol Physiol 2010; 300:L305-18. [PMID: 21112943 DOI: 10.1152/ajplung.00223.2010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Pulmonary fluid clearance is regulated by the active transport of Na(+) and Cl(-) through respiratory epithelial ion channels. Ion channel dysfunction contributes to the pathogenesis of various pulmonary fluid disorders including high-altitude pulmonary edema (HAPE) and neonatal respiratory distress syndrome (RDS). Nasal potential difference (NPD) measurement allows an in vivo investigation of the functionality of these channels. This technique has been used for the diagnosis of cystic fibrosis, the archetypal respiratory ion channel disorder, for over a quarter of a century. NPD measurements in HAPE and RDS suggest constitutive and acquired dysfunction of respiratory epithelial Na(+) channels. Acute lung injury (ALI) is characterized by pulmonary edema due to alveolar epithelial-interstitial-endothelial injury. NPD measurement may enable identification of critically ill ALI patients with a susceptible phenotype of dysfunctional respiratory Na(+) channels and allow targeted therapy toward Na(+) channel function.
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Affiliation(s)
- R Mac Sweeney
- Respiratory Medicine Research Programme, Centre for Infection and Immunity, Queen’s University, Belfast, Northern Ireland
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11
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Han DY, Nie HG, Gu X, Nayak RC, Su XF, Fu J, Chang Y, Rao V, Ji HL. K+ channel openers restore verapamil-inhibited lung fluid resolution and transepithelial ion transport. Respir Res 2010; 11:65. [PMID: 20507598 PMCID: PMC2889873 DOI: 10.1186/1465-9921-11-65] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2009] [Accepted: 05/27/2010] [Indexed: 12/19/2022] Open
Abstract
Background Lung epithelial Na+ channels (ENaC) are regulated by cell Ca2+ signal, which may contribute to calcium antagonist-induced noncardiogenic lung edema. Although K+ channel modulators regulate ENaC activity in normal lungs, the therapeutical relevance and the underlying mechanisms have not been completely explored. We hypothesized that K+ channel openers may restore calcium channel blocker-inhibited alveolar fluid clearance (AFC) by up-regulating both apical and basolateral ion transport. Methods Verapamil-induced depression of heterologously expressed human αβγ ENaC in Xenopus oocytes, apical and basolateral ion transport in monolayers of human lung epithelial cells (H441), and in vivo alveolar fluid clearance were measured, respectively, using the two-electrode voltage clamp, Ussing chamber, and BSA protein assays. Ca2+ signal in H441 cells was analyzed using Fluo 4AM. Results The rate of in vivo AFC was reduced significantly (40.6 ± 6.3% of control, P < 0.05, n = 12) in mice intratracheally administrated verapamil. KCa3.1 (1-EBIO) and KATP (minoxidil) channel openers significantly recovered AFC. In addition to short-circuit current (Isc) in intact H441 monolayers, both apical and basolateral Isc levels were reduced by verapamil in permeabilized monolayers. Moreover, verapamil significantly altered Ca2+ signal evoked by ionomycin in H441 cells. Depletion of cytosolic Ca2+ in αβγ ENaC-expressing oocytes completely abolished verapamil-induced inhibition. Intriguingly, KV (pyrithione-Na), K Ca3.1 (1-EBIO), and KATP (minoxidil) channel openers almost completely restored the verapamil-induced decrease in Isc levels by diversely up-regulating apical and basolateral Na+ and K+ transport pathways. Conclusions Our observations demonstrate that K+ channel openers are capable of rescuing reduced vectorial Na+ transport across lung epithelial cells with impaired Ca2+ signal.
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Affiliation(s)
- Dong-Yun Han
- Department of Biochemistry, University of Texas Health Science Center at Tyler, Tyler, TX 75708, USA
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Gallacher M, Brown SG, Hale BG, Fearns R, Olver RE, Randall RE, Wilson SM. Cation currents in human airway epithelial cells induced by infection with influenza A virus. J Physiol 2009; 587:3159-73. [PMID: 19403603 DOI: 10.1113/jphysiol.2009.171223] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Influenza A viruses cause lung disease via an incompletely understood mechanism that involves the accumulation of liquid within the lungs. The accumulation of lung liquid is normally prevented by epithelial Na(+) absorption, a transport process regulated via several pathways including phosphoinositide-3-kinase (PI3K). Since the influenza A virus encodes a non-structural protein (NS1) that can activate this kinase, we now explore the effects of NS1 upon the biophysical properties of human airway epithelial cells. Transient expression of NS1 depolarized electrically isolated cells maintained in glucocorticoid-free medium by activating a cation conductance identical to the glucocorticoid-induced conductance seen in single cells. This response involved PI3K-independent and PI3K-dependent mechanisms. Infecting glucocorticoid-deprived cells with influenza A virus disrupted the normal electrical coupling between neighbouring cells, but also activated a conductance identical to that induced by NS1. This response to virus infection was only partially dependent upon NS1-mediated activation of PI3K. The presence of NS1 allows influenza A to modify the biophysical properties of infected cells by activating a Na(+)-permeable conductance. Whilst the activation of Na(+)-permeable channels may be expected to increase the rate of Na(+) absorption and thus reduce the volume of liquid in the lung, liquid does normally accumulate in influenza A-infected lungs. The overall effect of influenza A on lung liquid volume may therefore reflect a balance between the activation and inhibition of Na(+)-permeable channels.
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Affiliation(s)
- M Gallacher
- Centre for Cardiovascular and Lung Research, University of Dundee, UK
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Li T, Koshy S, Folkesson HG. RNA interference for CFTR attenuates lung fluid absorption at birth in rats. Respir Res 2008; 9:55. [PMID: 18652671 PMCID: PMC2515309 DOI: 10.1186/1465-9921-9-55] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2008] [Accepted: 07/24/2008] [Indexed: 11/10/2022] Open
Abstract
Background Small interfering RNA (siRNA) against αENaC (α-subunit of the epithelial Na channel) and CFTR (cystic fibrosis transmembrane conductance regulator) was used to explore ENaC and CTFR function in newborn rat lungs. Methods Twenty-four hours after trans-thoracic intrapulmonary (ttip) injection of siRNA-generating plasmid DNA (pSi-0, pSi-4, or pSi-C2), we measured CFTR and ENaC expression, extravascular lung water, and mortality. Results αENaC and CFTR mRNA and protein decreased by ~80% and ~85%, respectively, following αENaC and CFTR silencing. Extravascular lung water and mortality increased after αENaC and CFTR-silencing. In pSi-C2-transfected isolated DLE cells there were attenuated CFTR mRNA and protein. In pSi-4-transfected DLE cells αENaC mRNA and protein were both reduced. Interestingly, CFTR-silencing also reduced αENaC mRNA and protein. αENaC silencing, on the other hand, only slightly reduced CFTR mRNA and protein. Conclusion Thus, ENaC and CFTR are both involved in the fluid secretion to absorption conversion around at birth.
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Affiliation(s)
- Tianbo Li
- Department of Integrative Medical Sciences, Northeastern Ohio Universities Colleges of Medicine and Pharmacy, Rootstown, OH 44272-0095, USA.
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14
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Vadász I, Dada LA, Briva A, Trejo HE, Welch LC, Chen J, Tóth PT, Lecuona E, Witters LA, Schumacker PT, Chandel NS, Seeger W, Sznajder JI. AMP-activated protein kinase regulates CO2-induced alveolar epithelial dysfunction in rats and human cells by promoting Na,K-ATPase endocytosis. J Clin Invest 2008; 118:752-62. [PMID: 18188452 DOI: 10.1172/jci29723] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2006] [Accepted: 11/16/2007] [Indexed: 12/12/2022] Open
Abstract
Hypercapnia (elevated CO(2) levels) occurs as a consequence of poor alveolar ventilation and impairs alveolar fluid reabsorption (AFR) by promoting Na,K-ATPase endocytosis. We studied the mechanisms regulating CO(2)-induced Na,K-ATPase endocytosis in alveolar epithelial cells (AECs) and alveolar epithelial dysfunction in rats. Elevated CO(2) levels caused a rapid activation of AMP-activated protein kinase (AMPK) in AECs, a key regulator of metabolic homeostasis. Activation of AMPK was mediated by a CO(2)-triggered increase in intracellular Ca(2+) concentration and Ca(2+)/calmodulin-dependent kinase kinase-beta (CaMKK-beta). Chelating intracellular Ca(2+) or abrogating CaMKK-beta function by gene silencing or chemical inhibition prevented the CO(2)-induced AMPK activation in AECs. Activation of AMPK or overexpression of constitutively active AMPK was sufficient to activate PKC-zeta and promote Na,K-ATPase endocytosis. Inhibition or downregulation of AMPK via adenoviral delivery of dominant-negative AMPK-alpha(1) prevented CO(2)-induced Na,K-ATPase endocytosis. The hypercapnia effects were independent of intracellular ROS. Exposure of rats to hypercapnia for up to 7 days caused a sustained decrease in AFR. Pretreatment with a beta-adrenergic agonist, isoproterenol, or a cAMP analog ameliorated the hypercapnia-induced impairment of AFR. Accordingly, we provide evidence that elevated CO(2) levels are sensed by AECs and that AMPK mediates CO(2)-induced Na,K-ATPase endocytosis and alveolar epithelial dysfunction, which can be prevented with beta-adrenergic agonists and cAMP.
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Affiliation(s)
- István Vadász
- Division of Pulmonary and Critical Care Medicine, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA
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15
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Developmental regulation of lumenal lung fluid and electrolyte transport. Respir Physiol Neurobiol 2007; 159:247-55. [PMID: 18006389 DOI: 10.1016/j.resp.2007.10.004] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2007] [Accepted: 10/09/2007] [Indexed: 11/20/2022]
Abstract
In the fetus, there is a net secretion of liquid (LL) by the lung as a result of active transport of chloride ions. The rate of secretion and the resulting volume of LL are vital for normal lung growth but how volume is sensed and how secretion may be regulated are still unknown. Towards term under the influence of thyroid and adrenocorticoid hormones, the epithelial sodium channel (ENaC) is increasingly expressed in the pulmonary epithelium. Adrenaline released by the fetus during labour activates ENaC and produces rapid absorption of liquid in preparation for air breathing; absence of ENaC is incompatible with survival. There may be other mechanisms involved in aiding liquid clearance including changes in epithelial permeability, an effect of oxygen on both ENaC and Na/K ATPase and perhaps the influence of additional hormones on ENaC activity. Some time after birth there are further developmental changes with the appearance of other cation channels (CNG1 and perhaps NSCC) which contribute to the liquid absorptive side of the balance existing across the epithelium between secretion and absorption to produce essentially almost no net liquid movement in the postnatal lung. The evidence for these processes is discussed and areas of uncertainty indicated.
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16
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Horinouchi T, Miyake Y, Nishiya T, Nishimoto A, Yorozu S, Jinno A, Kajita E, Miwa S. Characterization of noradrenaline-induced increases in intracellular Ca2+ levels in Chinese hamster ovary cells stably expressing human alpha1A-adrenoceptor. J Pharmacol Sci 2007; 105:103-11. [PMID: 17827867 DOI: 10.1254/jphs.fp0070891] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
The mechanism for noradrenaline (NA)-induced increases in intracellular Ca(2+) concentration ([Ca(2+)](i)) and physiological significance of Na(+) influx through receptor-operated channels (ROCs) and store-operated channels (SOCs) were studied in Chinese hamster ovary (CHO) cells stably expressing human alpha(1A)-adrenoceptor (alpha(1A)-AR). [Ca(2+)](i) was measured using the Ca(2+) indicator fura-2. NA (1 microM) elicited transient and subsequent sustained [Ca(2+)](i) increases, which were inhibited by YM-254890 (G(alphaq/11) inhibitor), U-73122 (phospholipase C (PLC) inhibitor), and bisindolylmaleimide I (protein kinase C (PKC) inhibitor), suggesting their dependence on G(alphaq/11)/PLC/PKC. Both phases were suppressed by extracellular Ca(2+) removal, SK&F 96365 (inhibitor of SOC and nonselective cation channel type-2 (NSCC-2)), LOE 908 (inhibitor of NSCC-1 and NSCC-2), and La(3+) (inhibitor of transient receptor potential canonical (TRPC) channel). Reduction of extracellular Na(+) and pretreatment with KB-R7943, a Na(+)/Ca(2+) exchanger (NCX) inhibitor, inhibited both phases of [Ca(2+)](i) increases. These results suggest that 1) stimulation of alpha(1A)-AR with NA elicits the transient and sustained increases in [Ca(2+)](i) mediated through NSCC-2 that belongs to a TRPC family; 2) Na(+) influx through these channels drives NCX in the reverse mode, causing Ca(2+) influx in exchange for Na(+) efflux; and 3) the G(alphaq/11)/PLC/PKC-dependent pathway plays an important role in the increases in [Ca(2+)](i).
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Affiliation(s)
- Takahiro Horinouchi
- Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Sapporo 060-8638, Japan
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17
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Yasuda M, Niisato N, Miyazaki H, Hama T, Dejima K, Hisa Y, Marunaka Y. Epithelial ion transport of human nasal polyp and paranasal sinus mucosa. Am J Respir Cell Mol Biol 2006; 36:466-72. [PMID: 17079782 DOI: 10.1165/rcmb.2006-0064oc] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Nasal cavity and paranasal sinus have various functions. However, little information is available on ion transport in these upper airway epithelia. In the present study, we measured the anion secretion and the anion channel activity to characterize the ion transport in epithelial cells prepared from human paranasal sinus mucosa (PSM) and nasal polyp (NP). To estimate the anion secretion and the anion channel activity, we measured the short-circuit current (Isc) and the transepithelial conductance (Gt) sensitive to NPPB (a Cl(-) channel blocker). The NPPB-sensitive Isc in PSM was larger than that in NP, correlating to the NPPB-sensitive Gt (Cl(-) channel activity). Forskolin stably elevated the NPPB-sensitive Isc associated with an increase in the NPPB-sensitive Gt in PSM and NP. UTP transiently stimulated the Isc associated with an elevation of Gt in PSM and NP. The stimulatory action of UTP on Isc and Gt was diminished by application of NPPB but not benzamil in PSM and NP, suggesting that UTP induced the NPPB-sensitive Isc (Cl(-) secretion) and Gt (Cl(-) channel activity). These observations suggest that in human PSM and NP, cAMP stably stimulates anion secretion by activating the Cl(-) (anion) channels, and that UTP just transiently elevates anion secretion via activation of some Cl(-) (anion) channels.
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Affiliation(s)
- Makoto Yasuda
- Department of Molecular Cell Physiology, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
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18
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Helms MN, Self J, Bao HF, Job LC, Jain L, Eaton DC. Dopamine activates amiloride-sensitive sodium channels in alveolar type I cells in lung slice preparations. Am J Physiol Lung Cell Mol Physiol 2006; 291:L610-8. [PMID: 16679376 DOI: 10.1152/ajplung.00426.2005] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Active Na+ reabsorption by alveolar epithelial cells generates the driving force used to clear fluids from the air space. Using single-channel methods, we examined epithelial Na+ channel (ENaC) activity of alveolar type I (AT1) cells from live 250- to 300-microm sections of lung tissue, circumventing concerns that protracted cell isolation procedures might compromise the innate transport properties of native lung cells. We used fluorescein-labeled Erythrina crystagalli lectin to positively identify AT1 cells for single-channel patch-clamp analysis. We demonstrated, for the first time, single-channel recordings of highly selective and nonselective amiloride-sensitive ENaC channels (HSC and NSC, respectively) from AT1 cells in situ, with mean conductances of 8.2+/-2.5 and 22+/-3.2 pS, respectively. Additionally, 25 nM amiloride in the patch electrode blocked Na+ channel activity in AT1 cells. Immunohistochemical studies demonstrated the presence of dopamine D1 and D2 receptors on the surface of AT1 cells, and single-channel recordings showed that 10 microM dopamine increased Na+ channel activity [product of the number of channels and single-channel open probability (NPo)] from 0.31+/-0.19 to 0.60+/-0.21 (P<0.001). The D1 receptor antagonist SCH-23390 (10 microM) blocked the stimulatory effect of dopamine on AT1 cells, but the D2 receptor antagonist sulpiride did not.
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Affiliation(s)
- My N Helms
- Department of Physiology, The Center for Cell and Molecular Signalling, Emory University School of Medicine, Whitehead Biomedical Research Bldg., 615 Michael St., Atlanta, GA 30322, USA
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19
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Folkesson HG, Matthay MA. Alveolar epithelial ion and fluid transport: recent progress. Am J Respir Cell Mol Biol 2006; 35:10-9. [PMID: 16514116 PMCID: PMC2658691 DOI: 10.1165/rcmb.2006-0080sf] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Affiliation(s)
- Hans G Folkesson
- Department of Physiology and Pharmacology, Northeastern Ohio Universities College of Medicine, Rootstown, USA
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20
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Abstract
The mechanisms of pulmonary edema resolution are different from those regulating edema formation. Absorption of excess alveolar fluid is an active process that involves vectorial transport of Na+out of alveolar air spaces with water following the Na+osmotic gradient. Active Na+transport across the alveolar epithelium is regulated via apical Na+and chloride channels and basolateral Na-K-ATPase in normal and injured lungs. During lung injury, mechanisms regulating alveolar fluid reabsorption are inhibited by yet unclear pathways and can be upregulated by pharmacological means. Better understanding of the mechanisms that regulate edema clearance may lead to therapeutic interventions to improve the ability of lungs to clear fluid, which is of clinical significance.
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Affiliation(s)
- Gökhan M Mutlu
- Pulmonary and Critical Care Medicine, Northwestern University, Feinberg School of Medicine, Chicago, IL 60611, USA
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21
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Swystun V, Chen L, Factor P, Siroky B, Bell PD, Matalon S. Apical trypsin increases ion transport and resistance by a phospholipase C-dependent rise of Ca2+. Am J Physiol Lung Cell Mol Physiol 2005; 288:L820-30. [PMID: 15626748 DOI: 10.1152/ajplung.00396.2004] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
We investigated the mechanisms by which serine proteases alter lung fluid clearance in rat lungs and vectorial ion transport in airway and alveolar epithelial cells. Inhibition of endogenous protease activity by intratracheal instillation of soybean trypsin inhibitor (SBTI) or α1-antitrypsin decreased amiloride-sensitive lung fluid clearance across rat fluid-filled lungs; instillation of trypsin partially restored this effect. Gelatin zymography demonstrated SBTI-inhibitable trypsin-like activity in rat lung lavage fluid. Apical trypsin and human neutrophil elastase, but not agonists of protease activated receptors, increased Na+and Cl−short-circuit currents ( Isc) and transepithelial resistance ( RTE) across human bronchial and nasal epithelial cells and rat alveolar type II cells, mounted in Ussing chambers, for at least 2 h. The increase in Iscwas fully reversed by amiloride and glibenclamide. The increase in RTEwas not prevented by ouabain, suggesting that trypsin decreased paracellular conductance. Apical trypsin also induced a transient increase in intracellular Ca2+in human airway cells; treatment of these cells with BAPTA-AM mitigated the trypsin-induced increases of intracellular Ca2+and of Iscand RTE. Increasing intracellular Ca2+in airway cells with either ionomycin or thapsigargin reproduced the increase in Isc, whereas inhibitors of phospholipase C (PLC) prevented the increases in both Ca2+and Isc. These data indicate trypsin-like proteases and elastase, either present in lung cells or released by inflammatory cells into the alveolar space, play an important role in the clearance of alveolar fluid by increasing ion transport and paracellular resistance via a PLC-initiated rise of intracellular Ca2+.
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Affiliation(s)
- Veronica Swystun
- University of Alabama at Birmingham, Dept. of Anesthesiology, AL 35205-3703, USA
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22
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Taguchi N, Niisato N, Sawabe Y, Miyazaki H, Hirai Y, Marunaka Y. Benzamil, a blocker of epithelial Na(+) channel-induced upregulation of artery oxygen pressure level in acute lung injury rabbit ventilated with high frequency oscillation. Biochem Biophys Res Commun 2005; 327:915-9. [PMID: 15649432 DOI: 10.1016/j.bbrc.2004.12.098] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2004] [Indexed: 11/20/2022]
Abstract
The epithelial Na(+) transport via an epithelial Na(+) channel (ENaC) expressed in the lung epithelium would play a key role in recovery from lung edema at acute lung injury by removing the fluid in lung luminal space. The lung edema causes dysfunction of gas exchange, decreasing oxygen pressure level of artery [P(aO(2))]. To study if ENaC plays a key role in recovering P(aO(2)) from a decreased level to a normal one in acute lung injury, we applied benzamil (20microM, a specific blocker of ENaC) to the lung luminal space in acute lung injury treated with high frequency oscillation ventilation (HFOV) that is a lung-protective ventilation with a lower tidal volume and a smaller pressure swing than conventional mechanical ventilation (CMV). Benzamil facilitated the recovery of P(aO(2)) in acutely injured lung with HFOV but not CMV. The observation suggests that in acutely injured lung treated with HFOV an ENaC blocker, benzamil, can be applied as a therapeutic drug for acute lung injury combing with HFOV.
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Affiliation(s)
- Nobuko Taguchi
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
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23
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Clunes MT, Butt AG, Wilson SM. A glucocorticoid-induced Na+ conductance in human airway epithelial cells identified by perforated patch recording. J Physiol 2004; 557:809-19. [PMID: 15090610 PMCID: PMC1665156 DOI: 10.1113/jphysiol.2004.061143] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2004] [Accepted: 04/06/2004] [Indexed: 01/22/2023] Open
Abstract
The perforated patch recording technique was used to investigate the effects of dexamethasone (0.2 microm, 24-30 h), a synthetic glucocorticoid, on membrane conductance in the human airway epithelial cell line H441. Under zero current clamp conditions this hormone induced amiloride-sensitive depolarization of the membrane potential (V(m)). Lowering external Na(+) to 10 mm by replacing Na(+) with N-methyl-d-glucammonium (NMDG(+)) also hyperpolarized the dexamethasome-treated cells, whilst replacing Na(+) with Li(+) caused a small depolarization. Although V(m) was insensitive to amiloride in control cells, NMDG(+) substitution caused a small hyperpolarization and so an amiloride-insensitive cation conductance is present. Replacing Na(+) with Li(+) had no effect on V(m) in such cells. Voltage clamp studies of dexamethasone-treated cells showed that the amiloride-sensitive component of the membrane current reversed at a potential close to the Na(+) equilibrium potential (E(Na)), and replacing Na(+) with K(+) caused a leftward shift in reversal potential (V(Rev)) that correlated with the corresponding shift in E(Na). Lowering [Na(+)](o) to 10 mm, the concentration in the pipette solution, by substitution with NMDG(+) shifted V(Rev) to 0 mV, whilst replacing Na(+) with Li(+) caused a rightward shift. Exposing dexamethasone-treated cells to a cocktail of cAMP-activating compounds (20 min) caused a approximately 2-fold increase in amiloride-sensitive conductance that was associated with no discernible change in ionic selectivity and an 18 mV depolarization. Dexamethasone thus induces the expression of a selective Na(+) conductance with a substantial permeability to Li(+) that is subject to acute regulation via cAMP. These data thus suggest that selective Na(+) channels underlie cAMP-regulated Na(+) transport in airway epithelia.
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Affiliation(s)
- M T Clunes
- Lung Membrane Transport Group, Division of Maternal and Child Health Sciences, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK
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24
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Ma HP, Al-Khalili O, Ramosevac S, Saxena S, Liang YY, Warnock DG, Eaton DC. Steroids and exogenous gamma-ENaC subunit modulate cation channels formed by alpha-ENaC in human B lymphocytes. J Biol Chem 2004; 279:33206-12. [PMID: 15187080 DOI: 10.1074/jbc.m405455200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous studies using whole-cell recording methods suggest that human B lymphocytes express an amiloride-sensitive, sodium-permeable channel. The present studies aim to determine whether this channel has biophysical properties and a molecular structure related to the alpha, beta, and gamma subunits of the epithelial sodium channel (ENaC). Reverse transcriptase polymerase chain reaction and Northern blots showed that human B lymphocytes express messages for both alpha- and beta- but not gamma-ENaC. Western blots showed that both alpha- and beta- but not gamma-ENaC proteins are expressed and strongly reduced by antisense oligonucleotides. Patch clamp experiments demonstrated that lymphocyte sodium channels are not active in cell-attached patches. However, membrane stretch can activate a 21-pS nonselective cation channel. The frequency of observance of this channel was significantly reduced by antisense oligonucleotide against alpha-ENaC but not by antisense oligonucleotide against beta-ENaC, indicating that only the alpha subunit of ENaC is necessary to form stretch-activated cation channels. Aldosterone (1.5 microm) reduced the frequency of observance of 21-pS alpha-ENaC channels and simultaneously induced the appearance of spontaneously active 10-pS channels. Antisense oligonucleotide experiments showed that this 10-pS channel is formed from alpha- and beta-ENaC. After expression of exogenous gamma-ENaC, aldosterone again reduced the frequency of observance of the 21-pS alpha-ENaC channel but induced the appearance of a 5-pS channel, presumably a alphabetagamma-ENaC channel. In the absence of aldosterone, the alpha subunit forms an alpha-cryptic channel that is activated by stretch, and in the presence of aldosterone, beta and alpha subunits together form an active channel that is modulated by aldosterone.
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Affiliation(s)
- He-Ping Ma
- Center for Cell and Molecular Signaling and Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
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25
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Xie Y, Schafer JA. Inhibition of ENaC by intracellular Cl- in an MDCK clone with high ENaC expression. Am J Physiol Renal Physiol 2004; 287:F722-31. [PMID: 15161604 DOI: 10.1152/ajprenal.00135.2004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We examined the effects of intracellular Cl- concentration ([Cl-]i) on the epithelial Na channel (ENaC) in a line of Madin-Darby canine kidney (MDCK) cells (FL-MDCK) with a high rate of Na+ transport produced by stable retroviral transfection with rENaC subunits (Morris RG and Schafer JA. J Gen Physiol 120: 71-85, 2002). Treatment with cAMP (100 microM 8-cpt-cAMP plus 100 microM IBMX) stimulated ENaC-mediated Na+ absorption as well as Cl- secretion via cystic fibrosis transmembrane conductance regulator, which was characterized in alpha-toxin-permeabilized monolayers to have the anion selectivity sequence NO3- > Br- > Cl- > I-. With the use of FL-MDCK monolayers in which the basolateral membrane was permeabilized by nystatin, the ENaC conductance of the apical membrane [determined from the amiloride-sensitive short-circuit current (AS-Isc) driven by an apical-to-basolateral Na+ concentration gradient] was progressively inhibited by increasing the [Cl-] in the basolateral solution (and hence in the cytosol), but it was insensitive to the [Cl-] in the apical solution. This inhibitory effect of [Cl-]i occurred regardless of the presence or absence of net Cl- transport. However, from fluorometric measurements using the Cl(-)-sensitive dye 6-methoxy-N-(3-sulfopropyl)-quinolinium in intact FL-MDCK monolayers on permeable supports, cAMP, which activates both Na+ absorption and Cl- secretion, produced a decrease of [Cl-]i from 76 +/- 14 to 36 +/- 8 mM (P = 0.03). Thus it might be expected that activation of Cl- secretion by cAMP would lead to stimulation rather than inhibition of ENaC. In the nystatin-treated monolayers, an increase in [Cl-]i from 15 to 145 mM decreased AS-Isc from 24.5 +/- 1.0 to 10.2 +/- 1.6 microA/cm2. This inhibition of ENaC could be attributed to nearly proportional decreases in the density of ENaC in the apical membrane from 1.91 +/- 0.16 to 1.32 +/- 0.17 fmol/cm2 and in the intrinsic channel activity (the average current per ENaC subunit) from 13.3 +/- 1.2 to 8.2 +/- 1.4 microA/fmol.
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Affiliation(s)
- Yi Xie
- Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
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26
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Ramminger SJ, Richard K, Inglis SK, Land SC, Olver RE, Wilson SM. A regulated apical Na(+) conductance in dexamethasone-treated H441 airway epithelial cells. Am J Physiol Lung Cell Mol Physiol 2004; 287:L411-9. [PMID: 15090368 DOI: 10.1152/ajplung.00407.2003] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Treating H441 cells with dexamethasone raised the abundance of mRNA encoding the epithelial Na(+) channel alpha- and beta-subunits and increased transepithelial ion transport (measured as short-circuit current, I(sc)) from <4 microA.cm(-2) to 10-20 microA.cm(-2). This dexamethasone-stimulated ion transport was blocked by amiloride analogs with a rank order of potency of benzamil >or= amiloride > EIPA and can thus be attributed to active Na(+) absorption. Studies of apically permeabilized cells showed that this increased transport activity did not reflect a rise in Na(+) pump capacity, whereas studies of basolateral permeabilized cells demonstrated that dexamethasone increased apical Na(+) conductance (G(Na)) from a negligible value to 100-200 microS.cm(-2). Experiments that explored the ionic selectivity of this dexamethasone-induced conductance showed that it was equally permeable to Na(+) and Li(+) and that the permeability to these cations was approximately fourfold greater than to K(+). There was also a small permeability to N-methyl-d-glucammonium, a nominally impermeant cation. Forskolin, an agent that increases cellular cAMP content, caused an approximately 60% increase in I(sc), and measurements made after these cells had been basolaterally permeabilized demonstrated that this response was associated with a rise in G(Na). This cAMP-dependent control over G(Na) was disrupted by brefeldin A, an inhibitor of vesicular trafficking. Dexamethasone thus stimulates Na(+) transport in H441 cells by evoking expression of an amiloride-sensitive apical conductance that displays moderate ionic selectivity and is subject to acute control via a cAMP-dependent pathway.
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Affiliation(s)
- S J Ramminger
- Division of Maternal and Child Health Sciences, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK
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27
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Abstract
The developing distal lung epithelium displays an evolving liquid transport phenotype, reflecting a changing and dynamic balance between Cl- ion secretion and Na+ ion absorption, which in turn reflects changing functional requirements. Thus in the fetus, Cl--driven liquid secretion predominates throughout gestation and generates a distending pressure to stretch the lung and stimulate growth. Increasing Na+ absorptive capacity develops toward term, anticipating the switch to an absorptive phenotype at birth and beyond. There is some empirical evidence of ligand-gated regulation of Cl- transport and of regulation via changes in the driving force for Cl- secretion. Epinephrine, O2, glucocorticoid, and thyroid hormones interact to stimulate Na+ absorption by increasing Na+ pump activity and apical Na+ conductance (GNa+) to bring about the switch from net secretion to net absorption as lung liquid is cleared from the lung at birth. Postnatally, the lung lumen contains a small Cl--based liquid secretion that generates a surface liquid layer, but the lung retains a large absorptive capacity to prevent alveolar flooding and clear edema fluid. This review explores the mechanisms underlying the functional development of the lung epithelium and draws upon evidence from classic integrative physiological studies combined with molecular physiology approaches.
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Affiliation(s)
- Richard E Olver
- Tayside Institute of Child Health, Lung Membrane Transport Group, Division of Maternal and Child Health Sciences, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, United Kingdom.
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28
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Fang X, Song Y, Zemans R, Hirsch J, Matthay MA. Fluid transport across cultured rat alveolar epithelial cells: a novel in vitro system. Am J Physiol Lung Cell Mol Physiol 2004; 287:L104-10. [PMID: 14990396 DOI: 10.1152/ajplung.00176.2003] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Previous studies have used fluid-instilled lungs to measure net alveolar fluid transport in intact animal and human lungs. However, intact lung studies have two limitations: the contribution of different distal lung epithelial cells cannot be studied separately, and the surface area for fluid absorption can only be approximated. Therefore, we developed a method to measure net vectorial fluid transport in cultured rat alveolar type II cells using an air-liquid interface. The cells were seeded on 0.4-microm microporous inserts in a Transwell system. At 96 h, the transmembrane electrical resistance reached a peak level (1,530 +/- 115 Omega.cm(2)) with morphological evidence of tight junctions. We measured net fluid transport by placing 150 microl of culture medium containing 0.5 microCi of (131)I-albumin on the apical side of the polarized cells. Protein permeability across the cell monolayer, as measured by labeled albumin, was 1.17 +/- 0.34% over 24 h. The change in concentration of (131)I-albumin in the apical fluid was used to determine the net fluid transported across the monolayer over 12 and 24 h. The net basal fluid transport was 0.84 microl.cm(-2).h(-1). cAMP stimulation with forskolin and IBMX increased fluid transport by 96%. Amiloride inhibited both the basal and stimulated fluid transport. Ouabain inhibited basal fluid transport by 93%. The cultured cells retained alveolar type II-like features based on morphologic studies, including ultrastructural imaging. In conclusion, this novel in vitro system can be used to measure net vectorial fluid transport across cultured, polarized alveolar epithelial cells.
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Affiliation(s)
- Xiaohui Fang
- Cardiovascular Research Institute, University of California, San Francisco, 94143-0130, USA
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29
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Shiima-Kinoshita C, Min KY, Hanafusa T, Mori H, Nakahari T. Beta 2-adrenergic regulation of ciliary beat frequency in rat bronchiolar epithelium: potentiation by isosmotic cell shrinkage. J Physiol 2003; 554:403-16. [PMID: 14594991 PMCID: PMC1664781 DOI: 10.1113/jphysiol.2003.056481] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Single bronchiolar ciliary cells were isolated from rat lungs. The beta(2)-adrenergic regulation of ciliary beat frequency (CBF) was studied using video-optical microscopy. Terbutaline (a beta(2)-adrenergic agonist) increased CBF in a dose-dependent manner, and it also decreased the volume of the ciliary cells. These terbutaline actions were inhibited by a PKA inhibitor (H-89) and mimicked by forskolin, IBMX and DBcAMP. Ion transport inhibitors were used to isosmotically manipulate the volume of the terbutaline-stimulated bronchiolar ciliary cells. Amiloride (1 microM) and bumetanide (20 microM) potentiated cell shrinkage and the CBF increase, and they shifted the terbutaline dose-response curve to the lower-concentration side. Quinidine (500 microM), in contrast, increased cell volume and suppressed the CBF increase. Moreover, a KCl solution containing amiloride (1 microM) and strophanthidin (100 microM) increased cell volume and suppressed the CBF increase, and then the subsequent removal of either amiloride or strophanthidin decreased cell volume and further increased CBF. NPPB (10 microM) or glybenclamide (200 microM) had no effect on the action of terbutaline. Thus, in terbutaline-stimulated ciliary cells, cell shrinkage enhances the CBF increase; in contrast, cell swelling suppresses it. However, the results of direct manupulation of cell volume by applying osmotic stresses (hyperosmotic shrinkage or hyposmotic swelling) were the opposite of the findings of the isosmotic experiments: hyposmotic cell swelling enhanced the CBF increase, while isosmotic swelling suppressed it. These results suggest that isosmotic and non-isosmotic volume changes in terbutaline-stimulated bronchiolar ciliary cells may trigger different signalling pathways. In conclusion, terbutaline increases CBF and decreases the volume of rat bronchiolar ciliary cells via cAMP accumulation under isosmotic conditions, and the isosmotic cell shrinkage enhances the CBF increase by increasing cAMP sensitivity.
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30
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Berthiaume Y. Long-term stimulation of alveolar epithelial cells by beta-adrenergic agonists: increased Na+ transport and modulation of cell growth? Am J Physiol Lung Cell Mol Physiol 2003; 285:L798-801. [PMID: 12959925 DOI: 10.1152/ajplung.00166.2003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
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31
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Marunaka Y, Niisato N. H89, an inhibitor of protein kinase A (PKA), stimulates Na+ transport by translocating an epithelial Na+ channel (ENaC) in fetal rat alveolar type II epithelium. Biochem Pharmacol 2003; 66:1083-9. [PMID: 12963496 DOI: 10.1016/s0006-2952(03)00456-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The present study was performed to clarify the effect of H89, an inhibitor of cAMP-activated protein kinase (protein kinase A; PKA), on Na(+) absorption in fetal rat alveolar type II epithelium. H89 stimulated the Na(+) absorption by increasing the open probability (Po) and number of a nonselective cation (NSC) channel composed of four alpha subunits of epithelial Na(+) channel (ENaC). Brefeldin A (BFA), an inhibitor of intracellular protein translocation, blocked the stimulatory action of H89 on the Na(+) absorption by interrupting the action of H89 on the Po and number of the NSC channel. H85, an inactive form of H89, showed an effect similar to H89, suggesting that H89 does not show its effect by inhibiting PKA, but acts on the channel depending the structure. These observations indicate that: (1) the H89 induced increase in number of the channel at the apical membrane is due to translocation of alpha subunit of ENaC to the apical membrane, (2) the elevation of Po of the channel is mediated through translocation of a protein activating alpha subunit of ENaC, and (3) the effect of H89 is dependent on its structure without any relation to PKA.
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Affiliation(s)
- Yoshinori Marunaka
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan.
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32
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Lazrak A, Matalon S. cAMP-induced changes of apical membrane potentials of confluent H441 monolayers. Am J Physiol Lung Cell Mol Physiol 2003; 285:L443-50. [PMID: 12704021 DOI: 10.1152/ajplung.00412.2002] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We recorded apical membrane potentials (Va) of H441 cells [a human lung cell line exhibiting both epithelial Na+ (ENaC) and CFTR-type channels] grown as confluent monolayers, using the microelectrode technique in current-clamp mode before, during, and after perfusion of the apical membranes with 10 microM forskolin. When perfused with normal Ringer solution, the cells had a Va of -43 +/- 10 mV (means +/- SD; n = 31). Perfusion with forskolin resulted in sustained depolarization by 25.0 +/- 3.5 mV (means +/- SD; n = 23) and increased the number, open time, and the open probability of a 4.2-pS ENaC. In contrast to a previous report (Jiang J, Song C, Koller BH, Matthay MA, and Verkman AS. Am J Physiol Cell Physiol 275: C1610-C1620, 1998), no transient hyperpolarization was observed. The forskolin-induced depolarization of Va was almost totally prevented by pretreatment of monolayers with 10 microM amiloride or by substitution of Na+ ions in the bath solution with N-methyl-d-glucamine. These findings indicate that cAMP stimulation of Na+ influx across H441 confluent monolayers results from activation of an amiloride-sensitive apical Na+ conductance and not from Va hyperpolarization due to Cl- influx through CFTR-type channels.
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Affiliation(s)
- Ahmed Lazrak
- Department of Anesthesiology, University of Alabama at Birmingham, Birmingham, AL 35205-3703, USA
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33
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Denda M, Fuziwara S, Inoue K. Beta2-adrenergic receptor antagonist accelerates skin barrier recovery and reduces epidermal hyperplasia induced by barrier disruption. J Invest Dermatol 2003; 121:142-8. [PMID: 12839574 DOI: 10.1046/j.1523-1747.2003.12310.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Effects of topical application of adrenergic receptor agonists and antagonists on epidermal barrier repair rate after barrier disruption were studied. Agonists and antagonists of beta1-adrenergic receptor did not affect the barrier repair rate. On the other hand, beta2-adrenergic receptor agonists, procaterol and alprenol, delayed barrier recovery and the beta2 receptor antagonist, ICI-118551, blocked the delay. Moreover, topical application of ICI-118551 or beta1,2 receptor antagonist, clenbuterol alone accelerated barrier recovery. Antagonists of alpha1 and alpha2 receptors did not affect barrier recovery. The delay of barrier repair induced by prodaterol hydrochloride was blocked by a voltage-gated calcium channel blocker, verapamil or nifedipine. In cultured human keratinocytes, procaterol increased the intracellular calcium concentration and the increase was blocked by ICI-118551 and also by verapamil or nifedipine. Topical application of ICI-118551 partially blocked the epidermal hyperplasia induced by acetone treatment under low environmental humidity. These results suggest that the beta2-adrenergic receptor is specifically associated with skin barrier homeostasis.
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34
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O'Grady SM, Lee SY. Chloride and potassium channel function in alveolar epithelial cells. Am J Physiol Lung Cell Mol Physiol 2003; 284:L689-700. [PMID: 12676759 DOI: 10.1152/ajplung.00256.2002] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Electrolyte transport across the adult alveolar epithelium plays an important role in maintaining a thin fluid layer along the apical surface of the alveolus that facilitates gas exchange across the epithelium. Most of the work published on the transport properties of alveolar epithelial cells has focused on the mechanisms and regulation of Na(+) transport and, in particular, the role of amiloride-sensitive Na(+) channels in the apical membrane and the Na(+)-K(+)-ATPase located in the basolateral membrane. Less is known about the identity and role of Cl(-) and K(+) channels in alveolar epithelial cells, but studies are revealing important functions for these channels in regulation of alveolar fluid volume and ionic composition. The purpose of this review is to examine previous work published on Cl(-) and K(+) channels in alveolar epithelial cells and to discuss the conclusions and speculations regarding their role in alveolar cell transport function.
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Affiliation(s)
- Scott M O'Grady
- Department of Physiology, University of Minnesota, St. Paul, Minnesota 55108, USA.
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35
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Sheng S, Perry CJ, Kleyman TR. External nickel inhibits epithelial sodium channel by binding to histidine residues within the extracellular domains of alpha and gamma subunits and reducing channel open probability. J Biol Chem 2002; 277:50098-111. [PMID: 12397059 DOI: 10.1074/jbc.m209975200] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Epithelial sodium channels (ENaC) are regulated by various intracellular and extracellular factors including divalent cations. We studied the inhibitory effect and mechanism of external Ni(2+) on cloned mouse alpha-beta-gamma ENaC expressed in Xenopus oocytes. Ni(2+) reduced amiloride-sensitive Na(+) currents of the wild type mouse ENaC in a dose-dependent manner. The Ni(2+) block was fast and partially reversible at low concentrations and irreversible at high concentrations. ENaC inhibition by Ni(2+) was accompanied by moderate inward rectification at concentrations higher than 0.1 mm. ENaC currents were also blocked by the histidine-reactive reagent diethyl pyrocarbonate. Pretreatment of the oocytes with the reagent reduced Ni(2+) inhibition of the remaining current. Mutations at alphaHis(282) and gammaHis(239) located within the extracellular loops significantly decreased Ni(2+) inhibition of ENaC currents. The mutation alphaH282D or double mutations alphaH282R/gammaH239R eliminated Ni(2+) block. All mutations at gammaHis(239) eliminated Ni(2+)-induced inward current rectification. Ni(2+) block was significantly enhanced by introduction of a histidine at alphaArg(280). Lowering extracellular pH to 5.5 and 4.4 decreased or eliminated Ni(2+) block. Although alphaH282C-beta-gamma channels were partially inhibited by the sulfhydryl-reactive reagent [2-(trimethylammonium)ethyl] methanethiosulfonate bromide (MTSET), alpha-beta-gamma H239C channels were insensitive to MTSET. From patch clamp studies, Ni(2+) did not affect unitary current but decreased open probability when perfused into the recording pipette. Our results suggest that external Ni(2+) reduces ENaC open probability by binding to a site consisting of alphaHis(282) and gammaHis(239) and that these histidine residues may participate in ENaC gating.
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MESH Headings
- Amiloride/pharmacology
- Amino Acid Sequence
- Animals
- Binding Sites
- Cloning, Molecular
- DNA, Complementary/metabolism
- Dose-Response Relationship, Drug
- Epithelial Sodium Channels
- Histidine/chemistry
- Kinetics
- Magnesium/pharmacology
- Mice
- Models, Biological
- Models, Chemical
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Mutation
- Nickel/pharmacology
- Oocytes/metabolism
- Patch-Clamp Techniques
- Point Mutation
- Protein Binding
- Protein Structure, Tertiary
- RNA, Complementary/metabolism
- Sequence Homology, Amino Acid
- Sodium/metabolism
- Sodium/pharmacology
- Sodium Channels/chemistry
- Sodium Channels/metabolism
- Time Factors
- Xenopus
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Affiliation(s)
- Shaohu Sheng
- Renal-Electrolyte Division, the Department of Medicine, University of Pittsburgh School of Medicine, 3550 Terrace Street, Pittsburgh, PA 15261, USA.
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36
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Olivier R, Scherrer U, Horisberger JD, Rossier BC, Hummler E. Selected contribution: limiting Na(+) transport rate in airway epithelia from alpha-ENaC transgenic mice: a model for pulmonary edema. J Appl Physiol (1985) 2002; 93:1881-7. [PMID: 12381779 DOI: 10.1152/japplphysiol.00413.2002] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The amiloride-sensitive epithelial Na(+) channel (ENaC) is essential for fluid clearance from the airways. An experimental animal model with a reduced expression of ENaC, the alpha-ENaC transgenic rescue mouse, is prone to develop edema under hypoxia exposure. This strongly suggests an involvement of ENaC in the pathogenesis of pulmonary edema. To investigate the pathogenesis of this type of edema, primary cultures of tracheal cells from these mice were studied in vitro. An ~60% reduction in baseline amiloride-sensitive Na(+) transport was observed, but the pharmacological characteristics and physiological regulation of the channel were similar to those observed in cells from wild-type mice. Aprotinin, an inhibitor of serine proteases, blocked 50-60% of the basal transepithelial current, hypoxia induced downregulation of Na(+) transport, and beta-adrenergic stimulation was effective to stimulate Na(+) transport after the hypoxia-induced decrease. When downregulation of ENaC activity (such as observed under hypoxia) is added to a low "constitutive" ENaC expression, the resulting reduced Na(+) transport rate may be insufficient for airway fluid clearance and favor pulmonary edema.
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Affiliation(s)
- Reynald Olivier
- Institut de Pharmacologie et de Toxicologie, Université de Lausanne, CH-1005 Lausanne, Switzerland
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37
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Matalon S, Lazrak A, Jain L, Eaton DC. Invited review: biophysical properties of sodium channels in lung alveolar epithelial cells. J Appl Physiol (1985) 2002; 93:1852-9. [PMID: 12381774 DOI: 10.1152/japplphysiol.01241.2001] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Amiloride-sensitive sodium channels in the lung play an important role in lung fluid balance. Particularly in the alveoli, sodium transport is closely regulated to maintain an appropriate fluid layer on the surface of the alveoli. Alveolar type II cells appear to play an important role in this sodium transport, with the role of alveolar type I cells being less clear. In alveolar type II cells, there are a variety of different amiloride-sensitive, sodium-permeable channels. This significant diversity appears to play a role in both normal lung physiology and in pathological states. In many epithelial tissues, amiloride-sensitive epithelial sodium channels (ENaC) are formed from three subunit proteins, designated alpha-, beta-, and gamma-ENaC. At least part of the diversity of sodium-permeable channels in lung arises from the assembling of different combinations of these subunits to form channels with different biophysical properties and different mechanisms for regulation. This leads to epithelial tissue in the lung, which has enormous flexibility to alter the magnitude and regulation of salt and water transport. In this review, we discuss the biophysical properties and occurrence of these various channels and some of the mechanisms for their regulation.
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Affiliation(s)
- Sadis Matalon
- Department of Anesthesiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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38
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Ramminger SJ, Inglis SK, Olver RE, Wilson SM. Hormonal modulation of Na(+) transport in rat fetal distal lung epithelial cells. J Physiol 2002; 544:567-77. [PMID: 12381827 PMCID: PMC2290596 DOI: 10.1113/jphysiol.2002.022459] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Isolated rat fetal distal lung epithelial (FDLE) cells were cultured (approximately 48 h) on permeable supports in medium devoid of hormones and growth factors whilst P(O2) was maintained at the level found in either the fetal (23 mmHg) or the postnatal (100 mmHg) alveolar regions. The cells became incorporated into epithelial layers that generated a basal short-circuit current (I(SC)) attributable to spontaneous Na(+) absorption. Cells at neonatal P(O2) generated larger currents than did cells at fetal P(O2), indicating that this Na(+) transport process is oxygen sensitive. Irrespective of P(O2), isoprenaline failed to elicit a discernible change in I(SC), demonstrating that beta-adrenoceptor agonists do not stimulate Na(+) transport under these conditions. However, isoprenaline did elicit cAMP accumulation in these cells, indicating that functionally coupled beta-adrenoceptors are present. Further experiments showed that isoprenaline did increase I(SC) in cells treated (24 h) with a combination of tri-iodothyronine (T(3), 10 nM) and dexamethasone (200 nM). Studies of basolaterally permeabilised cells showed that these hormones are essential for the isoprenaline-evoked increase in the apical membrane's Na(+) conductance (G(Na)), whereas isoprenaline-evoked changes in apical Cl(-) conductance (G(Cl)) can occur in both control and hormone-treated cells. Irrespective of their hormonal status, FDLE cells thus express beta-adrenoceptors that are functionally coupled to adenylate cyclase, and allow beta-adrenoceptor agonists to modulate the apical membrane's anion conductance. However, T(3) and dexamethasone are needed if these receptors are to exert control over G(Na). These hormones may thus play an important role in the functional maturation of the lung by allowing beta-adrenoceptor-mediated control over epithelial Na(+) channels in the apical plasma membrane.
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Affiliation(s)
- S J Ramminger
- Lung Membrane Transport Group, Tayside Institute of Child Health, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, UK
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39
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Barker PM, Olver RE. Invited review: Clearance of lung liquid during the perinatal period. J Appl Physiol (1985) 2002; 93:1542-8. [PMID: 12235057 DOI: 10.1152/japplphysiol.00092.2002] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
At birth, the distal lung epithelium undergoes a profound phenotypic switch from secretion to absorption in the course of adaptation to air breathing. In this review, we describe the developmental regulation of key membrane transport proteins and the way in which epinephrine, oxygen, glucocorticoids, and thyroid hormones interact to bring about this crucial change in function. Evidence from molecular, transgenic, cell culture, and whole lung studies is presented, and the clinical consequences of the failure of the physiological mechanisms that underlie perinatal lung liquid absorption are discussed.
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Affiliation(s)
- Pierre M Barker
- Department of Pediatrics, University of North Carolina, Chapel Hill, North Carolina 27599-7220, USA.
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40
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König J, Schreiber R, Mall M, Kunzelmann K. No evidence for inhibition of ENaC through CFTR-mediated release of ATP. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1565:17-28. [PMID: 12225848 DOI: 10.1016/s0005-2736(02)00502-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Both purinergic stimulation and activation of cystic fibrosis transmembrane conductance regulator (CFTR) increases Cl(-) secretion and inhibit amiloride-sensitive Na(+) transport. CFTR has been suggested to conduct adenosine 5'-triphosphate (ATP) or to control ATP release to the luminal side of epithelial tissues. Therefore, a possible mechanism on how CFTR controls the activity of epithelial Na(+) channels (ENaC) could be by release of ATP or uridine 5'-triphosphate (UTP), which would then bind to P2Y receptors and inhibit ENaC. We examined this question in native tissues from airways and colon and in Xenopus oocytes. Inhibition of amiloride-sensitive transport by both CFTR and extracellular nucleotides was observed in colon and trachea. However, nucleotides did not inhibit ENaC in Xenopus oocytes, even after coexpression of P2Y(2) receptors. Using different tools such as hexokinase, the P2Y inhibitor suramin or the Cl(-) channel blocker 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), we did not detect any role of a putative ATP secretion in activation of Cl(-) transport or inhibition of amiloride sensitive short circuit currents by CFTR. In addition, N(2),2'-O-dibutyrylguanosine 3',5'-cyclic monophosphate (cGMP) and protein kinase G (PKG)-dependent phosphorylation or the nucleoside diphosphate kinase (NDPK) do not seem to play a role for the inhibition of ENaC by CFTR, which, however, requires the presence of extracellular Cl(-).
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Affiliation(s)
- Jens König
- Department of Physiology and Pharmacology, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia
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41
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Niisato N, Nishio K, Marunaka Y. Activation of CFTR Cl(-) channel by tyrphostins via a protein tyrosine kinase-independent pathway in forskolin-stimulated renal epithelial A6 cells. Life Sci 2002; 71:1199-207. [PMID: 12095540 DOI: 10.1016/s0024-3205(02)01824-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
We studied effects of tyrphostin A23 (an inhibitor of protein tyrosine kinase; PTK) and tyrphostin A63 (an inactive analog of tyrphostin A23) on forskolin-activated cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channels and Cl(-) secretion in renal epithelial A6 cells. Tyrphostin A23 and A63 had no effects on the basal CFTR Cl(-) channel and Cl(-) secretion. However, under the forskolin-stimulated condition, tyrphostin A23 and A63 stimulated Cl(-) secretion by activating CFTR Cl(-) channels. These observations suggest that: 1) tyrphostin A23 and A63 stimulate the cAMP-activated CFTR Cl(-) channel via a PTK-independent, structure-dependent mechanism, and 2) tyrphostin A23 and A63 do not stimulate the basal CFTR Cl(-) channel. These lead us to an idea that: 1) cAMP might cause a conformational change of CFTR Cl(-) channel which is accessible by tyrphostins, and 2) tyrphostins would stimulate translocation of the cAMP-modified channel to the apical membrane by binding to the channel.
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Affiliation(s)
- Naomi Niisato
- Department of Cellular and Molecular Physiology, Kyoto Prefectural University of Medicine, Kyoto 602-0841, Japan
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42
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Matthay MA, Folkesson HG, Clerici C. Lung epithelial fluid transport and the resolution of pulmonary edema. Physiol Rev 2002; 82:569-600. [PMID: 12087129 DOI: 10.1152/physrev.00003.2002] [Citation(s) in RCA: 490] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The discovery of mechanisms that regulate salt and water transport by the alveolar and distal airway epithelium of the lung has generated new insights into the regulation of lung fluid balance under both normal and pathological conditions. There is convincing evidence that active sodium and chloride transporters are expressed in the distal lung epithelium and are responsible for the ability of the lung to remove alveolar fluid at the time of birth as well as in the mature lung when pathological conditions lead to the development of pulmonary edema. Currently, the best described molecular transporters are the epithelial sodium channel, the cystic fibrosis transmembrane conductance regulator, Na+-K+-ATPase, and several aquaporin water channels. Both catecholamine-dependent and -independent mechanisms can upregulate isosmolar fluid transport across the distal lung epithelium. Experimental and clinical studies have made it possible to examine the role of these transporters in the resolution of pulmonary edema.
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Affiliation(s)
- Michael A Matthay
- Cardiovascular Research Institute and Department of Medicine, University of California, San Francisco, California 94143-0624, USA.
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43
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Marunaka Y, Niisato N. Effects of Ca(2+) channel blockers on amiloride-sensitive Na(+) permeable channels and Na(+) transport in fetal rat alveolar type II epithelium. Biochem Pharmacol 2002; 63:1547-52. [PMID: 11996897 DOI: 10.1016/s0006-2952(02)00880-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
A beta-adrenergic agonist (beta-agonist), terbutaline, stimulated amiloride-sensitive Na(+) absorption in fetal rat alveolar type II epithelium, contributing to the clearance of lung fluid. Cytosolic Ca(2+) plays an important role in terbutaline-stimulated Na(+) absorption, since Ca(2+)-activated, amiloride-sensitive Na(+)-permeable channels are involved in transcellular Na(+) absorption and terbutaline stably elevates the cytosolic Ca(2+) concentration by stimulating Ca(2+) influx. Therefore, we studied whether Ca(2+) channel blockers (Ni(2+), verapamil, and nifedipine) affect terbutaline-stimulated transcellular Na(+) absorption. Ni(2+) partially blocked the channel responsible for the terbutaline-stimulated Na(+) absorption at the Na(+) entry pathway across the apical membrane of the epithelium, but did not diminish the terbutaline-stimulated transcellular Na(+) absorption. By measuring the capacity of the Na(+),K(+)-pump activity, we determined that the rate-limiting step of the terbutaline-stimulated transcellular Na(+) absorption was the extrusion step across the basolateral membrane by the Na(+),K(+)-pump. The other Ca(2+) channel blockers, verapamil and nifedipine, had effects identical to those of Ni(2+). Based upon these observations, we conclude that, in the beta-agonist-stimulated fetal rat alveolar type II epithelium, Ca(2+) channel blockers diminish amiloride-sensitive channels, but do not affect transcellular Na(+) absorption, since under the beta-agonist-stimulated condition the Na(+),K(+)-pump is the rate-limiting step in Na(+) transport.
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Affiliation(s)
- Yoshinori Marunaka
- Department of Cellular and Molecular Physiology, Kyoto Prefectural University of Medicine, Kyoto 602-0841, Japan.
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44
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Chen XJ, Eaton DC, Jain L. Beta-adrenergic regulation of amiloride-sensitive lung sodium channels. Am J Physiol Lung Cell Mol Physiol 2002; 282:L609-20. [PMID: 11880285 DOI: 10.1152/ajplung.00356.2001] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We investigated the mechanism by which cAMP increases sodium transport in lung epithelial cells. Alveolar type II (ATII) cells have two types of amiloride-sensitive, cation channels: a nonselective cation channel (NSC) and a highly selective channel (HSC). Exposure of ATII cells to cAMP, beta-adrenergic agonists, or other agents that increase adenylyl cyclase activity increased activity of both channel types, albeit by different mechanisms. NSC open probability (P(o)) increased severalfold when exposed to terbutaline, isoproterenol, forskolin, or cAMP analogs without any change in NSC number. In contrast, terbutaline increased HSC number with no significant change in HSC P(o). For both channels, the effect of terbutaline was blocked by propranolol and H-89, suggesting a protein kinase A (PKA) requirement for beta-adrenergic-induced changes in channel activity. Terbutaline increased cAMP levels in ATII cells, but intracellular calcium also increased. Calcium sequestration with BAPTA blocked beta-adrenergic-induced increases in NSC P(o) but did not alter HSC activity. These observations suggest that beta-adrenergic stimulation increases intracellular cAMP and activates PKA. PKA increases HSC number and increases intracellular calcium. The increase in calcium increases NSC P(o). Thus increased cAMP levels are likely to increase lung sodium transport regardless of which channel type is present.
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Affiliation(s)
- Xi-Juan Chen
- Department of Pediatrics, Emory University School of Medicine, 2040 Ridgewood Drive NE, Atlanta, GA 30322, USA
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Collett A, Ramminger SJ, Olver RE, Wilson SM. Beta-adrenoceptor-mediated control of apical membrane conductive properties in fetal distal lung epithelia. Am J Physiol Lung Cell Mol Physiol 2002; 282:L621-30. [PMID: 11880286 DOI: 10.1152/ajplung.00142.2001] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Distal lung epithelial cells isolated from fetal rats were cultured (48 h) on permeable supports so that transepithelial ion transport could be quantified electrometrically. Unstimulated cells generated a short-circuit current (I(sc)) that was inhibited (~80%) by apical amiloride. The current is thus due, predominantly, to the absorption of Na(+) from the apical solution. Isoprenaline increased the amiloride-sensitive I(sc) about twofold. Experiments in which apical membrane Na(+) currents were monitored in basolaterally permeabilized cells showed that this was accompanied by a rise in apical Na(+) conductance (G(Na(+))). Isoprenaline also increased apical Cl- conductance (G(Cl-)) by activating an anion channel species sensitive to glibenclamide but unaffected by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS). The isoprenaline-evoked changes in G(Na(+)) and G(Cl(minus sign)) could account for the changes in I(sc) observed in intact cells. Glibenclamide had no effect upon the isoprenaline-evoked stimulation of I(sc) or G(Na(+)) demonstrating that the rise in G(Cl-) is not essential to the stimulation of Na(+) transport.
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Affiliation(s)
- A Collett
- Lung Membrane Transport Group, Tayside Institute of Child Health, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, UK
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Norlin A, Folkesson HG. Ca(2+)-dependent stimulation of alveolar fluid clearance in near-term fetal guinea pigs. Am J Physiol Lung Cell Mol Physiol 2002; 282:L642-9. [PMID: 11880288 DOI: 10.1152/ajplung.00417.2000] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We investigated the importance of changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) for amiloride-sensitive alveolar fluid clearance (AFC) in late-gestational guinea pigs. Fetal guinea pigs of 61, 68, and 69 days (term) gestation were investigated under normal conditions and after oxytocin-induced preterm labor. AFC or alveolar fluid secretion was measured using an impermeable tracer technique. At 61 days gestation there was net secretion of fluid into the lungs, and at birth the lungs cleared 49 +/- 7% of the instilled fluid volume over 1 h. Induction of preterm labor with oxytocin induced AFC at 61 days gestation. When present, AFC was inhibited or reversed to net fluid secretion by amiloride (10(-3) M). Inhibition of membrane Ca(2+) channels by verapamil (10(-4) M) or depletion of intracellular Ca(2+) by thapsigargin (10(-5) M) reduced AFC when net AFC was evident. Amiloride lacked an inhibitory effect on AFC when instilled with verapamil or thapsigargin. The results indicate that AFC via amiloride-sensitive pathways develops during late gestation, and that inducing preterm labor precociously may activate such pathways. Our results suggest that Ca(2+) may act as a second messenger in mediating catecholamine-stimulated AFC.
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Affiliation(s)
- Andreas Norlin
- Department of Animal Physiology, Lund University, SE-223 62 Lund, Sweden
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Boucherot A, Schreiber R, Kunzelmann K. Role of CFTR's PDZ1-binding domain, NBF1 and Cl(-) conductance in inhibition of epithelial Na(+) channels in Xenopus oocytes. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1515:64-71. [PMID: 11597353 DOI: 10.1016/s0005-2736(01)00396-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) inhibits epithelial Na(+) channels (ENaC). Evidence has accumulated that both Cl(-) transport through CFTR Cl(-) channels and the first nucleotide binding domain (NBF1) of CFTR are crucial for inhibition of ENaC. A PDZ binding domain (PDZ-BD) at the C-terminal end links CFTR to scaffolding and cytoskeletal proteins, which have been suggested to play an important role in activation of CFTR and eventually inhibition of ENaC. We eliminated the PDZ-BD of CFTR and coexpressed Na(+)/H(+)-exchange regulator factors together with CFTR and ENaC. The results do not support a role of PDZ-BD in inhibition of ENaC by CFTR. However, inhibition of ENaC was closely linked to Cl(-) currents generated by CFTR and was observed in the presence of Cl(-), I(-) or Br(-) but not gluconate. Therefore, functional NBF1 and Cl(-) transport are required for inhibition of ENaC in Xenopus oocytes, while the PDZ-BD is not essential.
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Affiliation(s)
- A Boucherot
- School of Biomedical Sciences, Department of Physiology and Pharmacology, University of Queensland, St. Lucia, 4072, Brisbane, Qld, Australia
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Jovanovic S, Land SC, Olver RE, Wilson SM. Hypoxic activation of an amiloride-sensitive cation conductance in alveolar epithelial cells. Biochem Biophys Res Commun 2001; 286:622-7. [PMID: 11511105 DOI: 10.1006/bbrc.2001.5432] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Imposing hypoxia (P(O(2)) = 23 mmHg) upon A549 cells elicited increased G(amil) although previous work had predicted a fall in this parameter. G(amil) appeared to be dependent upon glucocorticoid-driven gene expression, a process inhibited by ERK, an enzyme activated by oxidative stress. However, hypoxia transiently activated this enzyme and the response was blocked by glucocorticoids, showing that the rise in G(amil) occurs only if ERK activation is suppressed. Fluorimetric assays showed that lowering P(O(2)) elicited H(2)O(2) formation indicating that this maneuver actually imposes oxidative stress, thus explaining how hypoxia can elicit responses normally associated with a rise in P(O(2)).
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Affiliation(s)
- S Jovanovic
- Lung Membrane Transport Group, Tayside Institute of Child Health, Ninewells Hospital and Medical School, University of Dundee, Dundee, Scotland, DD1 9SY, United Kingdom
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Baines DL, Ramminger SJ, Collett A, Haddad JJ, Best OG, Land SC, Olver RE, Wilson SM. Oxygen-evoked Na+ transport in rat fetal distal lung epithelial cells. J Physiol 2001; 532:105-13. [PMID: 11283228 PMCID: PMC2278525 DOI: 10.1111/j.1469-7793.2001.0105g.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Monolayer cultures of rat fetal distal lung epithelial (FDLE) cells generated larger spontaneous short circuit currents (ISC) when maintained (48 h) at neonatal alveolar PO2 (100 mmHg) than at fetal PO2 (23 mmHg). When cells were shifted between these atmospheres in order to impose a rise in PO2 equivalent to that seen at birth, no rise in ISC was seen after 6 h but the response was fully established by 24 h. Studies of basolaterally permeabilised cells revealed a small rise in apical Na+ conductance (GNa) 6 h after PO2 was raised but no further change had occurred by 24 h. A substantial rise was, however, seen after 48 h. Reporter gene assays showed that no activation of the -ENaC (epithelial Na+ channel -subunit) promoter was discernible 24 h after PO2 was raised but increased transcriptional activity was seen at 48 h. Studies of apically permeabilised cells showed that a small rise in Na+ pump capacity was evident 6 h after PO2 was raised and, in common with the rise in ISC, this effect was fully established by 24 h. The rise in ISC thus develops 6-24 h after PO2 is raised and is due, primarily, to increased Na+ pump capacity. The increase in GNa thus coincides with activation of the -ENaC promoter but these effects occur after the rise in ISC is fully established and so cannot underlie this physiological response. The increased transcription may be an adaptation to increased Na+ transport and not its cause.
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Affiliation(s)
- D L Baines
- Lung Membrane Transport Group, Tayside Institute of Child Health, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK
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Niisato N, Marunaka Y. Blocking action of cytochalasin D on protein kinase A stimulation of a stretch-activated cation channel in renal epithelial A6 cells. Biochem Pharmacol 2001; 61:761-5. [PMID: 11266662 DOI: 10.1016/s0006-2952(01)00534-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We have shown that the apical membrane of renal epithelial A6 cells has a 29-pS stretch-activated nonselective cation (NSC) channel, which is activated by cytosolic cyclic AMP (cAMP) (J Gen Physiol 1997;110:327-36). In general, downstream signalings of cAMP are mediated through a cAMP-activated protein kinase (protein kinase A, PKA)-dependent pathway. Therefore, to study if the channel is activated by a PKA-dependent pathway, we applied a PKA catalytic subunit directly to the channel from the cytosolic surface in cytosol-free excised inside-out patches, using the single channel recording (patch clamp) technique. Application of PKA catalytic subunit with 2 mM ATP increased the open probability (P(o)) of the channel from 0.11 +/- 0.04 to 0.58 +/- 0.10 (mean +/- SD, N = 11, P < 0.001). The channel has a gating kinetics "C(L) <--> C(S) <--> O, " where C(L,) C(S,) and O are the long closed state, the short closed state, and the open state, respectively. PKA influenced the communication of the channel between C(L) and C(S) without affecting the communication between C(S) and O, leading the channel to only stay in C(S) and O. The PKA-induced increase in P(o) was attributable to the interruption of communication between C(L) and C(S) or to the reduction of time the channel stays in C(L.) Pretreatment with cytochalasin D (Cyt-D), an inhibitor of the polymerization of actin filaments, blocked the stimulatory effect of PKA on the channel. These observations suggest that phosphorylation of polymerized actin filaments regulates the gating kinetics of a stretch-activated channel in renal epithelium.
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Affiliation(s)
- N Niisato
- Department of Cellular and Molecular Physiology, Kyoto Prefectural University of Medicine, 602-0841, Japan
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