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Miserocchi G. Early Endothelial Signaling Transduction in Developing Lung Edema. Life (Basel) 2023; 13:1240. [PMID: 37374024 DOI: 10.3390/life13061240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Revised: 05/17/2023] [Accepted: 05/23/2023] [Indexed: 06/29/2023] Open
Abstract
The lung promptly responds to edemagenic conditions through functional adaptations that contrast the increase in microvascular filtration. This review presents evidence for early signaling transduction by endothelial lung cells in two experimental animal models of edema, hypoxia exposure, and fluid overload (hydraulic edema). The potential role of specialized sites of the plasma membranes considered mobile signaling platforms, referred to as membrane rafts, that include caveolae and lipid rafts, is presented. The hypothesis is put forward that early changes in the lipid composition of the bilayer of the plasma membrane might trigger the signal transduction process when facing changes in the pericellular microenvironment caused by edema. Evidence is provided that for an increase in the extravascular lung water volume not exceeding 10%, changes in the composition of the plasma membrane of endothelial cells are evoked in response to mechanical stimuli from the interstitial compartment as well as chemical stimuli relating with changes in the concentration of the disassembled portions of structural macromolecules. In hypoxia, thinning of endothelial cells, a decrease in caveolae and AQP-1, and an increase in lipid rafts are observed. The interpretation of this response is that it favors oxygen diffusion and hinder trans-cellular water fluxes. In hydraulic edema, which generates greater capillary water leakages, an increase in cell volume and opposite changes in membrane rafts were observed; further, the remarkable increase in caveolae suggests a potential abluminal-luminal vesicular-dependent fluid reabsorption.
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Affiliation(s)
- Giuseppe Miserocchi
- Department of Medicine and Surgery, Università di Milano Bicocca, 20900 Monza, Italy
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2
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Zhao M, Li H, Fan L, Ma Y, Gong H, Lai W, Fang Q, Hu Z. Quantitative proteomic analysis to the first commercialized liposomal paclitaxel nano-platform Lipusu revealed the molecular mechanism of the enhanced anti-tumor effect. ARTIFICIAL CELLS NANOMEDICINE AND BIOTECHNOLOGY 2018; 46:S147-S155. [DOI: 10.1080/21691401.2018.1489822] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Minzhi Zhao
- CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology of China, Beijing, China
| | - Haiyun Li
- CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology of China, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Linyang Fan
- School of Life Science, Beijing Institute of Technology, Beijing, China
| | - Yan Ma
- CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology of China, Beijing, China
| | - He Gong
- CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology of China, Beijing, China
| | - Wenjia Lai
- CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology of China, Beijing, China
| | - Qiaojun Fang
- CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology of China, Beijing, China
| | - Zhiyuan Hu
- CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology of China, Beijing, China
- Sino-Danish College, University of Chinese Academy of Sciences, Beijing, P. R. China
- Center for Neuroscience Research, School of Basic Medical Sciences, Fujian Medical University, Fuzhou, Fujian Province, China
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3
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Tang CH, Hwang LY, Lee TH. Chloride channel ClC-3 in gills of the euryhaline teleost, Tetraodon nigroviridis: expression, localization and the possible role of chloride absorption. ACTA ACUST UNITED AC 2010; 213:683-93. [PMID: 20154183 DOI: 10.1242/jeb.040212] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Previous studies have reported the mechanisms of ion absorption and secretion by diverse membrane transport proteins in gills of various teleostean species. To date, however, the chloride channel expressed in the basolateral membrane of mitochondrion-rich (MR) cells for Cl(-) uptake in freshwater (FW) fish is still unknown. In this study, the combination of bioinformatics tools [i.e. National Center for Biotechnology Information (NCBI) database, Tetraodon nigroviridis (spotted green pufferfish) genome database (Genoscope), BLAT and BLASTn] were used to identify the gene of ClC-3 (TnClC-3), a member of the CLC chloride channel family in the T. nigroviridis genome. RT-PCR analysis revealed that the gene encoding for the ClC-3 protein was widely expressed in diverse tissues (i.e. gill, kidney, intestine, liver and brain) of FW- and seawater (SW)-acclimated pufferfish. In whole-mount double immunofluorescent staining, branchial ClC-3-like immunoreactive protein was localized to the basolateral membrane of Na(+)/K(+)-ATPase (NKA) immunoreactive cells in both the FW- and SW-acclimated pufferfish. In response to salinity, the levels of transcript of branchial TnClC-3 were similar between FW and SW fish. Moreover, the membrane fraction of ClC-3-like protein in gills was 2.7-fold higher in FW compared with SW pufferfish. To identify whether the expression of branchial ClC-3-like protein specifically responded to lower environmental [Cl(-)], the pufferfish were acclimated to artificial waters either with a normal (control) or lower Cl(-) concentration (low-Cl). Immunoblotting of membrane fractions of gill ClC-3-like protein showed the expression was about 4.3-fold higher in pufferfish acclimated to the low-Cl environment than in the control group. Furthermore, branchial ClC-3-like protein was rapidly elevated in response to acute changes of environmental salinity or [Cl(-)]. Taken together, pufferfish ClC-3-like protein was expressed in the basolateral membrane of gill MR cells, and the protein amounts were stimulated by hyposmotic and low-Cl environments. The enhancement of ClC-3-like protein may trigger the step of basolateral Cl(-) absorption of the epithelium to carry out iono- and osmoregulatory functions of euryhaline pufferfish gills.
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Affiliation(s)
- Cheng-Hao Tang
- Department of Life Sciences, National Chung-Hsing University, Taichung 402, Taiwan
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4
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Jayakumar AR, Norenberg MD. The Na-K-Cl Co-transporter in astrocyte swelling. Metab Brain Dis 2010; 25:31-8. [PMID: 20336356 DOI: 10.1007/s11011-010-9180-3] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/26/2009] [Accepted: 01/28/2010] [Indexed: 10/19/2022]
Abstract
Ion channels, exchangers and transporters are known to be involved in cell volume regulation. A disturbance in one or more of these systems may result in loss of ion homeostasis and cell swelling. In particular, activation of the Na(+)-K(+)-Cl(-) cotransporters has been shown to regulate cell volume in many conditions. The Na(+)-K(+)-Cl- cotransporters (NKCC) are a class of membrane proteins that transport Na, K, and Cl ions into and out of a wide variety of epithelial and nonepithelial cells. Studies have established the role of NKCC1 in astrocyte swelling/brain edema in ischemia and trauma. Our recent studies suggest that NKCC1 activation is also involved in astrocyte swelling induced by ammonia and in the brain edema in the thioacetamide model of acute liver failure. This review will focus on mechanisms of NKCC1 activation and its contribution to astrocyte swelling/brain edema in neurological disorders, with particular emphasis on ammonia neurotoxicity and acute liver failure.
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Affiliation(s)
- Arumugam R Jayakumar
- Department of Pathology (D-33), University of Miami Miller School of Medicine, P.O. Box 016960, Miami, FL 33125, USA.
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5
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Zong Z, Fujikawa-Yamamoto K, Li A, Yamaguchi N, Chang YG, Murakami M, Tanino M, Odashima S. Cell membrane changes of structure and function in protein kinase inhibitor-induced polyploid cells. Cell Prolif 2008; 33:29-38. [PMID: 10741642 PMCID: PMC6622355 DOI: 10.1046/j.1365-2184.1999.00154.x] [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: 11/20/2022] Open
Abstract
Exogenous cyclic AMP has been thought to be a chemical without marked pharmacological effect until now, as it is not capable of penetrating the cell membrane in most eucaryotic cells. The present study obtained results consistent with those of most previous studies, showing that exogenous cyclic AMP itself did not interfere with the cell cycle even at the high dose of 100 microM. However, it was found that K252a, a potent inhibitor of protein kinases including protein kinase C, induced DNA re-replication, i.e. DNA synthesis at a elevated DNA ploidy in cells that had not undergone cytokinesis (leading to polyploidization), and that exogenous cyclic AMP markedly potentiated the K252a-induced polyploidization at a very low dose similar to the effective dose of membrane-permeable cyclic AMP analogue dibutyryl cyclic AMP. These findings suggested that the cell membrane changed during the formation of polyploid cells. This supposition was confirmed by scanning electron microscopy to observe structural changes and by determination of cellular attachment to investigate functional changes.
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Affiliation(s)
- Z Zong
- Division of Basic Science, Medical Research Institute, Kanazawa Medical University, Uchinada, Ishikawa, Japan.
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6
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Petrunkina AM, Harrison RAP, Tsolova M, Jebe E, Töpfer-Petersen E. Signalling pathways involved in the control of sperm cell volume. Reproduction 2007; 133:61-73. [PMID: 17244733 DOI: 10.1530/rep.1.01137] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The ability to maintain cellular volume is an important general physiological function, which is achieved by specific molecular mechanisms. Hypotonically induced swelling results in the opening of K+ and Cl- ion channels, through which these ions exit with accompanying water loss. This process is known as regulatory volume decrease (RVD). The molecular mechanisms that control the opening of the ion channels in spermatozoa are as yet poorly understood. The present study investigated pathways of osmo-signalling using boar spermatozoa as a model. Spermatozoa were diluted into isotonic and hypotonic Hepes-buffered saline in the presence or absence of effector drugs, and at predetermined intervals volume measurements were performed electronically. Treatment with protein kinase C (PKC) inhibitors staurosporine, bismaleimide I and bismaleimide X led to dose-dependent increases of both isotonic and hypotonic volumes (P<0.05). However, as the isotonic volume was affected more than the hypotonic volume, the kinase inhibitors appeared to improve RVD, whereas activation of PKC with phorbol dibutyrate blocked RVD. The increase in isotonic cell volume induced by bismaleimide X was observed in chloride-containing medium but not in the medium in which chloride was replaced by sulphate, implying that PKC was involved in the control of chloride channel activity, e.g. by closing the channel after volume adjustment. The protein phosphatase PP1/PP2 inhibitors calyculin and okadaic acid increased the isotonic volume only slightly but they greatly increased the relative cell volume and blocked RVD. The activation of RVD processes was found to be cAMP-dependent; incubation with forskolin and papaverine improved volume regulation. Moreover, papaverine was able to overcome the negative effect of protein phosphatase inhibitors. The mechanism of sperm RVD appears to involve (a) alterations in protein phosphorylation/dephosphorylation balance brought about by PKC and PP1 and (b) a cAMP-dependent activating pathway.
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Affiliation(s)
- A M Petrunkina
- Unit for Reproductive Medicine of Clinics, Clinic for Horses, University of Veterinary Medicine Hannover Foundation, Bünteweg 15, 30559 Hannover, Germany.
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7
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Petrunkina AM, Waberski D, Günzel-Apel AR, Töpfer-Petersen E. Determinants of sperm quality and fertility in domestic species. Reproduction 2007; 134:3-17. [PMID: 17641084 DOI: 10.1530/rep-07-0046] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Fertilization success cannot be attributed solely to the absolute number of vital, motile, morphologically normal spermatozoa inseminated into the female but more especially to their functional competence. A range ofin vitrotests has therefore been developed to monitor crucial aspects of sperm function: their ability to adapt to changing osmotic conditions, to bind to the oviductal epithelium, and to undergo capacitation in an appropriate and timely manner. The tests employ flow cytometry in conjunction with fluorescent techniques, electronic cell counting, and computer-assisted image area analysis. The highly quantitative analysis provided by electronic sizing and flow cytometry enables assessment of representative cell numbers in a very short time with high reproducibility. More importantly, it allows the detection of physiological heterogeneity within an ejaculate in terms of the development of cell subpopulations and enables the kinetic analysis of changes in living cell suspensions. The tests offer a promising strategy for evaluating fertility in domestic animals. The capability for volume regulation ensures that sperm recover from the tonic shocks experienced at ejaculation and during cryopreservation. Assessment of capacitationin vitroprovides valuable information on both the sperm’s ability to respond to fertilizing conditions and the sequence and rates of ongoing capacitation/destabilization processes. The monitoring of response to capacitating conditions in kinetic terms allows the sensitive and adequate detection of sperm populations expressing fertilization attributes and their ability to respond to external stimuli in a timely manner. However, subfertility is likely to be associated with a suboptimal response (i.e. too high or too low) rather than a minimal response.
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Affiliation(s)
- A M Petrunkina
- Unit for Reproductive Medicine of Clinics, Clinic for Horses, University of Veterinary Medicine Hannover Foundation, Bünteweg 15, 30559 Hannover, Germany.
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8
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Lionetto MG, Schettino T. The Na+-K+-2Cl- cotransporter and the osmotic stress response in a model salt transport epithelium. Acta Physiol (Oxf) 2006; 187:115-24. [PMID: 16734748 DOI: 10.1111/j.1748-1716.2006.01536.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Epithelia are physiologically exposed to osmotic stress resulting in alteration of cell volume in several aspects of their functioning; therefore, the activation of 'emergency' systems of rapid cell volume regulation is fundamental in their physiology. In this review, the physiological response to osmotic stress, particularly hypertonic stress, was described in a salt-transporting epithelium, the intestine of the euryhaline teleost European eel. This epithelium is physiologically exposed to changes in extracellular osmolarity and represents a good physiological model for functional studies on cellular volume regulation, permitting the study of volume regulated ion transport mechanisms in a native tissue. An absorptive form of the cotransporter, homologue of the renal NKCC2, localized on the apical membrane, was found in the intestine of the euryhaline teleost European eel. This cotransporter accounts for the luminal uptake of Cl-; it operates in series with a basolateral Cl- conductance and presumably a basolateral electroneutral KCl cotransport and in parallel with a luminal K+ conductance. The ion transport model described for eel intestine, based on the operation of an absorptive luminal Na+-K+-2Cl-, is basically the same as the model that has been proposed for the thick ascending limb (cTAL) of the mammalian renal cortex. This paper focuses on the role of Na+-K+-2Cl- cotransport in the responses to hypertonic stress in the eel intestine and the role of cytoskeleton (either actin-based or tubulin based) is discussed.
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Affiliation(s)
- M G Lionetto
- Department of Biological and Environmental Sciences and Technologies, University of Lecce, Lecce, Italy.
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9
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Wang GL, Wang GX, Yamamoto S, Ye L, Baxter H, Hume JR, Duan D. Molecular mechanisms of regulation of fast-inactivating voltage-dependent transient outward K+ current in mouse heart by cell volume changes. J Physiol 2005; 568:423-43. [PMID: 16081489 PMCID: PMC1474744 DOI: 10.1113/jphysiol.2005.091264] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The K(v)4.2/4.3 channels are the primary subunits that contribute to the fast-inactivating, voltage-dependent transient outward K(+) current (I(to,fast)) in the heart. I(to,fast) is the critical determinant of the early repolarization of the cardiac action potential and plays an important role in the adaptive remodelling of cardiac myocytes, which usually causes cell volume changes, during myocardial ischaemia, hypertrophy and heart failure. It is not known, however, whether I(to,fast) is regulated by cell volume changes. In this study we investigated the molecular mechanism for cell volume regulation of I(to,fast) in native mouse left ventricular myocytes. Hyposmotic cell swelling caused a marked increase in densities of the peak I(to,fast) and a significant shortening in phase 1 repolarization of the action potential duration. The voltage-dependent gating properties of I(to,fast) were, however, not altered by changes in cell volume. In the presence of either protein kinase C (PKC) activator (12,13-dibutyrate) or phosphatase inhibitors (calyculin A and okadaic acid), hyposmotic cell swelling failed to further up-regulate I(to,fast). When expressed in NIH/3T3 cells, both K(v)4.2 and K(v)4.3 channels were also strongly regulated by cell volume in the same voltage-independent but PKC- and phosphatase-dependent manner as seen in I(to,fast) in the native cardiac myocytes. We conclude that K(v)4.2/4.3 channels in the heart are regulated by cell volume through a phosphorylation/dephosphorylation pathway mediated by PKC and serine/threonine phosphatase(s). These findings suggest a novel role of K(v)4.2/4.3 channels in the adaptive electrical and structural remodelling of cardiac myocytes in response to myocardial hypertrophy, ischaemia and reperfusion.
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Affiliation(s)
- Guan-Lei Wang
- Center of Biomedical Research Excellence, Department of Pharmacology, University of Nevada School of Medicine, Reno, 89557-0270, USA
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10
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Rasgado-Flores H, Peña-Rasgado C, Ehrenpreis S. Cell volume and drug action: Some interactions and perspectives. Drug Dev Res 2004. [DOI: 10.1002/ddr.430360202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Iwamoto LM, Fujiwara N, Nakamura KT, Wada RK. Na-K-2Cl cotransporter inhibition impairs human lung cellular proliferation. Am J Physiol Lung Cell Mol Physiol 2004; 287:L510-4. [PMID: 15155267 DOI: 10.1152/ajplung.00021.2004] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The widespread presence of the Na-K-2Cl (NKCC) cotransporter protein suggests that chronic administration of inhibitors may result in adverse effects. Inhibition of the NKCC cotransporter by loop diuretics is felt to underlie the diuretic and the pulmonary smooth muscle relaxant effects of this drug class. However, the fundamental regulation of salt and water movement by this cotransporter suggests that it may also mediate cell volume changes occurring during cell cycle progression. Thus we hypothesized that NKCC cotransporter inhibition by loop diuretics would decrease cellular proliferation. Normal human bronchial smooth muscle cells (BSMC) showed a significant concentration-dependent decrease in cell counts after 7 days of exposure to both bumetanide ( n = 5–10) and furosemide ( n = 6–16) compared with controls. Proliferation was similarly inhibited in normal human lung fibroblasts ( n = 5–9). To determine whether this was due to loss of cells, we performed apoptosis assays on BSMC. Both annexin V-propidium iodide staining ( n = 5–10) and single cell gel electrophoresis assays ( n = 4) were negative for necrosis and apoptosis in BSMC exposed to 10 μM bumetanide. Subsequent analysis of the cell cycle by flow cytometry showed that bumetanide-exposed BSMC were delayed in G1 phase compared with controls ( n = 4–8). This is the first evidence for loop diuretic inhibition of airway smooth muscle cell proliferation. NKCC cotransporter inhibition impeded G1-S phase transition without facilitating cell death. Thus although inhibition by loop diuretics relaxes airway smooth muscle, the NKCC cotransporter may have a more important role in cell proliferation regulation.
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12
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Flatman PW. Regulation of Na-K-2Cl cotransport by phosphorylation and protein-protein interactions. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1566:140-51. [PMID: 12421545 DOI: 10.1016/s0005-2736(02)00586-2] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The Na-K-2Cl cotransporter plays important roles in cell ion homeostasis and volume control and is particularly important in mediating the movement of ions and thus water across epithelia. In addition to being affected by the concentration of the transported ions, cotransport is affected by cell volume, hormones, growth factors, oxygen tension, and intracellular ionized Mg(2+) concentration. These probably influence transport through three main routes acting in parallel: cotransporter phosphorylation, protein-protein interactions and cell Cl(-) concentration. Many effects are mediated, at least in part, by changes in protein phosphorylation, and are disrupted by kinase and phosphatase inhibitors, and manoeuvres that reduce cell ATP content. In some cases, phosphorylation of the cotransporter itself on serine and threonine (but not tyrosine) is associated with changes in transport rate, in others, phosphorylation of associated proteins has more influence. Analysis of the stimulation of cotransport by calyculin A, arsenite and deoxygenation suggests that the cotransporter is phosphorylated by several kinases and dephosphorylated by several phosphatases. These kinases and phosphatases may themselves be regulated by phosphorylation of residues including tyrosine, with Src kinases possibly playing an important role. Protein-protein interactions also influence cotransport activity. Cotransporter molecules bind to each other to form high molecular weight complexes, they also bind to other members of the cation-chloride cotransport family, to a variety of cytoskeletal proteins, and to enzymes that are part of regulatory cascades. Many of these interactions affect transport and may override the effects of cotransporter phosphorylation. Cell Cl(-) may also directly affect the way the cotransporter functions independently of its role as substrate.
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Affiliation(s)
- Peter W Flatman
- Membrane Biology Group, Division of Biomedical and Clinical Laboratory Sciences, The University of Edinburgh, Hugh Robson Building, George Square, Edinburgh Scotland, UK.
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13
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Jiang G, Klein JD, O'Neill WC. Growth factors stimulate the Na-K-2Cl cotransporter NKCC1 through a novel Cl(-)-dependent mechanism. Am J Physiol Cell Physiol 2001; 281:C1948-53. [PMID: 11698253 DOI: 10.1152/ajpcell.2001.281.6.c1948] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Na-K-2Cl cotransporter NKCC1 is an important volume-regulatory transporter that is regulated by cell volume and intracellular Cl(-). This regulation appears to be mediated by phosphorylation of NKCC1, although there is evidence for additional, cytoskeletal regulation via myosin light chain (MLC) kinase. NKCC1 is also activated by growth factors and may contribute to cell hypertrophy, but the mechanism is unknown. In aortic endothelial cells, NKCC1 (measured as bumetanide-sensitive (86)Rb(+) influx) was rapidly stimulated by serum, lysophosphatidic acid, and fibroblast growth factor, with the greatest stimulation by serum. Serum increased bumetanide-sensitive influx significantly more than bumetanide-sensitive efflux (131% vs. 44%), indicating asymmetric stimulation of NKCC1, and produced a 17% increase in cell volume and a 25% increase in Cl(-) content over 15 min. Stimulation by serum and hypertonic shrinkage were additive, and serum did not increase phosphorylation of NKCC1 or MLC, and did not decrease cellular Cl(-) content. When cellular Cl(-) was replaced with methanesulfonate, influx via NKCC1 increased and was no longer stimulated by serum, whereas stimulation by hypertonic shrinkage still occurred. Based on these results, we propose a novel mechanism whereby serum activates NKCC1 by reducing its sensitivity to inhibition by intracellular Cl(-). This resetting of the Cl(-) set point of the transporter enables the cotransporter to produce a hypertrophic volume increase.
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Affiliation(s)
- G Jiang
- Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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14
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Al-Habori M. Macromolecular crowding and its role as intracellular signalling of cell volume regulation. Int J Biochem Cell Biol 2001; 33:844-64. [PMID: 11461828 DOI: 10.1016/s1357-2725(01)00058-9] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Macromolecular crowding has been proposed as a mechanism by means of which a cell can sense relatively small changes in volume or, more accurately, the concentration of intracellular solutes. According to the macromolecular theory, the kinetics and equilibria of enzymes can be greatly influenced by small changes in the concentration of ambient, inert macromolecules. A 10% change in the concentration of intracellular proteins can lead to changes of up to a factor of ten in the thermodynamic activity of putative molecular regulatory species, and consequently, the extent to which such regulator(s) may bind to and activate membrane-associated ion transporters. The aim of this review is to examine the concept of macromolecular crowding and how it profoundly affects macromolecular association in an intact cell with particular emphasis on its implication as a sensor and a mechanism through which cell volume is regulated.
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Affiliation(s)
- M Al-Habori
- Department of Clinical Biochemistry, Faculty of Medicine and Health Sciences, University of Sana'a, PO Box 19065, Sana'a, Republic of Yemen.
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15
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Akar F, Jiang G, Paul RJ, O'Neill WC. Contractile regulation of the Na(+)-K(+)-2Cl(-) cotransporter in vascular smooth muscle. Am J Physiol Cell Physiol 2001; 281:C579-84. [PMID: 11443057 DOI: 10.1152/ajpcell.2001.281.2.c579] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Vasoconstrictors activate the Na(+)-K(+)-2Cl(-) cotransporter NKCC1 in rat aortic smooth muscle, but the mechanism is unknown. Efflux of (86)Rb(+) from rat aorta in response to phenylephrine (PE) was measured in the absence and presence of bumetanide, a specific inhibitor of NKCC1. Removal of extracellular Ca(2+) completely abolished the activation of NKCC1 by PE. This was not due to inhibition of Ca(2+)-dependent K(+) channels since blocking these channels with Ba(2+) in Ca(2+)-replete solution did not prevent activation of NKCC1 by PE. Stimulation of NKCC1 by PE was inhibited 70% by 75 microM ML-9, 97% by 2 microM wortmannin, and 70% by 2 mM 2,3-butanedione monoxime, each of which inhibited isometric force generation in aortic rings. Bumetanide-insensitive Rb(+) efflux, an indication of Ca(2+)-dependent K(+) channel activity, was reduced by ML-9 but not by the other inhibitors. Stretching of aortic rings on tubing to increase lumen diameter to 120% of normal almost completely blocked the stimulation of NKCC1 by PE without inhibiting the stimulation by hypertonic shrinkage. We conclude that activation of the Na(+)-K(+)-2Cl(-) cotransporter by PE is the direct result of smooth muscle contraction through Ca(2+)-dependent activation of myosin light chain kinase. This indicates that the Na(+)-K(+)-2Cl(-) cotransporter is regulated by the contractile state of vascular smooth muscle.
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Affiliation(s)
- F Akar
- Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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16
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D'Andrea-Winslow L, Strohmeier GR, Rossi B, Hofman P. Identification of a sea urchin Na(+)/K(+)/2Cl(−) cotransporter (NKCC): microfilament-dependent surface expression is mediated by hypotonic shock and cyclic AMP. J Exp Biol 2001; 204:147-56. [PMID: 11104718 DOI: 10.1242/jeb.204.1.147] [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: 11/20/2022]
Abstract
We report the identification of an invertebrate Na(+)/K(+)/2Cl(−) cotransporter, NKCC. As a model system, we used the immune cells (coelomocytes) of the Mediterranean sea urchin Paracentrotus lividus. These cells are particularly interesting because they can be activated to undergo a rapid and dynamic change in cell shape. We demonstrate that forskolin, a cyclic AMP agonist known to regulate NKCC, induced coelomocyte transformation at doses of 10 micromol l(−)(1) and greater. Using two distinct monoclonal antibodies (T4 and T9) raised against the human intestinal epithelial NKCC, we have identified a high-molecular-mass (195 kDa) protein in coelomocyte extracts. We propose a novel method for the isolation of NKCC in one step by using bumetanide-Sepharose affinity chromatography under low-[Cl(−)] conditions. This method was successful in isolating coelomocyte 195 kDa NKCC. The T4 monoclonal antibody was used in immunocytochemical experiments to localize NKCC in resting and activated coelomocytes. In petalloid coelomocytes, a punctate, cytoplasmic distribution was observed in close proximity to actin filament bundles; in transformed coelomocytes, the immunofluorescence was distributed along the length of the filopodia and uniformly throughout the perinuclear region. The change in subcellular distribution of NKCC between the resting and the activated state was further investigated by using cell surface biotinylation followed by immunoprecipitation. These studies revealed an upregulation of NKCC at the plasma membrane upon activation, a process that was blocked by the F-actin-stabilizing drug phalloidin. These studies identify a novel model system in which to investigate a newly identified invertebrate Na(+)/K(+)/2Cl(−) cotransporter.
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Affiliation(s)
- L D'Andrea-Winslow
- College of General Studies, Division of Science and Mathematics, Boston University, Boston, MA 02215, USA
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17
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Abstract
Obligatory, coupled cotransport of Na(+), K(+), and Cl(-) by cell membranes has been reported in nearly every animal cell type. This review examines the current status of our knowledge about this ion transport mechanism. Two isoforms of the Na(+)-K(+)-Cl(-) cotransporter (NKCC) protein (approximately 120-130 kDa, unglycosylated) are currently known. One isoform (NKCC2) has at least three alternatively spliced variants and is found exclusively in the kidney. The other (NKCC1) is found in nearly all cell types. The NKCC maintains intracellular Cl(-) concentration ([Cl(-)](i)) at levels above the predicted electrochemical equilibrium. The high [Cl(-)](i) is used by epithelial tissues to promote net salt transport and by neural cells to set synaptic potentials; its function in other cells is unknown. There is substantial evidence in some cells that the NKCC functions to offset osmotically induced cell shrinkage by mediating the net influx of osmotically active ions. Whether it serves to maintain cell volume under euvolemic conditons is less clear. The NKCC may play an important role in the cell cycle. Evidence that each cotransport cycle of the NKCC is electrically silent is discussed along with evidence for the electrically neutral stoichiometries of 1 Na(+):1 K(+):2 Cl- (for most cells) and 2 Na(+):1 K(+):3 Cl(-) (in squid axon). Evidence that the absolute dependence on ATP of the NKCC is the result of regulatory phosphorylation/dephosphorylation mechanisms is decribed. Interestingly, the presumed protein kinase(s) responsible has not been identified. An unusual form of NKCC regulation is by [Cl(-)](i). [Cl(-)](i) in the physiological range and above strongly inhibits the NKCC. This effect may be mediated by a decrease of protein phosphorylation. Although the NKCC has been studied for approximately 20 years, we are only beginning to frame the broad outlines of the structure, function, and regulation of this ubiquitous ion transport mechanism.
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Affiliation(s)
- J M Russell
- Department of Biology, Biological Research Laboratories, Syracuse, New York, USA. .,edu
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18
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Klein JD, Lamitina ST, O'Neill WC. JNK is a volume-sensitive kinase that phosphorylates the Na-K-2Cl cotransporter in vitro. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:C425-31. [PMID: 10484329 DOI: 10.1152/ajpcell.1999.277.3.c425] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cell shrinkage phosphorylates and activates the Na-K-2Cl cotransporter (NKCC1), indicating the presence of a volume-sensitive protein kinase. To identify this kinase, extracts of normal and shrunken aortic endothelial cells were screened for phosphorylation of NKCC1 fusion proteins in an in-the-gel kinase assay. Hypertonic shrinkage activated a 46-kDa kinase that phosphorylated an NH2-terminal fusion protein, with weaker phosphorylation of a COOH-terminal fusion protein. This cytosolic kinase was activated by both hypertonic and isosmotic shrinkage, indicating regulation by cell volume rather than osmolarity. Subsequent studies identified this kinase as c-Jun NH2-terminal kinase (JNK). Immunoblotting revealed increased JNK activity in shrunken cells; there was volume-sensitive phosphorylation of NH2-terminal c-Jun fusion protein; immunoprecipitation of JNK from shrunken cells but not normal cells phosphorylated NKCC1 in gel kinase assays; and treatment of cells with tumor necrosis factor, a known activator of JNK, mimicked the effect of hypertonicity. We conclude that JNK is a volume-sensitive kinase in endothelial cells that phosphorylates NKCC1 in vitro. This is the first demonstration of a volume-sensitive protein kinase capable of phosphorylating a volume-regulatory transporter.
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Affiliation(s)
- J D Klein
- Renal Division, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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19
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Flatman PW, Creanor J. Stimulation of Na+-K+-2Cl- cotransport by arsenite in ferret erythrocytes. J Physiol 1999; 519 Pt 1:143-52. [PMID: 10432345 PMCID: PMC2269477 DOI: 10.1111/j.1469-7793.1999.0143o.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/1999] [Accepted: 05/19/1999] [Indexed: 11/29/2022] Open
Abstract
1. Na+-K+-2Cl- cotransport activity was measured in ferret erythrocytes as the bumetanide-sensitive uptake of 86Rb. 2. The Na+-K+-2Cl- cotransport rate was stimulated by treating erythrocytes with sodium arsenite but not by sodium arsenate (up to 1 mM). Stimulation took an hour to develop fully. Arsenite had no effect on bumetanide-resistant 86Rb uptake. 3. In cells stored for 3 days or less, cotransport stimulation by arsenite could be described by assuming arsenite either acts at a single site (EC50, 60+/-14 microM, mean +/- S.E.M., n = 3) or that it acts at both high- (EC50, 35+/-9 microM, mean +/- S.E.M., n = 3) and low- (EC50 >2 mM) affinity sites. 4. Stimulation by 1 mM arsenite was greatest on the day of cell collection (rate about 3 times that of the control), even exceeding that produced by 20 nM calyculin A, and declined during cell storage. Addition of calyculin A to arsenite-stimulated cells resulted in further stimulation of Na+-K+-2Cl- cotransport, suggesting that arsenite and calyculin act synergistically. This was most apparent in stored cells. 5. Stimulation by 1 mM arsenite was not affected by treating cells with the mitogen-activated protein kinase inhibitors SB203580 (20 microM) and PD98059 (50 microM), but was both prevented and reversed by the kinase inhibitors staurosporine (2 microM), 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1, 50 microM) and genistein (0.3 mM), and with a combination of 10 microM A23187 and 2 mM EDTA (to reduce intracellular Mg2+ concentration). Only treatment with EDTA and A23187 prevented stimulation by the combination of 1 mM arsenite and 20 nM calyculin, whereas no treatment was able to fully reverse this stimulation once elicited. 6. Our data are consistent with arsenite stimulating (perhaps indirectly) a kinase that phosphorylates and activates the Na+-K+-2Cl- cotransporter.
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Affiliation(s)
- P W Flatman
- Membrane Biology Group, Department of Biomedical Sciences, University Medical School, Teviot Place, Edinburgh EH8 9AG, UK.
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20
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Flatman PW, Creanor J. Regulation of Na+-K+-2Cl- cotransport by protein phosphorylation in ferret erythrocytes. J Physiol 1999; 517 ( Pt 3):699-708. [PMID: 10358111 PMCID: PMC2269378 DOI: 10.1111/j.1469-7793.1999.0699s.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
1. Na+-K+-2Cl- cotransport in ferret erythrocytes was measured as the bumetanide-sensitive uptake of 86Rb. 2. The resting cotransport rate was high but could be increased threefold by treating erythrocytes with calyculin A, a potent inhibitor of serine/threonine phosphatases. Twenty nanomolar was sufficient to maximally and rapidly (within 4 min) stimulate transport. 3. The effects of several kinase inhibitors were tested. High concentrations of K-252a, K-252b, calphostin C and hypericin caused less than 20 % inhibition. Staurosporine (IC50, 0.06 microM) and 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1; IC50, 2.5 microM) were more potent but still only partially (40-50 %) inhibited transport, an effect mimicked by reducing ionized intracellular Mg2+ concentration to submicromolar levels. Genistein may inhibit all transport at a sufficiently high dose (IC50, 0.36 mM) perhaps by directly inhibiting the transporter. 4. Staurosporine, PP1 and the removal of Mg2+ all prevented subsequent stimulation by calyculin A, and all inhibited calyculin-stimulated transport by 20-30 %. The effects of staurosporine, PP1 and Mg2+ removal were not additive. 5. The phosphatase that dephosphorylates the cotransporter is probably Mg2+ (or possibly Ca2+ or Mn2+) sensitive and not the target for calyculin A. The data suggest that this phosphatase is inhibited by phosphorylation, and that it is the regulation of this process which is affected by calyculin A and the kinase inhibitors tested here. Phosphorylation of the phosphatase is probably regulated by members of the Src family of tyrosine kinases.
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Affiliation(s)
- P W Flatman
- Membrane Biology Group, Department of Biomedical Sciences, University Medical School, Teviot Place, Edinburgh EH8 9AG, UK.
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21
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Peters LL, Jindel HK, Gwynn B, Korsgren C, John KM, Lux SE, Mohandas N, Cohen CM, Cho MR, Golan DE, Brugnara C. Mild spherocytosis and altered red cell ion transport in protein 4. 2-null mice. J Clin Invest 1999; 103:1527-37. [PMID: 10359562 PMCID: PMC408368 DOI: 10.1172/jci5766] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Protein 4.2 is a major component of the red blood cell (RBC) membrane skeleton. We used targeted mutagenesis in embryonic stem (ES) cells to elucidate protein 4.2 functions in vivo. Protein 4. 2-null (4.2(-/-)) mice have mild hereditary spherocytosis (HS). Scanning electron microscopy and ektacytometry confirm loss of membrane surface in 4.2(-/-) RBCs. The membrane skeleton architecture is intact, and the spectrin and ankyrin content of 4. 2(-/-) RBCs are normal. Band 3 and band 3-mediated anion transport are decreased. Protein 4.2(-/-) RBCs show altered cation content (increased K+/decreased Na+)resulting in dehydration. The passive Na+ permeability and the activities of the Na-K-2Cl and K-Cl cotransporters, the Na/H exchanger, and the Gardos channel in 4. 2(-/-) RBCs are significantly increased. Protein 4.2(-/-) RBCs demonstrate an abnormal regulation of cation transport by cell volume. Cell shrinkage induces a greater activation of Na/H exchange and Na-K-2Cl cotransport in 4.2(-/-) RBCs compared with controls. The increased passive Na+ permeability of 4.2(-/-) RBCs is also dependent on cell shrinkage. We conclude that protein 4.2 is important in the maintenance of normal surface area in RBCs and for normal RBC cation transport.
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Affiliation(s)
- L L Peters
- The Jackson Laboratory, Bar Harbor, Maine 04609, USA Department of Biomedical Research, St. Elizabeth's Medical Center, Boston, Massachusetts 02135, USA.
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22
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Akar F, Skinner E, Klein JD, Jena M, Paul RJ, O'Neill WC. Vasoconstrictors and nitrovasodilators reciprocally regulate the Na+-K+-2Cl- cotransporter in rat aorta. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:C1383-90. [PMID: 10362601 DOI: 10.1152/ajpcell.1999.276.6.c1383] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Little is known about the function and regulation of the Na+-K+-2Cl- cotransporter NKCC1 in vascular smooth muscle. The activity of NKCC1 was measured as the bumetanide-sensitive efflux of 86Rb+ from intact smooth muscle of the rat aorta. Hypertonic shrinkage (440 mosmol/kgH2O) rapidly doubled cotransporter activity, consistent with its volume-regulatory function. NKCC1 was also acutely activated by the vasoconstrictors ANG II (52%), phenylephrine (50%), endothelin (53%), and 30 mM KCl (54%). Both nitric oxide and nitroprusside inhibited basal NKCC1 activity (39 and 34%, respectively), and nitroprusside completely reversed the stimulation by phenylephrine. The phosphorylation of NKCC1 was increased by hypertonic shrinkage, phenylephrine, and KCl and was reduced by nitroprusside. The inhibition of NKCC1 significantly reduced the contraction of rat aorta induced by phenylephrine (63% at 10 nM, 26% at 30 nM) but not by KCl. We conclude that the Na+-K+-2Cl- cotransporter in vascular smooth muscle is reciprocally regulated by vasoconstrictors and nitrovasodilators and contributes to smooth muscle contraction, indicating that alterations in NKCC1 could influence vascular smooth muscle tone in vivo.
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Affiliation(s)
- F Akar
- Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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23
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O'Neill WC. Physiological significance of volume-regulatory transporters. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:C995-C1011. [PMID: 10329946 DOI: 10.1152/ajpcell.1999.276.5.c995] [Citation(s) in RCA: 185] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Research over the past 25 years has identified specific ion transporters and channels that are activated by acute changes in cell volume and that serve to restore steady-state volume. The mechanism by which cells sense changes in cell volume and activate the appropriate transporters remains a mystery, but recent studies are providing important clues. A curious aspect of volume regulation in mammalian cells is that it is often absent or incomplete in anisosmotic media, whereas complete volume regulation is observed with isosmotic shrinkage and swelling. The basis for this may lie in an important role of intracellular Cl- in controlling volume-regulatory transporters. This is physiologically relevant, since the principal threat to cell volume in vivo is not changes in extracellular osmolarity but rather changes in the cellular content of osmotically active molecules. Volume-regulatory transporters are also closely linked to cell growth and metabolism, producing requisite changes in cell volume that may also signal subsequent growth and metabolic events. Thus, despite the relatively constant osmolarity in mammals, volume-regulatory transporters have important roles in mammalian physiology.
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Affiliation(s)
- W C O'Neill
- Renal Division, Department of Medicine, and Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
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24
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Dall'Asta V, Bussolati O, Sala R, Parolari A, Alamanni F, Biglioli P, Gazzola GC. Amino acids are compatible osmolytes for volume recovery after hypertonic shrinkage in vascular endothelial cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:C865-72. [PMID: 10199817 DOI: 10.1152/ajpcell.1999.276.4.c865] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The response to chronic hypertonic stress has been studied in human endothelial cells derived from saphenous veins. In complete growth medium the full recovery of cell volume requires several hours and is neither associated with an increase in cell K+ nor hindered by bumetanide but depends on an increased intracellular pool of amino acids. The highest increase is exhibited by neutral amino acid substrates of transport system A, such as glutamine and proline, and by the anionic amino acid glutamate. Transport system A is markedly stimulated on hypertonic stress, with an increase in activity roughly proportional to the extent and the duration of the osmotic shrinkage. Cycloheximide prevents the increase in transport activity of system A and the recovery of cell volume. It is concluded that human endothelial cells counteract hypertonic stress through the stimulation of transport system A and the consequent expansion of the intracellular amino acid pool.
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Affiliation(s)
- V Dall'Asta
- Istituto di Patologia Generale, Università degli Studi di Parma, 43100 Parma, Italy
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25
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Duan D, Cowley S, Horowitz B, Hume JR. A serine residue in ClC-3 links phosphorylation-dephosphorylation to chloride channel regulation by cell volume. J Gen Physiol 1999; 113:57-70. [PMID: 9874688 PMCID: PMC2222988 DOI: 10.1085/jgp.113.1.57] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/1998] [Accepted: 11/12/1998] [Indexed: 01/30/2023] Open
Abstract
In many mammalian cells, ClC-3 volume-regulated chloride channels maintain a variety of normal cellular functions during osmotic perturbation. The molecular mechanisms of channel regulation by cell volume, however, are unknown. Since a number of recent studies point to the involvement of protein phosphorylation/dephosphorylation in the control of volume-regulated ionic transport systems, we studied the relationship between channel phosphorylation and volume regulation of ClC-3 channels using site-directed mutagenesis and patch-clamp techniques. In native cardiac cells and when overexpressed in NIH/3T3 cells, ClC-3 channels were opened by cell swelling or inhibition of endogenous PKC, but closed by PKC activation, phosphatase inhibition, or elevation of intracellular Ca2+. Site-specific mutational studies indicate that a serine residue (serine51) within a consensus PKC-phosphorylation site in the intracellular amino terminus of the ClC-3 channel protein represents an important volume sensor of the channel. These results provide direct molecular and pharmacological evidence indicating that channel phosphorylation/dephosphorylation plays a crucial role in the regulation of volume sensitivity of recombinant ClC-3 channels and their native counterpart, ICl.vol.
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Affiliation(s)
- D Duan
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557-0046, USA
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26
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Sun D, Murali SG. Stimulation of Na+-K+-2Cl- cotransporter in neuronal cells by excitatory neurotransmitter glutamate. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:C772-9. [PMID: 9730961 DOI: 10.1152/ajpcell.1998.275.3.c772] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Na+-K+-2Cl- cotransporters are important in renal salt reabsorption and in salt secretion by epithelia. They are also essential in maintenance and regulation of ion gradients and cell volume in both epithelial and nonepithelial cells. Expression of Na+-K+-2Cl- cotransporters in brain tissues is high; however, little is known about their function and regulation in neurons. In this study, we examined regulation of the Na+-K+-2Cl- cotransporter by the excitatory neurotransmitter glutamate. The cotransporter activity in human neuroblastoma SH-SY5Y cells was assessed by bumetanide-sensitive K+ influx, and protein expression was evaluated by Western blot analysis. Glutamate was found to induce a dose- and time-dependent stimulation of Na+-K+-2Cl- cotransporter activity in SH-SY5Y cells. Moreover, both the glutamate ionotropic receptor agonist N-methyl-D-aspartic acid (NMDA) and the metabotropic receptor agonist (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD) significantly stimulated the cotransport activity in these cells. NMDA-mediated stimulation of the Na+-K+-2Cl- cotransporter was abolished by the selective NMDA-receptor antagonist (+)-MK-801 hydrogen maleate. trans-ACPD-mediated effect on the cotransporter was blocked by the metabotropic receptor antagonist (+)-alpha-methyl-(4-carboxyphenyl)glycine. The results demonstrate that Na+-K+-2Cl- cotransporters in neurons are regulated by activation of both ionotropic and metabotropic glutamate receptors.
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Affiliation(s)
- D Sun
- Department of Neurological Surgery, School of Medicine, University of Wisconsin, Madison, Wisconsin 53792, USA
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27
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Krarup T, Jakobsen LD, Jensen BS, Hoffmann EK. Na+-K+-2Cl- cotransport in Ehrlich cells: regulation by protein phosphatases and kinases. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:C239-50. [PMID: 9688855 DOI: 10.1152/ajpcell.1998.275.1.c239] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
To identify protein kinases (PK) and phosphatases (PP) involved in regulation of the Na+-K+-2Cl- cotransporter in Ehrlich cells, the effect of various PK and PP inhibitors was examined. The PP-1, PP-2A, and PP-3 inhibitor calyculin A (Cal-A) was a potent activator of Na+-K+-2Cl- cotransport (EC50 = 35 nM). Activation by Cal-A was rapid (<1 min) but transient. Inactivation is probably due to a 10% cell swelling and/or the concurrent increase in intracellular Cl- concentration. Cell shrinkage also activates the Na+-K+-2Cl- cotransport system. Combining cell shrinkage with Cal-A treatment prolonged the cotransport activation compared with stimulation with Cal-A alone, suggesting PK stimulation by cell shrinkage. Shrinkage-induced cotransport activation was pH and Ca2+/calmodulin dependent. Inhibition of myosin light chain kinase by ML-7 and ML-9 or of PKA by H-89 and KT-5720 inhibited cotransport activity induced by Cal-A and by cell shrinkage, with IC50 values similar to reported inhibition constants of the respective kinases in vitro. Cell shrinkage increased the ML-7-sensitive cotransport activity, whereas the H-89-sensitive activity was unchanged, suggesting that myosin light chain kinase is a modulator of the Na+-K+-2Cl- cotransport activity during regulatory volume increase.
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Affiliation(s)
- T Krarup
- Department of Biochemistry, The August Krogh Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark
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28
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Lytle C. A volume-sensitive protein kinase regulates the Na-K-2Cl cotransporter in duck red blood cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:C1002-10. [PMID: 9575797 DOI: 10.1152/ajpcell.1998.274.4.c1002] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
When Na-K-2Cl cotransport is activated in duck red blood cells by either osmotic cell shrinkage, norepinephrine, fluoride, or calyculin A, phosphorylation of the transporter occurs at a common set of serine/threonine sites. To examine the kinetics and regulation of the activating kinase, phosphatase activity was inhibited abruptly with calyculin A and the subsequent changes in transporter phosphorylation and activity were determined. Increases in fractional incorporation of 32P into the transporter and uptake of 86Rb by the cells were closely correlated, suggesting that the phosphorylation event is rate determining in the activation process. Observed in this manner, the activating kinase was 1) stimulated by cell shrinkage, 2) inhibited by cell swelling, staurosporine, or N-ethylmaleimide, and 3) unaffected by norepinephrine or fluoride. The inhibitory effect of swelling on kinase activity was progressively relieved by calyculin A, suggesting that the kinase itself is switched on by phosphorylation. The kinetics of activation by calyculin A conformed to an autocatalytic model in which the volume-sensitive kinase is stimulated by a product of its own reaction (e.g., via autophosphorylation).
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Affiliation(s)
- C Lytle
- Division of Biomedical Sciences, University of California, Riverside 92521, USA
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29
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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: 1261] [Impact Index Per Article: 48.5] [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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30
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Riley MV, Winkler BS, Starnes CA, Peters MI. Fluid and ion transport in corneal endothelium: insensitivity to modulators of Na(+)-K(+)-2Cl- cotransport. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C1480-6. [PMID: 9374632 DOI: 10.1152/ajpcell.1997.273.5.c1480] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The role of Na(+)-K(+)-2Cl- cotransport in ion and fluid transport of the corneal endothelium was examined by measuring changes in corneal hydration and uptake of 86Rb by the endothelial cell layer. Isolated, intact rabbit corneas maintain normal hydration when they are superfused at the endothelial surface with bicarbonate (HCO3-)-Ringer solutions as a result of equilibrium between active ion and fluid transport out of the stromal tissue and leak of fluid into stromal tissue from the aqueous humor. Furosemide and bumetanide did not alter this equilibrium when they were added to the superfusion medium. Uptake of 86Rb by the endothelium of the incubated cornea was increased 25% by bumetanide, but uptake in the presence of ouabain (70% less than that of controls) was not changed by bumetanide. In Na(+)-free medium, uptake of 86Rb was reduced by 58%, but it was unchanged in Cl(-)-free medium. Calyculin A, a protein phosphatase inhibitor and activator of Na(+)-K(+)-Cl- cotransport, was without effect on 86Rb uptake. Hypertonicity (345 mosmol/kg) increased uptake slightly, whereas hypotonicity (226 mosmol/kg) caused a 33% decrease. Neither of these changes was significantly different when bumetanide was present in the media. It is concluded that Na(+)-K(+)-2Cl- cotransporter activity is not exhibited by the in situ corneal endothelium and does not play a role in the ion and fluid transport of this cell layer. Its presence in cultured endothelial cells may reflect the reported importance of this protein in growth, proliferation, and differentiation.
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Affiliation(s)
- M V Riley
- Eye Research Institute, Oakland University, Rochester, Michigan 48309-4401, USA
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31
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Jensen BS, Hoffmann EK. Hypertonicity enhances expression of functional Na+/K+/2Cl- cotransporters in Ehrlich ascites tumour cells. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1329:1-6. [PMID: 9370238 DOI: 10.1016/s0005-2736(97)00148-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Ehrlich cells exposed to a hypertonic medium for five hours respond by an increased expression of Na+/K+/2Cl- cotransport proteins as estimated from immunoprecipitations using polyclonal anti-cotransporter antibodies. The 3.4-fold increase in cotransport expression is followed by a concomitant 2.6-fold increase in the maximal bumetanide-sensitive K+ influx during regulatory volume increase, indicating a 2.6-fold increase in the number of functional cotransporters in the plasma membrane.
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32
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Mairbäurl H, Wodopia R, Eckes S, Schulz S, Bärtsch P. Impairment of cation transport in A549 cells and rat alveolar epithelial cells by hypoxia. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:L797-806. [PMID: 9357855 DOI: 10.1152/ajplung.1997.273.4.l797] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A reduced cation reabsorption across the alveolar epithelium decreases water reabsorption from the alveoli and could diminish clearing accumulated fluid. To test whether hypoxia restricts cation transport in alveolar epithelial cells, cation uptake was measured in rat lung alveolar type II pneumocytes (AII cells) in primary culture and in A549 cells exposed to normoxia and hypoxia. In AII and A549 cells, hypoxia caused a PO2-dependent inhibition of the Na-K pump, of Na-K-2Cl cotransport, and of total and amiloride-sensitive 22Na uptake. Nifedipine failed to prevent hypoxia-induced transport inhibition in both cell types. In A549 cells, the inhibition of the Na-K pump and Na-K-2Cl cotransport occurred within approximately 30 min of hypoxia, was stable >20 h, and was reversed by 2 h of reoxygenation. There was also a reduction in cell membrane-associated Na-K-ATPase and a decrease in Na-K-2Cl cotransport flux after full activation with calyculin A, indicating a decreased transport capacity. [14C]serine incorporation into cell proteins was reduced in hypoxic A549 cells, but inhibition of protein synthesis with cycloheximide did not reduce ion transport. In AII and A549 cells, ATP levels decreased slightly, and ADP and the ATP-to-ADP ratio were unchanged after 4 h of hypoxia. In A549 cells, lactate, intracellular Na, and intracellular K were unchanged. These results indicate that hypoxia inhibits apical Na entry pathways and the basolateral Na-K pump in A549 cells and rat AII pneumocytes in culture, indicating a hypoxia-induced reduction of transepithelial Na transport and water reabsorption by alveolar epithelium. If similar changes occur in vivo, the impaired cation transport across alveolar epithelial cells might contribute to the formation of hypoxic pulmonary edema.
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Affiliation(s)
- H Mairbäurl
- Department of Sports Medicine, University of Heidelberg, Germany
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Summers JC, Trais L, Lajvardi R, Hergan D, Buechler R, Chang H, Peña-Rasgado C, Rasgado-Flores H. Role of concentration and size of intracellular macromolecules in cell volume regulation. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C360-70. [PMID: 9277334 DOI: 10.1152/ajpcell.1997.273.2.c360] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
To gain insight into the mechanism(s) by which cells sense volume changes, specific predictions of the macromolecular crowding theory (A. P. Minton. In: Cellular and Molecular Physiology of Cell Volume Regulation, edited by K. Strange. Boca Raton, FL: CRC, 1994, p. 181-190. A. P. Minton, C. C. Colclasure, and J. C. Parker. Proc. Natl. Acad. Sci. USA 89: 10504-10506, 1992) were tested on the volume of internally perfused barnacle muscle cells. This preparation was chosen because it allows assessment of the effect on cell volume of changes in the intracellular macromolecular concentration and size while maintaining constant the ionic strength, membrane stretch, and osmolality. The predictions tested were that isotonic replacement of large macromolecules by smaller ones should induce volume decreases proportional to the initial macromolecular concentration and size as well as to the magnitude of the concentration reduction. The experimental results were consistent with these predictions: isotonic replacement of proteins or polymers with sucrose induced volume reductions, but this effect was only observed when the replacement was > or = 25% and the particular macromolecule had an average molecular mass of < or = 20 kDa and a concentration of at least 18 mg/ml. Volume reduction was effected by a mechanism identical with that of hypotonicity-induced regulatory volume decrease, namely, activation of verapamil-sensitive Ca2+ channels.
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Affiliation(s)
- J C Summers
- Department of Physiology and Biophysics, Finch University of Health Sciences/Chicago Medical School, Illinois 60064, USA
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Yerby TR, Vibat CR, Sun D, Payne JA, O'Donnell ME. Molecular characterization of the Na-K-Cl cotransporter of bovine aortic endothelial cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C188-97. [PMID: 9252456 DOI: 10.1152/ajpcell.1997.273.1.c188] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The Na-K-Cl cotransporter is an important regulator of endothelial cell volume and may also contribute to flux of Na and Cl across the endothelium of the blood-brain barrier. To date, two Na-K-Cl cotransport isoforms have been identified, the cotransporter in secretory epithelia, NKCC1, and that in absorptive renal epithelia, NKCC2. Our previous studies showed that a monoclonal antibody to the cotransporter of human colonic T84 epithelial cells, an NKCC1 isoform, recognizes a 170-kDa glycoprotein from endothelial cells. The molecular identity of the Na-K-Cl cotransporter present in endothelial cells, however, has been unknown. In addition, although evidence has been provided that phosphorylation of the endothelial cotransporter plays a role in regulating its activity, little is known about potential sites for protein kinase interaction with the cotransporter. The present study was conducted to determine the molecular structure of the endothelial Na-K-Cl cotransporter. Using a 1.0-kilobase (kb) cDNA fragment from a conserved region of the T84 cell cotransporter, we screened a bovine aortic endothelial cell cDNA library and subsequently identified and sequenced two overlapping clones that together spanned the entire coding region. The endothelial cotransporter is a 1,201-amino acid protein with 12 putative transmembrane segments and large amino and carboxy termini, each containing several consensus sites for phosphorylation by protein kinases. Comparison of the endothelial cotransporter amino acid sequence with known NKCC1 and NKCC2 sequences revealed a 96% identity with NKCC1. Northern blot analysis using a cDNA probe from the endothelial cotransporter revealed high expression of approximately 7.5-kb transcripts in a number of bovine tissues. Finally, a prominent expression of Na-K-Cl cotransporter was found by Western blot analysis in both cultured and freshly isolated endothelial cells of bovine aorta and cerebral microvessels.
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Affiliation(s)
- T R Yerby
- Department of Human Physiology, School of Medicine, University of California, Davis 95616, USA
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Schmiedl A, Schnabel PA, Richter J. Cellular edema and alterations in metabolite content in the ischemic and reperfused canine heart following different forms of cardiac arrest. Pathol Res Pract 1996; 192:1163-78. [PMID: 9122037 DOI: 10.1016/s0344-0338(96)80038-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
This study investigates firstly how far cellular edema correlates with parameters of the anaerobic energy turnover independent of the method used for cardiac arrest, and secondly to what extent cellular edema developing during reversible global ischemia is reduced after reperfusion. Canine hearts were arrested 1. by aortic cross clamping (ACC), 2. by coronary perfusion with St. Thomas solution, or 3. HTK (histidine tryptophan ketoglutarate) solution (Custodiol). Samples for biochemical and structural analysis were taken at different times during ischemia and after reperfusion with Tyrode solution. Cellular edema determined morphometrically and given as volume ratio of sarcoplasm and mitochondria to myofibrils (Vvsp + V vmi/Vvmf) varies significantly in the differently arrested hearts. Reperfusion after a decrease in ATP to 4 mumol/gww (revival time) leads to a nearly complete structural recovery. The relationship between cellular edema and defined over-all metabolite tissue concentrations and extracellular pHe values shows: 1. during the decrease of creatine phosphate to 3 mumol/gww, cellular edema does not change; it is, however, significantly higher after ACC and St. Thomas than after HTK perfusion; 2. at each lactate concentration, cellular edema differs significantly depending on the form of cardiac arrest; 3. during the decrease of ATP and pHe cellular edema increases and is comparable at concentrations < 4 mumol/gww and at pHe values < 6.5 independent of the form of cardiac arrest; 4. beyond 10 mumol/gww of inorganic phosphate (Pi), increasing values for cellular edema correspond to defined Pi values in the differently arrested hearts. Thus, the ratio VVSp+ VVMi/VVMf is a powerful parameter for the determination of cellular edema during ischemia, as well as for correlations with metabolic parameters.
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Affiliation(s)
- A Schmiedl
- Department of Anatomy, University of Göttingen, FRG
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Mountian I, Chou KY, Van Driessche W. Electrolyte transport mechanisms involved in regulatory volume increase in C6 glioma cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 271:C1041-8. [PMID: 8897808 DOI: 10.1152/ajpcell.1996.271.4.c1041] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Volume regulation of C6 glioma cells was studied with an automatic system for monitoring cell thickness, while increasing bath osmolality from 300 to 440 mosmol/kgH2O. At 37 degrees C, tissues incubated in solutions containing active substances (inositol, D-biotin, hydrocortisone, prostaglandin E1, insulin, transferrin, sodium selenite, and 3,5,3'-triiodothyronine) responded to hyperosmotic challenge with a typical regulatory volume increase (RVI). Lowering temperature or removing the active substances inhibited osmoregulation. Bumetanide, amiloride, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, or ouabain significantly reduced RVI. Ion substitutions of Na+, Cl-, NaCl, or HCO3- also importantly affected the process. Extracellular acidification rate (EAR) was studied by microphysiometry. Hyperosmotic shock induced an increase in EAR with a time course that matched volume recovery. This increase in EAR was prevented by amiloride. The data show that under hyperosmotic conditions C6 cells are able to regulate their volume. Ion substitutions and application of blockers demonstrate that Na+/H+ and Cl-/HCO3- exchangers and Na(+)-K(-)-2Cl- cotransporter are involved in RVI. The rise in EAR is due to the enhanced activity of Na+/H+ antiporter, which seems to be volume dependent but not osmotic dependent.
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Affiliation(s)
- I Mountian
- Laboratory of Physiology, KU Leuven, Gasthuisberg, Belgium
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37
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Sun D, O'Donnell ME. Astroglial-mediated phosphorylation of the Na-K-Cl cotransporter in brain microvessel endothelial cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 271:C620-7. [PMID: 8770003 DOI: 10.1152/ajpcell.1996.271.2.c620] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Our previous studies have shown that cerebral microvessel endothelial cells (CMEC) express a Na-K-Cl cotransporter and that exposure of CMEC to astroglial cells causes a nearly 2-fold increase in activity of the cotransporter but only 1.5-fold increase in expression of cotransport protein [D. Sun, C. Lytle, and M. E. O'Donnell. Am. J. Physiol. 269 (Cell Physiol. 38): C1506-C1512, 1995]. This finding suggests that the astroglial cell effects may be mediated by mechanisms involving cotransporter activation in addition to increased protein expression. In the present study, we evaluated the role of protein phosphorylation in elevation of CMEC cotransport activity by astroglial cells and extracellular hypertonicity. We also examined the effects of protein phosphatase and protein kinase inhibitors on both cotransporter activity and phosphorylation in CMEC. The phosphorylation level of Na-K-Cl cotransport protein was quantitatively evaluated by immunoprecipitation analysis with the use of a monoclonal antibody to the cotransporter after 32P labeling of cultured CMEC. Activity of the cotransporter was assessed as bumetanide-sensitive K influx. We found that the phosphatase inhibitors calyculin A and okadaic acid significantly increased both cotransport activity and phosphorylation of cotransport protein. Activity and phosphorylation level of the cotransporter were also markedly increased by exposing the cells to astroglial cell-conditioned or hypertonic medium. Moreover, the astroglial-induced stimulation of the CMEC cotransporter was inhibited by the protein kinase inhibitor K-252a. These findings suggest that phosphorylation of cotransport protein plays an important role in regulation of Na-K-Cl cotransport activity and that astroglial-induced elevation of cotransport activity involves both phosphorylation-associated stimulation of cotransport activity and increased expression of the cotransporter protein.
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Affiliation(s)
- D Sun
- Department of Human Physiology, School of Medicine, University of California, Davis 95616, USA
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38
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Raat NJ, Delpire E, van Os CH, Bindels RJ. Culturing induced expression of basolateral Na+-K+-2Cl- cotransporter BSC2 in proximal tubule, aortic endothelium, and vascular smooth muscle. Pflugers Arch 1996; 431:458-60. [PMID: 8584442 DOI: 10.1007/bf02207286] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
So far, two isoforms of the neutral Na+K+-2Cl- cotransporter have been cloned in mammals. One isoform, BSC1, mediates apical ion entry in the renal thick ascending limb of Henle and a second, BSC2, appears to be an ubiquitously expressed Na+K+-2Cl- cotransporter. In primary cultures of rabbit proximal tubule, porcine aortic endothelial cells, and rat vascular smooth muscle cells, expression of the second isoform BSC2 was demonstrated by Northern blot analysis and bumetanide-sensitive 86Rb+ uptake studies. A surprising finding was the absence of BSC2 in fully differentiated freshly-isolated proximal tubule, porcine aortic endothelial cells, and rat vascular smooth muscle cells. Several studies have reported modulation of Na+K+-2Cl- cotransport activity by vasoactive substances and suggested a role for disturbed cotransport in, for example, the pathogenesis of essential hypertension. All these observations, however, were made in cultured cells which, in view of our findings, makes the physiological relevance questionable.
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MESH Headings
- Animals
- Aorta
- Blotting, Northern
- Bumetanide/pharmacology
- Carrier Proteins/physiology
- Cells, Cultured
- Endothelium, Vascular/chemistry
- Endothelium, Vascular/cytology
- Hypertonic Solutions/pharmacology
- Isotonic Solutions/pharmacology
- Kidney Tubules, Proximal/chemistry
- Kidney Tubules, Proximal/cytology
- Male
- Muscle, Smooth, Vascular/chemistry
- Muscle, Smooth, Vascular/cytology
- Ouabain/pharmacology
- RNA, Messenger/analysis
- Rabbits
- Rats
- Rubidium Radioisotopes
- Sodium-Potassium-Chloride Symporters
- Swine
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Affiliation(s)
- N J Raat
- Department of Cell Physiology, University of Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands
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39
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O'Donnell ME, Martinez A, Sun D. Endothelial Na-K-Cl cotransport regulation by tonicity and hormones: phosphorylation of cotransport protein. THE AMERICAN JOURNAL OF PHYSIOLOGY 1995; 269:C1513-23. [PMID: 8572181 DOI: 10.1152/ajpcell.1995.269.6.c1513] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The Na-K-Cl cotransport system of vascular endothelial cells plays a central role in maintenance and regulation of intracellular volume. Activity of the cotransporter is modulated both by hormones and by extracellular tonicity. Vasopressin and other hormones that stimulate the endothelial cotransporter act via a Ca- and calmodulin-dependent pathway. Little is known, however, about the mechanisms that mediate cell shrinkage-induced stimulation of cotransport activity. In the present study, we evaluated the Ca dependence of cell shrinkage-stimulated Na-K-Cl cotransport activity and cell volume recovery of cultured bovine aortic endothelial cells and also the effects of protein kinase and phosphatase inhibitors on these processes. In addition, to investigate the possibility that hormones and/or hypertonicity regulate endothelial Na-K-Cl cotransport via direct phosphorylation of the cotransporter protein, we employed a monoclonal antibody to the human colonic T84 epithelial cell Na-K-Cl cotransport protein (T4 antibody) for Western blot analysis and immunoprecipitation of phosphoprotein. Our studies revealed that both cell shrinkage-stimulated net K uptake and recovery of intracellular volume were Ca dependent. We also found that hypertonicity-induced stimulation of cotransport activity was blocked by several inhibitors of Ca- and calmodulin-dependent protein kinases. Furthermore, inhibitors of myosin light chain kinase blocked cell shrinkage-stimulated cotransport and recovery of intracellular volume, while having no effect on vasopressin-stimulated cotransport. Western blot analysis of bovine aortic and cerebral microvascular endothelial cell membrane preparations revealed a 170-kDa protein recognized by the T4 antibody. In addition, we found that hypertonicity induced a marked increase in phosphorylation of the endothelial cotransport protein, as did vasopressin, bradykinin, okadaic acid, and calyculin A. Our findings indicate that modulation of endothelial cell Na-K-Cl cotransport activity by hypertonicity and by stimulatory hormones occurs via pathways involving Ca- and calmodulin-dependent protein kinases and direct phosphorylation of the cotransport protein.
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Affiliation(s)
- M E O'Donnell
- Department of Human Physiology, School of Medicine, University of California, Davis 95616, USA
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40
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Haas M, McBrayer D, Lytle C. [Cl-]i-dependent phosphorylation of the Na-K-Cl cotransport protein of dog tracheal epithelial cells. J Biol Chem 1995; 270:28955-61. [PMID: 7499426 DOI: 10.1074/jbc.270.48.28955] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Basolateral Na-K-Cl cotransport activity in primary cultures of dog tracheal epithelial cells is stimulated by beta-adrenergic agents, such as isoproterenol, and by apical UTP, which acts through an apical P2-purinergic receptor. While at least part of the stimulatory effect of isoproterenol appears to involve direct activation of the cotransporter via cAMP-dependent protein kinase, cotransport stimulation by apical UTP is entirely secondary to apical Cl- efflux and a resultant decrease in intracellular [Cl-] ([Cl-]i) and/or cell shrinkage (Haas, M., and McBrayer, D. G. (1994) Am. J. Physiol. 266, C1440-C1452). In the secretory epithelia of the shark rectal gland and avian salt gland, Na-K-Cl cotransport activation by both cAMP-dependent and cAMP-independent secretagogues has been shown to be accompanied by phosphorylation of the cotransport protein itself (Lytle, C., and Forbush, B., III (1992) J. Biol. Chem. 267, 25438-25443; Torchia, J., Lytle, C., Pon, D. J., Forbush, B., III, and Sen, A. K. (1992) J. Biol. Chem. 267, 25444-25450). In the present study, we immunoprecipitate the approximately 170-kDa Na-K-Cl cotransport protein of dog tracheal epithelial cells with a monoclonal antibody against the cotransporter of the intestinal cell line T84. Incubation of confluent primary cultures of tracheal cells with isoproterenol and apical UTP increases basolateral-to-apical 36Cl- flux 3.4- and 2.6-fold, respectively, and produces similar increases (3.2- and 2.8-fold, respectively) in 32P incorporation into the approximately 170-kDa cotransport protein. Decreasing [Cl-]i (without concomitant cell shrinkage) by incubating cultures with apical nystatin and reduced apical [Cl-] ([Cl-]alpha) likewise increases both cotransport activity and cotransport protein phosphorylation. These effects become more pronounced with greater reductions in [Cl-]alpha; after 20 min of incubation with nystatin and 32 mM [Cl-]alpha, cotransport activity and 32P incorporation into the cotransport protein are increased 2.8- and 2.7-fold, respectively, similar to increases seen with apical UTP. 2-3-fold increases in cotransporter activity and phosphorylation are also seen in nystatin-treated cells under hypertonic conditions (50 mM sucrose added apically and basolaterally). These findings suggest a close correlation between Na-K-Cl cotransport activity and phosphorylation of the approximately 170-kDa cotransport protein. The latter is phosphorylated in response to both reduced [Cl-]i and cell shrinkage, either or both of which are likely to be involved in secondary cotransport activation in response to apical UTP.
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Affiliation(s)
- M Haas
- Department of Pathology, University of Chicago, Illinois 60637, USA
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41
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Klein JD, O'Neill WC. Volume-sensitive myosin phosphorylation in vascular endothelial cells: correlation with Na-K-2Cl cotransport. THE AMERICAN JOURNAL OF PHYSIOLOGY 1995; 269:C1524-31. [PMID: 8572182 DOI: 10.1152/ajpcell.1995.269.6.c1524] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
To identify protein kinases that are regulated by cell volume, we examined protein phosphorylation in hypertonically shrunken aortic endothelial cells. Shrinkage reversibly increased, and swelling decreased, phosphorylation of a 19-kDa cytoskeletal protein identified as myosin light chain (MLC) by immune precipitation and immunoblotting. Shrinkage also increased MLC phosphorylation in human umbilical vein endothelial cells, rat aortic smooth muscle cells, and human dermal fibroblasts. Phosphorylation was blocked by ML-7, an inhibitor of MLC kinase (MLCK). Neither inhibition of protein kinase C nor inhibition of myosin phosphatase (with calyculin) altered MLC phosphorylation. Peptide mapping of MLC indicated phosphorylation by MLCK. Na-K-2Cl cotransport activation paralleled MLC phosphorylation in hypertonic medium. Na-K-2Cl was stimulated by low concentrations of ML-7 with no further stimulation by hypertonic shrinkage and was inhibited by higher concentrations, paralleling inhibition of MLC phosphorylation. Shrinkage-induced phosphorylation of the cotransporter was not blocked by ML-7. We conclude that cell volume regulates MLC phosphorylation by MLCK. MLCK influences Na-K-2Cl cotransport but independently of cotransporter phosphorylation. These data suggest an important link between cell volume, volume-regulatory transporters, and the contractile state of the cytoskeleton.
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Affiliation(s)
- J D Klein
- Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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Ramasamy R, Liu H, Anderson S, Lundmark J, Schaefer S. Ischemic preconditioning stimulates sodium and proton transport in isolated rat hearts. J Clin Invest 1995; 96:1464-72. [PMID: 7657818 PMCID: PMC185770 DOI: 10.1172/jci118183] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
One or more brief periods of ischemia, termed preconditioning, dramatically limits infarct size and reduces intracellular acidosis during subsequent ischemia, potentially via enhanced sarcolemmal proton efflux mechanisms. To test the hypothesis that preconditioning increases the functional activity of sodium-dependent proton efflux pathways, isolated rat hearts were subjected to 30 min of global ischemia with or without preconditioning. Intracellular sodium (Nai) was assessed using 23Na magnetic resonance spectroscopy, and the activity of the Na-H exchanger and Na-K-2Cl cotransporter was measured by transiently exposing the hearts to an acid load (NH4Cl washout). Creatine kinase release was reduced by greater than 60% in the preconditioned hearts (P < 0.05) and was associated with improved functional recovery on reperfusion. Preconditioning increased Nai by 6.24 +/- 2.04 U, resulting in a significantly higher level of Nai before ischemia than in the control hearts. Nai increased significantly at the onset of ischemia (8.48 +/- 1.21 vs. 2.57 +/- 0.81 U, preconditioned vs. control hearts; P < 0.01). Preconditioning did not reduce Nai accumulation during ischemia, but the decline in Nai during the first 5 min of reperfusion was significantly greater in the preconditioned than in the control hearts (13.48 +/- 1.73 vs. 2.54 +/- 0.41 U; P < 0.001). Exposure of preconditioned hearts to ethylisopropylamiloride or bumetanide in the last reperfusion period limited in the increase in Nai during ischemia and reduced the beneficial effects of preconditioning. After the NH4Cl prepulse, preconditioned hearts acidified significantly more than control hearts and had significantly more rapid recovery of pH (preconditioned, delta pH = 0.35 +/- 0.04 U over 5 min; control, delta pH = 0.15 +/- 0.02 U over 5 min). This rapid pH recovery was not affected by inhibition of the Na-K-2Cl cotransporter but was abolished by inhibition of the Na-H exchanger. These results demonstrate that preconditioning alters the kinetics of Nai accumulation during global ischemia as well as proton transport after NH4Cl washout. These observations are consistent with stimulation of the Na-K-2Cl cotransporter and Na-H exchanger by preconditioning.
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Affiliation(s)
- R Ramasamy
- Department of Internal Medicine, University of California, Davis 95616, USA
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Del Castillo JR, Sepúlveda FV. Activation of an Na+/K+/2Cl- cotransport system by phosphorylation in crypt cells isolated from guinea pig distal colon. Gastroenterology 1995; 109:387-96. [PMID: 7615187 DOI: 10.1016/0016-5085(95)90325-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
BACKGROUND & AIMS K+ secretion is believed to require the presence of a basolateral Na+/K+/2Cl- cotransporter. The aim of this study was to identify this transport system in epithelial cells from guinea pig colon and to study its possible regulation by phosphorylation. METHODS Cells were selectively isolated from crypt or surface epithelium of proximal or distal colon. Radioisotopes were used to measure K+, Na+, or Cl- influx. Bumetanide was used to discriminate for influx mediated by Na+/K+/2Cl- cotransport. RESULTS Under basal conditions, no bumetanide-sensitive K+ influx was observed. Pretreatment with the protein-phosphatase inhibitor calyculin A (50% effective concentration, 23 nmol/L) or ionomycin showed a bumetanide-sensitive K+ influx specifically in distal colon crypt cells. Okadaic acid and protein kinases C or A activators did not have effect. Bumetanide-sensitive K+ uptake was abolished by the removal of external Na+ or Cl- and occurred by cotransport in a 1Na+/1K+/2Cl- stoichiometry. CONCLUSIONS Evidence is presented for the presence of an Na+/K+/2Cl- cotransporter in crypt cells from distal colon epithelium. The activity of this transporter is proposed to be regulated by a phosphorylation/dephosphorylation cycle, controlled by a type I protein phosphatase. It is possible that this phosphatase(s) is modulated by intracellular Ca2+.
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Affiliation(s)
- J R Del Castillo
- Agricultural and Food Research Council Babraham Institute, Babraham Hall, Cambridge, England
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44
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Payne JA, Forbush B. Molecular characterization of the epithelial Na-K-Cl cotransporter isoforms. Curr Opin Cell Biol 1995; 7:493-503. [PMID: 7495568 DOI: 10.1016/0955-0674(95)80005-0] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Recent advances in the molecular characterization of specific isoforms of the Na-K-Cl cotransporter have allowed rapid progress in the study of the structure, function, and regulation of these members of a family of Cl-dependent cation cotransporters. Two distinct isoforms have been identified, one from Cl(-)-secretory epithelia and another found specifically in the diluting segment of the vertebrate kidney, a Cl(-)-absorptive epithelium. The discovery of three alternatively spliced variants of the absorptive isoform, which differ only by 31 amino acids and which appear to be differentially distributed within the mammalian thick ascending limb of the loop of Henle, highlight this spliced region as an important functional component of the protein.
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Affiliation(s)
- J A Payne
- Department of Human Physiology, University of California School of Medicine, Davis 95616, USA
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Rivas T, Urcelay E, González-Manchón C, Parrilla R, Ayuso MS. Role of amino acid-induced changes in ion fluxes in the regulation of hepatic protein synthesis. J Cell Physiol 1995; 163:277-84. [PMID: 7706372 DOI: 10.1002/jcp.1041630208] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Alanine is a powerful stimulator of hepatic protein synthesis whose mechanism of action has not yet been ascertained. The present work aimed to elucidate whether rate changes in ion fluxes accompanying the transport of this amino acid could play a role in the stimulation of protein synthesis. In perfused livers, the utilization of alanine produced a net uptake of K+ of 1.5 mumol/min/liver, a progressively increasing efflux of Ca2+ to reach a maximum of 0.9 mumol/min/liver, and alkalization of the extracellular medium. Inhibition of Na+/K+ exchange by ouabain reversed only the uptake of K+, indicating that this is the main way for the efflux of Na+ cotransported with alanine. In isolated hepatocytes, the uptake of alanine increased the intracellular content of K+ and the cell volume. The following observations suggest that these changes, and not an increased intracellular concentration of Na+, are associated with the stimulation of protein synthesis: 1) Ouabain inhibited the alanine stimulation of L-[3H]-valine incorporation into protein without altering the basal rate of protein labeling; 2) ouabain had no effects on alanine uptake indicating that Na+ influx is not involved in the alanine stimulation of protein synthesis; 3) disruption of Na+ gradient across the plasma membrane by specific ionophores, monensin and gramicidin D, inhibited both basal and alanine-stimulated protein synthesis, but substitution of extracellular Na+ by K+ did not prevent the stimulatory action of alanine. The observation that hypotonic buffer enhanced protein synthesis to the same degree than alanine in liver cells indicates that alanine-induced cell swelling could be sufficient to stimulate protein synthesis.
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Affiliation(s)
- T Rivas
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Cientificas, Madrid, Spain
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Hosoki E, Iijima T. Modulation of cytosolic Ca2+ concentration by thapsigargin and cyclopiazonic acid in human aortic endothelial cells. Eur J Pharmacol 1995; 288:131-7. [PMID: 7720774 DOI: 10.1016/0922-4106(95)90007-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
To clarify the agonist-induced Ca2+ entry mechanism, effects of thapsigargin and cyclopiazonic acid, selective inhibitors of endoplasmic reticulum Ca(2+)-ATPase, on intracellular free Ca2+ concentration ([Ca2+]i) were studied in cultured human aortic endothelial cells loaded with the fluorescent Ca2+ indicator fura-2. Thapsigargin (1-1000 nM) and cyclopiazonic acid (0.1-100 microM) produced a biphasic change in [Ca2+]i, which consisted of a transient peak elevation followed by a long-lasting decline of [Ca2+]i in a concentration-dependent manner. In the presence of thapsigargin or cyclopiazonic acid, the rapid transient elevation of [Ca2+]i elicited by histamine was attenuated in a time-dependent manner. The slow declining phase of the response to thapsigargin and cyclopiazonic acid was completely eliminated by removal of extracellular Ca2+, and it was also prevented by reduction of the extracellular Cl- concentration to 40 mM or by the Cl- channel blocker N-phenylanthranilic acid. These findings suggest that the initial transient rising phase and the slow declining phase of [Ca2+]i in response to thapsigargin and cyclopiazonic acid reflect a blockade of Ca2+ uptake into the endoplasmic reticulum and the Cl(-)-sensitive Ca2+ entry activated by the depletion of agonist-sensitive intracellular Ca2+ stores, respectively, in human aortic endothelial cells.
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Affiliation(s)
- E Hosoki
- Department of Pharmacology, Akita University School of Medicine, Japan
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Abstract
The Na-K-Cl cotransporters are a class of membrane proteins that transport Na, K, and Cl ions into and out of cells in an electrically neutral manner, in most cases with a stoichiometry of 1Na:1K:2Cl. Na-K-Cl cotransporters are present in a wide variety of cells and tissues, including reabsorptive and secretory epithelia, nerve and muscle cells, endothelial cells, fibroblasts, and blood cells. Na-K-Cl cotransport plays a vital role in renal salt reabsorption and in salt secretion by intestinal, airway, salivary gland, and other secretory epithelia. Cotransport function also appears to be important in the maintenance and regulation of cell volume and of ion gradients by both epithelial and nonepithelial cells. Na-K-Cl cotransport activity is inhibited by "loop" diuretics, including the clinically efficacious agents bumetanide and furosemide. The regulation of Na-K-Cl cotransport is mediated, at least in some cases, through direct phosphorylation of the cotransport protein. Cotransporter regulation is highly tissue specific, perhaps in part related to the presence of different Na-K-Cl cotransporter isoforms. In epithelia, both absorptive (kidney-specific) and secretory isoforms have been identified by cDNA cloning and sequencing and Northern blot analysis; alternatively spliced variants of the kidney-specific isoform have also been identified. The absorptive and secretory isoforms exhibit approximately 60% identity at the amino acid sequence level; these sequences in turn show approximately 45% overall homology with those of thiazide-sensitive, bumetanide-insensitive, Na-Cl cotransport proteins of winter flounder urinary bladder and mammalian kidney. This review focuses on recent developments in the identification of Na-K-Cl cotransport proteins in epithelial and on the regulation of epithelial Na-K-Cl cotransporter function at cellular and molecular levels.
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Affiliation(s)
- M Haas
- Department of Pathology, University of Chicago, Illinois 60637
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Suvitayavat W, Dunham PB, Haas M, Rao MC. Characterization of the proteins of the intestinal Na(+)-K(+)-2Cl- cotransporter. THE AMERICAN JOURNAL OF PHYSIOLOGY 1994; 267:C375-84. [PMID: 8074174 DOI: 10.1152/ajpcell.1994.267.2.c375] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Absorptive intestinal epithelia, such as that of the winter flounder, absorb salt via a bumetanide-sensitive Na(+)-K(+)-2Cl- cotransport mechanism on the brush-border membrane (BBM). The present study demonstrates the first molecular characterization of the intestinal Na(+)-K(+)-2Cl- cotransporter and its unique regulation. The photoaffinity bumetanide analogue, 4-[3H]benzoyl-5-sulfamoyl-3- (3-thenyloxy)benzoic acid, specifically labeled three groups of proteins in flounder intestinal microsomal membranes (MM): a approximately 180-kDa peptide, prominently labeled, and diffuse bands at approximately 110-70 and 50 kDa, less intensely labeled. Subcellular fractionation revealed a single prominently labeled protein of approximately 170 kDa in BBM but not in basolateral membranes (BLM) and little or no labeling of proteins of approximately 110-70 or 50 kDa. Polyclonal antiserum raised against the Ehrlich ascites cell cotransporter identified a 180-kDa peptide in MM and a 175-kDa peptide (pI approximately 5.4) in BBM but none in BLM or in the cytosol of flounder intestine. As predicted from the regulation of cotransport in this tissue, phosphorylation of this protein is increased by guanosine 3',5'-cyclic monophosphate (cGMP)-dependent but not by adenosine 3',5'-cyclic monophosphate-dependent protein kinase. In addition, phosphorylation of the protein is not increased by protein kinase C or Ca2+/calmodulin-dependent protein kinase but is increased by the phosphatase inhibitor calyculin A. Finally, calyculin A preserves the inhibitory effect of cGMP on ion transport, even in the absence of the nucleotide, suggesting that phosphorylation-dephosphorylation mechanisms are crucial in cotransporter regulation. Thus the flounder intestinal cotransporter is a approximately 175-kDa BBM protein that can be regulated by phosphorylation.
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Affiliation(s)
- W Suvitayavat
- Department of Physiology and Biophysics, University of Illinois at Chicago 60612
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Regulation by nerve growth factor and protein phosphorylation of Na/K/2Cl cotransport and cell volume in PC12 cells. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)34099-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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