101
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Häussinger D, Schliess F. Osmotic induction of signaling cascades: role in regulation of cell function. Biochem Biophys Res Commun 1999; 255:551-5. [PMID: 10049748 DOI: 10.1006/bbrc.1998.9946] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- D Häussinger
- Department of Internal Medicine, Heinrich-Heine-Universität, Düsseldorf, Germany
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102
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Tamás MJ, Luyten K, Sutherland FC, Hernandez A, Albertyn J, Valadi H, Li H, Prior BA, Kilian SG, Ramos J, Gustafsson L, Thevelein JM, Hohmann S. Fps1p controls the accumulation and release of the compatible solute glycerol in yeast osmoregulation. Mol Microbiol 1999; 31:1087-104. [PMID: 10096077 DOI: 10.1046/j.1365-2958.1999.01248.x] [Citation(s) in RCA: 305] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The accumulation of compatible solutes, such as glycerol, in the yeast Saccharomyces cerevisiae, is a ubiquitous mechanism in cellular osmoregulation. Here, we demonstrate that yeast cells control glycerol accumulation in part via a regulated, Fps1p-mediated export of glycerol. Fps1p is a member of the MIP family of channel proteins most closely related to the bacterial glycerol facilitators. The protein is localized in the plasma membrane. The physiological role of Fps1p appears to be glycerol export rather than uptake. Fps1 delta mutants are sensitive to hypo-osmotic shock, demonstrating that osmolyte export is required for recovery from a sudden drop in external osmolarity. In wild-type cells, the glycerol transport rate is decreased by hyperosmotic shock and increased by hypo-osmotic shock on a subminute time scale. This regulation seems to be independent of the known yeast osmosensing HOG and PKC signalling pathways. Mutants lacking the unique hydrophilic N-terminal domain of Fps1p, or certain parts thereof, fail to reduce the glycerol transport rate after a hyperosmotic shock. Yeast cells carrying these constructs constitutively release glycerol and show a dominant hyperosmosensitivity, but compensate for glycerol loss after prolonged incubation by glycerol overproduction. Fps1p may be an example of a more widespread class of regulators of osmoadaptation, which control the cellular content and release of compatible solutes.
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Affiliation(s)
- M J Tamás
- Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Flanders, Belgium
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103
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Galán JE. Interactions of Salmonella with host cells: encounters of the closest kind. Proc Natl Acad Sci U S A 1998; 95:14006-8. [PMID: 9826642 PMCID: PMC33922 DOI: 10.1073/pnas.95.24.14006] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Affiliation(s)
- J E Galán
- Section of Microbial Pathogenesis, Boyer Center for Molecular Medicine, Yale School of Medicine, New Haven, CT 06536-0812, USA.
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104
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Liu K, Luan S. Voltage-dependent K+ channels as targets of osmosensing in guard cells. THE PLANT CELL 1998; 10:1957-70. [PMID: 9811801 PMCID: PMC143957 DOI: 10.1105/tpc.10.11.1957] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Guard cell turgor responds to the osmogradient across the plasma membrane and controls the stomatal aperture. Here, we report that guard cells utilize voltage-dependent K+ channels as targets of the osmosensing pathway, providing a positive feedback mechanism for stomatal regulation. When exposed to a hypotonic condition, the inward K+ current (IKin) was highly activated, whereas the outward K+ current (IKout) was inactivated. In contrast, hypertonic conditions inactivated the IKin while activating IKout. Single-channel recording analyses indicated that an alteration in channel opening frequency was responsible for regulating IKin and IKout under different osmotic conditions. Further studies correlate osmoregulation of IKin with the pattern of organization of actin filaments, which may be a critical component in the osmosensing pathway in plant cells.
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Affiliation(s)
- K Liu
- Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA
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105
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van der Wijk T, Dorrestijn J, Narumiya S, Maassen JA, de Jonge HR, Tilly BC. Osmotic swelling-induced activation of the extracellular-signal-regulated protein kinases Erk-1 and Erk-2 in intestine 407 cells involves the Ras/Raf-signalling pathway. Biochem J 1998; 331 ( Pt 3):863-9. [PMID: 9560315 PMCID: PMC1219428 DOI: 10.1042/bj3310863] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Human Intestine 407 cells respond to hypo-osmotic stress with a rapid stimulation of compensatory ionic conductances accompanied by a transient increase in the activity of the extracellular-signal-regulated protein kinases Erk-1 and Erk-2. In this study, we examined the upstream regulators of hypotonicity-induced Erk-1/Erk-2 activation and their possible role in cell-volume regulation. The hypotonicity-provoked Erk-1/Erk-2 activation was greatly reduced in cells pretreated with the specific mitogen-activated/Erk-activating kinase inhibitor PD098059 and was preceded by a transient stimulation of Raf-1. Pretreatment of the cells with PMA, GF109203X, wortmannin or Clostridium botulinum C3 exoenzyme did not appreciably affect the hypotonicity-provoked Erk-1/Erk-2 stimulation, suggesting the osmosensitive signalling pathway to be largely independent of protein kinase C and p21(rho). In contrast, expression of dominant negative RasN17 completely abolished the hypotonicity-induced Erk-1/Erk-2 activation. Stimulation of the swelling-induced ion efflux was independent of activation of these mitogen-activated protein kinases, as revealed by hypotonicity-provoked isotope efflux from 125I-- and 86Rb+-loaded cells after pretreatment with PD098059 and after expression of RasN17. In addition, the epidermal-growth-factor-induced potentiation of the hypotonicity-provoked anionic response did not depend on the increase in Erk-1/Erk-2 activity but, instead, was found to depend on Ca2+ influx. Taken together, these results indicate that hypotonic stress induces Erk-1/Erk-2 activation through the Ras/Raf-signalling pathway, and argue against a direct role for this pathway in cell-volume control.
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Affiliation(s)
- T van der Wijk
- Department of Biochemistry, Cardiovascular Research Institute COEUR, Faculty of Medicine and Health Sciences, Erasmus University, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands.
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106
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Krapivinsky G, Pu W, Wickman K, Krapivinsky L, Clapham DE. pICln binds to a mammalian homolog of a yeast protein involved in regulation of cell morphology. J Biol Chem 1998; 273:10811-4. [PMID: 9556550 DOI: 10.1074/jbc.273.18.10811] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Since its cloning and tentative identification as a chloride channel, the function of the pICln protein has been debated. Although there is no consensus regarding the specific function of pICln, it was suggested to play a role, directly or indirectly, in the function of a swelling-induced chloride conductance. Previously, the protein was shown to exist in several discrete protein complexes. To determine the function of the protein, we have begun the systematic identification of all proteins to which it binds. Here we show that four proteins firmly bind to pICln and identify the 72-kDa pICln-binding protein by affinity purification and peptide microsequencing. The interaction between this protein and pICln was verified several ways, including the extraction of several pICln clones from a cDNA library using the 72-kDa protein as a bait in a yeast two-hybrid screen. The protein is homologous to the yeast Skb1 protein. Skb1 interacts with Shk1, a homolog of the p21(Cdc42/Rac)-activated protein kinases (PAKs). The known involvement of PAKs in cytoskeletal rearrangement suggests that pICln may be linked to a system regulating cell morphology.
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Affiliation(s)
- G Krapivinsky
- Howard Hughes Medical Institute, Cardiovascular Division, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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107
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Mitogen-activated protein and tyrosine kinases in the activation of astrocyte volume-activated chloride current. J Neurosci 1998. [PMID: 9454830 DOI: 10.1523/jneurosci.18-04-01196.1998] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Astrocytes swell during neuronal activity as they accumulate K+ to buffer the increase in external K+ released from neurons. This swelling activates volume-sensitive Cl- channels, which are thought to be important in regulatory volume decrease and in the response of the CNS to trauma and excitotoxicity. Mitogen-activated protein (MAP) kinases also are activated by cell volume changes, but their roles in volume regulation are unknown. We have investigated the role of tyrosine and MAP kinases in the activation of volume-activated Cl- channels in cultured astrocytes, using whole-cell patch-clamp recording and Western immunoblots. As previously described, hypo-osmotic solution induced an outwardly rectifying Cl- current, which was blocked by NPPB and SITS. This Cl- current did not depend on [Ca2+ ]i because it was still observed when 20 mM BAPTA was included in the pipette, but it did exhibit rundown when ATP was omitted. Inhibition of tyrosine kinases with genistein or tyrphostin A23 (but not the inactive agents daidzein and tyrphostin A1) blocked the Cl- current. The MAP kinase kinase (MEK) inhibitor PD 98059 reversibly inhibited activation of the Cl- current by hypo-osmotic solution. Western immunoblots showed that genistein or PD 98059 blocked activation of Erk-1 and Erk-2 by hypo-osmotic solution in astrocytes. Therefore, activation of tyrosine and MAP kinases by swelling is a critical step in the opening of volume-sensitive Cl- channels.
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108
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Nilius B, Eggermont J, Voets T, Buyse G, Manolopoulos V, Droogmans G. Properties of volume-regulated anion channels in mammalian cells. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1998; 68:69-119. [PMID: 9481145 DOI: 10.1016/s0079-6107(97)00021-7] [Citation(s) in RCA: 274] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- B Nilius
- KU Leuven, Laboratorium voor Fysiologie, Belgium.
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109
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Crépel V, Panenka W, Kelly ME, MacVicar BA. Mitogen-activated protein and tyrosine kinases in the activation of astrocyte volume-activated chloride current. J Neurosci 1998; 18:1196-206. [PMID: 9454830 PMCID: PMC6792730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Astrocytes swell during neuronal activity as they accumulate K+ to buffer the increase in external K+ released from neurons. This swelling activates volume-sensitive Cl- channels, which are thought to be important in regulatory volume decrease and in the response of the CNS to trauma and excitotoxicity. Mitogen-activated protein (MAP) kinases also are activated by cell volume changes, but their roles in volume regulation are unknown. We have investigated the role of tyrosine and MAP kinases in the activation of volume-activated Cl- channels in cultured astrocytes, using whole-cell patch-clamp recording and Western immunoblots. As previously described, hypo-osmotic solution induced an outwardly rectifying Cl- current, which was blocked by NPPB and SITS. This Cl- current did not depend on [Ca2+ ]i because it was still observed when 20 mM BAPTA was included in the pipette, but it did exhibit rundown when ATP was omitted. Inhibition of tyrosine kinases with genistein or tyrphostin A23 (but not the inactive agents daidzein and tyrphostin A1) blocked the Cl- current. The MAP kinase kinase (MEK) inhibitor PD 98059 reversibly inhibited activation of the Cl- current by hypo-osmotic solution. Western immunoblots showed that genistein or PD 98059 blocked activation of Erk-1 and Erk-2 by hypo-osmotic solution in astrocytes. Therefore, activation of tyrosine and MAP kinases by swelling is a critical step in the opening of volume-sensitive Cl- channels.
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Affiliation(s)
- V Crépel
- Neuroscience Research Group, University of Calgary, Calgary, Alberta, Canada T2N 4N1
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110
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Nilius B, Prenen J, Voets T, Eggermont J, Droogmans G. Activation of volume-regulated chloride currents by reduction of intracellular ionic strength in bovine endothelial cells. J Physiol 1998; 506 ( Pt 2):353-61. [PMID: 9490864 PMCID: PMC2230725 DOI: 10.1111/j.1469-7793.1998.353bw.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
1. We have studied the effects of intracellular ionic strength (gamma 1) on the swelling-activated whole-cell Cl- current (ICl,swell) in cultured calf pulmonary artery endothelial cells (CPAE cells). 2. Reducing gamma 1 from 155 to 95 mM at constant osmolarity and Cl- concentration activates an outwardly rectifying current that is mainly carried by Cl- ions and inactivates at positive potentials. The amplitude of the current is larger at more reduced levels of gamma 1. 3. The permeability ratio for the anions I-, Br-, Cl- and gluconate (PI: PBr: PCl: Pgluc) was 1.35:1.03:1:0.17. 4. Blockers of the swelling-activated Cl- current in CPAE cells also inhibit the current which is activated by a reduction in gamma 1 with an IC50 of 1.1 microM for tamoxifen, 1.3 microM for mibefradil, and 35 microM for quinidine. 5. The protein tyrosine kinase inhibitors tyrphostin B46 (50 microM) and genistein (100 microM), which inhibit ICl,swell in CPAE cells, also inhibited the gamma 1-induced current by 92.9 +/- 2.4% (n = 3) and 41.2 +/- 5.0% (n = 4), respectively. 6. Hypertonic extracellular solutions rapidly and reversibly antagonized the gamma 1-activated current, whereas increasing gamma 1 from 155 to 195 mM precluded activation of ICl,swell by hypotonic shock. 7. It is concluded that a reduction of gamma 1 activates an anion current that is identical to that activated by cell swelling. Changes in intracellular ionic strength may shift the volume set point for activation of ICl,swell.
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Affiliation(s)
- B Nilius
- Laboratorium voor Fysiologie, Katholieke Universiteit Leuven, Belgium.
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111
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Voets T, Manolopoulos V, Eggermont J, Ellory C, Droogmans G, Nilius B. Regulation of a swelling-activated chloride current in bovine endothelium by protein tyrosine phosphorylation and G proteins. J Physiol 1998; 506 ( Pt 2):341-52. [PMID: 9490863 PMCID: PMC2230737 DOI: 10.1111/j.1469-7793.1998.341bw.x] [Citation(s) in RCA: 128] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
1. The role of protein tyrosine phosphorylation and of G proteins in the activation of a swelling-activated Cl- current (ICl,swell) in calf pulmonary artery endothelial (CPAE) cells was studied using the whole-cell patch clamp technique. ICl,swell was activated by reducing the extracellular osmolality by either 12.5% (mild hypotonicity) or 25% (strong hypotonicity). 2. The protein tyrosine kinase (PTK) inhibitors tyrphostin B46, tyrphostin A25 and genistein inhibited ICl,swell with IC50 values of, respectively, 9.2 +/- 0.2, 61.4 +/- 1.7 and 62.9 +/- 1.3 microM. Tyrphostin A1, a tyrphostin analogue with little effect on PTK activity, and daidzein, an inactive genistein analogue, were without effect on ICl,swell. 3. The protein tyrosine phosphatase (PTP) inhibitors Na3VO4 (200 microM) and dephostatin (20 microM) potentiated ICl,swell activated by mild hypotonicity by 47 +/- 9 and 69 +/- 15%, respectively. 4. Intracellular perfusion with GTP gamma S (100 microM) transiently activated a Cl- current with an identical biophysical and pharmacological profile to ICl,swell. This current was inhibited by the tested PTK inhibitors and potentiated by the PTP inhibitors. Hypertonicity-induced cell shrinkage completely inhibited the GTP gamma S-activated Cl- current. 5. Intracellular perfusion with GDP beta S (1 mM) caused a time-dependent inhibition of ICl,swell, which was more pronounced when the current was activated by mild hypotonicity. 6. Our results demonstrate that the activity of endothelial swelling-activated Cl- channels is dependent on tyrosine phosphorylation and suggest that G proteins regulate the sensitivity to cell swelling.
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Affiliation(s)
- T Voets
- Laboratorium voor Fysiologie, Katholieke Universiteit Leuven, Belgium
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112
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Lang F, Busch GL, Ritter M, Völkl H, Waldegger S, Gulbins E, Häussinger D. Functional significance of cell volume regulatory mechanisms. Physiol Rev 1998; 78:247-306. [PMID: 9457175 DOI: 10.1152/physrev.1998.78.1.247] [Citation(s) in RCA: 1268] [Impact Index Per Article: 48.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
To survive, cells have to avoid excessive alterations of cell volume that jeopardize structural integrity and constancy of intracellular milieu. The function of cellular proteins seems specifically sensitive to dilution and concentration, determining the extent of macromolecular crowding. Even at constant extracellular osmolarity, volume constancy of any mammalian cell is permanently challenged by transport of osmotically active substances across the cell membrane and formation or disappearance of cellular osmolarity by metabolism. Thus cell volume constancy requires the continued operation of cell volume regulatory mechanisms, including ion transport across the cell membrane as well as accumulation or disposal of organic osmolytes and metabolites. The various cell volume regulatory mechanisms are triggered by a multitude of intracellular signaling events including alterations of cell membrane potential and of intracellular ion composition, various second messenger cascades, phosphorylation of diverse target proteins, and altered gene expression. Hormones and mediators have been shown to exploit the volume regulatory machinery to exert their effects. Thus cell volume may be considered a second message in the transmission of hormonal signals. Accordingly, alterations of cell volume and volume regulatory mechanisms participate in a wide variety of cellular functions including epithelial transport, metabolism, excitation, hormone release, migration, cell proliferation, and cell death.
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Affiliation(s)
- F Lang
- Institute of Physiology, University of Tübingen, Germany
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113
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Hwang JU, Suh S, Yi H, Kim J, Lee Y. Actin Filaments Modulate Both Stomatal Opening and Inward K+-Channel Activities in Guard Cells of Vicia faba L. PLANT PHYSIOLOGY 1997; 115:335-342. [PMID: 12223811 PMCID: PMC158491 DOI: 10.1104/pp.115.2.335] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Actin antagonists have previously been shown to alter responses of Commelina communis stomata to physiological stimuli, implicating actin filaments in the control of guard cell volume changes (M. Kim, P.K. Hepler, S.-O. Eun, K.S. Ha, Y. Lee [1995] Plant Physiol 109: 1077-1084). Since K+ channels in the guard cell play an important role in stomatal movements, we examined the possible regulation of K+-channel activities by the state of actin polymerization. Agents affecting actin polymerization altered light-induced stomatal opening and inward K+-channel activities measured by patch clamping in Vicia faba. Cytochalasin D, which induces depolymerization of actin filaments, promoted light-induced stomatal opening and potentiated the inward K+ current in guard cell protoplasts. Phalloidin, a stabilizer of filamentous actin, inhibited both light-induced stomatal opening and inward K+ current. Inward K+-channel activities in outside-out membrane patches showed responses to these agents that support results at the whole-cell current level, suggesting that cytochalasin D facilitates and phalloidin inhibits K+ influx in intact guard cells, thus resulting in enhancement and inhibition of stomatal opening, respectively. To our knowledge, this is the first report that provides evidence that actin filaments may regulate an important physiological process by modulating the activities of ion channels in plant cells.
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Affiliation(s)
- J. U. Hwang
- Department of Life Science (J.-U.H., S.S., H.Y., J.K., Y.L.), School of Environmental Engineering (Y.L.), Pohang University of Science and Technology, Pohang 790-784, Korea
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114
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Manolopoulos VG, Droogmans G, Nilius B. Hypotonicity and thrombin activate taurine efflux in BC3H1 and C2C12 myoblasts that is down regulated during differentiation. Biochem Biophys Res Commun 1997; 232:74-9. [PMID: 9125155 DOI: 10.1006/bbrc.1997.6222] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The efflux of organic osmolytes such as taurine is an important mechanism by which cells regulate their volume. The effects of hypotonicity and thrombin on taurine efflux were studied in BC3H1 and C2C12 cells, two mouse myoblastic cell lines that can be induced to differentiate with serum deprivation. In proliferating cultures of both cell types preloaded with [3H]taurine, exposure to 27% hypotonicity activated a 10- to 20-fold increase in [3H]taurine efflux (Jtau). This effect was blocked by the C1- channel inhibitors NPPB and flufenamic acid. Thrombin and the thrombin receptor agonist SFLLRN also activated Jtau that was abolished by NPPB and flufenamic acid. Together, hypotonicity and thrombin synergistically activated Jtau. In differentiated myocytes, the effect of thrombin was abolished, while that of hypotonicity was significantly reduced. These results suggest that (i) hypotonicity and thrombin activate taurine-permeable anion channels in BC3H1 and C2C12 cells, and (ii) these anion channels may be involved in cell proliferation.
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Affiliation(s)
- V G Manolopoulos
- Laboratorium voor Fysiologie, Katholieke Universiteit Leuven, Belgium
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