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Qian J, Mummalaneni S, Phan THT, Heck GL, DeSimone JA, West D, Mahavadi S, Hojati D, Murthy KS, Rhyu MR, Spielman AI, Özdener MH, Lyall V. Cyclic-AMP regulates postnatal development of neural and behavioral responses to NaCl in rats. PLoS One 2017; 12:e0171335. [PMID: 28192441 PMCID: PMC5305205 DOI: 10.1371/journal.pone.0171335] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2016] [Accepted: 01/18/2017] [Indexed: 02/07/2023] Open
Abstract
During postnatal development rats demonstrate an age-dependent increase in NaCl chorda tympani (CT) responses and the number of functional apical amiloride-sensitive epithelial Na+ channels (ENaCs) in salt sensing fungiform (FF) taste receptor cells (TRCs). Currently, the intracellular signals that regulate the postnatal development of salt taste have not been identified. We investigated the effect of cAMP, a downstream signal for arginine vasopressin (AVP) action, on the postnatal development of NaCl responses in 19-23 day old rats. ENaC-dependent NaCl CT responses were monitored after lingual application of 8-chlorophenylthio-cAMP (8-CPT-cAMP) under open-circuit conditions and under ±60 mV lingual voltage clamp. Behavioral responses were tested using 2 bottle/24h NaCl preference tests. The effect of [deamino-Cys1, D-Arg8]-vasopressin (dDAVP, a specific V2R agonist) was investigated on ENaC subunit trafficking in rat FF TRCs and on cAMP generation in cultured adult human FF taste cells (HBO cells). Our results show that in 19-23 day old rats, the ENaC-dependent maximum NaCl CT response was a saturating sigmoidal function of 8-CPT-cAMP concentration. 8-CPT-cAMP increased the voltage-sensitivity of the NaCl CT response and the apical Na+ response conductance. Intravenous injections of dDAVP increased ENaC expression and γ-ENaC trafficking from cytosolic compartment to the apical compartment in rat FF TRCs. In HBO cells dDAVP increased intracellular cAMP and cAMP increased trafficking of γ- and δ-ENaC from cytosolic compartment to the apical compartment 10 min post-cAMP treatment. Control 19-23 day old rats were indifferent to NaCl, but showed clear preference for appetitive NaCl concentrations after 8-CPT-cAMP treatment. Relative to adult rats, 14 day old rats demonstrated significantly less V2R antibody binding in circumvallate TRCs. We conclude that an age-dependent increase in V2R expression produces an AVP-induced incremental increase in cAMP that modulates the postnatal increase in TRC ENaC and the neural and behavioral responses to NaCl.
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Affiliation(s)
- Jie Qian
- Departments of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - Shobha Mummalaneni
- Departments of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - Tam-Hao T. Phan
- Departments of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - Gerard L. Heck
- Departments of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - John A. DeSimone
- Departments of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - David West
- Departments of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - Sunila Mahavadi
- Departments of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - Deanna Hojati
- Departments of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - Karnam S. Murthy
- Departments of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - Mee-Ra Rhyu
- Korea Food Research Institute, Bundang-gu, Sungnam-si, Gyeonggi-do, Korea
| | | | - Mehmet Hakan Özdener
- Monell Chemical Senses Center, Philadelphia, Pennsylvania, United States of America
| | - Vijay Lyall
- Departments of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
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Rauh R, Hoerner C, Korbmacher C. δβγ-ENaC is inhibited by CFTR but stimulated by cAMP in Xenopus laevis oocytes. Am J Physiol Lung Cell Mol Physiol 2016; 312:L277-L287. [PMID: 27941075 DOI: 10.1152/ajplung.00375.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Revised: 12/05/2016] [Accepted: 12/05/2016] [Indexed: 11/22/2022] Open
Abstract
The epithelial sodium channel (ENaC) and the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel critically regulate airway surface liquid by driving fluid absorption and secretion, respectively. Their functional interplay is complex and incompletely understood. ENaC is a heteromeric channel with three well-characterized subunits (α, β, and γ). In humans, an additional δ-ENaC subunit exists in lung and several other tissues, where it may replace the α-subunit to form δβγ-ENaC. Little is known about the physiological role of δβγ-ENaC and its possible interaction with CFTR. The aim of the present study was to investigate the effect of human CFTR on human δβγ-ENaC heterologously expressed in Xenopus laevis oocytes. In oocytes coexpressing δβγ-ENaC and CFTR the ENaC-mediated amiloride-sensitive whole cell current (ΔIami) was reduced by ~50% compared with that measured in oocytes expressing δβγ-ENaC alone. Moreover, basal level of proteolytic ENaC activation was reduced in the presence of CFTR. The inhibitory effect of CFTR on δβγ-ENaC was due to a combination of decreased average open probability (Po) and reduced channel expression at the cell surface. Interestingly, in oocytes expressing δβγ-ENaC, increasing intracellular [cAMP] by IBMX and forskolin increased ΔIami by ~50%. This stimulatory effect was not observed for human and rat αβγ-ENaC and was independent of CFTR coexpression and coactivation. Experiments with a mutant channel (δβS520Cγ-ENaC) which can be converted to a channel with a Po of nearly 1 suggested that cAMP activates δβγ-ENaC by increasing Po In conclusion, our results demonstrate that δβγ-ENaC is inhibited by CFTR but activated by cAMP.
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Affiliation(s)
- Robert Rauh
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Christian Hoerner
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
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Ji HL, Nie HG, Chang Y, Lian Q, Liu SL. CPT-cGMP Is A New Ligand of Epithelial Sodium Channels. Int J Biol Sci 2016; 12:359-66. [PMID: 27019621 PMCID: PMC4807156 DOI: 10.7150/ijbs.13764] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2015] [Accepted: 11/11/2015] [Indexed: 12/28/2022] Open
Abstract
Epithelial sodium channels (ENaC) are localized at the apical membrane of the epithelium, and are responsible for salt and fluid reabsorption. Renal ENaC takes up salt, thereby controlling salt content in serum. Loss-of-function ENaC mutations lead to low blood pressure due to salt-wasting, while gain-of-function mutations cause impaired sodium excretion and subsequent hypertension as well as hypokalemia. ENaC activity is regulated by intracellular and extracellular signals, including hormones, neurotransmitters, protein kinases, and small compounds. Cyclic nucleotides are broadly involved in stimulating protein kinase A and protein kinase G signaling pathways, and, surprisingly, also appear to have a role in regulating ENaC. Increasing evidence suggests that the cGMP analog, CPT-cGMP, activates αβγ-ENaC activity reversibly through an extracellular pathway in a dose-dependent manner. Furthermore, the parachlorophenylthio moiety and ribose 2'-hydroxy group of CPT-cGMP are essential for facilitating the opening of ENaC channels by this compound. Serving as an extracellular ligand, CPT-cGMP eliminates sodium self-inhibition, which is a novel mechanism for stimulating salt reabsorption in parallel to the traditional NO/cGMP/PKG signal pathway. In conclusion, ENaC may be a druggable target for CPT-cGMP, leading to treatments for kidney malfunctions in salt reabsorption.
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Affiliation(s)
- Hong-Long Ji
- 1. Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, Texas 75708, USA
| | - Hong-Guang Nie
- 2. Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang 110001, China
| | - Yongchang Chang
- 3. Barrow Neurological Institute, St Joseph's Hospital and Medical Center, Phoenix, Arizona, 85013, USA
| | - Qizhou Lian
- 4. Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
| | - Shan-Lu Liu
- 5. Department of Molecular Microbiology and Immunology, Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA
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Liddle-Mutation of the β-Subunit, but not the γ-Subunit, Attenuates Protein Kinase C-Mediated Inhibition of Human Epithelial Sodium Channels (hENaC). J Membr Biol 2016; 249:271-9. [PMID: 26759146 PMCID: PMC4875061 DOI: 10.1007/s00232-015-9866-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Accepted: 12/18/2015] [Indexed: 12/03/2022]
Abstract
Mammalian distal nephron and distal colon, prime sites for Na+ homeostasis, contain amiloride-sensitive epithelial sodium channels (ENaC). Protein kinase C (PKC) inhibits ENaC by phosphorylating serine and threonine residues within COOH termini of the β- and/or γ-subunits. Although some of these phosphorylation sites are close to the PY motifs, it is unclear whether they remain susceptible to PKC in Liddle-mutated ENaC β- and/or γ-subunits, where PY motifs are truncated, resulting in increased apical ENaC expression. We therefore studied the effects of PKC in wild-type and Liddle-mutated human epithelial Na+ channels (hENaC) expressed in Xenopus oocytes, using the dual-electrode voltage clamp technique. PKC activation using 500 nmol/l phorbol 12-myristate 13-acetate (PMA) decreased amiloride-sensitive Na+ currents by 80 % in oocytes expressing wild-type hENaC, an effect largely prevented by co-exposure to 50 µmol/l calphostin C (a specific inhibitor of PKC), whereas 500 nmol/l phorbol didecanoate (PDD), an inactive phorbol ester which does not stimulate PKC, had no effect. In oocytes expressing hENaC containing the Liddle-mutated β-subunit, PMA elicited a 54 % decrease in amiloride-sensitive Na+ currents, significantly (P < 0.0025) less than that in oocytes expressing wild-type hENaC. By contrast, in oocytes expressing hENaC containing the Liddle-mutated γ-subunit, PMA elicited a 68 % decrease in amiloride-sensitive Na+ current, similar (P = 0.10) to that in oocytes expressing wild-type hENaC. We conclude that hENaC incorporating the Liddle-mutated β-subunit lacks one or more PKC phosphorylation sites, thereby significantly reducing the inhibitory effect of PKC on Na+ channel activity, whereas hENaC incorporating Liddle-mutated γ-subunits remains as susceptible to PKC as wild-type hENaC.
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Vitzthum C, Clauss WG, Fronius M. Mechanosensitive activation of CFTR by increased cell volume and hydrostatic pressure but not shear stress. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:2942-51. [PMID: 26357939 DOI: 10.1016/j.bbamem.2015.09.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Revised: 09/03/2015] [Accepted: 09/05/2015] [Indexed: 12/20/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl(-) channel that is essential for electrolyte and fluid homeostasis. Preliminary evidence indicates that CFTR is a mechanosensitive channel. In lung epithelia, CFTR is exposed to different mechanical forces such as shear stress (Ss) and membrane distention. The present study questioned whether Ss and/or stretch influence CFTR activity (wild type, ∆F508, G551D). Human CFTR (hCFTR) was heterologously expressed in Xenopus oocytes and the response to the mechanical stimulus and forskolin/IBMX (FI) was measured by two-electrode voltage-clamp experiments. Ss had no influence on hCFTR activity. Injection of an intracellular analogous solution to increase cell volume alone did not affect hCFTR activity. However, hCFTR activity was augmented by injection after pre-stimulation with FI. The response to injection was similar in channels carrying the common mutations ∆F508 and G551D compared to wild type hCFTR. Stretch-induced CFTR activation was further assessed in Ussing chamber measurements using Xenopus lung preparations. Under control conditions increased hydrostatic pressure (HP) decreased the measured ion current including activation of a Cl(-) secretion that was unmasked by the CFTR inhibitor GlyH-101. These data demonstrate activation of CFTR in vitro and in a native pulmonary epithelium in response to mechanical stress. Mechanosensitive regulation of CFTR is highly relevant for pulmonary physiology that relies on ion transport processes facilitated by pulmonary epithelial cells.
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Affiliation(s)
- Constanze Vitzthum
- Institute of Animal Physiology, Justus-Liebig-University Giessen, Giessen, Germany
| | - Wolfgang G Clauss
- Institute of Animal Physiology, Justus-Liebig-University Giessen, Giessen, Germany
| | - Martin Fronius
- Department of Physiology, University of Otago, Dunedin, New Zealand.
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Mummalaneni S, Qian J, Phan THT, Rhyu MR, Heck GL, DeSimone JA, Lyall V. Effect of ENaC modulators on rat neural responses to NaCl. PLoS One 2014; 9:e98049. [PMID: 24839965 PMCID: PMC4026388 DOI: 10.1371/journal.pone.0098049] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2014] [Accepted: 04/28/2014] [Indexed: 01/31/2023] Open
Abstract
The effects of small molecule ENaC activators N,N,N-trimethyl-2-((4-methyl-2-((4-methyl-1H-indol-3-yl)thio)pentanoyl)oxy)ethanaminium iodide (Compound 1) and N-(2-hydroxyethyl)-4-methyl-2-((4-methyl-1H-indol-3-yl)thio)pentanamide (Compound 2), were tested on the benzamil (Bz)-sensitive NaCl chorda tympani (CT) taste nerve response under open-circuit conditions and under ±60 mV applied lingual voltage-clamp, and compared with the effects of known physiological activators (8-CPT-cAMP, BAPTA-AM, and alkaline pH), and an inhibitor (ionomycin+Ca2+) of ENaC. The NaCl CT response was enhanced at −60 mV and suppressed at +60 mV. In every case the CT response (r) versus voltage (V) curve was linear. All ENaC activators increased the open-circuit response (ro) and the voltage sensitivity (κ, negative of the slope of the r versus V curve) and ionomycin+Ca2+ decreased ro and κ to zero. Compound 1 and Compound 2 expressed a sigmoidal-saturating function of concentration (0.25–1 mM) with a half-maximal response concentration (k) of 0.49 and 1.05 mM, respectively. Following treatment with 1 mM Compound 1, 8-CPT-cAMP, BAPTA-AM and pH 10.3, the Bz-sensitive NaCl CT response to 100 mM NaCl was enhanced and was equivalent to the Bz-sensitive CT response to 300 mM NaCl. Plots of κ versus ro in the absence and presence of the activators or the inhibitor were linear, suggesting that changes in the affinity of Na+ for ENaC under different conditions are fully compensated by changes in the apical membrane potential difference, and that the observed changes in the Bz-sensitive NaCl CT response arise exclusively from changes in the maximum CT response (rm). The results further suggest that the agonists enhance and ionomycin+Ca2+ decreases ENaC function by increasing or decreasing the rate of release of Na+ from its ENaC binding site to the receptor cell cytosol, respectively. Irrespective of agonist type, the Bz-sensitive NaCl CT response demonstrated a maximum response enhancement limit of about 75% over control value.
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Affiliation(s)
- Shobha Mummalaneni
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - Jie Qian
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - Tam-Hao T. Phan
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - Mee-Ra Rhyu
- Korea Food Research Institute, Bundang-gu, Sungnam-si, Gyeonggi-do, Korea
| | - Gerard L. Heck
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - John A. DeSimone
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - Vijay Lyall
- Department of Physiology and Biophysics, Virginia Commonwealth University, Richmond, Virginia, United States of America
- * E-mail:
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Korbmacher JP, Michel C, Neubauer D, Thompson K, Mizaikoff B, Frick M, Dietl P, Wittekindt OH. Amiloride-sensitive fluid resorption in NCI-H441 lung epithelia depends on an apical Cl(-) conductance. Physiol Rep 2014; 2:e00201. [PMID: 24744880 PMCID: PMC3967684 DOI: 10.1002/phy2.201] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Revised: 12/12/2013] [Accepted: 12/21/2013] [Indexed: 01/12/2023] Open
Abstract
Proper apical airway surface hydration is essential to maintain lung function. This hydration depends on well‐balanced water resorption and secretion. The mechanisms involved in resorption are still a matter of debate, especially as the measurement of transepithelial water transport remains challenging. In this study, we combined classical short circuit current (ISC) measurements with a novel D2O dilution method to correlate ion and water transport in order to reveal basic transport mechanisms in lung epithelia. D2O dilution method enabled precise analysis of water resorption with an unprecedented resolution. NCI‐H441 cells cultured at an air–liquid interface resorbed water at a rate of 1.5 ± 0.4 μL/(h cm2). Water resorption and ISC were reduced by almost 80% in the presence of the bulk Cl− channel inhibitor 5‐nitro‐2‐(3‐phenylpropylamino)benzoic acid (NPPB) or amiloride, a specific inhibitor of epithelial sodium channel (ENaC). However, water resorption and ISC were only moderately affected by forskolin or cystic fibrosis transmembrane regulator (CFTR) channel inhibitors (CFTRinh‐172 and glybenclamide). In line with previous studies, we demonstrate that water resorption depends on ENaC, and CFTR channels have only a minor but probably modulating effect on water resorption. However, the major ENaC‐mediated water resorption depends on an apical non‐CFTR Cl− conductance. We investigated water transport across lung epithelia, using a novel D2O dilution method in combination with Ussing chamber experiments. Our results revealed that CFTR channels have a minor modulating effect on water resorption. The major ENaC‐mediated resorption depends on non‐CFTR channels.
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Affiliation(s)
- Jonas P Korbmacher
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Christiane Michel
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Daniel Neubauer
- Institute of Analytical and Bioanalytical Chemistry, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Kristin Thompson
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Boris Mizaikoff
- Institute of Analytical and Bioanalytical Chemistry, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Manfred Frick
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Paul Dietl
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
| | - Oliver H Wittekindt
- Institute of General Physiology, Ulm University, Albert-Einstein-Allee 11, Ulm, 89081, Germany
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Marunaka Y. Characteristics and Pharmacological Regulation of Epithelial Na+ Channel (ENaC) and Epithelial Na+ Transport. J Pharmacol Sci 2014. [DOI: 10.1254/jphs.14r01sr] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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