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Hoffmann EK, Schettino T, Marshall WS. The role of volume-sensitive ion transport systems in regulation of epithelial transport. Comp Biochem Physiol A Mol Integr Physiol 2007; 148:29-43. [PMID: 17289411 DOI: 10.1016/j.cbpa.2006.11.023] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2006] [Revised: 11/08/2006] [Accepted: 11/23/2006] [Indexed: 11/25/2022]
Abstract
This review focuses on using the knowledge on volume-sensitive transport systems in Ehrlich ascites tumour cells and NIH-3T3 cells to elucidate osmotic regulation of salt transport in epithelia. Using the intestine of the European eel (Anguilla anguilla) (an absorptive epithelium of the type described in the renal cortex thick ascending limb (cTAL)) we have focused on the role of swelling-activated K+- and anion-conductive pathways in response to hypotonicity, and on the role of the apical (luminal) Na+-K+-2Cl- cotransporter (NKCC2) in the response to hypertonicity. The shrinkage-induced activation of NKCC2 involves an interaction between the cytoskeleton and protein phosphorylation events via PKC and myosin light chain kinase (MLCK). Killifish (Fundulus heteroclitus) opercular epithelium is a Cl(-)-secreting epithelium of the type described in exocrine glands, having a CFTR channel on the apical side and the Na+/K+ ATPase, NKCC1 and a K+ channel on the basolateral side. Osmotic control of Cl- secretion across the operculum epithelium includes: (i) hyperosmotic shrinkage activation of NKCC1 via PKC, MLCK, p38, OSR1 and SPAK; (ii) deactivation of NKCC by hypotonic cell swelling and a protein phosphatase, and (iii) a protein tyrosine kinase acting on the focal adhesion kinase (FAK) to set levels of NKCC activity.
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Affiliation(s)
- E K Hoffmann
- Department of Molecular Biology, The August Krogh Building, University of Copenhagen, Denmark.
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Barfod ET, Moore AL, Roe MW, Lidofsky SD. Ca2+-activated IK1 channels associate with lipid rafts upon cell swelling and mediate volume recovery. J Biol Chem 2007; 282:8984-93. [PMID: 17264085 DOI: 10.1074/jbc.m607730200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Restoration of cell volume in the continued presence of osmotic stimuli is essential, particularly in hepatocytes, which swell upon nutrient uptake. Responses to swelling involve the Ca2+-dependent activation of K+ channels, which promote fluid efflux to drive volume recovery; however, the channels involved in hepatocellular volume regulation have not been identified. We found that hypotonic exposure of HTC hepatoma cells evoked the opening of 50 pS K+-permeable channels, consistent with intermediate conductance (IK) channels. We isolated from rat liver and HTC cells a cDNA with sequence identity to the coding region of IK1. Swelling-activated currents were inhibited by transfection with a dominant interfering IK1 mutant. The IK channel blockers clotrimazole and TRAM-34 inhibited whole cell swelling-activated K+ currents and volume recovery. To determine whether IK1 underwent volume-sensitive localization, we expressed a green fluorescent protein fusion of IK1 in HTC cells. The localization of IK1 was suggestive of distribution in lipid rafts. Consistent with this, there was a time-dependent increase in colocalization between IK1 and the lipid raft ganglioside GM1 on the plasma membrane, which subsequently decreased with volume recovery. Pharmacological disruption of lipid rafts altered the plasma membrane distribution of IK1 and inhibited volume recovery after hypotonic exposure. Collectively, these findings support the hypothesis that IK1 regulates compensatory responses to hepatocellular swelling and suggest that regulation of cell volume involves coordination of signaling from lipid rafts with IK1 function.
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Affiliation(s)
- Elisabeth T Barfod
- Department of Pharmacology, University of Vermont, Burlington, Vermont 05405, USA
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Lam HD, Lemay AM, Kelly J, Hill CE. Loss of Kv and MaxiK currents associated with increased MRP1 expression in small cell lung carcinoma. J Cell Physiol 2006; 209:535-41. [PMID: 16883578 DOI: 10.1002/jcp.20761] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Regulatory volume decrease and exocrine secretion studies suggest a functional relationship between K+ and organic anion efflux. To test the hypothesis that the expression of K+ channels and MRP1 is reciprocally related, we employed the patch clamp and RT-PCR techniques on weakly (H69) and strongly MRP1-expressing (H69AR) small cell lung cancer cells. H69AR cells do not express the time- and voltage-dependent delayed rectifying K+ current (Kv) reported earlier in H69 cells and confirmed here. About 80% of the Kv current in H69 cells inactivated at 0 mV, allowing us to identify other K+ currents present in these cells. Whole-cell currents from cells dialyzed and bathed in K-gluconate as the major ions exhibited inward rectification in both cell types. Inwardly rectifying (Kir) currents in both H69 and H69AR cells showed time-dependent activation and slow inactivation at large negative potentials. H69 cells also express a threefold larger Ca2+ -stimulated K+ -selective and iberiotoxin-sensitive current relative to H69AR cells. In excised inside-out patches exposed to 145 mM symmetrical K+ solutions, H69 cells expressed a voltage- and Ca2+ -sensitive large conductance (128 +/- 5 pS) K+ channel (MaxiK). MaxiK-like currents were not observed at the whole-cell or single-channel level in H69AR cells. RT-PCR identified MaxiKalpha transcripts in H69 but not H69AR cells. These results indicate that two K+ currents (MaxiK and Kv) and the organic anion transporter MRP1 are reciprocally expressed in H69 and H69AR cells.
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Affiliation(s)
- Hung D Lam
- GI Diseases Research Unit, Hotel Dieu Hospital and Queen's University, Kingston, Ontario, Canada
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Lan WZ, Abbas H, Lemay AM, Briggs MM, Hill CE. Electrophysiological and molecular identification of hepatocellular volume-activated K+ channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1668:223-33. [PMID: 15737333 DOI: 10.1016/j.bbamem.2004.12.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2004] [Revised: 11/26/2004] [Accepted: 12/17/2004] [Indexed: 11/30/2022]
Abstract
Although K+ channels are essential for hepatocellular function, it is not known which channels are involved in the regulatory volume decrease (RVD) in these cells. We have used a combination of electrophysiological and molecular approaches to describe the potential candidates for these channels. The dialysis of short-term cultured rat hepatocytes with a hypotonic solution containing high K+ and low Cl- concentration caused the slow activation of an outward, time-independent current under whole-cell configuration of the patch electrode voltage clamp. The reversal potential of this current suggested that K+ was the primary charge carrier. The swelling-induced K+ current (IKvol) occurred in the absence of Ca2+ and was inhibited with 1 microM Ca2+ in the pipette solution. The activation of IKvol required both Mg2+ and ATP and an increasing concentration of Mg-ATP from 0.25 through 0.5 to 0.9 mM activated IKvol increasingly faster and to a larger extent. The KCNQ1 inhibitor chromanol 293B reversibly depressed IKvol with an IC50 of 26 microM. RT-PCR detected the expression of members of the KCNQ family from KCNQ1 to KCNQ5 and of the accessory proteins KCNE1 to KCNE3 in the rat hepatocytes, but not KCNQ2 and KCNE2 in human liver. Western blotting showed KCNE3 expression in a plasma membrane-enriched fraction from rat hepatocytes. The results suggest that KCNQ1, probably with KCNE2 or KCNE3 as its accessory unit, provides a significant fraction of IKvol in rat hepatocytes.
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Affiliation(s)
- W-Z Lan
- GI Diseases Research Unit, Hotel Dieu Hospital and Queen's University, Kingston, Ontario, Canada K7L 5G2
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Wehner F, Olsen H, Tinel H, Kinne-Saffran E, Kinne RKH. Cell volume regulation: osmolytes, osmolyte transport, and signal transduction. Rev Physiol Biochem Pharmacol 2004; 148:1-80. [PMID: 12687402 DOI: 10.1007/s10254-003-0009-x] [Citation(s) in RCA: 242] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In recent years, it has become evident that the volume of a given cell is an important factor not only in defining its intracellular osmolality and its shape, but also in defining other cellular functions, such as transepithelial transport, cell migration, cell growth, cell death, and the regulation of intracellular metabolism. In addition, besides inorganic osmolytes, the existence of organic osmolytes in cells has been discovered. Osmolyte transport systems-channels and carriers alike-have been identified and characterized at a molecular level and also, to a certain extent, the intracellular signals regulating osmolyte movements across the plasma membrane. The current review reflects these developments and focuses on the contributions of inorganic and organic osmolytes and their transport systems in regulatory volume increase (RVI) and regulatory volume decrease (RVD) in a variety of cells. Furthermore, the current knowledge on signal transduction in volume regulation is compiled, revealing an astonishing diversity in transport systems, as well as of regulatory signals. The information available indicates the existence of intricate spatial and temporal networks that control cell volume and that we are just beginning to be able to investigate and to understand.
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Affiliation(s)
- F Wehner
- Max-Planck-Institut für molekulare Physiologie, Otto-Hahn-Str. 11, 44227, Dortmund, Germany.
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Hoffmann EK, Hougaard C. Intracellular signalling involved in activation of the volume-sensitive K+ current in Ehrlich ascites tumour cells. Comp Biochem Physiol A Mol Integr Physiol 2001; 130:355-66. [PMID: 11913449 DOI: 10.1016/s1095-6433(01)00419-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The cell swelling-activated K+ channel in Ehrlich ascites tumour cells has a conductance of 5 pS estimated from noise analysis of the volume-sensitive whole-cell K+ current (I(K,vol)). I(K,vol) exhibits Goldman-Hodgkin-Katz type behaviour and is insensitive to clotrimazole, apamin and charybdotoxin (ChTX), but inhibited by clofilium. Its small conductance, lack of intrinsic voltage-dependence and peculiar pharmacological profile are similar to properties described for the two-pore domain background K+ TASK channels. Neither Ca2+ nor ATP work as initiators in the activation of I(K,vol). In contrast, several investigations in Ehrlich cells suggest an important role for leukotriene D4 (LTD4) in the activation of I(K,vol). Under isotonic conditions, LTD4 activates Ca2+-dependent, ChTX-sensitive K+ channels as well as Ca2+-independent. ChTX-insensitive K+ channels. The LTD4-activated, ChTX-insensitive K+ current exhibits a current-voltage relation, pharmacological profile and single channel conductance similar to that of I(K,vol), indicating that LTD4 is the signalling molecule responsible for activation of the volume-sensitive K+ channels in Ehrlich cells. Hypotonic swelling of Ehrlich cells results in translocation of the 85-kDa cytosolic (c) PLA2alpha to the nucleus where it is activated. This activation leads to an increase in arachidonic acid release followed by an increased release of leukotrienes, and is essential in cell swelling-induced activation of I(K,vol) and of the organic osmolyte channels.
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Affiliation(s)
- E K Hoffmann
- August Krogh Institute, Department of Biochemistry, University of Copenhagen, Denmark.
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Malhi H, Irani AN, Rajvanshi P, Suadicani SO, Spray DC, McDonald TV, Gupta S. KATP channels regulate mitogenically induced proliferation in primary rat hepatocytes and human liver cell lines. Implications for liver growth control and potential therapeutic targeting. J Biol Chem 2000; 275:26050-7. [PMID: 10862612 DOI: 10.1074/jbc.m001576200] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
To determine whether K(ATP) channels control liver growth, we used primary rat hepatocytes and several human cancer cell lines for assays. K(ATP) channel openers (minoxidil, cromakalim, and pinacidil) increased cellular DNA synthesis, whereas K(ATP) channel blockers (quinidine and glibenclamide) attenuated DNA synthesis. The channel inhibitor glibenclamide decreased the clonogenicity of HepG2 cells without inducing cytotoxicity or apoptosis. To demonstrate the specificity of drugs for K(+) channels, whole-cell patch-clamp recordings were made. Hepatocytes revealed K(+) currents with K(ATP) channel properties. These K(+) currents were augmented by minoxidil and pinacidil and attenuated by glibenclamide as well as tetraethylammonium, in agreement with established responses of K(ATP) channels. Reverse transcription of total cellular RNA followed by polymerase chain reaction showed expression of K(ATP) channel-specific subunits in rat hepatocytes and human liver cell lines. Calcium fluxes were unperturbed in glibenclamide-treated HepG2 cells and primary rat hepatocytes following induction with ATP and hepatocyte growth factor, respectively, suggesting that the effect of K(ATP) channel activity upon hepatocyte proliferation was not simply due to indirect modulation of intracellular calcium. The regulation of mitogen-related hepatocyte proliferation by K(ATP) channels advances our insights into liver growth control. The findings have implications in mechanisms concerning liver development, regeneration, and oncogenesis.
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Affiliation(s)
- H Malhi
- Marion Bessin Liver Research Center, the Cancer Research Center, and the Departments of Medicine and Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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Niemeyer MI, Hougaard C, Hoffmann EK, Jorgensen F, Stutzin A, Sepúlveda FV. Characterisation of a cell swelling-activated K+-selective conductance of ehrlich mouse ascites tumour cells. J Physiol 2000; 524 Pt 3:757-67. [PMID: 10790156 PMCID: PMC2269893 DOI: 10.1111/j.1469-7793.2000.00757.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The K+ and Cl- currents activated by hypotonic cell swelling were studied in Ehrlich ascites tumour cells using the whole-cell recording mode of the patch-clamp technique. Currents were measured in the absence of added intracellular Ca2+ and with strong buffering of Ca2+. K+ current activated by cell swelling was measured as outward current at the Cl- equilibrium potential (ECl) under quasi-physiological gradients. It could be abolished by replacing extracellular Na+ with K+, thereby cancelling the driving force. Replacement with other cations suggested a selectivity sequence of K+ > Rb+ > NH4 approximately Na+ approximately Li+; Cs+ appeared to be inhibitory. The current-voltage relationship of the volume-sensitive K+ current was well fitted with the Goldman-Hodgkin-Katz current equation between -130 and +20 mV with a permeability coefficient of around 10(-6) cm s(-1) with both physiological and high-K+ extracellular solutions. The class III antiarrhythmic drug clofilium blocked the volume-sensitive K+ current in a voltage-independent manner with an IC50 of 32 microM. Clofilium was also found to be a strong inhibitor of the regulatory volume decrease response of Ehrlich cells. Cell swelling-activated K+ currents of Ehrlich cells are voltage and calcium insensitive and are resistant to a range of K+ channel inhibitors. These characteristics are similar to those of the so-called background K+ channels. Noise analysis of whole-cell current was consistent with a unitary conductance of 5.5 pS for the single channels underlying the K+ current evoked by cell swelling, measured at 0 mV under a quasi-physiological K+ gradient.
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Affiliation(s)
- M I Niemeyer
- Instituto de Ciencias Biomedicas, Facultad de Medicina, Universidad de Chile, Casilla 70058, Santiago-7, Chile
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Hill CE, Jacques JE. Cholestatic effects of the K+ channel blockers Ba2+ and TEA occur through different pathways in the rat liver. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:G43-8. [PMID: 9886977 DOI: 10.1152/ajpgi.1999.276.1.g43] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
The role of K+ channels in bile acid-independent bile flow (BAIF) was studied in the isolated and bile duct-cannulated perfused rat liver by changing the driving force on K+ and by using a variety of K+ channel blockers. Bile flow rate, effluent perfusate K+ content, and portal pressure were measured. Increase in perfusate K+ from 5.9 to 80 mM caused inhibition of bile flow that could be fitted to a Boltzmann distribution, indicating partial dependence of bile formation on the K+ equilibrium potential and hence K+ channel activity. To investigate this further, the effects of compounds established as K+ channel blockers in liver or other tissues were surveyed. Ba2+ (1-5 mM) inhibited mean bile flow by 20%. Tetraethylammonium (TEA) inhibition of basal bile flow was biphasic with saturable (IC50 approximately 0.7 mM) and linear components. In contrast, infusion of the K+ channel blockers 4-aminopyridine (5 mM), cesium (2.5 mM), quinidine (0.1 mM), iberiotoxin (90 nM), or paxilline (100 nM) did not affect bile flow. As expected for a K+ channel blocker, Ba2+ caused a net K+ uptake. Conversely, TEA did not affect basal K+ fluxes, although TEA-induced cholestasis was accompanied by a 26% decrease in biliary glutathione excretion. These results suggest that the partial cholestasis induced by the K+ channel blockers Ba2+ and TEA occurs by significantly different mechanisms. Whereas the Ba2+ response implicates K+ channel activity as a significant driving force in BAIF, TEA-sensitive K+ channels are not present or are not involved in bile formation.
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Affiliation(s)
- C E Hill
- Department of Physiology and the Gastrointestinal Diseases Research Unit, Queen's University, Kingston, Ontario, Canada K7L 5G2
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