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Bowley KA, Sandle GI. Calmodulin Antagonist W-7 Enhances Intermediate Conductance Ca 2+- Sensitive Basolateral Potassium Channel (IK Ca) Activity in Human Colonic Crypts. J Membr Biol 2021; 254:423-428. [PMID: 34313792 PMCID: PMC8328907 DOI: 10.1007/s00232-021-00193-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Accepted: 07/07/2021] [Indexed: 11/27/2022]
Abstract
Intermediate conductance potassium (IKCa) channels are exquisitively Ca2+ sensitive, intracellular Ca2+ regulating channel activity by complexing with calmodulin (CaM), which is bound to the cytosolic carboxyl tail. Although CaM antagonists might be expected to decrease IKCa channel activity, the effect of W-7 in human T lymphocytes are conflicting. We therefore evaluated the effect of W-7 on basolateral IKCa channels in human colonic crypt cells. Intact crypts obtained from normal human colonic biopsies by Ca2+ chelation were used for patch clamp studies of basolateral IKCa channels in the cell-attached configuration. IKCa channel activity was studied when the bath Ca2+ concentration was changed from 1.2 mmol/L to 100 μmol/L and back to 1.2 mmol/L, as well as from 100 μmol/L to 1.2 mmol/L and back to 100 μmol/L, both in the absence and presence of 25 μmol/L W-7. Decreasing bath Ca2+ from 1.2 mmol/L to 100 μmol/L decreased IKCa channel activity reversibly in the absence of W-7, whereas there was a uniformly high level of channel activity at both bath Ca2+ concentrations in the presence of W-7. In separate experiments, increasing bath Ca2+ from 100 μmol/L to 1.2 mmol/L increased IKCa channel activity reversibly in the absence of W-7, whereas there was again a uniformly high level of channel activity at both bath Ca2+ concentrations in the presence of W-7. We, therefore, propose that W-7 has a specific stimulatory effect on basolateral IKCa channel activity, despite its ability to inhibit Ca2+/CaM-mediated, IKCa channel-dependent Cl− secretion in human colonic epithelial cells. ![]()
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Affiliation(s)
- Kate A Bowley
- Leeds Institute of Medical Research at St James, St James University Hospital, Beckett Street, Leeds, LS9 7TF, UK
| | - Geoffrey I Sandle
- Leeds Institute of Medical Research at St James, St James University Hospital, Beckett Street, Leeds, LS9 7TF, UK.
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Ao M, Domingue JC, Khan N, Javed F, Osmani K, Sarathy J, Rao MC. Lithocholic acid attenuates cAMP-dependent Cl- secretion in human colonic epithelial T84 cells. Am J Physiol Cell Physiol 2016; 310:C1010-23. [PMID: 27076617 DOI: 10.1152/ajpcell.00350.2015] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Accepted: 04/12/2016] [Indexed: 01/14/2023]
Abstract
Bile acids (BAs) play a complex role in colonic fluid secretion. We showed that dihydroxy BAs, but not the monohydroxy BA lithocholic acid (LCA), stimulate Cl(-) secretion in human colonic T84 cells (Ao M, Sarathy J, Domingue J, Alrefai WA, Rao MC. Am J Physiol Cell Physiol 305: C447-C456, 2013). In this study, we explored the effect of LCA on the action of other secretagogues in T84 cells. While LCA (50 μM, 15 min) drastically (>90%) inhibited FSK-stimulated short-circuit current (Isc), it did not alter carbachol-stimulated Isc LCA did not alter basal Isc, transepithelial resistance, cell viability, or cytotoxicity. LCA's inhibitory effect was dose dependent, acted faster from the apical membrane, rapid, and not immediately reversible. LCA also prevented the Isc stimulated by the cAMP-dependent secretagogues 8-bromo-cAMP, lubiprostone, or chenodeoxycholic acid (CDCA). The LCA inhibitory effect was BA specific, since CDCA, cholic acid, or taurodeoxycholic acid did not alter FSK or carbachol action. While LCA alone had no effect on intracellular cAMP concentration ([cAMP]i), it decreased FSK-stimulated [cAMP]i by 90%. Although LCA caused a small increase in intracellular Ca(2+) concentration ([Ca(2+)]i), chelation by BAPTA-AM did not reverse LCA's effect on Isc LCA action does not appear to involve known BA receptors, farnesoid X receptor, vitamin D receptor, muscarinic acetylcholine receptor M3, or bile acid-specific transmembrane G protein-coupled receptor 5. LCA significantly increased ERK1/2 phosphorylation, which was completely abolished by the MEK inhibitor PD-98059. Surprisingly PD-98059 did not reverse LCA's effect on Isc Finally, although LCA had no effect on basal Isc, nystatin permeabilization studies showed that LCA both stimulates an apical cystic fibrosis transmembrane conductance regulator Cl(-) current and inhibits a basolateral K(+) current. In summary, 50 μM LCA greatly inhibits cAMP-stimulated Cl(-) secretion, making low doses of LCA of potential therapeutic interest for diarrheal diseases.
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Affiliation(s)
- Mei Ao
- Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois
| | - Jada C Domingue
- Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois
| | - Nabihah Khan
- Department of Biology, Benedictine University, Lisle, Illinois
| | - Fatima Javed
- Department of Biology, Benedictine University, Lisle, Illinois
| | - Kashif Osmani
- Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois
| | - Jayashree Sarathy
- Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois; Department of Biology, Benedictine University, Lisle, Illinois
| | - Mrinalini C Rao
- Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois; Department of Medicine, University of Illinois at Chicago, Chicago, Illinois; and
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Nichols JM, Maiellaro I, Abi-Jaoude J, Curci S, Hofer AM. "Store-operated" cAMP signaling contributes to Ca2+-activated Cl- secretion in T84 colonic cells. Am J Physiol Gastrointest Liver Physiol 2015; 309:G670-9. [PMID: 26316590 PMCID: PMC4609931 DOI: 10.1152/ajpgi.00214.2015] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 08/21/2015] [Indexed: 01/31/2023]
Abstract
Apical cAMP-dependent CFTR Cl(-) channels are essential for efficient vectorial movement of ions and fluid into the lumen of the colon. It is well known that Ca(2+)-mobilizing agonists also stimulate colonic anion secretion. However, CFTR is apparently not activated directly by Ca(2+), and the existence of apical Ca(2+)-dependent Cl(-) channels in the native colonic epithelium is controversial, leaving the identity of the Ca(2+)-activated component unresolved. We recently showed that decreasing free Ca(2+) concentration ([Ca(2+)]) within the endoplasmic reticulum (ER) lumen elicits a rise in intracellular cAMP. This process, which we termed "store-operated cAMP signaling" (SOcAMPS), requires the luminal ER Ca(2+) sensor STIM1 and does not depend on changes in cytosolic Ca(2+). Here we assessed the degree to which SOcAMPS participates in Ca(2+)-activated Cl(-) transport as measured by transepithelial short-circuit current (Isc) in polarized T84 monolayers in parallel with imaging of cAMP and PKA activity using fluorescence resonance energy transfer (FRET)-based reporters in single cells. In Ca(2+)-free conditions, the Ca(2+)-releasing agonist carbachol and Ca(2+) ionophore increased Isc, cAMP, and PKA activity. These responses persisted in cells loaded with the Ca(2+) chelator BAPTA-AM. The effect on Isc was enhanced in the presence of the phosphodiesterase (PDE) inhibitor 3-isobutyl-1-methylxanthine (IBMX), inhibited by the CFTR inhibitor CFTRinh-172 and the PKA inhibitor H-89, and unaffected by Ba(2+) or flufenamic acid. We propose that a discrete component of the "Ca(2+)-dependent" secretory activity in the colon derives from cAMP generated through SOcAMPS. This alternative mode of cAMP production could contribute to the actions of diverse xenobiotic agents that disrupt ER Ca(2+) homeostasis, leading to diarrhea.
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Affiliation(s)
- Jonathan M. Nichols
- Department of Veterans Affairs Boston Healthcare System and Department of Surgery, Brigham & Women's Hospital and Harvard Medical School, West Roxbury, Massachusetts
| | - Isabella Maiellaro
- Department of Veterans Affairs Boston Healthcare System and Department of Surgery, Brigham & Women's Hospital and Harvard Medical School, West Roxbury, Massachusetts
| | - Joanne Abi-Jaoude
- Department of Veterans Affairs Boston Healthcare System and Department of Surgery, Brigham & Women's Hospital and Harvard Medical School, West Roxbury, Massachusetts
| | - Silvana Curci
- Department of Veterans Affairs Boston Healthcare System and Department of Surgery, Brigham & Women's Hospital and Harvard Medical School, West Roxbury, Massachusetts
| | - Aldebaran M. Hofer
- Department of Veterans Affairs Boston Healthcare System and Department of Surgery, Brigham & Women's Hospital and Harvard Medical School, West Roxbury, Massachusetts
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Gustafsson JK, Lindén SK, Alwan AH, Scholte BJ, Hansson GC, Sjövall H. Carbachol-induced colonic mucus formation requires transport via NKCC1, K⁺ channels and CFTR. Pflugers Arch 2014; 467:1403-1415. [PMID: 25139191 DOI: 10.1007/s00424-014-1595-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Revised: 08/01/2014] [Accepted: 08/06/2014] [Indexed: 12/26/2022]
Abstract
The colonic mucosa protects itself from the luminal content by secreting mucus that keeps the bacteria at a distance from the epithelium. For this barrier to be effective, the mucus has to be constantly replenished which involves exocytosis and expansion of the secreted mucins. Mechanisms involved in regulation of mucus exocytosis and expansion are poorly understood, and the aim of this study was to investigate whether epithelial anion secretion regulates mucus formation in the colon. The muscarinic agonist carbachol was used to induce parallel secretion of anions and mucus, and by using established inhibitors of ion transport, we studied how inhibition of epithelial transport affected mucus formation in mouse colon. Anion secretion and mucin exocytosis were measured by changes in membrane current and epithelial capacitance, respectively. Mucus thickness measurements were used to determine the carbachol effect on mucus growth. The results showed that the carbachol-induced increase in membrane current was dependent on NKCC1 co-transport, basolateral K(+) channels and Cftr activity. In contrast, the carbachol-induced increase in capacitance was partially dependent on NKCC1 and K(+) channel activity, but did not require Cftr activity. Carbachol also induced an increase in mucus thickness that was inhibited by the NKCC1 blocker bumetanide. However, mice that lacked a functional Cftr channel did not respond to carbachol with an increase in mucus thickness, suggesting that carbachol-induced mucin expansion requires Cftr channel activity. In conclusion, these findings suggest that colonic epithelial transport regulates mucus formation by affecting both exocytosis and expansion of the mucin molecules.
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Affiliation(s)
- Jenny K Gustafsson
- Department of Medical Biochemistry, University of Gothenburg, Medicinaregatan 9A, Box 440, Gothenburg, 405 30, Sweden.
| | - Sara K Lindén
- Department of Medical Biochemistry, University of Gothenburg, Medicinaregatan 9A, Box 440, Gothenburg, 405 30, Sweden
| | - Ala H Alwan
- Department of Medical Biochemistry, University of Gothenburg, Medicinaregatan 9A, Box 440, Gothenburg, 405 30, Sweden
| | - Bob J Scholte
- Department of Cell Biology, Erasmus MC, Rotterdam, The Netherlands
| | - Gunnar C Hansson
- Department of Medical Biochemistry, University of Gothenburg, Medicinaregatan 9A, Box 440, Gothenburg, 405 30, Sweden
| | - Henrik Sjövall
- Department of Internal Medicine, University of Gothenburg, Gothenburg, Sweden
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Bzik VA, Medani M, Baird AW, Winter DC, Brayden DJ. Mechanisms of action of zinc on rat intestinal epithelial electrogenic ion secretion: insights into its antidiarrhoeal actions. ACTA ACUST UNITED AC 2012; 64:644-53. [PMID: 22471360 DOI: 10.1111/j.2042-7158.2011.01441.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
OBJECTIVES Zinc is a useful addition to oral rehydration therapy for acute diarrhoea. We have assessed the mechanism of its epithelial antisecretory action when intestinal epithelial tight junctions were pharmacologically opened. METHODS Rat isolated ileal and colonic mucosae were mounted in Ussing chambers and exposed to ZnSO(4) (Zn(2+) ) in the presence of secretagogues and inhibition of short circuit current (I(sc) ) was measured. KEY FINDINGS Pre-incubation with basolateral but not apical Zn(2+) reduced I(sc) stimulated by forskolin, carbachol and A23187. In the presence of the tight junction-opener, cytochalasin D, antisecretory effects of apically-applied Zn(2+) were enabled in colon and ileum. The apparent permeability coefficient (P(app) ) of Zn(2+) was increased 1.4- and 2.4-fold across rat ileum and colon, respectively, by cytochalasin D. Basolateral addition of Zn(2+) also reduced the I(sc) stimulated by nystatin in rat colon, confirming K channel inhibition. In comparison with other inhibitors, Zn(2+) was a relatively weak blocker of basolateral K(ATP) and K (Ca2+) channels. Exposure of ileum and colon to Zn(2+) for 60 min had minimal effects on epithelial histology. CONCLUSIONS Antisecretory effects of Zn(2+) on intestinal epithelia arose in part through nonselective blockade of basolateral K channels, which was enabled when tight junctions were open.
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Affiliation(s)
- Victoria A Bzik
- Conway Institute and School of Veterinary Medicine, University College Dublin, Belfield, Ireland
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Halm ST, Liao T, Halm DR. Distinct K+ conductive pathways are required for Cl- and K+ secretion across distal colonic epithelium. Am J Physiol Cell Physiol 2006; 291:C636-48. [PMID: 16641164 DOI: 10.1152/ajpcell.00557.2005] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Secretion of Cl(-) and K(+) in the colonic epithelium operates through a cellular mechanism requiring K(+) channels in the basolateral and apical membranes. Transepithelial current [short-circuit current (I(sc))] and conductance (G(t)) were measured for isolated distal colonic mucosa during secretory activation by epinephrine (Epi) or PGE(2) and synergistically by PGE(2) and carbachol (PGE(2) + CCh). TRAM-34 at 0.5 microM, an inhibitor of K(Ca)3.1 (IK, Kcnn4) K(+) channels (H. Wulff, M. J. Miller, W. Hänsel, S. Grissmer, M. D. Cahalan, and K. G. Chandy. Proc Natl Acad Sci USA 97: 8151-8156, 2000), did not alter secretory I(sc) or G(t) in guinea pig or rat colon. The presence of K(Ca)3.1 in the mucosa was confirmed by immunoblot and immunofluorescence detection. At 100 microM, TRAM-34 inhibited I(sc) and G(t) activated by Epi ( approximately 4%), PGE(2) ( approximately 30%) and PGE(2) + CCh ( approximately 60%). The IC(50) of 4.0 microM implicated involvement of K(+) channels other than K(Ca)3.1. The secretory responses augmented by the K(+) channel opener 1-EBIO were inhibited only at a high concentration of TRAM-34, suggesting further that K(Ca)3.1 was not involved. Sensitivity of the synergistic response (PGE(2) + CCh) to a high concentration TRAM-34 supported a requirement for multiple K(+) conductive pathways in secretion. Clofilium (100 microM), a quaternary ammonium, inhibited Cl(-) secretory I(sc) and G(t) activated by PGE(2) ( approximately 20%) but not K(+) secretion activated by Epi. Thus Cl(-) secretion activated by physiological secretagogues occurred without apparent activity of K(Ca)3.1 channels but was dependent on other types of K(+) channels sensitive to high concentrations of TRAM-34 and/or clofilium.
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Affiliation(s)
- Susan Troutman Halm
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University Boonshoft School of Medicine, Dayton, Ohio 45435, USA
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Cunderlíková B, Moan J, Sjaastad I. pH dependent uptake of porphyrin-type photosensitizers by solid tumor cells in vitro is not induced by modification of transmembrane potential. Cancer Lett 2005; 222:39-47. [PMID: 15837539 DOI: 10.1016/j.canlet.2004.09.032] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2004] [Revised: 09/15/2004] [Accepted: 09/20/2004] [Indexed: 11/25/2022]
Abstract
The uptake of HpIX, TPPS2a and mTHPC by WiDr, THX cells and skin fibroblasts at pH 7.4 and 6.8 was compared. In the absence of serum, the uptake of HpIX was higher at lower pH. The difference was significant in WiDr cells (P < 0.01) and skin fibroblasts (P < 0.05). TPPS2a nor mTHPC showed any pH dependent uptake. Lowering the extracellular pH resulted in a significant depolarization (3-8 mV) of the cells. Application of tetraethylammonium chloride did not affect the cellular uptake of any of the photosensitizers. We conclude that the pH dependent uptake of photosensitizers is not mainly related to altered transmembrane potential.
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Affiliation(s)
- Beata Cunderlíková
- Department of Biophysics, Institute for Cancer Research, Montebello, N-0310 Oslo, Norway.
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Li Y, Halm DR. Secretory modulation of basolateral membrane inwardly rectified K(+) channel in guinea pig distal colonic crypts. Am J Physiol Cell Physiol 2002; 282:C719-35. [PMID: 11880260 DOI: 10.1152/ajpcell.00065.2001] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cell-attached recordings revealed K(+) channel activity in basolateral membranes of guinea pig distal colonic crypts. Inwardly rectified currents were apparent with a pipette solution containing 140 mM K(+). Single-channel conductance (gamma) was 9 pS at the resting membrane potential. Another inward rectifier with gamma of 19 pS was observed occasionally. At a holding potential of -80 mV, gamma was 21 and 41 pS, respectively. Identity as K(+) channels was confirmed after patch excision by changing the bath ion composition. From reversal potentials, relative permeability of Na(+) over K(+) (P(Na)/P(K)) was 0.02 +/- 0.02, with P(Rb)/P(K) = 1.1 and P(Cl)/P(K) < 0.03. Spontaneous open probability (P(o)) of the 9-pS inward rectifier ((gp)K(ir)) was voltage independent in cell-attached patches. Both a low (P(o) = 0.09 +/- 0.01) and a moderate (P(o) = 0.41 +/- 0.01) activity mode were observed. Excision moved (gp)K(ir) to the medium activity mode; P(o) of (gp)K(ir) was independent of bath Ca(2+) activity and bath acidification. Addition of Cl(-) and K(+) secretagogues altered P(o) of (gp)K(ir). Forskolin or carbachol (10 microM) activated the small-conductance (gp)K(ir) in quiescent patches and increased P(o) in low-activity patches. K(+) secretagogues, either epinephrine (5 microM) or prostaglandin E(2) (100 nM), decreased P(o) of (gp)K(ir) in active patches. This (gp)K(ir) may be involved in electrogenic secretion of Cl(minus sign) and K(+) across the colonic epithelium, which requires a large basolateral membrane K(+) conductance during maximal Cl(-) secretion and, presumably, a lower K(+) conductance during primary electrogenic K(+) secretion.
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Affiliation(s)
- Yingjun Li
- Department of Physiology and Biophysics, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA
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10
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Calcium-mediated chloride secretion in the intestinal epithelium: Significance and regulation. CURRENT TOPICS IN MEMBRANES 2002. [DOI: 10.1016/s1063-5823(02)53037-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Jeong JS, Lee HJ, Jung JS, Shin SH, Son YJ, Yoon JH, Lee SH, Lee HS, Yun I, Hwang TH. Characterization of inwardly rectifying K(+) conductance across the basolateral membrane of rat tracheal epithelia. Biochem Biophys Res Commun 2001; 288:914-20. [PMID: 11688996 DOI: 10.1006/bbrc.2001.5831] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The rat primary cultured-airway monolayer has been an excellent model for deciphering the ion channel after nystatin permeabilization of its basolateral or apical membrane. Inwardly rectifying K(+) currents were characterized across the basolateral membrane in symmetrical HCO(-)(3)-free high K(+) Ringer's solution (125 mM) in this study. The potency of K(+) channel inhibitors against K(+) conductance was Ba(2+) (IC(50) = 5 microM) > Cs(+) (IC(50) = 2 mM) >> glybenclamide (IC(50) > 5 mM) >> TEA (IC(50) >> 100 mM). The application of basolateral Cs(+) changed K(+) conductance into an oscillating current, and its frequency (holding voltage = -100 mV) increased with increase in concentration of basolateral Cs(+) (0.05-5 mM) and in degree of hyperpolarization. Addition of basolateral Cs(+) blocked inward current strongly at -100 mV and hardly at all at -60 mV, giving a sharp curvature to the I-V relation of the IRK current. RT-PCR, Western blotting, and immunohistochemical analyses showed that Kir2.1 might be present in basolateral membrane of tracheal epithelia and plasma membrane of pulmonary alveolar cells.
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Affiliation(s)
- J S Jeong
- Department of Pathology, Dong-A Medical College, Busan, 602-103, South Korea
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12
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Sugi K, Musch MW, Di A, Nelson DJ, Chang EB. Oxidants potentiate Ca(2+)- and cAMP-stimulated Cl(-) secretion in intestinal epithelial T84 cells. Gastroenterology 2001; 120:89-98. [PMID: 11208717 DOI: 10.1053/gast.2001.20917] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
BACKGROUND & AIMS Diarrhea is one of the major complications of inflammatory bowel disease. The role of oxidants in promoting net intestinal secretion is important, but the cellular mechanisms underlying their effects are unclear. We examined the effects and defined the cellular actions of the oxidant monochloramine (NH(2)Cl) on anion secretion in human colonic T84 cells. METHODS Effects of NH(2)Cl on basal and agonist-stimulated short-circuit current (Isc) of T84 monolayers were determined. Apical Cl(-) and basolateral K(+) conductances were measured by efflux of (125)I(-) and (86)Rb(+), respectively. RESULTS NH(2)Cl alone had little effect on Isc and (125)I(-) efflux. However, pretreatment with NH(2)Cl led to a concentration-dependent potentiation of the Ca(2+)-mediated Isc and of submaximal cAMP-mediated responses. These effects were associated with increased basolateral K(+) channel conductance and were blocked by increasing cellular Ca(2+) buffering capacity with Quin-2. Whole-cell voltage clamp experiments showed that NH(2)Cl potentiated Ca(2+) activation of basolateral K(+) channel conductance. CONCLUSIONS Oxidants potentiate both Ca(2+)- and cAMP-stimulated Cl(-) secretion by a direct effect on calcium-activated basolateral K(+) channel conductance, lowering its Ca(2+) activation threshold. This effect may play an important role in amplifying and prolonging the secretory response of inflamed intestinal mucosa and enhancing the severity of diarrhea.
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Affiliation(s)
- K Sugi
- The Martin Boyer Laboratories, Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA
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Hrnjez BJ, Song JC, Prasad M, Mayol JM, Matthews JB. Ammonia blockade of intestinal epithelial K+ conductance. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:G521-32. [PMID: 10484376 DOI: 10.1152/ajpgi.1999.277.3.g521] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Ammonia profoundly inhibits cAMP-dependent Cl- secretion in model T84 human intestinal crypt epithelia. Because colonic lumen concentrations of ammonia are high (10-70 mM), ammonia may be a novel regulator of secretory diarrheal responsiveness. We defined the target of ammonia action by structure-function analysis with a series of primary amines (ammonia, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, and octylamine) that vary principally in size and lipid solubilities. The amine concentrations required for 50% inhibition of Cl- secretion in intact monolayers and 50% inhibition of outward K+ current (IK) in apically permeabilized monolayers vs. the logs of the respective amine partition coefficients give two plots that are strikingly similar in character. Half-maximal inhibition of short-circuit current (Isc) by ammonia was seen at 6 mM and for IK at 4 mM; half-maximal inhibition for octylamine was 0.24 mM and 0.19 mM for Isc and IK, respectively. The preferentially water-soluble hydrophilic amines (ammonia, methylamine, ethylamine) increase in blocking ability with decreasing size and lipophilicity. Conversely, the preferentially lipid-soluble hydrophobic (propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine) amines increase in blocking ability with increasing size and lipophilicity. Ammonia does not affect isolated apical Cl- conductance; amine-induced changes in cytosolic and endosomal pH do not correlate with secretory inhibition. We propose that ammonia in its protonated ammonium form (NH4+) inhibits cAMP-dependent Cl- secretion in T84 monolayers by blocking basolateral K+ channels.
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Affiliation(s)
- B J Hrnjez
- Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, and the Harvard Digestive Diseases Center, Boston, Massachusetts 02215, USA
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14
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Grubb BR. Ion transport across the normal and CF neonatal murine intestine. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:G167-74. [PMID: 10409164 DOI: 10.1152/ajpgi.1999.277.1.g167] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
Neonatal mice with cystic fibrosis (CF) exhibit a very high mortality due to intestinal obstruction localized primarily to the ileum and colon. It has been hypothesized that lack of Cl(-) secretion and possibly elevated Na(+) absorption contribute to the gut problems in CF neonates. Therefore, intestines (ileum, proximal colon, and distal colon) from normal and CF day-old mouse pups were studied on ultra-small-aperture (0.0135 cm(2)) Ussing chambers. All three regions of the normal neonatal intestine responded to forskolin with an increase in short-circuit current, which was completely absent in the CF intestine. The neonatal distal colon exhibited a high rate of amiloride-sensitive electrogenic Na(+) absorption, which did not differ between the normal and CF preparations. The ileum and proximal colon of both genotypes exhibited a small but significant electrogenic Na(+) absorption. The neonatal proximal colon and ileum also exhibited electrogenic Na(+)-glucose cotransport, which was significantly greater in the normal compared with the CF ileum. In addition, all three intestinal regions exhibited electrogenic Na(+)-alanine cotransport, which was significantly reduced in two of the regions of the CF neonatal intestine. It is speculated that: 1) the reduced rate of Na(+)-nutrient cotransport in the CF intestine contributes to the lower rate of growth in CF pups, whereas 2) the elevated electrogenic Na(+) absorption in the neonatal intestine, coupled with an inability to secrete Cl(-), contributes to the intestinal obstruction in the CF pups.
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Affiliation(s)
- B R Grubb
- Cystic Fibrosis/Pulmonary Research and Treatment Center, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7248, USA.
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Devor DC, Singh AK, Lambert LC, DeLuca A, Frizzell RA, Bridges RJ. Bicarbonate and chloride secretion in Calu-3 human airway epithelial cells. J Gen Physiol 1999; 113:743-60. [PMID: 10228185 PMCID: PMC2222914 DOI: 10.1085/jgp.113.5.743] [Citation(s) in RCA: 230] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Serous cells are the predominant site of cystic fibrosis transmembrane conductance regulator expression in the airways, and they make a significant contribution to the volume, composition, and consistency of the submucosal gland secretions. We have employed the human airway serous cell line Calu-3 as a model system to investigate the mechanisms of serous cell anion secretion. Forskolin-stimulated Calu-3 cells secrete HCO-3 by a Cl-offdependent, serosal Na+-dependent, serosal bumetanide-insensitive, and serosal 4,4'-dinitrostilben-2,2'-disulfonic acid (DNDS)-sensitive, electrogenic mechanism as judged by transepithelial currents, isotopic fluxes, and the results of ion substitution, pharmacology, and pH studies. Similar studies revealed that stimulation of Calu-3 cells with 1-ethyl-2-benzimidazolinone (1-EBIO), an activator of basolateral membrane Ca2+-activated K+ channels, reduced HCO-3 secretion and caused the secretion of Cl- by a bumetanide-sensitive, electrogenic mechanism. Nystatin permeabilization of Calu-3 monolayers demonstrated 1-EBIO activated a charybdotoxin- and clotrimazole- inhibited basolateral membrane K+ current. Patch-clamp studies confirmed the presence of an intermediate conductance inwardly rectified K+ channel with this pharmacological profile. We propose that hyperpolarization of the basolateral membrane voltage elicits a switch from HCO-3 secretion to Cl- secretion because the uptake of HCO-3 across the basolateral membrane is mediated by a 4,4 '-dinitrostilben-2,2'-disulfonic acid (DNDS)-sensitive Na+:HCO-3 cotransporter. Since the stoichiometry reported for Na+:HCO-3 cotransport is 1:2 or 1:3, hyperpolarization of the basolateral membrane potential by 1-EBIO would inhibit HCO-3 entry and favor the secretion of Cl-. Therefore, differential regulation of the basolateral membrane K+ conductance by secretory agonists could provide a means of stimulating HCO-3 and Cl- secretion. In this context, cystic fibrosis transmembrane conductance regulator could serve as both a HCO-3 and a Cl- channel, mediating the apical membrane exit of either anion depending on basolateral membrane anion entry mechanisms and the driving forces that prevail. If these results with Calu-3 cells accurately reflect the transport properties of native submucosal gland serous cells, then HCO-3 secretion in the human airways warrants greater attention.
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Affiliation(s)
- D C Devor
- Department of Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA. dd2+@pitt.edu
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Taylor CT, Winter DC, Skelly MM, O'Donoghue DP, O'Sullivan GC, Harvey BJ, Baird AW. Berberine inhibits ion transport in human colonic epithelia. Eur J Pharmacol 1999; 368:111-8. [PMID: 10096776 DOI: 10.1016/s0014-2999(99)00023-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The effects of berberine on ion transport in both human colonic mucosal epithelia and an intestinal epithelial cell line (T84) were examined. Berberine (concentration range 0-500 microM) reduced both basal and stimulated ion transport responses in human colonic mucosae in a manner which was non-specific for Ca2+ -or cAMP-mediated signals. Similarly, in cultured intestinal epithelial monolayers, berberine inhibited Ca2+ -and cAMP-mediated responses indicating an inhibitory activity directly at the level of the epithelium rather than an indirect effect through other mucosal element(s). Berberine did not alter the rate of generation of cAMP by adenylyl cyclase or the activity of protein kinase A, the effector enzyme of the cAMP pathway. Berberine inhibited carbachol-stimulated 86Rb+ efflux from T84 monolayers. Berberine also inhibited K+ conductance in apically-permeabilised re-sected mucosae. These results indicate i) that berberine exerts an anti-secretory action directly upon epithelial cells and ii) the mechanism of action may be at the level of blockade of K+ channels.
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Affiliation(s)
- C T Taylor
- Department of Pharmacology, University College Dublin, Belfield, Ireland
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17
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Mun EC, Mayol JM, Riegler M, O'Brien TC, Farokhzad OC, Song JC, Pothoulakis C, Hrnjez BJ, Matthews JB. Levamisole inhibits intestinal Cl- secretion via basolateral K+ channel blockade. Gastroenterology 1998; 114:1257-67. [PMID: 9609763 DOI: 10.1016/s0016-5085(98)70432-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
BACKGROUND & AIMS Phenylimidazothiazoles have recently been shown to activate wild-type and mutant cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels in transfected cells and were proposed as therapy for cystic fibrosis. The aim of this study was to investigate the effects of phenylimidazothiazoles on regulated transepithelial Cl- transport in intact epithelia. METHODS T84 intestinal epithelial cells grown on permeable supports and stripped human colonic mucosal sheets were studied by conventional current-voltage clamping. Selective permeabilization of apical or basolateral membranes with the monovalent ionophore nystatin was used to isolate basolateral K+ and apical Cl- channel activity, respectively. 86Rb+ uptake was assessed for Na/K/2Cl cotransporter and Na+,K(+)-adenosine triphosphatase activity. RESULTS In T84 monolayers and human colon, levamisole and its brominated derivative bromotetramisole failed to activate transepithelial secretion. In fact, these compounds dose-dependently inhibited secretory responses to the cyclic adenosine monophosphate agonist forskolin and the Ca2+ agonist carbachol. In permeabilized T84 monolayers, phenylimidazothiazoles weakly activated apical Cl- currents (consistent with their reported action on CFTR) and did not affect bumetanide-sensitive or bumetanide-insensitive 86+Rb+ uptake. Instead, they profoundly inhibited the basolateral Ba(2+)-sensitive and Ba(2+)-insensitive K+ currents. CONCLUSIONS Phenylimidazothiazoles block K+ channels required for Cl(-)-secretory responses elicited by diverse pathways in model epithelia and native colon, an effect that outweighs their ability to activate apical Cl- channels.
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Affiliation(s)
- E C Mun
- Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA
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18
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Mayol JM, Hrnjez BJ, Akbarali HI, Song JC, Smith JA, Matthews JB. Ammonia effect on calcium-activated chloride secretion in T84 intestinal epithelial monolayers. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C634-42. [PMID: 9277361 DOI: 10.1152/ajpcell.1997.273.2.c634] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We recently showed that ammonia profoundly inhibits cyclic nucleotide-regulated Cl- secretion in model human T84 intestinal epithelia but does not impair the secretory response to the Ca2+ agonist carbachol. Using transepithelial transport, fura 2 fluorescence, and radioisotopic efflux techniques, we further explored this dichotomy and arrived at a preliminary explanation for the inhibitory action of ammonia. The secretory response to the Ca(2+)-adenosinetriphosphatase inhibitor thapsigargin is unaffected by ammonia, which suggests that an increase in intracellular Ca2+ stimulates secretory pathways that are insensitive to ammonia. Surprisingly, Cl- secretion elicited by the Ca2+ ionophores ionomycin and A23187 is markedly blunted in monolayers pretreated with ammonia. However, ammonia posttreatment does not inhibit the secretory response to ionophore, which suggests that ammonia may interfere with the ability of these ionophores to increase intracellular [Ca2+]. This hypothesis is directly supported by fura 2 experiments. The inhibitory action of ammonia parallels the behavior of the K+ channel blocker Ba2+, and ammonia reduces the basolateral 86Rb+ efflux rate constant in forskolin- but not in carbachol-treated monolayers. Ammonia, which is present in high concentrations in the normal gastro-intestinal tract, may serve as a novel endogenous regulator of epithelial electrolyte transport by interfering with a Ba(2+)-sensitive basolateral K+ conductance distinct from the Ca(2+)-activated basolateral K+ conductance.
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Affiliation(s)
- J M Mayol
- Department of Surgery, Beth Israel Hospital, Harvard Medical School, Boston, Massachusetts, USA
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Mauro T, Dixon DB, Komuves L, Hanley K, Pappone PA. Keratinocyte K+ channels mediate Ca2+-induced differentiation. J Invest Dermatol 1997; 108:864-70. [PMID: 9182812 DOI: 10.1111/1523-1747.ep12292585] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
K+ channel activation has been associated with growth or differentiation in many cells. We have previously identified a 70-pS K+ channel that was found only in differentiated involucrin-positive cells. In this study we examined the role of K+ channels in Ca2+-induced keratinocyte differentiation. Consistent with our previous report, we found that a K+ conductance developed only in cells cultured in high extracellular Ca2+. Addition of charybdotoxin or verapamil blocked these K+ channels and inhibited Ca2+-induced differentiation, as assessed by cornified envelope formation or transglutaminase activity. These results suggest that K+ channel activation is necessary for Ca2+-induced differentiation. Finally, we used (125)I-labeled charybdotoxin to demonstrate the presence of K+ channels in intact human and mouse epidermis, hair follicles, and eccrine glands, indicating that these channels are found in keratinocytes both in vitro and in vivo. Thus K+ channels may moderate Ca2+ influx in more differentiated keratinocytes and may play a central role in keratinocyte differentiation.
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Affiliation(s)
- T Mauro
- Department of Dermatology, University of CA, San Francisco, California, USA
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