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Guo J, She J, Zeng W, Chen Q, Bai XC, Jiang Y. Structures of the calcium-activated, non-selective cation channel TRPM4. Nature 2017; 552:205-209. [PMID: 29211714 PMCID: PMC5901961 DOI: 10.1038/nature24997] [Citation(s) in RCA: 135] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2017] [Accepted: 11/03/2017] [Indexed: 12/12/2022]
Abstract
TRPM4 is a calcium-activated, phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) -modulated, non-selective cation channel that belongs to the family of melastatin-related transient receptor potential (TRPM) channels. Here we present the electron cryo-microscopy structures of the mouse TRPM4 channel with and without ATP. TRPM4 consists of multiple transmembrane and cytosolic domains, which assemble into a three-tiered architecture. The N-terminal nucleotide-binding domain and the C-terminal coiled-coil participate in the tetrameric assembly of the channel; ATP binds at the nucleotide-binding domain and inhibits channel activity. TRPM4 has an exceptionally wide filter but is only permeable to monovalent cations; filter residue Gln973 is essential in defining monovalent selectivity. The S1-S4 domain and the post-S6 TRP domain form the central gating apparatus that probably houses the Ca2+- and PtdIns(4,5)P2-binding sites. These structures provide an essential starting point for elucidating the complex gating mechanisms of TRPM4 and reveal the molecular architecture of the TRPM family.
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Affiliation(s)
- Jiangtao Guo
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040, USA.,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8816, USA
| | - Ji She
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040, USA.,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8816, USA
| | - Weizhong Zeng
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040, USA.,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8816, USA.,Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040, USA
| | - Qingfeng Chen
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040, USA.,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8816, USA.,Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040, USA
| | - Xiao-Chen Bai
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8816, USA.,Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9039, USA
| | - Youxing Jiang
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040, USA.,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8816, USA.,Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040, USA
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52
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Electron cryo-microscopy structure of a human TRPM4 channel. Nature 2017; 552:200-204. [DOI: 10.1038/nature24674] [Citation(s) in RCA: 112] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 10/23/2017] [Indexed: 12/18/2022]
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Keckeis S, Wernecke L, Salchow DJ, Reichhart N, Strauß O. Activation of a Ca 2+-dependent cation conductance with properties of TRPM2 by reactive oxygen species in lens epithelial cells. Exp Eye Res 2017; 161:61-70. [PMID: 28603015 DOI: 10.1016/j.exer.2017.06.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2016] [Revised: 05/23/2017] [Accepted: 06/01/2017] [Indexed: 02/03/2023]
Abstract
Ion channels are crucial for maintenance of ion homeostasis and transparency of the lens. The lens epithelium is the metabolically and electrophysiologically active cell type providing nutrients, ions and water to the lens fiber cells. Ca2+-dependent non-selective ion channels seem to play an important role for ion homeostasis. The aim of the study was to identify and characterize Ca2+- and reactive oxygen species (ROS)-dependent non-selective cation channels in human lens epithelial cells. RT-PCR revealed gene expression of the Ca2+-activated non-selective cation channels TRPC3, TRPM2, TRPM4 and Ano6 in both primary lens epithelial cells and the cell line HLE-B3, whereas TRPM5 mRNA was only found in HLE-B3 cells. Using whole-cell patch-clamp technique, ionomycin evoked non-selective cation currents with linear current-voltage relationship in both cell types. The current was decreased by flufenamic acid (FFA), 2-APB, 9-phenanthrol and miconazole, but insensitive to DIDS, ruthenium red, and intracellularly applied spermine. H2O2 evoked a comparable current, abolished by FFA. TRPM2 protein expression in HLE-B3 cells was confirmed by means of immunocytochemistry and western blot. In summary, we conclude that lens epithelial cells functionally express Ca2+- and H2O2-activated non-selective cation channels with properties of TRPM2.
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Affiliation(s)
- Susanne Keckeis
- Experimental Ophthalmology, Department of Ophthalmology, Charité University Medicine Berlin, Berlin, Germany
| | - Laura Wernecke
- Experimental Ophthalmology, Department of Ophthalmology, Charité University Medicine Berlin, Berlin, Germany
| | - Daniel J Salchow
- Department of Ophthalmology, Charité University Medicine Berlin, Berlin, Germany
| | - Nadine Reichhart
- Experimental Ophthalmology, Department of Ophthalmology, Charité University Medicine Berlin, Berlin, Germany.
| | - Olaf Strauß
- Experimental Ophthalmology, Department of Ophthalmology, Charité University Medicine Berlin, Berlin, Germany.
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54
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Lin EC, Combe CL, Gasparini S. Differential Contribution of Ca 2+-Dependent Mechanisms to Hyperexcitability in Layer V Neurons of the Medial Entorhinal Cortex. Front Cell Neurosci 2017; 11:182. [PMID: 28713246 PMCID: PMC5491848 DOI: 10.3389/fncel.2017.00182] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 06/13/2017] [Indexed: 11/13/2022] Open
Abstract
Temporal lobe epilepsy is characterized by recurrent seizures in one or both temporal lobes of the brain; some in vitro models show that epileptiform discharges initiate in entorhinal layer V neurons and then spread into other areas of the temporal lobe. We previously found that, in the presence of GABAA receptor antagonists, stimulation of afferent fibers, terminating both at proximal and distal dendritic locations, initiated hyperexcitable bursts in layer V medial entorhinal neurons. We investigated the differential contribution of Ca2+-dependent mechanisms to the plateaus underlying these bursts at proximal and distal synapses. We found that the NMDA glutamatergic antagonist D,L-2-amino-5-phosphonovaleric acid (APV; 50 μM) reduced both the area and duration of the bursts at both proximal and distal synapses by about half. The L-type Ca2+ channel blocker nimodipine (10 μM) and the R- and T-type Ca2+ channel blocker NiCl2 (200 μM) decreased the area of the bursts to a lesser extent; none of these effects appeared to be location-dependent. Remarkably, the perfusion of flufenamic acid (FFA; 100 μM), to block Ca2+-activated non-selective cation currents (ICAN) mediated by transient receptor potential (TRP) channels, had a location-dependent effect, by abolishing burst firing and switching the suprathreshold response to a single action potential (AP) for proximal stimulation, but only minimally affecting the bursts evoked by distal stimulation. A similar outcome was found when FFA was pressure-applied locally around the proximal dendrite of the recorded neurons and in the presence of a selective blocker of melastatin TRP (TRPM) channels, 9-phenanthrol (100 μM), whereas a selective blocker of canonical TRP (TRPC) channels, SKF 96365, did not affect the bursts. These results indicate that different mechanisms might contribute to the initiation of hyperexcitability in layer V neurons at proximal and distal synapses and could shed light on the initiation of epileptiform activity in the entorhinal cortex.
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Affiliation(s)
- Eric C Lin
- Neuroscience Center of Excellence, Louisiana State University Health Sciences CenterNew Orleans, LA, United States
| | - Crescent L Combe
- Neuroscience Center of Excellence, Louisiana State University Health Sciences CenterNew Orleans, LA, United States
| | - Sonia Gasparini
- Neuroscience Center of Excellence, Louisiana State University Health Sciences CenterNew Orleans, LA, United States.,Department of Cell Biology and Anatomy, Louisiana State University Health Sciences CenterNew Orleans, LA, United States
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Angstadt JD, Giordano JR, Goncalves AJ. 9-Phenanthrol modulates postinhibitory rebound and afterhyperpolarizing potentials in an excitatory motor neuron of the medicinal leech. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2017; 203:613-633. [DOI: 10.1007/s00359-017-1178-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Revised: 05/01/2017] [Accepted: 05/02/2017] [Indexed: 12/19/2022]
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56
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Steviol glycosides enhance pancreatic beta-cell function and taste sensation by potentiation of TRPM5 channel activity. Nat Commun 2017; 8:14733. [PMID: 28361903 PMCID: PMC5380970 DOI: 10.1038/ncomms14733] [Citation(s) in RCA: 116] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Accepted: 01/26/2017] [Indexed: 02/07/2023] Open
Abstract
Steviol glycosides (SGs), such as stevioside and rebaudioside A, are natural, non-caloric sweet-tasting organic molecules, present in extracts of the scrub plant Stevia rebaudiana, which are widely used as sweeteners in consumer foods and beverages. TRPM5 is a Ca2+-activated cation channel expressed in type II taste receptor cells and pancreatic β-cells. Here we show that stevioside, rebaudioside A and their aglycon steviol potentiate the activity of TRPM5. We find that SGs potentiate perception of bitter, sweet and umami taste, and enhance glucose-induced insulin secretion in a Trpm5-dependent manner. Daily consumption of stevioside prevents development of high-fat-diet-induced diabetic hyperglycaemia in wild-type mice, but not in Trpm5-/- mice. These results elucidate a molecular mechanism of action of SGs and identify TRPM5 as a potential target to prevent and treat type 2 diabetes.
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Tykocki NR, Boerman EM, Jackson WF. Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles. Compr Physiol 2017; 7:485-581. [PMID: 28333380 DOI: 10.1002/cphy.c160011] [Citation(s) in RCA: 222] [Impact Index Per Article: 31.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.
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Affiliation(s)
- Nathan R Tykocki
- Department of Pharmacology, University of Vermont, Burlington, Vermont, USA
| | - Erika M Boerman
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri, USA
| | - William F Jackson
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan, USA
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58
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The TRPM4 channel is functionally important for the beneficial cardiac remodeling induced by endurance training. J Muscle Res Cell Motil 2017; 38:3-16. [DOI: 10.1007/s10974-017-9466-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 02/02/2017] [Indexed: 10/20/2022]
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59
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Trpm5 expression in the olfactory epithelium. Mol Cell Neurosci 2017; 80:75-88. [PMID: 28188885 DOI: 10.1016/j.mcn.2017.02.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Revised: 02/02/2017] [Accepted: 02/05/2017] [Indexed: 11/20/2022] Open
Abstract
The Ca2+-activated monovalent cation channel Trpm5 is a key element in chemotransduction of taste receptor cells of the tongue, but the extent to which Trpm5 channels are expressed in olfactory sensory neurons (OSNs) of the main olfactory epithelium (MOE) of adult mice as part of a specific pheromonal detection system is debated. Here, we used a novel Trpm5-IRES-Cre knockin strain to drive Cre recombinase expression, employed previously validated Trpm5 antibodies, performed in situ hybridization experiments to localize Trpm5 RNA, and searched extensively for Trpm5 splice variants in genetically-labeled, Trpm5-expressing MOE cells. In contrast to previous reports, we find no evidence for the existence in adult mouse OSNs of the classical Trpm5 channel known from taste cells. We show that Trpm5-expressing adult OSNs express a novel Trpm5 splice variant, Trpm5-9, that is unlikely to form a functional cation channel by itself. We also demonstrate that Trpm5 is transiently expressed in a subpopulation of mature OSNs in the embryonic olfactory epithelium, indicating that Trpm5 channels could play a specific role in utero during a narrow developmental time window. Ca2+ imaging with GCaMP3 under the control of the Trpm5-IRES-Cre allele using a newly developed MOE wholemount preparation of the adult olfactory epithelium reveals that Trpm5-GCaMP3 OSNs comprise a heterogeneous group of sensory neurons many of which can detect general odorants. Together, these studies are essential for understanding the role of transient receptor potential channels in mammalian olfaction.
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Respiratory Rhythm Generation: The Whole Is Greater Than the Sum of the Parts. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1015:147-161. [DOI: 10.1007/978-3-319-62817-2_9] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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61
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Wu MM, Zhai YJ, Li YX, Hu QQ, Wang ZR, Wei SP, Zou L, Alli AA, Thai TL, Zhang ZR, Ma HP. Hydrogen peroxide suppresses TRPM4 trafficking to the apical membrane in mouse cortical collecting duct principal cells. Am J Physiol Renal Physiol 2016; 311:F1360-F1368. [PMID: 27956381 DOI: 10.1152/ajprenal.00439.2016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Revised: 10/31/2016] [Accepted: 10/31/2016] [Indexed: 01/14/2023] Open
Abstract
A Ca2+-activated nonselective cation channel (NSCCa) is found in principal cells of the mouse cortical collecting duct (CCD). However, the molecular identity of this channel remains unclear. We used mpkCCDc14 cells, a mouse CCD principal cell line, to determine whether NSCCa represents the transient receptor potential (TRP) channel, the melastatin subfamily 4 (TRPM4). A Ca2+-sensitive single-channel current was observed in inside-out patches excised from the apical membrane of mpkCCDc14 cells. Like TRPM4 channels found in other cell types, this channel has an equal permeability for Na+ and K+ and has a linear current-voltage relationship with a slope conductance of ~23 pS. The channel was inhibited by a specific TRPM4 inhibitor, 9-phenanthrol. Moreover, the frequency of observing this channel was dramatically decreased in TRPM4 knockdown mpkCCDc14 cells. Unlike those previously reported in other cell types, the TRPM4 in mpkCCDc14 cells was unable to be activated by hydrogen peroxide (H2O2). Conversely, after treatment with H2O2, TRPM4 density in the apical membrane of mpkCCDc14 cells was significantly decreased. The channel in intact cell-attached patches was activated by ionomycin (a Ca2+ ionophore), but not by ATP (a purinergic P2 receptor agonist). These data suggest that the NSCCa current previously described in CCD principal cells is actually carried through TRPM4 channels. However, the physiological role of this channel in the CCD remains to be further determined.
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Affiliation(s)
- Ming-Ming Wu
- Departments of Cardiology and Clinic Pharmacy, Harbin Medical University Cancer Hospital, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Harbin, China; and.,Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Yu-Jia Zhai
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Yu-Xia Li
- Departments of Cardiology and Clinic Pharmacy, Harbin Medical University Cancer Hospital, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Harbin, China; and
| | - Qing-Qing Hu
- Departments of Cardiology and Clinic Pharmacy, Harbin Medical University Cancer Hospital, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Harbin, China; and
| | - Zhi-Rui Wang
- Departments of Cardiology and Clinic Pharmacy, Harbin Medical University Cancer Hospital, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Harbin, China; and
| | - Shi-Peng Wei
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Li Zou
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Abdel A Alli
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Tiffany L Thai
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
| | - Zhi-Ren Zhang
- Departments of Cardiology and Clinic Pharmacy, Harbin Medical University Cancer Hospital, Institute of Metabolic Disease, Heilongjiang Academy of Medical Science, Harbin, China; and
| | - He-Ping Ma
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
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62
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Bidaux G, Sgobba M, Lemonnier L, Borowiec AS, Noyer L, Jovanovic S, Zholos AV, Haider S. Functional and Modeling Studies of the Transmembrane Region of the TRPM8 Channel. Biophys J 2016; 109:1840-51. [PMID: 26536261 DOI: 10.1016/j.bpj.2015.09.027] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2015] [Revised: 09/18/2015] [Accepted: 09/28/2015] [Indexed: 12/15/2022] Open
Abstract
Members of the transient receptor potential (TRP) ion channel family act as polymodal cellular sensors, which aid in regulating Ca(2+) homeostasis. Within the TRP family, TRPM8 is the cold receptor that forms a nonselective homotetrameric cation channel. In the absence of TRPM8 crystal structure, little is known about the relationship between structure and function. Inferences of TRPM8 structure have come from mutagenesis experiments coupled to electrophysiology, mainly regarding the fourth transmembrane helix (S4), which constitutes a moderate voltage-sensing domain, and about cold sensor and phosphatidylinositol 4,5-bisphosphate binding sites, which are both located in the C-terminus of TRPM8. In this study, we use a combination of molecular modeling and experimental techniques to examine the structure of the TRPM8 transmembrane and pore helix region including the conducting conformation of the selectivity filter. The model is consistent with a large amount of functional data and was further tested by mutagenesis. We present structural insight into the role of residues involved in intra- and intersubunit interactions and their link with the channel activity, sensitivity to icilin, menthol and cold, and impact on channel oligomerization.
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Affiliation(s)
- Gabriel Bidaux
- Inserm, U1003, Laboratoire de Physiologie Cellulaire, Equipe labellisée par la Ligue contre le Cancer, Villeneuve d'Ascq, France; Laboratory of Excellence, Ion Channels Science and Therapeutics, Université de Lille 1, Villeneuve d'Ascq, France; Laboratoire Biophotonique Cellulaire Fonctionnelle. Institut de Recherche Interdisciplinaire, Villeneuve d'Ascq, France
| | - Miriam Sgobba
- Centre for Cancer Research and Cell Biology, Queen's University of Belfast, Belfast, United Kingdom
| | - Loic Lemonnier
- Inserm, U1003, Laboratoire de Physiologie Cellulaire, Equipe labellisée par la Ligue contre le Cancer, Villeneuve d'Ascq, France; Laboratory of Excellence, Ion Channels Science and Therapeutics, Université de Lille 1, Villeneuve d'Ascq, France
| | - Anne-Sophie Borowiec
- Inserm, U1003, Laboratoire de Physiologie Cellulaire, Equipe labellisée par la Ligue contre le Cancer, Villeneuve d'Ascq, France; Laboratory of Excellence, Ion Channels Science and Therapeutics, Université de Lille 1, Villeneuve d'Ascq, France
| | - Lucile Noyer
- Inserm, U1003, Laboratoire de Physiologie Cellulaire, Equipe labellisée par la Ligue contre le Cancer, Villeneuve d'Ascq, France; Laboratory of Excellence, Ion Channels Science and Therapeutics, Université de Lille 1, Villeneuve d'Ascq, France
| | | | - Alexander V Zholos
- Department of Biophysics, Educational and Scientific Centre, "Institute of Biology" Taras Shevchenko, Kiev National University, Kiev, Ukraine.
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Leitner MG, Michel N, Behrendt M, Dierich M, Dembla S, Wilke BU, Konrad M, Lindner M, Oberwinkler J, Oliver D. Direct modulation of TRPM4 and TRPM3 channels by the phospholipase C inhibitor U73122. Br J Pharmacol 2016; 173:2555-69. [PMID: 27328745 DOI: 10.1111/bph.13538] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Revised: 06/10/2016] [Accepted: 06/15/2016] [Indexed: 02/01/2023] Open
Abstract
BACKGROUND AND PURPOSE Signalling through phospholipase C (PLC) controls many cellular processes. Much information on the relevance of this important pathway has been derived from pharmacological inhibition of the enzymatic activity of PLC. We found that the most frequently employed PLC inhibitor, U73122, activates endogenous ionic currents in widely used cell lines. Given the extensive use of U73122 in research, we set out to identify these U73122-sensitive ion channels. EXPERIMENTAL APPROACH We performed detailed biophysical analysis of the U73122-induced currents in frequently used cell lines. KEY RESULTS At concentrations required to inhibit PLC, U73122 modulated the activity of transient receptor potential melastatin (TRPM) channels through covalent modification. U73122 was shown to be a potent agonist of ubiquitously expressed TRPM4 channels and activated endogenous TRPM4 channels in CHO cells independently of PLC and of the downstream second messengers PI(4,5)P2 and Ca(2+) . U73122 also potentiated Ca(2) (+) -dependent TRPM4 currents in human Jurkat T-cells, endogenous TRPM4 in HEK293T cells and recombinant human TRPM4. In contrast to TRPM4, TRPM3 channels were inhibited whereas the closely related TRPM5 channels were insensitive to U73122, showing that U73122 exhibits high specificity within the TRPM channel family. CONCLUSIONS AND IMPLICATIONS Given the widespread expression of TRPM4 and TRPM3 channels, these actions of U73122 must be considered when interpreting its effects on cell function. U73122 may also be useful for identifying and characterizing TRPM channels in native tissue, thus facilitating the analysis of their physiology.
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Affiliation(s)
- Michael G Leitner
- Institute of Physiology and Pathophysiology, Department of Neurophysiology, Philipps-University Marburg, Marburg, Germany
| | - Niklas Michel
- Institute of Physiology and Pathophysiology, Department of Neurophysiology, Philipps-University Marburg, Marburg, Germany
| | - Marc Behrendt
- Institute of Physiology and Pathophysiology, Department of Neurophysiology, Philipps-University Marburg, Marburg, Germany
| | - Marlen Dierich
- Institute of Physiology and Pathophysiology, Department of Neurophysiology, Philipps-University Marburg, Marburg, Germany
| | - Sandeep Dembla
- Institute of Physiology and Pathophysiology, Department of Neurophysiology, Philipps-University Marburg, Marburg, Germany
| | - Bettina U Wilke
- Institute of Physiology and Pathophysiology, Department of Neurophysiology, Philipps-University Marburg, Marburg, Germany
| | - Maik Konrad
- Institute of Physiology and Pathophysiology, Department of Neurophysiology, Philipps-University Marburg, Marburg, Germany
| | - Moritz Lindner
- Institute of Physiology and Pathophysiology, Department of Neurophysiology, Philipps-University Marburg, Marburg, Germany.,Department of Ophthalmology, University of Bonn, Bonn, Germany
| | - Johannes Oberwinkler
- Institute of Physiology and Pathophysiology, Department of Neurophysiology, Philipps-University Marburg, Marburg, Germany
| | - Dominik Oliver
- Institute of Physiology and Pathophysiology, Department of Neurophysiology, Philipps-University Marburg, Marburg, Germany
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Suzuki H, Sasaki E, Nakagawa A, Muraki Y, Hatano N, Muraki K. Diclofenac, a nonsteroidal anti-inflammatory drug, is an antagonist of human TRPM3 isoforms. Pharmacol Res Perspect 2016; 4:e00232. [PMID: 27433342 PMCID: PMC4876142 DOI: 10.1002/prp2.232] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Revised: 03/04/2016] [Accepted: 03/07/2016] [Indexed: 11/15/2022] Open
Abstract
The effects of diclofenac (Dic), an acetic acid derivative-type nonsteroidal anti-inflammatory drug, were examined on the function of transient receptor potential (TRP) melastatin (TRPM) 3 (TRPM3) in human embryonic kidney 293 cell-line (HEK293) cells with recombinant human TRPM3 isoforms (TRPM31325, TRPM3-3, TRPM3-9, and TRPM3-S) and in a neuroblastoma cell line human neuroblastoma IMR-32 cells (IMR-32 cells) derived from human peripheral neurons. TRPM3 responses evoked by pregnenolone sulfate (PregS) were effectively inhibited by Dic in a concentration-dependent manner in Ca(2+) measurement and electrophysiological assays. The apparent IC 50 for PregS-induced Ca(2+) response of TRPM31325, TRPM3-3, and TRPM3-9 was calculated to be 18.8, 42.5, and 7.1 μmol/L, respectively. The TRPM3-dependent Ca(2+) responses evoked by nifedipine, another TRPM3 agonist, were also significantly inhibited by Dic. In contrast, aceclofenac, an acetoxymethyl analog of Dic, had no effects on PregS-induced TRPM3 responses. Constitutive channel activity of TRPM3-S without TRPM3 agonists was substantially inhibited by Dic, ruling out the possibility of interaction of Dic against TRPM3 agonists to the channel binding sites. Moreover, Dic reversibly inhibited TRPM3 single-channel activity recorded in excised outside-out patches without affecting the channel conductance. In differentiated neuronal IMR-32 cells with endogenous TRPM3, Dic inhibited PregS-evoked Ca(2+) responses with an apparent IC 50 of 17.1 μmol/L. Taken together, our findings demonstrate that Dic inhibits human TRPM3 without interacting with the channel pore.
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Affiliation(s)
- Hiroka Suzuki
- Laboratory of Cellular PharmacologySchool of PharmacyAichi‐Gakuin University1‐100 KusumotoChikusa, Nagoya464‐8650Japan
| | - Eiji Sasaki
- Laboratory of Cellular PharmacologySchool of PharmacyAichi‐Gakuin University1‐100 KusumotoChikusa, Nagoya464‐8650Japan
| | - Ayumi Nakagawa
- Laboratory of Cellular PharmacologySchool of PharmacyAichi‐Gakuin University1‐100 KusumotoChikusa, Nagoya464‐8650Japan
| | - Yukiko Muraki
- Laboratory of Cellular PharmacologySchool of PharmacyAichi‐Gakuin University1‐100 KusumotoChikusa, Nagoya464‐8650Japan
| | - Noriyuki Hatano
- Laboratory of Cellular PharmacologySchool of PharmacyAichi‐Gakuin University1‐100 KusumotoChikusa, Nagoya464‐8650Japan
| | - Katsuhiko Muraki
- Laboratory of Cellular PharmacologySchool of PharmacyAichi‐Gakuin University1‐100 KusumotoChikusa, Nagoya464‐8650Japan
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Limon A, Mamdani F, Hjelm BE, Vawter MP, Sequeira A. Targets of polyamine dysregulation in major depression and suicide: Activity-dependent feedback, excitability, and neurotransmission. Neurosci Biobehav Rev 2016; 66:80-91. [PMID: 27108532 DOI: 10.1016/j.neubiorev.2016.04.010] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Revised: 04/09/2016] [Accepted: 04/13/2016] [Indexed: 01/19/2023]
Abstract
Major depressive disorder (MDD) is a leading cause of disability worldwide characterized by altered neuronal activity in brain regions involved in the control of stress and emotion. Although multiple lines of evidence suggest that altered stress-coping mechanisms underlie the etiology of MDD, the homeostatic control of neuronal excitability in MDD at the molecular level is not well established. In this review, we examine past and current evidence implicating dysregulation of the polyamine system as a central factor in the homeostatic response to stress and the etiology of MDD. We discuss the cellular effects of abnormal metabolism of polyamines in the context of their role in sensing and modulation of neuronal, electrical, and synaptic activity. Finally, we discuss evidence supporting an allostatic model of depression based on a chronic elevation in polyamine levels resulting in self-sustained stress response mechanisms maintained by maladaptive homeostatic mechanisms.
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Affiliation(s)
- Agenor Limon
- Functional Genomics Laboratory, Department of Psychiatry and Human Behavior, University of California, Irvine, CA 92627, USA
| | - Firoza Mamdani
- Functional Genomics Laboratory, Department of Psychiatry and Human Behavior, University of California, Irvine, CA 92627, USA
| | - Brooke E Hjelm
- Functional Genomics Laboratory, Department of Psychiatry and Human Behavior, University of California, Irvine, CA 92627, USA
| | - Marquis P Vawter
- Functional Genomics Laboratory, Department of Psychiatry and Human Behavior, University of California, Irvine, CA 92627, USA
| | - Adolfo Sequeira
- Functional Genomics Laboratory, Department of Psychiatry and Human Behavior, University of California, Irvine, CA 92627, USA.
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66
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Neyer C, Herr D, Kohmann D, Budde T, Pape HC, Coulon P. mGluR-mediated calcium signalling in the thalamic reticular nucleus. Cell Calcium 2016; 59:312-23. [PMID: 27041217 DOI: 10.1016/j.ceca.2016.03.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Revised: 03/22/2016] [Accepted: 03/23/2016] [Indexed: 10/22/2022]
Abstract
The thalamic reticular nucleus (TRN) plays a major role in modulating the transfer of information from the thalamus to the cortex. GABAergic inhibition via the TRN is differentially regulated by metabotropic glutamate receptors (mGluRs) and the effect of mGluRs on the membrane potential, on ion channels, and on the plasticity of electrical coupling of TRN neurons has been studied previously. Although mGluRs are generally known to trigger Ca(2+) transients, mGluR-mediated Ca(2+)-transients in TRN neurons have not yet been investigated. In this study, we show that mGluRs can trigger Ca(2+)-transients in TRN neurons, that these transients depend on intracellular Ca(2+)-stores, and are mediated by IP3 receptors. Ca(2+) transients caused by the group I mGluR agonist DHPG elicit a current that is sensitive to flufenamic acid and has a reversal potential around -40mV. Our results add mGluR-mediated Ca(2+)-signalling in the TRN to the state-dependent modulators of the thalamocortical system.
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Affiliation(s)
- Christina Neyer
- Institut für Physiologie I, Westfälische Wilhelms-Universität, Münster, Germany
| | - David Herr
- Institut für Physiologie I, Westfälische Wilhelms-Universität, Münster, Germany
| | - Denise Kohmann
- Institut für Physiologie I, Westfälische Wilhelms-Universität, Münster, Germany
| | - Thomas Budde
- Institut für Physiologie I, Westfälische Wilhelms-Universität, Münster, Germany
| | - Hans-Christian Pape
- Institut für Physiologie I, Westfälische Wilhelms-Universität, Münster, Germany
| | - Philippe Coulon
- Institut für Physiologie I, Westfälische Wilhelms-Universität, Münster, Germany; Center For Integrative Brain Research, Seattle Children's Research Institute, Seattle, WA, USA.
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67
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Hristov KL, Smith AC, Parajuli SP, Malysz J, Rovner ES, Petkov GV. Novel regulatory mechanism in human urinary bladder: central role of transient receptor potential melastatin 4 channels in detrusor smooth muscle function. Am J Physiol Cell Physiol 2016; 310:C600-11. [PMID: 26791488 DOI: 10.1152/ajpcell.00270.2015] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 01/13/2016] [Indexed: 11/22/2022]
Abstract
Transient receptor potential melastatin 4 (TRPM4) channels are Ca(2+)-activated nonselective cation channels that have been recently identified as regulators of detrusor smooth muscle (DSM) function in rodents. However, their expression and function in human DSM remain unexplored. We provide insights into the functional role of TRPM4 channels in human DSM under physiological conditions. We used a multidisciplinary experimental approach, including RT-PCR, Western blotting, immunohistochemistry and immunocytochemistry, patch-clamp electrophysiology, and functional studies of DSM contractility. DSM samples were obtained from patients without preoperative overactive bladder symptoms. RT-PCR detected mRNA transcripts for TRPM4 channels in human DSM whole tissue and freshly isolated single cells. Western blotting and immunohistochemistry with confocal microscopy revealed TRPM4 protein expression in human DSM. Immunocytochemistry further detected TRPM4 protein expression in DSM single cells. Patch-clamp experiments showed that 9-phenanthrol, a selective TRPM4 channel inhibitor, significantly decreased the transient inward cation currents and voltage step-induced whole cell currents in freshly isolated human DSM cells. In current-clamp mode, 9-phenanthrol hyperpolarized the human DSM cell membrane potential. Furthermore, 9-phenanthrol attenuated the spontaneous phasic, carbachol-induced and nerve-evoked contractions in human DSM isolated strips. Significant species-related differences in TRPM4 channel activity between human, rat, and guinea pig DSM were revealed, suggesting a more prominent physiological role for the TRPM4 channel in the regulation of DSM function in humans than in rodents. In conclusion, TRPM4 channels regulate human DSM excitability and contractility and are critical determinants of human urinary bladder function. Thus, TRPM4 channels could represent promising novel targets for the pharmacological or genetic control of overactive bladder.
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Affiliation(s)
- Kiril L Hristov
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina; and
| | - Amy C Smith
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina; and
| | - Shankar P Parajuli
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina; and
| | - John Malysz
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina; and
| | - Eric S Rovner
- Medical University of South Carolina, Charleston, South Carolina
| | - Georgi V Petkov
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina; and Medical University of South Carolina, Charleston, South Carolina
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68
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Calcium Entry Through Thermosensory Channels. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 898:265-304. [PMID: 27161233 DOI: 10.1007/978-3-319-26974-0_12] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
ThermoTRPs are unique channels that mediate Na(+) and Ca(2+) currents in response to changes in ambient temperature. In combination with their activation by other physical and chemical stimuli, they are considered key integrators of environmental cues into neuronal excitability. Furthermore, roles of thermoTRPs in non-neuronal tissues are currently emerging such as insulin secretion in pancreatic β-cells, and links to cancer. Calcium permeability through thermoTRPs appears a central hallmark for their physiological and pathological activities. Moreover, it is currently being proposed that beyond working as a second messenger, Ca(2+) can function locally by acting on protein complexes near the membrane. Interestingly, thermoTRPs can enhance and expand the inherent plasticity of signalplexes by conferring them temperature, pH and lipid regulation through Ca(2+) signalling. Thus, unveiling the local role of Ca(2+) fluxes induced by thermoTRPs on the dynamics of membrane-attached signalling complexes as well as their significance in cellular processes, are central issues that will expand the opportunities for therapeutic intervention in disorders involving dysfunction of thermoTRP channels.
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TRPM4 protein expression in prostate cancer: a novel tissue biomarker associated with risk of biochemical recurrence following radical prostatectomy. Virchows Arch 2015; 468:345-55. [DOI: 10.1007/s00428-015-1880-y] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2015] [Revised: 10/20/2015] [Accepted: 11/10/2015] [Indexed: 11/25/2022]
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Flannery RJ, Kleene NK, Kleene SJ. A TRPM4-dependent current in murine renal primary cilia. Am J Physiol Renal Physiol 2015; 309:F697-707. [PMID: 26290373 PMCID: PMC4609916 DOI: 10.1152/ajprenal.00294.2015] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Accepted: 08/13/2015] [Indexed: 12/13/2022] Open
Abstract
Defects in primary cilia lead to a variety of human diseases. One of these, polycystic kidney disease, can be caused by defects in a Ca²⁺-gated ion channel (TRPP2) found on the cilium. Other ciliary functions also contribute to cystogenesis, and defects in apical Ca²⁺ homeostasis have been implicated. By recording directly from the native cilia of mIMCD-3 cells, a murine cell line of renal epithelial origin, we have identified a second Ca²⁺-gated channel in the ciliary membrane: the transient receptor potential cation channel, subfamily M, member 4 (TRPM4). In excised primary cilia, TRPM4 was found to have a low sensitivity to Ca²⁺, with an EC₅₀ of 646 μM at +100 mV. It was inhibited by MgATP and by 9-phenanthrol. The channel was not permeable to Ca²⁺ or Cl⁻ and had a permeability ratio PK/PNa of 1.42. Reducing the expression of Trpm4 mRNA with short hairpin (sh) RNA reduced the TRPM4 current by 87% and shortened primary cilia by 43%. When phospholipase C was inhibited, the sensitivity to cytoplasmic Ca²⁺ greatly increased (EC₅₀ = 26 μM at +100 mV), which is consistent with previous reports that phosphatidylinositol 4,5-bisphosphate (PIP2) modulates the channel. MgATP did not restore the channel to a preinactivation state, suggesting that the enzyme or substrate necessary for making PIP2 is not abundant in primary cilia of mIMCD-3 cells. The function of TRPM4 in renal primary cilia is not yet known, but it is likely to influence the apical Ca²⁺ dynamics of the cell, perhaps in tandem with TRPP2.
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Affiliation(s)
- Richard J Flannery
- Department of Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, Ohio
| | - Nancy K Kleene
- Department of Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, Ohio
| | - Steven J Kleene
- Department of Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, Ohio
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71
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Bencze M, Behuliak M, Vavřínová A, Zicha J. Broad-range TRP channel inhibitors (2-APB, flufenamic acid, SKF-96365) affect differently contraction of resistance and conduit femoral arteries of rat. Eur J Pharmacol 2015; 765:533-40. [PMID: 26384458 DOI: 10.1016/j.ejphar.2015.09.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Revised: 09/07/2015] [Accepted: 09/10/2015] [Indexed: 11/27/2022]
Abstract
Transient receptor potential (TRP) channels are proposed to contribute to membrane depolarization and Ca2+ influx into vascular smooth muscle (VSM) cells. Our aim was to study the effects of widely used broad-range TRP channel inhibitors--2-aminoethoxydiphenyl borate (2-APB), flufenamic acid (FFA) and SKF-96365--on the contraction of freshly isolated small and large arteries. Endothelium-denuded resistance (≈250 µm) and conduit (≈1000 µm) femoral arteries were isolated from adult Wistar rats and mounted in wire myograph. The effects of the above mentioned TRP channel inhibitors and voltage-dependent calcium channel inhibitor nifedipine were studied on arterial contractions induced by phenylephrine, U-46619 or K+. Phenylephrine-induced contractions were also studied in the absence of extracellular Na+. mRNA expression of particular canonical and melastatin TRP channel subunits in femoral vascular bed was determined. TRP channel inhibitors attenuated K+-induced contraction less than nifedipine. Phenylephrine-induced contraction was more influenced by 2-APB in resistance arteries, while FFA completely prevented U-46619-induced contraction in both sizes of arteries. The absence of extracellular Na+ prevented the inhibitory effects of 2-APB, but not those of FFA. The observed effects of broad-range TRP channel inhibitors, which were dependent on the size of the artery, confirmed the involvement of TRP channels in agonist-induced contractions. The inhibitory effects of 2-APB (but not those of FFA or SKF-96365) were dependent on the presence of extracellular Na+.
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Affiliation(s)
- Michal Bencze
- Department of Experimental Hypertension, Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic; Department of Physiology, Faculty of Science, Charles University, Prague, Czech Republic.
| | - Michal Behuliak
- Department of Experimental Hypertension, Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic
| | - Anna Vavřínová
- Department of Experimental Hypertension, Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic; Department of Physiology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Josef Zicha
- Department of Experimental Hypertension, Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic
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72
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Kadala A, Verdier D, Morquette P, Kolta A. Ion Homeostasis in Rhythmogenesis: The Interplay Between Neurons and Astroglia. Physiology (Bethesda) 2015; 30:371-88. [DOI: 10.1152/physiol.00023.2014] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Proper function of all excitable cells depends on ion homeostasis. Nowhere is this more critical than in the brain where the extracellular concentration of some ions determines neurons' firing pattern and ability to encode information. Several neuronal functions depend on the ability of neurons to change their firing pattern to a rhythmic bursting pattern, whereas, in some circuits, rhythmic firing is, on the contrary, associated to pathologies like epilepsy or Parkinson's disease. In this review, we focus on the four main ions known to fluctuate during rhythmic firing: calcium, potassium, sodium, and chloride. We discuss the synergistic interactions between these elements to promote an oscillatory activity. We also review evidence supporting an important role for astrocytes in the homeostasis of each of these ions and describe mechanisms by which astrocytes may regulate neuronal firing by altering their extracellular concentrations. A particular emphasis is put on the mechanisms underlying rhythmogenesis in the circuit forming the central pattern generator (CPG) for mastication and other CPG systems. Finally, we discuss how an impairment in the ability of glial cells to maintain such homeostasis may result in pathologies like epilepsy and Parkinson's disease.
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Affiliation(s)
- Aklesso Kadala
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada; and
| | - Dorly Verdier
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada; and
| | - Philippe Morquette
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada; and
| | - Arlette Kolta
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada; and
- Faculté de Médecine Dentaire and Réseau de Recherche en Santé Bucco-dentaire et Osseuse du Fonds de Recherche Québec-Santé, Université de Montréal, Montréal, Québec, Canada
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73
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Guinamard R, Bouvagnet P, Hof T, Liu H, Simard C, Sallé L. TRPM4 in cardiac electrical activity. Cardiovasc Res 2015; 108:21-30. [PMID: 26272755 DOI: 10.1093/cvr/cvv213] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Accepted: 07/31/2015] [Indexed: 11/12/2022] Open
Abstract
TRPM4 forms a non-selective cation channel activated by internal Ca(2+). Its functional expression was demonstrated in cardiomyocytes of several mammalian species including humans, but the channel is also present in many other tissues. The recent characterization of the TRPM4 inhibitor 9-phenanthrol, and the availability of transgenic mice have helped to clarify the role of TRPM4 in cardiac electrical activity, including diastolic depolarization from the sino-atrial node cells in mouse, rat, and rabbit, as well as action potential duration in mouse cardiomyocytes. In rat and mouse, pharmacological inhibition of TRPM4 prevents cardiac ischaemia-reperfusion injuries and decreases the occurrence of arrhythmias. Several studies have identified TRPM4 mutations in patients with inherited cardiac diseases including conduction blocks and Brugada syndrome. This review identifies TRPM4 as a significant actor in cardiac electrophysiology.
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Affiliation(s)
- Romain Guinamard
- Groupe Signalisation, Electrophysiologie et Imagerie des Lésions d'Ischémie-Reperfusion Myocardique, EA4650, Université de Caen Basse-Normandie, Sciences D, Esplanade de la Paix, CS 14032, 14032 Caen Cedex 5, France
| | | | - Thomas Hof
- Groupe Signalisation, Electrophysiologie et Imagerie des Lésions d'Ischémie-Reperfusion Myocardique, EA4650, Université de Caen Basse-Normandie, Sciences D, Esplanade de la Paix, CS 14032, 14032 Caen Cedex 5, France
| | - Hui Liu
- Department of Anatomy, Hainan Medical College, Haikou, Hainan 571101, China
| | - Christophe Simard
- Groupe Signalisation, Electrophysiologie et Imagerie des Lésions d'Ischémie-Reperfusion Myocardique, EA4650, Université de Caen Basse-Normandie, Sciences D, Esplanade de la Paix, CS 14032, 14032 Caen Cedex 5, France
| | - Laurent Sallé
- Groupe Signalisation, Electrophysiologie et Imagerie des Lésions d'Ischémie-Reperfusion Myocardique, EA4650, Université de Caen Basse-Normandie, Sciences D, Esplanade de la Paix, CS 14032, 14032 Caen Cedex 5, France
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Ronco V, Potenza DM, Denti F, Vullo S, Gagliano G, Tognolina M, Guerra G, Pinton P, Genazzani AA, Mapelli L, Lim D, Moccia F. A novel Ca²⁺-mediated cross-talk between endoplasmic reticulum and acidic organelles: implications for NAADP-dependent Ca²⁺ signalling. Cell Calcium 2015; 57:89-100. [PMID: 25655285 DOI: 10.1016/j.ceca.2015.01.001] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 01/01/2015] [Indexed: 12/31/2022]
Abstract
Nicotinic acid adenine dinucleotide phosphate (NAADP) serves as the ideal trigger of spatio-temporally complex intracellular Ca(2+) signals. However, the identity of the intracellular Ca(2+) store(s) recruited by NAADP, which may include either the endolysosomal (EL) or the endoplasmic reticulum (ER) Ca(2+) pools, is still elusive. Here, we show that the Ca(2+) response to NAADP was suppressed by interfering with either EL or ER Ca(2+) sequestration. The measurement of EL and ER Ca(2+) levels by using selectively targeted aequorin unveiled that the preventing ER Ca(2+) storage also affected ER Ca(2+) loading and vice versa. This indicates that a functional Ca(2+)-mediated cross-talk exists at the EL-ER interface and exerts profound implications for the study of NAADP-induced Ca(2+) signals. Extreme caution is warranted when dissecting NAADP targets by pharmacologically inhibiting EL and/or the ER Ca(2+) pools. Moreover, Ca(2+) transfer between these compartments might be essential to regulate vital Ca(2+)-dependent processes in both organelles.
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Affiliation(s)
- Virginia Ronco
- Department of Pharmaceutical Sciences, Università del Piemonte Orientale "Amedeo Avogadro", 28100 Novara, Italy
| | - Duilio Michele Potenza
- Laboratory of General Physiology, Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, 27100 Pavia, Italy
| | - Federico Denti
- Laboratory of General Physiology, Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, 27100 Pavia, Italy
| | - Sabrina Vullo
- Laboratory of General Physiology, Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, 27100 Pavia, Italy
| | - Giuseppe Gagliano
- Laboratory of General Physiology, Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, 27100 Pavia, Italy
| | - Marialuisa Tognolina
- Laboratory of Neurophysiology, Department of Brain and Behavioural Sciences, University of Pavia, 27100 Pavia, Italy
| | - Germano Guerra
- Department of Medicine and Health Sciences, University of Molise, 86100 Campobasso, Italy
| | - Paolo Pinton
- Department of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, 44121 Ferrara, ItalyfCentro Fermi, 00184 Roma, Italy
| | - Armando A Genazzani
- Department of Pharmaceutical Sciences, Università del Piemonte Orientale "Amedeo Avogadro", 28100 Novara, Italy
| | - Lisa Mapelli
- Laboratory of Neurophysiology, Department of Brain and Behavioural Sciences, University of Pavia, 27100 Pavia, Italy; Centro Fermi, 00184 Roma, Italy
| | - Dmitry Lim
- Department of Pharmaceutical Sciences, Università del Piemonte Orientale "Amedeo Avogadro", 28100 Novara, Italy.
| | - Francesco Moccia
- Laboratory of General Physiology, Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, 27100 Pavia, Italy.
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Yamaguchi S, Tanimoto A, Otsuguro KI, Hibino H, Ito S. Negatively charged amino acids near and in transient receptor potential (TRP) domain of TRPM4 channel are one determinant of its Ca2+ sensitivity. J Biol Chem 2014; 289:35265-82. [PMID: 25378404 DOI: 10.1074/jbc.m114.606087] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Transient receptor potential (TRP) channel melastatin subfamily member 4 (TRPM4) is a broadly expressed nonselective monovalent cation channel. TRPM4 is activated by membrane depolarization and intracellular Ca(2+), which is essential for the activation. The Ca(2+) sensitivity is known to be regulated by calmodulin and membrane phosphoinositides, such as phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2). Although these regulators must play important roles in controlling TRPM4 activity, mutation analyses of the calmodulin-binding sites have suggested that Ca(2+) binds to TRPM4 directly. However, the intrinsic binding sites in TRPM4 remain to be elucidated. Here, by using patch clamp and molecular biological techniques, we show that there are at least two functionally different divalent cation-binding sites, and the negatively charged amino acids near and in the TRP domain in the C-terminal tail of TRPM4 (Asp-1049 and Glu-1062 of rat TRPM4) are required for maintaining the normal Ca(2+) sensitivity of one of the binding sites. Applications of Co(2+), Mn(2+), or Ni(2+) to the cytosolic side potentiated TRPM4 currents, increased the Ca(2+) sensitivity, but were unable to evoke TRPM4 currents without Ca(2+). Mutations of the acidic amino acids near and in the TRP domain, which are conserved in TRPM2, TRPM5, and TRPM8, deteriorated the Ca(2+) sensitivity in the presence of Co(2+) or PI(4,5)P2 but hardly affected the sensitivity to Co(2+) and PI(4,5)P2. These results suggest a novel role of the TRP domain in TRPM4 as a site responsible for maintaining the normal Ca(2+) sensitivity. These findings provide more insights into the molecular mechanisms of the regulation of TRPM4 by Ca(2+).
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Affiliation(s)
- Soichiro Yamaguchi
- From the Laboratory of Pharmacology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Hokkaido, 060-0818 and the Department of Molecular Physiology, Niigata University School of Medicine, Niigata 951-8510, Japan
| | - Akira Tanimoto
- From the Laboratory of Pharmacology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Hokkaido, 060-0818 and
| | - Ken-ichi Otsuguro
- From the Laboratory of Pharmacology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Hokkaido, 060-0818 and
| | - Hiroshi Hibino
- the Department of Molecular Physiology, Niigata University School of Medicine, Niigata 951-8510, Japan
| | - Shigeo Ito
- From the Laboratory of Pharmacology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Hokkaido, 060-0818 and
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76
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Nilius B, Szallasi A. Transient Receptor Potential Channels as Drug Targets: From the Science of Basic Research to the Art of Medicine. Pharmacol Rev 2014; 66:676-814. [DOI: 10.1124/pr.113.008268] [Citation(s) in RCA: 348] [Impact Index Per Article: 34.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
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77
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Alvares TS, Revill AL, Huxtable AG, Lorenz CD, Funk GD. P2Y1 receptor-mediated potentiation of inspiratory motor output in neonatal rat in vitro. J Physiol 2014; 592:3089-111. [PMID: 24879869 DOI: 10.1113/jphysiol.2013.268136] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
PreBötzinger complex inspiratory rhythm-generating networks are excited by metabotropic purinergic receptor subtype 1 (P2Y1R) activation. Despite this, and the fact that inspiratory MNs express P2Y1Rs, the role of P2Y1Rs in modulating motor output is not known for any MN pool. We used rhythmically active brainstem-spinal cord and medullary slice preparations from neonatal rats to investigate the effects of P2Y1R signalling on inspiratory output of phrenic and XII MNs that innervate diaphragm and airway muscles, respectively. MRS2365 (P2Y1R agonist, 0.1 mm) potentiated XII inspiratory burst amplitude by 60 ± 9%; 10-fold higher concentrations potentiated C4 burst amplitude by 25 ± 7%. In whole-cell voltage-clamped XII MNs, MRS2365 evoked small inward currents and potentiated spontaneous EPSCs and inspiratory synaptic currents, but these effects were absent in TTX at resting membrane potential. Voltage ramps revealed a persistent inward current (PIC) that was attenuated by: flufenamic acid (FFA), a blocker of the Ca(2+)-dependent non-selective cation current ICAN; high intracellular concentrations of BAPTA, which buffers Ca(2+) increases necessary for activation of ICAN; and 9-phenanthrol, a selective blocker of TRPM4 channels (candidate for ICAN). Real-time PCR analysis of mRNA extracted from XII punches and laser-microdissected XII MNs revealed the transcript for TRPM4. MRS2365 potentiated the PIC and this potentiation was blocked by FFA, which also blocked the MRS2365 potentiation of glutamate currents. These data suggest that XII MNs are more sensitive to P2Y1R modulation than phrenic MNs and that the P2Y1R potentiation of inspiratory output occurs in part via potentiation of TRPM4-mediated ICAN, which amplifies inspiratory inputs.
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Affiliation(s)
- T S Alvares
- Department of Physiology, Centre for Neuroscience, Women and Children's Health Research Institute (WCHRI), Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - A L Revill
- Department of Physiology, Centre for Neuroscience, Women and Children's Health Research Institute (WCHRI), Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - A G Huxtable
- Department of Physiology, Centre for Neuroscience, Women and Children's Health Research Institute (WCHRI), Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - C D Lorenz
- Department of Physiology, Centre for Neuroscience, Women and Children's Health Research Institute (WCHRI), Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - G D Funk
- Department of Physiology, Centre for Neuroscience, Women and Children's Health Research Institute (WCHRI), Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
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78
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Sakuraba M, Murata J, Teruyama R, Kamiya K, Yamaguchi J, Okano H, Uchiyama Y, Ikeda K. Spatiotemporal expression of TRPM4 in the mouse cochlea. J Neurosci Res 2014; 92:1409-18. [PMID: 24840118 DOI: 10.1002/jnr.23410] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Revised: 02/26/2014] [Accepted: 04/14/2014] [Indexed: 11/11/2022]
Abstract
The present study was conducted to elucidate the presence of the transient receptor potential cation channel subfamily M member 4, TRPM4, in the mouse inner ear. TRPM4 immunoreactivity (IR) was found in the cell body of inner hair cells (IHCs) in the organ of Corti in the apical side of marginal cells of the stria vascularis, in the apical portion of the dark cells of the vestibule, and in a subset of the type II neurons in the spiral ganglion. Subsequently, changes in the distribution and expression of TRPM4 in the inner ear during embryonic and postnatal developments were also evaluated. Immunohistochemical localization demonstrated that the emergence of the TRPM4-IR in IHCs occurs shortly before the onset of hearing, whereas that in the marginal cells happens earlier, at the time of birth, coinciding with the onset of endolymph formation. Furthermore, semiquantitative real-time PCR assay showed that expressions of TRPM4 in the organ of Corti and in the stria vascularis increased dramatically at the onset of hearing. Because TRPM4 is a Ca(2+) -activated monovalent-selective cation channel, these findings imply that TRPM4 contributes to potassium ion transport, essential for the signal transduction in IHCs and the formation of endolymph by marginal cells.
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Affiliation(s)
- Mayumi Sakuraba
- Department of Otorhinolaryngology, Juntendo University Graduate School of Medicine, Tokyo, Japan
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79
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Guinamard R, Hof T, Del Negro CA. The TRPM4 channel inhibitor 9-phenanthrol. Br J Pharmacol 2014; 171:1600-13. [PMID: 24433510 PMCID: PMC3966741 DOI: 10.1111/bph.12582] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Revised: 12/17/2013] [Accepted: 01/08/2014] [Indexed: 01/06/2023] Open
Abstract
The phenanthrene-derivative 9-phenanthrol is a recently identified inhibitor of the transient receptor potential melastatin (TRPM) 4 channel, a Ca(2+) -activated non-selective cation channel whose mechanism of action remains to be determined. Subsequent studies performed on other ion channels confirm the specificity of the drug for TRPM4. In addition, 9-phenanthrol modulates a variety of physiological processes through TRPM4 current inhibition and thus exerts beneficial effects in several pathological conditions. 9-Phenanthrol modulates smooth muscle contraction in bladder and cerebral arteries, affects spontaneous activity in neurons and in the heart, and reduces lipopolysaccharide-induced cell death. Among promising potential applications, 9-phenanthrol exerts cardioprotective effects against ischaemia-reperfusion injuries and reduces ischaemic stroke injuries. In addition to reviewing the biophysical effects of 9-phenanthrol, here we present information about its appropriate use in physiological studies and possible clinical applications.
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Affiliation(s)
- R Guinamard
- EA 4650, Groupe Signalisation, Electrophysiologie et Imagerie des Lésions d'Ischémie-Reperfusion Myocardique, UCBN, Normandie UniversitéCaen, France
- Department of Applied Science, The College of William and MaryWilliamsburg, VA, USA
| | - T Hof
- EA 4650, Groupe Signalisation, Electrophysiologie et Imagerie des Lésions d'Ischémie-Reperfusion Myocardique, UCBN, Normandie UniversitéCaen, France
| | - C A Del Negro
- Department of Applied Science, The College of William and MaryWilliamsburg, VA, USA
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80
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Kang D, Wang J, Hogan JO, Vennekens R, Freichel M, White C, Kim D. Increase in cytosolic Ca2+ produced by hypoxia and other depolarizing stimuli activates a non-selective cation channel in chemoreceptor cells of rat carotid body. J Physiol 2014; 592:1975-92. [PMID: 24591572 DOI: 10.1113/jphysiol.2013.266957] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The current model of O2 sensing by carotid body chemoreceptor (glomus) cells is that hypoxia inhibits the outward K(+) current and causes cell depolarization, Ca(2+) influx via voltage-dependent Ca(2+) channels and a rise in intracellular [Ca(2+)] ([Ca(2+)]i). Here we show that hypoxia (<5% O2), in addition to inhibiting the two-pore domain K(+) channels TASK-1/3 (TASK), indirectly activates an ∼20 pS channel in isolated glomus cells. The 20 pS channel was permeable to K(+), Na(+) and Cs(+) but not to Cl(-) or Ca(2+). The 20 pS channel was not sensitive to voltage. Inhibition of TASK by external acid, depolarization of glomus cells with high external KCl (20 mm) or opening of the Ca(2+) channel with FPL64176 activated the 20 pS channel when 1 mm Ca(2+) was present in the external solution. Ca(2+) (10 μm) applied to the cytosolic side of inside-out patches activated the 20 pS channel. The threshold [Ca(2+)]i for activation of the 20 pS channel in cell-attached patches was ∼200 nm. The reversal potential of the 20 pS channel was estimated to be -28 mV. Our results reveal a sequential mechanism in which hypoxia (<5% O2) first inhibits the K(+) conductance and then activates a Na(+)-permeable, non-selective cation channel via depolarization-induced rise in [Ca(2+)]i. Our results suggest that inhibition of K(+) efflux and stimulation of Na(+) influx both contribute to the depolarization of glomus cells during moderate to severe hypoxia.
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Affiliation(s)
- Dawon Kang
- Department of Physiology and Biophysics, Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL 60064, USA.
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81
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Gees M, Alpizar YA, Luyten T, Parys JB, Nilius B, Bultynck G, Voets T, Talavera K. Differential Effects of Bitter Compounds on the Taste Transduction Channels TRPM5 and IP3 Receptor Type 3. Chem Senses 2014; 39:295-311. [DOI: 10.1093/chemse/bjt115] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
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82
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Abstract
TRPM5 is a Ca(2+)-activated cation channel that mediates signaling in taste and other chemosensory cells. Within taste cells, TRPM5 is the final element in a signaling cascade that starts with the activation of G protein-coupled receptors by bitter, sweet, or umami taste molecules and that requires the enzyme PLCβ2. PLCβ2 breaks down PIP2 into DAG and IP3, and the ensuing release of Ca(2+) from intracellular stores activates TRPM5. Since its initial discovery in the taste system, TRPM5 has been found to be distributed in sparse chemosensory cells located throughout the digestive track, in the respiratory system, and in the olfactory system. It is also found in pancreatic islets, where it contributes to insulin secretion. This review highlights recent work on the mechanisms of the activation of the TRPM5 channel and its regulation by voltage, phosphoinositides, temperature, and pH. The distribution of the channel in the body and its functional contribution to various sensory and nonsensory processes are discussed.
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Affiliation(s)
- Emily R Liman
- Section of Neurobiology, Department of Biological Sciences, University of Southern California, 3641 Watt Way, Los Angeles, CA, 90089, USA,
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83
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Abstract
TRPM4 is a Ca(2+)-activated nonselective cation channel. The channel is activated by an increase of intracellular Ca(2+) and is regulated by several factors including temperature and Pi(4,5)P2. TRPM4 allows Na(+) entry into the cell upon activation, but is completely impermeable to Ca(2+). Unlike TRPM5, its closest relative in the transient receptor potential family, TRPM4 proteins are widely expressed in the body. Currents with properties that are reminiscent of TRPM4 have been described in a variety of tissues since the advent of the patch clamp technology, but their physiological role is only beginning to be clarified with the increasing characterization of knockout mouse models for TRPM4. Furthermore, mutations in the TRPM4 gene have been associated with cardiac conduction disorders in human patients. This review aims to overview the currently available data on the functional properties of TRPM4 and the current understanding of its physiological role in healthy and diseased tissue.
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Affiliation(s)
- Ilka Mathar
- Laboratory of Ion Channel Research, Department of Cellular and Molecular Medicine, Katholieke Universiteit Leuven, Herestraat 49, bus 802, 3000, Leuven, Belgium
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84
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Nilius B, Flockerzi V. What do we really know and what do we need to know: some controversies, perspectives, and surprises. Handb Exp Pharmacol 2014; 223:1239-80. [PMID: 24961986 DOI: 10.1007/978-3-319-05161-1_20] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
TRP channels comprise one of the most rapid growing research topics in ion channel research, in fields related to ion channels including channelopathies and translational medicine. We provide here a critical survey on our current knowledge of TRP channels and highlight some of the still open or controversial questions. This comprises questions related to evolution of TRP channels; biophysics, i.e., permeation; pore properties and gating; modulation; the still-elusive 3D structure; and channel subunits but also their role as general sensory channels and in human diseases. We will conclude that our knowledge on TRP channels is still at the very beginning of an exciting research journey.
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Affiliation(s)
- Bernd Nilius
- Department Cell Mol Medicine, Laboratory Ion Channel Research, KU Leuven, Campus Gasthuisberg, O&N 1, Herestraat 49-Bus 802, 3000, Leuven, Belgium,
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85
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Expression, purification, and projection structure by single particle electron microscopy of functional human TRPM4 heterologously expressed in Xenopus laevis oocytes. Protein Expr Purif 2013; 95:169-76. [PMID: 24333049 DOI: 10.1016/j.pep.2013.11.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Revised: 11/28/2013] [Accepted: 11/30/2013] [Indexed: 01/23/2023]
Abstract
Despite efforts implicating the cationic channel transient receptor potential melastatin member 4 (TRPM4) to cardiac, nervous, and immunological pathologies, little is known about its structure and function. In this study, we optimized the requirements for purification and extraction of functional human TRPM4 protein and investigated its supra-molecular assembly. We selected the Xenopus laevis oocyte expression system because it lacks endogenous TRPM4 expression, it is known to overexpress functional human membrane channels, can be used for structure-function analysis within the same system, and is easily scaled to improve yield and develop moderate throughput capabilities through the use of robotics. Negative-stain electron microscopy (EM) revealed various sized low-resolution particles. Single particle analysis identified the majority of the projections represented the monomeric form with additional oligomeric structures potentially characterized as tetramers. Two-electrode voltage clamp electrophysiology demonstrated that human TRPM4 is functionally expressed at the oocyte plasma membrane. This study opens the door for medium-throughput screening and structure-function determination of this important therapeutically relevant target.
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86
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Gonzales AL, Earley S. Regulation of cerebral artery smooth muscle membrane potential by Ca²⁺-activated cation channels. Microcirculation 2013; 20:337-47. [PMID: 23116477 DOI: 10.1111/micc.12023] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Accepted: 10/26/2012] [Indexed: 12/24/2022]
Abstract
Arterial tone is dependent on the depolarizing and hyperpolarizing currents regulating membrane potential and governing the influx of Ca²⁺ needed for smooth muscle contraction. Several ion channels have been proposed to contribute to membrane depolarization, but the underlying molecular mechanisms are not fully understood. In this review, we will discuss the historical and physiological significance of the Ca²⁺-activated cation channel, TRPM4, in regulating membrane potential of cerebral artery smooth muscle cells. As a member of the recently described transient receptor potential super family of ion channels, TRPM4 possesses the biophysical properties and upstream cellular signaling and regulatory pathways that establish it as a major physiological player in smooth muscle membrane depolarization.
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Affiliation(s)
- Albert L Gonzales
- Vascular Physiology Research Group, Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA
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87
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Alexander SPH, Benson HE, Faccenda E, Pawson AJ, Sharman JL, Catterall WA, Spedding M, Peters JA, Harmar AJ. The Concise Guide to PHARMACOLOGY 2013/14: ion channels. Br J Pharmacol 2013; 170:1607-51. [PMID: 24528239 PMCID: PMC3892289 DOI: 10.1111/bph.12447] [Citation(s) in RCA: 224] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. Ion channels are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.
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Affiliation(s)
- Stephen PH Alexander
- School of Life Sciences, University of Nottingham Medical SchoolNottingham, NG7 2UH, UK
- *
Author for correspondence;
| | - Helen E Benson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Elena Faccenda
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Adam J Pawson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Joanna L Sharman
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - William A Catterall
- University of Washington, School of Medicine, Department of PharmacologyBox 357280, Seattle, WA 98195-7280, USA
| | | | - John A Peters
- Neuroscience Division, Medical Education Institute, Ninewells Hospital and Medical School, University of DundeeDundee, DD1 9SY, UK
| | - Anthony J Harmar
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
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88
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Woo SK, Kwon MS, Ivanov A, Geng Z, Gerzanich V, Simard JM. Complex N-glycosylation stabilizes surface expression of transient receptor potential melastatin 4b protein. J Biol Chem 2013; 288:36409-17. [PMID: 24214984 DOI: 10.1074/jbc.m113.530584] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
N-glycosylation is important for the function and regulation of ion channels. We examined the role of N-glycosylation of transient receptor potential melastatin (Trpm) 4b, a membrane glycoprotein that regulates calcium influx. Trpm4b was expressed in vivo in all rat tissues examined. In each tissue, Trpm4b had a different molecular mass, between ∼129 and ∼141 kDa, but all reverted to ∼120 kDa following treatment with peptide:N-glycosidase F, consistent with N-glycosylation being the principal form of post-translational modification of Trpm4b in vivo. In six stable isogenic cell lines that express different levels of Trpm4b, two forms were found, high mannose, core-glycosylated and complex, highly glycosylated (HG), with HG-Trpm4b comprising 85% of the total Trpm4b expressed. For both forms, surface expression was directly proportional to the total Trpm4b expressed. Complex N-glycosylation doubled the percentage of Trpm4b at the surface, compared with high mannose N-glycosylation. Mutation of the single N-glycosylation consensus sequence at Asn-988 (Trpm4b-N988Q), located near the pore-forming loop between transmembrane helices 5 and 6, prevented glycosylation, but did not prevent surface expression, impair formation of functional membrane channels, or alter channel conductance. In transfection experiments, the time courses for appearance of HG-Trpm4b and Trpm4b-N988Q on the surface were similar. In experiments with cycloheximide inhibition of protein synthesis, the time course for disappearance of HG-Trpm4b from the surface was much slower than that for Trpm4b-N988Q. We conclude that N-glycosylation is not required for surface expression or channel function, but that complex N-glycosylation plays a crucial role in stabilizing surface expression of Trpm4b.
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89
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Abstract
TRP channels constitute a large superfamily of cation channel forming proteins, all related to the gene product of the transient receptor potential (trp) locus in Drosophila. In mammals, 28 different TRP channel genes have been identified, which exhibit a large variety of functional properties and play diverse cellular and physiological roles. In this article, we provide a brief and systematic summary of expression, function, and (patho)physiological role of the mammalian TRP channels.
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Affiliation(s)
- Maarten Gees
- Laboratory Ion Channel Research and TRP Research Platform Leuven (TRPLe), KU Leuven, Campus Gasthuisberg, Leuven, Belgium
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90
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Parajuli SP, Hristov KL, Sullivan MN, Xin W, Smith AC, Earley S, Malysz J, Petkov GV. Control of urinary bladder smooth muscle excitability by the TRPM4 channel modulator 9-phenanthrol. Channels (Austin) 2013; 7:537-40. [PMID: 24037125 DOI: 10.4161/chan.26289] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The Ca (2+)-activated monovalent cation selective transient receptor potential melastatin 4 (TRPM4) channel has been recently identified in detrusor smooth muscle (DSM) of the urinary bladder. Two recent publications by our research group provide evidence in support of the novel hypothesis that TRPM4 channels enhance DSM excitability and contractility. This is a critical question as prior studies have primarily targeted hyperpolarizing currents facilitated by K(+) channels, but the depolarizing component in DSM cells is not well understood. For the first time, we utilized the selective TRPM4 channel inhibitor, 9-phenanthrol, to investigate TRPM4 channel functional effects in DSM at both cellular and tissue levels in rodents. Our new data presented here showed that in rat DSM cells, 9-phenanthrol attenuates spontaneous inward currents in the presence of the muscarinic receptor agonist, carbachol, thus reducing DSM cell excitability. In support of our original hypothesis, we found that TRPM4 channel mRNA levels are much higher in DSM vs. vascular smooth muscle and that inhibition of TRPM4 channels can potentially attenuate DSM excitability. Thus, we postulate the novel concept that selective pharmacological inhibition of TRPM4 channels can limit both excitability and contractility of DSM.
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Affiliation(s)
- Shankar P Parajuli
- Department of Drug Discovery and Biomedical Sciences; South Carolina College of Pharmacy; University of South Carolina; Columbia, SC USA
| | - Kiril L Hristov
- Department of Drug Discovery and Biomedical Sciences; South Carolina College of Pharmacy; University of South Carolina; Columbia, SC USA
| | - Michelle N Sullivan
- Vascular Physiology Research Group; Department of Biomedical Sciences; Colorado State University; Fort Collins, CO USA
| | - Wenkuan Xin
- Department of Drug Discovery and Biomedical Sciences; South Carolina College of Pharmacy; University of South Carolina; Columbia, SC USA
| | - Amy C Smith
- Department of Drug Discovery and Biomedical Sciences; South Carolina College of Pharmacy; University of South Carolina; Columbia, SC USA
| | - Scott Earley
- Vascular Physiology Research Group; Department of Biomedical Sciences; Colorado State University; Fort Collins, CO USA
| | - John Malysz
- Department of Drug Discovery and Biomedical Sciences; South Carolina College of Pharmacy; University of South Carolina; Columbia, SC USA
| | - Georgi V Petkov
- Department of Drug Discovery and Biomedical Sciences; South Carolina College of Pharmacy; University of South Carolina; Columbia, SC USA
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91
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Son SJ, Filosa JA, Potapenko ES, Biancardi VC, Zheng H, Patel KP, Tobin VA, Ludwig M, Stern JE. Dendritic peptide release mediates interpopulation crosstalk between neurosecretory and preautonomic networks. Neuron 2013; 78:1036-49. [PMID: 23791197 DOI: 10.1016/j.neuron.2013.04.025] [Citation(s) in RCA: 116] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/17/2013] [Indexed: 01/08/2023]
Abstract
Although communication between neurons is considered a function of the synapse, neurons also release neurotransmitter from their dendrites. We found that dendritic transmitter release coordinates activity across distinct neuronal populations to generate integrative homeostatic responses. We show that activity-dependent vasopressin release from hypothalamic neuroendocrine neurons in the paraventricular nucleus stimulates neighboring (~100 μm soma-to-soma) presympathetic neurons, resulting in a sympathoexcitatory population response. This interpopulation crosstalk was engaged by an NMDA-mediated increase in dendritic Ca(2+), influenced by vasopressin's ability to diffuse in the extracellular space, and involved activation of CAN channels at the target neurons. Furthermore, we demonstrate that this interpopulation crosstalk plays a pivotal role in the generation of a systemic, polymodal neurohumoral response to a hyperosmotic challenge. Because dendritic release is emerging as a widespread process, our results suggest that a similar mechanism could mediate interpopulation crosstalk in other brain systems, particularly those involved in generating complex behaviors.
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Affiliation(s)
- Sook Jin Son
- Department of Physiology, Georgia Regents University, Augusta, GA 30912, USA
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92
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Burt R, Graves BM, Gao M, Li C, Williams DL, Fregoso SP, Hoover DB, Li Y, Wright GL, Wondergem R. 9-Phenanthrol and flufenamic acid inhibit calcium oscillations in HL-1 mouse cardiomyocytes. Cell Calcium 2013; 54:193-201. [PMID: 23831210 DOI: 10.1016/j.ceca.2013.06.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Revised: 05/27/2013] [Accepted: 06/09/2013] [Indexed: 11/17/2022]
Abstract
It is well established that intracellular calcium ([Ca2+]i) controls the inotropic state of the myocardium, and evidence mounts that a "Ca2+ clock" controls the chronotropic state of the heart. Recent findings describe a calcium-activated nonselective cation channel (NSCCa) in various cardiac preparations sharing hallmark characteristics of the transient receptor potential melastatin 4 (TRPM4). TRPM4 is functionally expressed throughout the heart and has been implicated as a NSCCa that mediates membrane depolarization. However, the functional significance of TRPM4 in regards to Ca2+ signaling and its effects on cellular excitability and pacemaker function remains inconclusive. Here, we show by Fura2 Ca-imaging that pharmacological inhibition of TRPM4 in HL-1 mouse cardiac myocytes by 9-phenanthrol (10 μM) and flufenamic acid (10 and 100 μM) decreases Ca2+ oscillations followed by an overall increase in [Ca2+]i. The latter occurs also in HL-1 cells in Ca(2+)-free solution and after depletion of sarcoplasmic reticulum Ca2+ with thapsigargin (10 μM). These pharmacologic agents also depolarize HL-1 cell mitochondrial membrane potential. Furthermore, by on-cell voltage clamp we show that 9-phenanthrol reversibly inhibits membrane current; by fluorescence immunohistochemistry we demonstrate that HL-1 cells display punctate surface labeling with TRPM4 antibody; and by immunoblotting using this antibody we show these cells express a 130-150 kDa protein, as expected for TRPM4. We conclude that 9-phenanthrol inhibits TRPM4 ion channels in HL-1 cells, which in turn decreases Ca2+ oscillations followed by a compensatory increase in [Ca2+]i from an intracellular store other than the sarcoplasmic reticulum. We speculate that the most likely source is the mitochondrion.
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Affiliation(s)
- Rees Burt
- Department of Biomedical Sciences, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614, USA
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93
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Nelson P, Ngoc Tran TD, Zhang H, Zolochevska O, Figueiredo M, Feng JM, Gutierrez DL, Xiao R, Yao S, Penn A, Yang LJ, Cheng H. Transient receptor potential melastatin 4 channel controls calcium signals and dental follicle stem cell differentiation. Stem Cells 2013; 31:167-77. [PMID: 23081848 DOI: 10.1002/stem.1264] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2012] [Accepted: 10/04/2012] [Indexed: 11/11/2022]
Abstract
Elevations in the intracellular Ca(2+) concentration are a phenomena commonly observed during stem cell differentiation but cease after the process is complete. The transient receptor potential melastatin 4 (TRPM4) is an ion channel that controls Ca(2+) signals in excitable and nonexcitable cells. However, its role in stem cells remains unknown. The aim of this study was to characterize TRPM4 in rat dental follicle stem cells (DFSCs) and to determine its impact on Ca(2+) signaling and the differentiation process. We identified TRPM4 gene expression in DFSCs, but not TRPM5, a closely related channel with similar function. Perfusion of cells with increasing buffered Ca(2+) resulted in a concentration-dependent activation of currents typical for TRPM4, which were also voltage-dependent and had Na(+) conductivity. Molecular suppression with shRNA decreased channel activity and cell proliferation during osteogenesis but not adipogenesis. As a result, enhanced mineralization and phosphatase enzyme activity were observed during osteoblast formation, although DFSCs failed to differentiate into adipocytes. Furthermore, the normal agonist-induced first and secondary phases of Ca(2+) signals were transformed into a gradual and sustained increase which confirmed the channels' ability to control Ca(2+) signaling. Using whole genome microarray analysis, we identified several genes impacted by TRPM4 during DFSC differentiation. These findings suggest an inhibitory role for TRPM4 on osteogenesis while it appears to be required for adipogenesis. The data also provide a potential link between the Ca(2+) signaling pattern and gene expression during stem cell differentiation.
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Affiliation(s)
- Piper Nelson
- Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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94
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Biochemical, single-channel, whole-cell patch clamp, and pharmacological analyses of endogenous TRPM4 channels in HEK293 cells. Neurosci Lett 2013; 541:105-10. [DOI: 10.1016/j.neulet.2013.02.011] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2012] [Revised: 12/15/2012] [Accepted: 02/03/2013] [Indexed: 01/24/2023]
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95
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Chen GL, Zeng B, Eastmond S, Elsenussi SE, Boa AN, Xu SZ. Pharmacological comparison of novel synthetic fenamate analogues with econazole and 2-APB on the inhibition of TRPM2 channels. Br J Pharmacol 2013; 167:1232-43. [PMID: 22646516 DOI: 10.1111/j.1476-5381.2012.02058.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND AND PURPOSE Fenamate analogues, econazole and 2-aminoethoxydiphenyl borate (2-APB) are inhibitors of transient receptor potential melastatin 2 (TRPM2) channels and are used as research tools. However, these compounds have different chemical structures and therapeutic applications. Here we have investigated the pharmacological profile of TRPM2 channels by application of newly synthesized fenamate analogues and the existing channel blockers. EXPERIMENTAL APPROACH Human TRPM2 channels in tetracycline-regulated pcDNA4/TO vectors were transfected into HEK293 T-REx cells and the expression was induced by tetracycline. Whole cell currents were recorded by patch-clamp techniques. Ca(2+) influx or release was monitored by fluorometry. KEY RESULTS Flufenamic acid (FFA), mefenamic acid (MFA) and niflumic acid (NFA) concentration-dependently inhibited TRPM2 current with potency order FFA > MFA = NFA. Modification of the 2-phenylamino ring by substitution of the trifluoromethyl group in FFA with -CH(3), -F, -CF(3), -OCH(3), -OCH(2)CH(3), -COOH, and -NO(2) at various positions, reduced channel blocking potency. The conservative substitution of 3-CF(3) in FFA by -CH(3) (3-MFA), however, gave the most potent fenamate analogue with an IC(50) of 76 µM, comparable to that of FFA, but unlike FFA, had no effect on Ca(2+) release. 3-MFA and FFA inhibited the channel intracellularly. Econazole and 2-APB showed non-selectivity by altering cytosolic Ca(2+) movement. Econazole also evoked a non-selective current. CONCLUSION AND IMPLICATIONS The fenamate analogue 3-MFA was more selective than other TRPM2 channel blockers. FFA, 2-APB and econazole should be used with caution as TRPM2 channel blockers, as these compounds can interfere with intracellular Ca(2+) movement.
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Affiliation(s)
- Gui-Lan Chen
- Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, UK
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96
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TRPM4 channels in smooth muscle function. Pflugers Arch 2013; 465:1223-31. [PMID: 23443854 DOI: 10.1007/s00424-013-1250-z] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Revised: 02/08/2013] [Accepted: 02/09/2013] [Indexed: 01/03/2023]
Abstract
The melastatin (M) transient receptor potential (TRP) channel TRPM4 is selective for monovalent cations and is activated by high levels of intracellular Ca(2+). TRPM4 is broadly distributed and may be involved in numerous functions, including electrical conduction in the heart, respiratory rhythm, immune response, and secretion of insulin by pancreatic β-cells. The significance of TRPM4 in smooth muscle cell function is reviewed here. Several studies indicate that TRPM4 channels are critically important for pressure-induced cerebral arterial myocyte depolarization and myogenic vasoconstriction as well as autoregulation of cerebral blood flow. Regulation of TRPM4 activity in arterial smooth muscle cells is complex and involves release of Ca(2+) from the sarcoplasmic reticulum through inositol 1,4,5-trisphosphate receptors and translocation of TRPM4 channels to the plasma membrane in response to protein kinase Cδ. TRPM4 is also present in colonic, urinary bladder, aortic, interlobar pulmonary and renal artery, airway, and corpus cavernosum smooth muscle cells, but its significance and regulation in these tissues is less well characterized.
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97
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The TRPM4 non-selective cation channel contributes to the mammalian atrial action potential. J Mol Cell Cardiol 2013; 59:11-9. [PMID: 23416167 DOI: 10.1016/j.yjmcc.2013.01.019] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Revised: 01/15/2013] [Accepted: 01/28/2013] [Indexed: 01/21/2023]
Abstract
The TRPM4 calcium-activated non-selective monovalent cation channel has been reported in mammalian atrial cardiomyocytes, but its implication in this tissue remains unknown. We used a combination of pharmacological tools and disruption of the Trpm4 gene in mice to investigate the channel implication in atrial action potential (AP). To search for TRPM4 activity, single channel currents were recorded on freshly isolated atrial cardiomyocytes using the patch-clamp technique. To investigate TRPM4 implication in AP, the transmembrane potential was recorded on the multicellular preparation using intracellular microelectrodes after isolating the mouse atrium, under electrical stimulation (rate=5Hz). Isolated atrial cardiomyocytes from the Trpm4(+/+) mouse expressed a typical TRPM4 current while cardiomyocytes from Trpm4(-/-) mouse did not. The Trpm4(+/+) mouse atrium exhibited AP durations at 50, 70 and 90% repolarization of 8.9±0.5ms, 16.0±1.0ms, and 30.2±1.6ms, respectively. The non-selective cation channel inhibitor flufenamic acid (10(-6) and 10(-5)mol·L(-1)) produced a concentration-dependent decrease in AP duration. Similarly, the TRPM4-inhibitor 9-phenanthrol reversibly reduced the duration of AP with an EC50 at 21×10(-6)mol·L(-1), which is similar to that reported for TRPM4 current inhibition in HEK-293 cells. 9-Phenanthrol had no effect on other AP parameters. The effect of 9-phenanthrol is markedly reduced in the mouse ventricle, which displays only weak expression of the channel. Moreover, atria from Trpm4(-/-) mice exhibited an AP that was 20% shorter than that of atria from littermate control mice, and the effect of 9-phenanthrol on AP was abolished in the Trpm4(-/-) mice. Our results showed that TRPM4 is implicated in the waveform of the atrial action potential. It is thus a potential target for pharmacological approaches against atrial arrhythmias.
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98
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Guinamard R, Simard C, Del Negro C. Flufenamic acid as an ion channel modulator. Pharmacol Ther 2013; 138:272-84. [PMID: 23356979 DOI: 10.1016/j.pharmthera.2013.01.012] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2012] [Accepted: 12/26/2012] [Indexed: 12/29/2022]
Abstract
Flufenamic acid has been known since the 1960s to have anti-inflammatory properties attributable to the reduction of prostaglandin synthesis. Thirty years later, flufenamic acid appeared to be an ion channel modulator. Thus, while its use in medicine diminished, its use in ionic channel research expanded. Flufenamic acid commonly not only affects non-selective cation channels and chloride channels, but also modulates potassium, calcium and sodium channels with effective concentrations ranging from 10(-6)M in TRPM4 channel inhibition to 10(-3)M in two-pore outwardly rectifying potassium channel activation. Because flufenamic acid effects develop and reverse rapidly, it is a convenient and widely used tool. However, given the broad spectrum of its targets, experimental results have to be interpreted cautiously. Here we provide an overview of ion channels targeted by flufenamic acid to aid in interpreting its effects at the molecular, cellular, and system levels. If it is used with good practices, flufenamic acid remains a useful tool for ion channel research. Understanding the targets of FFA may help reevaluate its physiological impacts and revive interest in its therapeutic potential.
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99
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Smith AC, Hristov KL, Cheng Q, Xin W, Parajuli SP, Earley S, Malysz J, Petkov GV. Novel role for the transient potential receptor melastatin 4 channel in guinea pig detrusor smooth muscle physiology. Am J Physiol Cell Physiol 2013; 304:C467-77. [PMID: 23302778 DOI: 10.1152/ajpcell.00169.2012] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Members of the transient receptor potential (TRP) channel superfamily, including the Ca(2+)-activated monovalent cation-selective TRP melastatin 4 (TRPM4) channel, have been recently identified in the urinary bladder. However, their expression and function at the level of detrusor smooth muscle (DSM) remain largely unexplored. In this study, for the first time we investigated the role of TRPM4 channels in guinea pig DSM excitation-contraction coupling using a multidisciplinary approach encompassing protein detection, electrophysiology, live-cell Ca(2+) imaging, DSM contractility, and 9-phenanthrol, a recently characterized selective inhibitor of the TRPM4 channel. Western blot and immunocytochemistry experiments demonstrated the expression of the TRPM4 channel in whole DSM tissue and freshly isolated DSM cells with specific localization on the plasma membrane. Perforated whole cell patch-clamp recordings and real-time Ca(2+) imaging experiments with fura 2-AM, both using freshly isolated DSM cells, revealed that 9-phenanthrol (30 μM) significantly reduced the cation current and decreased intracellular Ca(2+) levels. 9-Phenanthrol (0.1-30 μM) significantly inhibited spontaneous, 0.1 μM carbachol-induced, 20 mM KCl-induced, and nerve-evoked contractions in guinea pig DSM-isolated strips with IC50 values of 1-7 μM and 70-80% maximum inhibition. 9-Phenanthrol also reduced nerve-evoked contraction amplitude induced by continuous repetitive electrical field stimulation of 10-Hz frequency and shifted the frequency-response curve (0.5-50 Hz) relative to the control. Collectively, our data demonstrate the novel finding that TRPM4 channels are expressed in guinea pig DSM and reveal their critical role in the regulation of guinea pig DSM excitation-contraction coupling.
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Affiliation(s)
- Amy C Smith
- Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208, USA
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100
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Yang H, Kim A, David T, Palmer D, Jin T, Tien J, Huang F, Cheng T, Coughlin SR, Jan YN, Jan LY. TMEM16F forms a Ca2+-activated cation channel required for lipid scrambling in platelets during blood coagulation. Cell 2012; 151:111-22. [PMID: 23021219 DOI: 10.1016/j.cell.2012.07.036] [Citation(s) in RCA: 335] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Revised: 06/12/2012] [Accepted: 07/05/2012] [Indexed: 01/15/2023]
Abstract
Collapse of membrane lipid asymmetry is a hallmark of blood coagulation. TMEM16F of the TMEM16 family that includes TMEM16A/B Ca(2+)-activated Cl(-) channels (CaCCs) is linked to Scott syndrome with deficient Ca(2+)-dependent lipid scrambling. We generated TMEM16F knockout mice that exhibit bleeding defects and protection in an arterial thrombosis model associated with platelet deficiency in Ca(2+)-dependent phosphatidylserine exposure and procoagulant activity and lack a Ca(2+)-activated cation current in the platelet precursor megakaryocytes. Heterologous expression of TMEM16F generates a small-conductance Ca(2+)-activated nonselective cation (SCAN) current with subpicosiemens single-channel conductance rather than a CaCC. TMEM16F-SCAN channels permeate both monovalent and divalent cations, including Ca(2+), and exhibit synergistic gating by Ca(2+) and voltage. We further pinpointed a residue in the putative pore region important for the cation versus anion selectivity of TMEM16F-SCAN and TMEM16A-CaCC channels. This study thus identifies a Ca(2+)-activated channel permeable to Ca(2+) and critical for Ca(2+)-dependent scramblase activity during blood coagulation. PAPERFLICK:
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Affiliation(s)
- Huanghe Yang
- Department of Physiology, Howard Hughes Medical Institute, University of California, San Francisco, 94143, USA
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