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Zhang CH, Lifshitz LM, Uy KF, Ikebe M, Fogarty KE, ZhuGe R. The cellular and molecular basis of bitter tastant-induced bronchodilation. PLoS Biol 2013; 11:e1001501. [PMID: 23472053 PMCID: PMC3589262 DOI: 10.1371/journal.pbio.1001501] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2012] [Accepted: 01/24/2013] [Indexed: 01/13/2023] Open
Abstract
Bitter tastants can activate bitter taste receptors on constricted smooth muscle cells to inhibit L-type calcium channels and induce bronchodilation. Bronchodilators are a standard medicine for treating airway obstructive diseases, and β2 adrenergic receptor agonists have been the most commonly used bronchodilators since their discovery. Strikingly, activation of G-protein-coupled bitter taste receptors (TAS2Rs) in airway smooth muscle (ASM) causes a stronger bronchodilation in vitro and in vivo than β2 agonists, implying that new and better bronchodilators could be developed. A critical step towards realizing this potential is to understand the mechanisms underlying this bronchodilation, which remain ill-defined. An influential hypothesis argues that bitter tastants generate localized Ca2+ signals, as revealed in cultured ASM cells, to activate large-conductance Ca2+-activated K+ channels, which in turn hyperpolarize the membrane, leading to relaxation. Here we report that in mouse primary ASM cells bitter tastants neither evoke localized Ca2+ events nor alter spontaneous local Ca2+ transients. Interestingly, they increase global intracellular [Ca2+]i, although to a much lower level than bronchoconstrictors. We show that these Ca2+ changes in cells at rest are mediated via activation of the canonical bitter taste signaling cascade (i.e., TAS2R-gustducin-phospholipase Cβ [PLCβ]- inositol 1,4,5-triphosphate receptor [IP3R]), and are not sufficient to impact airway contractility. But activation of TAS2Rs fully reverses the increase in [Ca2+]i induced by bronchoconstrictors, and this lowering of the [Ca2+]i is necessary for bitter tastant-induced ASM cell relaxation. We further show that bitter tastants inhibit L-type voltage-dependent Ca2+ channels (VDCCs), resulting in reversal in [Ca2+]i, and this inhibition can be prevented by pertussis toxin and G-protein βγ subunit inhibitors, but not by the blockers of PLCβ and IP3R. Together, we suggest that TAS2R stimulation activates two opposing Ca2+ signaling pathways via Gβγ to increase [Ca2+]i at rest while blocking activated L-type VDCCs to induce bronchodilation of contracted ASM. We propose that the large decrease in [Ca2+]i caused by effective tastant bronchodilators provides an efficient cell-based screening method for identifying potent dilators from among the many thousands of available bitter tastants. Bitter taste receptors (TAS2Rs), a G-protein-coupled receptor family long thought to be solely expressed in taste buds on the tongue, have recently been detected in airways. Bitter substances can activate TAS2Rs in airway smooth muscle to cause greater bronchodilation than β2 adrenergic receptor agonists, the most commonly used bronchodilators. However, the mechanisms underlying this bronchodilation remain elusive. Here we show that, in resting primary airway smooth muscle cells, bitter tastants activate a TAS2R-dependent signaling pathway that results in an increase in intracellular calcium levels, albeit to a level much lower than that produced by bronchoconstrictors. In bronchoconstricted cells, however, bitter tastants reverse the bronchoconstrictor-induced increase in calcium levels, which leads to the relaxation of smooth muscle cells. We find that this reversal is due to inhibition of L-type calcium channels. Our results suggest that under normal conditions, bitter tastants can activate TAS2Rs to modestly increase calcium levels, but that when smooth muscle cells are constricted, they can block L-type calcium channels to induce bronchodilation. We postulate that this novel mechanism could operate in other extraoral cells expressing TAS2Rs.
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Affiliation(s)
- Cheng-Hai Zhang
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
| | - Lawrence M. Lifshitz
- Biomedical Imaging Group, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
| | - Karl F. Uy
- Department of Surgery, Division of Thoracic Surgery, University of Massachusetts Memorial Medical Center, Worcester, Massachusetts, United States of America
| | - Mitsuo Ikebe
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
| | - Kevin E. Fogarty
- Biomedical Imaging Group, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
| | - Ronghua ZhuGe
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
- Biomedical Imaging Group, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
- * E-mail:
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Marigo V, Courville K, Hsu WH, Feng JM, Cheng H. TRPM4 impacts on Ca2+ signals during agonist-induced insulin secretion in pancreatic beta-cells. Mol Cell Endocrinol 2009; 299:194-203. [PMID: 19063936 DOI: 10.1016/j.mce.2008.11.011] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Revised: 10/02/2008] [Accepted: 11/06/2008] [Indexed: 12/22/2022]
Abstract
TRPM4 is a Ca(2+)-activated non-selective cation (CAN) channel that functions in cell depolarization, which is important for Ca(2+) influx and insulin secretion in pancreatic beta-cells. We investigated TRPM4 expression and function in the beta-cell lines HIT-T15 (hamster), RINm5F (rat), beta-TC3 (mouse), MIN-6 (mouse) and the alpha-cell line INR1G9 (hamster). By RT-PCR, we identified TRPM4 transcripts in alpha- and beta-cells. Patch-clamp recordings with increasing Ca(2+) concentrations resulted in a dose-dependent activation of TRPM4 with the greatest depolarizing currents recorded from hamster-derived cells. Further, Ca(2+) imaging experiments revealed that inhibition of TRPM4 by a dominant-negative effect significantly decreased the magnitude of the Ca(2+) signals generated by agonist stimulation compared to control cells. The decrease in the [Ca(2+)](i) resulted in reduced insulin secretion. Our data suggest that depolarizing currents generated by TRPM4 are an important component in the control of intracellular Ca(2+) signals necessary for insulin secretion and perhaps glucagon from alpha-cells.
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Affiliation(s)
- V Marigo
- Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA
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Mergler S, Singh V, Grötzinger C, Kaczmarek P, Wiedenmann B, Strowski MZ. Characterization of voltage operated R-type Ca2+ channels in modulating somatostatin receptor subtype 2- and 3-dependent inhibition of insulin secretion from INS-1 cells. Cell Signal 2008; 20:2286-95. [PMID: 18793718 DOI: 10.1016/j.cellsig.2008.08.015] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2008] [Accepted: 08/24/2008] [Indexed: 11/28/2022]
Abstract
Somatostatin (SST) inhibits Ca(2+) entry into pancreatic B-cells via voltage-operated Ca(2+) channels (VOCCs) of L-type, leading to the suppression of insulin secretion. Activation of R-type channels increases insulin secretion. However, the role of R-type Ca(2+) channels (Ca(V)2.3) in mediating the effects of SST on insulin secretion has not been so far investigated. Here, we identify the SST-receptor subtypes (SSTR) expressed on insulin-producing INS-1 cells by RT-PCR and by functional assays. The role of R-type channels in regulating [Ca(2+)](i) in response to SST-treatment was detected by cell fluorescence imaging and patch-clamp technique. INS-1 expressed SSTR2 and SSTR3 and agonists (ag.) selective for these receptors reduced 10 nM exendin-4/20 mM glucose-stimulated insulin secretion. Surprisingly, SST and SST2-ag. transiently increased [Ca(2+)](i). Subsequently, these agonists led to a decrease in [Ca(2+)](i) below the basal levels. In contrast, SST3-ag. failed to induce a transient peak of [Ca(2+)](i). Instead, a persistent minor suppression of [Ca(2+)](i) was detected from 25 min. R-type channel blocker SNX-482 altered [Ca(2+)](i) in SST- and SST2-ag.-treated cells. Notably, the inhibition of insulin secretion by SST and SST2-ag., but not SST3-ag. was attenuated by SNX-482. Taken together, SST and SSTR2 regulate [Ca(2+)](i) and insulin secretion in INS-1 cells via R-type channels. In contrast, the R-type calcium channel does not mediate the effects of SST3-ag. on insulin secretion. We conclude that R-type channels play a major role in the inhibition of insulin secretion by somatostatin in INS-1 cells.
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Affiliation(s)
- Stefan Mergler
- Augenklinik, Charité-Universitätsmedizin Berlin, Campus Virchow-Klinikum, 13353 Berlin, Germany
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Cervia D, Bagnoli P. An update on somatostatin receptor signaling in native systems and new insights on their pathophysiology. Pharmacol Ther 2007; 116:322-41. [PMID: 17719647 DOI: 10.1016/j.pharmthera.2007.06.010] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2007] [Accepted: 06/28/2007] [Indexed: 12/20/2022]
Abstract
The peptide somatostatin (SRIF) has important physiological effects, mostly inhibitory, which have formed the basis for the clinical use of SRIF compounds. SRIF binding to its 5 guanine nucleotide-binding proteins-coupled receptors leads to the modulation of multiple transduction pathways. However, our current understanding of signaling exerted by receptors endogenously expressed in different cells/tissues reflects a rather complicated picture. On the other hand, the complexity of SRIF receptor signaling in pathologies, including pituitary and nervous system diseases, may be studied not only as alternative intervention points for the modulation of SRIF function but also to exploit new chemical space for drug-like molecules.
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Affiliation(s)
- Davide Cervia
- Department of Environmental Sciences, University of Tuscia, largo dell'Università snc, blocco D, 01100 Viterbo, Italy.
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Cheng H, Beck A, Launay P, Gross SA, Stokes AJ, Kinet JP, Fleig A, Penner R. TRPM4 controls insulin secretion in pancreatic beta-cells. Cell Calcium 2006; 41:51-61. [PMID: 16806463 PMCID: PMC5663640 DOI: 10.1016/j.ceca.2006.04.032] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2006] [Accepted: 04/28/2006] [Indexed: 11/28/2022]
Abstract
TRPM4 is a calcium-activated non-selective cation channel that is widely expressed and proposed to be involved in cell depolarization. In excitable cells, TRPM4 may regulate calcium influx by causing the depolarization that drives the activation of voltage-dependent calcium channels. We here report that insulin-secreting cells of the rat pancreatic beta-cell line INS-1 natively express TRPM4 proteins and generate large depolarizing membrane currents in response to increased intracellular calcium. These currents exhibit the characteristics of TRPM4 and can be suppressed by expressing a dominant negative TRPM4 construct, resulting in significantly decreased insulin secretion in response to a glucose stimulus. Reduced insulin secretion was also observed with arginine vasopressin stimulation, a Gq-coupled receptor agonist in beta-cells. Moreover, the recruitment of TRPM4 currents was biphasic in both INS-1 cells as well as HEK-293 cells overexpressing TRPM4. The first phase is due to activation of TRPM4 channels localized within the plasma membrane followed by a slower secondary phase, which is caused by the recruitment of TRPM4-containing vesicles to the plasma membrane during exocytosis. The secondary phase can be observed during perfusion of cells with increasing [Ca(2+)](i), replicated with agonist stimulation, and coincides with an increase in cell capacitance, loss of FM1-43 dye, and vesicle fusion. Our data suggest that TRPM4 may play a key role in the control of membrane potential and electrical activity of electrically excitable secretory cells and the dynamic translocation of TRPM4 from a vesicular pool to the plasma membrane via Ca(2+)-dependent exocytosis may represent a key short- and midterm regulatory mechanism by which cells regulate electrical activity.
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Affiliation(s)
- Henrique Cheng
- Laboratory of Cell and Molecular Signaling, Center for Biomedical Research at The Queen’s Medical Center and John A. Burns School of Medicine at the University of Hawaii, 1301 Punchbowl St., UHT 8, Honolulu, HI 96813, United States
| | - Andreas Beck
- Laboratory of Cell and Molecular Signaling, Center for Biomedical Research at The Queen’s Medical Center and John A. Burns School of Medicine at the University of Hawaii, 1301 Punchbowl St., UHT 8, Honolulu, HI 96813, United States
| | - Pierre Launay
- Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, United States
| | - Stefan A. Gross
- Laboratory of Cell and Molecular Signaling, Center for Biomedical Research at The Queen’s Medical Center and John A. Burns School of Medicine at the University of Hawaii, 1301 Punchbowl St., UHT 8, Honolulu, HI 96813, United States
| | - Alexander J. Stokes
- Laboratory of Cell and Molecular Signaling, Center for Biomedical Research at The Queen’s Medical Center and John A. Burns School of Medicine at the University of Hawaii, 1301 Punchbowl St., UHT 8, Honolulu, HI 96813, United States
| | - Jean-Pierre Kinet
- Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, United States
| | - Andrea Fleig
- Laboratory of Cell and Molecular Signaling, Center for Biomedical Research at The Queen’s Medical Center and John A. Burns School of Medicine at the University of Hawaii, 1301 Punchbowl St., UHT 8, Honolulu, HI 96813, United States
| | - Reinhold Penner
- Laboratory of Cell and Molecular Signaling, Center for Biomedical Research at The Queen’s Medical Center and John A. Burns School of Medicine at the University of Hawaii, 1301 Punchbowl St., UHT 8, Honolulu, HI 96813, United States
- Corresponding author. Tel.: +1 808 585 5366; fax: +1 808 585 5377. (R. Penner)
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Yao CY, Gill M, Martens CA, Coy DH, Hsu WH. Somatostatin inhibits insulin release via SSTR2 in hamster clonal beta-cells and pancreatic islets. ACTA ACUST UNITED AC 2005; 129:79-84. [PMID: 15927701 DOI: 10.1016/j.regpep.2005.01.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2004] [Revised: 01/17/2005] [Accepted: 01/18/2005] [Indexed: 01/31/2023]
Abstract
Somatostatin (SST) inhibits pancreatic endocrine secretion. It is generally accepted that SSTR2 and SSTR5 mediate the inhibition of glucagon and insulin release, respectively. The present study was performed to test the hypothesis that SSTR2, but not SSTR5, mediates SST-induced inhibition of insulin release in hamster beta-cells. Both hamster clonal beta-cells HIT-T15 and pancreatic islets were used to test this hypothesis. Both SST and a nonpeptide SSTR2 agonist L-779,976 (1-100 nM) inhibited insulin release from HIT-T15 and islets in a concentration-dependent manner. In contrast, nonpeptide agonists for SSTR1, 3, 4 and 5 at the highest concentration studied (1 microM) failed to inhibit insulin release. PRL-2903, a peptide SSTR2 antagonist (0.1-1 muicroM), antagonized SST-induced inhibition of insulin release in a concentration-dependent manner. Taken together, we conclude that, in hamster beta-cells, SST inhibits insulin release via SSTR2 but not SSTR5.
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Affiliation(s)
- Cheng-Yu Yao
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
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Arena S, Pattarozzi A, Corsaro A, Schettini G, Florio T. Somatostatin receptor subtype-dependent regulation of nitric oxide release: involvement of different intracellular pathways. Mol Endocrinol 2004; 19:255-67. [PMID: 15388796 DOI: 10.1210/me.2004-0280] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
We reported previously that, in addition to direct effects, somatostatin (SST) affects tumor growth inhibiting the tumoral neoangiogenesis, via an interference with NO synthesis. Here, we analyzed the effects of SST on nitric oxide (NO) production induced by different agonists [basic fibroblast growth factor (bFGF), insulin, cholecystokinin (CCK)] and the intracellular signaling involved, using Chinese hamster ovary-k1 cells stably transfected with individual SSTR1-SSTR4. bFGF and insulin induced endothelial nitric oxide synthase activity via the generation of ceramide or the Akt-dependent phosphorylation of endothelial nitric oxide synthase, respectively. CCK regulates neuronal nitric oxide synthase activity in a Ca++-dependent manner. SST inhibited NO production stimulated by bFGF through SST receptor 1 (SSTR1), SSTR2, and SSTR3 and by CCK through SSTR2 and SSTR3. In all the cell lines, SST treatment did not modify NO synthesis induced by insulin. SSTR4 activation was not effective on any of the stimuli tested. The effects on bFGF-induced NO production were downstream from receptor phosphorylation and ceramide synthesis. SSTR2 and -3 on CCK activity were related to the inhibition of intracellular Ca++ mobilization, whereas the lack of effects on insulin was paralleled by the absence of SST activity on Akt phosphorylation. These data, identifying for the first time a selective receptor subtype-inhibitory role of SST on NO generation, may open new perspectives in the use of SST agonists to control tumoral angiogenesis.
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Affiliation(s)
- Sara Arena
- Section of Pharacology, Department of Oncology, Biology and Genetics, University of Genova, and Pharmacology and Neuroscience, National Institute for Cancer Research (IST), 16132 Genova, Italy
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Rhie DJ, Sung JH, Ha US, Kim HJ, Min DS, Hahn SJ, Kim MS, Jo YH, Yoon SH. Endogenous somatostatin receptors mobilize calcium from inositol 1,4,5-trisphosphate-sensitive stores in NG108-15 cells. Brain Res 2003; 975:120-8. [PMID: 12763599 DOI: 10.1016/s0006-8993(03)02596-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Somatostatin receptors are members of the G-protein-coupled receptor superfamily and exert their principal effects by coupling to inhibitory G-proteins. We used fura-2-based digital calcium imaging and assayed for [3H]inositol phosphates (IPs) to study the effects of somatostatin on intracellular calcium signaling in neuroblastomaxglioma NG108-15 cells. Both somatostatin-14 and octreotide induced concentration-dependent increases in intracellular Ca(2+) concentration ([Ca(2+)](i)). Thirty-four percent of the cells responded to treatment with 100 nM somatostatin-14. Somatostatin-induced responses were not blocked by the removal of extracellular calcium; instead, they were abolished by pretreatment with 100 nM thapsigargin, an agent that depletes and prevents refilling of intracellular Ca(2+) stores. Pretreatment with the inositol 1,4,5-trisphosphate (IP(3)) receptor antagonist xestospongin C (10 microM) for 20 min inhibited markedly the somatostatin-induced response. Somatostatin (100 nM) increased [3H]IPs formation. U73122 (1 microM), an inhibitor of phospholipase C (PLC), completely blocked the somatostatin-induced [Ca(2+)](i) increases and the formation of [3H]IPs. Pretreatment with pertussis toxin (PTX, 200 ng/ml) for 24 h blocked the somatostatin-induced responses. Thus, we conclude that activation of endogenous somatostatin receptors in NG108-15 cells induces the release of calcium from IP(3)-sensitive intracellular stores through PTX-sensitive G-protein-coupled PLC.
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Affiliation(s)
- Duck-Joo Rhie
- Department of Physiology, College of Medicine, The Catholic University of Korea, 505 Banpo-dong, Socho-gu, Seoul 137-701, South Korea
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