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Keating N, Dev K, Hynes AC, Quinlan LR. Mechanism of luminal ATP activated chloride secretion in a polarized epithelium. J Physiol Sci 2019; 69:85-95. [PMID: 29949063 PMCID: PMC10717936 DOI: 10.1007/s12576-018-0623-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 06/06/2018] [Indexed: 10/14/2022]
Abstract
There are both secretory and absorptive pathways working in tandem to support ionic movement driving fluid secretion across epithelia. The mechanisms exerting control of fluid secretion in the oviduct is yet to be fully determined. This study explored the role of apical or luminal extracellular ATP (ATPe)-stimulated ion transport in an oviduct epithelium model, using the Ussing chamber short-circuit current (Isc) technique. Basal Isc in oviduct epithelium in response to apical ATPe comprises both chloride secretion and sodium absorption and has distinct temporal phases. A rapid transient peak followed by a sustained small increase above baseline. Both phases of the apical ATPe Isc response are sensitive to anion (HCO3-, Cl-) and cation (Na+) replacement. Additionally, the role of apical chloride channels, basolateral potassium channels and intracellular calcium in supporting the peak Isc current was confirmed. The role of ATP breakdown to adenosine resulting in the activation of P2 receptors was supported by examining the effects of non-hydrolyzable forms of ATP. A P2YR2 potency profile of ATP = UTP > ADP was generated for the apical membrane, suggesting the involvement of the P2YR2 subtype of purinoceptor. A P2X potency profile of ATP = 2MeSATP > alpha,beta-meATP > BzATP was also generated for the apical membrane. In conclusion, these results provide strong evidence that purinergic activation of apical P2YR2 promotes chloride secretion and is thus an important factor in fluid formation by the oviduct.
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Affiliation(s)
- N Keating
- Physiology, School of Medicine, National University of Ireland, Galway, University Road, Galway, Ireland
| | - K Dev
- Physiology, School of Medicine, National University of Ireland, Galway, University Road, Galway, Ireland
| | - A C Hynes
- Physiology, School of Medicine, National University of Ireland, Galway, University Road, Galway, Ireland
| | - L R Quinlan
- Physiology, School of Medicine, National University of Ireland, Galway, University Road, Galway, Ireland.
- CÚRAM, Centre for Research in Medical Devices, NUI Galway, University Road, Galway, Ireland.
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Pondugula SR, Raveendran NN, Marcus DC. Ion transport regulation by P2Y receptors, protein kinase C and phosphatidylinositol 3-kinase within the semicircular canal duct epithelium. BMC Res Notes 2010; 3:100. [PMID: 20398257 PMCID: PMC2862037 DOI: 10.1186/1756-0500-3-100] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2009] [Accepted: 04/14/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The ionic composition of the luminal fluid in the vestibular labyrinth is maintained within tight limits by the many types of epithelial cells bounding the lumen. Regulatory mechanisms include systemic, paracrine and autocrine hormones along with their associated intracellular signal pathways. The epithelium lining the semicircular canal duct (SCCD) is a tissue that is known to absorb sodium and calcium and to secrete chloride. FINDINGS Transport function was assessed by measurements of short circuit current (Isc) and gene transcript expression was evaluated by microarray. Neither ATP nor UTP (100 microM) on the apical side of the epithelium had any effect on Isc. By contrast, basolateral ATP transiently increased Isc and transepithelial resistance dropped significantly after basolateral ATP and UTP. P2Y2 was the sole UTP-sensitive purinergic receptor expressed. Isc was reduced by 42%, 50% and 63% after knockdown of alpha-ENaC, stimulation of PKC and inhibition of PI3-K, while the latter two increased the transepithelial resistance. PKCdelta, PKCgamma and PI3-K were found to be expressed. CONCLUSIONS These observations demonstrate that ion transport by the SCCD is regulated by P2Y2 purinergic receptors on the basolateral membrane that may respond to systemic or local agonists, such as ATP and/or UTP. The sodium absorption from endolymph mediated by ENaC in SCCD is regulated by signal pathways that include the kinases PKC and PI3-K. These three newly-identified regulatory components may prove to be valuable drug targets in the control of pathologic vestibular conditions involving dysfunction of transport homeostasis in the ear, such as Meniere's disease.
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Lazrak A, Iles KE, Liu G, Noah DL, Noah JW, Matalon S. Influenza virus M2 protein inhibits epithelial sodium channels by increasing reactive oxygen species. FASEB J 2009; 23:3829-42. [PMID: 19596899 DOI: 10.1096/fj.09-135590] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The mechanisms by which replicating influenza viruses decrease the expression and function of amiloride-sensitive epithelial sodium channels (ENaCs) have not been elucidated. We show that expression of M2, a transmembrane influenza protein, decreases ENaC membrane levels and amiloride-sensitive currents in both Xenopus oocytes, injected with human alpha-, beta-, and gamma-ENaCs, and human airway cells (H441 and A549), which express native ENaCs. Deletion of a 10-aa region within the M2 C terminus prevented 70% of this effect. The M2 ENaC down-regulation occurred at normal pH and was prevented by MG-132, a proteasome and lysosome inhibitor. M2 had no effect on Liddle ENaCs, which have decreased affinity for Nedd4-2. H441 and A549 cells transfected with M2 showed higher levels of reactive oxygen species, as shown by the activation of redox-sensitive dyes. Pretreatment with glutathione ester, which increases intracellular reduced thiol concentrations, or protein kinase C (PKC) inhibitors prevented the deleterious effects of M2 on ENaCs. The data suggest that M2 protein increases steady-state concentrations of reactive oxygen intermediates that simulate PKC and decrease ENaCs by enhancing endocytosis and its subsequent destruction by the proteasome. These novel findings suggest a mechanism for the influenza-induced rhinorrhea and life-threatening alveolar edema in humans.
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Affiliation(s)
- Ahmed Lazrak
- Department of Anesthesiology, Schools of Medicine and Public Health, University of Alabama at Birmingham, Birmingham, Alabama, USA
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O'Mullane LM, Cook DI, Dinudom A. Purinergic regulation of the epithelial Na+ channel. Clin Exp Pharmacol Physiol 2009; 36:1016-22. [PMID: 19566815 DOI: 10.1111/j.1440-1681.2009.05256.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
1. The epithelial Na(+) channel (ENaC) is a major conductive pathway that transports Na(+) across the apical membrane of the distal nephron, the respiratory tract, the distal colon and the ducts of exocrine glands. The ENaC is regulated by hormonal and humoral factors, including extracellular nucleotides that are available from the epithelial cells themselves. 2. Extracellular nucleotides, via the P2Y2 receptors (P2Y2Rs) at the basolateral and apical membrane of the epithelia, trigger signalling systems that inhibit the activity of the ENaC and activate Ca(2+) -dependent Cl(-) secretion. 3. Recent data from our laboratory suggest that stimulation of the P2Y2Rs at the basolateral membrane inhibits ENaC activity by a signalling mechanism that involves G beta gamma subunits freed from a pertussis toxin (PTX)-sensitive G-protein and phospholipase C (PLC) beta 4. A similar signalling mechanism is also partially responsible for inhibition of the ENaC during activation of apical P2Y2Rs. 4. Stimulation of apical P2Y2Rs also activates an additional signalling mechanism that inhibits the ENaC and involves the activated Galpha subunit of a PTX-insensitive G-protein and activation of an unidentified PLC. The effect of this PTX-insensitive system requires the activity of the basolateral Na(+)/K(+)/2Cl(-) cotransporter.
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Affiliation(s)
- Lauren M O'Mullane
- Discipline of Physiology, The Bosch Institute, Faculty of Medicine, The University of Sydney, Sydney, New South Wales, Australia
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Ji HL, Song W, Gao Z, Su XF, Nie HG, Jiang Y, Peng JB, He YX, Liao Y, Zhou YJ, Tousson A, Matalon S. SARS-CoV proteins decrease levels and activity of human ENaC via activation of distinct PKC isoforms. Am J Physiol Lung Cell Mol Physiol 2008; 296:L372-83. [PMID: 19112100 DOI: 10.1152/ajplung.90437.2008] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Among the multiple organ disorders caused by the severe acute respiratory syndrome coronavirus (SARS-CoV), acute lung failure following atypical pneumonia is the most serious and often fatal event. We hypothesized that two of the hydrophilic structural coronoviral proteins (S and E) would regulate alveolar fluid clearance by decreasing the cell surface expression and activity of amiloride-sensitive epithelial sodium (Na(+)) channels (ENaC), the rate-limiting protein in transepithelial Na(+) vectorial transport across distal lung epithelial cells. Coexpression of either S or E protein with human alpha-, beta-, and gamma-ENaC in Xenopus oocytes led to significant decreases of both amiloride-sensitive Na(+) currents and gamma-ENaC protein levels at their plasma membranes. S and E proteins decreased the rate of ENaC exocytosis and either had no effect (S) or decreased (E) rates of endocytosis. No direct interactions among SARS-CoV E protein with either alpha- or gamma-ENaC were indentified. Instead, the downregulation of ENaC activity by SARS proteins was partially or completely restored by administration of inhibitors of PKCalpha/beta1 and PKCzeta. Consistent with the whole cell data, expression of S and E proteins decreased ENaC single-channel activity in oocytes, and these effects were partially abrogated by PKCalpha/beta1 inhibitors. Finally, transfection of human airway epithelial (H441) cells with SARS E protein decreased whole cell amiloride-sensitive currents. These findings indicate that lung edema in SARS infection may be due at least in part to activation of PKC by SARS proteins, leading to decreasing levels and activity of ENaC at the apical surfaces of lung epithelial cells.
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Affiliation(s)
- Hong-Long Ji
- Department of Anesthesiology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama 35233-6810, USA
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Hurt EM, Saykally JN, Anose BM, Kalli KR, Sanders MM. Expression of the ZEB1 (deltaEF1) transcription factor in human: additional insights. Mol Cell Biochem 2008; 318:89-99. [PMID: 18622689 DOI: 10.1007/s11010-008-9860-z] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2008] [Accepted: 06/25/2008] [Indexed: 01/13/2023]
Abstract
The zinc finger E-box binding transcription factor ZEB1 (deltaEF1/Nil-2-a/AREB6/zfhx1a/TCF8/zfhep/BZP) is emerging as an important regulator of the epithelial to mesenchymal transitions (EMT) required for development and cancer metastasis. ZEB1 promotes EMT by repressing genes contributing to the epithelial phenotype while activating those associated with the mesenchymal phenotype. TCF8 (zfhx1a), the gene encoding ZEB1, is induced by several potentially oncogenic ligands including TGF-beta, estrogen, and progesterone. TGF-beta appears to activate EMT, at least in part, by inducing ZEB1. However, our understanding of how ZEB1 contributes to signaling pathways elicited by estrogen and progesterone is quite limited, as is our understanding of its functional roles in normal adult tissues. To begin to address these questions, a human tissue mRNA array analysis was done. In adults, the highest ZEB1 mRNA expression is in bladder and uterus, whereas in the fetus highest expression is in lung, thymus, and heart. To further investigate the regulation of TCF8 by estrogen, ZEB1 mRNA was measured in ten estrogen-responsive cell lines, but it is only induced in the OV266 ovarian carcinoma line. Although high expression of ZEB1 mRNA is estrogen-dependent in normal human ovarian and endometrial biopsies, high expression is estrogen-independent in late stage ovarian and endometrial carcinomas, raising the possibility that deregulated expression promotes cancer progression. In contrast, TCF8 is at least partially deleted in 4 of 5 well-differentiated, grade I endometrial carcinomas, which may contribute to their non-aggressive phenotype. These data support the contention that high ZEB1 encourages gynecologic carcinoma progression.
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Affiliation(s)
- Elaine M Hurt
- Cancer Stem Cell Section, Laboratory of Cancer Prevention, Center for Cancer Research, National Cancer Institute at Frederick, National Institutes of Health, Frederick, MD 21702, USA
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Brown DR, O’Grady SM. The Ussing Chamber and Measurement of Drug Actions on Mucosal Ion Transport. ACTA ACUST UNITED AC 2008; Chapter 7:Unit 7.12. [DOI: 10.1002/0471141755.ph0712s41] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- David R. Brown
- University of Minnesota, Departments of Veterinary & Biomedical Sciences (DRB) and Animal Science (SMO) St. Paul Minnesota
| | - Scott M. O’Grady
- University of Minnesota, Departments of Veterinary & Biomedical Sciences (DRB) and Animal Science (SMO) St. Paul Minnesota
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Palmer ML, Schiller KR, O'Grady SM. Apical SK potassium channels and Ca2+-dependent anion secretion in endometrial epithelial cells. J Physiol 2007; 586:717-26. [PMID: 18048454 DOI: 10.1113/jphysiol.2007.142877] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Apical uridine triphosphate (UTP) stimulation was shown to increase short circuit current (I(sc)) in immortalized porcine endometrial gland epithelial monolayers. Pretreatment with the bee venom toxin apamin enhanced this response. Voltage-clamp experiments using amphotericin B-permeablized monolayers revealed that the apamin-sensitive current increased immediately after UTP stimulation and was K(+) dependent. The current-voltage relationship was slightly inwardly rectifying with a reversal potential of -52 +/- 2 mV, and the P(K)/P(Na) ratio was 14, indicating high selectivity for K(+). Concentration-response relationships for apamin and dequalinium had IC(50) values of 0.5 nm and 1.8 microm, respectively, consistent with data previously reported for SK3 channels in excitable cells and hepatocytes. Treatment of monolayers with 50 microm BAPTA-AM completely blocked the effects of UTP on K(+) channel activation, indicating that the apamin-sensitive current was also Ca(2+) dependent. Moreover, channel activation was blocked by calmidazolium (IC(50) = 5 microm), suggesting a role for calmodulin in Ca(2+)-dependent regulation of channel activity. RT-PCR experiments demonstrated expression of mRNA for the SK1 and SK3 channels, but not SK2 channels. Treatment of monolayers with 20 nm oestradiol-17beta produced a 2-fold increase in SK3 mRNA, a 2-fold decrease in SK1 mRNA, but no change in GAPDH mRNA expression. This result correlated with a 2.5-fold increase in apamin-sensitive K(+) channel activity in the apical membrane. We speculate that SK channels provide a mechanism for rapidly sensing changes in intracellular Ca(2+) near the apical membrane, evoking immediate hyperpolarization necessary for increasing the driving force for anion efflux following P2Y receptor activation.
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Affiliation(s)
- Melissa L Palmer
- Department of Physiology, 495 Animal Science/Veterinary Medicine Bldg, University of Minnesota, 1988 Fitch Ave., St Paul, MN 55108, USA
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Palmer ML, Lee SY, Carlson D, Fahrenkrug S, O'Grady SM. Stable knockdown of CFTR establishes a role for the channel in P2Y receptor-stimulated anion secretion. J Cell Physiol 2006; 206:759-70. [PMID: 16245306 DOI: 10.1002/jcp.20519] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
P2Y receptor regulation of anion secretion was investigated in porcine endometrial gland (PEG) epithelial cells. P2Y2, P2Y4, and P2Y6 receptors were detected in monolayers of PEG cells and immunocytochemistry indicated that P2Y4 receptors were located in the apical membrane. Apical membrane current measurements showed that Ca2+-dependent and PKC-dependent Cl- channels were activated following treatment with uridine triphosphate (UTP) (5 microM). Current-voltage relationships comparing calcium-dependent and PKC-dependent UTP responses under biionic conditions showed significant differences in selectivity between Cl-)and I- for the PKC-dependent conductance (P(I)/P(Cl) = 0.76), but not for Ca2+-dependent conductance (PI/P(Cl) = 1.02). The I-/Cl- permeability ratio for the PKC-dependent conductance was identical to that measured for 8-cpt cAMP. Furthermore, PKC stimulation using phorbol 12-myristate 13-acetate (PMA) activated an apical membrane Cl- conductance that was blocked by the CFTR selective inhibitor, CFTRinh-172. CFTR silencing, accomplished by stable expression of small hairpin RNAs (shRNA), blocked the PKC-activated conductance associated with UTP stimulation and provided definitive evidence of a role for CFTR in anion secretion. CFTR activation increased the initial magnitude of Cl- secretion, and provided a more sustained secretory response compared to conditions where only Ca2+-activated Cl- channels were activated by UTP. Measurements of [cAMP]i following UTP and PMA stimulation were not significantly different than untreated controls. Thus, these results demonstrate that UTP and PMA activation of CFTR occurs independently of increases in intracellular cAMP and extend the findings of earlier studies of CFTR regulation by PKC in Xenopus oocytes to a mammalian anion secreting epithelium.
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Affiliation(s)
- Melissa L Palmer
- Department of Physiology, University of Minnesota, St. Paul, Minnesota 55108, USA
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Vetter AE, O'Grady SM. Sodium and anion transport across the avian uterine (shell gland) epithelium. ACTA ACUST UNITED AC 2005; 208:479-86. [PMID: 15671336 DOI: 10.1242/jeb.01409] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The uterine (shell gland) epithelium from the domestic chicken was mounted in Ussing chambers, bathed in symmetric avian saline solution on both apical and basolateral aspects and voltage clamped at 0 mV. The epithelium exhibited a basal short circuit current (I(sc)) that was partially inhibited by the epithelial Na(+) channel (ENaC) blockers, amiloride and benzamil (IC(50) values of 0.8 and 0.12 micromol l(-1), respectively). Inhibition of basal Na(+) absorption by 10 micromol l(-1) amiloride was confirmed by measurements of transepithelial Na(+) and Cl(-) fluxes, where inhibition of the apical-to-basolateral and net Na(+) flux occurred, but no significant effects on Cl(-) fluxes were detected. The amiloride-insensitive portion of the basal I(sc) was both Cl(-) and HCO(3)(-) dependent and was inhibited by the Cl(-) channel blocker, diphenyl-2-carboxylate (DPC; 100 micromol l(-1)). Stimulation with 8-(4-chlorophenylthio)-cyclic 3'-5', adenosine monophosphate (8-cpt cAMP) produced a sustained increase in I(sc) that was dependent on both Cl(-) and HCO(3)(-). The magnitude of the amiloride-sensitive I(sc) was approximately twofold greater in birds where shell formation was complete, but oviposition had not yet occurred. In addition, the amiloride-sensitive I(sc) was greater in hens over the age of 55 weeks and in molting birds. The anion-dependent component of the basal I(sc) was reduced in older birds, and electrogenic HCO(3)(-) transport was nearly absent in molting birds. These results demonstrated that electrogenic Na(+) transport in avian shell gland was similar to the mammalian uterine epithelium and increased with age and during molting. Electrogenic Cl(-) and HCO(3)(-) transport were coupled under basal and cAMP stimulated conditions and basal anion transport decreased with age and during molting.
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Affiliation(s)
- Alisen E Vetter
- Cardiac Rhythm Management, Medtronic Corporation, 7000 Central Avenue NE, Minneapolis, MN 55432, USA
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Falin R, Veizis IE, Cotton CU. A role for ERK1/2 in EGF- and ATP-dependent regulation of amiloride-sensitive sodium absorption. Am J Physiol Cell Physiol 2005; 288:C1003-11. [PMID: 15634742 DOI: 10.1152/ajpcell.00213.2004] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Receptor-mediated inhibition of amiloride-sensitive sodium absorption was observed in primary and immortalized murine renal collecting duct cell (mCT12) monolayers. The addition of epidermal growth factor (EGF) to the basolateral bathing solution of polarized monolayers reduced amiloride-sensitive short-circuit current (I(sc)) by 15-25%, whereas the addition of ATP to the apical bathing solution decreased I(sc) by 40-60%. Direct activation of PKC with phorbol 12-myristate 13-acetate (PMA) and mobilization of intracellular calcium with 2,5-di-tert-butyl-hydroquinone (DBHQ) reduced amiloride-sensitive I(sc) in mCT12 monolayers by 46 +/- 4% (n = 8) and 22 +/- 2% (n = 8), respectively. Exposure of mCT12 cells to EGF, ATP, PMA, and DBHQ caused an increase in phosphorylation of p42/p44 (extracellular signal-regulated kinase; ERK1/2). Pretreatment of mCT12 monolayers with an ERK kinase inhibitor (PD-98059; 30 microM) prevented phosphorylation of p42/p44 and significantly reduced EGF, ATP, and PMA-induced inhibition of amiloride-sensitive I(sc). In contrast, pretreatment of monolayers with a PKC inhibitor (bisindolylmaleimide I; GF109203x; 1 microM) almost completely blocked the PMA-induced decrease in I(sc), but did not alter the EGF- or ATP-induced inhibition of I(sc). The DBHQ-mediated decrease in I(sc) was due to inhibition of basolateral Na(+)-K(+)-ATPase, but EGF-, ATP-, and PMA-induced inhibition was most likely due to reduced apical sodium entry (epithelial Na(+) channel activity). The results of these studies demonstrate that acute inhibition of amiloride-sensitive sodium transport by extracelluar ATP and EGF involves ERK1/2 activation and suggests a role for MAP kinase signaling as a negative regulator of electrogenic sodium absorption in epithelia.
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Affiliation(s)
- Rebecca Falin
- Case Western Reserve Univ., 2109 Adelbert Rd., Cleveland, OH 44106-4948, USA
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