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Yartsev VN. Effects of Nephrectomy on the Electrical Field Stimulation-Evoked Changes in Tone of Arteries from the Normotensive and Spontaneously Hypertensive Rats. J EVOL BIOCHEM PHYS+ 2022. [DOI: 10.1134/s0022093022050301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Mijares A, Allen PD, Lopez JR. Senescence Is Associated With Elevated Intracellular Resting [Ca 2 +] in Mice Skeletal Muscle Fibers. An in vivo Study. Front Physiol 2021; 11:601189. [PMID: 33510646 PMCID: PMC7837333 DOI: 10.3389/fphys.2020.601189] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 11/23/2020] [Indexed: 11/13/2022] Open
Abstract
Aging causes skeletal muscles to become atrophied, weak, and easily fatigued. Here, we have tested the hypothesis that normal aging in skeletal muscle cells is associated with Ca2+ intracellular dyshomeostasis and oxidative stress. Intracellular Ca2+ concentration ([Ca2+]i), resting intracellular Na+ concentration ([Na+]i) and reactive oxygen species (ROS) production were measured in vivo (superficial gastrocnemius fibers) using double-barreled ion-selective microelectrodes, and in vitro [isolated single flexor digitorum brevis fibers] using fluorescent ROS sensor CM-H2DCFDA in young (3 months of age), middle-aged (12 months of age), and aged (24 months of age) mice. We found an age-related increase in [Ca2+]i from 121 ± 4 nM in young muscle cells which rose to 255 ± 36 nM in middle-aged and to 409 ± 25 nM in aged cells. [Na+]i also showed an age-dependent elevation, increasing from 8 ± 0.5 mM in young muscle fibers, to 12 ± 1 mM in middle-aged and to 17 ± 1 mM in old muscle fibers. Using the fluorescent ROS sensor CM-H2DCFDA we found that these increases in intracellular cation concentrations were associated with significantly increased basal ROS production as demonstrated by age related increases in the rate of dichlorodihydrofluorescein fluorescence. To determine is this could be modified by reducing ROS and/or blocking sarcolemmal Ca2+ influx we administered flufenamic acid (FFA), a non-steroidal anti-inflammatory drug which is also a non-selective blocker of the transient receptor potential canonical channels (TRPCs), for 4 weeks to determine if this would have a beneficial effect. FFA treatment reduced both basal ROS production and muscle [Ca2+]i and [Na+]i in middle-aged and aged muscle fibers compared to fibers and muscles of untreated 12 and 24-months old mice. [Ca2+]i was reduced to 134 ± 8 nM in middle-aged muscle and to 246 ± 40 nM in muscle from aged mice. Likewise [Na+]i was reduced to 9 ± 0.7 mM in middle-aged muscles and to 13 ± 1 mM in muscle from aged mice. FFA treatment also reduced age associated increases in plasma interleukin 6 and tumor necrosis factor-alpha (TNF-α) concentrations which were elevated in 12 and 24-months old mice compared to young mice and decreased age-related muscle damage as indicated by a reduction in serum creatine kinase (CK) activity. Our data provides a direct demonstration that normal aging is associated with a significant elevation [Ca2+]i, [Na+]i, and intracellular ROS production in skeletal muscle fibers. Furthermore, the fact that FFA reduced the intracellular [Ca2+], [Na+], and ROS production as well as the elevated IL6, TNF-α, and CK levels, led us to suggest that its pharmacological effect may be related to its action both as a TRPC channel blocker and as an anti-inflammatory.
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Affiliation(s)
- Alfredo Mijares
- Centro de Biofísica y Bioquímica, Instituto Venezolano de Investigaciones Científicas, Caracas, Venezuela
| | - Paul D Allen
- Malignant Hyperthermia Investigation Unit, St James' University Hospital, University of Leeds, Leeds, United Kingdom
| | - Jose R Lopez
- Department of Research, Mount Sinai Medical Center, Miami, FL, United states
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Sato-Numata K, Numata T, Ueta Y, Okada Y. Expression and functions of N-type Cav2.2 and T-type Cav3.1 channels in rat vasopressin neurons under normotonic conditions. J Physiol Sci 2020; 70:49. [PMID: 33059597 PMCID: PMC10717235 DOI: 10.1186/s12576-020-00775-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Accepted: 09/28/2020] [Indexed: 11/10/2022]
Abstract
Arginine vasopressin (AVP) neurons play essential roles in sensing the change in systemic osmolarity and regulating AVP release from their neuronal terminals to maintain the plasma osmolarity. AVP exocytosis depends on the Ca2+ entry via voltage-gated Ca2+ channels (VGCCs) in AVP neurons. In this study, suppression by siRNA-mediated knockdown and pharmacological sensitivity of VGCC currents evidenced molecular and functional expression of N-type Cav2.2 and T-type Cav3.1 in AVP neurons under normotonic conditions. Also, both the Cav2.2 and Cav3.1 currents were found to be sensitive to flufenamic acid (FFA). TTX-insensitive spontaneous action potentials were suppressed by FFA and T-type VGCC blocker Ni2+. However, Cav2.2-selective ω-conotoxin GVIA failed to suppress the firing activity. Taken together, it is concluded that Cav2.2 and Cav3.1 are molecularly and functionally expressed and both are sensitive to FFA in unstimulated rat AVP neurons. Also, it is suggested that Cav3.1 is primarily involved in their action potential generation.
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Affiliation(s)
- Kaori Sato-Numata
- Japan Society for the Promotion of Science, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo, 102-0083, Japan
- Department of Physiology, School of Medicine, Fukuoka University, 7-45-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan
| | - Tomohiro Numata
- Department of Physiology, School of Medicine, Fukuoka University, 7-45-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan
| | - Yoichi Ueta
- Department of Physiology, School of Medicine, University of Occupational and Environmental Health, 1-1, Iseigaoka, Yahatanishi-ku, Kitakyushu-shi, Fukuoka, 807-8555, Japan
| | - Yasunobu Okada
- National Institute for Physiological Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi, 444-8787, Japan.
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Jean P, Anttonen T, Michanski S, de Diego AMG, Steyer AM, Neef A, Oestreicher D, Kroll J, Nardis C, Pangršič T, Möbius W, Ashmore J, Wichmann C, Moser T. Macromolecular and electrical coupling between inner hair cells in the rodent cochlea. Nat Commun 2020; 11:3208. [PMID: 32587250 PMCID: PMC7316811 DOI: 10.1038/s41467-020-17003-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 05/30/2020] [Indexed: 11/10/2022] Open
Abstract
Inner hair cells (IHCs) are the primary receptors for hearing. They are housed in the cochlea and convey sound information to the brain via synapses with the auditory nerve. IHCs have been thought to be electrically and metabolically independent from each other. We report that, upon developmental maturation, in mice 30% of the IHCs are electrochemically coupled in 'mini-syncytia'. This coupling permits transfer of fluorescently-labeled metabolites and macromolecular tracers. The membrane capacitance, Ca2+-current, and resting current increase with the number of dye-coupled IHCs. Dual voltage-clamp experiments substantiate low resistance electrical coupling. Pharmacology and tracer permeability rule out coupling by gap junctions and purinoceptors. 3D electron microscopy indicates instead that IHCs are coupled by membrane fusion sites. Consequently, depolarization of one IHC triggers presynaptic Ca2+-influx at active zones in the entire mini-syncytium. Based on our findings and modeling, we propose that IHC-mini-syncytia enhance sensitivity and reliability of cochlear sound encoding.
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Affiliation(s)
- Philippe Jean
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany
- Collaborative Research Center 889, University of Göttingen, Göttingen, Germany
- Auditory Neuroscience Group, Max Planck Institute of Experimental Medicine, Göttingen, Germany
- Göttingen Graduate School for Neurosciences and Molecular Biosciences, University of Göttingen, Göttingen, Germany
| | - Tommi Anttonen
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany
- Collaborative Research Center 889, University of Göttingen, Göttingen, Germany
- Synaptic Nanophysiology Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany
| | - Susann Michanski
- Collaborative Research Center 889, University of Göttingen, Göttingen, Germany
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany
- Center for Biostructural Imaging of Neurodegeneration, Göttingen, Germany
| | - Antonio M G de Diego
- UCL Ear Institute and Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK
| | - Anna M Steyer
- Electron Microscopy Core Unit, Department of Neurogenetics, Max Planck Institute of Experimental Medicine, Göttingen, Germany
- Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University of Göttingen, Göttingen, Germany
| | - Andreas Neef
- Neurophysics laboratory, Campus Institute for Dynamics of Biological Networks, University of Göttingen, Göttingen, Germany
| | - David Oestreicher
- Experimental Otology Group, Institute for Auditory Neuroscience, InnerEarLab, and Department of Otolaryngology, University Medical Center Göttingen, Göttingen, Germany
| | - Jana Kroll
- Collaborative Research Center 889, University of Göttingen, Göttingen, Germany
- Göttingen Graduate School for Neurosciences and Molecular Biosciences, University of Göttingen, Göttingen, Germany
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany
- Center for Biostructural Imaging of Neurodegeneration, Göttingen, Germany
| | - Christos Nardis
- Electron Microscopy Core Unit, Department of Neurogenetics, Max Planck Institute of Experimental Medicine, Göttingen, Germany
- Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University of Göttingen, Göttingen, Germany
| | - Tina Pangršič
- Collaborative Research Center 889, University of Göttingen, Göttingen, Germany
- Experimental Otology Group, Institute for Auditory Neuroscience, InnerEarLab, and Department of Otolaryngology, University Medical Center Göttingen, Göttingen, Germany
| | - Wiebke Möbius
- Electron Microscopy Core Unit, Department of Neurogenetics, Max Planck Institute of Experimental Medicine, Göttingen, Germany
- Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University of Göttingen, Göttingen, Germany
| | - Jonathan Ashmore
- UCL Ear Institute and Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK
| | - Carolin Wichmann
- Collaborative Research Center 889, University of Göttingen, Göttingen, Germany.
- Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.
- Center for Biostructural Imaging of Neurodegeneration, Göttingen, Germany.
- Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, Göttingen, Germany.
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.
- Collaborative Research Center 889, University of Göttingen, Göttingen, Germany.
- Auditory Neuroscience Group, Max Planck Institute of Experimental Medicine, Göttingen, Germany.
- Synaptic Nanophysiology Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany.
- Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University of Göttingen, Göttingen, Germany.
- Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, Göttingen, Germany.
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Transient Receptor Potential Channels TRPM4 and TRPC3 Critically Contribute to Respiratory Motor Pattern Formation but not Rhythmogenesis in Rodent Brainstem Circuits. eNeuro 2018; 5:eN-NWR-0332-17. [PMID: 29435486 PMCID: PMC5806591 DOI: 10.1523/eneuro.0332-17.2018] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Revised: 01/12/2018] [Accepted: 01/16/2018] [Indexed: 12/17/2022] Open
Abstract
Transient receptor potential channel, TRPM4, the putative molecular substrate for Ca2+-activated nonselective cation current (ICAN), is hypothesized to generate bursting activity of pre-Bötzinger complex (pre-BötC) inspiratory neurons and critically contribute to respiratory rhythmogenesis. Another TRP channel, TRPC3, which mediates Na+/Ca2+ fluxes, may be involved in regulating Ca2+-related signaling, including affecting TRPM4/ICAN in respiratory pre-BötC neurons. However, TRPM4 and TRPC3 expression in pre-BötC inspiratory neurons and functional roles of these channels remain to be determined. By single-cell multiplex RT-PCR, we show mRNA expression for these channels in pre-BötC inspiratory neurons in rhythmically active medullary in vitro slices from neonatal rats and mice. Functional contributions were analyzed with pharmacological inhibitors of TRPM4 or TRPC3 in vitro as well as in mature rodent arterially perfused in situ brainstem-spinal cord preparations. Perturbations of respiratory circuit activity were also compared with those by a blocker of ICAN. Pharmacologically attenuating endogenous activation of TRPM4, TRPC3, or ICANin vitro similarly reduced the amplitude of inspiratory motoneuronal activity without significant perturbations of inspiratory frequency or variability of the rhythm. Amplitude perturbations were correlated with reduced inspiratory glutamatergic pre-BötC neuronal activity, monitored by multicellular dynamic calcium imaging in vitro. In more intact circuits in situ, the reduction of pre-BötC and motoneuronal inspiratory activity amplitude was accompanied by reduced post-inspiratory motoneuronal activity, without disruption of rhythm generation. We conclude that endogenously activated TRPM4, which likely mediates ICAN, and TRPC3 channels in pre-BötC inspiratory neurons play fundamental roles in respiratory pattern formation but are not critically involved in respiratory rhythm generation.
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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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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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8
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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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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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Simard C, Sallé L, Rouet R, Guinamard R. Transient receptor potential melastatin 4 inhibitor 9-phenanthrol abolishes arrhythmias induced by hypoxia and re-oxygenation in mouse ventricle. Br J Pharmacol 2012; 165:2354-64. [PMID: 22014185 DOI: 10.1111/j.1476-5381.2011.01715.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE Hypoxia and subsequent re-oxygenation are associated with cardiac arrhythmias such as early afterdepolarizations (EADs), which may be partly explained by perturbations in cytosolic calcium concentration. Transient receptor potential melastatin 4 (TRPM4), a calcium-activated non-selective cation channel, is functionally expressed in the heart. Based on its biophysical properties, it is likely to participate in EADs. Hence, modulators of TRPM4 activity may influence arrhythmias. The aim of this study was to investigate the possible anti-arrhythmic effect of 9-phenanthrol, a TRPM4 inhibitor in a murine heart model of hypoxia and re-oxygenation-induced EADs. EXPERIMENTAL APPROACH Mouse heart was removed, and the right ventricle was pinned in a superfusion chamber. After a period of normoxia, the preparation was superfused for 2 h with a hypoxic solution and then re-oxygenated. Spontaneous electrical activity was investigated by intracellular microelectrode recordings. KEY RESULTS In normoxic conditions, the ventricle exhibited spontaneous action potentials. Application of the hypoxia and re-oxygenation protocol unmasked hypoxia-induced EADs, the occurrence of which increased under re-oxygenation. The frequency of these EADs was reduced by superfusion with either flufenamic acid, a blocker of Ca(2+) -dependent cation channels or with 9-phenanthrol. Superfusion with 9-phenanthrol (10(-5) or 10(-4) mol·L(-1) ) caused a dramatic dose-dependent abolition of EADs. CONCLUSIONS AND IMPLICATIONS Hypoxia and re-oxygenation-induced EADs can be generated in the mouse heart model. 9-Phenanthrol abolished EADs, which strongly suggests the involvement of TRPM4 in the generation of EAD. This identifies non-selective cation channels inhibitors as new pharmacological candidates in the treatment of arrhythmias.
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Mutolo D, Bongianni F, Cinelli E, Pantaleo T. Role of neurokinin receptors and ionic mechanisms within the respiratory network of the lamprey. Neuroscience 2010; 169:1136-49. [PMID: 20540991 DOI: 10.1016/j.neuroscience.2010.06.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2010] [Revised: 05/04/2010] [Accepted: 06/03/2010] [Indexed: 11/27/2022]
Abstract
We have suggested that in the lamprey, a medullary region called the paratrigeminal respiratory group (pTRG), is essential for respiratory rhythm generation and could correspond to the pre-Bötzinger complex (pre-BötC), the hypothesized kernel of the inspiratory rhythm-generating network in mammals. The present study was performed on in vitro brainstem preparations of adult lampreys to investigate whether some functional characteristics of the respiratory network are retained throughout evolution and to get further insights into the recent debated hypotheses on respiratory rhythmogenesis in mammals, such as for instance the "group-pacemaker" hypothesis. Thus, we tried to ascertain the presence and role of neurokinins (NKs) and burst-generating ion currents, such as the persistent Na(+) current (I(NaP)) and the Ca(2+)-activated non-specific cation current (I(CAN)), described in the pre-Bötzinger complex. Respiratory activity was monitored as vagal motor output. Substance P (SP) as well as NK1, NK2 and NK3 receptor agonists (400-800 nM) applied to the bath induced marked increases in respiratory frequency. Microinjections (0.5-1 nl) of SP as well as the other NK receptor agonists (1 microM) into the pTRG increased the frequency and amplitude of vagal bursts. Riluzole (RIL) and flufenamic acid (FFA) were used to block I(NaP) and I(CAN), respectively. Bath application of either RIL or FFA (20-50 microM) depressed, but did not suppress respiratory activity. Coapplication of RIL and FFA at 50 microM abolished the respiratory rhythm that, however, was restarted by SP microinjected into the pTRG. The results show that NKs may have a modulatory role in the lamprey respiratory network through an action on the pTRG and that I(NaP) and I(CAN) may contribute to vagal burst generation. We suggest that the "group-pacemaker" hypothesis is tenable for the lamprey respiratory rhythm generation since respiratory activity is abolished by blocking both I(NaP) and I(CAN), but is restored by enhancing network excitability.
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Affiliation(s)
- D Mutolo
- Dipartimento di Scienze Fisiologiche, Università degli Studi di Firenze, Viale GB Morgagni 63, 50134 Firenze, Italy.
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Fellner SK, Arendshorst WJ. Angiotensin II-stimulated Ca2+ entry mechanisms in afferent arterioles: role of transient receptor potential canonical channels and reverse Na+/Ca2+ exchange. Am J Physiol Renal Physiol 2008; 294:F212-9. [DOI: 10.1152/ajprenal.00244.2007] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In afferent arterioles, the signaling events that lead to an increase in cytosolic Ca2+ concentration ([Ca2+]i) and initiation of vascular contraction are increasingly being delineated. We have recently studied angiotensin II (ANG II)-mediated effects on sarcoplasmic reticulum (SR) mobilization of Ca2+ and the role of superoxide and cyclic adenosine diphosphoribose in these processes. In the current study we investigated the participation of transient receptor potential canonical channels (TRPC) and a Na+/Ca2+ exchanger (NCX) in Ca2+ entry mechanisms. Afferent arterioles, isolated with the magnetized polystyrene bead method, were loaded with fura-2 to measure [Ca2+]i ratiometrically. We observed that the Ca2+-dependent chloride channel blocker niflumic acid (10 and 50 μ M) affects neither the peak nor plateau [Ca2+]i response to ANG II. Arterioles were pretreated with ryanodine (100 μM) and TMB-8 to block SR mobilization via the ryanodine receptor and inositol trisphosphate receptor, respectively. The peak [Ca2+]i response to ANG II was reduced by 40%. Addition of 2-aminoethoxydiphenyl borane to block TRPC-mediated Ca2+ entry inhibited the peak [Ca2+]i ANG II response by 80% and the plateau by 74%. Flufenamic acid (FFA; 50 μM), which stimulates TRPC6, caused a sustained increase of [Ca2+]i of 146 nM. This response was unaffected by diltiazem or nifedipine. KB-R7943 (at the low concentration of 10 μM) inhibits reverse (but not forward) mode NCX. KB-R7943 decreased the peak [Ca2+]i response to ANG II by 48% and to FFA by 38%. We conclude that TRPC6 and reverse-mode NCX may be important Ca2+ entry pathways in afferent arterioles.
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Johnson SM, Wiegel LM, Majewski DJ. Are pacemaker properties required for respiratory rhythm generation in adult turtle brain stems in vitro? Am J Physiol Regul Integr Comp Physiol 2007; 293:R901-10. [PMID: 17522127 DOI: 10.1152/ajpregu.00912.2006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The role of pacemaker properties in vertebrate respiratory rhythm generation is not well understood. To address this question from a comparative perspective, brain stems from adult turtles were isolated in vitro, and respiratory motor bursts were recorded on hypoglossal (XII) nerve rootlets. The goal was to test whether burst frequency could be altered by conditions known to alter respiratory pacemaker neuron activity in mammals (e.g., increased bath KCl or blockade of specific inward currents). While bathed in artificial cerebrospinal fluid (aCSF), respiratory burst frequency was not correlated with changes in bath KCl (0.5-10.0 mM). Riluzole (50 microM; persistent Na(+) channel blocker) increased burst frequency by 31 +/- 5% (P < 0.05) and decreased burst amplitude by 42 +/- 4% (P < 0.05). In contrast, flufenamic acid (FFA, 20-500 microM; Ca(2+)-activated cation channel blocker) reduced and abolished burst frequency in a dose- and time-dependent manner (P < 0.05). During synaptic inhibition blockade with bicuculline (50 microM; GABA(A) channel blocker) and strychnine (50 muM; glycine receptor blocker), rhythmic motor activity persisted, and burst frequency was directly correlated with extracellular KCl (0.5-10.0 mM; P = 0.005). During synaptic inhibition blockade, riluzole (50 microM) did not alter burst frequency, whereas FFA (100 microM) abolished burst frequency (P < 0.05). These data are most consistent with the hypothesis that turtle respiratory rhythm generation requires Ca(2+)-activated cation channels but not pacemaker neurons, which thereby favors the group-pacemaker model. During synaptic inhibition blockade, however, the rhythm generator appears to be transformed into a pacemaker-driven network that requires Ca(2+)-activated cation channels.
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Affiliation(s)
- Stephen M Johnson
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, 2015 Linden Drive, Madison, WI 53706, USA.
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Hotta A, Kito Y, Suzuki H. The effects of flufenamic acid on spontaneous activity of smooth muscle tissue isolated from the guinea-pig stomach antrum. J Smooth Muscle Res 2005; 41:207-20. [PMID: 16258234 DOI: 10.1540/jsmr.41.207] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The effects of flufenamic acid were investigated on slow waves, follower potentials and pacemaker potentials recorded respectively from circular smooth muscle cells, longitudinal smooth muscle cells and interstitial cells of Cajal distributed in the myenteric layers (ICC-MY) of the guinea-pig stomach antrum. Flufenamic acid (>10(-5) M) inhibited the amplitude and rate of rise of the upstroke phase of the slow waves, with no marked alteration in their frequency of occurrence. The inhibitory actions of flufenamic acid appeared to be mainly on slow potentials recorded from circular smooth muscle cells, but not on follower or pacemaker potentials. After abolishing spontaneous slow potentials with flufenamic acid, depolarizing current stimuli could evoke slow potentials with an amplitude that was much smaller than in the absence of flufenamic acid, with no significant alteration to the input resistance of the membrane. The time elapsed for the generation of the 2nd component of the slow waves or the slow potentials evoked during depolarizing current pulse stimulation was increased by flufenamic acid. The rate of rise of unitary potentials, but not the frequency of occurrence, was inhibited by flufenamic acid. These results indicate that the inhibitory actions of flufenamic acid appear to be mainly on the circular muscle layer including the interstitial cells of Cajal distributed within the muscle bundles (ICC-IM). Nifedipine-sensitive spike potentials were not inhibited by flufenamic acid. It is concluded that the selective inhibition of the 2nd component of slow waves by flufenamic acid may be mainly due to the inhibition of ion channels, possibly Ca2+-sensitive Cl--channels, activated during generation of slow potentials in the ICC-IM distributed in the circular muscle layer.
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Affiliation(s)
- Aya Hotta
- Department of Physiology, Nagoya City University Medical School, Japan
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